JPH0685232A - Manufacture of solid-state image sensing device - Google Patents

Abstract

PURPOSE:To reduce a rough texture and a white defect which are caused on a screen and to reduce the drop in sensitivity on the screen. CONSTITUTION:A photodiode part 3 which converts incident light into a signal charge and a buried channel 5 which transfers the signal charge converted in the photodiode part 3 are formed respectively on the surface of a semiconductor substrate 1. Then, a transfer gate electrode 6 is formed on the upper side of the buried channel 5 via an insulating layer 7. Then, a light-shielding layer 8 is formed on the upper side of parts other than the photodiode part 3 on the semiconductor substrate 1 and on the upper side of the transfer gate electrode 6. Then, a protective film 10 is formed on the upper part of the light- shielding layer 8 and the photodiode part 3 on the semiconductor substrate 1 by a photo-CVD method under a film-formation condition under which the temperature of the semiconductor substrate 1 is at 300 deg.C or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a solid-state image pickup device for detecting an optical signal.

[0002]

2. Description of the Related Art In recent years, solid-state image pickup devices have been required to improve the dynamic range by increasing the number of pixels and to improve the image quality under low and high illuminance.

A solid-state image pickup device obtained by a conventional manufacturing method will be described below.

FIG. 4 is a sectional view of a unit pixel of a solid-state image pickup device obtained by a conventional manufacturing method. In FIG.
Reference numeral 1 is an N-type semiconductor substrate, 2 is a P-type well layer formed on the surface of the semiconductor substrate 1, 3 is a photodiode portion formed of an N ⁺ layer for accumulating signal charges, and 4 is crosstalking with other pixels. A channel stopper made of a P ⁺ layer for preventing 5 is an embedded channel made of an N ⁺ layer for transferring signal charges, 6 is a transfer gate electrode for sending a transfer clock to the embedded channel 5, and 7 is an insulation covering the transfer gate electrode 6. The layer 8 is a light-shielding layer made of an Al—Si-based material that determines the light receiving region 9 formed on the upper side of the photodiode section 3.

Further, in the figure, reference numeral 10 denotes a protective film which covers the exposed portion of the insulating layer 7 and the light shielding layer 8. The protective film 10 is conventionally 300 in consideration of spectral sensitivity.
A silicon oxide film, a PSG film or a silicon nitride film having a thickness of nm or more is used.

The operation of the solid-state image pickup device will be described below.

First, when light passes through the protective film 10 and is incident on the light receiving region 9, a PN formed by the photodiode portion 3 formed of an N ⁺ layer and the P-type well layer 2 in accordance with the amount of the incident light. Photoelectric conversion is performed in the depletion layer of the junction,
The generated signal charge is accumulated in the photodiode unit 3.

Next, when a voltage for lowering the potential on the buried channel 5 side is applied to the transfer gate electrode 6, signal charges are transferred from the photodiode portion 3 to the buried channel 5.
Transferred to.

Next, a transfer clock for sequentially changing the potential in the forward direction of FIG. 4 is sent to sequentially transfer the signals on each line.

By the way, in forming the protective film 10 in the above-mentioned solid-state image pickup device, a plasma CVD method has been conventionally adopted in order to improve the coverage of the step of the underlying layer.

[0011]

However, the protective film 10 is used.
When the film is formed by the plasma CVD method, the photodiode portion 3 is exposed to plasma through the insulating film 7. Depending on the amount of plasma particle irradiation, and depending on the plasma CVD apparatus, the substrate temperature under the film forming condition may be 30.
Since the temperature needs to be 0 ° C. or higher, a defect layer may be formed on the surface layer of the photodiode section 3. Therefore, the silicon dangling bond on the silicon surface forming the photodiode part 3 cannot be completely terminated. The existence of the dangling bonds causes carriers to be generated, and there is a problem that rough and white scratches are generated on the screen.

In addition, in the film formation by the plasma CVD method, infrared absorption due to hydrogen bonding occurs, so that the light shielding layer 8 which is the base of the protective film 10 has an effect of light halation, which results in a decrease in sensitivity on the screen. Alternatively, there is a problem that graininess, unevenness, white scratches, etc. occur on the screen.

In view of the above, it is an object of the present invention to reduce graininess and white scratches on the screen, which are important for visually evaluating image quality, and reduction in sensitivity on the screen.

[0014]

In order to achieve the above object, the invention of claim 1 is to form a final protective film by a photo-CVD method. Specifically, the solving means taken by the present invention is Forming a light receiving part for converting incident light into a signal charge and a signal transfer part for transferring the signal charge converted by the light receiving part on the surface of the semiconductor substrate; and the signal transfer part above the signal transfer part. A step of forming a transfer gate electrode for transferring a signal charge to the semiconductor substrate, a step of forming a light shielding layer on a portion of the semiconductor substrate other than the light receiving portion and above the transfer gate electrode, the light shielding layer and the semiconductor substrate On the premise of the method for manufacturing a solid-state image pickup device, which comprises the step of forming a protective film on the upper side of the light receiving part in step 1, in the step of forming the protective film, the protective film is formed at a semiconductor substrate temperature of 300 ° C. or lower. conditions A step of forming a photo CVD method below.

According to a second aspect of the present invention, the final protective film has a multi-layered structure, and a lower protective film for suppressing the amorphization of the underlayer is formed as a lower layer of the multi-layered structure. Based on the same method for manufacturing a solid-state imaging device as the invention of Item 1, in the step of forming the protective film, the underlying layer is amorphized over the entire surface above the light-shielding layer and the light-receiving portion of the semiconductor substrate. After forming a lower protective film that suppresses the above, an upper protective film is formed on the entire lower protective film by photo CVD under the film forming conditions in which the temperature of the semiconductor substrate is 300 ° C. or lower. And a step of forming a protective film including the lower protective film and the upper protective film.

According to a third aspect of the present invention, the final protective film is formed of a polysilicon film whose surface is nitrided by the photo-CVD method. Specifically, the solid state is the same as that of the first aspect of the invention. Based on the method of manufacturing an image pickup device, a polysilicon film is formed over the entire surface of the light shielding layer and the light receiving portion of the semiconductor substrate, and then the dry etching process is selectively performed on the polysilicon film. By removing all or most of the upper part of the light receiving part in the polysilicon film by nitriding the surface part of the polysilicon film by a photo-CVD method, Is a step of forming a protective film.

[0017]

According to the structure of claim 1, the temperature of the semiconductor substrate is 3
Since the protective film is formed by the photo-CVD method under the film forming condition of 00 ° C. or less, the thickness of the protective film can be reduced, and the curved surface of the protective film covering the upper end corner of the side wall of the light shielding layer can be formed. As the radius of curvature becomes smaller and the curved surface portion is formed at a position farther from the center of the light receiving portion, 90% or more of the amount of signal received by the light receiving portion is affected by irregular reflection of incident light caused by the curved surface portion. The extent to the central part occupying is greatly reduced.

Further, since the protective film is formed under the film forming conditions in which the temperature of the semiconductor substrate is 300 ° C. or lower by the photo CVD method which does not generate the interface state, the interface state does not occur during the formation of the protective film. Therefore, it becomes difficult for the dangling bond of silicon to change with time, and the level of the silicon surface becomes stable.

According to the structure of claim 2, after forming the lower protective film for suppressing the amorphization of the underlayer over the entire surface of the light shielding layer and the light receiving portion of the semiconductor substrate,
The upper protective film is formed on the lower protective film over the entire surface by photo CVD under the film forming conditions in which the temperature of the semiconductor substrate is 300 ° C. or lower.
Since it is formed by the method, it is possible to prevent the phenomenon that the light receiving portion becomes amorphous due to a photochemical reaction due to photons generated when the upper protective film is formed.

According to the structure of claim 3, a polysilicon film is formed over the entire surface of the light-shielding layer and the light receiving portion of the semiconductor substrate, and then the dry etching process is selectively performed on the polysilicon film. Removing all or most of the upper part of the light receiving part in the polysilicon film,
After that, the surface portion of the polysilicon film is nitrided by the photo-CVD method to form the protective film, so that the surface protective layer made of silicon nitride is formed on the surface portion of the protective layer.

Further, since the protective film is formed of polysilicon having a light shielding effect, halation in the unit pixel portion other than the light receiving portion is greatly reduced.

[0022]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 shows a sectional structure of a solid-state image pickup device obtained by a manufacturing method according to the first embodiment of the present invention. In FIG. 1, 1 is an N-type semiconductor substrate and 2 is a surface of a semiconductor substrate 1. The P-type well layer, 3 is a photodiode section as a light receiving section made of an N ⁺ layer for accumulating signal charges, 4
Is a channel stopper made of a P ⁺ layer for preventing crosstalking with other pixels, and 5 is an N ⁺ for transferring a signal charge.
A buried channel serving as a signal transfer unit made of a layer, 6 a transfer gate electrode for sending a transfer clock to the buried channel 5, 7 an insulating layer covering the transfer gate electrode 6, and 8 formed on the upper side of the photodiode unit 3. A light-shielding layer made of an Al-Si-based material that determines the light-receiving region 9 and an insulating layer 7
It is a protective film that covers the exposed portion and the light shielding layer 8.

The feature of the first embodiment resides in that the protective film 10 is formed by the photo CVD method under the film forming condition that the temperature of the semiconductor substrate 1 is 300 ° C. or less. In this case, a low-pressure mercury lamp, a continuous wave laser, or a pulse laser is used for light irradiation.

As described above, in the first embodiment, the protective film 10 is used.
Is formed by the photo-CVD method, which has better step coverage than the plasma CVD method, so that the thickness of the protective film 10 can be made thinner than that by the plasma CVD method. For this reason, the radius of curvature of the curved surface portion 10a of the protective film 10 covering the upper end corner portion of the side wall of the light shielding layer 8 becomes smaller, and the curved surface portion 10a is formed at a position far from the central portion of the light receiving region 9. Therefore, the influence of the irregular reflection of the incident light caused by the curved surface portion 10a is largely reduced to the extent that the central portion occupying 90% or more of the signal amount received by the light receiving area 9 is uniformly reduced. Since various spectral sensitivities are obtained and variations in the signal amount are reduced, the image quality can be improved as compared with the conventional case. In addition, the protective film 10
Since it is possible to reduce the thickness, the film formation time can be shortened and the influence on the light shielding layer 8 is reduced.
Further, since the thickness of the protective film 10 is thin, the stress generated in the light shielding layer 8 can be relaxed, and the generation of Al—Si hillocks can be reduced.

Further, in the first embodiment, since the protective film 10 is formed by the photo-CVD method which does not generate the interface state due to the ion irradiation, the interface state does not occur during the formation of the protective film 10, so that the dangling of silicon is performed. It becomes difficult for the ring bond to change over time, and the level on the silicon surface becomes stable.

Further, in the first embodiment, as described above, the protective film 10 is formed by the photo-CVD method under the film forming conditions in which the temperature of the semiconductor substrate 1 is 300 ° C. or lower.
The stress generated in the light shielding layer 8 is relaxed.

FIG. 2 shows a sectional structure of a solid-state image pickup device obtained by the manufacturing method according to the second embodiment of the present invention.
In the second embodiment, a PSG film (phosphorus / silicate glass) capable of relieving the stress on the side wall of the light shielding layer 8 over the exposed insulating layer 7 and the light shielding layer 8 is formed. After the lower protective film 10b made of a film capable of trapping an alkali metal is formed by the atmospheric pressure CVD method or the photo CVD method, the upper protective film 10c is entirely formed on the lower protective film 10b and the semiconductor substrate 1 is formed. The film is formed by the photo-CVD method under the film forming condition that the temperature is 300 ° C. or lower.

As described above, in the second embodiment, since the lower protective film 10b as described above is formed below the upper protective film 10c, photons generated when the upper protective film 10c is formed. It is possible to prevent a phenomenon in which the underlayer becomes amorphous due to the photochemical reaction caused by.

FIG. 3 shows a sectional structure of a solid-state image pickup device obtained by a manufacturing method according to a third embodiment of the present invention.
In the second embodiment, the polysilicon film 12 is formed over the entire exposed portion of the insulating layer 7 and the light shielding layer 8. Next, a resist mask is formed on the polysilicon film 12 leaving the light receiving region 9 and then the polysilicon film 12 is subjected to dry etching.
In this case, in order to reduce damage to the light receiving region 9 due to ion irradiation, dry etching is performed so that the polysilicon film 12 having a film thickness of 100 nm remains on the light receiving region 9. Next, the surface portion 12a of the polysilicon film 12 is nitrided with NH ₃ gas using an optical CVD apparatus to form a surface protective layer made of silicon nitride on the surface portion 12a.

As described above, in the third embodiment, the protective film is made of the polysilicon film 12, and the surface portion 12a of the polysilicon film 12 is nitrided by the photo-CVD method to be a surface protective layer made of silicon nitride. Therefore, the moisture resistance of the protective film is improved.

Further, the polysilicon film 12 having a light shielding effect
Since the protective film is formed by, the halation in the unit pixel portion other than the light receiving region 9 is significantly reduced, and the ability to shield visible light is improved.

[0033]

As described above, according to the method of manufacturing a solid-state image pickup device of the first aspect of the present invention, the protective film is formed by the photo-CVD method under the film forming conditions in which the temperature of the semiconductor substrate is 300 ° C. or less. Since the protective film is formed, the thickness of the protective film can be reduced, the radius of curvature of the curved surface portion of the protective film that covers the upper end corner of the side wall of the light shielding layer becomes small, and the curved surface portion is located far from the center of the light receiving region. Therefore, the influence of irregular reflection of incident light caused by the curved surface portion on the central portion occupying 90% or more of the signal amount received in the light receiving region is greatly reduced. Therefore, uniform spectral sensitivity can be obtained in the central portion of the light receiving region, and the variation in the signal amount is reduced, so that the image quality is improved as compared with the conventional case.

Further, since the protective film is formed under the film forming conditions in which the temperature of the semiconductor substrate is 300 ° C. or less by the photo-CVD method which does not generate the interface state, the interface state does not occur during the formation of the protective film. Therefore, it becomes difficult for the dangling bond of silicon to change with time, and the level of the silicon surface is stabilized, and along with this, roughness and white scratches on the screen are reduced.

According to the method of manufacturing a solid-state image pickup device according to the second aspect of the present invention, after the lower layer protective film for suppressing the amorphization of the underlying layer is formed on the light-shielding layer and the light receiving portion of the semiconductor substrate, the lower layer is formed. Since the upper protective film is formed on the protective film by the photo CVD method under the film forming conditions in which the temperature of the semiconductor substrate is 300 ° C. or less, the photoreceptive portion is formed by photochemical reaction caused by photons generated when the upper protective film is formed. Since it is possible to prevent the phenomenon of becoming amorphous, the image quality is further improved.

According to the method of manufacturing a solid-state image pickup device according to the third aspect of the present invention, after the polysilicon film is formed on the light-shielding layer and the light receiving portion of the semiconductor substrate, dry etching is selectively performed on the polysilicon film. The polysilicon film on the upper side of the light receiving portion is removed by performing a treatment, and then the surface portion of the polysilicon film is nitrided by a photo-CVD method to form a protective film. Since the surface protective layer made of ride is formed, the moisture resistance of the protective film is improved.

Further, since the protective film is formed of polysilicon having a light-shielding effect, halation in the unit pixel portion other than the light-receiving portion is significantly reduced, so that the ability to shield visible light is improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a solid-state imaging device obtained by a method for manufacturing a solid-state imaging device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a solid-state image pickup device obtained by a method for manufacturing a solid-state image pickup device according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a solid-state imaging device obtained by a method for manufacturing a solid-state imaging device according to a third embodiment of the present invention.

FIG. 4 is a cross-sectional view of a solid-state imaging device obtained by a conventional method for manufacturing a solid-state imaging device.

[Explanation of symbols]

 1 semiconductor substrate 2 P-type well layer 3 photodiode part (light receiving part) 4 channel stopper 5 buried channel (signal transfer part) 6 transfer gate electrode 7 insulating layer 8 light shielding layer 9 light receiving region 10 protective film 10b lower layer protective film 10c upper layer Protective film 12 Polysilicon film 12a Surface part

Claims (3)

[Claims] 1. A step of forming a light receiving section for converting incident light into a signal charge and a signal transfer section for transferring the signal charge converted by the light receiving section on a surface of a semiconductor substrate, and above the signal transfer section. A step of forming a transfer gate electrode for transferring a signal charge to the signal transfer section, a step of forming a light shielding layer on a portion of the semiconductor substrate other than the light receiving section and above the transfer gate electrode; In the method for manufacturing a solid-state imaging device, which comprises the step of forming a protective film on the upper side of the light receiving portion in the layer and the semiconductor substrate, in the step of forming the protective film, the temperature of the semiconductor substrate is 30
A method of manufacturing a solid-state imaging device, which is a step of forming by a photo-CVD method under a film forming condition of 0 ° C. or less. 2. A step of forming a light receiving section for converting incident light into a signal charge and a signal transfer section for transferring the signal charge converted by the light receiving section on the surface of the semiconductor substrate, and above the signal transfer section. A step of forming a transfer gate electrode for transferring a signal charge to the signal transfer section, a step of forming a light shielding layer on a portion of the semiconductor substrate other than the light receiving section and above the transfer gate electrode; In a method for manufacturing a solid-state imaging device, which comprises a step of forming a protective film on the upper side of the light receiving portion in the layer and the semiconductor substrate, the step of forming the protective film includes forming the protective film on the upper side of the light receiving portion in the light shielding layer and the semiconductor substrate. After forming a lower protective film that suppresses the amorphization of the underlying layer over the entire surface, an upper protective film is formed over the lower protective film over the entire surface when the temperature of the semiconductor substrate is 300 ° C. or less. A method of manufacturing a solid-state imaging device, comprising the step of forming a protective film composed of the lower protective film and the upper protective film by forming the protective film by a photo CVD method under a certain film forming condition. 3. A step of forming a light receiving part for converting incident light into a signal charge and a signal transfer part for transferring the signal charge converted by the light receiving part on the surface of the semiconductor substrate, and above the signal transfer part. A step of forming a transfer gate electrode for transferring a signal charge to the signal transfer section, a step of forming a light shielding layer on a portion of the semiconductor substrate other than the light receiving section and above the transfer gate electrode; In a method for manufacturing a solid-state imaging device, which comprises a step of forming a protective film on the upper side of the light receiving portion in the layer and the semiconductor substrate, the step of forming the protective film includes After the polysilicon film is formed over the entire surface, the polysilicon film is selectively dry-etched to form an upper side of the polysilicon film above the light receiving portion. All or most of the portion is removed, and then the surface portion of the polysilicon film is nitrided by a photo-CVD method to form a protective film made of a polysilicon film whose surface portion is nitrided. A method for manufacturing a characteristic solid-state imaging device.