JP4670266B2 - Manufacturing method of solid-state imaging device - Google Patents

Description

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

A schematic configuration diagram of a conventional CCD solid-state imaging device is shown in FIG. 6A is a plan view of the CCD solid-state imaging device, and FIG. 6B is a cross-sectional view taken along line BB of FIG. 6A.
In this CCD solid-state imaging device, sensor units 2 that perform photoelectric conversion are arranged in a matrix, and a vertical transfer register 3 is provided on the left side of each column of the sensor units 2 to form an imaging region 1.
A horizontal transfer register 4 is connected to one end side of each vertical transfer register 3.
Further, an output unit 5 is connected to one end of the horizontal transfer register 4, and the signal charge is converted into a voltage by the output unit 5 and output to the outside.
Further, as shown in the cross-sectional view of FIG. 6B, a semiconductor region 7 constituting the sensor unit 2 and the vertical transfer register 3 is formed on the surface of the semiconductor substrate 6. A vertical transfer electrode 9 made of polysilicon is formed on the semiconductor substrate 6 via a thermal oxide film 8 that also forms a gate insulating film. A light shielding film 11 is formed on the vertical transfer electrode 9 via an interlayer insulating film 10. The light shielding film 11 has an opening 12 on the sensor unit 2.

By the way, the conventional solid-state imaging device has a problem that characteristics, particularly high-speed performance, are restricted when miniaturization progresses.
This is because the vertical transfer electrode and the horizontal transfer electrode have to be miniaturized as the number of pixels increases and the solid-state imaging device is miniaturized. However, when the transfer electrode is miniaturized, the resistance increases, and the conventional transfer electrode This is because there is a non-negligible electrode resistance in the polysilicon film used in the process, which becomes a rate-determining factor for high speed.

For this reason, the necessity of using a low-resistance electrode material has been recognized, and a technique for forming an electrode with a refractory metal polycide film such as tungsten polycide has been developed.
This is a case where a refractory metal silicide film such as tungsten silicide WSi is laminated on the surface of the polysilicon film, and the electrode has a metal as a composition component, and the electrode is composed only of polysilicon. In comparison, this is a technique capable of remarkably reducing the electrode resistance, and it can be said that it is excellent in that respect (for example, see Patent Document 1).
JP 11-168204 A

  However, when the electrode is formed of tungsten polycide, tungsten W is ejected from the tungsten polycide electrode in the process of oxidizing the surface of the silicon semiconductor substrate after the electrode formation process in the manufacturing process. It has been found that there is a problem that it diffuses into the semiconductor substrate and causes crystal defects.

  For this reason, a CCD solid-state imaging device in which an electrode is formed using a refractory metal such as tungsten polycide greatly deteriorates white scratches and is difficult to put into practical use.

In order to solve the above-described problem, in the present invention, even when an electrode containing a metal element such as a refractory metal is employed, a solid having a configuration capable of preventing the metal element from diffusing from the electrode A method for manufacturing an image sensor is provided.

The solid-state imaging device manufacturing method of the present invention includes a step of forming a conductive layer in which a tungsten silicide layer is stacked on a polycrystalline silicon layer on a semiconductor substrate, and patterning the conductive layer to form a transfer electrode. And a step of forming a silicon nitride film on the surface of the transfer electrode by directly nitriding the transfer electrode using a plasma nitriding apparatus.

According to the above-described method for manufacturing a solid-state imaging device of the present invention, a conductive layer in which a tungsten silicide layer is stacked on a polycrystalline silicon layer is formed on a semiconductor substrate, and the transfer layer is formed by patterning the conductive layer. As a result, a transfer electrode in which a tungsten silicide layer is stacked on the polycrystalline silicon layer is formed. Then, by directly nitriding the transfer electrodes using a plasma nitriding apparatus, by forming a silicon nitride film on the surface of the transfer electrodes, the surface of the transfer electrode is passivated, the transfer of the tungsten in the transfer electrodes Diffusion to the outside of the electrode , for example, a semiconductor substrate can be prevented.
As a result, it is possible to prevent the occurrence of white flaws by preventing the occurrence of crystal defects and level formation in the semiconductor substrate (semiconductor substrate or epitaxial layer) due to the diffusion of tungsten into the semiconductor substrate. .

According to the present invention described above, the transfer electrodes external metal elements in the transfer electrode (metal alone or a metal oxide, etc.), for example, diffusion into the semiconductor substrate can be prevented, crystal defects and quasi in the base body It is possible to prevent the formation of white spots and suppress the occurrence of white scratches.
As a result, the resistance of the transfer electrode can be reduced by containing a metal element without causing the possibility of white scratches, and characteristics such as high speed can be prevented from being deteriorated even if the transfer electrode is miniaturized.
Accordingly, it is possible to realize a solid-state imaging device that operates at a high speed by reducing the resistance of the transfer electrode and has good characteristics, and it is possible to reduce the size and increase the number of pixels of the solid-state imaging device by miniaturization. .
In addition, a solid-state imaging device having favorable characteristics can be manufactured with a high yield.

As an embodiment of the present invention, a schematic configuration diagram (a cross-sectional view of a main part) of a solid-state imaging device is shown in FIG. In the present embodiment, the present invention is applied to a CCD solid-state imaging device.
FIG. 1 shows a cross-sectional view of a vertical transfer register and a sensor unit, similar to the cross-sectional view of FIG. 6B. Since the plan view of the solid-state imaging device is the same as the plan view of the conventional configuration in FIG. 6A, the illustration is omitted.

This solid-state imaging device is configured such that photoelectric conversion is performed on a surface portion of a semiconductor substrate (a semiconductor substrate such as a silicon substrate or an epitaxial layer formed thereon) 6 and a semiconductor region of the sensor unit 2 constituting the photoelectric conversion device. The semiconductor region (transfer channel region) 7 constituting the vertical transfer register 3 is formed.
A thermal oxide film 8 that also constitutes a gate insulating film is formed on the surface of the semiconductor substrate 6.
In some cases, instead of the thermal oxide film 8, a sandwich structure of an oxide film / nitride film / oxide film called a so-called ONO structure may be used as a gate insulating film.

Further, a tungsten polycide 15 is formed on the thermal oxide film 8 as a transfer electrode of the vertical transfer portion by laminating a polycrystalline silicon layer 13 and a tungsten silicide (WSi) layer 14 thereon.
A light shielding film 11 made of metal such as tungsten is formed above the transfer electrode made of tungsten polycide 15 via an interlayer insulating film 10. The light shielding film 11 has an opening 12 on the sensor unit 2.

  Although not shown, a color filter and a microlens are formed above the light shielding film 11 as necessary. These parts are not shown because they are not directly related to the essence of the present invention. Further, since the structure of the surface portion of the semiconductor substrate 6 is not directly related to the essence of the present invention, the detailed illustration is omitted.

In the solid-state imaging device of the present embodiment, a silicon nitride film 16 is formed on the surface (upper surface and side surface) of the transfer electrode made of tungsten polycide 15 in particular.
Thereby, the silicon nitride film 16 acts as a metal scattering prevention film, and the scattering of tungsten contained in the tungsten polycide 15 of the transfer electrode can be prevented.

The above-described solid-state imaging device of the present embodiment can be manufactured, for example, as follows.
First, after forming the thermal oxide film 8 on the surface of the semiconductor substrate 6, the polycrystalline silicon layer 13 is formed on the surface of the thermal oxide film (gate insulating film) 8.
Subsequently, a tungsten silicide layer 14 is formed on the polycrystalline silicon layer 13. Thereby, tungsten polycide 15 is formed.
Thereafter, the tungsten polycide 15 is patterned by selective etching to form a transfer electrode made of the tungsten polycide 15 (see FIG. 2A).

  Next, as shown in FIG. 2B, a silicon nitride film 16 serving as a metal scattering prevention film is formed on the entire surface of the wafer by a CVD method. As a result, the surface (upper surface and side surface) of the transfer electrode made of tungsten polycide 15 is covered with the silicon nitride film 16.

Next, as shown in FIG. 2C, portions of the silicon nitride film 16 other than the portions covering the top and side surfaces of the tungsten polycide 15 are removed by etching. Thereby, the transfer electrode 15 whose surface is covered with the silicon nitride film 16 is formed.
Thereafter, a light shielding film 11 is formed via the interlayer insulating film 10, and the light shielding film 11 is patterned to form an opening 12 on the sensor unit 2.
Further, a planarizing film, a color filter, and an on-chip lens are formed as necessary.
In this way, the solid-state imaging device of the present embodiment shown in FIG. 1 can be manufactured.

In the step shown in FIG. 2B, it has been described that the silicon nitride film 16 serving as the metal scattering prevention film is formed by the CVD method. However, the method for forming the silicon nitride film 16 is not necessarily limited to the CVD method. .
For example, the silicon nitride film 16 as a diffusion preventing layer can be formed on the surface by nitriding in a diffusion furnace type heat treatment furnace or lamp annealing furnace or nitriding by plasma nitriding.
Further, for example, a silicon nitride film can be formed by direct nitridation of tungsten polycide of the transfer electrode 15. For example, the tungsten polycide 15 can be directly nitrided by using a plasma nitriding apparatus having strong nitriding power.
In this case, since the step of etching and removing the silicon nitride film at unnecessary portions shown in FIG. 2C is not necessary, the number of manufacturing steps can be reduced and the time required for manufacturing can be shortened.

According to the configuration of the solid-state imaging device of the present embodiment described above, the silicon nitride film 16 is formed so as to cover the surface (upper surface and side surface) of the transfer electrode made of the tungsten polycide 15.
Thereby, since the silicon nitride film 16 can prevent scattering and diffusion of tungsten (single tungsten or tungsten oxide) from the transfer electrode 15 to the outside of the electrode, for example, the semiconductor substrate 6 during manufacturing, the semiconductor substrate 6 of tungsten can be prevented. Occurrence of crystal defects in the semiconductor substrate 6 due to diffusion into the semiconductor substrate 6 can be prevented.
Accordingly, it is possible to suppress the occurrence of white scratches by preventing the occurrence of crystal defects and the formation of levels in the semiconductor substrate 6.

Even when the high temperature heat treatment step is performed after the silicon nitride film 16 is formed, the silicon nitride film 16 allows the transfer electrode 15 to be connected to the outside of the tungsten (single tungsten or tungsten oxide) electrode, for example, to the semiconductor substrate 6 at the time of manufacture. Scattering / spreading can be prevented.
This eliminates the possibility that the conditions for oxidation after forming the transfer electrode 15 are restricted in order to prevent tungsten from scattering.

Further, according to the manufacturing method of the present embodiment, the silicon nitride film 16 is formed on the surface (upper surface and side surface) of the transfer electrode made of the tungsten polycide 15 by depositing a silicon nitride film or directly nitriding. In the subsequent heat treatment step, the silicon nitride film 16 can prevent tungsten from scattering and diffusing.
Thereby, there is no possibility that tungsten is scattered and diffused from the transfer electrode 15 in the subsequent heat treatment process and diffused outside the electrode, for example, into the semiconductor substrate 6.

According to the present embodiment, it is possible to prevent the occurrence of crystal defects and the formation of levels in the semiconductor substrate 6 and to suppress the occurrence of white scratches.
Accordingly, the tungsten polycide 15 can reduce the resistance of the transfer electrode without causing a possibility of white scratches, and characteristics such as high speed can be prevented from being deteriorated even if the transfer electrode is miniaturized.
Therefore, it is possible to realize a solid-state imaging device that operates at high speed and has good characteristics, and it is possible to reduce the size and increase the number of pixels of the solid-state imaging device by miniaturization.
In addition, a solid-state imaging device having favorable characteristics can be manufactured with high yield.

The transfer electrode 15 may have a configuration in which two conductive layers similar to the conventional one partially overlap, but more preferably, the transfer electrode 15 is formed of the same conductive layer (tungsten polycrystal). Side) only.
FIG. 3 shows a cross-sectional view of the vertical transfer register 3 in this configuration.
As shown in FIG. 3, each transfer electrode of the vertical transfer register 3 is formed of only the tungsten polycide 15 of the first layer. That is, the transfer electrode of the vertical transfer register 3 has a so-called single layer electrode structure.
Thus, since the transfer electrode 15 of the vertical transfer register 3 has a single-layer electrode structure, there is no overlap portion of the tungsten polycide of the transfer electrode. Further, since the height of the transfer electrode 15 and the height of the light shielding film 11 formed above the transfer electrode 15 are reduced, light in a wide angle range can be incident on the photoelectric conversion element.

By the way, when the transfer electrode has a structure in which two conductor layers partially overlap, an insulating film formed between the first conductor layer and the second conductor layer has a signal charge. In order to prevent transfer residue and efficiently transfer the film, a thin film is used, and a breakdown voltage between the transfer electrode made of the first conductive layer and the transfer electrode made of the second conductive layer is secured. In addition, it is necessary to form a dense and firm silicon oxide film. Therefore, conventionally, heat treatment at a relatively high temperature has been performed for the purpose of forming a thin and firm silicon oxide film.
When a transfer electrode made of tungsten polycide is employed, this relatively high temperature heat treatment promotes the oxidation reaction in the direction of the transfer electrode, and diffusion of tungsten or tungsten oxide to the outside of the electrode, for example, the semiconductor substrate. Occur.

On the other hand, since the transfer electrode 15 has a single-layer electrode structure, the above-described relatively high-temperature heat treatment process is not required. It is possible to reduce the number of steps, thereby reducing the opportunity (number of times and time) of the oxidation reaction on the surface of the transfer electrode 15.
Therefore, the silicon nitride film 16 covering the surface of the transfer electrode 15 prevents the diffusion of tungsten to the outside of the electrode 15 and reduces the chance of an oxidation reaction on the surface of the transfer electrode 15, thereby more effectively returning to the outside of the electrode 15. The diffusion of tungsten can be prevented.

Next, as another embodiment of the present invention, a schematic configuration diagram (cross-sectional view) of a solid-state imaging device is shown in FIG.
In particular, as shown in the cross-sectional view of FIG. 4, the solid-state imaging device of the present embodiment covers the surface (upper surface and side surface) of the transfer electrode 15 made of tungsten polycide of the vertical transfer register 3, and a silicon oxide film ( A silicon nitride film 16 is formed via a (silicon oxide film) 17.
Since other configurations are the same as those of the previous embodiment shown in FIG. 1, the same reference numerals are given and redundant description is omitted.

For example, as described above, when the silicon nitride film 16 is formed on the surface by the method of directly nitriding the tungsten polycide 15, there are problems in the surface roughness and crystallinity of the polycrystalline silicon layer 13 and the tungsten silicide layer 14. Therefore, it is possible that the high-quality silicon nitride film 16 having a uniform and high anti-scattering performance is not formed on the surface of the tungsten polycide 15.
On the other hand, as in the present embodiment, polycrystalline silicon is formed by forming a silicon oxide film 17 between the tungsten polycide 15 and the silicon nitride film 16 which is a metal scattering prevention film. Regardless of the surface roughness and crystallinity of the layer 13 and the tungsten silicide layer 14, it is possible to form a high-quality silicon nitride film 16 that is homogeneous and has high anti-scattering performance.

The structure of the transfer electrode in the present embodiment is, for example, by forming a silicon oxide film (silicon oxide film) 17 having a certain thickness or more on the surface of the tungsten polycide 15 and directly nitriding the silicon oxide film 17. Can be produced.
As a method of forming the silicon oxide film 17 having a certain thickness or more on the surface of the tungsten polycide 15, an oxidation treatment method at a lower temperature and in a shorter time is desirable. For example, an atmospheric pressure CVD apparatus at 450 ° C. or lower, a plasma CVD apparatus, a lamp annealing furnace, or a plasma oxidation method may be used. This is because if the oxidation treatment is performed at a high temperature for a long time, the oxidation of the tungsten silicide layer 14 proceeds, and the generated tungsten oxide may be scattered and diffused into the semiconductor substrate 6.

The solid-state imaging device of the present embodiment can be manufactured as follows, for example.
First, a thermal oxide film (gate insulating film) 8 is formed on the surface of the semiconductor substrate 6, and then a polycrystalline polysilicon layer 13 is formed on the surface.
Subsequently, a tungsten silicide layer 14 is formed on the polycrystalline silicon layer 13. Thereby, tungsten polycide 15 is formed.
Thereafter, this tungsten polycide 15 is patterned by selective etching to form a transfer electrode made of tungsten polycide 15 (see FIG. 5A above).

  Next, as shown in FIG. 5B, a silicon oxide film 17 is formed on the surface of the transfer electrode made of tungsten polycide 15 at a low temperature by a plasma oxidation method. As a result, the surface (upper surface and side surface) of the transfer electrode made of tungsten polycide 15 is covered with the silicon oxide film (silicon oxide film) 17.

Subsequently, as shown in FIG. 5C, a silicon nitride film 16 serving as a metal scattering prevention film is formed on the silicon oxide film 17 on the tungsten polycide 15 by using a method such as plasma nitriding. Thereby, the transfer electrode 15 whose surface is covered with the silicon nitride film 16 via the silicon oxide film 17 is formed.
Thereafter, a light shielding film 11 is formed via the interlayer insulating film 10, and the light shielding film 11 is patterned to form an opening 12 on the sensor unit 2.
Further, a planarizing film, a color filter, and an on-chip lens are formed as necessary.
In this way, the solid-state imaging device of the present embodiment shown in FIG. 4 can be manufactured.

According to the configuration of the solid-state imaging device of the present embodiment described above, the silicon nitride film 16 that is a metal scattering prevention film is formed on the surface (upper surface and side surface) of the transfer electrode made of tungsten polycide 15 via the silicon oxide film 17. Since the silicon nitride film 16 can prevent scattering and diffusion of the transfer electrode 15 from the transfer electrode 15 to the outside of the electrode, for example, the semiconductor substrate 6 at the time of manufacture, it is caused by diffusion of tungsten into the semiconductor substrate 6. Thus, the occurrence of crystal defects in the semiconductor substrate 6 can be prevented.
Accordingly, it is possible to suppress the occurrence of white scratches by preventing the occurrence of crystal defects and the formation of levels in the semiconductor substrate 6.

Even when the high temperature heat treatment step is performed after the silicon nitride film 16 is formed, the silicon nitride film 16 allows the transfer electrode 15 to be connected to the outside of the tungsten (single tungsten or tungsten oxide) electrode, for example, to the semiconductor substrate 6 at the time of manufacture. Scattering / spreading can be prevented.
This eliminates the possibility that the conditions for oxidation after forming the transfer electrode 15 are restricted in order to prevent tungsten from scattering.

Further, according to the manufacturing method of the present embodiment, after the silicon oxide film (silicon oxide film) 17 is formed on the surface (upper surface and side surface) of the transfer electrode made of tungsten polycide 15, the silicon oxide film 17 By forming the silicon nitride film 16 by nitriding the surface, the silicon nitride film 16 can prevent the tungsten from scattering and diffusing from the tungsten polycide 15 in the subsequent heat treatment step.
Thereby, there is no possibility that tungsten is scattered and diffused from the transfer electrode 15 and diffused into the semiconductor substrate 6 in the subsequent heat treatment process.

According to the present embodiment, it is possible to prevent the occurrence of crystal defects and the formation of levels in the semiconductor substrate 6 and to suppress the occurrence of white scratches.
Accordingly, the tungsten polycide 15 can reduce the resistance of the transfer electrode without causing a possibility of white scratches, and characteristics such as high speed can be prevented from being deteriorated even if the transfer electrode is miniaturized.
Therefore, it is possible to realize a solid-state imaging device that operates at high speed and has good characteristics, and it is possible to reduce the size and increase the number of pixels of the solid-state imaging device by miniaturization.
In addition, a solid-state imaging device having favorable characteristics can be manufactured with high yield.

  In each of the above-described embodiments, the present invention is applied to the transfer electrode (vertical transfer electrode) 15 of the vertical transfer register 3 of the CCD solid-state imaging device, but the transfer electrode (horizontal transfer electrode) of the horizontal transfer register is used. Similarly, the present invention can be applied.

In each of the above embodiments, the present invention is applied to the CCD solid-state imaging device. However, the present invention can be applied to other configurations.
For example, the present invention can also be applied to a MOS solid-state image sensor or an amplification solid-state image sensor. In that case, for example, in the readout gate electrode or the gate electrode of the pixel transistor, the electrode may contain a metal element and a silicon nitride film may be formed on the surface of the electrode.

  Further, the present invention can be applied not only to an area sensor in which sensor units are arranged in a matrix but also to a line sensor in which sensor units are arranged in a row.

  The present invention is not limited to the above-described embodiment, and various other configurations can be taken without departing from the gist of the present invention.

1 is a schematic configuration diagram (cross-sectional view) of a solid-state imaging device according to an embodiment of the present invention. FIGS. 2A to 2C are manufacturing process diagrams illustrating a method for manufacturing the solid-state imaging device of FIG. 1. It is sectional drawing of the vertical transfer register part of the solid-state image sensor of FIG. 1 at the time of setting it as a single layer electrode structure. It is a schematic block diagram (sectional drawing) of the solid-state image sensor of other embodiment of this invention. FIGS. 5A to 5C are manufacturing process diagrams illustrating a method for manufacturing the solid-state imaging device of FIG. A and B are schematic configuration diagrams of a conventional CCD solid-state imaging device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Image pick-up area, 2 sensor part, 3 vertical transfer register, 4 horizontal transfer register, 5 output part, 6 semiconductor substrate, 7 semiconductor area of vertical transfer register, 8 thermal oxide film (gate insulating film), 10 interlayer insulating film, 11 Light shielding film, 13 Polycrystalline silicon layer, 14 Tungsten silicide layer, 15 Tungsten polycide, 16 Silicon nitride film, 17 Silicon oxide film (silicon oxide film)

Claims (1)

Forming a conductive layer in which a tungsten silicide layer is stacked on a polycrystalline silicon layer on a semiconductor substrate, and patterning the conductive layer to form a transfer electrode ;
Forming a silicon nitride film on the surface of the transfer electrode by directly nitriding the transfer electrode using a plasma nitriding apparatus.

Images