JPH04181773A - Solid-state image sensing element - Google Patents

Abstract

PURPOSE:To enhance a smear-resistant property and to maintain the dielectric breakdown strength of an interlayer insulating film at a high level by a method wherein the refractive index of the interlayer insulating film is set to be larger than the refractive index of a protective film. CONSTITUTION:An Si3N4 film 27 whose refractive index is larger than the refractive index of a passivation film 29 is used as an interlayer insulating film. Thereby, the angle of incidence of light which is obliquely incident on a photosensitive part from an opening part 28a in a light-shielding film 28 can be made small, and the quantity of light which is directly incident on a charge transfer passage 23 can be reduced. Since the number of reflections at the interface between a substrate 21 and an oxide film 22 is increased, the amount of light which is absorbed by the substrate is increased. As a result, light is easy to attenuate, and the quantity of light to the charge transfer passage 23 can be reduced. In addition, the step coverage of the Si3N4 film 27 is good. Thereby, a smear-resistant property is enhanced, and the dielectric breakdown strength of the interlayer insulating film can be maintained at a high level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state image sensor, and particularly to a CCD solid-state image sensor in which an interlayer insulating film with a high refractive index is disposed under a light-shielding film.

[Prior Art] As is well known, a CCD solid-state image pickup device includes a photosensitive section and a charge transfer section, and conventionally known structures are shown in FIGS. 2 and 3, for example.

As shown in FIG. 2 in plan view, the CCD solid-state image sensor includes a plurality of vertical CCD sections 1, a light receiving section 2 disposed between these vertical CCD sections 1, a horizontal CCD section 3, and an output section 4. It is composed of.

Further, the cross-sectional shape of the main part of the above element is as shown in FIG. 5 in the figure is a p-type St substrate. On the surface of this substrate 1, an n-type diffusion layer (photodiode) 6 and a charge transfer path 7, which serve as a light receiving section, are formed. A charge transfer electrode 9 made of polycrystalline silicon is formed on the substrate 5 with a gate oxide film 8 interposed therebetween. An oxide film lO is formed on the surface of this electrode 9. A SiO2 film 11 is formed on the entire surface of the substrate including this oxide film 1O. A light shielding film 12 made of Ag and having an opening 12a in a portion corresponding to a portion of the photodiode 6 is formed on the 5in2 film 11.

The purpose of this light shielding film 12 is to prevent light from entering the charge transfer section and causing smear. A passivation film 13 is formed on the entire surface.

[Problem to be solved by the invention] However, according to the conventional solid-state image sensor, when incident light enters obliquely from the opening of the light shielding film 73112, multiple reflections occur between the substrate 1 and the light shielding film I2. There was a problem in that the charge leaked into the charge transfer path, causing smear.

For this reason, one conceivable measure for suppressing smear is to increase the light-shielding length (H) from the end of the charge transfer electrode 9 to the end of the light-shielding film 12. However, in this case, the size of the opening 12a of the light shield 812 becomes smaller, resulting in a decrease in sensitivity.

In particular, this will be fatal if miniaturization of structures continues in the future. In addition, as another smear countermeasure, the substrate 1 and the light shielding film 12 are
It is conceivable to reduce the thickness of the 5 in 2 film 11 between them, but in this case there is a risk that a short circuit may occur due to deterioration of the withstand voltage between the charge transfer electrode 9 and the light shielding film 12.

The present invention has been made in consideration of the above circumstances, and by using a material with a higher refractive index than the protective film as the interlayer insulating film, the incident angle of light obliquely entering the photosensitive area is reduced, thereby preventing smearing. It is an object of the present invention to provide a solid-state image sensor that can improve the performance and maintain a high dielectric strength voltage of an interlayer insulating film.

Means and Effects for Solving Problem U] The present invention provides a substrate, a photosensitive portion and a charge transfer path formed on the surface of the substrate, and a charge transfer electrode formed on the substrate via an insulating film. , an interlayer insulating film formed on the entire surface of the substrate including the charge transfer electrode, a light shielding film formed on the interlayer insulating film and having an opening corresponding to a part of the photosensitive area, and a light shielding film formed on the light shielding film. The solid-state imaging device is characterized in that the refractive index of the interlayer insulating film is larger than the refractive index of the protective film.

According to the present invention, since an interlayer insulating film having a refractive index higher than that of the passivation film is used, the angle of incidence of light that obliquely enters the photosensitive area from the opening of the light shielding film is made small, and the charge transfer path is can reduce the amount of light directly incident on the

In addition, for the same reason as above, the number of reflections at the interface between the substrate and oxide film increases, which increases the amount of light absorbed by the substrate, making it easier to attenuate the light and reducing the amount of light to the charge transfer path. can. Therefore, smear resistance can be improved compared to the conventional method. Furthermore, since less light reaches the charge transfer path, the light shielding length can be reduced to widen the aperture of the light receiving section, and the sensitivity can be improved accordingly.

[Example] An embodiment of the present invention will be described below with reference to FIG.

21 in the figure is a p-type Si substrate. On the surface of this substrate 21, an n-type diffusion layer (photodiode) 22 and a charge transfer path 23, which serve as a light receiving section, are formed. A charge transfer electrode 25 made of polycrystalline silicon is formed on the substrate 21 with a gate oxide film 24 interposed therebetween. An oxide film 2B is formed on the surface of this electrode 25. On the entire surface of the substrate including this oxide film 26, Si and N411!27 are formed as an interlayer insulating film by a plasma method.

On the Si, N4 film 27, the photodiode 2
A light-shielding film 28 made of AΩ and having an opening 28a is formed in a portion corresponding to a portion of 2. The purpose of this light shielding film 28 is to prevent light from entering the charge transfer section and causing smear. A 5in2 bass vane film 29 is formed on the entire surface. Here, the Si
The refractive index of the 3N4 film 27 is larger than that of the passivation film 29.

However, according to the above embodiment, the passivation film 2
S i 3N4 with a refractive index greater than 9
11!27 is used as an interlayer insulating film, the angle of incidence of light that obliquely enters the photosensitive section through the opening 28a of the light shielding film 28 can be made small, and the amount of light that enters directly into the charge transfer path 23 can be reduced. Furthermore, for the same reason as above, the number of times the light is reflected at the interface between the substrate 21 and the oxide film 22 increases, and the amount of light absorbed by the substrate increases, making it easier for the light to attenuate and pass through the charge transfer path 23. can reduce the amount of light. Therefore, smear resistance can be improved compared to the conventional method. Furthermore, since less light reaches the charge transfer path 23, the light shielding length can be reduced to widen the opening of the light receiving section, and the sensitivity can be improved accordingly. Furthermore, since the Si3N4 film 27 has good step coverage, it can be used as a 5i02 film or PSGII film.
The film thickness does not become thinner in areas with severe steps, such as
The dielectric strength between the charge transfer electrode 25 and the light shielding film 28 can be improved.

In the above embodiment, a case was described in which a Si3N4 film was used as the interlayer insulating film, but the present invention is not limited to this, and any insulating material having a refractive index higher than that of the passivation film, such as amorphous Si, may be used.

[Effects of the Invention] As detailed above, according to the present invention, by using a material having a higher refractive index than the protective film as the interlayer insulating film, the amount of light directly incident on the charge transfer path is reduced, and the oxidation It is possible to provide a solid-state imaging device that increases the number of reflections at the interface with the film, attenuates the light, reduces the amount of light to the charge transfer path, improves smear resistance, and maintains a high dielectric strength voltage of the interlayer insulating film. .

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the main parts of a solid-state image sensor according to an embodiment of the present invention, FIG. 2 is a schematic plan view of the solid-state image sensor, and FIG. 3 is a cross-sectional view of the main parts of a conventional solid-state image sensor. be. 21...81 substrate, 22... photodiode, 2
3... Charge transfer path, 25... Charge transfer electrode, 27
... Si, N4 film (interlayer insulating film), 28... Light shielding film, 28a... Opening, 29... Passivation film. Applicant's representative Patent attorney Takehiko Suzue 29th Edition 1st vR 112al Figure 3

Claims (1)

[Claims] A substrate, a photosensitive portion and a charge transfer path formed on the surface of the substrate, a charge transfer electrode formed on the substrate via an insulating film, and an interlayer formed on the entire surface of the substrate including the charge transfer electrode. In the solid-state imaging device, the solid-state imaging device includes an insulating film, a light-shielding film formed on the interlayer insulating film and having an opening corresponding to a part of the photosensitive part, and a protective film formed on the light-shielding film. 1. A solid-state imaging device, wherein the refractive index of the interlayer insulating film is greater than the refractive index of the protective film.