JP2013076859A - Manufacturing method for color filter, manufacturing method for solid state imager, and solid state imager - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently form a color filter with a light condensing function on an imager substrate.SOLUTION: The color filter is formed in such a manner that a grid of separation walls 22 with openings 22 corresponding to photoelectric conversion elements is formed on an imager substrate 20, a color resist 42 is applied to the openings 22a, and exposure and development are carried out. The exposure of the color resist 42 is carried out by reduction projecting exposure with a reduction magnification r, which uses a photo-mask 50 having a predetermined mask aperture 52. As an example of the photo-mask 50, one in which, where the area of each of the openings 22a of separation walls 22 is S, the aperture area Sm of the mask aperture 52 is Sm<S/r is used. Exposure light L is condensed in a position 56 higher than the surface position 57 of each separation wall 22 so that the exposure area of the color resist 42 in the surface position 57 of the separation wall 22 is equal to or smaller than the area of each opening 22 of the separation wall 22.

Description

  The present invention relates to a method for manufacturing a color filter provided in a solid-state imaging device, a method for manufacturing a solid-state imaging device using the method for manufacturing a color filter, and a solid-state imaging device.

  In a normal front-illuminated CMOS image sensor that is currently widely used as a solid-state image sensor, the incident surface of the subject light is improved in order to improve the aperture efficiency of the pixel and guide the imaging light flux to the photoelectric conversion unit for each pixel as much as possible. Microlenses are laid on the top. Thereby, the aperture efficiency is improved and the photoelectric conversion efficiency is improved as compared with the case where no microlens is laid.

However, in recent years, with the reduction in pixel size, attention has been paid to a design in which a lens function is provided not only to a microlens but also to a color filter.
In Patent Document 1, it is proposed that a material having a lower refractive index than that of the color filter or a condensing function between the pixels is provided as a gap between the pixels of the color filter. Similar proposals are made in Patent Documents 2 to 6. A structure in which a separation wall is provided between color filters has been proposed for a long time as proposed in Patent Document 7.

JP 2006-295125 A JP 2009-111225 A JP 2010-67827 A JP 2010-67828 A JP 2010-204154 A Patent No. 4741015 JP-A-3-282403

  There are several methods for producing a color filter with a separation wall proposed in Patent Documents 1 to 7, each of which has a problem.

  In Patent Document 7, after a separation wall is first formed, a layer that becomes a color filter is formed by coating, and after the selective exposure, excess color filter material placed on the separation wall is exposed until the surface of the separation wall is exposed. The filter is formed by developing after etching. However, in this manufacturing method, since a dry etching process is included in the middle of normal exposure and development processes such as coating, exposure, etch back, development, and color filter, the manufacturing process is complicated and long, and etching control is difficult. In other words, the process is long and complicated, which causes a deterioration in yield.

  In Patent Documents 1 and 2, a color filter array is first prepared, a region to be a separation wall is opened with a photoresist, a groove is formed between the color filters by dry etching, and a low refractive index material is applied and cured. Are made. However, in this manufacturing method, when a low refractive index material is applied, bubbles do not enter well in the groove, and bubbles remain when it hardens, forming a bump on the surface. This causes scattering loss and color mixing.

  In Patent Document 5, a separation wall is first produced, then a color filter made of a non-photosensitive material is produced in order, and finally a color filter array is produced by CMP (chemical polishing). However, in this manufacturing method, it is difficult to control the remaining film thickness by CMP, which causes a deterioration in yield.

  This invention is made | formed in view of the said situation, Comprising: It aims at providing the manufacturing method of the color filter layer which can produce efficiently the color filter which has a condensing function provided with the separation wall. Is. It is another object of the present invention to provide a solid-state imaging device having a small color mixture even when the pixel pitch is reduced, which includes a color filter having a condensing function including a separation wall, and a method for manufacturing the same.

The method for producing a color filter according to the present invention includes a transparent separation that separates a color filter of two or more colors and a color filter of each color on an imaging element substrate having a plurality of photoelectric conversion elements on a circuit board. A method for producing a color filter layer comprising a wall,
Forming a grid-like separation wall having an opening corresponding to each photoelectric conversion element on the imaging element substrate;
An application step of applying a color resist to the openings of the grid-like separation walls;
An exposure step of exposing the color resist; and a development step of developing the exposed color resist;
In the exposure step, the color resist is exposed by using a photomask having a predetermined mask opening and reducing and projecting the mask opening corresponding to the opening position of the separation wall,
As the photomask, an opening area Sm of the mask opening is such that Sm <S / r, where S is the opening area of the separation wall and r is the reduction magnification of the reduction projection,
The exposure light is condensed at a position above the surface position of the separation wall so that the exposure area of the color resist at the surface position of the separation wall is equal to or less than the area of the opening of the separation wall.

  The color resist coating, exposure, and development steps are repeated for each color, whereby a color filter layer having a plurality of colors can be obtained.

  The exposure light is preferably condensed so that an exposure area of the color resist at a surface position of the separation wall substantially coincides with an area of the opening of the separation wall.

  In the coating step, it is preferable to apply the color resist until the opening of the separation wall is filled with the color resist and the surface of the separation wall is covered.

The solid-state imaging device of the present invention is a method for manufacturing a solid-state imaging device comprising a color filter layer on an imaging device substrate comprising a plurality of photoelectric conversion elements on a circuit board,
Forming the plurality of photoelectric conversion elements on the circuit board to produce an image sensor board;
The color filter layer is manufactured on the plurality of photoelectric conversion elements by the method for manufacturing a color filter of the present invention.

The solid-state imaging device of the present invention includes an imaging device substrate comprising a plurality of photoelectric conversion elements on a circuit board,
A color filter layer comprising two or more color filters disposed above the plurality of photoelectric conversion elements and a transparent separation wall separating the color filters of each color;
The color filter has a plano-convex lens shape.

  The photoelectric conversion layer of the photoelectric conversion element is preferably composed of an organic material.

  According to the color filter manufacturing method of the present invention, in the color resist exposure step, a photomask having a predetermined mask opening is used, and the mask opening is reduced and projected in correspondence with the opening position of the separation wall. As the photomask, an opening area Sm of the mask opening is such that Sm <S / r, where S is the opening area of the separation wall and r is the reduction magnification of the reduction projection, By condensing the exposure light at a position above the surface position of the separation wall so that the exposure area of the color resist at the surface position of the separation wall is less than the area of the opening of the separation wall, The shape can be a convex shape (plano-convex lens shape). Etching is not required after development, and a color filter can be produced efficiently.

  According to the solid-state imaging device of the present invention, the color filter layer including the transparent separation wall that separates the color filters of each color is provided on the imaging device substrate, and the shape of each color filter is a plano-convex lens. Due to the shape, the light condensing property is remarkably improved, and crosstalk between adjacent pixels can be significantly suppressed.

Schematic sectional view showing the structure of a solid-state imaging device manufactured using the method for manufacturing a color filter of the present invention Process drawing which shows embodiment of the color filter manufacturing method of this invention Schematic diagram showing reduced projection exposure using a photomask A plan view schematically showing a photomask and a grid-like separation wall Process diagram showing a conventional color filter manufacturing method

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a schematic configuration of an embodiment of a solid-state imaging device manufactured using the method for manufacturing a color filter of the present invention.

  As shown in FIG. 1, the solid-state imaging device 10 includes a semiconductor circuit substrate 11, a plurality of pixel electrodes (lower electrodes) 12 formed in a two-dimensional array on the semiconductor circuit substrate 11, and a plurality of pixel electrodes 12. And a common electrode (upper electrode) provided as a single layer, which is a photoelectric conversion layer 14 made of an organic material formed continuously, and a counter electrode that is formed on the photoelectric conversion layer 14 and faces a plurality of pixel electrodes. 16. In addition, a transparent insulating layer 18 is laminated on the upper electrode 16, and here, the semiconductor circuit substrate 11 to the insulating layer 18 are collectively referred to as an image sensor substrate 20. A transparent separation wall that separates the color filters 21r, 21g, and 21b of two or more colors (three colors in the present embodiment) and the color filters 21r, 21g, and 21b of each color on the insulating layer 18 of the image sensor substrate 20 22 is provided, and a low reflection layer 25 is provided on the color filter layer CF.

  Details of each component will be described below.

(Semiconductor circuit board)
The semiconductor circuit substrate 11 includes a p-type well region 2 on the surface of an n-type silicon substrate 1 (hereinafter simply referred to as the substrate 1), and a plurality of n-type impurity diffusion regions 3 are formed in the well region 2. Yes. The impurity diffusion region 3 is formed in a two-dimensional array corresponding to the pixel electrode 12 formed on the circuit substrate 11. In addition, on the surface of the well region 2, in the vicinity of the impurity diffusion region 3, a signal reading unit 4 that outputs a signal corresponding to the charge accumulated in the impurity diffusion region 3 is provided.

  The signal reading unit 4 is a circuit that converts the charge accumulated in the impurity diffusion region 3 into a voltage signal and outputs the voltage signal, and can be configured by, for example, a known CCD or CMOS circuit.

  Further, an insulating layer 5 is laminated on the surface of the substrate 1 where the well region 2 is formed. On the insulating layer 5, a plurality of pixel electrodes 12 having a substantially rectangular shape in plan view are arrayed at a predetermined interval. Each pixel electrode 12 is electrically connected to the impurity diffusion region 3 of the substrate 1 through a connection portion 6 made of a conductive material so as to penetrate the insulating layer 5.

  When light enters the photoelectric conversion layer 14, the imaging element 10 moves, for example, holes to the upper electrode 16 among the charges (holes and electrons) generated in the photoelectric conversion layer 14, and moves the electrons to the lower electrode. 12, a bias voltage is applied between the lower electrode 12 and the upper electrode 16 by a voltage supply unit (not shown). In this case, the upper electrode 16 is a hole collecting electrode and the lower electrode 12 is an electron collecting electrode.

(electrode)
The upper electrode 16 and the lower electrode 12 are selected in consideration of adhesion to the photoelectric conversion layer 14, electron affinity, ionization potential, stability, and the like.
Various methods are used to manufacture the upper electrode 16 and the lower electrode 12 depending on the material. For example, in the case of ITO, an electron beam method, a sputtering method, a resistance heating vapor deposition method, a chemical reaction method (such as a sol-gel method), an oxidation method, and the like. A film is formed by a method such as application of a dispersion of indium tin. In the case of ITO, UV-ozone treatment, plasma treatment, etc. can be performed.
The upper electrode 16 is made of a transparent conductive material because light needs to be incident on the photoelectric conversion layer 14. Here, the transparent electrode material preferably has a transmittance of about 80% or more in the visible light range where the wavelength is in the range of about 420 nm to about 660 nm, for example.

  Specific examples of the material for the upper electrode 16 include conductive metal oxides such as tin oxide, zinc oxide, indium oxide, and indium tin oxide (ITO), metals such as gold, silver, chromium, and nickel, and these Or conductive metal oxide mixtures or laminates, inorganic conductive materials such as copper iodide and copper sulfide, organic conductive materials such as polyaniline, polythiophene and polypyrrole, silicon compounds and laminates of these with ITO Preferred are conductive metal oxides, and ITO, ZnO, and InO are particularly preferred from the viewpoints of productivity, high conductivity, transparency, and the like.

  The lower electrode 12 may be any conductive material and need not be transparent. However, when it is necessary to transmit light also to the substrate 1 side below the lower electrode 12, the lower electrode 12 also needs to be made of a transparent electrode material. At this time, as the transparent electrode material of the lower electrode 12, it is preferable to use ITO similarly to the upper electrode 16.

(Photoelectric conversion layer)
The photoelectric conversion layer 14 made of an organic material is formed to have a thickness in the range of 0.1 μm to 1.0 μm. The thinner the photoelectric conversion layer 14 is, the more effective the color mixing of the image sensor is. However, there is a trade-off with light absorption, and the optimum layer thickness is substantially about 0.5 μm.

  As a machine material constituting the photoelectric conversion layer 14, various organic semiconductor materials such as those used in electrophotographic photosensitive materials can be used. Among them, the quinacridone skeleton is selected from the viewpoints of having high photoelectric conversion performance, excellent color separation at the time of spectroscopy, high durability against long-time light irradiation, and easy vacuum deposition. Particularly preferred are materials containing and organic materials containing a phthalocyanine skeleton.

  The organic material constituting the photoelectric conversion layer 14 preferably includes at least one of a p-type organic semiconductor and an n-type organic semiconductor. For example, as the p-type organic semiconductor and the n-type organic semiconductor, any of quinacridone derivatives, naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, tetracene derivatives, pyrene derivatives, perylene derivatives, and fluoranthene derivatives can be particularly preferably used.

  If the photoelectric conversion layer 14 is made of an organic material, the light absorption coefficient with respect to visible light is larger than a structure using a photodiode formed on a silicon substrate or the like as a photoelectric conversion portion. For this reason, the light incident on the photoelectric conversion layer 14 is easily absorbed. According to this property, light obliquely incident on the photoelectric conversion layer 14 is less likely to leak to the adjacent pixel portion, and is photoelectrically converted at the pixel portion, thereby improving transmission efficiency and suppressing crosstalk. it can.

  One pixel electrode, and the photoelectric conversion layer and the upper electrode on the pixel electrode constitute one photoelectric conversion element.

(Insulating layer)
The insulating layer 18 can be made of Al ₂ O ₃ , SiO ₂ , SiN, or a mixed film thereof.

(Color filter layer)
As shown in FIG. 1, the color filter layer CF includes a plurality of color filters that transmit light of different wavelengths. Here, the color filter CF includes color filters 21r, 21g, and 21b made of organic materials containing red / blue / green pigments or dyes arranged for each pixel, and a color filter between the color filters 21r, 21g, and 21b. A separation wall 22 made of a transparent material having a refractive index smaller than that of the material is provided.

  The color filters 21r, 21g, and 21b transmit light having different wavelengths, and the color filter 21r functions as an R light color filter having a configuration that transmits red light of incident light. Similarly, the color filter 21g functions as a G light color filter having a configuration that transmits green light in the incident light, and the color filter 21b functions as a B light color filter having a configuration that transmits blue light in the incident light.

  Any one of the plurality of color filters 21r, 21g, and 21b is included in each pixel portion, and is arranged in a color pattern such as a Bayer arrangement according to the arrangement of the pixel portions.

The refractive index of the color filter is different for each color of red, blue, and green, and also varies depending on the wavelength of incident light. However, any of the color filters 21r, 21g, and 21b has an incident light wavelength (at least a wavelength in the visible light region (400 nm). With a refractive index in the range of 1.5 to 1.8.
The thickness of each color filter 21r, 21g, 21b is in the range of 0.3 μm to 1.0 μm.

  The color filters 21r, 21g, and 21b have an upward convex cross-sectional structure, and have a plano-convex lens function.

An embodiment of a method for producing a color filter of the present invention will be described.
FIG. 2 is a process diagram showing a method for manufacturing a color filter according to an embodiment of the present invention.
First, the low refractive index material 40 is applied on the image sensor substrate 20 and cured. As the low-refractive index material 40, those using a fluorine-based material, hollow silica, and those containing porous silica are commercially available, and these may be used. Subsequently, a lattice pattern for forming a separation wall is formed using the photoresist 41 (step a in FIG. 2), and the lattice separation wall 22 made of the low refractive index material 40 is formed by dry etching using this pattern as a mask. Form (step b in FIG. 2).

A color resist 42 is applied on the substrate 20 on which the separation wall 22 is formed so as to fill the opening 22a of the separation wall 22 (step c in FIG. 2).
In the case of the color resist 42, it is preferable to apply the color resist 42 so that the opening 22a of the separation wall 22 is filled and covers the surface of the separation wall 22, as shown in FIG.
In the present embodiment, a color resist 42 for the G light color filter is first applied.

  Further, selective exposure and development of the color resist are performed. Only the portion for forming the G light filter is selectively exposed. Step d in FIG. 2 shows a color resist exposure step.

The color resist 42 is exposed by reducing and projecting a photomask pattern at a predetermined reduction ratio r (r <1) by a stepper or a scanner. FIG. 3A is a schematic diagram for explaining reduction projection exposure.
As shown in FIG. 3A, a photomask 50 in which a light shielding film 53 made of Cr or the like is formed in a pattern having an opening 52 on a transparent substrate 51 such as glass is used, and exposure light L such as UV light is applied to the photomask 50. The exposure light irradiated from above and transmitted through the photomask 50 is projected onto the color resist 42 through the reduction projection lens system 55 at a predetermined reduction magnification.

  FIG. 3B is a plan view schematically showing a photomask 50 and a grid-like separation wall 22 used for exposure of a color resist. The photomask 50 has an opening 52 so that only the pixels that are to be exposed at one time are exposed to light. Selective exposure is performed over the entire region while shifting the exposure position using such a photomask. Here, as an example, an opening pattern for forming a G light color filter in a Bayer arrangement is shown. In the case of forming the R light color filter and the B light color filter, a photomask having an opening pattern corresponding to each is used.

The area Sm of the opening 52 of the photomask 50 is designed according to the area S of the opening 22a of the grid-like separation wall 22.
In the method for manufacturing a color filter of the present invention, when the mask opening area Sm is r as the reduction magnification by the reduction projection lens system 55, the photo satisfying Sm <S / r with respect to the area S of the opening 22a of the separation wall 22. The mask 50 is used. A region surrounded by a broken line 54 shown in the photomask 50 of FIG. 3B is an area S / r of the opening 22 a of the separation wall 22.

  2, the exposure light L is condensed such that the condensing position (focus position) 56 is higher than the surface position 57 of the separation wall 22. The exposure light L gradually spreads from the focus position 56. At this time, the focus position is controlled so that the size (exposure area) of the projected image at the surface position 57 of the separation wall 22 is equal to or smaller than the area S of the opening 22a. To do. It is desirable that the size of the projected image at the surface position 57 of the separation wall 22 is the same as the area of the opening 22a.

  In step d of FIG. 2, the exposure area of the color resist 42 by the exposure light L is an area indicated by a broken line. The resist on the surface of the separation wall is controlled so as not to be exposed to exposure light. By developing the color resist 42 thus exposed, the end of the color filter surface adjacent to the separation wall becomes round, As shown in step e of FIG. 2, a convex G light color filter 21g can be formed on the top.

The color resist coating, exposure, and development steps are continuously repeated for each color, the R light color filter and the B light color filter, and a color filter having three color filters as shown in step f of FIG. The layer CF can be formed.
By making the shape of each filter convex upward in the cross section, the filter itself can have a condensing function of a convex lens, and the condensing efficiency in the image sensor can be improved.

In the conventional exposure method, when the color resist is exposed, the relationship between the pixel size to be produced (here, the opening area S of the grid-like separation wall 22) and the area Sm of the opening of the photomask is Sm = S / r. Using a photomask, the exposure was performed so that the focus position was in alignment with or on the color resist surface.
For example, as shown in step d ′ of FIG. 4, the exposure light L is condensed so that the focus position coincides with the height position 57 of the separation wall, and the size of the projected image at this condensing position is the lattice. It exposes so that it may become equal to the area S of the opening 22a of the shape separation wall 22. FIG.

However, when exposure / development is performed by this conventional method, as shown in step e ′ of FIG. 4, the filter 21g ′ has an acute angle portion 28 formed on the surface adjacent to the separation wall, and the cross-sectional shape is a plano-concave lens. It becomes a shape.
When each color filter is repeatedly manufactured in this procedure, as shown in step f ′ of FIG. 4, all the filters 21r ′, 21g ′, and 21b ′ have a plano-concave lens shape, and light incident on the vicinity of the end of each filter is obtained. It enters adjacent pixels and causes color mixing.

  In order to solve the problem of color mixing of the filter formed in such a plano-concave lens shape, the above-mentioned Patent Document 7 removes the surplus on the separation wall and the pixel before development by etching the surface before development. However, this etching has a problem that it is difficult to control the remaining film thickness and the reproducibility is poor.

  As described above, according to the color filter manufacturing method of the present invention, the shape of each color filter can be made into a plano-convex lens shape as shown in step f of FIG. Therefore, the color filter layer CF can be manufactured with good manufacturing efficiency.

(Low reflective layer)
The low reflection layer 25 is provided to reduce reflection loss when light directly enters the color filter CF from the air. When the refractive index of the material used for the color filter CF (for example, the average value of the refractive indexes of the three color filters) is nc, a material having a refractive index of √nc is selected as the low reflection layer 25, and the layer thickness is selected. May be set to a ¼ nm film thickness of 550 nm, which is substantially the center wavelength of visible light.
For example, in the case of this element, since the refractive index of the color filter CF is 1.5 to 1.8, a material having a refractive index of about 1.28 is used, and the thickness is 550/4 / 1.28 = 107 nm. Therefore, the thickness may be about 0.1 μm.

  In the method for manufacturing the solid-state imaging device having the above-described configuration, the method for forming the lower electrode layer, the photoelectric conversion layer, the upper electrode layer, and the like on the circuit substrate 11 is not particularly limited, and the color filter layer on the imaging device substrate 20 The manufacturing may be performed using the manufacturing method described in the above-mentioned color filter.

  The color filter layer CF of the solid-state imaging device 10 includes a color filter layer having a conventional separation wall because each of the color filters 21r, 21g, and 21b has a convex lens shape and a light collecting function. Compared with a solid-state imaging device, the light collection efficiency can be improved, and crosstalk between adjacent pixels can be significantly suppressed.

  In the said embodiment, although the photoelectric conversion film showed the example by an organic material, it is not limited to this, A silicon material may be sufficient. In particular, the present invention is also effective for a back-illuminated solid-state imaging device developed in recent years.

  Moreover, as a solid-state image sensor, in order to improve the condensing rate further, you may use a micro lens together.

DESCRIPTION OF SYMBOLS 10 Solid-state image sensor 11 Semiconductor circuit board 12 Lower electrode (pixel electrode)
14 Organic photoelectric conversion layer 16 Upper electrode (common electrode)
18 Insulating layer 20 Image sensor substrate 21r, 21g, 21b Color filter 22 Lattice-like separation wall 22a Opening CF of lattice-like separation wall Color filter layer with separation wall 40 Low refractive index material 41 Photo resist 42 Color resist 50 Photo mask 52 Photo mask Opening

Claims (5)

A color filter layer including a color filter of two or more colors and a transparent separation wall that separates the color filters of each color is manufactured on an image sensor substrate having a plurality of photoelectric conversion elements on a circuit board. A color filter manufacturing method comprising:
Forming a grid-like separation wall having an opening corresponding to each photoelectric conversion element on the imaging element substrate;
An application step of applying a color resist to the openings of the separation walls of the lattice;
An exposure step of exposing the color resist; and a development step of developing the exposed color resist;
In the exposure step, the color resist is exposed by using a photomask having a predetermined mask opening and reducing and projecting the mask opening corresponding to the opening position of the separation wall,
As the photomask, an opening area Sm of the mask opening is such that Sm <S / r, where S is the opening area of the separation wall and r is the reduction magnification of the reduction projection,
A color characterized in that the exposure light is condensed at a position above the surface position of the separation wall so that the exposure area of the color resist at the surface position of the separation wall is equal to or less than the area of the opening of the separation wall. A method for manufacturing a filter.   2. The color filter according to claim 1, wherein the exposure light is condensed so that an exposure area of the color resist at a surface position of the separation wall substantially coincides with an opening area of the separation wall. Method.   3. The method of manufacturing a color filter according to claim 1, wherein in the applying step, the color resist is applied until the opening of the separation wall is filled with the color resist and the surface of the separation wall is covered. . A method for producing a solid-state imaging device comprising a color filter layer on an imaging device substrate comprising a plurality of photoelectric conversion elements on a circuit board,
Forming the plurality of photoelectric conversion elements on the circuit board to produce an image sensor board;
The method for manufacturing a solid-state imaging device, wherein the color filter layer is manufactured on the plurality of photoelectric conversion elements by the method for manufacturing a color filter according to any one of claims 1 to 3. An image sensor substrate comprising a plurality of photoelectric conversion elements on a circuit board;
A color filter layer comprising two or more color filters disposed above the plurality of photoelectric conversion elements and a transparent separation wall separating the color filters of each color;
A solid-state imaging device, wherein the color filter has a plano-convex lens shape.

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