JPH05129584A - Solid-state image sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a solid state image sensor in which influence of process variation due to an Si nodule and a hillock is eliminated and the quality of image is improved by improving the step coverage of the light shielding film without increasing the quantity of light incident through between the film and a photodiode. CONSTITUTION:In order to smooth the step of the sidewall of an insulating film 7 on a transfer gate 6, a sidewall insulating film 11 is provided, and a light shielding film 8 is formed from above. Since an Si nodule is largely grown with the step of the film 7 as a nucleus forming site, the step is eliminated to reduce the site. Further, the deterioration of the quality of image due to transmitted light from the nodule produced in an Al-Si series material is prevented by the uniform light shielding effect produced by the improvement of the step coverage. Hillocks are less produced due to the alleviation of the stress in the multilayer filem, and variation in the quantity of incident light due to the halation of the sidewall of the shielding film is reduced.

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 for detecting an optical signal and its manufacturing method.

[0002]

2. Description of the Related Art In recent years, the number of pixels of a solid-state image pickup device has been increased to improve the dynamic range and the image quality under low and high illuminance.

A conventional solid-state image pickup device will be described below.
It FIG. 2 shows a cross-sectional view of a unit pixel of a conventional solid-state imaging device.
It is something. In FIG. 2, 1 is an N-type semiconductor substrate, 2
Is a P-type well, 3 is N for accumulating charges⁺Layer photo die
Aude section, 4 avoid crosstalking with other pixels
Formed for P ⁺Layer channel stoppers, 5
N to transfer charge⁺Layer embedded channel, 6 transfer
Transfer gate for sending clock, 7 for insulating film, 8 for Al-S
The light-shielding film made of an i-based material determines the area of the light receiving portion 9.
It

The operation of the solid-state image pickup device configured as described above will be described below. First, the light receiving section 9
The light incident from the P-type well 2 and the N ⁺ layer forming the photodiode section 3 accumulates charges from the PN junction in the depletion layer according to the amount of the incident light. Reading to the buried channel 5 for transfer is performed by applying to the transfer gate 6 a voltage that lowers the potential on the buried channel 5 side. A transfer clock that sequentially changes the potential is sent in the front direction of the cross section to detect the light amount of each pixel.

[0005]

However, in the above-mentioned conventional structure, the Al--Si based light shielding film 8 is used,
In the Al-Si system, Si nodules are formed on the stepped portion of the underlying dielectric. This is because the nucleation site of Si nodules generated inside Al-Si can be formed in the stepped portion of the dielectric where the stress is concentrated. When Si nodules are generated in the light-shielding portion on the photodiode side, the transmission of light in that portion causes variations in the signal charges incident on each pixel portion, resulting in variations in the contrast on the screen. Further, there is a defect that white scratches are generated on the screen when the signal amount is large.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a solid-state image pickup device in which variations in image quality and white scratches, which are important in visual image quality evaluation, are reduced.

[0007]

To achieve this object, a solid-state image pickup device of the present invention comprises a semiconductor substrate which has been subjected to a predetermined process, a transfer gate formed on the semiconductor substrate,
An insulating film formed on the surface of the transfer gate, a sidewall insulating layer formed to smooth the step portion of the sidewall of the insulating film, and a light shielding film formed on the sidewall insulating layer and the insulating film. At least it has a configuration. Further, if necessary, the insulating film and the sidewall insulating layer are made of different materials.

[0008]

With the first structure, the step coverage of the light-shielding film itself can be improved, and Si nodules can be significantly reduced. As a result, the amount of light entering the light receiving portion region through the Si nodules is significantly reduced, and variations in the shape of the light shielding film do not affect the light receiving portion.

Further, in this structure, the distance between the photodiode and the light shielding film can be made as thin as possible to improve the light shielding ability. Further, in the subsequent patterning process, flattening process, and on-chip dyeing process, the conventional stepped portion of the light-shielding film is reduced, which leads to elimination of variations in characteristics among the photosensitive portions.

The second configuration facilitates dry etching endpoint monitoring when forming the sidewall insulating layer.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid-state image pickup device according to an embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the same parts as those of the conventional example of FIG. That is, the feature of the present invention is that the sidewall insulating layer 11 is provided to make the step portion of the sidewall of the insulating film 7 smooth. S
Since the i-nodule grows largely by using the step portion of the insulating film 7 as a nucleation site, the step portion is smoothed to reduce the nucleation site. Further, the uniform light-shielding effect due to the improvement of the step coverage can improve the deterioration of the image quality due to the transmitted light from the Si nodules, and the relaxation of the stress in the stack can reduce the occurrence of hillocks.

Further, it is possible to reduce variation in the amount of incident light due to halation on the side wall of the light shielding film. When dry etching such as RIE (reactive ion etching) is used to form the sidewall insulating layer 11, a material different from that of the base insulating film such as polysilicon is used. Since the step portion is a place where the actual laminated film becomes thick, the optimum shape of the sidewall insulating layer 11 can be easily formed by the etching endpoint monitor. However, it is necessary to form a pattern of the insulating film 7 or oxidize the sidewall insulating layer 11 in the peripheral wiring portion.

[0013]

As described above, the solid-state image pickup device of the present invention is
Since the side wall insulating layer for smoothing the step portion of the side wall of the insulating film on the transfer gate is provided, the step coverage of the light shielding film is improved, the deterioration of the image quality due to the transmitted light of the Si nodules is prevented, and the hillock of It is possible to reduce the occurrence of defects and improve the processing accuracy deterioration due to the halation of light generated at the step of the light shielding film around the photodiode part.
It is possible to provide a solid-state imaging device having improved image quality uniformity and dynamic range and a method for manufacturing the same.

[Brief description of drawings]

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

FIG. 2 is a sectional view of a main part of a conventional solid-state imaging device.

[Explanation of symbols]

 1 N-type semiconductor substrate (semiconductor substrate) 2 P-type well 3 Photodiode part 4 Channel stopper 5 Embedded channel 6 Transfer gate 7 Insulating film 8 Light-shielding film 11 Sidewall insulating layer

Claims (3)

[Claims] 1. A semiconductor substrate which has been subjected to a predetermined process, a transfer gate formed on the semiconductor substrate, an insulating film formed on the surface of the transfer gate, and a step portion of a sidewall of the insulating film which is gentle. A sidewall insulating layer formed to
A solid-state imaging device having at least a sidewall insulating layer and a light-shielding film formed on the insulating film. 2. The insulating film formed for smoothing the step of the side wall of the insulating film is replaced with the side wall insulating layer formed for smoothing the step of the side wall of the insulating film. The solid-state imaging device according to claim 1, wherein different side wall insulating layers are used. 3. A step of forming a transfer gate on a semiconductor substrate that has been subjected to a predetermined process, and forming a first insulating film on the surface of the transfer gate, and a region including a sidewall of the first insulating film. A step of forming a second insulating film made of a material different from that of the first insulating film; and etching the second insulating film by a dry etching method such as reactive ion etching to remove the first insulating film. And a step of forming a side wall insulating layer for smoothing the step portion on the side wall.