JP2851849B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

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

[Summary of the Invention]

The present invention relates to a method of manufacturing a solid-state imaging device in which a reflow film is formed on a drive electrode made of polysilicon formed in a charge transmission unit, and thereafter wiring is performed on the reflow film after heat treatment of the reflow film is performed. By forming a refractory metal film made of tungsten as a light-shielding film in the region excluding the light source conversion region and forming a reflow film after forming the light-shielding film, it is possible to improve fine wiring and interlayer breakdown voltage while preventing smear. Realize.

[Conventional technology]

Generally, in a solid-state imaging device, a light-shielding film is formed in order to determine a photoelectric conversion region as an opening. In a conventional solid-state imaging device, an aluminum film is used as a light-shielding film.

As shown in FIG. 2, a conventional solid-state imaging device includes a reflow film 24 on a drive electrode 22 formed on a silicon substrate 21 and on a photoelectric conversion region 23 of the silicon substrate 21.
Are formed. On the reflow film 24, an aluminum film 25 as a light-shielding film as described above is formed. Here, the reflow film 24 is formed in order to process the aluminum film 25 and to secure an interlayer withstand voltage.

As another conventional example, as shown in FIG. 3, a drive electrode 31 on a silicon substrate 30 is made of a refractory metal silicide such as a tungsten silicide layer, and the light shielding characteristics of the drive electrode 31 are used. Such a technique is disclosed in
There is one described in JP-A-159564.

[Problems to be solved by the invention]

However, as shown in FIG. 2, in the technique of forming the aluminum film 25 as a light-shielding film on the reflow film 24, it is not possible to achieve both reduction of smear and securing of the interlayer breakdown voltage depending on the film thickness.

In other words, when the film thickness is increased, it is advantageous in terms of flattening and interlayer breakdown voltage, but the effect of obliquely incident light on the charge transfer portion 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 also 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 workability of the aluminum film 25 also decreases.

Next, as shown in FIG. 3, 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 inter-layer breakdown voltage. However, in the case of a CCD, it is necessary to form the drive electrode 31 in at least a first layer and a second layer, and thus it is necessary to directly oxidize the refractory metal silicide.
However, direct oxidation of the high-melting-point metal silicide is not easy, and even if it is possible, a high-quality insulating film cannot be obtained, so that the withstand voltage between the layers of the drive electrode is degraded.

In view of the above technical problems, the present invention has an object to provide a method of manufacturing a solid-state imaging device that realizes reduction of smear, securing of interlayer breakdown voltage, reduction of parasitic capacitance, improvement of workability, and the like. And

[Means for solving the problem]

According to the present invention, in order to achieve the above object, a step of forming a drive electrode made of at least one layer of polysilicon on a charge transfer portion, and an oxide film is formed so as to cover the drive electrode by linear oxidation. Forming a light-shielding film made of a high-melting-point metal film or a film containing a high-melting-point metal so as to cover the oxide film covering the driving electrode and to cover the side of the lowermost driving electrode. Forming a reflow film having a thickness sufficient to reduce the parasitic capacitance and improve the interlayer breakdown voltage on the light-shielding film, and performing a heat treatment; and forming a lower resistance than the light-shielding film on the reflow film. And a step of wiring using materials to manufacture a solid-state imaging device.

In the method for manufacturing a solid-state imaging device according to the present invention, tungsten is used as the high melting point metal film. The film containing the high melting point metal may be a silicide film of the high melting point metal, or a film obtained by combining the high melting point metal silicide film with a polysilicon film or another film. The reflow film can be made of a material softened by heat, such as PSG, AsSG, BSG, and BPSG. The heat treatment may be performed by a normal electric furnace, and a method such as RTA (rapid thermal annealing) is used.

[Action]

In the method for manufacturing a solid-state imaging device according to the present invention, after forming a drive electrode made of polysilicon, a light-shielding film made of a high-melting-point metal film or a film containing a high-melting-point metal is formed without using a reflow film. Thereby, the light obliquely incident on the charge transfer unit is reduced, and the smear is reduced. After that, a reflow film is formed and heat treatment is performed to flatten the reflow film.

〔Example〕

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

The present embodiment is applied to the manufacture of a CCD as a solid-state imaging device, in which a drive electrode is a polysilicon layer and a light-shielding film is a tungsten silicide film.

Hereinafter, the manufacturing method according to the present invention will be described step by step with reference to FIGS. 1A to 1D.

Note that various types of impurity diffusion regions formed in the silicon substrate 11 can be used, and thus are not shown.

(A) First, as shown in FIG. 1a, a drive electrode 2 made of a polysilicon layer is formed in a required pattern on a charge transfer portion of a silicon substrate 11 via a thermal oxide film 12 on the silicon substrate 11. . The 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. Drive electrode 2
Since polysilicon is used as a material, a good oxide film 5 can be easily obtained from direct oxidation.

(B) Next, as shown in FIG. 1B, a tungsten silicide film 1 as a light-shielding film containing a refractory metal is selectively formed in a region excluding the photoelectric conversion region 13. The opening of the photoelectric conversion region 13 can be determined by the tungsten silicide film 1, and the incident light to the charge transmission unit can be blocked. The etching for selectively forming the tungsten silicide film 1 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. Since the thickness of the oxide film 5 is small, smear can be reduced.

(C) After forming the tungsten silicide film 1 as a light-shielding film as described above, as shown in FIG. 1c, a PSG film 3 as a reflow film is formed on the entire surface. At this time PSG
The thickness of the film 3 can be determined in consideration of the reliability of the element, the withstand voltage between the wiring layer and the drive electrode, the workability of the wiring layer, the parasitic capacitance, and the like. Therefore, the film 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. The heat treatment may be RTA or the like using infrared rays or the like.

(D) After the PSG film is reflowed by the heat treatment, as shown in FIG. 1d, a contact hole 14 is formed at a required position, and the aluminum wiring layer 4 having a lower resistance than the tungsten silicide film 1 constituting the light shielding film. To form Hereinafter, a solid-state imaging device is completed by performing overcoating and the like.

The formation of the contact hole 14 may be performed before the heat treatment, and the region to which the aluminum wiring layer 4 is connected is not limited to the silicon substrate 11 as shown.

In the solid-state imaging device manufactured through the above-described steps, the tungsten silicide film 1 as a light-shielding film is formed without the interposition of a reflow film, so that adverse effects of obliquely incident light can be suppressed, and smear can be reduced. Is performed.
Further, in the method of the present embodiment, the thickness of the reflow film can be increased, so that the aluminum wiring layer can be easily processed by flattening, the parasitic capacitance can be reduced, and the interlayer breakdown voltage can be improved. Also, since the reflow film can be made thicker,
The adverse effects of mobile ions can also be suppressed.

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

Further, the method of manufacturing a solid-state imaging device according to the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the gist thereof.

〔The invention's effect〕

As described above, the method of the present invention covers a high melting point metal wire such as tungsten or tungsten so as to cover the oxide film covering the drive electrode made of polysilicon and to cover the side of the lowermost drive electrode. After forming a light-shielding film made of a film containing a high-melting-point metal as described above, a reflow film having a thickness sufficient to reduce the parasitic capacitance and increase the interlayer withstand voltage is formed on the light-shielding film and heat-treated. Since wiring is performed on the reflow film using a material having a lower resistance than the light-shielding film, it is possible to dramatically reduce smear while maintaining characteristics such as parasitic capacitance of the wiring.

Since the wiring is formed on the reflow film formed on the light-shielding film, a low-resistance material which is formed as a layer different from the light-shielding film and is desirable for the wiring can be used.

In particular, the method of the present invention uses a polysilicon which can be thermally oxidized very easily for the drive electrode, so that good insulation between the electrode layers can be easily achieved, and light shielding is provided so as to cover the side of the lowermost drive electrode. The film can be easily formed, and a drastic reduction in smear can be achieved while maintaining characteristics such as the parasitic capacitance of the wiring.

Therefore, a highly reliable solid-state imaging device can be manufactured by using the method of the present invention.

[Brief description of the drawings]

1A to 1D are cross-sectional views illustrating an example of a method for manufacturing a solid-state imaging device according to the present invention in the order of steps. FIG. 2 is a cross-sectional view of a main part showing an example of a conventional solid-state imaging device, and FIG. 3 is a cross-sectional view of a main part showing another example of a conventional solid-state imaging device. 1 ... Tungsten silicide film 2 ... Drive electrode 3 ... PSG film 4 ... Aluminum wiring layer

Claims (2)

(57) [Claims] 1. A step of forming a drive electrode made of at least one layer of polysilicon on a charge transfer section; a step of forming an oxide film so as to cover the drive electrode by direct oxidation; Forming a light-shielding film made of a high-melting-point metal film or a film containing a high-melting-point metal so as to cover the above-described oxide film and to cover the side of the lowermost drive electrode; Forming a reflow film having a thickness sufficient to reduce the parasitic capacitance and increase the interlayer withstand voltage, and performing a heat treatment; and performing wiring on the reflow film using a material having a lower resistance than the light-shielding film. A method for manufacturing a solid-state imaging device, comprising: 2. The method according to claim 1, wherein the refractory metal is tungsten.