RU2188878C2 - Method of application of amorphous silicon films and device for realization of this method - Google Patents

Abstract

FIELD: process of obtaining amorphous silicon films. SUBSTANCE: proposed method is based on deposition of decomposition products of silane-containing gaseous mixtures of preheated substrate. Decomposition of gas mixture is effected in highfrequency discharge plasma outside deposition chamber followed by forming supersonic jets flowing to vacuum deposition chamber through system of supersonic nozzles mounted in wall of chamber and so position relative to each other that supersonic jets intersect at distance of about 69% of distance between substrate and nozzles. Device proposed for realization of this method includes vacuum deposition chamber with substrate located inside it, system for delivery of gas mixture and extraction of reaction products as well as unit for generation of active plasma from silane-containing gaseous mixture. Active plasma generation unit is located outside deposition chamber and is connected with this chamber through system of nozzles mounted in wall of deposition chamber which is simultaneously wall of active plasma generation unit. Active plasma generation unit is made in form of electronic unit connected to high- frequency generator containing discharge chamber connected with silane-containing mixture source through pipe union which is simultaneously first electrode; membrane with nozzles found in it performs function of second electrode and is simultaneously used as well of discharge chamber and deposition chamber. EFFECT: simplified procedure of obtaining films; increased productivity due to possibility of applying films of homogeneous thickness, density and composition over extensive surfaces. 3 cl, 3 dwg

Description

 The invention relates to a technology for producing amorphous silicon films and can be used in modern optoelectronics and integrated optics to create thin-film solar cells and large area transistor arrays for liquid crystal displays.

 Known methods for depositing amorphous silicon films by decomposing a silicon-containing gas and precipitating reaction products on a heated substrate, in which a glow discharge is used to decompose the gas mixture (see Japanese applications IPC N 01 L 21/205 6044552 B4, 6091010 B4, 5056648 B4, 5073250 B4 , 1-42125, 6082623 B4, 5068097, IPC H 01 L / 04, 21/205 2-27824 B4). A common drawback of these methods is the low deposition rate and, in addition, the processes in these discharges are fundamentally poorly controlled, since changing any external parameter requires changing almost all the others, thereby causing a change in the composition and electrophysical properties of the films, therefore, the range of conditions under which it is possible get high-quality films, always turns out to be narrow.

There is also known a method of deposition of amorphous silicon films (Japanese application 63-32863, IPC 4 C 23 C 16/24), which consists in the fact that gaseous monosilane is introduced into a vacuum chamber, an electric field is applied and a glow discharge is induced, under which the working decompose gas and deposit the film on the surface of the substrate. The process is carried out at a partial pressure of monosilane 0.2-1 mm Hg, substrate temperature 250-450 ^o C. The deposition rate of silicon with the formation of an amorphous film ≥20 A / s. The reaction products are deposited not only on the substrate, but also on the chamber walls, since the discharge zone is not limited by anything, which leads to an unjustifiably high gas flow rate. This is the main disadvantage of this method.

Closest to the claimed method is a method of deposition of films of hydrogenated silicon (RF patent 2100477, C 23 C 16/24, 16/50). In this method, a silicon-containing gas is supplied from a source with a pressure of 1-200 Top into a vacuum chamber with a pressure of 0.1-10 ^-5 Top through a sound or supersonic nozzle at a pressure of 0.1-10 ^-5 Torr. The gas stream is activated by transmission through an electron-beam plasma, and the film is formed on a substrate located in the gas stream. From the description of the method it is obvious that the device for implementing the known method comprises a vacuum chamber with a heated substrate located therein. A sound or supersonic nozzle is installed at the inlet of the vacuum chamber to supply silicon-containing gas to the chamber. The device also has an electron beam generation unit for activating a silicon-containing gas located in the deposition chamber. The substrate is located at a distance of 50-150 mm from the electron beam. The disadvantage of this method is the technical complexity of the operation of devices for generating electron beams at high gas pressures and limited spraying areas, due to the finite size of the nozzle. In addition, electron beam activation of gases is characterized by a low specific energy input.

 The objective of the present invention is to provide a method for producing films of amorphous silicon and a device for its implementation, providing a simplification of the technology for producing films of amorphous silicon and increasing productivity when applied in mass production due to the possibility of applying a film uniform in thickness, density and composition over large areas.

The specified technical result is achieved by the fact that in the method for producing amorphous silicon films based on the deposition of the decomposition products of a silane-containing gas mixture on a substrate, this mixture is decomposed in a plasma of high-frequency capacitive (RFE) discharge outside the deposition chamber, followed by the formation of supersonic jets from the decomposition products flowing out the deposition chamber, in particular, the decomposition products of the silane-containing mixture are fed into the deposition chamber through a system of supersonic nozzles, while before the deposition begins Ia deposition chamber was evacuated to 10 ^-4 Torr, and the process of decomposition of the gas mixture is carried out at a pressure of 10 ^-2 -1 Torr and power VCHE - discharge 50-100 watts.

The specified technical result is also achieved by the fact that in the device for producing amorphous silicon films containing a deposition chamber with a substrate located therein, a gas mixture supply system and exhaust products of the reaction, as well as an active plasma generation unit, an active plasma generation unit are located outside the deposition chamber and connected with it through a system of nozzles installed in the wall of the deposition chamber, which is also the wall of the active plasma generation unit. In particular, the active plasma generation unit is made in the form of an electrode unit connected to an RF generator and contains a discharge chamber connected through a nozzle to a source of a silane-containing mixture, the nozzle simultaneously serving as the first electrode, and the membrane with located in it with nozzles. The formation of free low-density supersonic jets contributes to the freezing of recombination processes, since density and temperature rapidly decrease with distance from the source in the jet. The film is formed on a substrate located at a distance of 70-100 mm from the nozzle. The substrate temperature is 250-300 ^o C. In this case, the following process parameters are used: the pressure in the discharge chamber of the active plasma generation unit is of the order of 10 ^-2 -1 mm Hg, gas flow rate is about 50 g / s. The RF power is supplied through a feeder 150 mm long, the diameter of the discharge chamber 20 mm, length 35 mm, the electrodes are made of stainless steel. Parameters of the nozzle: diameter 0.75 mm, half-opening Θ = 15 ^o . The nozzle matrix is selected from the condition that the intersection of supersonic jets emerging from the nozzles occurs at a distance equal to ~ 60% of the distance between the nozzles and the substrate, so that a uniform gas mixture flows onto the substrate and a film is deposited that is uniform in thickness and composition. The film is applied to a glass or sieve substrate.

 A search by the sources of patent and other scientific and technical literature showed that the preparation of amorphous silicon films by decomposition of a silane-containing gas mixture in an RFE plasma with the subsequent outflow of plasma with the products of film-forming media into a vacuum chamber through a nozzle system in which free supersonic jets form, not used.

 The method of depositing amorphous silicon films and a device for its implementation is illustrated by drawings, where in FIG. 1 shows a general view of the device, FIG. 2 is a profile of an active plasma generation unit; FIG. 3 - nozzle system.

The apparatus for applying an amorphous silicon film contains a vacuum deposition chamber 1, in which a substrate 3 is located, heated by an ohmic heater, with a thermocouple for temperature control. To create a discharge, an active plasma generation unit 2 is built into the flange of the side surface of the chamber 1. Block 2 is isolated from the walls of the chamber 1 using a fluoroplastic insulator 6. Through the nozzle 5, which is the first electrode, the gas mixture is supplied to the discharge chamber 9 of block 2, the role of the second the electrode is played by a membrane 7, which is in contact with the wall of the chamber 1. A matrix of nozzles 8 is built into the membrane 7, through which the reaction products flow. The distance between the centers of the exit sections of two adjacent nozzles R _t is the distance between the centers of the exit sections, S _t is the distance from the plane of the exit sections of the nozzles to the intersection of the supersonic jets emerging from the nozzles, α is the angle of expansion of the jet.

Power from the RF oscillator is supplied through the feeder 4 to the nozzle 5. The RF oscillator and the chamber 1 are grounded by a common contact through the ground bus. In chamber 1 there is a system for pumping exhaust gases. The substrate 3 is mounted on a holder mounted on a tripod of the table of the working volume at a distance of 70-100 mm from the nozzle, the temperature of the substrate is 250-300 ^o C. The gas flows from the leak through the nozzle 5.

The method of applying a film of amorphous silicon is as follows. Prepared substrates, for example glass or glass, are placed in a vacuum chamber 1 and the chamber is evacuated to a residual pressure of 10 ^-4 mm Hg. Art. then the HF oscillation generator is turned on and silicon-containing gas enters through the nozzle 5 into the discharge chamber 9, in which the HF discharge is initiated, with a gas flow rate of about 50 g / cm, pressure 10 ^-2 -1 mm Hg The discharge power is 50-100 watts. The decomposition products freely flow into the vacuum chamber 1 through a system of nozzles 8 at a supersonic speed, where they are deposited on the substrate 3. The formation of free supersonic jets of low density, in which density and temperature rapidly decrease with distance from the source, is necessary to freeze recombination processes.

.The formation of the coating occurs at a speed of 80-100

.

 In this method of forming films, the contacts of the reactants with the walls of the reactor and the corresponding channels of the secondary reactions associated with heterogeneous processes on the walls are excluded. In addition, this method makes it possible to significantly increase the growth rate without compromising the quality of the films. A nonequilibrium RFE discharge is characterized by a high specific energy input, the efficiency is high due to vibrational excitation of the ground electronic state of the molecules (V.D. Rusanov, A.A. Fridman. Physics of chemically active plasma. - M .: Nauka, 1984). Using a nozzle system allows to increase the area of the deposited surface.

Example 1. Films of amorphous silicon are obtained in the working area of the VUP-5M universal vacuum station, into which an active plasma generation unit, made on the basis of a plasma torch with a discharge chamber, is inserted, where the silane-containing gas mixture decomposes by RF discharge. A plasma stream with decomposition products through a nozzle system with supersonic speed is directed to a substrate opposite the nozzles. The substrates were pre-washed for 1-2 minutes in a 1-2% solution of hydrofluoric acid, followed by washing in water, then an additional activated carbon purification was used. For this, the glass was wiped with activated carbon powder for 1-2 minutes. Prepared glass substrates are placed in a vacuum chamber. The distance from the substrate to the nozzle is 70-100 mm. The substrate is heated by an ohmic heater to 300 ^o C. the Camera is pumped up to 10 ^-4 mm RT.article pumps N-160/700, which are part of the VUP-5M. Initiate a glow discharge to clean the camera. At the end of the etching process, the reaction chamber is again pumped to a pressure of 10 ^-4 mm RT. Art. and a gas mixture of 4.8% SiH ₄ + 95.2% Ar is introduced through the nozzle into the discharge chamber in which the RF discharge is initiated. The pressure is measured by a PMT-2 vacuum gauge. In the discharge chamber of the plasma torch, the pressure is 10 ^-2 -1 mm Hg.

 The decomposition products freely flow into the vacuum chamber through a system of nozzles at a supersonic speed, where they are deposited on a substrate. The formation time of the films is 20 minutes The area of the sprayed film depends on the distance to the substrate and the parameters of the nozzle.

The resulting coating was analyzed on a DRON-5M diffractometer. The analysis showed the absence of reflection from crystallographic planes. This indicates that the structure of these films is noncrystalline. The existence of a homogeneous background suggests that this structure has a short range order, that is, it is amorphous. To accurately determine the film structure from the absorption spectrum, the band gap was found. To record the transmission spectrum, a standard SF-20M spectrophotometer with automatically adjustable slit width was used. The sought value of the band gap E _g = l, 7 eV. According to published data, it corresponds to the band gap of amorphous silicon.

Claims (3)

 1. A method of producing amorphous silicon films based on the deposition of decomposition products of a silane-containing gas mixture on a heated substrate, characterized in that the gas mixture decomposes in the RF RF plasma outside the deposition chamber, followed by the formation of supersonic jets from the decomposition products that flow into the vacuum deposition chamber through a system of supersonic nozzles installed in the chamber wall and located relative to each other from the condition of ensuring intersection of supersonic jets at a distance of about 6 0% of the distance between the substrate and nozzles. 2. A method of producing amorphous silicon films according to claim 1, characterized in that before the deposition begins, the chamber is pumped to a pressure of 10 ^-4 mm RT. Art. and the process of decomposition of the gas mixture is carried out at a pressure of 10 ^-2 -1 mm RT. Art. and discharge power of 50-100 watts.  3. A device for producing amorphous silicon films, containing a vacuum deposition chamber with a substrate located in it, a system for supplying a gas mixture and extracting reaction products, as well as an active plasma generation unit from a silane-containing gas mixture, characterized in that the active plasma generation unit is located outside the chamber deposition and is connected with it through a system of nozzles installed in the wall of the deposition chamber, which is also the wall of the active plasma generation unit, while the active plasma generation unit is made in the form of an electric of the trod block connected to the HF generator, and contains a discharge chamber connected through a nozzle to a source of a silane-containing mixture, the nozzle being both the first electrode and the membrane with nozzles located in it serving as the second electrode and at the same time as the wall of the discharge chamber and the wall of the deposition chamber.

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