JPS60127295A - Production of single crystal of gaas and device therefor - Google Patents

Abstract

PURPOSE:A single crystal of GaAs is produced by the LEC method, as continuous gas flow is formed from the top to downward in the high-pressure vessel, to achieve great increase in yield of production of the thermally stable and semiconductive crystal. CONSTITUTION:The high-pressure vessel 1 is provided inside with heater 2 and with a carbon crucible 3 and pBN crucible 4 on the crucible-driving shaft 5 inside the heater. The melt of GaAs as a starting materials and encapsulating agent of B2O3 are put in the crucibles. In order to allow GaAs single crystal to grow up, the seed crystal 8 is accustomed to the melt 6 for a while, then pulled up, as the shaft 10 is rotated. During the process of crystal growth, an Ar gas pressurized to about 10 atom is continuously fed from the inlet 21 on the top and simultaneously the same volume of the gas is sucked out of the vessel from the outlet 22 on the bottom to form an almost steady downward gas flow.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] This invention relates to a method for pulling up liquid capsules.
The present invention relates to a single crystal manufacturing method and manufacturing apparatus.

[Prior art and problems]

GaAs is a direct transition type semiconductor with a wide forbidden band width, and because it has higher electron mobility than Si and can produce semi-insulating, high-resistivity crystals, it is used as a substrate for high-frequency and high-speed devices. is gaining importance as a G a A
Methods for producing s single crystals are broadly classified into horizontal board growth method (HB method) and liquid capsule pulling method (LEC method). Until now, the HB method has been the mainstream, and semi-insulating crystals have been obtained by doping Cr, which is a deep acceptor impurity, to compensate for shallow donor impurities such as 8i. In a device process in which an active layer is formed using Cr, the redistribution of the added Cr occurs, causing serious problems in device uniformity, reproducibility, and reliability. Recently, in the LEC method, it has become possible to obtain undoped semi-insulating crystals by changing the crucible material from quartz to pyrolytic boron nitride (pBN), so it has become a semi-insulating substrate manufacturing method. The emphasis has shifted to the LEC method. However, the manufacturing technology for undoped semi-insulating crystals using the LEC method has not yet been fully established, and the reproducibility and stability of semi-insulating crystal manufacturing are limited.
There are various problems with the uniformity and stability of crystal properties.

The mechanism behind undoped semi-insulating properties using the LEC method is that the intrinsic defect called EL2, which forms a deep donor level, becomes the center of compensation for shallow acceptor impurities such as carbon, and as a result, the Fermi level falls below the forbidden band. It is thought that it will be located roughly in the center,
The EL2 concentration of the crystal changes sensitively depending on the crystal manufacturing conditions such as the composition ratio of the starting material melt and the pulling speed, and the contamination of electrically active impurities such as carbon varies greatly depending on the cleanliness of the crystal manufacturing atmosphere. This is because there are many factors that make the compensation effect unstable. That is, the composition ratio of the starting material melt is lower than the stoichiometric composition ratio.
As the EL2 concentration becomes excessive, the EL2 concentration decreases, and the resistivity of the crystal decreases accordingly.

It has been reported that P-type conductivity is exhibited (
J, Appl, Phs,, vnl, 53, m8
(1982, 5771) Since it is technically difficult to control the stoichiometric composition ratio in the LEC method, a deviation occurs in the composition ratio of the raw material melt between the early and late stages of crystal growth. Therefore, it is often difficult to stably obtain the desired semi-insulating region throughout the pulled ingot.

In addition, there are many impurities mixed in from the crystal manufacturing atmosphere, and in addition to the above-mentioned compensation effect of shallow acceptor impurities such as EL2 and carbon, compensation of shallow donor and acceptor impurities is added, and the case becomes semi-insulating. There is. When such a substrate is subjected to a process, the heat treatment during the process tends to cause a decrease in resistivity and a change in conductivity type.

Therefore, in the production of single crystals using the LEC method, important issues are improving the yield through semi-insulating control with good reproducibility and creating stable semi-insulating crystals that are not subject to thermal transformation during the process.

[Purpose of the invention]

The present invention is an attempt to improve the above-mentioned drawbacks in the production of semi-insulating GaAs by the LEC method, and particularly to provide a method and apparatus that can significantly improve the production yield of thermally stable semi-insulating crystals. The purpose is

[Summary of the invention]

That is, the present invention provides pGa by LEC method in a high-pressure container.
In producing As single crystal, As from the raw material melt
The pressurized inert gas needed to suppress the evaporation of the crystals cannot be simply sealed and stored near the crystal growth field as in the past, but instead the pressurized inert gas is continuously supplied and exhausted. It is characterized by producing a continuous and steady flow of gas from above to below in the vicinity of the crystal growth field.

Furthermore, the method is characterized in that the supplied gas is heated in advance in order to reduce the temperature difference between the supplied gas and the crystal growth atmosphere. Further, a gas circulation circuit is provided for reusing the exhaust gas as a supply gas. This circulation circuit is provided with a pressure booster to control the pressure of the pressurized supply gas to a constant level, a filtration device to purify the exhaust gas, and an auxiliary heating device to keep the temperature of the pressurized supply gas constant at a high temperature. It is characterized by

〔Effect of the invention〕

As in the present invention, by continuously supplying and exhausting pressurized inert gas, cleanliness near the crystal growth field is maintained,
It goes without saying that the contamination of impurities into the crystal raw material melt is reduced, but by forming a continuous flow of the inert gas from above to below, it is possible to reduce the incorporation of impurities into the crystal raw material melt. The inherent problem of impurities floating up due to high-pressure gas convection can be suppressed, and contamination of impurities into the raw material melt due to such floating can be minimized. In particular, carbon is used as a material for heaters, heat-insulating cylinders, etc. in the crystal growth furnace section from the viewpoint of thermal properties and economy, and the above-mentioned method can greatly suppress the contamination of carbon. This leads to stability of the compensation effect by EL2 mentioned above. That is, even if the EL2 concentration varies depending on the pulling conditions, the shallow acceptor impurity can be sufficiently compensated for, so that free carriers are not generated and the resistance is high enough to maintain semi-insulating characteristics. Furthermore, as mentioned above, the improved cleanliness of the crystal growth atmosphere simultaneously suppresses the contamination of other electrically active impurities, making it possible to produce crystals with high purity and high free carrier mobility with a low degree of compensation. can get. Such crystals are thermally stable and do not undergo thermal transformation during device processes.

In addition, by supplying preheated gas, it is possible to not only eliminate disturbances in crystal growth due to large temperature differences between the supply gas and the crystal growth atmosphere, but also to adjust the temperature of the supply gas appropriately. It is possible to further stabilize the thermal environment that fluctuates as crystal growth progresses, leading to improved stability in single crystal production.

Furthermore, by providing a gas circulation circuit for reusing the exhausted gas as supply gas, the consumption of a large amount of gas caused by continuously supplying and exhausting gas can be suppressed, and as a result, the present invention can be made more effective. Become.

[Embodiments of the invention]

Examples according to the present invention will be described below.

Example 1 FIGS. 1 and 2 respectively show the conventional LEC method--
The method for producing a G a As single crystal and the L of the present invention
FIG. 2 is an explanatory diagram of a method for manufacturing a GaAs single crystal using an EC method. 1 is a high-pressure container in which a heater 2 is installed, and a carbon crucible 3 and a pBN crucible 4 in the high-pressure container.
is provided on the crucible drive shaft 5. 6 is a GaAs raw material melt, and 7 is B2O3 which is a capsule. Ga
To grow the As science crystal 9, the seed crystal 8 is made to bite into the raw material melt 6, and then pulled up while rotating the pulling shaft 10. In the conventional method, crystal growth is performed while the inert atmospheric gas pressurized and filled into the high-pressure container 1 is confined, so a complex high-pressure gas convection 12 occurs within the high-pressure container 1. Impurity sources such as carbon dust generated from the heater 2, carbon crucible 3, heat insulating cylinder 12, etc. were caused to convect within the high pressure container.

In this example, a pBN crucible with an inner diameter of 96 m contains 100% G
An aAs raw material melt was prepared, and a 2-inch GaAs crystal was pulled at a speed of about 10 m/Hr while rotating the pulling shaft at a speed of about 3 r, p, m. In the crystal creation process, gas pressurized to about 10 atmospheres is continuously supplied into the high-pressure container from the upper gas supply port 21 at a rate of about 20 t/min, and at the same time, the same amount of gas is exhausted from the lower gas exhaust port 22. As a result, an almost constant upward-to-downward gas flow 13 was formed within the high-pressure vessel. This means that
This was confirmed by the fact that carbon dust, etc., which had been observed using conventional methods (visually), disappeared. When the resistivity of the crystal obtained by the above method was measured, it showed a value of 10Ω above the subplate from the head to the tail of the ingot, as shown in Figure 3 (a), indicating uniform semi-insulating properties. Obtained. Comparing this result with the results obtained by the conventional method (b) in Figure 3, the results obtained by the conventional method showed that semi-insulating properties could be obtained at a solidification rate of 0.2 to 0.5, but K was not too high. In the present invention, the solidification rate is 0.
Semi-insulating properties were obtained over the entire 2-inch straight body portion of 1 to 0.9. Furthermore, in both the conventional method and the method of the present invention, the conductivity type in the semi-insulating region was n-type, but in the conventional method, the electron mobility in the semi-insulating region was ~ The book was about 3000 ctI/v, s, ec, but by the method of the present invention, it was about 400 ctI/v, s, ec.
It became significantly larger than 0 cJ/v, sec. When the semi-insulating crystal substrates obtained by both methods were heat-treated at 850°C for 30 minutes in a hydrogen atmosphere and changes in resistivity were investigated, the resistivity of the substrates obtained by the conventional method was ~1oΩ.
- Although the resistivity decreased to 10 to 1 OΩ·m compared to (7), no change in resistivity was observed at all due to the heat treatment in the substrate prepared by the method of the present invention.

Example 2 In this example, as shown in FIG. 4, an auxiliary heating device 42 is provided in the gas supply system 41 to preheat the supplied gas to ~500°C, which is higher than the ~300°C temperature near the inner wall of the high-pressure vessel. We used a method of supplying Up until now, in order to reduce thermal distortion etc. in the growing crystal, a heat insulating cylinder etc. have been installed to reduce the temperature gradient in the furnace, but the method of this example allows for easy reduction of the temperature gradient in the furnace without using a heat insulating cylinder etc. The temperature gradient was reduced, and in addition to the same or better effects as in the example in terms of electrical properties such as resistivity, the thermal strain in the crystal was further reduced. That is, since the method of the present invention eliminates the contamination of impurities from the heat insulating cylinder, it has become possible to more stable control of semi-insulating properties in the production of single crystals. Furthermore, by simply adjusting the temperature of the supplied gas, it is possible to optimize the temperature gradient within the furnace according to the crystal manufacturing conditions, resulting in a reduction in thermal strain in the crystal and an improvement in crystal manufacturing yield. Ta.

Example 3 In this example, a gas circulation circuit was provided to use the gas exhausted in the above example as a supply gas again. As shown in FIG. 5, this circulation circuit includes a filtration device 51 for removing impurities in the exhaust gas, a booster 52 for adjusting the pressure and flow rate of the supply gas, and the supply gas already shown in Example 2. Auxiliary heating device 4 for adjusting gas temperature
2 in the series. This method has great industrial advantages because the effects of the present invention shown in Example 2 can be obtained without consuming a large amount of gas.

[Other embodiments of the invention]

In the embodiments described above, all semi-insulating Ga A
Although the present invention relates to the production of single crystals, it is clear from its principle that the application of the present invention is not limited thereto. Even when manufacturing conductive GaAs crystals by intentionally adding impurities, suppressing the incorporation of undesirable impurities is fundamental to controlling semiconductor characteristics, and the present invention is applicable to this. and its effects will be demonstrated. Further, by applying the present invention to GaP, InP, etc. other than GaAs crystals, which are manufactured by the same LEC method, it becomes possible to manufacture high-purity, high-quality crystals.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the conventional method, FIG. 2 is a diagram for explaining the present invention in detail, FIG. 3 is a diagram for explaining the present invention in detail, and FIGS. 4 and 5 are diagrams for explaining the present invention in detail. FIG. 6 is a diagram illustrating Examples 2 and 3 of the present invention, respectively. DESCRIPTION OF SYMBOLS 1... High pressure container, 2... Heater, 3... Carbon crucible, 4... PBN crucible, 5... Crucible drive shaft, 6... Raw material melt, 7... Btus, 8 ... Amber crystal, 9 ... Single crystal, 10 ... Pulling shaft, 11 ... Heat insulation cylinder, 12 ... High pressure gas convection, 13 ... Steady gas flow, 21 ... Gas supply Port, 22... Gas exhaust port, 41
...Gas supply system, 42...Auxiliary heating device, 51...
- Filtration device, 52...pressure boosting device.

Claims (4)

[Claims] (1) GaA obtained by liquid capsule pulling method in a high-pressure container
In producing the GaAs single crystal, a continuous flow of gas is produced from the top to the bottom of the high-pressure container by means of continuously supplying and exhausting pressurized inert gas. Production method. (2) The method for producing a Ga, As single crystal according to claim 1, wherein the pressurized inert gas is a preheated gas. (3) GaA by liquid capsule pulling method in a high-pressure container
1. An apparatus for producing a GaAs single crystal, characterized in that the apparatus is equipped with a gas circulation circuit for continuously supplying and exhausting pressurized inert gas. (4) The GaAs single crystal manufacturing apparatus according to claim 3, wherein the gas circulation circuit includes a filtration device, a pressure booster, and an auxiliary heating device.