JPS62124736A - Silicon thin-film and manufacture thereof - Google Patents

Abstract

PURPOSE:To increase On currents by approximately one column by manufactur ing a TFT by using silicon thin-films deposited in the same device in order of a silicon thin-film under an amorphous state and a silicon thin-film consisting of a polycrystal from the substrate side. CONSTITUTION:A TFT is manufactured in such a manner that a first layer is brought to a low substrate temperature where a silicon thin-film 2 under an amorphous state is acquired when the first layer is deposited on a substrate 1 and a second layer is brought to a high substrate temperature where a silicon thin-film 3 in which crystalline orientation appears is obtained. The preparation may be conducted by changing a set temperature in the device with locations or at a proper time. Crystalline orientation distinctly appears on the surface of the thin-films having double layer structure by a function, in which the stress of the second polycrystalline thin-film 3 is absorbed by the first amorphous thin-film 2, by employing such a method, and the silicon thin-films with the smooth and uniform surface are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to the production of silicon thin films by low-pressure pyrolysis (hereinafter referred to as LPCVD).
method).

Conventional techniques A method for forming a silicon thin film on an insulating substrate is, for example, developed by Japan J.O.P. Applied Physics (J.
pn J, of Applied Physics)
22, No. 7, 1983, page L438. The substrate is made of sapphire, and the buffer layer is an amorphous silicon film prepared at room temperature by DC quadrupole sputtering.
A silicone epitaxial film was obtained at oo°C.

On the other hand, conventionally, when forming a silicon thin film by the LPCVD method, the substrate temperature was about 600 to 660° C., and the temperature was not intentionally changed.

Further, when the gaseous silicon compound is diluted and created by the LPCVD method, the dilution gas has a constant composition.

Problems to be Solved by the Invention When forming an epitaxial silicon thin film, since the substrate temperature is 100° C., it is necessary to use a large electric furnace with a long soaking length. Furthermore, when semiconductor layers are stacked, impurities in the lower semiconductor layer diffuse during film formation, making it difficult to construct a fine device structure.

LPCVD was developed to solve these drawbacks.
It is the law. In the conventional LPCVD method, when forming an amorphous silicon thin film, the silicon thin film has a smooth surface, but since it is amorphous silicon, the mobility of carriers is low, and when semiconductor devices are created with this The characteristics were bad. On the other hand, silicon thin films in which crystal orientation planes clearly appear have high carrier mobility, but when formed on a substrate, they become white, and non-uniformity is accentuated by dust, dirt, scratches, etc. on the substrate, and the characteristics It was difficult to obtain semiconductor elements with uniform characteristics.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a silicon thin film with a smooth surface, no white rivers, and clearly showing crystal orientation. The silicon thin film according to the present invention can be continuously produced within the same manufacturing apparatus.

The silicon thin film has at least a two-layer structure, with the side near the substrate being an amorphous thin film, and the other layer being a thin film with clear crystal orientation. The first means to obtain this structure is to deposit the first layer on the substrate using a low substrate temperature that allows an amorphous silicon thin film to be obtained, and then to use a high substrate temperature for the second layer to obtain a silicon thin film that exhibits crystal orientation. It is created by adjusting the temperature. This can be done by changing the set temperature inside the device depending on the location or by changing it by taking time into account.

The second method is to change the dilution gas for the silicon compound. This is based on the discovery that even at the same substrate temperature, an amorphous thin film can be obtained with He, while a polycrystalline thin film can be obtained with N2.The layer near the substrate is diluted with He, Next, two layers of silicon thin film are deposited by diluting with N2. This method can also be realized by switching the diluent gas in the device at predetermined intervals.

Effect By using such a method, the first amorphous thin film absorbs the stress of the second polycrystalline thin film, so that the surface of the two-layered thin film has a clear crystal orientation, and moreover, the surface is A smooth and uniform silicon thin film can be obtained.

Example Examples of the present invention will be described below.

Example 1 Using a quartz glass substrate, 5iH420tzccM, He
A mixed gas of 60 s+ccM is introduced into the LPGVD apparatus, and the exhaust amount is controlled so that the degree of vacuum is approximately 0.5 Torr. The deposition time was 60 minutes in each case, with the substrate temperature being 610°C and 630°C. The surface condition was smooth at 610°C, and white at 630°C. Unless carefully cleaned, uneven deposition occurred at 630°C.

From X-ray diffraction, no peak appeared at 610'C, but several peaks such as (220) appeared at 630°C, indicating that it was polycrystalline.

Quartz glass substrate, S 1H420sccM, degree of vacuum 0
．． 5Torr, without changing the substrate temperature of 610℃, S L
When N2 gas e o sccM was used as a diluent gas for H4, peaks such as (220) appeared in the X-ray diffraction pattern, indicating that it was polycrystalline.

Based on these facts, a two-layer silicon thin film according to the present invention was fabricated, and a TPT was fabricated as an application example of a semiconductor device. The method is shown below.

S 1H 420sccM, He 60sccM, degree of vacuum 0.6Torr, substrate temperature of quartz glass substrate 1 6
Deposit 20 to 500 amorphous silicon thin films 2 for 1 to 5 minutes at 10°C, then lower the substrate temperature to 630 to 60°C.
The temperature was increased to 50° C., and approximately 500000000 polycrystalline silicon thin film 3 was deposited for 60 minutes. From the X-ray diffraction pattern, (220
) was obtained at 630° C. to 650° C., which was larger than the peak obtained when a single layer was deposited, and the silicon thin film surface was smooth without white spots. Similar thin films were obtained using both methods: changing the substrate temperature by creating a temperature gradient in the electric furnace and moving the substrate, and changing the temperature of the electric furnace itself.

Next, the surface of the silicon thin film 3 is oxidized by 200 to 300 layers to form a protective film, and then an island-shaped silicon thin film 2.3 is etched, and after removing the 200 to 300 protective oxide film, the silicon thin film 2 is oxidized to form a gate oxide film 11 (FIG. 2(a)).

Contact holes 12 and 13 for source and drain electrodes are formed in the gate oxide film 11, and phosphorus ions are implanted through the holes. This is to ensure ohmic contact between the electrode and the silicon thin film 3. When heat treatment is performed after ion implantation, n-type pocket regions 14 and 15 are formed. A gate electrode 16 and a source are formed on this by a metal evaporation film, for example, an Al evaporation film.

Drain electrodes 17 and 18 are formed. (Figure 2(b))
TPT was created as described above. In this way, the TPT using a silicon thin film having a double structure and produced in the same manufacturing equipment had a larger ○N10FF ratio than the TPT produced using a conventional silicon thin film.

Example 2 1 to 6 under the conditions of SiH 420 sccM, He 60 sacM, vacuum degree 0.5 Torr, and substrate temperature 610°C
Deposit an amorphous silicon thin film for 20-500 min, then add N2 instead of He 60 sccM for 60 s.
Approximately 4,000 polycrystalline silicon thin films were deposited for 60 minutes while flowing ccM. A large peak (220) similar to that in Example 3 was observed in the X-ray diffraction pattern. When changing the diluent gas from He to N2, either when 5lH4 was stopped, that is, the deposition was interrupted, or when the mixing ratio was gradually changed from He to N2 but the deposition was not interrupted.
A similar silicon thin film was obtained. In addition, He and N2
When 2 was mixed, the deposition rate decreased depending on the mixing ratio with SiH4, but the same X-ray diffraction pattern was obtained and the surface was smooth.

Nao, instead of SiH, S i) (cg3. Si
H,,C12゜5iH3C1! , Si2H6 were used to obtain thin films similar to those shown in the examples, although the deposition rate was different.

A TFT having characteristics similar to those shown in Example 1 was also produced using the silicon thin film thus produced.

Effects of the invention When a TPT (thin film transistor) is created using silicon thin films deposited in the same apparatus in the order of an amorphous silicon thin film and a polycrystalline silicon thin film from the substrate side, carrier mobility increases. , the ON current increased by about one order of magnitude.

Also, it is industrially significant because it is possible to create a high-quality silicon thin film with a two-layer structure by using only one device.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a two-layer silicon thin film according to an embodiment of the present invention, and FIG. 2 is a diagram showing a process for producing a TPT using the silicon thin film according to the present invention. 2... Amorphous silicon thin film, 3...
... Polycrystalline silicon thin film, 11 ... Gate oxide film, 16 ... Gate electrode, 17.18 ...
...Source and drain electrodes. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2/ZJ//

Claims (3)

[Claims] (1) X created on the substrate by low pressure pyrolysis method
A first silicon thin film in which a peak indicating a crystal plane does not appear in a diffraction pattern by an X-ray, an electron beam, etc., and a low pressure at which a peak indicating a crystal plane appears in a diffraction pattern by at least an X-ray, an electron beam, etc. on the first silicon thin film; A silicon thin film characterized in that at least a constituent element thereof is a second silicon thin film created by a pyrolysis method. (2) When creating a silicon thin film consisting of at least two layers on a substrate by thermally decomposing a gaseous silicon compound at low pressure, the silicon thin film on the side closer to the substrate becomes amorphous, and the other film becomes polycrystalline. A method for producing a silicon thin film, characterized in that the films are produced at different thermal decomposition temperatures so that the films have different thermal decomposition temperatures. (3) When creating a silicon thin film consisting of at least two layers on a substrate by thermally decomposing the gaseous silicon compound at low pressure, the gaseous silicon compound is heated using He so that the silicon thin film on the side closer to the substrate becomes amorphous. or He
The above gaseous silicon compound is diluted with a mixed gas of N_2 or N_2 so that the other film becomes polycrystalline.
A method for creating a silicon thin film, characterized by diluting it with a mixed gas of _2 and H_2.