JPH0878651A - Manufacturing for pick-up device - Google Patents

Abstract

PURPOSE: To improve a shielding effect in metallic shielding film and reduce reflectivity at the same time. CONSTITUTION: A photodiode part and an MIS transistor part are formed on a semiconductor substrate 1, and a silicon dioxide film 4 as an interlayer insulating film and a WSi film 7 as a metallic shielding film are formed thereon. A resist pattern 8 is formed on the WSi film 7, and an etching step is carried out to from an opening for the photodiode part. The semiconductor substrate 1 is heated at 800 deg.C or above in a heart treatment step to form the polycrystalline WSi film 7 except for the photodiode part. The semiconductor substrate 1 is heat-treated in an oxidizing atmosphere at a temperature of 800 deg.C or above to form a silicon dioxide film 9 on the surface of the polycrystalline WSi film 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state image pickup device having a metal light-shielding film for preventing light from entering a portion other than a photodiode portion.

[0002]

2. Description of the Related Art In recent years, solid-state image pickup devices have been widely used as image pickup means for electronic cameras, and due to their ease of use, the environment in which they can be used has become wider, and there is a growing demand for smaller size and higher performance. It's coming.

A conventional method of manufacturing a solid-state image pickup device will be described below with reference to the drawings.

3 (a) and 3 (b) are sectional views showing the outline of a conventional method for manufacturing a solid-state image pickup device, and a method for manufacturing the solid-state image pickup device will be described below.

First, a gate oxide film 2 and a gate electrode 3 are formed on the main surface of a semiconductor substrate 1 made of silicon or the like, and then,
A photodiode section that generates electric charges when light enters and a MOS transistor section (not shown) that transfers the electric charges are formed.

Next, a silicon dioxide film 4 having a thickness of about 400 nm is formed on the entire surface of the semiconductor substrate 1, and an aluminum alloy film 5 having a thickness of 0.8 μm containing 2 wt% of silicon on the entire surface of the silicon dioxide film 4 ( (Hereinafter referred to as "Al-Si film 5") is formed by the chemical vapor deposition method, and then the photoresist applied to the entire surface of the Al-Si film 5 is exposed and developed to open the photodiode portion. A resist pattern 6 for forming is formed [see FIG. 3 (a)].

Then, after etching the Al-Si film 5 using the resist pattern 6 as a mask and removing the photoresist, a portion other than the photodiode portion is Al-.
A solid-state image pickup device covered with the Si film 5 is formed [FIG.
reference〕.

When light is incident on the surface of the solid-state image pickup device manufactured as described above, the light is incident on the photodiode portion, but the portion other than the photodiode portion is an Al-Si film as a metal light-shielding film. Reflected by 5, M
It does not enter the OS type transistor section.

[0009]

However, if the Al-Si film 5 is formed thick in order to prevent the transmission of light,
When the Al-Si film 5 is dry-etched or when the Al-Si film 5 covering a portion other than the photodiode portion is miniaturized, the surface of the semiconductor substrate 1 is likely to be damaged and the photodiode characteristics are remarkably increased. There was the first problem of deterioration.

In order to solve this first problem, A
When the thickness of the silicon dioxide film 4 below the l-Si film 5 is increased, a part of the light reflected by the Al-Si film 5 is obliquely incident from the silicon dioxide film 4 to the MOS type transistor portion, M
There is a second problem that the smear characteristic is deteriorated because the amount of light incident on the OS type transistor portion increases.

Further, if the film thickness of the silicon dioxide film 4 is reduced to solve the second problem, the surface of the semiconductor substrate 1 is likely to be damaged when the Al-Si film 5 is dry-etched. The third problem is that the photodiode characteristics are significantly deteriorated.

Further, the Al-Si film 5 is heat-treated to form an Al-Si film 5.
When the Si film 5 is crystallized, grain boundaries are formed in the Al-Si film 5,
There is a fourth problem that light is transmitted along the grain boundaries to the MOS type transistor section.

The present invention has been made in view of the above problems, and improves the light-shielding property of a metal light-shielding film.
It is an object of the present invention to provide a method for manufacturing a solid-state image pickup device having a reduced reflectance.

[0014]

According to the present invention, an interlayer insulating film is formed on a main surface of a semiconductor substrate on which a photodiode portion that generates electric charges when light is incident and a MIS type transistor portion that transfers the electric charges are formed. And a step of forming a metal light-shielding film made of a refractory metal or a refractory metal silicide, or a refractory metal or a refractory metal silicide having a polycide structure on the surface of the interlayer insulating film, and a metal light-shielding film is formed. And a step of heat-treating the semiconductor substrate at a temperature of 800 ° C. or higher.

Further, a metal light-shielding film of refractory metal silicide or refractory metal silicide having a polycide structure is further formed to 800
The heat treatment is performed in an oxidizing atmosphere at a temperature of ℃ or higher.

The semiconductor substrate is heat-treated in a high temperature oxidizing atmosphere to form an interlayer insulating film.

[0017]

According to the present invention, the semiconductor substrate is heat-treated at a high temperature to polycrystallize the refractory metal or refractory metal silicide, or the refractory metal or refractory metal silicide having a polycide structure. By
The film stress can be reduced and the film quality can be made uniform, and the light-shielding property of the metal light-shielding film can be improved.

Further, according to the present invention, the semiconductor substrate is further heat treated in an oxidizing atmosphere at a higher temperature to remove the surface of the metal light-shielding film made of polycrystallized refractory metal silicide or polycide structure refractory metal silicide. By oxidizing, the reflectance of the metal light-shielding film can be reduced.

Further, since the metal light-shielding film of the present invention has improved light-shielding properties and reduced reflectance, it is possible to form a thin film, and the film is formed on the surface of the semiconductor substrate during dry etching. Damage is less likely to occur and the photodiode characteristics will not deteriorate.

Furthermore, since the surface of the semiconductor substrate is less likely to be damaged during dry etching, the interlayer insulating film can be formed thin, and part of the light reflected by the metal light-shielding film is separated by the interlayer insulating film. The film does not obliquely enter the MIS type transistor section, the amount of light incident on the MIS type transistor section does not increase, and the smear characteristic does not deteriorate.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a solid-state image pickup device according to the present invention will be described in detail below with reference to the drawings.

1 (a) and 1 (b) are sectional views showing the outline of the method of manufacturing the solid-state image pickup device of the present invention. The same reference numerals as those in FIG. 3 denote the same parts.

First, a gate oxide film 2 and a gate electrode 3 are formed on the main surface of a semiconductor substrate 1 made of silicon or the like, and then,
A photodiode section that generates electric charges when light enters and a MIS transistor section (not shown) that transfers the electric charges are formed.

Next, a silicon dioxide film 4 having a thickness of about 200 nm is formed as an interlayer insulating film on the entire surface of the semiconductor substrate 1, and a refractory metal silicide film, for example, a thick film, is formed on the entire surface of the silicon dioxide film 4 as a metal light shielding film. A tungsten silicide film 7 (hereinafter referred to as "WSi film 7") having a thickness of 0.3 μm,
After being formed by the chemical vapor deposition method, the photoresist applied to the entire surface of the WSi film 7 is exposed and developed to form a resist pattern 8 for opening the photodiode portion.
Are formed [see FIG. 1 (a)].

Then, the WSi film 7 is etched using the resist pattern 8 as a mask, and then the photoresist is removed.

After that, the semiconductor substrate 1 is heat-treated at a temperature of 800 ° C. or higher to polycrystallize the WSi film 7 covering the portion other than the photodiode portion, and the semiconductor substrate 1 is again made to 800 ° C.
The WSi film 7 is heat-treated in an oxidizing atmosphere at a temperature of ℃ or more.
Poly-crystallized WSi by oxidizing the surface of
A silicon dioxide film 9 is formed on the surface of the film 7 [see FIG. 1 (b)].

In the solid-state imaging device thus manufactured, the WSi film 7 immediately after being formed by the sputtering method or the low temperature CVD method is amorphous, has a large film stress, and has a nonuniform film quality. It is not very popular.

However, when the WSi film 7 is heat-treated at a high temperature, crystallization progresses, the film stress decreases, and the film quality becomes uniform, so that the light-shielding property is improved.

When the crystalline state of the WSi film 7 at this time is observed by X-ray diffraction, it becomes hexagonal when heat-treated at 800 ° C. for 30 minutes, and tetragonal when heat-treated at 900 ° C. for 30 minutes. Crystallization of the film 7 is progressing [Fig. 2
reference〕.

When the crystallized WSi film 7 is heat-treated at a high temperature in an oxidizing atmosphere, the surface of the WSi film 7 is oxidized and the reflectance is lowered.

Further, WSi manufactured by the above-mentioned process
The film 7 has improved light-shielding properties and reduced reflectance,
Since the film thickness can be made thin, the time for dry etching the WSi film 7 of the photodiode portion is shortened, the surface of the semiconductor substrate 1 is less likely to be damaged, and the surface of the semiconductor substrate 1 is not damaged. The thickness of the silicon dioxide film 4 as an interlayer insulating film for preventing
It becomes difficult for the light reflected by the Si film 7 to enter the MIS type transistor portion from the silicon dioxide film 4.

In the present embodiment, the refractory metal silicide film, especially the WSi film 7 is described as an example of the metal light-shielding film, but the metal light-shielding film is not limited to this, and may have a high W, Mo or the like. It may be a melting point metal or a high melting point metal silicide, and the film thickness of the metal light shielding film is not limited to the above-mentioned numerical values.

Further, in this embodiment, the refractory metal silicide film may be a single substance as described above, or has a so-called polycide structure in which a polycrystalline silicon film is formed under the refractory metal silicide film. It may be.

Further, in the present embodiment, an example in which the film thickness of the interlayer insulating film under the metal light shielding film is formed thin by the chemical vapor deposition method in order to reduce the amount of light incident on the MIS type transistor portion has been described. Alternatively, the gate interlayer insulating film of polycrystalline silicon or the like may be oxidized in a high temperature oxidizing atmosphere to form a thin film.

Further, although the high melting point metal silicide film of the photodiode portion is etched by the dry etching method as an example, a wet etching method which does not damage the surface of the semiconductor substrate 1 may be used. However, since the metal light-shielding film thickness is thin, the pattern forming accuracy of the photodiode portion is high.

[0036]

As described above, according to the present invention,
The semiconductor substrate is heat-treated at a high temperature to polycrystallize the refractory metal or refractory metal silicide, or the refractory metal or refractory metal silicide having a polycide structure to reduce the film stress and the film quality. The effect of being able to uniformize and improving the light-shielding property of the metal light-shielding film.

Further, according to the present invention, the semiconductor substrate is further heat-treated in an oxidizing atmosphere at a higher temperature so that the surface of the metal light shielding film made of polycrystallized refractory metal silicide or polycide refractory metal silicide is removed. Oxidation has the effect of reducing the reflectance of the metal light-shielding film.

Further, since the metal light-shielding film of the present invention has improved light-shielding properties and reduced reflectance, it becomes possible to form a thin film, and the film is formed on the surface of the semiconductor substrate during dry etching. There is an effect that damage is less likely to occur and the photodiode characteristics are not deteriorated.

Furthermore, since the surface of the semiconductor substrate is less likely to be damaged during dry etching, the film thickness of the interlayer insulating film can be reduced so that a part of the light reflected by the metal light-shielding film is separated by the interlayer insulating film. There is an effect that the film does not obliquely enter the MIS type transistor section, the amount of light incident on the MIS type transistor section does not increase, and the smear characteristic does not deteriorate.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a method for manufacturing a solid-state imaging device according to the present invention.

FIG. 2 is a diagram showing a crystal state of a refractory metal silicide film when heat-treated, as viewed by X-ray diffraction.

FIG. 3 is a cross-sectional view showing an outline of a conventional method for manufacturing a solid-state imaging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Gate oxide film, 3 ... Gate electrode, 4 ... Silicon dioxide film (interlayer insulating film), 7 ... WSi film (metal light shielding film), 8 ... Resist pattern, 9 ... Silicon dioxide film.

Claims (3)

[Claims] 1. A step of forming an interlayer insulating film on a main surface of a semiconductor substrate on which a photodiode section that generates charges when light enters and a MIS type transistor section that transfers the charges are formed, and the interlayer insulating film. Forming a metal light-shielding film made of a high-melting point metal or a high-melting point metal silicide or a high-melting point metal or a high-melting point metal silicide having a polycide structure on the surface of the A method of manufacturing a solid-state imaging device, comprising: performing a first heat treatment at the above temperature. 2. The metal light shielding film made of the refractory metal silicide or the refractory metal silicide having a polycide structure is subjected to a second heat treatment in an oxidizing atmosphere at 800 ° C. or higher after the first heat treatment. The method for manufacturing a solid-state image pickup device according to claim 1, wherein the solid-state image pickup device is manufactured. 3. The method of manufacturing a solid-state imaging device according to claim 1, wherein the interlayer insulating film is formed by heat-treating the semiconductor substrate in a high temperature oxidizing atmosphere.