JPH07101734B2 - Method of manufacturing solid-state imaging device - Google Patents

Description

The present invention relates to a method for manufacturing a solid-state imaging device.

[Conventional technology]

Conventionally, in this type of solid-state image pickup device, a P
Those using a photodiode with a −N junction have been widely used.

3 (a) and 3 (b) are a plan view and an AA 'sectional view of an example of a conventional solid-state imaging device. As shown in FIG. 3 (a), this solid-state imaging device has an aluminum light-shielding film 1
The windows 11 _b are provided by regularly opening in a matrix. In addition, as shown in FIG. 3 (b), the photodiode PD provided below the window 11 _b of the aluminum light shielding film 1
Is a P-N junction between a P-type silicon substrate 2 and an N-type diffusion layer 3 formed on the P-type silicon substrate 2. The light L incident through the window 11 _b is photoelectrically converted by the silicon substrate 1 and then a photodiode. It is accumulated in PD as signal charge.

The signal charges accumulated in each photodiode PD are separated from each other by the high-concentration P-type region 4 of the channel stop. Since the amount of signal charges accumulated in each photodiode PD is proportional to the amount of light L incident on each photodiode PD, when the amount of incident light is constant, the amount of signal charges accumulated in each photodiode is equal to the light-shielding film. It will be proportional to the area of the window 11 _b .

In the solid-state imaging device, it is desirable that the amount of electric charge accumulated in each photodiode PD be equal when uniform light is incident. Thus as the properties of the light-shielding film, it is required that the area of that does not transmit light and the window 11 _b is accurately machined so as not vary.

Conventionally, the aluminum light-shielding film 1 has been used as a film that satisfies these two requirements.

[Problems to be Solved by the Invention]

The conventional solid-state imaging device described above has the aluminum light-shielding film 1
However, there are two drawbacks as described below.

The first drawback is that a projection called hillock is formed on the surface of the aluminum film by heat treatment at 300 to 450 ° C.

In the manufacture of a solid-state imaging device, it was necessary to anneal at 300 to 450 ° C. in a hydrogen atmosphere in order to erase the surface states of the semiconductor substrate after processing the light shielding film with high precision. However, as described above, the aluminum light-shielding film causes hillocks during this annealing, so that the side wall and the surface of the light-shielding film partially protrude, resulting in variations in the window area.

The second drawback is that the aluminum light-shielding film has a very high light reflectance. In the conventional solid-state imaging device shown in FIG. 3, color sensitivity can be obtained by coating each light-receiving element with an emulsion such as gelatin or casein, selectively patterning it, and dyeing it so as to have desired spectral characteristics. It is possible to realize a solid-state imaging device having the same.

However, as a patterning method, an ultraviolet ray transfer technology that transfers a pattern using ultraviolet rays of 300 to 400 nm wavelength is used. It became difficult.

[Means for Solving the Problems]

The structure of the method for manufacturing a solid-state imaging device according to the present invention is such that an interlayer insulating film is formed on the surface of one main surface of a semiconductor substrate having a plurality of light receiving element regions which are periodically arranged in proximity to each other and are separated from each other by a channel stop layer. The step of forming a film, and after forming an aluminum light-shielding film on the surface of this interlayer insulating film by a sputtering method, a refractory metal film for hillock prevention and an antireflection film are sequentially formed on the surface of this aluminum light-shielding film by a sputtering method. Forming step, forming an opening window from the surface area corresponding to the light receiving element area by photo-etching to expose the surface of the one main surface, and stabilizing the surface level of the exposed one main surface. And a step of annealing in a hydrogen atmosphere.

〔Example〕

Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a reference example of a solid-state imaging device related to the present invention. FIG. 1 corresponds to the cross-sectional view of FIG. 3 (b).

In this solid-state imaging device, the light shielding film 20 is formed on the surface of the aluminum light shielding film 1 shown in FIG.
And the sputtered silicon film 8 are sequentially formed, which is the same as the conventional example.

The thickness of the silicon oxide film 7 is 100 to 200 nm, which is effective in preventing hillocks. Further, the thickness of the sputtered silicon film 8 on the surface is set to a value that reduces the reflectance of ultraviolet rays having a wavelength of 300 to 400 nm.

The light shielding film 20 of this solid-state imaging device can be formed by the following method.

First, an aluminum film, a silicon oxide film, and a silicon film are sequentially formed with a desired film thickness by a sputtering method. Next, the window 11 is processed in the aluminum, the silicon oxide film, and the silicon film by the photo-etching technique which is commonly used in the manufacture of semiconductors.

After that, annealing is performed in a hydrogen atmosphere at 300 to 450 ° C., but since the sputtered silicon oxide film 7 exists between the aluminum light-shielding film 1 and the sputtered silicon film 8, the aluminum film 1 formed at the time of formation thereof is formed. Along with the intervening alumina, it has the effect of preventing hillocks of the aluminum film 1 and the reaction between the aluminum film 1 and the sputtered silicon film 8, and therefore the processing accuracy of the window 11 is good.

FIG. 2 is a sectional view for explaining an embodiment of the present invention. Shielding film 20 _a of the solid-state imaging device of this embodiment is to prevent hillocks covering the surface top of the aluminum light-shield film 1 _a tungsten film 9 which is a refractory metal. The upper portion of the tungsten film 9 is covered with a tungsten silicide film 10 which is a compound of tungsten and silicon to enhance the antireflection effect.

Shielding film 20 _a of the solid-state imaging device can also be formed in the following manner.

First, the aluminum film 1 _a , the tungsten film 9 and the tungsten silicide film 10 are sequentially formed in a desired thickness by the sputtering method. Next, the window 11 is processed in the aluminum, the tungsten film 9 and the tungsten silicide film 10 by a general photolithography technique in the semiconductor manufacturing method.

Although subsequently annealed in a hydrogen atmosphere at 300 to 450 ° C., the aluminum light shielding film 1 _a and a tungsten silicide film
Since the tungsten film 9 exists between 10 and 10, the hillock of the aluminum film 1 _a is prevented together with the alumina between the aluminum films 1 _a generated during the formation of the tungsten film 9 and the aluminum film 1 _a is prevented.
There are reactions to prevent the effect of the 1 _a and the tungsten silicide film 10, the better processing accuracy of the sub connexion window 11.

Further, in this embodiment since the upper portion of the aluminum light-shield film 1 _a are covered with the refractory metal, which is resistant to stress migration due to heat. Therefore, even if the aluminum light-shielding film 1 _a is thinner than the aluminum light-shielding film of the reference example,
Pinholes do not occur due to stress migration caused by heat treatment at 300-450 ℃.

That is, by covering the upper portion of the aluminum light-shielding film 1 _a with _a refractory metal, the effect as the light-shielding film can be sufficiently achieved even if the thickness of the aluminum light-shielding film 1 _a is reduced from 800 nm to 400 nm.

Generally, in a solid-state image pickup device, light incident on the side wall of the light shielding film is reflected, so that the sensitivity of each light receiving element varies, and smear occurs due to light leakage under the light shielding film.
Therefore, by reducing the thickness of the light shielding film, it is possible to reduce variations in sensitivity and smear caused by reflection on the side wall.

In the solid-state imaging device of the present embodiment, the aluminum light shielding film
30% sensitivity variation by the sidewalls of 1 _a with the conventional half 400 nm, it was possible to reduce the smear 15%.

〔The invention's effect〕

As described above, the present invention forms the light-shielding film from the aluminum film and the hillock-preventing refractory metal film provided on the upper surface of the aluminum film, and the antireflection film further provided thereon, It is possible to prevent variations in window area due to hillocks in the light-shielding film and reflection of ultraviolet rays of 300 to 400 nm.

Therefore, by using the light-shielding film according to the present invention, it is possible to easily manufacture a solid-state image pickup device having color sensitivity by suppressing the sensitivity variation due to hillocks of the aluminum film and using the ultraviolet transfer technique.

Therefore, the effect of the present invention is remarkable for a solid-state imaging device having a small opening area of the light shielding film, that is, a solid-state imaging device having a small imaging area and high resolution.

[Brief description of drawings]

FIG. 1 is a sectional view of a reference example of a solid-state imaging device related to the present invention, FIG. 2 is a sectional view illustrating an embodiment of the present invention, and FIG.
FIGS. 1A and 1B are a plan view and an AA ′ sectional view of an example of a conventional solid-state imaging device. 1,1 _a …… Aluminum light-shielding film, 2 …… P type silicon substrate, 3 …… N type diffusion layer, 7 …… Sputtered silicon oxide film, 8 …… Sputtered silicon film, 9 …… Tungsten film, Tungsten silicide film , 20,20 _a …… Shading film, PD
…… Photodiode.

Claims (1)

[Claims] 1. A plurality of light receiving element regions, which are arranged periodically close to one main surface of a semiconductor substrate, and are arranged periodically close to each other by a light shielding film, and are separated from each other by a channel stop layer. A step of forming an interlayer insulating film on the surface of the one main surface of the semiconductor substrate having, and after forming a light shielding film of aluminum on the surface of the interlayer insulating film by a sputtering method, a hillock preventing film is formed on the surface of the aluminum light shielding film. A step of sequentially forming a refractory metal film and an antireflection film by a sputtering method, and a step of forming an opening window from the surface region corresponding to the light receiving element region by a photo-etching method to expose the surface of the one main surface, And a step of annealing in a hydrogen atmosphere so as to stabilize the surface level of the exposed one main surface.