JP2000164837A - Method for forming lens in layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a lens in layer by which focal length of a lens can by adjusted to a desired length, over a wide range. SOLUTION: When a lens 7 is formed in a layer by forming a mask of resist in the form of a lens on a layer 15 of material of the lens in layer and by etching back for transferring the form of the lens of a resist 16 onto the layer 15 of the material of the lens in layer, the etching selection ratio of the resist 16 relative to the material 15 of the lens in layer is set larger than 1, for forming a lens 7 in the layer which is thinner than the resist 16. Alternatively, the etching selection ratio of the resist 16 relative to the material 15 of the lens in layer is set smaller than 1 for forming a lens 7, in a layer thickness larger than that of the resist 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an in-layer lens suitable for use in a device such as a solid-state image pickup device or a liquid crystal display device.

[0002]

2. Description of the Related Art In a solid-state image pickup device, it is necessary to improve the sensitivity as pixels become finer, and it is no longer possible to sufficiently improve the sensitivity only with a lens (on-chip lens) on a conventional color filter. . Therefore, a technique called a so-called intra-layer lens, in which a lens is formed inside a laminated structure between a color filter and a semiconductor portion of a sensor, is also used in combination.

[0003] One of the above-described methods of forming an inner lens is described below.
As one of the methods, there is a method of dry-etching a laminated film of a material layer of an inner lens and a resist. This is a method of forming a material layer of an inner lens, patterning a resist laminated thereon into a lens shape, and then transferring the lens shape of the resist to a material layer of the inner lens by dry etching.

Conventionally, in order to accurately transfer the lens thickness of the lens shape of the resist in the upper layer during dry etching, the etching selectivity between the resist and the lens material in the layer has been set to be one. .

[0005]

However, if the etching selectivity is set to 1 as described above, the thickness of the inner lens is limited to the range of the thickness limit of the resist. The thickness limit of the resist is defined by conditions such as a limit of a thickness capable of forming a good film, a limit of a correct formation of a curved lens shape, and a limit of a thickness capable of developing by exposure.

Therefore, when it is desired to make the thickness of the in-layer lens out of the limit of the thickness of the resist for the purpose of adjusting the focal length of the lens to a desired distance, it is impossible to actually form the in-layer lens. It was possible.

In order to solve the above-mentioned problems, the present invention provides a method of forming an in-layer lens which enables a focal length of a lens to be adjusted to a desired distance over a wide range.

[0008]

According to the method of forming an inner lens of the present invention, a mask made of a lens-shaped resist is formed on a layer of an inner lens material, and the mask is etched back to change the lens shape of the mask to an inner lens. When transferring to a material layer to form an inner lens, the etching selectivity of the resist to the inner lens material is made greater than 1 to form an inner lens thinner than the resist thickness.

In the method of forming an inner lens according to the present invention, a mask made of a resist having a lens shape is formed on a layer of the inner lens material, and the mask shape is etched back to transfer the lens shape of the mask to the layer of the inner lens material. When forming the inner layer lens by etching, the etching selectivity of the resist to the inner layer lens material is set to 1
This is to form an inner lens that is smaller and thicker than the thickness of the resist.

According to the above-described method of the present invention, the etching selectivity of the resist to the in-layer lens material is made greater than 1 to form an in-layer lens having a thickness smaller than the thickness of the resist. It is possible to form thin intralayer lenses.

Similarly, by making the etching selectivity smaller than 1 to form an inner lens thicker than the resist thickness, it becomes possible to form an inner lens thicker than the maximum limit of the resist thickness.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a mask made of a lens-shaped resist is formed on a layer of a lens material in a layer, and the lens shape of the mask is transferred to a layer of the lens material in a layer by etching back. This is a method of forming an inner layer lens in which, when forming a lens, the etching selectivity of the resist to the inner layer lens material is greater than 1 to form an inner lens thinner than the thickness of the resist.

Further, the present invention provides the method for forming an inner lens, wherein the step of forming a concave portion and the step of forming a layer of an inner lens material so as to fill the concave portion are performed. A step of forming a mask made of a lens-shaped resist on the layer is performed.

Further, the present invention provides the method for forming an inner lens, wherein after the step of forming the layer of the inner lens material,
A step of flattening the surface of the layer of the intra-layer lens material and a step of laminating and forming a layer of the intra-layer lens material thereon are performed. A resist mask is formed.

According to the present invention, an in-layer lens is formed by forming a lens-shaped resist mask on a layer of an intra-layer lens material, etching it back, and transferring the lens shape of the mask to the layer of the intra-layer lens material. In this case, a method of forming an inner lens in which the etching selectivity of the resist to the inner lens material is smaller than 1 to form an inner lens thicker than the thickness of the resist.

Further, in the present invention, in the method for forming an inner layer lens, a step of forming a concave portion and a step of forming a layer of an inner layer lens material so as to fill the concave portion are performed. A step of forming a mask made of a lens-shaped resist on the layer is performed.

The present invention also provides the above method for forming an inner lens, wherein after the step of forming the layer of the inner lens material,
A step of flattening the surface of the layer of the intra-layer lens material and a step of laminating and forming a layer of the intra-layer lens material thereon are performed. A resist mask is formed.

FIG. 1 is a schematic cross-sectional view of one CCD solid-state imaging device used in the method of forming an inner lens according to the present invention.
The CCD solid-state imaging device 1 includes a semiconductor substrate (semiconductor unit)
11, a sensor (light receiving unit) 12 and a readout gate unit 1
3. A CCD transfer channel 14 is formed, and the semiconductor section 11 other than the light receiving section 12, ie, the readout gate section 13, and the CCD
The transfer electrode 3 is formed on the transfer channel 14 via the insulating film 2. A light-shielding film 5 is formed on the transfer electrode 3 via an interlayer insulating film 4, and the light-shielding film 5 prevents light from entering the transfer electrode 3. An opening is provided in the light-shielding film 5 above the light-receiving part 12 so that light is incident on the light-receiving part 12.

Then, by covering the light shielding film 5, for example, BPS
The first planarization layer 6 is formed by a reflow film such as a G (boron phosphorus silicate glass) film or an HDP (high density plasma) CVD film. The first flattening layer 6 is a layer that flattens the surface with respect to a step due to the light shielding film 5.

Further, the upper surface of the first flattening layer 6 above the light receiving section 12 is formed of a high refractive index material such as a SiN film (refractive index n = 1.9 to 2.0) by plasma CVD. The convex inner lens 7 is formed.

On the inner lens 7, a second flattening layer 8 made of, for example, an acrylic resin film (refractive index n = 1.3 to 1.4) or the like is formed. The surface is flattened by the formation, and the color filter 9 is formed thereon. Further, on the color filter 9, a micro lens 10 which is a so-called on-chip lens is formed.

In this case, the light incident on the surface of the inner lens 7, that is, the boundary between the two layers of the inner lens (high refractive index layer) 7 and the second flattening layer 8 is focused on the light receiving section 12. In addition, the refractive index of the material of the underlying interlayer lens 7 is set to be higher than the refractive index of the material of the upper second planarization layer 8.

As described above, by providing the in-layer lens 7 below the on-chip lens formed by the microlenses 10, incident light can be condensed in two stages and more light can be made incident on the light receiving section 12. it can. Therefore, the sensitivity of the CCD solid-state imaging device can be improved as compared with the case where only the on-chip lens is formed.

Next, as one embodiment of the method of forming an inner lens according to the present invention, the CCD solid-state imaging device 1 shown in FIG.
2 to 3 are shown in FIGS.

First, as shown in FIG.
The light receiving section 1 is ion-implanted with necessary impurities into the inside.
2. After forming the readout gate section 13 and the CCD transfer channel (transfer section) 14, respectively, a transfer electrode 3 is formed in a predetermined pattern on the surface via the insulating film 2, and the transfer electrode 3 is formed via the interlayer insulating film 4. 3, a light-shielding film 5 is formed. Then, patterning is performed so that the light shielding film 5 has an opening on the light receiving portion 12.

Next, as shown in FIG. 2B, a film formed by reflow, for example, a BPSG film or an HD
The first flattening layer 6 is formed from a film formed by a P (high-density plasma) CVD method, and the surface is flattened.

The BPSG film can have a flat surface after the reflow by defining the composition of the BPSG and the reflow temperature.

At this time, a material for the light-shielding film 5 is selected and the light-shielding film 5 is formed in accordance with the flattening method used for the material of the first flattening layer 6. For example,
When reflow at a high temperature is required for planarization, a high melting point metal such as tungsten, tungsten silicide, molybdenum, titanium, or the like is formed on the light shielding film 5.

On the other hand, when the HDPCVD film is used for the first flattening layer 6, the light-shielding film 5 may be an aluminum film or the like because the first flattening layer 6 can be formed at a low temperature.

Next, although not shown, after forming the peripheral wiring, the wiring is covered and the entire layer 15 of the high-refractive-index lens material, for example, as shown in FIG. 0.5-2.0 μm SiN film by plasma CVD
Formed to a thickness of

Here, the refractive index of the inner lens 7 is set to 1.9 to
In the case of 2.0, an SiN film is formed as the layer 15 of the inner layer lens material by plasma CVD. When the refractive index of the inner lens 7 is set to 1.5 to 1.9, the inner lens material layer 15 is made of Si by plasma CVD.
An ON film is formed.

Next, as shown in FIG. 3D, a resist 16 is applied on the lens material layer 15, and the resist 16 is patterned to obtain a desired inner lens 7. In order to further obtain a lens shape, reflow is performed on the patterned resist 16 at, for example, 140 to 180 ° C.

As the resist 16, a resin which can be dry-etched by oxygen, for example, a novolak resin can be used.

Next, as shown in FIG. 3E, the lens shape of the resist 16 is transferred to the lens material layer 15 by dry etching to form the inner lens 7.

Thereafter, a second flattening layer 8 is formed so as to cover the inner lens 7, and the surface is flattened. Then, a color filter 9 and a microlens 10 are sequentially formed, and the CCD solid-state shown in FIG. The imaging device 1 can be formed.

In the present invention, the etching selectivity between the resist 16 and the material of the inner lens 7 is set to 1 particularly during the dry etching shown in FIGS. 3D to 3E.
By changing the value to a value other than the above, it is possible to form the convex inner lens 7 to an arbitrary thickness.

At this time, the dry etching apparatus and dry etching conditions are, for example, a process gas (etching gas) using a microwave plasma etching apparatus.
A gas in which SF ₆ and oxygen are mixed is used. Also,
At this time, for example, the RF (harmonic) output is 20 to 100 W,
The output of the microwave is 1000 to 2000 W, and the pressure is 0.
5 to 2 Pa.

When the mixed gas of SF ₆ and oxygen is used as the etching gas, the etching selectivity between the resist 16 and the material of the inner lens 7 is changed by changing the mixing ratio of the etching gas. Can be.

Next, as specific embodiments of the method of forming an inner lens according to the present invention, two details of the dry etching process shown in FIGS. 3D and 3E will be described with reference to FIGS.
Are shown below.

First, when the ratio of oxygen in the above-mentioned mixed gas is large, the etching rate of the resist 16 is higher and the etching selectivity of the resist 16 to the material of the inner lens 7 becomes larger than 1, so that FIG. As shown in FIG. 4B, the inner lens 7 is formed thinner than the thickness of the lens-shaped resist 16.

On the other hand, if the oxygen ratio is small, the resist 1
6 has a lower etching rate, and the etching selectivity of the resist 16 to the material of the inner lens 7 is smaller than 1. Therefore, as shown in FIG. 5A and FIG. A thick inner lens 7 is formed.

The mixing ratio between SF ₆ and oxygen is 2: 1.
The etching selectivity of the resist 16 with respect to the material of the in-layer lens 7 is set to 0.5
It can be varied between ~ 2.0.

The limit of the thickness of the resist 16 is, for example, 0.6.
When the etching selectivity is kept at 1.0 as in the related art when the thickness is in the range of 2.5 to 2.5 μm, the thickness of the convex inner lens 7 obtained by dry etching is 0.6 to 2.0. 5
It can be formed only in the range of μm.

On the other hand, if the etching selectivity is variable in the range of 0.5 to 2.0 by the above-described method, the thickness of the convex inner lens 7 is set to 0.3 to 5.0 μm. It can be formed in the range of.

In the etching apparatus, other parallel plate RI
E (reactive ion etching) apparatus, high pressure narrow gap type plasma etching apparatus, ECR (electron cyclotron resonance) type etching apparatus, magnetron RIE apparatus, other high density plasma type etching apparatus (for example, TCP)
(Transition-coupled plasma), ICP (inductively-coupled plasma), HDP (high-density plasma), helicon (etching apparatus using plasma such as helicon wave-discharged plasma), or the like may be used.

The etching gas is CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₈ , CHF ₃ , C ₄ instead of SF _6.
Freon-based gas such as H ₂ F ₂ , Cl ₂ , HCl, HB
A mixed gas with oxygen may be produced using a halogen system such as r or BCl.

When another fluorine-based gas is used instead of SF _6, the mixing ratio at which the etching selectivity between the resist 16 and the material of the inner lens 7 becomes 1 may be different.

As the etching gas, in addition to a mixed gas of the above two gases, a mixed gas of three or more gases such as a gas obtained by mixing two or more of the above gases with oxygen is used. Is also good.

The above-mentioned dry etching can also be performed by a single etching gas. However, in this case, the etching selectivity between the resist 16 and the material of the inner lens 7 has a constant value determined by the etching gas. Thus, the inner lens 7 having a thickness uniquely determined by the etching selectivity with respect to the thickness of the lens-shaped resist 16 is formed.

In the CCD solid-state imaging device 1 shown in FIG. 1, the material of the inner lens 7 can be made of a resin having a high refractive index. In this case, the inner lens 7 is formed by dry etching. At this time, the etching selectivity between the resist 16 and the material of the inner lens 7 becomes almost 1 regardless of the mixing ratio of the etching gas. That is, in this case,
The thickness of the inner lens 7 is the same as the thickness of the lens-shaped resist 16, and the range of the thickness of the inner lens 7 that can be formed is the thickness of the lens-shaped resist 16.

According to the above-described embodiment, the etching selectivity of the lens-shaped resist 16 with respect to the material of the inner lens 7 is made larger than 1 or the etching selectivity is made smaller than 1. The thickness of the resist 7 can be out of the range of the limit of the thickness of the resist 16 in the form of a lens, whereby the range of the focal length of incident light can be widened. This makes it possible to adjust the focal length of the inner lens 7 to a desired distance in a wider range.

Therefore, the sensitivity can be improved for a CCD solid-state imaging device having various unit cell sizes.

Next, another embodiment of the method of the present invention will be described. FIG. 6 is a schematic cross-sectional view of another CCD solid-state imaging device used in the method for forming an inner lens according to the present invention.

This CCD solid-state imaging device 21 has an upwardly convex lens surface 19A similarly to the in-layer lens 7 of the CCD solid-state imaging device 1 shown in FIG.
7 is formed by a boundary surface between a concave portion formed at a position on the light receiving portion 12 and a layer (high refractive index layer) 18 of an in-layer lens material (made of, for example, a SiN film by plasma CVD) filling the concave portion. An inner lens 19 having a downwardly convex lens surface 19B is formed.

With this configuration, the upper lens surface 19 A of the micro lens 10 and the inner lens 19,
The light is condensed in three stages with the lower lens surface 19B of the inner lens 19, and the sensitivity can be further improved as compared with the CCD solid-state imaging device 1 of FIG.

The other configuration is the same as that of the CCD solid-state imaging device 1 shown in FIG.

Next, as another embodiment of the method of forming an inner lens according to the present invention, a manufacturing process of the CCD solid-state imaging device 21 shown in FIG. 6 is shown in FIGS.

First, as in the case of FIG.
1 is ion-implanted with necessary impurities into the light-receiving section 1
2. After forming the readout gate section 13 and the CCD transfer channel (transfer section) 14, respectively, a transfer electrode 3 is formed in a predetermined pattern on the surface via the insulating film 2, and the transfer electrode 3 is formed via the interlayer insulating film 4. 3, a light-shielding film 5 is formed. Then, patterning is performed so that the light shielding film 5 has an opening on the light receiving portion 12.

Next, an interlayer insulating layer 17 made of, for example, BPSG (boron phosphorus silicate glass) is formed entirely over the step formed by the light shielding film 5. At this time, for example, BP
By setting the SG composition to a predetermined composition, the surface of the interlayer insulating layer 17 is formed so as to have a concave portion on the sensor section 12. Further, as shown in FIG.
The high refractive index layer 18 is formed entirely of the material of the inner layer lens, for example, a SiN film by plasma CVD or the like by filling the concave portion of FIG. The surface of the high refractive index layer 18 has a concave portion corresponding to the concave portion of the interlayer insulating layer 17.

Next, as shown in FIG. 7B, the high refractive index layer 1
Then, a resist 20 for planarization is formed covering the surface 8. At this time, the surface of the resist 20 is flattened by characteristics such as the viscosity of the resist 20.

Then, the resist 20 and the high refractive index layer 18
Is subjected to dry etching. In this dry etching, conditions such as an etching gas are set so that the etching selectivity of the resist 20 to the high refractive index layer (in-layer lens material) 18 is 1 (1: 1).
This flattens the surface of the high refractive index layer 18 as shown in FIG. 7C.

Next, as shown in FIG. 7D, on the flattened high refractive index layer 18, a high refractive index layer 18, for example, an SiN film by plasma CVD is further formed. The surface of the second high refractive index layer 18 is formed flat.

Next, a resist is formed on the high refractive index layer 18, and after patterning the resist, reflow is performed to obtain a lens-shaped resist 16 as shown in FIG. 7E.

Then, dry etching is performed under the condition that the above-mentioned etching selectivity is larger than 1 or smaller than 1, and the lens shape of the resist 16 is transferred to the high refractive index layer 18 as shown in FIG. 7F.

In the above-described manufacturing process, the high refractive index layer 18 between the inner lenses 19, that is, the inner lens 1 of a certain pixel,
The surface of the high-refractive-index layer (layer of the lens material in the layer) 18 between the pixel 9 and the inner lens 19 of the next pixel is
In the case where the incident light is sufficiently narrowed at 0 and there is no incidence between the inner lenses 19, or the case where almost all the light that has entered between the inner lenses 19 is incident on the light shielding film 5 and does not reach the sensor unit 12, However, it does not necessarily have to be completely flat.

As still another embodiment of the present invention, FIG. 8 is a process diagram of a manufacturing process which is effective in such a case and is a simplified version of the manufacturing process shown in FIG.
First, as shown in FIG. 7A, a high refractive index layer 18 is formed on an interlayer insulating layer 17 having a concave portion.

Next, a resist is formed on the high refractive index layer 18, and the resist is patterned, and then reflow is performed. Thereby, as shown in FIG. 8B, the high refractive index layer 18 is formed.
A resist 16 in the form of a lens is formed in the concave portion.

Next, dry etching is performed under the etching conditions under which the etching selection ratio of the resist 16 to the material of the inner lens of the layer becomes a desired selection ratio, thereby transferring the lens shape of the resist 16 to form a layer having a desired thickness. Inner lens 1
9 is formed.

As a result, the inner lens 19 can be formed in a smaller number of steps than the steps shown in FIG. 7, and the manufacturing cost can be reduced.

In this case, some irregularities may remain in the high refractive index layer 18 between the respective inner lenses 19, and therefore, when there is no influence of the incident light between the respective inner lenses 19 as described above. It is a suitable manufacturing method.

Note that, in each of the above-described embodiments, CC
Although the description has been given by applying to the D solid-state imaging device, the method of forming the inner-layer lens of the present invention can be applied to other solid-state imaging devices such as a MOS-type imaging device and a liquid crystal display device.
An inner lens having a desired thickness can be obtained by defining the etching selectivity similarly to the above-described embodiment.

Therefore, by applying the method for forming an inner layer lens of the present invention to the above-described element, the sensitivity and the focal length of the inner layer lens can be adjusted to optimize the characteristics of the element.

The method of forming the inner layer lens of the present invention is not limited to the above-described embodiment, but may take various other configurations without departing from the gist of the present invention.

[0074]

According to the present invention described above, it is possible to make the thickness of the inner lens out of the limit of the thickness of the resist in the upper layer, thereby expanding the range of the focal length of incident light. Can be. It allows the focal length of the intralayer lens to be adjusted over a wide range to the desired distance.

Therefore, it is possible to improve the sensitivity of the solid-state imaging device having various unit cell sizes. Further, in a liquid crystal display device or the like, the sensitivity and the focal length of the inner lens can be adjusted over a wide range to optimize the characteristics.

[Brief description of the drawings]

FIG. 1 shows a CCD used in the method for forming an intralayer lens according to the present invention.
FIG. 3 is a schematic cross-sectional view corresponding to one pixel of a solid-state imaging device.

2A to 2C are manufacturing process diagrams of a method for manufacturing the CCD solid-state imaging device of FIG. 1;

3D and 3E are manufacturing process diagrams of a method for manufacturing the CCD solid-state imaging device of FIG.

4A and 4B are manufacturing process diagrams showing one embodiment of details of the dry etching process of FIGS. 3D and 3E.

5A and 5B are manufacturing process diagrams showing another embodiment of the details of the dry etching process of FIGS. 3D and 3E.

FIG. 6 shows another C used in the method of forming an intralayer lens according to the present invention.
FIG. 3 is a schematic sectional view corresponding to one pixel of a CD solid-state imaging device.

7A to 7F are manufacturing process diagrams of a method for manufacturing the CCD solid-state imaging device in FIG.

8A and 8B are manufacturing process diagrams of another manufacturing method of the CCD solid-state imaging device of FIG.

[Explanation of symbols]

1, 21 CCD solid-state imaging device, 2 insulating films, 3 transfer electrodes, 4 interlayer insulating films, 5 light-shielding films, 6 first planarizing layers, 7, 19 internal lenses, 8 second planarizing layers, 9 color filters, Reference Signs List 10 micro lens (on-chip lens), 11 semiconductor base (semiconductor part), 12 light receiving part (sensor), 13 readout gate part, 14 CCD transfer channel, 15, 18 high refractive index layer (material layer of inner lens), 16 , 20 resist, 17 interlayer insulating layer, 19
A, 19B Lens surface

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4M118 BA01 CA03 CA07 DA02 FA33 GA07 GB03 GB08 GD03 GD07 HA23 5C024 AA01 CA00 CA31 EA04 FA01 GA11 5G435 AA03 AA17 BB12 FF07 GG02 HH02 KK07

Claims (6)

[Claims] A mask made of a resist having a lens shape is formed on a layer of an inner lens material, and the lens shape of the mask is transferred to the layer of the inner lens material by etching back to form an inner lens. A method for forming an inner layer lens, comprising: forming an inner layer lens having a thickness smaller than the thickness of the resist by making an etching selectivity of the resist to the inner lens material greater than 1 when forming the resist. 2. A step of forming a concave portion and a step of filling the concave portion to form a layer of the inner lens material, and thereafter forming a mask of a lens-shaped resist on the inner lens material layer The method for forming an intra-layer lens according to claim 1, wherein the step of performing is performed. 3. A step of flattening the surface of the layer of the intra-layer lens material after the step of forming the layer of the intra-layer lens material, and a step of laminating and forming a layer of the intra-layer lens material thereon. 3. The method according to claim 2, wherein a mask made of the lens-shaped resist is formed on the layer of the inner-layer lens material formed afterwards. 4. A mask made of a lens-shaped resist is formed on the layer of the inner-layer lens material, and etched back to transfer the lens shape of the mask to the inner-layer lens material layer to form an inner-layer lens. Forming an inner lens having a thickness greater than the thickness of the resist by making the etching selectivity of the resist to the material of the inner lens smaller than 1. 5. A step of forming a concave portion and a step of forming a layer of the inner lens material so as to fill the concave portion, and thereafter, a mask made of a lens-shaped resist is formed on the inner lens material layer. The method for forming an intra-layer lens according to claim 4, wherein a forming step is performed. 6. A step of flattening the surface of the layer of the intra-layer lens material after the step of forming the layer of the intra-layer lens material, and a step of laminating and forming a layer of the intra-layer lens material thereon. 6. The method according to claim 5, wherein a mask made of the lens-shaped resist is formed on the layer of the inner-layer lens material formed by laminating thereafter.