JPH05218371A - Solid-state image sensor - Google Patents

Abstract

PURPOSE:To suppress the reflection of incident light on a light shielding side wall, prevent the incidence of stray light in a charge transfer area and improve smear characteristics by forming a reflection preventing film which has lower reflectance than the light shielding film on the side wall of the light shielding film which covers the charge transfer area provided in the surface area of a semiconductor substrate. CONSTITUTION:A first layer gate electrode 7 and a second layer gate electrode 8 for charge transfer is provided at the top of a charge transfer area 4 through an oxide film 6 on a semiconductor substrate 1 and a light shielding film 9 composed of aluminum which prevents incident light on the charge transfer area 4 is formed on the electrode 8. Then, an oxide film 10 is formed by CVD method and tungsten silicide which allows low reflectance is accumulated. Only the top plane and the light receiving area of the light shielding film 9 are etched and a reflection preventing film 11 is formed leaving the side wall of the light shielding film 9. The light diagonally directed on the light shielding film 9 is absorbed by the reflection preventing film 11 which has the reflectance of approximately 1/5 of the light shielding film and smear ingredients are attenuated.

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 sensor,
In particular, it relates to a solid-state imaging device using a charge coupled device (CCD).

[0002]

2. Description of the Related Art FIG. 2 is a sectional view of a conventional solid-state image pickup device. As shown in the figure, p is formed on the n-type semiconductor substrate 1.
A type well 2 is provided, and an n-type photoelectric conversion region 3 and an n-type charge transfer region 4 are formed in the surface region thereof, and both are separated by a p ⁺ -type element isolation layer 5 provided therebetween. Has been done.

Further, above the charge transfer region 4, a first layer gate electrode 7 and a second layer gate electrode 8 for charge transfer are provided via an oxide film 6, and the charge transfer is further provided thereon. A light-shielding film 9 having an opening is formed on the photoelectric conversion region 3 in order to block incident light on the region 4. As a material for the light-shielding film 9, aluminum which is excellent in light-shielding property is usually used.

[0004]

In the above-mentioned conventional solid-state image pickup device, as shown in FIG. 2, when the incident light a is incident on the device surface from an oblique direction, the reflectance of the light shielding film 9 is almost 100%. Therefore, the incident light is totally reflected on the side wall of the light-shielding film, and while being repeatedly reflected and scattered by the surface of the semiconductor substrate and the surface of the oxide film 6, enters the charge transfer region 4 with a certain probability.

The light that has entered the charge transfer region 4 is photoelectrically converted there to generate electron-hole pairs, of which electrons are mixed with the signal charges being transferred to form a false signal. This is a false signal called smear, which is peculiar to the CCD type solid-state image pickup device, and thereby the image quality of the imaged is remarkably deteriorated. Although smear occurs due to causes other than the above-mentioned causes, it is considered that 70 to 80% of the entire smear component is due to the reflected light on the side wall of the light shielding film.

[0006]

In a solid-state image pickup device of the present invention, a photoelectric conversion region and a charge transfer region are formed in a surface region of a semiconductor substrate, and a transfer gate electrode and a light shielding film are formed on the semiconductor substrate. An antireflection film made of a material having a low reflectance is formed on the side wall of the light shielding film.

[0007]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the present invention. In the device structure of this embodiment, a p-type well 2 is formed on the surface of an n-type semiconductor substrate 1, and an n-type photoelectric conversion region 3 and an n-type charge transfer region 4 are p ⁺ -type devices on the surface side. A first layer gate electrode 7 and a second layer gate electrode 8 for charge transfer are provided above the charge transfer region 4 on the semiconductor substrate via the oxide film 6 so as to be separated by the separation layer 5. A light-shielding film 9 made of aluminum and having a film thickness of 0.8 to 1.0 μm for preventing incident light on the charge transfer region 4 is formed thereon.
Are formed. The device structure up to this point is the same as that of the above-described conventional solid-state imaging device.

Next, the manufacturing process of the antireflection film of this embodiment will be described. First, an element similar to the conventional example shown in FIG. 2 is formed by a normal manufacturing process. Next, the oxide film 10 is formed to a thickness of about 500Å by the CVD method, and then tungsten silicide, which is a material having a low reflectance, is deposited to a thickness of about 1000Å by a sputtering technique.

Next, anisotropic dry etching is performed from the direction perpendicular to the surface of the semiconductor substrate under the condition that a tungsten silicide having a film thickness of 1000 Å is etched.
Under this condition, only the flat portion, that is, the upper surface of the light-shielding film 9 or the light-receiving region portion without the light-shielding film is etched, and the side wall portion of the light-shielding film 9 remains without being etched.
That is, the antireflection film of this embodiment can be formed without using the photolithography technique.

The oxide film 10 on the light-shielding film 9 serves as a stopper during the anisotropic dry etching and also serves as a light-shielding film 9.
It plays the role of preventing the eutectic of aluminum and tungsten silicide, which are the materials.

According to this embodiment, light incident on the light-shielding film obliquely is absorbed by the antireflection film 11 whose reflectance is about ⅕ of that of the light-shielding film. The components can be attenuated sufficiently low. Specifically, when the element having the structure of the present example and the element having the conventional structure were simultaneously manufactured and the smear characteristics were compared, the smear value of the conventional structure was 0.003%, whereas the structure of the present example was That of the element of 0.008% was 0.0008% and could be reduced to about 1/4.

The preferred embodiment has been described above, but the present invention is not limited to this embodiment, and various modifications can be made. For example, the oxide film 10 in the above embodiment may be a nitride film, and the antireflection film 1 may be used.
1 can be formed using another material such as titanium nitride.

[0013]

As described above, in the solid-state image pickup device of the present invention, since the antireflection film is provided on the side wall of the light shielding film, the reflection of incident light on the side wall of the light shielding film can be suppressed, and the charge transfer can be performed. It is possible to prevent stray light from entering the region. Therefore, according to the present invention, generation of a false signal is suppressed, and the smear characteristic can be significantly improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional example.

[Explanation of symbols]

 1 n-type semiconductor substrate 2 p-type well 3 photoelectric conversion region 4 charge transfer region 5 element isolation layer 6, 10 oxide film 7 first layer gate electrode 8 second layer gate electrode 9 light-shielding film 11 antireflection film a incident light

Claims (1)

[Claims] 1. A semiconductor substrate provided in a surface region of the semiconductor substrate,
A photoelectric conversion region for photoelectrically converting incident light and accumulating signal charges generated as a result, a charge transfer region provided in a surface region of the semiconductor substrate and serving as a transfer path for the signal charges, and the semiconductor A gate electrode provided on the substrate for transferring the signal charge; a light-shielding film having an opening above the photoelectric conversion region and covering the charge transfer region;
In the solid-state image pickup device including: a light-shielding film, an antireflection film having a reflectance lower than that of the light-shielding film is formed on a side wall portion of the light-shielding film.