JPH04297018A - Manufacture of semiconductor film - Google Patents

Abstract

PURPOSE:To obtain a crystallite (less than 10nm) silicon film, in which dangling bonds are decreased. CONSTITUTION:An amorphous silicon film 14 is deposited on an insulating substrate 10. The amorphous silicon film 14 can be acquired by implanting Si ions to a polycrystalline silicon film 13 deposited through an LPCVD method. The amorphous silicon is thermally treated for thirsty hr or more at 600 deg.C in a hydrogen atmosphere, and solid-phase grown, thus obtaining a crystallite silicon film 15 less than 100nm. Defect density is reduced by bonding hydrogen with the dangling bonds of the crystallite silicon film 15 in the film 15, it is considered that crystal growth is inhibited by the hydrogen bonds and the film 15 is changed into crystallites, and mobility is improved and the dispersion of threshold voltage can be suppressed when a TFT is constituted.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to thin film transistors (T
This invention relates to a method of manufacturing a semiconductor film suitable for use in FT) and the like.

0002

2. Description of the Related Art Conventionally, amorphous silicon and polycrystalline silicon have been studied as active layer materials for thin film transistors.

[0003] However, amorphous silicon is highly sensitive to light, and its electrical properties change due to light, such as a decrease in resistance, so there is a problem that the manufacturing process becomes complicated, such as the need to form a light-shielding film. .

Therefore, polycrystalline silicon, which has excellent carrier mobility and reliability, is attracting attention. By the way, the following three methods are known as methods for obtaining a polycrystalline silicon film.

The first method is a thermal CVD method. However, although the polycrystalline silicon film obtained by thermal CVD is said to have a structure of microcrystalline silicon, it is known that there are many dangling bonds and many crystal defects in the grain boundaries. There is a problem that carrier mobility cannot be increased.

Next, as second and third methods, methods of modifying an amorphous silicon film to obtain a polycrystalline silicon film are known. This second method is a laser recrystallization method in which an amorphous silicon film is crystallized by scanning with a laser beam. However, since this method uses a laser beam, there are problems with the stability of the laser light source and process problems such as inability to increase productivity.

The third method is a solid phase growth method in which an amorphous silicon film is grown in a solid phase by heat treatment in an inert gas atmosphere such as N2 or Ar. However, although this solid-phase growth method can increase the mobility of the transistor compared to the above-mentioned thermal CVD method, the crystal grains have a grain size of 1 μm or more, which is 10 μm or more.
This becomes a value that cannot be ignored for the channel length of a thin film transistor, which is approximately μm. That is, there is a problem in that the characteristics (particularly the threshold voltage) of the transistor vary depending on the ratio of grain boundaries to the channel.

[0008]

[Problems to be Solved by the Invention] The present invention has been made in view of the various problems mentioned above, and it is an object of the present invention to increase the mobility of a thin film transistor when it is constructed, and to suppress variations in threshold voltage. The object of the present invention is to provide a method for manufacturing a semiconductor film that can perform the following steps.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the method for manufacturing a semiconductor film of the present invention includes heating an amorphous semiconductor film formed on an insulating substrate in a hydrogen atmosphere to crystallize it. It is characterized by allowing

0010

[Operation] By crystallizing an amorphous semiconductor film in a hydrogen atmosphere according to the above manufacturing method, hydrogen bonds to dangling bonds existing at the outer periphery of crystal grains, thereby reducing defect density. Furthermore, hydrogen bonded to dangling bonds on the outer periphery of the crystal grains suppresses crystal growth. In other words, the increase in the crystal grain size of the semiconductor film is suppressed, and for example, when the crystal grain size is several to one
A semiconductor film with crystal grains having a fine grain size of 0.00 nm or less can be obtained.

[0011]

As described above, the semiconductor film formed according to the present invention can have its defect density reduced and its crystal grains can have a fine grain size. Therefore,
Even if a device is configured using the active layer material of a thin film transistor, its mobility can be increased, and variations in the ratio of grain boundaries to the channel length can be ignored, so the threshold voltage varies depending on the device. This has an excellent effect in that it can also suppress this.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on embodiments shown in the drawings. FIG. 1 shows the main cross-sectional structure of a thin film transistor according to an embodiment of the present invention in the order of manufacturing steps. Moreover, FIG. 2 is a schematic configuration diagram of a heat treatment furnace used in this example. below,
This embodiment will be explained in the order of manufacturing steps using FIGS. 1 and 2.

First, an oxide film 12 is formed on the surface of a silicon substrate 11 by thermal oxidation or the like to obtain an insulating substrate 10, and then an LPCV is formed on the insulating substrate 10 as shown in FIG. 1(a).
D (low pressure chemical vapor deposition) method, for example, when the substrate temperature is 58.
A polycrystalline silicon film 13 of about 200 nm is deposited using monosilane gas or disilane gas at 0° C. or higher.

Then, silicon ions are implanted into this polycrystalline silicon film 13 to make it amorphous, thereby obtaining an amorphous silicon film 14 as shown in FIG. 1(b).

Thereafter, the amorphous silicon film 14 is transported to a heat treatment furnace shown in FIG. 2 and grown in a solid phase in a hydrogen atmosphere to form a microcrystalline silicon film 15 as shown in FIG. 1(c).
shall be.

That is, as shown in FIG. 2, an insulating substrate 10 having an amorphous silicon film 14 formed on its surface is held by a sample holder 2 and placed in the interior of a vacuum vessel 1. The sample holder 2 is heated to a temperature of 500 to 700°C, which is the recrystallization temperature of amorphous silicon, by a substrate heater 3.
Desirably, the temperature is set at 550 to 650°C, and in this example, 600°C. In this state, hydrogen is introduced into the vacuum vessel 1 via the mass flow controller 4 at a rate of 20 sccm (20 sccm).
cc/min) and sprayed onto the substrate 10 in an atmosphere of 600°C. The inside of the vacuum container 1 is appropriately evacuated by a vacuum pump 5, and the pressure is reduced to 20To
It is controlled by rr.

By performing solid phase growth in a hydrogen atmosphere for 50 hours or more under the above conditions, the amorphous silicon film 14 is formed into a microcrystalline silicon film 15 with a grain size of 100 nm or less.
becomes.

Elements were formed on the microcrystalline silicon film 15 obtained in the above manner according to the usual process, and as shown in FIG.
) is constructed. In the figure, element isolation is performed using the LOCOS method, and the channel region and source/drain region are formed by implanting boron and arsenic ions, respectively.

Next, evaluation results of the silicon film 15 actually formed by solid phase growth under the above conditions will be explained. In fact, when the crystal structure of a silicon film grown in a solid phase in a hydrogen atmosphere was observed using a transmission electron microscope as in this example, a large number of fine particles were present in a scale of 1 μm, and each Particle size is extremely small, several 10
It was confirmed that the diameter was less than ~100 nm. Further, when evaluated using electron beam diffraction, a ring-shaped diffraction pattern was confirmed, indicating that a large number of microcrystals were assembled.

For comparison, a silicon film grown in solid phase in a conventional N2 atmosphere (the heat treatment temperature of the substrate was 6
Using a transmission electron microscope, we observed the crystal structure of 00℃), and found that the grain size was 1μ in this N2 atmosphere.
Crystal grains of m or more were confirmed. Further, in the evaluation by electron beam diffraction, a spot-like diffraction pattern indicating the presence of a single crystal or a large number of crystal grains each having a relatively large grain size as a single crystal was confirmed.

Furthermore, compared to depositing a microcrystalline silicon film by thermal CVD, by growing amorphous silicon in solid phase in a hydrogen atmosphere as in this example, dangling bonds existing at grain boundaries are eliminated. It is possible to reduce the amount of energy and improve mobility. This is considered to be because the defect density is reduced by hydrogen atoms H terminating the dangling bonds of Si present at the outer periphery of the crystal grains.

Note that the microcrystalline silicon film 1 actually formed
5 has excellent insulation properties with a dark current rate of 10-8 S/cm or less,
It has a photoconductivity of 10-8 S/cm, and the dangling bond density estimated from the electron spin density is 1017
cm-3, which is the same value as that obtained by solid phase growth performed under a normal N2 atmosphere.

As described above, the thin film transistor manufactured according to this example (see FIG. 1(d)) can increase its mobility, and by making the crystal grain size microcrystalline. Variations in the ratio of grain boundaries to the channel length can be ignored, and variations in threshold voltage depending on the device can be prevented. In the above embodiment, the heat treatment is performed for 50 hours or more, but the heat treatment is not limited to this, and the heat treatment may be performed for 30 hours or more.

[0024] Furthermore, the solid phase growth conditions are not limited to those described above. In the above embodiment, hydrogen H2 was introduced into the vacuum vessel, but hydrogen radicals obtained by exciting the hydrogen gas may also be introduced.

Furthermore, in the above embodiment, the amorphous silicon film 14 is obtained by ion-implanting silicon into the polycrystalline silicon film, but the present invention is not limited to this.
In the PCVD method, an amorphous silicon film may be obtained by keeping the substrate temperature at 550° C. or lower and using monosilane gas or disilane gas.

[Brief explanation of drawings]

FIGS. 1A to 1D are cross-sectional views provided in order of process to explain the manufacturing process of a thin film transistor to which an embodiment of the present invention is applied.

FIG. 2 is a schematic diagram of a hydrogen atmosphere heat treatment furnace used in one example.

[Explanation of symbols]

1 Vacuum container 2 Sample holder 3　Substrate heating heater 4 Mass flow controller 5 Vacuum pump 10 Insulating substrate 14 Amorphous silicon film 15 Microcrystalline silicon film

Claims (3)

[Claims] 1. A method for manufacturing a semiconductor film, which comprises heating an amorphous semiconductor film formed on an insulating substrate in a hydrogen atmosphere to crystallize it. 2. The method of manufacturing a semiconductor film according to claim 1, wherein the hydrogen atmosphere is hydrogen gas or hydrogen radicals obtained by exciting hydrogen gas. 3. The heat treatment is performed at 500°C to 700°C.
3. The method of manufacturing a semiconductor film according to claim 1, wherein the temperature is preferably between 550°C and 650°C.