JPH0730101A - Image pick-up device and its manufacture - Google Patents

Abstract

PURPOSE:To prevent light from infiltrating into a charge transfer part by providing a first metal film and a second metal film, each having a grain boundary of a different size, which are formed by stacking in order on the surface of an insulating film, at the upper part of the insulating film and the charge transfer part formed on the main surface of a semiconductor substrate. CONSTITUTION:After a silicon dioxide (insulating film) is formed on the main surface of a semiconductor substrate 1, an Al-Si film 15 including silicon as a first metal film is formed to produce a photoresist pattern 16. After the Al-Si film 15 is removed by etching with the pattern 16 as a mask, the photoresist 16 is removed and a tungsten silicide film 17 which is a second metal film is formed. Subsequently, an Al-Si film 18 is formed as a third metal film. A grain size of the Al film which grows in the sintering process is large with a small silicide film. By putting a small-grain metal film between metal films of large grains, a defect of the positional slippage of the grain boundary causing light to pass up to the silicon substrate 1 is eliminated.

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 and its manufacturing method.

[0002]

2. Description of the Related Art In recent years, solid-state image pickup devices have been widely used in electronic cameras, and due to their ease of use, the environment in which they are used has spread, and there is a demand for those that are compact and have high performance. An example of a conventional solid-state imaging device and a method for manufacturing the same will be described below with reference to the drawings.

2A and 2B are sectional views showing the outline of a conventional method for manufacturing a solid-state image pickup device. On the main surface of the semiconductor substrate 1 on which the photodiode section A as a light receiving element and the MOS type transistor section B as a charge transfer section are formed,
After forming silicon dioxide 4 to a thickness of about 400 nm by a chemical vapor deposition method, an aluminum alloy (hereinafter referred to as an Al-Si film) 5 containing 2 wt% of silicon 5 is formed to a thickness of 0.8 μm, and a photoresist is formed. Form pattern 6 (see FIG. 2).
(A)). Next, using the photoresist pattern 6 as a mask, the Al—Si film 5 is etched and then the photoresist 6 is removed (FIG. 2B). Reference numeral 2 is a gate oxide film and 3 is a gate electrode.

[0004]

However, in the above-mentioned conventional structure, since the Al—Si film 5 is crystallized by heat treatment to form a grain boundary, of the light incident from the surface of the solid-state image pickup device, the charge is transferred to the charge transfer portion B. There is a problem that light is transmitted along the grain boundaries of the Al-Si film 5, which is a film for preventing the incidence of light.

An object of the present invention is to provide a solid-state image pickup device capable of preventing light from entering the charge transfer section and a method of manufacturing the same.

[0006]

According to another aspect of the present invention, there is provided a solid-state image pickup device comprising: a semiconductor substrate having a light receiving element and a charge transfer portion formed thereon; an insulating film formed on a main surface of the semiconductor substrate; The first and second metal films having different grain boundaries are formed by sequentially laminating on the surface of the insulating film.

According to a second aspect of the present invention, there is provided a method of manufacturing a solid-state image pickup device, wherein an insulating film is formed on a main surface of a semiconductor substrate on which a light receiving element and a charge transfer section are formed, and the surface of the insulating film is made of aluminum or an aluminum alloy. A metal film is formed, a first photoresist pattern is formed on the surface of the first metal film in the charge transfer portion, and the first metal film is etched using the first photoresist pattern as a mask to remove the first metal film. A second metal film made of a refractory metal or a silicide of a refractory metal is formed on the surfaces of the film and the insulating film, and a third metal film made of aluminum or an aluminum alloy is formed on the surface of the second metal film, A second photoresist pattern is formed above the charge transfer portion, and the second metal film and the third metal film are formed using the second photoresist pattern as a mask. It is intended to etching.

[0008]

According to the structure of the present invention, the grain boundaries of the first and second metal films formed by the heat treatment differ depending on the selected metal. Even if light is transmitted along the grain boundaries of the second metal film, the grain boundaries of the first metal film therebelow are displaced, so that the grain boundaries of the first and second metal films are displaced. It is possible to eliminate the inconvenience that light is transmitted to the silicon substrate along.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid-state image pickup device and a method of manufacturing the same according to an embodiment of the present invention will be described with reference to the drawings. Figure 1
(A)-(c) is sectional drawing which shows the outline of the manufacturing method of the solid-state imaging device in one Example.

A photodiode section A serving as a light receiving element,
After a silicon dioxide (insulating film) 4 having a thickness of about 400 nm is formed on the main surface of the semiconductor substrate (silicon substrate) 1 on which the MOS type transistor portion B serving as a charge transfer portion is formed by a chemical vapor deposition method, An Al-Si film 15 containing about 2 wt% of silicon is formed to a thickness of about 0.4 μm as a first metal film to form a photoresist pattern 16 (FIG. 1).
(A)). Next, using the photoresist pattern 16 as a mask, the Al-Si film 15 is etched, and then the photoresist 16 is removed, so that the tungsten silicide film (hereinafter referred to as WSi film) 17 of the second metal film is reduced to about 0. .1
formed to a thickness of μm, and then Al-S is formed as a third metal film.
The i film 18 is formed to a thickness of about 0.6 μm (see FIG. 1).
(B)). After that, by forming a photoresist pattern 19, the WSi film 17 which is the second metal film and the Al-Si film 18 which is the third metal film are etched and formed into a predetermined pattern. (FIG. 1 (c)). Reference numeral 2 is a gate oxide film and 3 is a gate electrode.

The operation of the solid-state image pickup device configured as described above will be described. The Al film has a large grain size that grows in the sintering process in a later step, and a partial product such as Si added in Al occurs. The refractory metal or the silicide film thereof has a small grain size formed at the Al sintering temperature (about 400 to 500 degrees) and has no uneven product. In the two-layer structure of the refractory metal or the silicide film thereof and the Al film, the light passing through the gap of the large grain of Al or the unevenly distributed Si portion passes through the gap of the small grain of the lower layer, resulting in poor characteristics. Was found to cause Therefore, by forming an Al film having a larger grain in the lower layer of the refractory metal or the silicide film thereof, a metal film having a smaller grain is sandwiched by a metal film having a larger grain, thereby causing a characteristic defect due to passage of light. It can be lost.

First, FIG. 1 (c) shows a schematic cross section of a solid-state image pickup device formed by the method of this embodiment. The first and third solid-state image pickup devices formed by heat treatment have the above-mentioned structure. Al-Si films 15 and 18 which are metal films
, And the grain boundary of the WSi film 17 of the second metal film are different from each other, the light incident from the surface of the solid-state imaging device is along the grain boundary of the upper Al—Si film 18. Even if the light is transmitted, the underlying WSi film 17 and Al-Si film 15
Since the positions of the grain boundaries of the silicon substrate 1 are deviated, light is transmitted along the grain boundaries of the first to third metal films 15, 17, and 18 to the silicon substrate 1.
The inconvenience of penetrating up to is eliminated.

Although the first metal film 15 and the third metal film 18 are Al--Si films in the above embodiment,
It is not limited to this, but pure Al or Cu,
It may be an aluminum alloy with Ti or the like, and neither the concentration ratio in the alloy film nor the film thickness is limited. The second metal film 17 is not limited to the WSi film, and may be a refractory metal such as W or Mo or a silicide thereof, and the film thickness is not limited.

[0014]

According to the solid-state image pickup device and the method of manufacturing the same of the present invention, since the grain boundaries of the first and second metal films formed by heat treatment differ depending on the selected metal, the solid-state image pickup device. Of the light incident from the surface of the second metal film even if the light is transmitted along the grain boundaries of the second metal film,
Since the position of the grain boundary of the metal film is shifted, it is possible to eliminate the inconvenience that light is transmitted to the silicon substrate along the grain boundary of the first and second metal films. .

[Brief description of drawings]

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

FIG. 2 is a sectional view of a manufacturing process of a conventional solid-state imaging device.

[Explanation of symbols]

 A light receiving element B charge transfer section 1 silicon substrate (semiconductor substrate) 4 silicon dioxide film (insulating film) 15 Al-Si film (first metal film) 16 first photoresist pattern 17 WSi film (second metal film) ) 18 Al-Si film (third metal film) 19 Second photoresist pattern

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical indication H01L 27/148

Claims (2)

[Claims] 1. A semiconductor substrate on which a light receiving element and a charge transfer portion are formed, an insulating film formed on a main surface of the semiconductor substrate,
A solid-state imaging device comprising: a first metal film and a second metal film, which have different grain boundaries from each other and which are sequentially stacked on the surface of the insulating film above the charge transfer unit. 2. A step of forming an insulating film on a main surface of a semiconductor substrate on which a light receiving element and a charge transfer portion are formed, and a step of forming a first metal film made of aluminum or aluminum alloy on the surface of the insulating film. A step of forming a first photoresist pattern on the surface of the first metal film above the charge transfer portion, and a step of etching the first metal film using the first photoresist pattern as a mask Forming a second metal film made of a refractory metal or a silicide of a refractory metal on the surfaces of the first metal film and the insulating film; and using aluminum or an aluminum alloy on the surface of the second metal film. Forming a third metal film, and forming a second photoresist pattern above the charge transfer portion; And a step of etching the second metal film and the third metal film using a photoresist pattern as a mask.