JPH04267324A - Semiconductor thin-film substrate and its manufacture - Google Patents

Abstract

PURPOSE:To provide a semiconductor thin-film substrate having a high electron mobility and being free of variation in characteristics and the manufacture of the substrate in the semiconductor thin-film substrate to be used for the formation of a thin film transistor, etc., and the manufacture of the substrate. CONSTITUTION:After a crystal nucleus 4 or polycrystalline thin film composed of silicon-germanium has been formed on an insulating material 2, a semiconductor layer 5 is formed on the crystal nucleus or polycrystalline thin film.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor thin film substrate used for forming thin film transistors and a method for manufacturing the same.

0002

2. Description of the Related Art As semiconductor thin film substrates used in conventional thin film transistors, for example, semiconductor thin film substrates used in thin film transistors for liquid crystal panels include those in which a silicon thin film is formed on a low melting point glass substrate.

Further, as a semiconductor thin film substrate used in a thin film transistor for a semiconductor integrated circuit, there is one in which a silicon thin film is formed on an integrated circuit layer formed on a silicon wafer with an insulating film interposed therebetween.

0004

However, the semiconductor thin film substrate according to the conventional example described above has the following problems.

[0005] For semiconductor thin film substrates in which a silicon thin film is formed on a low melting point glass substrate, the silicon thin film must be formed in a temperature range that does not deform the low melting point glass substrate, that is, at a temperature of 600° C. or lower. Therefore, this thin film has an amorphous structure, making it impossible to obtain a thin film transistor with high electron mobility.

On the other hand, in semiconductor thin film substrates in which a silicon thin film is formed on an integrated circuit layer formed on a silicon wafer through an insulating film, the silicon thin film can be formed at a high temperature of 600° C. or higher, so that a polycrystalline structure can be obtained. Although a silicon thin film can be obtained, a thin film transistor with uniform characteristics cannot be obtained. That is, the crystal grains in the silicon thin film have non-uniform grain shapes and grain sizes, resulting in variations in properties such as electron mobility.

The present invention has been made in view of the above-mentioned circumstances, and aims to provide a semiconductor thin film substrate having high electron mobility and no variation in characteristics, and a method for manufacturing the same.

[0008]

Means for Solving the Problems In order to solve the above problems, the invention as set forth in claim 1 provides a semiconductor thin film substrate characterized by having a silicon-germanium mixed crystal layer on an insulator.

In order to solve the above problem, the invention according to claim 2 is a semiconductor thin film characterized in that a semiconductor layer is formed after forming a crystal nucleus or a polycrystalline thin film made of silicon-germanium on an insulator. This is the method for manufacturing the substrate.

[0010] In order to solve the above problem, the invention according to claim 3 forms an amorphous semiconductor layer on an insulator, and then forms silicon-germanium crystal nuclei or a polycrystalline thin film. The method of manufacturing a semiconductor thin film substrate is characterized by heat treatment at a temperature of °C.

[0011] In order to solve the above problem, the invention according to claim 4 provides a method for manufacturing a semiconductor thin film substrate according to claim 2 or 3, in which silicon-germanium crystal nuclei or polycrystalline thin films are formed using SiH4 gas. The method of manufacturing a semiconductor thin film substrate is characterized in that a mixed gas of GeH4 gas is used, and SiH4 gas or SiH6 gas is used to form a silicon layer.

0012

[Operation] The above technical means operates as follows.

By epitaxially growing a silicon layer on a silicon-germanium polycrystalline thin film or crystal nuclei, a polycrystalline semiconductor thin film substrate with uniform and large grain size can be produced even at a manufacturing temperature of 600° C. or lower. Obtainable. In addition, by forming a silicon-germanium polycrystalline thin film or crystal nuclei on an amorphous semiconductor thin film made of silicon, etc., and heat-treating it, solid-phase epitaxial growth is performed using the polycrystalline semiconductor as a medium. A thin film substrate can be obtained.

[0014] Furthermore, by using a mixed gas of SiH4 gas and GeH4 gas when forming silicon-germanium mixed crystal nuclei and adjusting the mixing ratio of this mixed gas, the particle size of the silicon-germanium mixed crystal liquid can be changed. can be controlled, and large grain size and uniform grain size crystals can be obtained.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings.

(Embodiment 1) FIG. 1 is a cross-sectional structural diagram showing an embodiment of a semiconductor thin film substrate according to the present invention.

The semiconductor thin film substrate in FIG. 1 includes a substrate 3 on which a silicon oxide film 2 is formed on a silicon substrate 1;
It is composed of nuclei 4 made of silicon-germanium formed in dots on this silicon oxide film 2 and a semiconductor thin film made of a silicon layer 5. This silicon layer 5
In this case, the silicon crystal grains have a nearly uniform grain size and shape.

Next, a method for manufacturing the semiconductor thin film substrate shown in FIG. 1 will be explained.

First, a substrate 3 on which a silicon oxide film 2 is formed on a silicon substrate 1 by an ordinary sputtering method is subjected to a CVD process.
Installed inside the reaction chamber of D device. At this time, the reaction chamber contains 5
It is heated to 00 to 600°C and kept in a state where N2 gas is flowed.

Next, after making the reaction chamber a vacuum state,
Flow H2 gas to a pressure of 13 to 140 Pa. continue,
The total gas pressure of this H2 gas is 27 Pa, the partial pressure of SiH4 gas is 1.3 Pa, and the partial pressure of GeH4 gas is 0-1.
5Pa, the balance was switched to a mixed gas of H2 gas, and the pressure was increased to 10
By reacting for ~40 minutes, nuclei 4 made of silicon-germanium are formed scattered on the silicon oxide film 2, and immediately after that, the mixed gas is switched to H2 gas again.

Next, by switching this H2 gas to SiH4 gas or Si2H6 gas and reacting for 4 hours, a silicon layer 5 is deposited on the silicon oxide film 2 in which the nuclei 4 made of silicon-germanium have been formed. A semiconductor thin film substrate as shown in FIG. 1 is obtained.

FIG. 2 shows the silicon oxide film formed on the silicon oxide film 2 using the partial pressure of GeH4 gas in the mixed gas in the reaction chamber heated to 550°C as a parameter.
The nuclear density of germanium nuclei 4 is plotted against the reaction time, that is, the exposure time of the substrate 3 to the mixed gas atmosphere.

In FIG. 2, the vertical axis shows the nuclear density of the silicon-germanium nuclei 4, and the horizontal axis shows the exposure time of the substrate 3 and the mixed gas atmosphere.

As can be understood from the figure, the density of the nuclei 4 made of silicon-germanium is the same as that of Si in the mixed gas.
Mixing ratio of H4 gas and GeH4 gas or substrate 1
can be controlled and adjusted by the exposure time of the mixed gas in the atmosphere.

FIG. 3 shows the results of examining the crystallinity of the semiconductor thin film substrate thus obtained by X-ray diffraction. In the figure, (a) shows only a nucleus 4 made of silicon-germanium formed on a silicon oxide film 2, and (b) shows a case in which a nucleus 4 made of silicon-germanium is formed on a silicon oxide film 2. One in which a silicon layer 5 is formed thereon, and (c) one in which only a silicon layer 5 is formed on a silicon oxide film 2 for reference.

From FIG. 3, it can be seen that when only the silicon layer 5 is formed on the silicon oxide film 2, the silicon layer 5 is amorphous, but the silicon-germanium nucleus 4 formed on the silicon oxide film 2 is polycrystalline, and it can be seen that the silicon layer 5 formed on the silicon oxide film 2 in which the nucleus 4 made of silicon-germanium is formed is polycrystalline. In other words, a silicon film deposited directly on an amorphous layer such as a silicon oxide film is amorphous, but a silicon layer formed on a polycrystalline silicon-germanium nucleus becomes polycrystalline. I understand that.

This is because the silicon-germanium mixed crystal nucleus can be formed as a polycrystalline nucleus on the amorphous layer even at 600° C. or lower, and the silicon layer can be epitaxially grown thereon. thus,
It becomes possible to form a polycrystalline semiconductor thin film using silicon as the main raw material on an amorphous layer at a low temperature of 600° C. or lower.

Furthermore, as shown in FIG. 2, the density of silicon-germanium polycrystalline nuclei on the amorphous layer is
It is determined by the mixing ratio of H4 gas and GeH4 gas and the exposure time of the substrate 3 to this mixed gas, so these should be adjusted and
By controlling this, a polycrystalline semiconductor thin film with uniform and large grain size can be formed.

In particular, in this treatment at 600° C. or lower, the crystal grain size of the silicon layer above it is reduced by reducing the nucleus density of polycrystalline nuclei made of silicon-germanium (1×1010 cm−2 or less). It can be made large (more than 1000 angstroms).

(Embodiment 2) FIG. 4 is a cross-sectional structural diagram showing another embodiment of the semiconductor thin film substrate according to the present invention.

The semiconductor thin film substrate in FIG.
The only difference from the semiconductor thin film substrate according to the present invention is that the polycrystalline silicon-germanium layer formed on the silicon oxide film 2 is a continuous film. On the other hand, in this method of manufacturing a semiconductor thin film substrate, the exposure time of the substrate 3 to the mixed gas atmosphere is set at 40 minutes or more, and the partial pressure of the GeH4 gas is set at 1.5.
This is the same method as in Example 1 except that the pressure was set at Pa or more.

As a result, a polycrystalline silicon-germanium thin film can be formed on the amorphous layer even at temperatures below 600°C.
It has been found that a silicon layer can be grown epitaxially thereon.

Therefore, as in Example 1, it is possible to form a polycrystalline thin film mainly made of silicon on an amorphous layer at a low temperature of 600° C. or lower.

Furthermore, although this example shows an example in which a silicon layer is formed on a polycrystalline silicon-germanium thin film, a substrate in which only a polycrystalline silicon-germanium thin film is formed on a silicon oxide film may be used. Needless to say, it can be used as a semiconductor thin film substrate.

(Embodiment 3) FIG. 5 is a cross-sectional structural diagram showing another embodiment of the semiconductor thin film substrate according to the present invention.

The semiconductor thin film substrate in FIG.
The only difference from this semiconductor thin film substrate is that polycrystalline silicon-germanium cores 4 are formed on a silicon layer 5. This method of manufacturing a semiconductor thin film substrate has the following points: The step of forming the polycrystalline silicon-germanium nucleus 4 is performed after the step of forming the silicon layer 5.
The method was the same as in Example 1, except that a step of heat treatment at 550° C. for 10 hours was added as the final step.

As a result, the amorphous silicon layer 5 formed on the silicon oxide film 2 has polycrystalline silicon-germanium nuclei 4 formed on the silicon layer 5, and is heated at 500 to 600°C. It was found that it can be crystallized by heat treatment for a certain period of time.

Therefore, polycrystalline silicon-germanium nuclei are formed on the amorphous silicon layer, and then heated at 600°C.
By performing heat treatment at the following temperature, it is possible to polycrystallize this amorphous silicon layer by solid phase epitaxial growth using the polycrystalline nuclei as a medium.

Further, in this embodiment, an example was shown in which polycrystalline silicon-germanium nuclei 4 were formed in dots on the silicon layer 5, but it is not a continuous film of polycrystalline silicon-germanium. It goes without saying that similar results can be obtained with
Needless to say, the temperature is appropriately selected within the range of 0°C.

In the above embodiments, polycrystalline silicon-germanium was formed at a temperature of 500 to 600°C by chemical vapor deposition using a SiH4-GeH4 mixed gas.
Alternatively, by exciting a carrier gas, it is possible to form crystalline nuclei or a continuous film at lower temperatures and at higher speeds.

Furthermore, in the present invention, expensive GeH4
The present invention is also economically advantageous since only a small amount of gas is required.

[0042]

As explained above, according to the present invention, silicon-germanium can be formed as a polycrystalline thin film or crystal nucleus on an amorphous substrate even at temperatures below 600°C, and the silicon layer formed thereon can be It can be epitaxially grown.

Furthermore, the density of silicon-germanium crystal nuclei on the amorphous substrate is different from that of SiH4 gas and GeH4 gas.
It is determined by the mixing ratio of each gas in the mixed gas consisting of gas and H2 gas and the exposure time of the amorphous substrate to this mixed gas, so by adjusting and controlling these, the silicon layer formed on it can be It is possible to make the crystal grain size uniform and larger.

Furthermore, according to the present invention, silicon-germanium can be formed as a polycrystalline thin film or crystal nuclei on an amorphous semiconductor layer made of silicon or the like even at temperatures below 600°C, and it can be heated at 500 to 600°C. By processing, this amorphous semiconductor layer can be crystallized by solid phase epitaxial growth using this polycrystalline thin film or crystal nuclei as a medium.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a semiconductor thin film substrate of the present invention.

FIG. 2 is a graph showing the relationship between the exposure time of a silicon oxide film to a mixed gas and the nuclear density at different mixing ratios of SiH4 gas and GeH4 gas.

FIG. 3 is a diagram showing the results of X-ray diffraction showing the crystallinity of a thin film.

FIG. 4 is a sectional view showing another example of the semiconductor thin film substrate of the present invention.

FIG. 5 is a sectional view showing another example of the semiconductor thin film substrate of the present invention.

[Explanation of symbols]

1 Silicon substrate 2 Silicon oxide film 4 Silicon-germanium mixed crystal nucleus 5 Silicon layer

Claims (4)

[Claims] 1. A semiconductor thin film substrate comprising a silicon-germanium mixed crystal layer on an insulator. 2. A method for manufacturing a semiconductor thin film substrate, characterized in that a crystal nucleus or a polycrystalline thin film made of silicon-germanium is formed on an insulator, and then a semiconductor layer is formed. 3. Forming an amorphous semiconductor layer on the insulator,
A method for manufacturing a semiconductor thin film substrate, which comprises forming silicon-germanium crystal nuclei or a polycrystalline thin film, and then heat-treating the resultant at a temperature of 500 to 600°C. 4. The method for manufacturing a semiconductor thin film substrate according to claim 2 or 3, in which silicon-germanium crystal nuclei or polycrystalline thin films are formed using SiH4 gas and GeH4 gas.
4 A mixed gas of SiH4 is used to form the silicon layer.
A method for manufacturing a semiconductor thin film substrate, characterized in that gas or SiH6 gas is used.