JPH07169927A - Semiconductor device - Google Patents

Abstract

PURPOSE:To make it possible to ensure high stability for a high temperature heating process after a film formation process which covers the portion of a light shielding film on a charge transfer device area and inhibit film separation and the increase in optical permeability and the decrease in device characteristic margins. CONSTITUTION:There are provided an insulation film 14 formed on a semiconductor substrate 11 and a polysilicon film 15 formed in an optical shielding formation scheduled area on the insulation film and a barrier layer 20 which inhibits silicon diffusion formed on the polysilicon film and an Mo film 16 or a W film formed on the barrier layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a structure of a light shielding film portion on a charge transfer element in a semiconductor device having an image sensor region.

[0002]

2. Description of the Related Art Generally, in a semiconductor device having an image sensor area, for example, an area sensor using a CCD (charge coupled device) as a charge transfer element, it is necessary to shield light from entering (photoelectric conversion element forming area). The light shielding film is formed so as to cover the gate portion and the charge transfer portion that control the transfer of the charge generated in (1).
As the light shielding film, aluminum, refractory metal silicide, refractory metal, or the like can be used. In particular,
The refractory metal and its silicide have a high melting point and have a high degree of freedom in the process for gettering or flattening after processing the light shielding film.

However, it is known that the refractory metal silicide has a high light transmittance after crystallization and deteriorates the device characteristics. Therefore, it has been considered to use a refractory metal itself, such as Mo (molybdenum) or W (tungsten), which is less likely to deteriorate the light shielding property, as the light shielding film.

In this case, as shown in FIG. 3, a charge transfer electrode using polysilicon 33 is formed on a gate insulating film 32 formed on a silicon substrate 31, and an interlayer insulating film 34 is formed on the charge transfer electrode. Further, a light shielding film made of a refractory metal itself such as a Mo film 36 (or a W film) is formed on the interlayer insulating film 34 with a polysilicon film 35 interposed therebetween.

The reason for interposing the polysilicon 35 between the interlayer insulating film 34 and the Mo film 36 is to prevent defects from entering the silicon substrate 31. Also,
Since Mo and W are easily oxidized in the air at about 200 to 300 ° C., a Mo silicide film 37 is formed on the Mo film 36 in order to prevent this.

In the semiconductor device shown in FIG. 3, 3
Reference numeral 8 is a substrate region in which a photodiode for photoelectric conversion is formed, and 39 is a substrate region in which a charge transfer control gate and a charge transfer element are formed.

By the way, when a semiconductor device having the above-mentioned structure is manufactured, if a ringer at a high temperature or a melt process for flattening is performed, the following two phenomena occur.

In order to explain this phenomenon, FIG. 4 (a) shows an example of the structure of the light shielding film portion in FIG. 3 immediately after the film forming step, and FIG. 4 (b) shows a high temperature. 7 shows an example of the structure of the light shielding film portion after the heating step of FIG. Where 4
Reference numeral 0 is an interlayer insulating film formed on the Mo silicide film 37.

First, as a first phenomenon, in a high temperature heat step, the polysilicon 35 on the interlayer insulating film 34 and the Mo film 36 react with each other to form a new silicide film 41. As a result of the silicidation reaction, As a result of the generation of stress, the film is peeled off (the peeled portion is indicated by 42) and the like.

Further, the remaining film thickness of the Mo film 36 is reduced, the light transmittance is increased, and the margin of the device characteristics is reduced. Furthermore, as a result of the incomplete presence of the natural oxide film on the surface of the polysilicon 35, the polysilicon 35 is consumed (supplied) unevenly, and the voids 43 are formed in the polysilicon 35.
Occurs, the polysilicon 35 disappears, or the film peels from the interface.

As a second phenomenon, in the high temperature heating process, the light shielding Mo film 36 reacts with the silicide film 37 formed on the Mo film 36 so that the excess Mo film 36 exists in the silicide film 37. The resulting silicon diffuses in the silicide film 37 to convert Mo into a silicide, and stress is generated as a result of the contraction of the volume due to this silicide formation, resulting in peeling of the film. Also in this case, as a result of the reduction in the film thickness of the Mo film 36 due to the silicidation of Mo, the light transmittance is increased and the margin of the element characteristics is reduced.

[0012]

As described above, a semiconductor device having a light-shielding film made of a refractory metal itself on a charge transfer element region as conventionally considered is required after a film-forming step of the light-shielding film portion. Due to the high temperature heating process, the peeling of the film, the increase of the light transmittance, the decrease of the margin of the device characteristics, etc. occur, and there is a problem that the reliability is lowered.

The present invention has been made to solve the above problems, and has high stability to a high temperature heat process after the film formation process of the light shielding film portion on the charge transfer element region, and the film peeling,
It is an object of the present invention to provide a semiconductor device which can suppress an increase in light transmittance, a decrease in element characteristic margin, etc., and can improve reliability.

[0014]

The semiconductor device of the present invention comprises:
A semiconductor substrate, an insulating film formed on this semiconductor substrate, a polysilicon film formed in a region of the insulating film where a light shielding film is to be formed, and a silicon diffusion formed on this polysilicon film are suppressed. It is characterized by comprising a barrier layer and a Mo film or a W film formed on this barrier layer.

[0015]

A Mo film or a W film with little deterioration of the light shielding property is used for at least one layer of the light shielding film having a laminated structure, and a barrier layer for suppressing silicon diffusion is formed under the Mo film or W film. ing.

As a result, the reaction between the polysilicon and the Mo film or W film in the high temperature heating process is suppressed by the existence of the barrier layer, and the formation of the silicide film on the barrier layer interface side of the Mo film or W film is suppressed. Since it is suppressed, it becomes possible to keep the entire film thickness at the same level as immediately after the film formation and prevent the film from peeling.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows a part of a charge transfer device according to an embodiment of the semiconductor device of the present invention.

In this device, 11 is a semiconductor substrate (silicon substrate in this example), 18 is a substrate region in which a photodiode for photoelectric conversion is formed, and 19 is a substrate region in which a charge transfer control gate and a charge transfer element are formed. Is.

Reference numeral 12 is a gate insulating film (silicon oxide film in this example) formed on the semiconductor substrate, 13 is polysilicon for a charge transfer electrode formed on this gate insulating film, and 14 is the gate insulating film. It is an interlayer insulating film (a CVD oxide film in this example) formed so as to cover 12 and the charge transfer electrode 13.

Reference numeral 15 is a polysilicon film formed in the light shielding film formation planned region on the interlayer insulating film, and is used to prevent defects from entering the silicon substrate 11. Reference numeral 20 is a barrier layer formed on the polysilicon film 15 for suppressing silicon diffusion, 16 is a Mo film formed on this barrier layer, and 17 is a Mo silicide film formed on this Mo film. Is. The polysilicon film 15, the barrier layer 20, the Mo film 16, and the Mo silicide film 17 which are formed in this manner form a light shielding film.

The barrier layer 20 is composed of, for example, a silicon oxide film formed by thermal oxidation, CVD (chemical vapor deposition) oxidation, other oxidation treatment, or natural oxidation, and its thickness is, for example, 50 nm or less. ,
In the case of a natural oxide film, it is approximately 6 to 8 nm. Even if the thickness of this silicon oxide film is 50 nm or more, there is no problem in the buffer property, but if it is 100 nm or more, a dedicated RIE device is required for patterning, or the film thickness under the light-shielding film is unnecessarily thick. Therefore, the light-shielding property is deteriorated.

The film thickness of the Mo silicide 17 is 100.
nm or less. When the thickness of the Mo silicide is 100 nm or more, the effect of preventing the oxidation of Mo is not changed, but not only the thickness of the film having a small light-shielding property is unnecessarily increased, but also the absolute amount of excess silicon of the silicide is used. As a result, excess silicon causes silicidation of Mo due to excess silicon, resulting in deterioration of light-shielding performance, and film peeling due to stress associated with silicidation reaction.

When manufacturing the device having the above structure, a silicon oxide film is formed as the gate insulating film 12 on the silicon substrate 11 by a normal charge transfer element forming process, and the polysilicon 13 is formed thereon. Is selectively formed, and a silicon oxide film is further formed as a interlayer insulating film 14 by a CVD method so as to cover the gate insulating film 12 and the charge transfer electrode 13.

Next, in order to cover the charge transfer control gate / charge transfer element forming region with a light shielding film, first, a film thickness of 100 n is formed.
After the polysilicon 15 having a thickness of m is formed by the low pressure CVD method, a silicon oxide film having a film thickness of 10 nm is formed on the surface of the polysilicon 15 by a thermal oxidation method as a barrier layer 20 for suppressing silicon diffusion. Furthermore, a 200 nm Mo film 16 and a 50 nm Mo film were formed by sputtering.
The silicide film 17 is continuously formed in vacuum.

After that, by a normal process, an etching mask is formed, a light shielding film is patterned (etching), an interlayer insulating film is covered, PSG (phosphorus silicate glass) melt is flattened, and a high temperature at 900 ° C. A device is completed through a gettering process by phosphorus diffusion and an aluminum wiring process.

In the above manufacturing process, an example of the structure of the light shielding film portion immediately after the film forming step is shown in FIG. 2A, and an example of the structure of the light shielding film portion after the high temperature heat step is shown. It is shown in FIG. Here, 21 is an interlayer insulating film formed on the Mo silicide film 17.

From these figures, the following two things can be seen. First, since the barrier layer (silicon oxide film having a film thickness of 10 nm) 20 is present in the high temperature heating process, the reaction between the polysilicon 15 as the lower layer and the Mo film 16 as the upper layer is suppressed, so that the Mo film 16 can be formed. Mo on the interface side of the barrier layer
No formation of silicide film is observed. Therefore, the entire film thickness is maintained at the same level as immediately after film formation, and peeling of the film does not occur.

Second, Mo silicide film (MoSi film) 17
Is formed as thin as 50 nm, the reaction amount with the underlying Mo film 16 is suppressed, and as a result of the reaction, the reduction in the total film thickness of the Mo film 16 and the Mo silicide film 17 is about 5 nm. It is suppressed to the following.

As a result, 100 n before the high temperature heating step
m polysilicon 15 and 10 nm silicon oxide film 2
The film thickness of the light shielding film including the four layers of the 0 and 200 nm Mo film 16 and the 50 nm Mo silicide film 17 was 360 nm, but it remains 355 nm or more even after the high temperature heating step. As a result, the stress associated with the reduction in the thickness of the light shielding film is relieved, the peeling of the film does not occur at all, and a stable process can be realized.

Further, Mo that determines the light transmittance of the light shielding film
Since the film thickness of the film 16 is as high as 195 nm or more even after the high temperature heating process of 200 nm, it is sufficient to have a margin of at least 2.5% or more with respect to the light transmittance.

Although the silicon oxide film is formed as the barrier layer 20 in the above embodiment, a silicon nitride film may be used instead of the barrier layer 20, and a W film may be used instead of the Mo film 16 and the Mo silicide film 17. A film and a W silicide film may be used, and further, a combination of a Mo film and a W silicide film,
A combination of W film and Mo silicide film may be used.

Further, in the above embodiment, the effect of the present invention can be obtained even when the Mo silicide film 17 is not formed. In addition, the barrier layer 20 and the Mo film 16 (or W film)
Even when a layer having a small effect of restricting the diffusion of Si (for example, a silicide film of Mo or W) is formed at the interface with and, the effect of the present invention can be obtained.

[0033]

As described above, according to the present invention, the stability of the light shielding film portion on the charge transfer device region against the high temperature heat process after the film forming process is high, and the film peeling and the light transmittance increase. ,
It is possible to realize a semiconductor device capable of suppressing the decrease in the margin of element characteristics and improving the reliability.

[Brief description of drawings]

FIG. 1 is a sectional view showing a part of an image sensor according to a first embodiment of a semiconductor device of the invention.

2A and 2B are cross-sectional views showing an example of a structure immediately after a film forming process and an example of a structure after a high temperature heating process for a light shielding film portion in FIG.

FIG. 3 is a cross-sectional view showing a part of a conventionally considered image sensor.

4A and 4B are cross-sectional views showing an example of a substrate structure immediately after a film forming process and an example of a substrate structure after a high temperature heating process for the light shielding film portion in FIG.

[Explanation of symbols]

11 ... Semiconductor substrate (silicon substrate), 12 ... Gate insulating film (silicon oxide film), 13 ... Polysilicon for charge transfer electrode, 14 ... Interlayer insulating film (CVD oxide film), 15 ... Polysilicon film, 16 ... Mo Film, 17 ... Mo silicide film, 1
8 ... Photoelectric conversion photodiode formation region, 19 ... Charge transfer control gate and charge transfer element formation region, 20 ...
Barrier layer.

Front page continuation (72) Inventor Seigo Abe 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Horikawa-cho factory

Claims (4)

[Claims] 1. A semiconductor substrate, an insulating film formed on the semiconductor substrate, a polysilicon film formed on a region of the insulating film where a light shielding film is to be formed, and a polysilicon film formed on the polysilicon film. A semiconductor device comprising: a barrier layer for suppressing silicon diffusion; and a Mo film or a W film formed on the barrier layer. 2. The semiconductor device according to claim 1, wherein the barrier layer is a silicon oxide film having a film thickness of 100 nm or less. 3. The semiconductor device according to claim 1, wherein a silicide film of Mo or W is formed on the Mo film or the W film. 4. The semiconductor device according to claim 3, wherein the silicide film has a thickness of 100 nm or less.