JPH1070260A - Solid state image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce smear drastically while sustaining the characteristics of interconnection, e.g. parasitic capacitance, by forming a light shielding layer while covering an oxide deposited on a drive electrode, forming a reflow layer of specified thickness on the light shielding layer and then forming an interconnection on the reflow layer. SOLUTION: A drive electrode 2 is formed of a polysilicon layer through a thermal oxide 12 deposited on a semiconductor substrate, i.e., a silicon substrate 11, and an oxide 5 is deposited on the surface of the electrode. A light shielding layer of tungsten silicide 1 containing a high melting point metal is then formed thereon except the region of a photoelectric converting section 13 followed by formation of a reflow layer of PSG 3. Subsequently, the PSG 3 is subjected to reflow and a contact hole 14 is made at a required point before forming an aluminum interconnection 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid-state imaging device such as a CCD.

[0002]

2. Description of the Related Art Conventionally, in a solid-state imaging device, a light-shielding film is provided to determine an opening of a photoelectric conversion region.
In a conventional solid-state imaging device, an aluminum film is used as a light-shielding film.

FIG. 5 is a cross-sectional view of an essential part of an example of such a conventional solid-state image pickup device, in which a drive electrode 22 formed on a silicon substrate 21 and a photoelectric conversion region 23 of the silicon substrate 21 (where impurities The illustration of the diffusion region is omitted.) A reflow film 24 is formed on the diffusion region. On the reflow film 24, an aluminum film 25 is formed as a light shielding film as described above. Here, the reflow film 24 is formed for the purpose of processing the aluminum film 25, securing the interlayer breakdown voltage, and the like.

As another prior art, as shown in FIG. 6, a drive electrode 31 on a silicon substrate 30 is made of a refractory metal silicide such as a tungsten silicide layer, and the drive electrode 31 is shielded from light. There are technologies that make use of characteristics. Such a technique is disclosed in Japanese Patent Application Laid-Open No. 59-1595.
No. 64 is disclosed.

[0005]

However, in the technique of forming an aluminum film 25 as a light-shielding film on the reflow film 24 as shown in FIG. 5, the reduction of smear and the securing of an interlayer breakdown voltage are both achieved by the film thickness. I can't let it.

That is, when the film thickness is increased, it is advantageous in terms of flattening and interlayer breakdown voltage, but the influence of obliquely incident light on the charge transfer section increases, and smear increases. On the other hand, when the thickness of the reflow film 24 is reduced, the withstand voltage between the aluminum film 25 and the lower drive electrode 22 deteriorates, and the parasitic capacitance increases. In addition, the reliability of the device is reduced due to the penetration of mobile ions. Further, when the film thickness is small, planarization becomes difficult, and the workability of the aluminum film 25 also decreases.

Next, as shown in FIG. 6, when the drive electrode 31 is made of a refractory metal silicide or the like, it is possible to achieve both a reduction in smear due to an improvement in light-shielding characteristics and a sufficient withstand voltage between layers. . However, in the case of a CCD, it is necessary to form at least the first and second layers of the drive electrode 31 and a plurality of layers, and therefore, it is necessary to directly oxidize the refractory metal silicide. However, direct oxidation of the refractory metal silicide is not easy, and even if it can be performed, a high-quality insulating film cannot be obtained, so that the breakdown voltage between the layers of the drive electrode is degraded.

In view of the above-mentioned technical problems, the present invention provides a solid-state imaging device in which smear is reduced, interlayer breakdown voltage is ensured, parasitic capacitance is reduced, and reliability is improved. Aim.

[0009]

SUMMARY OF THE INVENTION A solid-state imaging device according to the present invention proposed to achieve the above-mentioned object is as follows.
A charge transfer portion formed on the semiconductor substrate, a drive electrode formed on the charge transfer portion via an oxide film, an oxide film covering the top and side surfaces of the drive electrode, and the drive electrode A light-shielding film made of a high-melting-point metal film or a film containing a high-melting-point metal formed so as to cover the oxide film and also to cover the side of the drive electrode disposed facing the semiconductor substrate. Film, a photoelectric conversion portion whose opening is defined by the light-shielding film, a reflow film formed with a required thickness on the light-shielding film, and a wiring layer formed on the reflow film. It has.

The refractory metal film used in the solid-state imaging device according to the present invention is made of a material such as tungsten, molybdenum, tantalum, titanium, or niobium. A high-melting-point metal silicide film, or a combination of a high-melting-point metal silicide film and a polysilicon film or another film is used. In addition, for example, PSG, AsS
A material film that is softened by various kinds of heat, such as G, BSG, and BPSG, is used.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid-state imaging device according to the present invention will be described with reference to the drawings.

[0012] The solid-state imaging device according to the present invention shown here comprises:
The drive electrode is a polysilicon layer, and the light shielding film is a tungsten silicide film.

A solid-state imaging device according to the present invention will be described with reference to FIGS.

The impurity diffusion region formed on the silicon substrate 11 can be of various types, and is not shown.

First, in order to manufacture a solid-state imaging device according to the present invention, as shown in FIG. And a drive electrode 2 made of a polysilicon layer.
Is formed in a required pattern. This drive electrode 2 can be composed of, for example, first and second polysilicon layers, and an oxide film 5 is formed between both layers and on each electrode surface. Since the drive electrode 2 is made of polysilicon, a good oxide film 5 can be easily obtained from direct oxidation.

Next, as shown in FIG.
A tungsten silicide film 1 as a light-shielding film containing a high melting point metal is selectively formed in a region excluding the region.
The photoelectric conversion unit 13 is formed by the tungsten silicide film 1.
Can be determined, and light incident on the charge transfer unit can be blocked. Etching for selective formation may be either dry or wet. Here, the tungsten silicide film 1 is formed so as to cover the oxide film 5 covering the drive electrode 2, and since the thickness of the oxide film 5 is small, smear can be reduced.

After forming such a tungsten silicide film 1 as a light shielding film, a PSG film 3 as a reflow film is formed on the entire surface as shown in FIG. At this time,
The thickness of the PSG film 3 can be determined in consideration of the reliability of the element, the withstand voltage between the wiring layer and the driving electrode, the workability of the wiring layer, the parasitic capacitance, and the like. Since the silicide film 1 is used, the thickness can be made sufficiently large.

After the formation of the PSG film 3, a heat treatment is performed to reflow the PSG film 3. This reflow is intended for flattening, and may be performed at, for example, 1000 ° C. for about 30 minutes. For the heat treatment, RTA using infrared rays or the like can be used.

After the PSG film 3 is reflowed by heat treatment, a contact hole 14 is formed at a required position as shown in FIG. 4, and an aluminum wiring layer 4 is formed. Then, an overcoat or the like is performed to complete the solid-state imaging device.

The formation of the contact hole 14 may be performed before the heat treatment, and the region to which the aluminum wiring layer 14 is connected is not limited to the silicon substrate 11 as shown.

In the solid-state imaging device according to the present invention manufactured by the above-described process, since the light-shielding film (tungsten silicide film 1) is formed without the interposition of the reflow film, the adverse effect of obliquely incident light is suppressed. Thus, smear is reduced. Further, in the solid-state imaging device according to the present invention, since the reflow film can be made thicker, the aluminum wiring layer 4 can be easily processed by flattening, the parasitic capacitance can be reduced, and the interlayer withstand voltage can be improved. Further, since the reflow film can be made thicker, the adverse effects of mobile ions can be suppressed.

In the above description, the tungsten silicide film is used as the film containing the high melting point metal. However, the present invention is not limited to this, and other materials may be used, and a high melting point metal film may be used. . In the above-described example, the reflow film is a PSG film, but is not limited to this.

[0023]

As described above, according to the present invention, a high melting point metal film or a high melting point metal is formed so as to cover the oxide film covering the driving electrode and also to cover the side of the lowermost driving electrode. Since a light-shielding film made of a film containing the film is formed, a reflow film is formed on the light-shielding film to a required thickness, and wiring is performed on the reflow film. Can be drastically reduced while maintaining the above, and a highly reliable solid-state imaging device can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a state in which a drive electrode is formed on a charge transfer section of a silicon substrate via a thermal oxide film.

FIG. 2 is a cross-sectional view showing a state in which light shielding containing a high melting point metal is formed in a region excluding a region of a photoelectric conversion unit.

FIG. 3 is a cross-sectional view showing a state in which a reflow film is formed on the entire surface.

FIG. 4 is a sectional view showing a solid-state imaging device according to the present invention.

FIG. 5 is a sectional view of a main part showing an example of a conventional solid-state imaging device.

FIG. 6 is a sectional view of a main part showing another example of a conventional solid-state imaging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tungsten silicide film 2 Drive electrode 3 PSG film 4 Aluminum wiring layer 5 Oxide film 11 Semiconductor substrate 13 Photoelectric conversion part

Claims (1)

[Claims] A charge transfer portion formed on a semiconductor substrate; a drive electrode formed on the charge transfer portion via an oxide film; an oxide film covering upper and side surfaces of the drive electrode; A high-melting-point metal film or a high-melting-point metal is formed so as to cover the oxide film covering the drive electrode and also to cover the side of the drive electrode disposed facing the semiconductor substrate. A light-shielding film composed of a film, a photoelectric conversion unit having an opening defined by the light-shielding film, a reflow film formed with a required thickness on the light-shielding film, and a reflow film formed on the reflow film. Solid-state imaging device having a wiring layer provided.