JPH04206571A - Solid-state image sensing device - Google Patents

Abstract

PURPOSE:To enable an image sensing device to be lessened in unnecessary reflection by a method wherein an insulating film and a high refractive index film on a sensor section are set 600Angstrom or below in thickness, and a protective film is set as large in refractive index as a filter layer. CONSTITUTION:For instance, the sensor section 17 of a photodiode is provided onto an Si substrate 11, an SiO2 insulating film 12 and an Si3N4 film 13 of high refractive index are laminated thereon, where the sum of the thickness of the films 11 and 12 is set to 600Angstrom or below. As a result, an antireflection film comparatively flat in spectral characteristics in a region of visible rays can be obtained. An Si electrode layer 14 is provided thereon, and an SiO2 film 15 and an Al light shielding layer 16 are laminated thereon. A PSG protective film 18 and a color filter 19 are deposited thereon. The protective film 18 and the color filter layer 19 are nearly equal to each other in refractive index, so that an interference effect induced on the Si3N4 film 13 can be relaxed. Therefore, a solid-state image sensing device of this design can be enhanced in sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state imaging device in which a filter layer is formed on a passivation film.

[Summary of the invention]

The present invention provides a solid-state imaging device in which an insulating film, a high refractive index film, a passivation film, and a filter layer are laminated on a sensor portion formed on a semiconductor substrate, in which the insulating film and the high refractive index film have a thickness of about 600 Å. The purpose is to reduce unnecessary reflection by having a structure in which the passivation film has the following film thickness and a refractive index that is approximately the same as that of the filter layer.

[Conventional technology]

A CCD type solid-state imaging device has a structure in which light is incident on a portion of a sensor formed on the surface of a semiconductor substrate, and a video signal is obtained by signal charges generated on the sensor portion.

FIG. 3 is a cross-sectional view of an example of a conventional solid-state imaging device, which has a transfer electrode 3 formed on a silicon substrate 1 with a silicon oxide film 2 interposed therebetween. The surface of the substrate between the pair of transfer electrodes 3 is used as a sensor part 4, and a light shielding layer 5 made of an aluminum layer is opened above the sensor part 4. The light shielding layer 5 is covered with a passivation film 6 made of a silicon oxide film such as PSG, and a color filter layer 7 is formed on the passivation film 6.

Furthermore, an example in which the passivation film is formed from a silicon nitride film instead of a silicon oxide film is also known. For example, in JP-A-60-177778, a plasma silicon nitride film is formed on polycrystalline silicon, which is a transparent electrode, and in a structure in which such silicon nitride films are stacked, short wavelength sensitivity increases due to multiple interference effects. is expected.

[Problem to be solved by the invention]

However, in the solid-state imaging device having the structure shown in FIG. 3, the loss of incident light is large due to reflection on the surface of the silicon substrate 1, and sufficient sensitivity cannot be obtained. In addition, in an example in which a plasma silicon nitride film is formed under the filter layer, ripples occur in the spectral transmittance due to the interference effect between the silicon nitride film and the silicon oxide film below it, and the spectral characteristics of the color filter change. It becomes easier.

SUMMARY OF THE INVENTION In view of the above-mentioned technical problems, it is an object of the present invention to provide a solid-state imaging device that achieves stable reflection prevention while preventing problems such as fluctuations in the spectral characteristics of a filter.

[Means to solve the problem]

In order to achieve the above-mentioned object, the solid-state imaging device of the present invention includes a sensor section formed on a semiconductor substrate, an insulating film formed on the surface of the sensor section, and an insulating film formed on the insulating film. In a solid-state imaging device, a high refractive index film having a high refractive index is formed, a passivation film is formed on the high refractive index film, and a filter layer is formed on the passivation film. The passivation film has a thickness of about 600 Å or less, and the passivation film has a refractive index that is approximately the same as that of the filter layer. An example of the high refractive index film is a silicon nitride film, and an example of the passivation film is a phosphorus silicate glass (PSG) film.

[Effect]

By making the insulating film and the high refractive index film thin films of about 600 Å or less, they can function as an antireflection film that develops relatively flat spectral characteristics for light in the visible light range. Therefore, reflection from the substrate surface is prevented, and ripples in the spectral characteristics are also prevented. Furthermore, by making the passivation film have a refractive index that is approximately the same as that of the filter layer, it becomes possible to suppress the interference effect from the high refractive index film onward, thereby realizing high sensitivity in a part of the sensor.

〔Example〕

Preferred embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the solid-state imaging device of this embodiment is constructed using a silicon substrate 11.
A sensor portion 17 for obtaining signal charges by photoelectric conversion is formed on the surface of the sensor. The sensor portion 17 is not shown in the drawings or is composed of, for example, a photodiode made of an impurity diffusion region. A thin silicon oxide film I2 is formed on the silicon substrate 11, and a thin silicon nitride film 1, which is a high refractive index film, is formed on the thin silicon oxide film 12.
3 is formed. The silicon oxide film I2 has a refractive index of about 1.45, and the silicon nitride film 13 has a refractive index of about 2.0.

FIG. 2 is a diagram showing each layer on a portion of the sensor, in which the silicon oxide film 12 has a thickness d, and the silicon nitride film 13 has a thickness d. The silicon oxide film 12 and the silicon nitride film 13 have film thicknesses d* and d3 of 60 mm, respectively.
The film thickness is set to 0 Å or less, preferably about 250 to 350 layers.

By setting the film thicknesses d x and d t in this way, it is possible to obtain an antireflection film with relatively flat spectral characteristics within the visible light region. For example, the film thickness d of the silicon oxide film 12 and the silicon nitride film I3 2. By setting d to an appropriate value, it is possible to suppress the reflectance to about 12 to 13% on average, which is about one-third of the 40% reflection of conventional silicon substrates. It will be suppressed to .

Silicon oxide film 1 that functions as an antireflection film in this way
2 and silicon nitride film 13, a polysilicon layer 14 functioning as a transfer electrode is formed. This polysilicon layer 14 has a two-layer structure, and transfer signals of about 2 to 4 phases are supplied so as to constitute a shift register. The polysilicon layer 14 is covered with a silicon oxide film 15 and further covered with a light shielding layer 16 for blocking incident light. The light shielding layer 16 is made of an aluminum layer. This light-shielding layer 16 has an opening above the sensor portion 17, and the silicon nitride film 13 faces the opened region.

A passivation film 18 is formed on the light shielding layer 16. The passivation film 18 is made of a PSG film, which is a silicon-based passivation film, and has a refractive index of approximately 1.46. A color filter layer 19 is formed on this passivation film 18. This color filter layer 19 has a structure in which a flattening film 19a and a filter film 19b are laminated. The refractive index of the color filter layer 19 is about 1.5 to 1.6, which is about the same as that of the passivation film 18. Therefore, the interference effect on the silicon nitride film 13 is alleviated, and as a result, higher sensitivity is achieved.

As described above, in the solid-state imaging device of this embodiment, since the silicon oxide film 12 and the silicon nitride film 13 are controlled to have a thin film thickness of 600 Å or less, reflection on the surface of the silicon substrate 11 can be prevented. I was very impressed with the fact that it was possible to obtain transmittance with reduced ripples at the same time. Furthermore, since the passivation film and the filter layer have similar refractive indexes, interference at the interface is suppressed. Therefore, in the solid-state imaging device of this embodiment, unnecessary reflections resulting in flare and ghosts are sufficiently suppressed, and the transmittance is improved, so that the sensitivity of a portion of the sensor is improved.

In the above embodiment, the silicon oxide film and the silicon nitride film are formed in the lower layer of the transfer electrode, but the structure is not limited to this. The structure may be formed as an upper layer.

Further, it is also possible to adopt a structure in which a thin polysilicon film is provided as part of the antireflection film on or below the silicon oxide film or silicon nitride film.

〔Effect of the invention〕

As described above, the solid-state imaging device of the present invention has an insulating film and a high refractive index film disposed with a film thickness of about 600 Å or less, which prevents reflection on the substrate surface and provides stable spectral characteristics. It is possible to achieve this. In addition, by making the refractive index of the passivation film and filter layer similar,
Interference greater than that of a high refractive index film can be alleviated. Therefore, by using the solid-state imaging device of the present invention, it is possible to reduce reflection at the sensor section, suppressing phenomena such as flare and ghosting, and furthermore, by improving transmittance, it is possible to increase sensitivity. It can be realized.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an example of a solid-state imaging device of the present invention, FIG. 2 is an enlarged view of a main part of the example, and FIG. 3 is a sectional view of an example of a conventional solid-state imaging device. 11...Silicon substrate 12...Silicon oxide film 13...Silicon nitride film 14...Polysilicon layer 18...Passivation film 19...Color filter layer Patent applicant Sony Corporation representative patent attorney Akira Koba (2 others)

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Claims (1)

[Claims] A sensor section is formed on a semiconductor substrate, an insulating film is formed on the surface of the sensor section, and a high refractive index film having a higher refractive index than the insulating film is formed on the insulating film. and a passivation film is formed on the high refractive index film, and a filter layer is formed on the passivation film. A solid-state imaging device, wherein the passivation film has a refractive index that is approximately the same as that of the filter layer.