JPH03181119A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To decrease the interface level so as to improve electric properties by forming insulating films to become barriers against the diffusion of hydrogen above and below a silicon film, and injecting hydrogen so that it may have plural concentration distributions within the silicon film, and then heat-treating it. CONSTITUTION:A silicon nitride insulating film 12 to become a barrier to the diffusion of hydrogen is made on an insulating substrate 11, and then a crystal silicon film 13 is made. Next, a silicon nitride insulating film 14 to become a barrier against the diffusion of hydrogen is made on the film 13. And when injecting hydrogen into the film 13 by ion implantation method, by setting the accelerating voltage of implantation to a proper value, it can have the concentration distribution which has a peak near the surface of the film 13 or near the base interface. Next, it is heat-treated in the mixed gas atmosphere of N2, Ar,and H2. Hereby, interface level can be decreased and back channel effect can be suppressed, and electric properties can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a semiconductor device formed on an insulating substrate.

[Prior Art] Conventionally, a thin film transistor on an insulating substrate (hereinafter referred to as TPT) has an insulating substrate 61 made of glass or the like, as shown in FIG.
A semiconductor thin film 62 was formed thereon, and elements were built therein.

Furthermore, in recent years, crystalline semiconductor thin films are often used as semiconductor thin films in order to improve the characteristics of TPT. The term "crystalline semiconductor" as used herein refers to a single-crystal semiconductor that has more defects than a normally used single-crystal wafer, or a polycrystalline semiconductor that has one or more internal crystal grain boundaries.

[Problems to be Solved by the Invention] However, in the above conventional example, the crystalline semiconductor thin film 62
A large number of interface states 66, 64 exist at the interface between the crystalline semiconductor thin film 62 and the gate insulator 63, and at the interface between the crystalline semiconductor thin film 62 and the gate insulation @63.
When a T is formed, carriers are trapped in the level in the channel part, forming a so-called back channel, causing fluctuations in threshold voltage, decrease in on/off ratio, etc.
This resulted in deterioration of device characteristics.

Furthermore, although polycrystalline silicon is often used as a crystalline semiconductor thin film, there are many interface states 65 at the grain boundaries that exist in polycrystalline silicon, and these trap carriers. This reduces carrier mobility in the channel portion.

In addition, if an inexpensive material such as glass is used for the substrate, alkali ions such as Na''' contained in the substrate material will move during heat treatment during the process, and exist as mobile ions at the interface with the substrate or in the silicon thin film. However, this has caused problems with deterioration of device characteristics and reliability.

To solve these problems, for example, hydrogen passivation using a silicon nitride film by plasma CVD is used as a protective film for the device after the device is formed, thereby reducing the levels in the silicon thin film and increasing the mobility. Ta. Further, in order to prevent alkali ion contamination, high-purity quartz, alkali-free glass, or the like may be used as the substrate.

However, even with the above method, the problem of the interface with the substrate has not been solved. This is because the hydrogen concentration distribution in the crystalline semiconductor thin film after hydrogen passivation has a peak relatively on the surface of the crystalline semiconductor thin film, as shown in Figure 7, and the hydrogen concentration distribution in the thin film and the underlying layer. This is because it is not sufficient to passivate the levels at the interface.

Further, substrates made of high-purity quartz or alkali-free glass are expensive, and there is a problem in forming TPT on a large-area substrate at low cost.

[Means for Solving the Problems] A method for manufacturing a semiconductor device of the present invention is a method for manufacturing a semiconductor device comprising forming a crystalline semiconductor thin film on an insulating substrate. a step of forming first and second insulating films that act as barriers against the diffusion of hydrogen; a step of introducing hydrogen into the semiconductor thin film so as to have a concentration distribution having multiple peaks in the film thickness direction; The method is characterized by including a step of performing heat treatment.

[Function] In the present invention, hydrogen is diffused in the gap between the crystalline semiconductors into which hydrogen is introduced, and the interface states existing at the interface between the crystalline semiconductor thin film and the substrate are affected by the hydrogen. It is possible to reduce the number of trapped interface states and improve the electrical characteristics of semiconductor devices such as TFTs.

In addition, the hydrogen that has diffused in the thin film is absorbed by the defect levels in the thin film,
By being trapped in the interface states of grain boundaries, TP
The electrical characteristics of semiconductor devices such as T can be improved.

Further, hydrogen is introduced so as to have a concentration distribution having multiple peaks in the film thickness direction.For example, one is introduced so that the peak of the distribution is on the surface of the crystalline semiconductor thin film, and one is
First, by introducing the material so that its peak is at the interface between the base of the crystalline semiconductor thin film, it becomes possible to passivate the entire semiconductor thin film, and the above-mentioned effect can be further enhanced.

Note that by forming a silicon nitride film between the substrate and the semiconductor as an insulating film that acts as a barrier against hydrogen diffusion, a blocking effect is produced against alkali ions such as Na from the substrate such as glass. Reliability can be improved.

Further, by forming an insulating film that acts as a barrier against hydrogen diffusion on the upper and lower surfaces of the semiconductor thin film, out-diffusion of hydrogen diffused into the thin film can be prevented, and the above-mentioned effects can be obtained more stably.

[Embodiment] FIG. 1 is a cross-sectional view of a semiconductor device that characterizes the present invention.

In the first embodiment of the present invention, first, a first layer is placed on an insulating substrate such as glass, which serves as a barrier to hydrogen diffusion.
For example, as an insulating film of plasma CVD? A silicon nitride film 12 is formed by the method 1 or low pressure CVD method.

Thereafter, a crystalline silicon thin film 13 is formed.

Crystalline silicon thin films include polycrystalline silicon formed by low pressure CVD or plasma CVD, amorphous silicon that is annealed and recrystallized, and plasma CVD.
In the VD method, large-grain polycrystalline silicon (Japanese Patent Application No. 1983-73630) obtained by adding hydrogen halide gas such as MCI to the film-forming atmosphere, and Large-grain polycrystalline silicon proposed in No. 73629, and
Single-crystal silicon formed on an amorphous substrate, as proposed in No. 6, is used.

Next, a second insulator 11j14 that acts as a barrier against hydrogen diffusion is formed on the crystalline silicon thin film 13. As an insulating film that acts as a barrier against hydrogen diffusion, a silicon nitride film formed by a low pressure CVD method, a silicon nitride film or a silicon nitride oxide film formed by a plasma CVD method can be used.

Next, hydrogen is introduced into the crystalline silicon thin film by a normal ion implantation method or an ion shower implantation method (FIG. 15).

According to these methods, by selecting an appropriate value for accelerating the implantation, the depth of the peak of the implanted region can be selected to a desired value. Table 1 shows the relationship between hydrogen ion acceleration voltage and implantation range in silicon based on the LSS theory.

Table 1 The hydrogen ion implantation range was determined multiple times by selecting an accelerating voltage so that the implantation range was at an appropriate position, for example, near the surface of the crystalline silicon thin film, near the base interface of the crystalline silicon thin film, or near the center of the crystalline silicon thin film. The injection is divided into two parts.

Thereby, sufficient hydrogen can be introduced to be trapped in the interface levels and defect levels distributed in the silicon thin film, and the passivation effect can be further enhanced.

FIG. 2 shows the hydrogen concentration distribution after injection. low acceleration voltage,
By appropriately combining implantation with a high acceleration voltage, it is possible to implant with a constant distribution near the surface of the crystalline silicon thin film and near the base interface, as shown in FIG. 2, 16.17. The accelerating voltage for implantation should be divided as finely as possible so that there are many peaks in the concentration distribution in the crystalline silicon thin film, but if throughput is taken into account, two to three types of implantation are sufficient to achieve the desired effect. It is possible to show that

Next, heat treatment is performed in an atmosphere of N, Ar%H2, or a mixed gas thereof.

FIG. 2 shows the hydrogen concentration distribution 18 in the crystalline silicon thin film after heat treatment. Hydrogen diffuses and redistributes in the crystalline silicon thin film through heat treatment, but at this time, first and second insulating films are formed on the upper and lower surfaces of the crystalline silicon thin film to act as a barrier against hydrogen diffusion. The introduced hydrogen diffuses and redistributes only within the silicon thin film 13 without changing the absolute amount of hydrogen introduced.

In addition, during the process of diffusion and redistribution, hydrogen in the thin film forms interface states that exist at the surface and underlying interface, defect levels in the crystalline silicon thin film, and interfaces that exist at the grain boundaries of the crystalline silicon thin film. It is trapped in the level, suppresses the generation of back channels at the base interface, reduces the potential of grain boundaries, and increases mobility.

Note that the temperature of the heat treatment is 300°C, at which hydrogen diffusion begins to occur.
The temperature may be higher than 600° C. and lower than 600° C., at which hydrogen diffused into crystalline silicon will not diffuse out again.

Furthermore, by forming a silicon nitride film between the substrate and the crystalline silicon thin film, a blocking effect is imparted to alkali ions such as Na''' from the substrate, thereby improving reliability.

In addition, by forming an insulating film on both sides of the crystalline silicon thin film that acts as a barrier against hydrogen diffusion, out-diffusion from the surface of the crystalline silicon thin film is prevented when hydrogen diffuses during heat treatment. I can do it,
The passivation effect of hydrogen can be roughly enhanced.

FIG. 3 schematically shows a second embodiment of the invention.

In the second embodiment of the present invention, first, a first insulating film that serves as a barrier against hydrogen diffusion is formed on an insulating substrate 11 made of glass or the like by, for example, plasma CVD, at a substrate temperature of 200° C. to 300° C. A silicon nitride film 12 is formed. This silicon nitride film 12 contains several percent to several tens of percent of hydrogen.

Thereafter, a crystalline silicon thin film 13 is formed at a temperature comparable to or lower than the temperature at which silicon nitride@12 was formed.

Crystalline silicon thin films include polycrystalline silicon formed by low-pressure CVD and plasma CVD, and the effect of adding hydrogen halide gas such as MCI to the film-forming atmosphere in our proposed plasma CVD method. (Japanese Patent Application No. 73630/1982) can be used. The large-grain polycrystalline silicon thin film proposed by us is most suitable for this example from the viewpoint of lowering the process temperature and electrical properties.

Next, a second insulating film 14 that acts as a barrier against hydrogen diffusion is formed on the crystalline silicon. As an insulating film that acts as a barrier against hydrogen diffusion, low pressure C
A silicon nitride film formed by a VD method or a silicon nitride film or a silicon nitride oxide film formed by a plasma CVD method can be used in the same manner as the first insulating film.

Next, using an ion implantation method or an ion shower implantation method, hydrogen is implanted into the crystalline silicon thin film through the second insulating film (FIG. 15). The acceleration voltage during implantation is selected so that the peak of the concentration distribution is at the interface between the second insulating film and the crystalline silicon thin film.

Next, N2. Ar, N2. Alternatively, in an atmosphere of these mixed gases, for hydrogen diffusion, +I = pL, +
, x whistle + zntaf! L [ff1nd child l → rel S
/I+"'j~) film, at a temperature higher than the temperature at which the film was formed (3
Heat treatment is performed at a temperature of 00°C to 600°C.

The hydrogen concentration distribution after heat treatment is shown in FIG. 418.

During this heat treatment, the hydrogen present in the silicon nitride film is
By diffusing into the crystalline silicon thin film, it particularly affects the interface states existing at the underlying interface, defect levels in the crystalline silicon thin film, and interface states existing at the grain boundaries of the crystalline silicon. Hydrogen that is trapped and introduced by ion implantation is trapped, especially at the interface between the crystalline silicon thin film and the second insulating film, and furthermore, at the defect units in the crystalline silicon thin film and the hydrogen introduced by ion implantation. It is trapped in the interface states existing at the grain boundaries, suppresses the generation of back channels at the underlying interface, reduces the potential at the grain boundaries, and increases mobility.

In addition, the temperature of the heat treatment is 300°C, at which hydrogen diffusion begins to occur.
℃ and lower than 600℃ at which hydrogen diffused into crystalline silicon does not diffuse out again. It has a blocking effect against alkali ions such as Na'' from substrates such as glass, improving reliability.

In addition, by forming an insulating film that acts as a barrier against hydrogen diffusion on both sides of the crystalline silicon thin film, it is possible to prevent out-diffusion from the surface of the crystalline silicon thin film when hydrogen diffuses through heat treatment. The passivation effect can be further enhanced.

FIG. 3 schematically shows a third embodiment of the invention.

As a third embodiment of the present invention, first, a first containing insulating film that serves as a barrier against hydrogen diffusion is formed on an insulating substrate 11 such as glass by, for example, a plasma CVD method.
A silicon nitride film 12 is formed at a substrate temperature of 200°C to 300°C. This silicon nitride film 12 contains several percent to several tens of
Contains % hydrogen.

Thereafter, an amorphous silicon thin film 13 is formed at a temperature comparable to or lower than the temperature at which the silicon nitride film 12 was formed.

As the amorphous silicon thin film, amorphous silicon formed by low pressure CVD or plasma CVD, or polycrystalline silicon made amorphous by ion-implanting S and + is used.

Next, an insulating film 14 that acts as a barrier against hydrogen diffusion is formed on the amorphous silicon. As an insulating film that acts as a barrier against hydrogen diffusion, a silicon nitride film formed by a low pressure CVD method, or a silicon nitride film or a silicon nitride oxide film formed by a plasma CVD method in the same way as the first insulating film is used. Can be used.

Next, hydrogen is implanted into the crystalline silicon thin film through the second insulating film using an ion implantation method or an ion shower implantation method (FIG. 15). At this time, for example, the acceleration voltage at the time of implantation is selected so that the peak of the hydrogen concentration distribution after implantation is at the interface between the second insulating film and the crystalline silicon thin film.

Next, in an atmosphere of N2, Ar, N2, or a hot gas mixture thereof, the insulating film 12 containing hydrogen, for example, a silicon nitride film, is formed at a temperature higher than the temperature (300°C to 300°C).
600°C).

Regarding the temperature of this heat treatment, it is desirable to set the temperature at which the formed amorphous silicon undergoes solid phase crystal growth and crystallization, in order to produce a higher performance TPT. Therefore, the temperature of the heat treatment is more preferably 500°C to
It is desirable to set the temperature to 600°C in order to make a higher performance TPT.

The hydrogen concentration distribution after heat treatment is shown in FIG. 418.

During this heat treatment, the hydrogen present in the silicon nitride film is
By diffusing into the crystalline silicon thin film, it particularly affects the interface states existing at the underlying interface, defect levels in the crystalline silicon thin film, and interface states existing at the grain boundaries of the crystalline silicon. Hydrogen that is trapped and introduced by ion implantation is trapped, especially at the interface between the crystalline silicon thin film and the second insulating film, and furthermore, at the defect levels in the crystalline silicon thin film and at the interface between the crystalline silicon thin film and the second insulating film. is trapped by the interface states existing at the grain boundaries, suppressing the generation of back channels at the underlying interface, reducing the potential at the grain boundaries, and increasing mobility.

In addition, the temperature of the heat treatment is 300°C, at which hydrogen diffusion begins to occur.
The temperature is higher than 600° C. and lower than 600° C., at which hydrogen that has diffused into crystalline silicon does not diffuse out again.

Further, by forming a silicon nitride film between the substrate and the crystalline silicon thin film, a blocking effect is provided to alkali ions such as Na'' from the substrate such as glass, and reliability is improved.

In addition, both sides of the amorphous silicon thin film act as a barrier to hydrogen diffusion, i! By forming [, when hydrogen is diffused by heat treatment, out-diffusion from the crystalline silicon surface can be prevented, and the passivation effect by hydrogen can be further enhanced.

FIG. 3 schematically shows a fourth embodiment of the present invention.

As the fourth embodiment of the present invention, first, the insulating substrate 11
As a first insulating film that acts as a barrier against hydrogen diffusion, for example, a plasma CVD method or a low pressure CVD method is applied to
A silicon nitride film 12 is formed.

Thereafter, a crystalline silicon thin film 13 is formed.

Claims (7)

[Claims] (1) In a method for manufacturing a semiconductor device in which a crystalline semiconductor thin film is formed on an insulating substrate, first and second insulating films are respectively provided on both sides of the crystalline semiconductor thin film to serve as a barrier against hydrogen diffusion. manufacturing a semiconductor device, comprising the steps of: forming a semiconductor thin film; introducing hydrogen into the semiconductor thin film so as to have a concentration distribution having a plurality of peaks in the film thickness direction; and then performing heat treatment. Method. (2) The method for manufacturing a semiconductor device according to claim 1, wherein the step of introducing hydrogen is performed by a combination of two or more types of methods. (3) The method for manufacturing a semiconductor device according to claim 2, wherein at least one of the two or more types of hydrogen introduction methods is ion implantation or ion shower implantation. (4) A silicon nitride film formed by a low pressure CVD method or a plasma CVD method, or a silicon nitride oxide film is used as the insulating film serving as a barrier against hydrogen diffusion. A method for manufacturing a semiconductor device. (5) The method of manufacturing a semiconductor device according to any one of claims 1 to 4, wherein the crystalline semiconductor thin film material is silicon. (6) The method of manufacturing a semiconductor device according to any one of claims 1 to 5, wherein the temperature of the heat treatment is a temperature at which amorphous silicon becomes polycrystalline. (7) The method of manufacturing a semiconductor device according to claim 6, wherein the temperature of the heat treatment is 300°C to 600°C.