JPH06342896A - Solid-state image sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To suppress shading and deterioration of color reproducibility due to mixing colors. CONSTITUTION:An oxide film 6 and a nitride film 7 are laminated on a semiconductor substrate 1, and a thin oxide film 8 is formed on the film 7. A polysilicon electrode 9 is grown, and a polysilicon oxide film 10 is so formed as to cover the surface. An interlayer insulating film 11 is formed on the films 10, 7. An Al light shielding film 12 is formed on the film 11, and a TiN reflection preventive film 14 having a reflectivity of 20% or less of the Al film and a thickness of 25-45nm is formed. A transparent hole burying layer 15 is provided on a part on an Ntype diffused region 3 of a photodiode of the films 12, 14, and a protective film 13 is formed thereon. A transparent flattened layer 16 is formed on the layer 15, and a color filter 17 is formed on the layer 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device.

[0002]

2. Description of the Related Art An example of the above-mentioned conventional solid-state image pickup device will be described below with reference to the drawings. FIG. 4 is a sectional view of a conventional solid-state image pickup device.

In FIG. 4, 1 is a semiconductor substrate, 2 is a P-type diffusion region, 3 is an N-type diffusion region of a photodiode portion,
Reference numeral 4 is an N-type diffusion area of the vertical CCD portion, and 5 is a P ^++- type diffusion area. 6 is an oxide film, 7 is a nitride film, 8 is an oxide film, 9 is a polysilicon electrode, 10 is a polysilicon oxide film, 11 is an interlayer film, 12 is an Al light-shielding film, and 13 is a protective film.

The semiconductor substrate 1 is an N-type silicon substrate.
A P-type diffusion region 2 diffused from the main surface of the substrate is formed in the semiconductor substrate 1. In this P-type diffusion region 2, N ⁻ -type diffusion region 3 and N-type diffusion region 4 diffused from the main surface of the substrate are formed with a predetermined interval. An oxide film 6 is formed on the main surface of the semiconductor substrate 1. A nitride film 7 is formed on the oxide film 6. A thin oxide film 8 is formed on the silicon nitride film 7.

Next, a polysilicon electrode 9 is grown by low pressure CVD, and the polysilicon electrode 9 is subjected to a dry etching process.
Then, the thin oxide film 8 on the silicon nitride film 7 and the silicon nitride film are etched at predetermined intervals. Next, the oxide film 8 is formed by etching using the polysilicon electrode 9 as a mask.
Remove a predetermined part of. A polysilicon oxide film 10 is formed so as to cover the surface of the polysilicon electrode 9. The polysilicon oxide film is formed so as to cover only the sidewalls of thin oxide film 8, silicon nitride film 8 and the surface of polysilicon electrode 9.

A BPSG film which is an interlayer film 11 is formed on the polysilicon oxide film 10 and the nitride film 7 by a CVD apparatus.

A light-shielding film 12 of aluminum (hereinafter referred to as Al) is formed by a sputtering apparatus with an interlayer film 11 interposed therebetween. This Al light-shielding film 12 is a polysilicon oxide film 1.
The width of the upper part of 0 (widthwise to the paper surface) is formed to be almost equal. The protective film is an Al light shielding film 12 and an interlayer film 11.
Formed on.

The operation of the solid-state image pickup device configured as described above will be described. The N ⁻ type diffusion region 3 formed in the P type diffusion region 2 in the semiconductor substrate 1 is a photodiode that generates signal charges by photoelectric conversion. Then, by applying a pulse voltage to the second-layer polysilicon electrode 9, the signal charges are moved to the N-type diffusion region 4 below the second-layer polysilicon electrode 9. Next, a pulse signal is alternately applied to the first-layer polysilicon electrode and the second-layer polysilicon electrode 9 to transfer the signal charge.

Further, the protective film 1 is formed on the semiconductor substrate 11.
After growing 3, the transparent hole filling layer 15 and the transparent flat film layer 16 are formed in order to flatten the steps on the upper surface of the device and make the heights uniform. Red, green, and blue color filters 1 are provided on the upper surface of the transparent flat film layer 16 to color the solid-state imaging device.
7R, 17G, and 17B are formed. The color filters 17R, 17G and 17B are formed so as to correspond to the respective N ⁻ type diffusion regions 3. Therefore, monochromatic light is incident on each N ⁻ type diffusion region 3.

[0010]

However, the above-mentioned structure has a drawback that the reflectance of the g-line or i-line with respect to the Al light-shielding film 12 is large and halation occurs when the color filter 17 is formed. Since the material of the color filter 17 is a negative type, the shape of the color filter 17 has a taper due to the reflection from the Al light shielding film 12. Therefore, the shape of the color filter 17 narrows the opening area and reduces the sensitivity of the solid-state imaging device.

Further, since the thickness of each color filter 17 varies, color unevenness occurs, which causes deterioration of color reproducibility due to shading and color mixing.

In view of the above problems, the present invention provides a solid-state image pickup device which suppresses the deterioration of color reproducibility due to shading and color mixture and has good sensitivity.

[0013]

In order to solve the above problems, a solid-state image pickup device according to the present invention comprises a photodiode formed on a semiconductor substrate, and a charge transfer section for transferring charges formed by the photodiode. A high melting point formed on the metal light-shielding film, having a transfer electrode formed on the semiconductor substrate excluding the photodiode and a metal light-shielding film formed on the transfer electrode via an interlayer film. A metal nitride and a color filter are provided on the nitride via a protective film.

In order to solve the above-mentioned problems, in the method of manufacturing a solid-state image pickup device of the present invention, a photodiode and a charge transfer section are formed on a semiconductor substrate and transferred onto the charge transfer section on the semiconductor substrate. Forming an electrode, forming a metal light-shielding film through the interlayer film on the transfer electrode, forming a refractory metal nitride on the metal light-shielding film, and forming a protective film on the nitride The step of forming a transparent hole filling layer in the protective film, forming a transparent flattening film layer in the transparent hole filling layer, and forming a color filter on the transparent flattening film layer. There is.

[0015]

The present invention has the above-described structure to suppress the reflection of the Al film and reduce the influence of halation.

Therefore, since the natural protein / dichromic acid used for the color filter material is a negative type, it is possible to suppress an extra taper caused by the reflected light reaching the opening. This improves the dimensional accuracy of the filter and suppresses the shape from narrowing the opening area,
Keep good sensitivity.

Further, the thickness of each color filter is reduced in variation to suppress the occurrence of shading due to color unevenness and the deterioration of color reproducibility due to color mixing.

[0018]

EXAMPLE As a light source for reduction projection exposure, g (λ = 436n)
The structure of the solid-state imaging device according to the embodiment of the present invention when the color filter is formed by using the line (m) will be described with reference to the drawings.

FIG. 1 is a sectional view of a solid-state image pickup device according to an embodiment of the present invention. In FIG. 1, 1 is a semiconductor substrate, 2
Is a P type diffusion region, 3 is a photodiode N ⁻ type diffusion region, 4 is vertical charge transfer (hereinafter referred to as vertical CCD)
The N-type diffusion regions 5 and 5 are P ⁺⁺ -type diffusion regions. 6
Is an oxide film, 7 is a nitride film, 8 is an oxide film, 9 is a polysilicon electrode, 10 is a gate oxide film, 11 is an interlayer film, and 12 is Al.
Light-shielding film, 13 is a protective film, 14 is a titanium nitride (hereinafter, referred to as TiN) antireflection film which is a nitride of a refractory metal, 15
Is a transparent filling layer, 16 is a transparent flat lower layer, and 17 is a color filter. The semiconductor substrate 1 is an N-type silicon substrate. A P-type diffusion region 2 diffused from the main surface of the substrate is formed in a semiconductor substrate 1. In the P-type diffusion region 2, an N ⁻ -type diffusion region 3 and an N-type diffusion region 4 diffused from the main surface of the substrate are formed with a predetermined interval. An oxide film 6 is formed on the main surface of the semiconductor substrate 1. Oxide film 6
A nitride film 7 is formed on the top. A thin oxide film 8 is formed on the silicon nitride film 7.

Next, a polysilicon electrode 9 is formed by low pressure CVD, and the polysilicon electrode 9, the thin oxide film 8 on the silicon nitride film 7 and the silicon nitride film are etched at a predetermined interval in a dry etching process. . Then, a predetermined portion of the oxide film 8 is removed by an etching process using the polysilicon electrode 9 as a mask. Polysilicon oxide film 10 is formed so as to cover the surface of polysilicon electrode 9. The polysilicon oxide film is formed so as to cover only the sidewalls of thin oxide film 8, silicon nitride film 8 and the surface of polysilicon electrode 9.

An interlayer film 11 is formed on the polysilicon oxide film 10 and the nitride film 7 by a CVD device. The Al light-shielding film 12 is an interlayer film 11 formed by a sputtering device.
Is formed through. The Al light-shielding film 12 is formed to have a width substantially equal to the width of the upper part of the polysilicon oxide film 10 (in the horizontal direction with respect to the paper surface).

A TiN antireflection film 14 is formed on the Al light shielding film 12 by sputtering.

The TiN film has a smaller reflectance than the Al film conventionally used as a light-shielding film. FIG. 2 shows the wavelength dependence of reflectance in the TiN film thickness range. As the film thickness increases, the wavelength exhibiting the lowest reflectance shifts to the higher wavelength side. For g-line, TiN film thickness is 35 nm or more 4
When the thickness is 5 nm or less, the lowest reflectance region is shown.

As described above, the reflectance depends on the wavelength, and the wavelength at which the reflectance becomes the minimum depends on the TiN film thickness. The minimum reflectance is 20% or less of that of the Al film.

In forming the color filter 17, Al
The taper generated by the reflection of the light-shielding film 12 extends to the adjacent photodiodes, causing a problem such as deterioration of color reproducibility due to color mixing. If the reflectance can be reduced to 20% of that of the Al film, the shape of the color filter, which is a problem in the prior art, becomes a taper or a taper in the pattern formation up to 1 μm which is the limit resolution of filter materials such as synthetic materials and natural proteins. The pulling can be reduced, and the taper or the pulling of the taper can be prevented from reaching the photodiode.

Therefore, the TiN film having the reflectance of 20% or less can be most effectively used as an antireflection film.
An iN film is used.

When the TiN film thickness is 40 nm, its reflectance is about 15% of that of the Al film. Therefore, for the g-line,
For example, a TiN antireflection film having a film thickness of 40 nm is used. Further, the protective film 13 is the Al light shielding film 12 and the antireflection film 1.
4 are formed.

The operation of the solid-state image pickup device configured as described above will be described. The N ⁻ type diffusion region 3 formed in the P type diffusion region 2 in the semiconductor substrate 1 is a photodiode that generates signal charges by photoelectric conversion. Then, by applying a pulse voltage to the second-layer polysilicon electrode 9, the signal charges are moved to the N-type region 4 below the second-layer polysilicon electrode 9. Next, a pulse signal is alternately applied to the first-layer polysilicon electrode and the second-layer polysilicon electrode 9 to transfer the signal charge.

A color filter is formed in the solid-state image pickup device having such a structure and operation.

The structure using the g-line as the light source of the reduction projection exposure apparatus will be described below. In order to make the height of the upper surface of the N ⁻ type diffusion region 3 and the TiN antireflection film 14 uniform,
The transparent filling layer 15 is formed. Further, in order to accurately flatten the step between the transparent filling layer 15 and the TiN antireflection film 14, the transparent filling layer 15 and the TiN antireflection film 1 are formed.
4 and the transparent flat film layer 16 is formed on the upper surface. On the upper surface of the transparent flat film layer 16, red, green, and blue color filters 17R, 17 are provided for colorizing the solid-state imaging device.
G and 17B are formed. Color filter 17
R, 17G, 17B are formed as for each N-type region 3. Monochromatic light is incident on each N-type region 3.

When only the Al film is used as the light-shielding film, g
The reflectance of the line is large and the influence of halation is large.

Since the natural protein / dichromic acid used for the material of the color filter 17 is a negative type, the shape of the color filter 17 is extremely tapered due to reflection from the Al light shielding film 12. For this reason, the dimensional accuracy of the filter is lowered, the filter reaches the opening portion, the opening area is narrowed, and the sensitivity of the solid-state imaging device is lowered. In addition, the thickness of each color filter 17 varies to cause color unevenness, which causes deterioration of color reproducibility due to shading and color mixing.

As a method of preventing this halation, there is a method of forming a transparent hole-filling layer and a transparent flat film layer formed under the color filter. But in this way,
Since visible light of 435 nm is used for patterning using a reduction projection exposure apparatus using a g-line as a light source, the transparent hole-filling layer and the transparent flattening film layer must be colored. The function of the filter will be impaired.

However, in this embodiment, since the antireflection film having the reflectance of 20% or less is used and the thickness thereof is 40 nm, the transparent filling layer 15 is formed at the time of patterning by the g-line.
The transparent flat film layer 16 can be made colorless and transparent in the visible light region. Therefore, the transparent filling layer 15 and the transparent flat film layer 16 do not absorb the light incident on the N ⁻ type diffusion region 3. Therefore, the TiN antireflection film 14 can reduce halation light without reducing the sensitivity of the solid-state imaging device.

Actually, the natural protein / dichromic acid was irradiated with g rays, and the color filter 1 was formed under the condition that the TiN film thickness was 40 nm.
When No. 7 was formed, the problematic taper was reduced, and the dimensional variation of the filter was about 20%, but could be improved to 5%. It was also confirmed that the sensitivity and shading characteristics were improved at this time.

As a light source for reduction projection exposure, i-line (λ
= 356 nm), the case of forming a color filter will be described.

Here again, the TiN film can be utilized as an antireflection film, and a TiN film having a reflectance of 20% or less is used. Regarding the wavelength dependence of the reflectance, the wavelength showing the lowest reflectance is shifted to the higher wavelength side. Therefore, for the i-line, when the TiN film thickness is 25 nm or more and 35 nm or less, the lowest reflectance region is shown. In this case, when the TiN film thickness is 30 nm, the reflectance is about 15% of the Al film.

When the color filter 17 is formed by using the i-line, the color filter 17 is made of natural protein /
It is useful to use a dichromate-based material. Although this material has the following features, it cannot be exposed to g-line due to its nature. First of all, the advantages of this method are as follows: (1) The natural protein / dichromic acid system absorbs light in a wide exposure region from ultraviolet rays to the visible region, and the absorption amount is
The area around the i-line is larger than that near the g-line. Therefore, high sensitivity can be achieved by patterning the natural protein / dichromic acid-based material with i-line. (2) When the natural protein / dichromic acid-based material is patterned by i-line, the exposure time is shorter than that when patterned by g-line, and the throughput can be improved. As a result, the temperature rise of the optical system portion of the exposure apparatus can be prevented and the transfer pattern quality can be improved. (3) When dichromate is used, a difference reaction occurs between the initial exposure shot pattern and the final exposure shot pattern within one wafer due to a post-exposure reaction called a residual reaction peculiar to this material. This problem can be reduced.

On the other hand, the disadvantages of the natural protein / dichromic acid type material are: (1) The material combining natural protein / dichromic acid is
Problems such as treatment of chromium used as photosensitive material, variation in quality of natural protein, short storage time after addition of dichromic acid to natural protein, or harmfulness of human body to dichromic acid used as photosensitive material have. (2) A material in which dichromic acid is combined with natural protein is water-soluble and exhibits non-Newtonian properties. Therefore, in spin coating, the shear stress changes non-uniformly with respect to the change in rotation speed. Furthermore, since natural proteins are sensitive to heat,
A film having excellent flatness cannot be formed. Therefore, in a finer solid-state imaging device, sufficient characteristics cannot be obtained as the color filter 17.

In order to solve this problem, a photocrosslinking agent such as an azide compound or a diazo compound is added to the polymer, or a photosensitive group such as chalcone which causes photocrosslinking is introduced into the polymer to perform patterning. There is a method using a synthetic photosensitive material. However, in any of these methods, practical sensitivity to g-rays cannot be obtained, so it is necessary to expose with ultraviolet rays such as i-rays.

Next, in order to absorb i-rays in the transparent hole-filling layer 15 and the transparent flat film layer 16, a method of binding and dispersing a dye or a pigment in the material and a resin itself which absorbs i-rays are used. There is a way. Examples of the latter include salicylic acid-based, benzophenone-based, and chalcone-based resins, which are hydrocarbon derivatives.

However, it is difficult for the above method to satisfy the other characteristics of the transparent filling layer 15 and the transparent flat film layer 16. For example, in the former method, the dye or pigment is sublimated by repeating the heat treatment, so that the i-ray absorption effect is reduced. Also in the latter method, the resin itself reacts by the heat treatment, and coloring occurs in the visible light region. Both of them have lower film hardness as compared with a material such as polyglycyl methacrylate (hereinafter referred to as PGMA) which does not have an i-ray absorption effect, and have lower resistance to an organic solvent as compared with a material based on PGMA.

Therefore, when the transparent filling layer 15 and the transparent flat film layer 16 are formed and the heat treatment and the organic solvent treatment are repeated, cracks and surface roughness occur. Further, since the flatness of the surface of the solid-state image pickup device is not improved even if it is overcoated by a normal spin coating method, the flatness is improved by filling the step by patterning. The material used for the transparent filling layer is required to have negative or positive patterning characteristics.

As materials for the transparent filling layer 15 and the transparent flat film layer 16 satisfying the above characteristics, PGMA-4-
There is a metachlorooxy chalcone copolymer. However, as shown in FIG. 4, in order to obtain the transmittance, heat resistance, film hardness, and organic solvent resistance in the visible light region necessary for use in a solid-state image device, the i-line reflectance is set to 80% of that of an Al film. % Can only be reduced. Therefore, Ti having a reflectance of 20% or less
These materials can be easily used by using the N antireflection film.

For example, it was confirmed that by using a TiN antireflection film having a film thickness of 30 nm, the taper, which is a problem at the time of patterning by i-line, is reduced, and the filter dimensional accuracy is most improved. It was also confirmed that the sensitivity and shading characteristics were improved. Also, TiN
By using the antireflection film 14, the halation light can be suppressed to a maximum of 10% as compared with the Al film by optimizing the film thickness without being affected by heat resistance characteristics and organic solvent resistance. Therefore, the TiN antireflection film 14 having a film thickness of 30 nm can prevent halation light without deteriorating other characteristics of the solid-state imaging device, and the effect of preventing halation reflection is that the transparent hole filling layer 15 and the transparent flat film layer are provided. Compared to the 16 materials, 40% higher effect can be obtained with i-line.

[0046]

As described above, according to the present invention, by using the TiN film as the antireflection film, the color filter material is a negative type when the color filter is formed.
It suppresses the extreme taper caused by the reflection of the l film.

As a result, the shape of the filter is prevented from narrowing the opening area, and the sensitivity is kept good. Also,
Variations in the thickness of each color filter reduce shading due to color unevenness and deterioration of color reproducibility due to color mixing.

[Brief description of drawings]

FIG. 1 is a sectional view of a solid-state imaging device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the measurement wavelength dependence of the reflectance depending on the TiN film thickness.

FIG. 3 is a diagram showing the transmittance characteristics of PGMA-4-metachlorooxy chalcone copolymer.

FIG. 4 is a schematic diagram of a conventional solid-state imaging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 P type diffusion region 3 N ⁻ type diffusion region 4 N type diffusion region 5 P ⁺⁺ type diffusion region 6 Oxide film 7 Nitride film 8 Oxide film 9 Polysilicon electrode 10 Polysilicon oxide film 11 Interlayer film 12 Aluminum light shielding Film 13 Protective Film 14 Titanium Nitride Antireflection Film 15 Transparent Filling Layer 16 Transparent Flattening Film Layer 17 Color Filter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location H01L 21/318 C 7352-4M M 7352-4M 31/10 H04N 5/335 Z (72) Inventor Watakami Uesaka 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electronics Industrial Co., Ltd.

Claims (6)

[Claims] 1. A photodiode formed on a semiconductor substrate, a charge transfer portion for transferring charges formed by the photodiode, a transfer electrode formed on the semiconductor substrate except on the photodiode, A metal light-shielding film formed on the transfer electrode via an interlayer film, a nitride made of a refractory metal formed on the metal light-shielding film, and a color filter on the nitride via a protective film. A solid-state image pickup device comprising. 2. The solid-state imaging device according to claim 1, wherein a transparent filling layer is formed on the protective film, and a transparent planarizing film layer is formed on the transparent filling layer. 3. The reflectivity of the nitride is 2 that of an aluminum film.
It is 0% or less, The solid-state imaging device of Claim 2 characterized by the above-mentioned. 4. The solid-state imaging device according to claim 2, wherein the nitride is titanium nitride. 5. The film thickness of the nitride is 25 nm or more and 45 n.
The solid-state imaging device according to claim 4, wherein the solid-state imaging device has a thickness of m or less. 6. A step of forming a photodiode and a charge transfer portion on a semiconductor substrate, forming a transfer electrode on the charge transfer portion on the semiconductor substrate, and a metal light-shielding film via the transfer electrode upper interlayer film. And forming a nitride of a refractory metal on the metal light-shielding film, forming a protective film on the nitride, forming a transparent filling layer on the protective film, the transparent A method for manufacturing a solid-state imaging device, comprising: a step of forming a transparent flattening film layer on a hole filling layer; and a step of forming a color filter on the transparent flattening film layer.