JPS6124239A - Manufacture of thin film semiconductor device - Google Patents

Abstract

PURPOSE:To form an excellent oxide film within a short time without heating a substrate at all by a method wherein the substrate coated with a semiconductor thin film is left in the oxidizing gas atmosphere to be irradiated with light including the absorbable wavelength of the semiconductor thin film. CONSTITUTION:A substrate 11 coated with a silicon thin film 10 is placed on a substrate supporter 12 to be contained in a quartz chamber 13 filled with oxidizing gas. As for the oxidizing gas, dry oxygen, wet oxygen, steam in addition to said elements mixed with chlorine gas for getter are applicable in general while as for irradiating light, halogen lamp light or xenon lamp light are applicable. These lamps are provided outside the quartz chamber 13 to prevent them from being exposed to oxidizing atmosphere with the silicon thin film 10 irradiated with the light through quartz material. Most of the irradiating light energy is absorbed into the silicon thin film 10 to be converted into heat energy silicon is provided with high absorption coefficient in the region with wavelength not exceeding 1mum. Resultantly, glass substrate, quartz chamber etc. may not be heated at all with the silicon thin film 10 only heated to forn an excellent oxide film with high dielectric strength and low interfacial level.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for manufacturing a thin film semiconductor device, and particularly to an oxidation step in the manufacturing method.

(Prior Art) Semiconductor devices such as thin film transistors, solar cells, and photosensors are being developed using semiconductor thin films deposited on substrates. A wide variety of materials are used for semiconductor thin films, such as silicon, cadmium selenide, and gallium arsenide. Among them, silicon thin films have a wide range of applicability due to their economic efficiency, reliability, and other characteristics. In these semiconductor devices, an oxide film obtained by directly oxidizing a semiconductor thin film is used as an interlayer insulating film between a semiconductor thin film and an upper wiring layer, and as a gate insulating film of a thin film transistor or photosensor.

As oxidation methods, thermal oxidation, anodic oxidation, and plasma oxidation are well known, but thermal oxidation is superior in that it requires fewer steps and can stably form a high-quality oxide film.

Particularly in silicon thin films, it is frequently used because it provides an oxide film with high dielectric strength and few interface states with the silicon thin film. The thermal oxidation method of a silicon thin film will be explained below as an example.

Conventionally, an electric furnace method has been used as a thermal oxidation method for silicon thin films. Figure 1 shows a typical method.

1 in a quartz tube 2 surrounded by a kanthal heater 1
A silicon thin film 5 deposited on a substrate 4 is placed together with a quartz boat 3, and an oxidizing gas 6 is introduced to raise the ambient temperature to 800°C.
℃~1300℃. As the oxidizing gas 6, oxygen, water vapor, etc. are used. On the fifth surface of the silicon thin film, a silicon oxide film (Si
O2) is formed, and its rate increases as the temperature increases, and as the partial pressure of water vapor increases. Such conventional methods have the following drawbacks.

(1) Since the substrate 4 as well as the silicon thin film 5 is exposed to a high temperature atmosphere, a heat-resistant substrate material must be used. For example, a silicon oxide film coated with quartz or St 02 can be used, but both are expensive and
The drawback is that there are significant restrictions on formation. For forming the semiconductor device described above, it is desirable to use glass as a low-friction, large-area substrate material. However, since the heat resistance limit of glass is about 600° C., it has been impossible to oxidize a silicon thin film on a glass substrate using the electric furnace method.

(2) Regarding temperature control, the electric furnace method is composed of parts with large heat capacity such as a heater, a quartz tube, and a quartz boat for insulation, so it is impossible to raise and lower the temperature in a short period of time.

Therefore, it was unsuitable for short-term acid quenching or fine-grained temperature control.

(3) Quartz tube 2 and quartz boat 3 along with substrate 4
Since these materials are also heated to high temperatures, there is a high possibility that impurities contained in those materials will be incorporated into the oxide film and adversely affect the characteristics of the semiconductor device.

(Purpose of the Invention) The present invention provides a semiconductor thin film deposited on a substrate, which is placed in an oxidizing gas atmosphere, and is irradiated with light containing the light absorption wavelength of the semiconductor thin film in a short time without heating the substrate. The present invention provides a method for manufacturing a thin film semiconductor device that can produce a high quality oxide film.

(Structure and operation of the invention) The present invention will be explained in detail below.

FIG. 2 shows an example of the configuration of a light irradiation oxidation device used in the present invention. 10 is a semiconductor thin film deposited on a substrate 11;
2 is a substrate support stand, 13 is a chamber, and 12 and 13 are both made of quartz. 14 is a light irradiation lamp arranged to irradiate the semiconductor thin film 10 with light all at once; 15 is a light reflection plate; 16 is an oxidizing gas inlet; 17 is an oxidizing gas exhaust port; and 18 is a substrate inlet/outlet.

Next, as an embodiment of the present invention, a method of forming a silicon oxide film on the surface of a silicon thin film deposited on a glass substrate will be described. As the glass substrate material, borosilicate glass, which has relatively good heat resistance and a small coefficient of thermal expansion, is suitable, and in order to stabilize the characteristics of the oxide film, it is desirable to use a material that contains few impurity components such as alkali metals. The silicon thin film is deposited to a thickness of 1100 nm to several μm by sputtering, CVD, vapor deposition, or the like. Silicon thin film 10 and deposited substrate 1
1 is placed on a substrate support stand 12 and installed in a quartz chamber 13. The chamber 13 is filled with oxidizing gas. The oxidizing gas may be the same as the gas used in the electric furnace method, and generally dry oxygen, humidified oxygen, water vapor, and a mixture of these and a chlorine-based gas for getter are used.

As the irradiation light, Norlog 7 lamp light or xenon lamp light is used. These lamps are installed outside the quartz tube (13) to avoid exposure to an acidic atmosphere, and the light is irradiated onto the silicon thin film 10 through the quartz.

Next, the oxidation mechanism will be explained. ) The 10-gen lamp light and the xenon lamp light are light sources having a spectrum in a wide wavelength range ranging from 0.3 μm to 2 μm. The light absorption coefficients of glass and quartz are extremely small in this band, and most of the light energy is absorbed by the glass substrate.

Transmit through the quartz chamber. On the other hand, silicon has a wavelength of 1
Since it has a large light absorption coefficient in the region of μm or less, most of the irradiated light energy is absorbed by the silicon thin film 10 and converted into heat. That is, the glass substrate 2, the chamber, etc. do not generate heat, and only the silicon thin film is heated. The temperature increase rate due to light irradiation reaches several 100° C./second, and the temperature required for oxidation (800° C. or higher) is reached in a short time of 10 seconds or less. The heat generated in the silicon thin film warms the substrate/substrate 11 by thermal conduction, but it takes about 10 seconds to several minutes to raise the temperature of the substrate 11, which has a large heat capacity, to its heat resistance limit. Therefore, if oxidation is completed during this period, a thermal oxide film can be formed without damaging the substrate 11.

The thickness of the oxide film that can be formed by the present invention reaches 50 nm or more in about 30 seconds when a silicon thin film is heated to 1200° C. in a water vapor atmosphere where the oxidation rate is the highest. This value is a practical thickness for a gate insulating film or an interlayer insulating film. The oxide film formed by such a method is considered to be based on the same principle of thermal oxidation as the electric furnace method, and is therefore a high-quality film with high dielectric strength and few interface states. In particular, when oxidizing polycrystalline/recon thin films, high-temperature oxidation of over 1100°C is possible, resulting in a smooth surface morphology (morphology) with a small oxidation rate difference between the inside of the crystal grain and the grain boundary.
can be realized.

Although the present invention has been described above using the oxidation of a silicon thin film as an example, it goes without saying that the present invention is also effective in oxidizing semiconductor thin films other than silicon, such as indium phosphide. Further, as for the light irradiation source, one having a wavelength that heats only the semiconductor thin film without heating the substrate can be selected depending on the type of semiconductor thin film and the type of substrate material. Also,
It is also possible to provide an optical filter between the light source and the sample to irradiate only the desired wavelength. 1. Because the irradiation is carried out all at once, it has the advantage of superior uniformity and production efficiency compared to other light irradiation heating methods that use scanning laser light.

(Effects of the Invention) As explained above, according to the present invention, only the semiconductor thin film on the substrate can be heated without heating the substrate, and a high-quality oxide film can be formed even if a glass substrate with low heat resistance is used. Is possible. In fact, since the temperature needs to be raised and lowered only by a semiconductor thin film with a small heat capacity, high-speed temperature control is possible. Therefore, the short oxidation time can be precisely controlled and the reproducibility of the film thickness can be improved.Furthermore, the temperature recovery time when introducing the substrate, which is required in the electric furnace method, is no longer required, and production This has the advantage of improving efficiency.Also, since the quartz tube and substrate support are hardly heated, impurities contained in them are not incorporated into the oxide film.
A semiconductor device with excellent characteristics can be formed.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus for the electric furnace method, which is a conventional oxidation method, and FIG. 2 is a schematic vertical cross-sectional view showing an example of the configuration of the light irradiation oxidation apparatus of the present invention. 1... Kanthal heater, 2... Quartz tube,
3... Quartz g-), 4.11... Substrate, 5.10.
... Semiconductor thin film, 6... Oxidizing gas, 12... Substrate support stand, 13... Quartz chamber, 14... Light irradiation lamp, 15... Light reflecting plate, 16... Oxidizing gas Inlet, 17... Oxidizing gas outlet, 18... Board entrance/exit.

Claims (2)

[Claims] (1) A semiconductor thin film deposited on a substrate is placed in an oxidizing gas atmosphere, and an oxide film is formed on the surface of the semiconductor thin film by irradiating the semiconductor thin film with light that includes the light absorption wavelength of the semiconductor thin film. 1. A method of manufacturing a thin film semiconductor device, the method comprising the step of forming a thin film semiconductor device. (2) Claim 1, characterized in that a glass substrate is used as the substrate, a silicon thin film is used as the semiconductor thin film, and a gas containing water vapor as the main component is used as the oxidizing gas.
A method for manufacturing a thin film semiconductor device according to section 1.