CN101015062A - Solid-state image sensor - Google Patents

Abstract

An object of the present invention is to provide a solid-state image sensor having good light resistance and capable of thin filter membrane. A solid-state image sensor (1) having a plurality of pixels, wherein each of the plurality of pixels includes a filter film (21) for transmitting light of a predetermined color, and for transmitting light through the filter film (21) ) into a photoelectric conversion unit (17) of electric charge; the filter film (21) is a single-layer film made of inorganic materials; and the optical thickness ratio of the single-layer film is half of the wavelength of the predetermined color The equal thickness is smaller than the thickness corresponding to the amount of light of the predetermined color absorbed by the inorganic material.

Description

Solid State Image Sensor

technical field

The present invention relates to solid-state image sensors used in digital cameras and the like, and more particularly to filter membranes for color separation.

Background technique

The solid-state image sensor includes a plurality of pixels, and each of the plurality of pixels includes a filter film and a photoelectric conversion unit. This filter is used for color separation of light. For example, each red (R), green (G) and blue (B) filter is used as a primary color filter, and each cyan (C), magenta (M), yellow (Y) and green (G) filter The membrane acts as a complementary color filter. The photoelectric conversion unit converts light passing through the filter membrane into electrical charges. The converted charge amount is output to the outside as a signal corresponding to the amount of light received by the photoelectric conversion unit. (Patent Document 1)

A conventional filter membrane is composed of a transparent resin such as acrylic resin or the like, in which pigments and dyes as organic materials are dispersed (Patent Document 2). That is, color separation can be achieved by using pigments and dyes according to individual colors.

Patent Document 1: Japanese Laid-Open Patent Application No.H05-6986

Patent Document 2: Japanese Laid-Open Patent Application No.H07-311310

Contents of the invention

The technical problem that the present invention solves

However, the membrane filter has the following problems.

The first problem is that the light resistance is insufficient because the filter membrane is composed of an organic material. For example, organic pigments have the characteristic of fading when exposed to light. If discoloration occurs, color separation cannot be performed correctly due to a change in the transmission characteristics of the filter.

The second problem is that it is difficult to thin the filter membrane composed of dispersed pigments and the like. For this filter membrane, the smaller the film thickness of the filter membrane, the higher the transparency. Therefore, the color separation characteristics of the filter will deteriorate. When pigments are used, membrane thinning is limited due to the particle size of the pigments. Color mixing between multiple pixels can be effectively prevented by making the filter thin. Since color mixing may occur due to the miniaturization of pixels in recent years, the film thickness of the filter is increasingly required to be reduced.

An object of the present invention is to provide a solid-state image sensor including a filter film that has better light resistance than conventional filters and can be thinned.

means of solving the problem

The above-mentioned problems are solved by a solid-state image sensor having a plurality of pixels each including a filter for transmitting light of a predetermined color, and for converting light transmitted through the filter to is a photoelectric conversion unit of charge; the filter film is a single-layer film made of an inorganic material; and the optical thickness of the single-layer film is smaller than a thickness equal to half the wavelength of the predetermined color and is made of the inorganic material. The amount of light absorbed by the predetermined color corresponds to the thickness.

Invention effect

With the above structure, the filter membrane is composed of inorganic materials. Therefore, the filter membrane has better light resistance than the traditional filter membrane. In addition, the optical thickness of the monolayer film is smaller than a thickness equal to half the wavelength of the predetermined color by a thickness corresponding to the amount of light of the predetermined color absorbed by the inorganic material. This causes local maxima of light transmission to occur at wavelengths of predetermined colors in the transmission spectrum of the filter. Therefore, the optical thickness of the filter can be thinned to a thickness equal to half the wavelength of each color without deteriorating the color separation characteristics of the filter.

And, the larger the absorption coefficient of the inorganic material for the light of the wavelength of the predetermined color is, the smaller the optical thickness of the single layer film is.

This prevents the transmittance of the filter from being reduced due to the large light absorption coefficient.

Also, the composition of the inorganic material is the same for the plurality of pixels.

With the above structure, since each filter is made of the same material, there is no need to manage the material according to the color in the manufacturing process of the filter. Therefore, the manufacturing cost of the filter membrane can be reduced.

And, the composition of the inorganic material differs according to the color to be transmitted among the colors; and the shorter the wavelength of each of the colors, the smaller the refractive index of the inorganic material.

With the above structure, the difference in physical thickness of the filter membrane can be small between pixels each having a different color to be transmitted. Therefore, the layer in which the filter membrane is formed can be easily flattened.

In addition, the inorganic material has a refractive index equal to or greater than 3.

Because the refractive index of the filter is equal to or greater than 3, even if oblique incident light enters the filter, the refraction angle is small. Therefore, color mixture between pixels can be prevented.

Also, the inorganic material is amorphous silicon, polycrystalline silicon, single crystal silicon or a material mainly containing silicon.

Amorphous silicon, polycrystalline silicon, single crystal silicon, or a material mainly containing silicon has a large absorption coefficient. Therefore, even if the filter membrane is very thin, color separation can be achieved.

Also, the refractive index of amorphous silicon, polycrystalline silicon, single crystal silicon, or a material mainly containing silicon is about 4 to 5, and larger than that of a conventional insulating film or the like (for example, a silicon dioxide film has a refractive index of 1.46). Therefore, even if oblique incident light enters the filter, the angle of refraction is small, and color mixing can be prevented.

In addition, with amorphous silicon, films can be formed at low temperatures. Therefore, the filter film can be formed after the light-shielding film such as low melting point aluminum is formed. As a result, the manufacturing process can be freely changed. Also, if amorphous silicon is used, stress on the photoelectric conversion unit can be reduced. Therefore, damage to the photoelectric conversion unit can be reduced.

Also, the inorganic material is titanium oxide, tantalum oxide or niobium oxide.

For oxides of titanium (titanium dioxide, etc.), tantalum oxides (tantalum pentoxide, etc.), or niobium oxides (niobium pentoxide, etc.), the light absorption coefficient in the optical wavelength range is small. Therefore, the permeability of the filter membrane can be improved. As a result, a solid-state image sensor with high sensitivity can be realized.

In addition, titanium oxide, tantalum oxide, or niobium oxide has a refractive index equal to or greater than 2, which is relatively large among dielectric materials. Therefore, oxides of titanium, tantalum, or niobium are suitable as a material for forming the interference filter.

Also, each of the plurality of pixels further includes an anti-reflection film formed on a main surface of the filter film facing the light source and having a refractive index smaller than that of the filter film.

With the above structure, the difference in refractive index between the media through which the incident light passes is small, and the reflection of the incident light on the filter surface is reduced. Therefore, a solid-state image sensor with high sensitivity can be realized. In addition, the peak wavelength of the light transmittance of the filter can be controlled by changing the thickness of the anti-reflection film. As a result, color separation characteristics and design freedom can be improved.

Also, the antireflection film is made of silicon nitride, silicon dioxide, or silicon oxynitride.

With the above structure, the antireflection film can be manufactured by a semiconductor process. Therefore, the manufacturing cost of the filter membrane can be reduced.

In addition, the photoelectric conversion unit is formed in a part of the substrate; each of the photoelectric conversion units further includes a light-shielding film covering the substrate and having an opening provided at a position corresponding to the photoelectric conversion unit ; and the filter film is disposed between the light-shielding film and the substrate.

With the above structure, interference of light between the photoelectric conversion unit and the filter can be prevented. This improves the sensitivity of the solid-state image sensor. Also, the above structure can be used as an effective method for preventing color mixing. Since the physical thickness of the filter film is very thin, the filter film can be easily formed between the light-shielding film and the photoelectric conversion unit.

Moreover, each of the plurality of pixels is arranged so that the main surface of the filter membrane facing the photoelectric conversion unit is arranged on the same plane; each of the plurality of pixels also includes a main surface arranged on the filter membrane facing the light source. a smoothing layer on the surface; and the greater the physical thickness of the filter membrane, the smaller the thickness of the smoothing layer.

With the above structure, between pixels, the main surface of the flat layer facing the light source can be flat. This can improve the expandability of the device.

Moreover, each of the plurality of pixels further includes a microlens disposed on the main surface of the planar layer facing the light source.

With the above structure, light focusing efficiency can be improved and a high-sensitivity solid-state image sensor can be realized.

The above-mentioned problems are also solved by a solid-state image sensor having a plurality of pixels each including a filter for transmitting light of a predetermined color, and a filter for transmitting light through the filter. a photoelectric conversion unit that converts light into electric charge; the filter film is a single-layer film composed of an inorganic material; and the optical thickness of the single-layer film depends on the color to be transmitted in the range of 150nm to 400nm inclusive. Color settings.

Using the setup described above, the filter membrane is constructed of inorganic materials. Therefore, the filter membrane has better light resistance than the traditional filter membrane. The optical thickness of the monolayer film is in the range of 150nm inclusive to 400nm inclusive. This causes a local maximum of light transmission to occur at the wavelength of the color to be transmitted in the transmission spectrum of the filter. Therefore, the optical thickness of the filter can be thinned to a thickness equal to half the wavelength of each color without deteriorating the color separation characteristics of the filter.

The above-mentioned problems are solved by a solid-state image sensor having a plurality of pixels each including a filter for transmitting light of a predetermined color, and for converting light transmitted through the filter to It is a photoelectric conversion unit of charge; the shorter the wavelength of the predetermined color, the smaller the light absorption coefficient in the optical wavelength range of the inorganic material constituting the filter membrane.

With the above structure, the filter membrane is composed of inorganic materials. Therefore, the filter membrane has better light resistance than the traditional filter membrane.

And, the light absorption coefficient of the filter is changed by changing the composition of the inorganic material.

With the above-mentioned structure, the materials of the inorganic materials according to the colors are the same, so there is no need to manage the materials according to the colors in the manufacturing process of the filter membrane. In addition, the filter membrane can be manufactured more simply than the conventional filter membrane, which requires an additional process of dispersing the pigment into the transparent resin according to the color because the composition of the conventional filter membrane changes according to the color in its forming step. Therefore, the manufacturing cost of the filter membrane can be reduced.

And, an optical thickness of the filter film is smaller than a thickness equal to half the wavelength of the predetermined color by a thickness corresponding to an amount of light of the predetermined color absorbed by the inorganic material.

With the above structure, the optical thickness of the filter film is smaller than a thickness equal to half the wavelength of the predetermined color by a thickness corresponding to the amount of light of the predetermined color absorbed by the inorganic material. This causes local maxima of light transmission to occur at wavelengths of predetermined colors in the transmission spectrum of the filter. Therefore, the optical thickness of the filter can be thinned to a thickness equal to half the wavelength of each color without deteriorating the color separation characteristics of the filter.

Description of drawings

Figure 1 shows the structure of the camera system;

2 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the first embodiment;

Fig. 3 shows the transmission spectra of the filter membranes 21a, 21b and 21c of the first embodiment;

Fig. 4 shows the internal structure of signal processing circuit;

Fig. 5 is used for the determinant of this signal processing circuit;

Figure 6 shows a color signal spectrum generated by processing a digital signal;

7 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the second embodiment;

Fig. 8 shows the transmission spectra of the filter membranes 21a, 21b and 21c of the second embodiment;

9 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the third embodiment;

10 is a cross-sectional view showing the steps of the method of manufacturing the filter membrane 21 of the fourth embodiment;

FIG. 11 is a cross-sectional view of a filter membrane 21 manufactured by the manufacturing method of the fourth embodiment;

12 is a cross-sectional view showing the steps of the method of manufacturing the filter membrane 21 of the fifth embodiment;

13 is a cross-sectional view of a filter membrane 21 manufactured by the manufacturing method of the fifth embodiment;

14 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the fifth embodiment;

Fig. 15 shows the transmission spectra of the filter membranes 51a, 51b and 51c of the sixth embodiment;

16 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the seventh embodiment;

Fig. 17 shows the transmission spectra of the filter membranes 61a, 61b and 61c of the seventh embodiment;

18 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the eighth embodiment;

Fig. 19 shows the transmission spectra of the filter membranes 61a, 61b and 61c of the eighth embodiment;

20 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the ninth embodiment;

Fig. 21 shows the transmission spectra of the filter membranes 71a, 71b and 71c of the ninth embodiment;

FIG. 22 is a cross-sectional view showing the steps of the method of manufacturing the filter membrane 61 according to the tenth embodiment.

Explanation of reference signs

1: Solid-state image sensor

2: Drive circuit

3: Vertical scanning circuit

4: Horizontal scanning circuit

5: Analog front end

6: Signal processing circuit

7: Working memory

8: Record memory

9: Control unit

11: Substrate

12: Photoelectric conversion unit formation layer

13: insulation layer

14: Shading film forming layer

15: Color filter formation layer

16: P-type well

17: Photoelectric conversion unit

19: shading film

20: opening

21, 51, 61, 71: filter membrane

22: leveling layer

23: micro lens

30: Anti-reflection film

Best Mode for Carrying Out the Invention

A solid-state image sensor according to an embodiment of the present invention is described below with reference to the drawings. Note that the present invention is not limited to the following embodiments.

<First Embodiment>

FIG. 1 shows the structure of the camera system of the present invention.

The camera system is mounted on a digital camera, digital video camera, etc. to generate image data, and includes a solid-state image sensor 1, a drive circuit 2, a vertical scanning circuit 3, a horizontal scanning circuit 4, an analog front end 5, a signal processing circuit 6, and a work memory 7 , recording memory, 8 and control unit 9.

This solid-state image sensor 1 is a MOS type image sensor, and has a plurality of pixels (1a, 1b, 1c, etc.). Each of the plurality of pixels is represented as "R", "RG" or "RGB" in FIG. 1 . "R" transmits light in the red region in the optical wavelength range, and indicates a pixel having a local maximum in the light transmission spectrum in the red region. "RG" transmits light in the red and green regions of the optical wavelength range, and denotes a pixel having a local maximum of the light transmission spectrum in the green region. "RGB" transmits light in the red, green, and blue regions of the optical wavelength range, and denotes a pixel having a local maximum of the light transmission spectrum in the blue region.

For example, the pixel 1 a has sensitivity mainly to a red region, and outputs a signal corresponding to the amount of received light. The pixel 1b has sensitivity mainly to green and red regions, and outputs a signal corresponding to the amount of received light. The pixel 1c has sensitivity mainly to blue, green, and red regions, and outputs a signal corresponding to the amount of received light.

As shown in Figure 1, the arrangement of the color filters conforms to the Bayer arrangement (Bayer arrangement).

Please note that in this specification, the wavelength of the blue region is in the range of 400nm to 490nm and including 490nm, the wavelength of the green region is in the range of 490nm to 580nm and including 580nm, and the wavelength of the red region is in the range of 580nm to 700nm And including 700nm. In addition, a wavelength range of 400 nm or less is an ultraviolet region, and a wavelength range of 700 nm or more is an infrared region.

The driving circuit 2 drives the vertical scanning circuit 3 and the horizontal scanning circuit 4 based on a trigger signal from the control unit 9 .

The vertical scanning circuit 3 sequentially activates each of the plurality of pixels row by row according to the driving instruction from the driving circuit 2 , and transmits the activated pixel signals of one row to the horizontal scanning circuit 4 at the same time.

The horizontal scanning circuit 4 operates synchronously with the vertical scanning circuit 3 according to the driving instruction from the driving circuit 2 , and outputs a row of transmitted pixel signals to the analog front end 5 sequentially and column by column. The signal of each pixel of a plurality of pixels arranged in a planar matrix is converted into a voltage by the driving circuit 2 , the vertical scanning circuit 3 and the horizontal scanning circuit 4 , so as to be serially output to the analog front end 5 .

The analog front end 5 samples and amplifies the voltage signal, and converts the voltage signal from an analog signal to a digital signal for output to the signal processing circuit 6 .

This signal processing circuit 6 is a DSP (Digital Signal Processor), and converts the digital signal from the analog front end 5 into a red signal, a green signal, and a blue signal to generate image data.

Specifically, the work memory 7 is an SDRAM used when the signal processing circuit 6 converts a digital signal corresponding to each of the plurality of pixels into a color signal of each color.

The recording memory 8 is an SDRAM for recording image data generated by the signal processing circuit 6 .

The control unit 9 controls the drive circuit 2 and the signal processing circuit 6 . For example, when the user presses the shutter button, the control unit 9 outputs a trigger signal to the drive circuit 2 .

The structure of each of the plurality of pixels of the solid-state image sensor 1 is described below.

FIG. 2 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the first embodiment.

Each pixel is composed of the following layers on a substrate 11 made of silicon doped with N-type impurities.

The photoelectric conversion unit formation layer 12 includes a P-type well 16 and a photoelectric conversion unit 17 . The P-type well 16 is formed by ion implantation of P-type impurities in the substrate 11 . Photoelectric conversion unit 17 as an N-type region is formed by ion implantation of N-type impurities in P-type well 16 .

The insulating layer 13 is composed of silicon dioxide 18 and serves to insulate the photoelectric conversion unit formation layer 12 from the light shielding film formation layer 14 and to level the image sensor.

The light-shielding film forming layer 14 includes leads from the vertical scanning circuit 3 and leads that transfer signal charges to the horizontal scanning circuit 4, and the leads are formed by the CVD method. The light-shielding film 19 is also formed by the CVD method, and the silicon dioxide 18 is formed in order to planarize the image sensor.

The color filter forming layer 15 includes respective filter films (21a, 21b, and 21c) and a leveling layer 22 formed of silicon dioxide. The greater the physical thickness (da, db, and dc) of each filter membrane (21a, 21b, and 21c), the smaller the thickness of the smoothing layer 22.

Incident light 24 enters from the upper portion of the pixel, is condensed by the microlens 23 , and passes through the respective filter films ( 21 a , 21 b , and 21 c ) and the opening 20 formed in the light-shielding film 19 to reach the photoelectric conversion unit 17 .

Of the incident light 24 entering the pixel 1 a , light whose wavelength range has a local maximum in the red region passes through the filter film 21 a to reach the photoelectric conversion unit 17 . Of the incident light 24 entering the pixel 1 b , light whose wavelength range has a local maximum in the green region reaches the photoelectric conversion unit 17 . Of the incident light 24 entering the pixel 1 c , light whose wavelength range has a local maximum in the blue region reaches the photoelectric conversion unit 17 .

The incident light 24 transmitted through the respective filter films ( 21 a , 21 b , and 21 c ) passes through the opening 20 formed in the light shielding film 19 .

The light-shielding film 19 is formed by a method such as CVD. In order to prevent light scattered from adjacent pixels from reaching photoelectric conversion unit 17 , a portion immediately above photoelectric conversion unit 17 is opened by forming opening 20 , and light shielding film 19 shields light from a portion other than opening 20 . With this structure, only incident light nearly perpendicular to the substrate 11 can reach the photoelectric conversion unit 17, and obliquely incident light is shielded.

The photoelectric conversion unit 17 forms a photodiode through a PN junction with the P-type well 16 , and generates signal charges according to the brightness of light reaching the photoelectric conversion unit 17 through the respective filters ( 21 a , 21 b , and 21 c ) and the opening 20 . The following is the structure of photoelectric conversion.

In the photoelectric conversion unit 17, a depletion region in which electrons as carriers recombine with electron holes as P-type well carriers and disappear is formed. This relatively increases the potential of the photoelectric conversion unit 17 and relatively decreases the potential of the P-type well 16 . Therefore, an internal electric field is generated in the depletion region.

In this state, when incident light 24 reaches the photoelectric conversion unit 17, electron-hole pairs are generated by photoelectric conversion, and the electrons and electron-holes drift in opposite directions by the internal electric field. In other words, electrons drift toward the center of the photoelectric conversion unit 17, while electron holes drift toward the P-type well. As a result, electrons are accumulated in the photoelectric conversion unit 17, and the accumulated electrons become signal charges of the respective pixels.

Subsequently, the pixel 1a generates signal charges according to the luminance of the light of the incident light 24 whose wavelength range has a local maximum in the red region. The pixel 1b generates signal charges according to the brightness of light whose wavelength range has a local maximum in the green region. The pixel 1c generates signal charges according to the brightness of light whose wavelength range has a local maximum in the blue region.

In the first embodiment, each filter membrane (21a, 21b, and 21c) is a single-layer membrane made of amorphous silicon. The optical thicknesses of the respective filters (21a, 21b, and 21c) are less than a thickness equal to half the wavelength of the color to be transmitted by a thickness corresponding to the amount of light of the color to be transmitted absorbed by the amorphous silicon . The colors to be transmitted are each of red (R), green (G), and blue (B).

Considering only the interference effect of light in the filter, in the light transmission spectrum, the local maximum of the transmittance occurs at the wavelength λ corresponding to a thickness twice as thick as the optical thickness nd of the filter. In other words, if the optical thickness nd of the filter is equal to half the wavelength of the color to be transmitted, the local maximum of the transmission occurs at the wavelength according to the relation nd=λ/2.

Because the filter actually absorbs the light, not only the interference effect of the light, but also the absorption effect must be considered. Regarding the absorption coefficient of general inorganic materials, the shorter the wavelength of light, the larger the absorption coefficient. In other words, as the wavelength of light becomes shorter, transmittance decreases due to absorption of light. As a result, the wavelength representing the local maximum value of the light transmittance is shifted to the longer wavelength side. Therefore, by adjusting the optical thickness of each filter film to be less than a thickness equal to half the wavelength of the color to be transmitted, and the difference between the two is a thickness corresponding to the amount of light of the color to be transmitted absorbed by the amorphous silicon, the light A local maximum of transmittance may occur at the wavelength of the color to be transmitted.

Here, the red wavelength λ is 650 nm, the green wavelength λ is 560 nm, and the blue wavelength λ is 490 nm. Therefore, half of the red wavelength λ is 325nm, half of the green wavelength λ is 280nm, and half of the blue wavelength λ is 245nm. Since the optical thickness is smaller than the thickness equal to half the wavelength of the color to be transmitted, the thickness corresponding to the amount of light of the color to be transmitted absorbed by the amorphous silicon is smaller, so the optical thickness of the red filter is 315nm, and the green filter is 315nm. The optical thickness of the blue filter is 260nm, and the optical thickness of the blue filter is 200nm. The amount of light absorbed is obtained from the absorption coefficient of amorphous silicon and the optical thickness of the filter membrane.

Amorphous silicon has a refractive index of 4.5 at a wavelength of 650 nm. Amorphous silicon has a refractive index of 4.75 at a wavelength of 560 nm. Amorphous silicon has a refractive index of 5.0 at a wavelength of 490 nm. Therefore, the physical thicknesses (da, db, and dc) of the respective filters (21a, 21b, and 21c) are da=70nm, db=55nm, and dc=40nm, respectively.

FIG. 3 shows the transmission spectra of the filter membranes 21a, 21b and 21c of the first embodiment. Curve 31a represents the transmission spectrum of filter membrane 21a. Curve 31b represents the transmission spectrum of filter 21b. Curve 31c represents the transmission spectrum of filter 21c.

The filter 21a has a local maximum of light transmittance at a red wavelength of 650 nm. The filter 21b has a local maximum of light transmittance at a green wavelength of 560 nm. The filter 21c has a local maximum of light transmittance at a blue wavelength of 490 nm. The larger the optical thickness of the filter, the longer the wavelength of the local maximum of light transmittance. For this reason, it can be expected that a local maximum appears in the light transmission spectrum due to the interference effect of light.

The local maximum value of the permeability of the filter membrane 21a is 78%. The local maximum value of the transmittance of the filter membrane 21b is 61%. The local maximum value of the transmittance of the filter membrane 21c is 38%.

It is expected that the local maxima will be smaller for shorter color wavelengths because the absorption coefficient of amorphous silicon is larger for shorter color wavelengths.

Also, when focusing on the transmission spectrum of one filter (for example, filter 21b: curve 31b), the slope of the curve (31d) on the short wavelength side of the wavelength (560nm) at which it is a local maximum is larger than that of the long wavelength The slope of the curve (31e) on one side. Since the absorption coefficient of amorphous silicon increases as the wavelength of light becomes shorter, the transmittance on the shorter wavelength side decreases. Since the light on the short wavelength side is easily cut off, this absorption effect improves the color separation characteristics.

As shown in Figure 3, any filter can transmit light in the entire visible wavelength range (400nm to 700nm). As a result, for example, each component of the color signal (R, G, and B) is included in the signal obtained by the pixel 1a having the filter 21a based on the ratio of the transmission spectrum 31a. The same applies to pixels 1b and 1c.

Therefore, the digital signals (Sa, Sb and Sc) obtained from the pixels 1a, 1b and 1c have to be processed in order to derive the color signals (R, G and B) used to generate the image data. The method thereof is described below.

Fig. 4 shows the internal structure of the signal processing circuit.

The signal processing circuit 6 includes a transformation matrix holding unit 61 , an operation unit 62 and a memory control unit 63 .

The transformation matrix holding unit 61 holds a transformation matrix that converts digital signals (Sa, Sb, and Sc) generated in the analog front end 5 into color signals (R, G, and B).

The relationship between digital signals (Sa, Sb, and Sc) and color signals (R, G, and B) is shown in FIG. 5( a ).

Here, the respective elements W ₁₁ to W ₃₃ in the matrix are weighting factors based on the transmission spectra of the respective filters 21a, 21b and 21c.

Each element W ₁₁ to W ₃₃ in the matrix is inversely transformed into a transformation matrix. The relationship between digital signals (Sa, Sb, and Sc) and color signals (R, G, and B) is shown in FIG. 5( b ).

Here, each element X ₁₁ to X ₃₃ in the matrix is obtained by performing inverse transformation on the matrix in Fig. 5(a).

The memory control unit 63 controls access to the work memory 7 and the recording memory 8 . The memory control unit 63 receives a digital signal from the analog front end 5 and stores the digital signal in the work memory 7 at a time. When image data corresponding to one frame is accumulated in the work memory 7 , the memory control unit 63 acquires part of the image data from the work memory 7 and inputs the part of image data to the operation unit 62 .

The arithmetic unit 62 obtains color signals (R, G, and B) by multiplying the digital signals (Sa, Sb, and Sc) by the transformation matrix held in the transformation matrix holding unit 61 .

The memory control unit 63 stores the color signals (R, G, and B) obtained by the arithmetic unit 62 in the recording memory 8 . As a result, image data corresponding to one frame is recorded in the recording memory 8 .

Fig. 6 shows a color signal spectrum generated by processing a digital signal.

Various parameters can be determined in order to approximate ideal NTSC spectroscopy.

As described above, in the first embodiment, the optical thickness of each filter is appropriately adjusted according to the color to be transmitted. Using this structure, the transmission spectrum shown in Fig. 3 can be obtained and each filter acts as a color filter.

Since the respective filters (21a, 21b, and 21c) are made of the same material (amorphous silicon), there is no need to manage materials according to color in the manufacturing process of the filters. Therefore, the manufacturing cost of the filter membrane can be reduced.

Each filter membrane (21a, 21b, and 21c) can be manufactured by a semiconductor process. If a semiconductor process can be used, it is not necessary to provide a color filter production line dedicated to organic materials. Therefore, the manufacturing cost of the filter membrane can be reduced.

Recently, color filters are required to be thinned in order to prevent color mixture between pixels. Color mixing occurs when obliquely incident light entering a color filter of a pixel reaches the photoelectric conversion unit of a pixel adjacent to the pixel. By making the filter membrane thinner, color mixing can be prevented. In the first embodiment, the physical thickness of each filter membrane (21a, 21b, and 21c) is very thin, and is 70nm at most. Therefore, color mixing can be effectively prevented.

The refractive index of amorphous silicon is about 5, which is larger than that of conventional insulating films and the like (for example, the refractive index of silicon dioxide is 1.46). Therefore, even if obliquely incident light enters the filter, the angle of refraction is small and color mixing between pixels is prevented.

In addition, regarding amorphous silicon, a film can be formed at a low temperature. Therefore, the filter film can be formed after the light-shielding film such as low melting point aluminum is formed. As a result, the manufacturing process can be freely changed. Also, if amorphous silicon is used, stress on the photoelectric conversion unit can be reduced. Therefore, damage to the photoelectric conversion unit can be reduced.

For general interference filters, if the incident angle of light changes, the interference wavelength shifts to the shorter wavelength side because the optical path length becomes shorter. Therefore, there is a technical problem in using a general interference filter for a solid-state image sensor due to the different color separation characteristics of normally incident light and obliquely incident light. When light enters at an angle of 30 degrees, since the refractive index of amorphous silicon is about 5 and greater, the refraction angle of amorphous silicon is 5.7 degrees. Therefore, there is a slight effect on obliquely incident light. For general interference filters, the greater the film thickness, the greater the effect on oblique incident light. However, the membrane thickness of each filter membrane of the first embodiment is not more than 100 nm. As a result, there is a slight influence on obliquely incident light.

Note that the amorphous silicon used for each filter membrane (21a, 21b and 21c) is an absorbent material. In this specification, an absorbing material is defined as a material whose extinction coefficient is equal to or greater than 0.1 for wavelengths in a range of wavelengths from 400 nm to 700 nm including 700 nm. The relationship between the absorption coefficient α, the extinction coefficient k, and the wavelength λ is k=α×λ/4π.

<Second Embodiment>

In the second embodiment, an example in which the antireflection film 30 is formed on the main surface facing the light source of each filter film (21a, 21b, and 21c) is described. Since the structure other than the antireflection film 30 is the same as that of the first embodiment, explanation thereof is omitted.

7 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the second embodiment.

The anti-reflection film 30 is formed on the main surface of each filter film (21a, 21b, and 21c) facing the light source. The antireflection film 30 is composed of silicon nitride and has a physical thickness of 50 nm.

Note that the physical thicknesses of the respective filters 21a, 21b, and 21c are the same as those of the first embodiment and are 70nm, 55nm, and 40nm, respectively.

Fig. 8 shows the transmission spectra of the filters 21a, 21b and 21c of the second embodiment.

Curve 32a represents the transmission spectrum of filter membrane 21a. Curve 32b represents the transmission spectrum of filter 21b. Curve 32c represents the transmission spectrum of filter 21c.

The filter 21a has a local maximum of light transmittance at a red wavelength of 650 nm. The filter 21b has a local maximum of light transmittance at a green wavelength of 560 nm. The filter 21c has a local maximum of light transmittance at a blue wavelength of 490 nm.

Comparing the transmission spectra of the same filter membranes of the first embodiment and the second embodiment (for example, filter membrane 21b: curves 31b and 32b), the local maximum (65%) of the transmittance of the second embodiment is greater than that of the first embodiment The local maximum (61%) of the transmittance of the mode. This is because the antireflection film 30 reduces light reflection.

The material and the refractive index of each portion into which the incident light 24 enters are described below. Note that this refractive index is expressed as a value when the wavelength of incident light is 560 nm.

Opening 20: silicon dioxide, refractive index: 1.46

Filter membrane 21: amorphous silicon, refractive index: 4.77

Insulating film 13: silicon dioxide, refractive index: 1.46

Photoelectric conversion unit 17: N-type silicon, refractive index: 4

The incident light 24 is converged by the microlens 23 and reaches the photoelectric conversion unit 17 through the opening 20 and the respective filters ( 21 a , 21 b and 21 c ). In general, when light passes from one medium to another, the reflectivity is determined by the ratio of the refractive indices of the two media. The reflectance R when light enters a medium having a refractive index n2 from a medium having a refractive index n1 is described below.

R=((n1-n2)/(n1+n2)) ²

When light enters amorphous silicon (refractive index: 4.77) from silicon dioxide (refractive index: 1.46) which is generally a planarization layer, the reflectance is 28%. On the other hand, when light enters amorphous silicon (refractive index: 4.77) from silicon nitride (refractive index: 2.00), the reflectance is 17%. In other words, since the reflectance is reduced by 10%, the transmittance is increased. As a result, the amount of light entering the photoelectric conversion unit 17 of each pixel is increased, and the sensitivity of the solid-state image sensor 1 is improved. This serves as an effective method for preventing a reduction in sensitivity due to miniaturization of pixels.

By forming silicon nitride on the amorphous silicon as the respective filters (21a, 21b, and 21c), not only the sensitivity is effectively improved but also the reliability and moisture resistance of the solid-state image sensor 1 are increased.

<Third Embodiment>

In the third embodiment, an example in which the respective filter films ( 21 a , 21 b , and 21 c ) are formed between the photoelectric conversion unit 17 and the light shielding film 19 is described. Since other structures are the same as those of the first embodiment, explanations thereof are omitted.

9 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the third embodiment.

The respective filter films ( 21 a , 21 b , and 21 c ) are formed between the photoelectric conversion unit 17 and the light shielding film 19 . Note that the physical thicknesses of the respective filters (21a, 21b, and 21c) are the same as those of the first embodiment, and are 70nm, 55nm, and 40nm, respectively.

The color filter forming layer 15 includes respective filter films (21a, 21b, and 21c), and can be formed by a conventional semiconductor process. Therefore, the color filter forming layer 15 may be formed between the photoelectric conversion unit forming layer 12 and the light shielding film forming layer 14 .

Also, since the color filter forming layer 15 can be formed before the wiring process, it is possible to use polysilicon which requires processing at a high temperature.

Since the respective filter films (21a, 21b, and 21c) are made of amorphous silicon, unless the filter film 21 is insulated from the photoelectric conversion unit formation layer 12, the signal charge generated in the photoelectric conversion unit 17 may leak to the respective filter films (21a, 21c). 21b and 21c). Therefore, the insulating layer 13 is provided between the respective filter films ( 21 a , 21 b , and 21 c ) and the photoelectric conversion unit forming layer 12 .

As described above, in addition to the effect of the pixel of the first embodiment, in the third embodiment, since the respective filter films (21a, 21b, and 21c) are formed between the photoelectric conversion unit 17 and the light shielding film 19, photoelectric conversion can be prevented. Interference of light between the unit 17 and the respective filters (21a, 21b and 21c). This improves the sensitivity of the solid-state image sensor 1 .

Also, the above structure can be used as an effective method for preventing color mixing due to miniaturization of pixels.

<Fourth Embodiment>

The manufacturing method of each filter membrane (21a, 21b, and 21c) in the fourth embodiment is described below.

Fig. 10 is a cross-sectional view showing a process of a method of manufacturing each filter membrane (21a, 21b, and 21c) of the fourth embodiment.

Fig. 10(a) shows a pixel after the film formation process.

In the film forming process, the amorphous silicon film 201 is formed in the entire upper portion of the silicon oxide film of the light shielding film forming layer 14 . Regarding the amorphous silicon film, when the film is formed, a PVD (Physical Vapor Deposition) method can be used. The temperature for film formation is set within a range from ambient temperature to 400°C inclusive. The film formation was stopped when the thickness of the amorphous silicon film 201 was 70 nm.

Figure 10(b) shows the pixel after the first coating process.

In the first coating process, a photoresist (PR) 202 is coated on the entire upper portion of the amorphous silicon film 201 formed in the film forming process.

Figure 10(c) shows the pixel after the first exposure and development process.

In the first exposure and development process, the photoresist (PR) 202 coated in the first coating process is exposed using a patterned mask. Subsequently, the exposed portions are removed and the remaining portion of the photoresist is cured. With this structure, only the photoresist 202 corresponding to the pixel 1c is removed.

Figure 10(d) shows the pixel after the first etching process.

In the first etching process, dry etching is performed on the amorphous silicon film 201 after the first exposure and development process. As a result, the amorphous silicon film 201 of the region corresponding to the pixel 1c is etched. Etching was stopped when the thickness of the amorphous silicon film 201 of the pixel 1c was 40 nm.

Note that film thickness can be controlled within 3% accuracy by dry etching.

Figure 10(e) shows the pixel after the second coating process.

In the second coating process, a photoresist (PR) 203 is coated on the entire upper portion of the etched amorphous silicon film 201 .

Figure 10(f) shows the pixel after the second exposure and development process.

In the second exposure and development process, only the photoresist 202 corresponding to the pixel 1b is removed.

Figure 10(g) shows the pixel after the second etching process.

In the second etching step, the amorphous silicon film 201 in the region corresponding to the pixel 1b is etched. Etching was stopped when the thickness of the amorphous silicon film 201 of the pixel 1b was 55 nm.

Figure 10(h) shows the pixel after the photoresist removal process.

In the photoresist removal process, unnecessary photoresist 203 is removed.

As described above, since each filter is made of the same material (amorphous silicon), there is no need to manage the material according to the color in the manufacturing process of the filter. Therefore, the manufacturing cost of the filter membrane can be reduced.

Individual filter membranes can be manufactured by semiconductor processes. Therefore, the manufacturing cost of the filter membrane can be reduced.

In the fourth embodiment, the temperature at which the film is formed can be set within a range from ambient temperature to 400° C. inclusive. In addition, for amorphous silicon, the film can be formed at low temperature. Therefore, the filter film can be formed after the light-shielding film such as low melting point aluminum is formed.

Fig. 11 is a cross-sectional view of each filter membrane (21a, 21b, and 21c) manufactured by the manufacturing method of the fourth embodiment.

By using the above-described manufacturing method, an oxide film 211 such as a natural oxide film having a thickness equal to or less than 10 nm can be formed on the amorphous silicon film 201 . However, since the thickness of the oxide film 211 is equal to or less than 10 nm and is very thin, the oxide film 211 has little influence on the transmission spectrum. Good color separation characteristics can be obtained by designing the device in consideration of the oxide film thickness.

<Fifth Embodiment>

The manufacturing method of each filter membrane (21a, 21b, and 21c) in the fifth embodiment will be described below.

Fig. 12 is a process sectional view showing a method of manufacturing each filter membrane (21a, 21b, and 21c) of the fifth embodiment.

Fig. 12(a) shows a pixel after the first film forming process.

In the first film forming step, the amorphous silicon film 301 is formed on the entire upper portion of the silicon oxide film of the light-shielding film forming layer 14 . Regarding amorphous silicon, when the film is formed, a PVD (Physical Vapor Deposition) method can be used. The temperature for film formation is set within a range from ambient temperature to 400°C inclusive. The film formation was stopped when the thickness of the amorphous silicon film 301 was 15 nm.

Figure 12(b) shows the pixel after the first exposure and development process.

In the first exposure and development process, the entire upper portion of the amorphous silicon film 301 formed in the first film formation process is coated with a photoresist (PR) 302 . Subsequently, the photoresist 302 is exposed using a stepper to remove the photoresist 302 corresponding to the pixels 1b and 1c.

Figure 12(c) shows the pixel after the first etching process.

In the first etching process, a dry etching process is performed on the amorphous silicon film 301 after the first exposure and development process. As a result, the amorphous silicon film 301 of the regions corresponding to the pixels 1b and 1c is removed.

Figure 12(d) shows the pixel after the first photoresist removal process.

In the first photoresist removal process, unnecessary photoresist 302 is removed. With this structure, an amorphous silicon film 301 having a thickness of 15 nm is formed in a region corresponding to the pixel 1a.

Fig. 12(e) shows the pixel after the second film forming process.

In the second film formation process, the amorphous silicon film 303 is formed after the first resist removal process. When the thickness of the amorphous silicon film was 15 nm, the film formation was stopped. As a result, the thicknesses of the amorphous silicon films 303 of the respective pixels 1a, 1b, and 1c were 30 nm, 15 nm, and 15 nm, respectively.

Figure 12(f) shows the pixel after the second exposure and development process.

In the second exposure and development process, the entire upper portion of the amorphous silicon film 303 formed in the second film formation process is coated with a photoresist (PR) 304 . Subsequently, the photoresist 304 is exposed using a stepper to remove the photoresist 304 corresponding to the pixel 1c.

Figure 12(g) shows the pixel after the second etching process.

In the second etching step, the amorphous silicon film 303 in the region corresponding to the pixel 1c is removed.

Figure 12(h) shows the pixel after the second photoresist removal process.

In the second resist removal process, an amorphous silicon film having a thickness of 30 nm was formed in a region corresponding to the pixel 1 a, and an amorphous silicon film having a thickness of 15 nm was formed in a region corresponding to the pixel 1 b.

Fig. 12(i) shows a pixel after the third film forming process.

In the third film forming process, an amorphous silicon film having a thickness of 40 nm was formed. Therefore, the thicknesses of the respective filters (21a, 21b and 21c) in the respective pixels 1a, 1b and 1c are 70nm, 55nm and 40nm, respectively.

In this case, filter membranes (21a, 21b and 21c) having three types such as 70nm, 55nm and 40nm are formed. That is, an amorphous silicon film having a thickness of 70 nm is formed in a region corresponding to the pixel 1a, an amorphous silicon film having a thickness of 55 nm is formed in a region corresponding to the pixel 1b, and an amorphous silicon film having a thickness of 40 nm is formed in a region corresponding to the pixel 1c. Amorphous silicon film.

As described above, since each filter is made of the same material (amorphous silicon), there is no need to manage the material according to the color in the manufacturing process of the filter. Therefore, the manufacturing cost of the filter membrane can be reduced.

Individual filter membranes can be manufactured by semiconductor processes. Therefore, the manufacturing cost of the filter membrane can be reduced.

In the fifth embodiment, since the film thickness is controlled in the film forming process, in-plane variation of the film thickness can be reduced compared to the method of controlling the thickness by etching described in the fourth embodiment. As a result, the accuracy of film thickness can be increased.

In the fifth embodiment, the temperature at which the film is formed can be set within a range from ambient temperature to 400° C. inclusive. In addition, with amorphous silicon, a film can be formed at a low temperature. Therefore, the filter film can be formed after the light-shielding film such as low melting point aluminum is formed.

Fig. 13 is a cross-sectional view of each filter membrane (21a, 21b, and 21c) manufactured by the manufacturing method of the fifth embodiment.

By using the above-described manufacturing method, an oxide film 211 such as a natural oxide film can be formed on the amorphous silicon films 301, 302, and 305. However, since the thickness of the oxide film 211 is equal to or less than 10 nm and is very thin, the oxide film 211 has little influence on the transmission spectrum. Good color separation characteristics can be obtained by designing the device in consideration of the oxide film thickness.

Note that in the fifth embodiment, the filter membrane is completed at the stage of Fig. 12(i). However, the filter membrane can be completed at the stage of Fig. 12(h).

In the filter membrane in Fig. 12(h), the thicknesses of the three types of membranes are 30nm, 15nm and 0nm respectively. With this structure, two colors (30nm and 15nm) in pixels 1a and 1b, and white (0nm) in pixel 1c have different transmission bands, and color filtering can be realized. For this color filter, the thickness of amorphous silicon is about 30 nm and is very thin, so less light is absorbed and more light is transmitted. Therefore, a solid-state image sensor with high sensitivity can be obtained.

On the other hand, in the structure of FIG. 12(i), color separation is performed by interference effect and absorption effect. Compared to the structure of Fig. 12(h), the amount of transmitted light is reduced due to the absorption of amorphous silicon. However, solid-state image sensors with color reproducibility are available.

In Figure 12(h) and Figure 12(i), three different transmission bands can be obtained and color separation can be achieved. Since there is more transmitted light in FIG. 12(h), the color filter shown in FIG. 12(h) can be applied to occasions emphasizing high sensitivity. In addition, the color filter shown in FIG. 12(i) can be applied to occasions where color reproducibility is emphasized.

<Sixth Embodiment>

In the sixth embodiment, an example of each filter membrane ( 51 a , 51 b , and 51 c ) composed of titanium dioxide is described. Since other structures are the same as those of the first embodiment, explanations thereof are omitted.

14 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the sixth embodiment.

In the sixth embodiment, each filter membrane (51a, 51b, and 51c) is a single-layer membrane composed of titanium dioxide. The optical thickness of each filter is less than a thickness equal to half the wavelength of the color to be transmitted by a thickness corresponding to the amount of light of the color to be transmitted absorbed by the titanium dioxide.

As described in the first embodiment, with this structure, a local maximum of light transmittance can appear at the wavelength of the color to be transmitted.

Titanium dioxide differs from amorphous silicon in that it has little absorption in the optical wavelength range (400nm to 700nm), and its extinction coefficient is close to zero. Therefore, the correction based on the amount of light absorption is also close to 0.

Here, the red wavelength λ is 630 nm, the green wavelength λ is 530 nm, and the blue wavelength λ is 470 nm. So, half of the red wavelength λ is 315nm, half of the green wavelength λ is 265nm, and half of the blue wavelength λ is 235nm. Since the correction according to the amount of light absorption is close to 0, the optical thickness of the red filter is 315 nm, the optical thickness of the green filter is 265 nm, and the optical thickness of the blue filter is 235 nm.

Titanium dioxide has a refractive index of 2.46 at a wavelength of 630 nm. Titanium dioxide has a refractive index of 2.53 at a wavelength of 530 nm. Titanium dioxide has a refractive index of 2.60 at a wavelength of 470 nm. Therefore, the physical thicknesses (da, db, and dc) of the respective filters (51a, 51b, and 51c) are da=125nm, db=105nm, and dc=90nm, respectively.

FIG. 15 shows the transmission spectra of the filters 51a, 51b, and 51c of the sixth embodiment.

Curve 33a represents the transmission spectrum of filter 51a. Curve 33b represents the transmission spectrum of filter 51b. Curve 33c represents the transmission spectrum of filter 51c.

The filter 51a has a local maximum of light transmittance at a red wavelength of 630 nm. The filter 51b has a local maximum of light transmittance at a green wavelength of 530 nm. The filter 51c has a local maximum of light transmittance at a blue wavelength of 470 nm. The larger the optical thickness of the filter, the longer the wavelength of the local maximum. For this reason, it can be expected that a local maximum occurs in the light transmission spectrum due to the interference effect of light.

The local maximum value of the transmittance of the filter membrane 51a is 96%. The local maximum value of the transmittance of the filter membrane 51b is 96%. The local maximum value of the transmittance of the filter membrane 51c is 96%.

It is expected that since the absorption coefficient of titanium dioxide is constant independent of wavelength, the local value is constant independent of color wavelength.

Comparing the transmission spectra of the same filter membranes of the first embodiment and the sixth embodiment, the transmittance of the sixth embodiment is greater than that of the first embodiment. This is because the absorption coefficient of titanium dioxide is close to zero in the optical wavelength range.

Since titanium dioxide has little absorption in the optical wavelength range, high transmittance can be obtained on the short-wavelength side where the transmittance of amorphous silicon decreases. As a result, the sensitivity of the solid-state image sensor can be improved.

As described above, in the sixth embodiment, each filter membrane (51a, 51b, and 51c) is composed of titanium dioxide as a transparent material. Therefore, the sensitivity of the solid-state image sensor can be improved. In addition, other effects are the same as those of the first embodiment. In the present specification, the transparent material is defined as a material having an extinction coefficient equal to or less than 0.05 with respect to a wavelength within a wavelength range of 400 nm to 700 nm inclusive.

<Seventh embodiment>

In the seventh embodiment, an example in which each filter membrane (61a, 61b, and 61c) is composed of an oxide of amorphous silicon is described. Since other structures are the same as those of the first embodiment, explanations thereof are omitted here.

16 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the seventh embodiment.

The seventh embodiment differs from the first embodiment in that each filter membrane (61a, 61b, and 61c) is composed of _SiOx, an oxide of amorphous silicon. In addition, the seventh embodiment differs from the first embodiment in that the refractive index of each filter membrane (61a, 61b, and 61c) can be adjusted by adjusting the composition of amorphous silicon oxide _SiOx .

The optical thickness of each filter film is less than a thickness equal to half the wavelength of the color to be transmitted, and the difference between the two is a thickness corresponding to the amount of light of the color to be transmitted absorbed by the amorphous silicon. This is the same as that of the first embodiment. With this structure, a local maximum of light transmittance can appear at the wavelength of the color to be transmitted.

Here, the red wavelength λ is 650 nm, the green wavelength λ is 560 nm, and the blue wavelength λ is 490 nm. Therefore, half of the red wavelength λ is 325nm, half of the green wavelength λ is 280nm, and half of the blue wavelength λ is 245nm. Since the optical thickness is smaller than the thickness equal to half the wavelength of the color to be transmitted, the thickness corresponding to the amount of light of the color to be transmitted absorbed by the amorphous silicon is smaller, so the optical thickness of the red filter is 315nm, and the green filter is 315nm. The optical thickness of the blue filter is 265nm, and the optical thickness of the blue filter is 235nm. The amount of light absorption is obtained by the absorption coefficient of the amorphous silicon oxide _SiOx and the optical thickness of the filter film.

The refractive indices na, nb and nc of the amorphous silicon oxide _SiOx constituting the filters (61a, 61b and 61c) were adjusted to 4.5, 4.25 and 4.0, respectively. The refractive index can be adjusted by adjusting the amount of oxygen added when the amorphous silicon oxide _SiOx is formed. For SiO _x , the larger the amount of oxygen added, the smaller the refractive index.

As a result, the physical thicknesses (da, db, and dc) of the respective filters (61a, 61b, and 61c) were da=70 nm, db=62 nm, and dc=59 nm, respectively.

Comparing the difference in membrane thickness between the filter membranes in the seventh embodiment and the first embodiment, the difference in membrane thickness in the seventh embodiment is smaller than that in the first embodiment. This is because the refractive index of each filter is adjusted to be smaller as the wavelength of the color to be transmitted is shorter in the seventh embodiment. The smaller the difference in film thickness, the easier it is to form the planarization layer 22 and the microlens 23 .

FIG. 17 shows transmission spectra of the filters 61a, 61b, and 61c of the seventh embodiment.

Curve 34a represents the transmission spectrum of filter 61a. Curve 34b represents the transmission spectrum of filter 61b. Curve 34c represents the transmission spectrum of filter 61c.

The filter 61a has a local maximum of light transmittance at a red wavelength of 650 nm. The filter 61b has a local maximum of light transmittance at a green wavelength of 560 nm. The filter 61c has a local maximum of light transmittance at a blue wavelength of 490 nm.

The local maximum value of the transmittance of the filter membrane 61a is 79%. The local maximum value of the transmittance of the filter membrane 61b is 64%. The local maximum value of the transmittance of the filter membrane 61c is 43%. Comparing the transmission spectra (for example, curves 34b and 31b) of the same filter membranes of the first embodiment and the seventh embodiment, the local maximum (64%) of the transmittance of the seventh embodiment is greater than that of the first embodiment. rate local maximum (61%). It is expected that the transmittance is increased because the absorption coefficient of the amorphous silicon oxide _SiOx is smaller than that of amorphous silicon.

Note that the image sensor can be easily planarized if the difference in film thickness of the filters is equal to or less than 15% of the maximum film thickness in the filters (61a, 61b, and 61c).

<Eighth Embodiment>

In the eighth embodiment, an example in which the antireflection film 30 is formed on the main surface of each filter film (61a, 61b, and 61c) facing the light source is described. Since other structures are the same as those of the seventh embodiment, explanations thereof are omitted.

18 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the eighth embodiment.

The anti-reflection film 30 is formed on the main surface of each filter film (61a, 61b, and 61c) facing the light source. The antireflection film 30 is composed of silicon nitride and has a physical thickness of 50 nm.

Note that the physical thicknesses of the respective filters 61a, 61b, and 61c are the same as those of the seventh embodiment and are 70 nm, 62 nm, and 59 nm, respectively.

FIG. 19 shows the transmission spectra of the filters 61a, 61b and 61c of the eighth embodiment.

Curve 35a represents the transmission spectrum of filter 61a. Curve 35b represents the transmission spectrum of filter 61b. Curve 35c represents the transmission spectrum of filter 61c.

The filter 61a has a local maximum of light transmittance at a red wavelength of 650 nm. The filter 61b has a local maximum of light transmittance at a green wavelength of 560 nm. The filter 61c has a local maximum of light transmittance at a blue wavelength of 490 nm.

Comparing the transmission spectra of the same filter membranes of the eighth embodiment and the seventh embodiment (for example, filter membrane 61b: curves 35b and 34b), the local maximum value (67%) of the transmittance of the eighth embodiment is greater than that of the seventh embodiment The local maximum (64%) of the transmittance of the mode. This is because the antireflection film 30 reduces light reflection.

The material and the refractive index of each portion into which the incident light 24 enters are described below. Note that this refractive index is expressed as a value when the wavelength of incident light is 560 nm.

Opening 20: silicon dioxide, refractive index: 1.46

Filter membrane 61: oxide of amorphous silicon, refractive index: 4 to 5

Insulating film 13: silicon dioxide, refractive index: 1.46

Photoelectric conversion unit 17: N-type silicon, refractive index: 4

The incident light 24 is converged by the microlens 23 and reaches the photoelectric conversion unit 17 through the opening 20 and the respective filters ( 61 a , 61 b and 61 c ). In general, when light passes from one medium to another, the reflectivity is determined by the ratio of the refractive indices of the two media. The reflectance R when light enters a medium having a refractive index n2 from a medium having a refractive index n1 is described below.

R=((n1-n2)/(n1+n2)) ²

When light enters oxide (refractive index: 4 to 5) of amorphous silicon from silicon dioxide (refractive index: 1.46) which is generally a planarization layer, the reflectance is about 25%. On the other hand, when light enters oxide (refractive index: 4 to 5) of amorphous silicon from silicon nitride (refractive index: 2.00), the reflectance is about 15%. In other words, since the reflectance is reduced by 10%, the transmittance is increased. As a result, the amount of light entering the photoelectric conversion unit 17 of each pixel is increased, and the sensitivity of the solid-state image sensor 1 is improved. This is an effective method for preventing a decrease in sensitivity due to miniaturization of pixels.

By forming silicon nitride on the oxide of amorphous silicon as the respective filters (61a, 61b, and 61c), not only the sensitivity of the solid-state image sensor 1 is effectively improved but also the reliability and moisture resistance are increased.

When the reflectance is lowered due to the formation of the anti-reflection film 30 on the main surface of each filter film (61a, 61b and 61c), the wavelength representing the local maximum value of the transmittance of each filter film (61a, 61b and 61c) may shift to shifted to the long wavelength side. In this case, it is necessary to correct the optical thicknesses of the respective filters (61a, 61b and 61c), or the weighting factors of the transformation matrix.

<Ninth Embodiment>

In the ninth embodiment, an example is described in which the wavelength distributions of the absorption coefficients of the respective filters ( 71 a , 71 b , and 71 c ) are different.

20 is a cross-sectional view of a substrate showing the structure of pixels (1a, 1b, and 1c) of the ninth embodiment.

In the ninth embodiment, each filter membrane (71a, 71b, and 71c) is composed of amorphous silicon (a-Si), polycrystalline silicon (p-Si), and titanium dioxide (TiO ₂ ), respectively. In other words, the filter with the shorter wavelength of the color to be transmitted consists of an inorganic material that has a lower light absorption coefficient in the optical wavelength range. Since the materials constituting the respective filters (71a, 71b, and 71c) have different absorption coefficients in the optical wavelength range, the light transmittance varies more.

FIG. 21 shows transmission spectra of the filters 71a, 71b, and 71c of the ninth embodiment.

Curve 36a represents the transmission spectrum of filter 71a. Curve 36b represents the transmission spectrum of filter 71b. Curve 36c represents the transmission spectrum of filter 71c.

For amorphous silicon (a-Si), the wavelength distribution of light absorption coefficient is different by controlling the growth method and growth temperature. In other words, the transmittance varies with wavelength, and the same is true for polysilicon (p-Si) and titanium dioxide (TiO ₂ ). Therefore, as shown in FIG. 21, the transmittance varies in the optical wavelength range. By determining the respective coefficients X ₁₁ to X ₃₃ of the transformation matrix from the transmission spectrum, the respective signals of red, green and blue can be obtained.

As described above, with the filter of the ninth embodiment, the wavelength range of transmitted light can be determined by adjusting the light absorption coefficient so that it differs according to the color.

<Tenth Embodiment>

The manufacturing method of each filter membrane (61a, 61b, and 61c) in the ninth embodiment will be described below.

FIG. 22 is a cross-sectional view showing the steps of the method of manufacturing the filter membrane 61 according to the tenth embodiment.

Figure 22(a) shows the pixel after the first coating process.

In the first coating process, a photoresist (PR) 401 is coated on the entire upper portion of the silicon oxide film of the light-shielding film forming layer 14 .

Figure 22(b) shows the pixel after the first exposure and development process.

In the first exposure and development process, the photoresist (PR) 401 coated in the first coating process is exposed using a patterned mask. Subsequently, the exposed portions are removed and the remaining portion of the photoresist is cured. With this structure, only the photoresist 401 corresponding to the pixel 1a is removed.

Fig. 22(c) shows a pixel after the first film forming process.

In the first film formation process, an oxide of amorphous silicon 402 is formed after the first exposure and development process. As for the oxide of amorphous silicon, when the film is formed, a PVD (Physical Vapor Deposition) method can be used. At this time, the oxygen flow rate is controlled so that the oxide of the amorphous silicon 402 has a composition with a refractive index of 4.5. The temperature for film formation is set within the range of ambient temperature to 400°C inclusive. The film formation was stopped when the thickness of the oxide of amorphous silicon 402 was 70 nm.

Fig. 22(d) shows the pixel after the first removal process.

In the first removal process, the photoresist 401 remaining in the first exposure and development process is removed. At the same time, the amorphous silicon 402 formed on the photoresist 401 is also removed.

Figure 22(e) shows the pixel after the second coating process.

In the second coating process, a photoresist (PR) 403 is coated after the first removal process.

Figure 22(f) shows the pixel after the second exposure and development process.

In the second exposure and development process, the photoresist (PR) 403 coated in the second coating process is exposed using a patterned mask. Subsequently, the exposed portions are removed and the remaining portion of the photoresist is cured. With this structure, only the photoresist 403 corresponding to the pixel 1b is removed.

Fig. 22(g) shows a pixel after the second film forming process.

In the second film formation process, an oxide of amorphous silicon 404 is formed after the second exposure and development process. As for the oxide of amorphous silicon, when the film is formed, a PVD (Physical Vapor Deposition) method can be used. At this time, the oxygen flow rate was controlled so that the oxide of the amorphous silicon 404 had a composition with a refractive index of 4.25. The temperature for film formation is set within the range of ambient temperature to 400°C inclusive. When the thickness of the oxide of amorphous silicon 404 was 62 nm, the film formation was stopped.

Fig. 22(h) shows the pixel after the second removal process.

In the second removal process, the photoresist 403 remaining in the second exposure and development process is removed. At the same time, the amorphous silicon 404 formed on the photoresist 403 is also removed.

Fig. 22(i) shows the pixel after the third removal process.

Next to the second removal process, an oxide of amorphous silicon 405 is formed by performing the same process as described above. The thickness of the oxide of amorphous silicon 405 was set to 59 nm.

As mentioned above, since each filter differs only in the composition, there is no need to control the material according to the color in the filter manufacturing process. Therefore, the manufacturing cost of the filter membrane can be reduced.

Individual filter membranes can be manufactured by semiconductor processes. Therefore, the manufacturing cost of the filter membrane can be reduced.

So far, the solid-state image sensor of the present invention has been specifically described through the embodiments. However, the technical scope of the present invention is not limited to the above-mentioned embodiments. The following is the modification:

(1) In the first embodiment, although the physical thicknesses (da, db, and dc) of the respective filters are da=70nm, db=55nm, and dc=40nm, respectively, the physical thicknesses are not limited thereto. The physical thicknesses (da, db, and dc) need only satisfy the following conditions. The conditions are da>db>dc, 0<dc<100, 10<db<150, and 20<da<200. As a result, RGB color separation can be achieved by controlling the weighting factors of the transformation matrix.

Likewise, in the first embodiment, although the filter film 21c is used, RGB color separation can be realized without using the filter film 21c by controlling the weighting factors of the transformation matrix. The same applies to the sixth embodiment.

Also, by making each physical thickness thinner, light transmittance can be improved.

(2) In the second embodiment, the antireflection film 30 is formed on the main surface of each filter film (21a, 21b, and 21c). If the antireflection film 30 is formed, the wavelength at which the local maximum value of the transmittance of each filter film (21a, 21b, and 21c) is represented may be shifted to the long wavelength side. In this case, it is necessary to correct the optical thicknesses of the respective filters (21a, 21b and 21c), or the weighting factors of the transformation matrix. As a result, color separations are correctly achieved.

(3) In the fourth embodiment, only amorphous silicon is used as a color filter material. However, the color filter material is not limited to amorphous silicon, and polycrystalline silicon, single crystal silicon, or a material mainly containing silicon may be used. The same applies to the fifth embodiment.

(4) In the sixth embodiment, although titanium dioxide is used as the transparent material constituting the filter membrane, the transparent material is not limited thereto. For example, oxides of tantalum (tantalum pentoxide, etc.) or niobium (niobium pentoxide, etc.) may also be used in order to realize a solid-state image sensor with high sensitivity.

(5) In the sixth embodiment, antireflection films may be formed on the main surfaces of the respective filter films (51a, 51b, and 51c). This can further improve the sensitivity of the solid-state image sensor. Silicon nitride, silicon oxynitride, silicon oxide, and the like can be used as a material for the antireflection film.

When the reflectance is lowered due to the anti-reflection film being formed on the main surface of each filter (51a, 51b, and 51c), the wavelength representing the local maximum of the transmittance of each filter (51a, 51b, and 51c) may be longer The wavelength is shifted on one side. In this case, it is necessary to correct the optical thicknesses of the respective filters (51a, 51b, and 51c), or the weighting factors of the transformation matrix.

(6) In the sixth embodiment, although the physical thicknesses (da, db, and dc) of the respective filters are da=125 nm, db=105 nm, and dc=90 nm, respectively, the physical thicknesses are not limited thereto. The physical thicknesses (da, db, and dc) need only satisfy the following conditions. The conditions are da>db>dc, 0<dc<200, 50<db<250, and 75<da<300. As a result, RGB color separation can be achieved by controlling the weighting factors of the transformation matrix.

(7) In the embodiments, only the characteristics of the color filter in the optical wavelength range are shown. However, light having different bands can also be transmitted in wavelength ranges such as infrared region, ultraviolet region, etc. by appropriately changing the thickness of the color filter.

(8) In an embodiment, the optical thickness of each filter is smaller than a thickness equal to half the wavelength of the color to be transmitted by a thickness corresponding to the amount of light of the color to be transmitted absorbed by the inorganic material. When the filter is used in a color image sensor, the optical thickness ranges from 150nm to including 400nm.

Industrial Applicability

The solid-state image sensor of the present invention can be used as a solid-state image sensor for digital still cameras, video cameras, and the like.

Claims (16)

1. solid state image sensor with a plurality of pixels, wherein,

Described a plurality of pixel respectively comprises the filter membrane that is used for through the light of predetermined color, and is used for being converted to the photoelectric conversion unit of electric charge through the light of described filter membrane;

The monofilm of described filter membrane for constituting by inorganic material; And

The optical thickness of described monofilm than with the corresponding thickness of amount of the light of the described predetermined color of the little and described inorganic material absorption of half thickness that equates of the wavelength of described predetermined color.

2. solid state image sensor according to claim 1 is characterized in that, described inorganic material is big more for the absorption coefficient of the light of the wavelength of described predetermined color, and the described optical thickness of described monofilm is more little.

3. solid state image sensor according to claim 1 is characterized in that, the composition of described inorganic material is all identical for described a plurality of pixels.

4. solid state image sensor according to claim 1 is characterized in that,

The composition of described inorganic material is according to color to be seen through in a plurality of colors and difference; And

The wavelength of each described color is short more, and the refractive index of described inorganic material is more little.

5. solid state image sensor according to claim 1 is characterized in that the refractive index of described inorganic material is equal to or greater than 3.

6. solid state image sensor according to claim 1 is characterized in that, described inorganic material is amorphous silicon, polysilicon, monocrystalline silicon or the material that mainly contains silicon.

7. solid state image sensor according to claim 1 is characterized in that, described inorganic material is the oxide of titanium dioxide, tantalum or the oxide of niobium.

8. solid state image sensor according to claim 1 is characterized in that, described a plurality of pixels respectively also comprise antireflection film, and described antireflection film is formed at described filter membrane in the face of the first type surface of light source and have refractive index less than described filter membrane.

9. solid state image sensor according to claim 8 is characterized in that, described antireflection film is made of the nitrogen oxide of nitride, silicon dioxide or the silicon of silicon.

10. solid state image sensor according to claim 1 is characterized in that,

Described photoelectric conversion unit is formed in a part of substrate;

Described a plurality of pixel respectively also comprises photomask, and described photomask covers described substrate and has the opening that is arranged on the corresponding position of described photoelectric conversion unit; And

Described filter membrane is arranged between described photomask and the described substrate.

11. solid state image sensor according to claim 1 is characterized in that,

Described a plurality of pixel is arranged so that respectively described filter membrane is arranged at identical plane in the face of the first type surface of described photoelectric conversion unit;

Described a plurality of pixel respectively also comprises and is arranged at described filter membrane in the face of the levelling blanket on the first type surface of light source; And

The physical thickness of described filter membrane is big more, and the thickness of described levelling blanket is more little.

12. solid state image sensor according to claim 11 is characterized in that, described a plurality of pixels also respectively comprise and are arranged at described levelling blanket in the face of the lenticule on the first type surface of described light source.

13. the solid state image sensor with a plurality of pixels is characterized in that,

Described a plurality of pixel respectively comprises the filter membrane that is used for through the light of predetermined color, and is used for being converted to the photoelectric conversion unit of electric charge through the light of described filter membrane;

The monofilm of described filter membrane for constituting by inorganic material; And

The optical thickness of described monofilm is according in 150nm color settings to be seen through in a plurality of colors in the scope that contains 400nm.

14. the solid state image sensor with a plurality of pixels is characterized in that,

Described a plurality of pixel respectively comprises the filter membrane that is used for through the light of predetermined color, and is used for being converted to the photoelectric conversion unit of electric charge through the light of described filter membrane;

The wavelength of described predetermined color is short more, and the absorption coefficient of light in the optical wavelength range of the inorganic material that constitutes described filter membrane is more little.

15. the solid state image sensor according to claim 14 is characterized in that, the described absorption coefficient of light of described filter membrane is difference by the composition that changes described inorganic material.

16. the solid state image sensor according to claim 14 is characterized in that, the corresponding thickness of amount of the littler light with the described predetermined color that is absorbed by described inorganic material than half thickness that equates of the wavelength of described predetermined color of the optical thickness of described filter membrane.

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