JPH0355432B2 - - Google Patents

Description

Detailed Description of the Invention Field of Industrial Use For example, when forming - group compound semiconductor devices such as gallium phosphide (GaP) and gallium arsenide (GaAs), epitaxial growth is performed on a - group semiconductor substrate as a starting material. It is essential to grow layers and a boat is required during this epitaxial growth. In addition, the boat is highly heat resistant,
Moreover, it must have high purity, and carbon members are widely used as members for forming this.

The present invention thus relates to a high purity processing method for purifying carbon members used in fields where high purity is required.

Structure and Problems of Conventional Examples In epitaxial growth, various impurities are doped as donors and acceptors. Carbon is generally used in this epitaxial growth process. However, carbon, which is a member forming the boat, has a strong adsorption effect on impurities, and therefore, the carbon boat adsorbs a large amount of these impurities during epitaxial growth. By the way, carbon boats are used repeatedly in the epitaxial growth process, and if the purification process is insufficient, the next epitaxial layer to be grown will be contaminated, and the characteristics of the resulting semiconductor device will be greatly affected. .

For example, nitrogen (N)-doped GaP (marginal) light emitting diodes (LEDs) or GaAsP (yellow) LEDs.
As the donor concentration of the n-layer is lowered, the luminous output is improved. However, if the carbon boat is insufficiently purified and donor impurities remain, it is impossible to grow an epitaxial layer with a low donor concentration.
The light output of the LED decreases. Furthermore, if acceptor impurities remain, this acceptor impurity causes a characteristic defect in which a part of the n-layer is inverted to a p-layer.

In this way, in epitaxial growth,
Purification treatment of carbon boats is essential.

Conventionally, for this purification treatment, a method has been adopted in which carbon boats are heat treated in a resistance heating furnace. In this method, the quartz tube was directly heated, so the heat treatment temperature could not be raised above the melting point of quartz (approximately 1200°C), and the purification effect was small. For this reason, carbon boats are purified by performing heat treatment over a long period of time in hydrogen, vacuum, or halogen gas. In this method, the purification process takes time and workability is significantly impaired.

Furthermore, since the quartz tube is directly heated, silicon (Si) contamination from the quartz cannot be avoided, and this silicon contamination causes deterioration of characteristics.

Purpose of the Invention The present invention is capable of completely removing impurities adsorbed on carbon members such as carbon boats, and eliminating silicon contamination from quartz, and is particularly suitable for use in carbon boats for growing highly pure epitaxial layers. The purpose of the present invention is to provide a method for purifying a carbon member, which is suitable for purifying a carbon member.

Structure of the Invention In the carbon member purification treatment method of the present invention, instead of the conventional heat treatment using the resistance heating method, a high frequency induction heating method that can selectively heat only the carbon member is adopted, The carbon member is heat-treated using this heating method in a vacuum or under reduced pressure. According to this method, unlike the resistance heating method, the quartz tube is not directly heated, so it is possible to set the heat treatment temperature to a temperature that exceeds the melting point of quartz, which not only increases purification efficiency. However, by lowering the heating temperature of the quartz tube, silicon contamination from the quartz tube can be significantly reduced. Furthermore, since the heat treatment is performed in a vacuum or under reduced pressure, impurities can be easily evaporated and impurities adsorbed deep within the carbon member can also be removed.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows a schematic diagram of a carbon member purification treatment apparatus that enables the purification treatment method of the present invention. As shown in the figure, the carbon member purification processing device includes a quartz tube 1, a high-frequency coil 2 surrounding the outer periphery of the quartz tube, a flange 3 that closes the open end of the quartz tube, and a flange 3 connected to one end of the quartz tube 1. It consists of an exhaust pipe 4, a vacuum pump 5 connected to the exhaust pipe, and a three-way cock 6, and the carbon member 7 to be purified is thermally insulated from the quartz tube 1 by a heat insulator. It is arranged as follows.

In the purification treatment method of the present invention using the purification treatment apparatus configured as described above, the quartz tube 1 is not heated, but only the carbon member 7 disposed inside the quartz tube 1 is heated. Therefore, the evaporation of silicon from the quartz tube 1, which was a problem in the conventional purification treatment method using resistance heating, is effectively suppressed, and silicon contamination is extremely reduced.

Further, since only the carbon member 7 is selectively heated, it becomes possible to heat the carbon member 7 to a temperature of 1500° C. or more, and the purification treatment effect is dramatically improved. In the epitaxial growth of − group compound semiconductors, zinc (Zn), magnesium (Mg), etc. are used as acceptor impurities.
On the other hand, sulfur (S), tellurium (Te), etc. are used as donor impurities. In order to remove these impurities from the adsorbed carbon member, it is desirable to perform heat treatment at a high temperature higher than the boiling point. The boiling point of Zn is 907℃, the boiling point of Mg is 1107℃, S
The boiling point of Te is 444℃, and the boiling point of Te is 1390℃.

The above-mentioned temperature of 1500°C exceeds the boiling point of any of them and is sufficient as the temperature for each treatment. However, it is difficult to remove impurities adsorbed deep into the carbon member 7 by heat treatment in a gas at 1 atm. In the present invention, the heat treatment is further performed in vacuum or reduced pressure to promote evaporation of impurities and to significantly shorten the purification treatment time for the carbon member.

Next, a specific example of the purification treatment of carbon boats by the method of the present invention will be explained.

Figure 2 shows a carbon boat once used in the epitaxial growth process that is heated by high-frequency induction heating.
After heating to 1500℃ and heat treatment in a vacuum of 5 × 10 ^-3 Torr, the carbon boat was used to remove 20μ from the surface of the GaP epitaxial layer grown by the liquid phase method.
FIG. 3 is a diagram showing the relationship between the impurity concentration at a depth of m and the time of the above heat treatment performed on the carbon boat.

As shown in the figure, as the heat treatment time increases, the carbon boats become more purified and the donor impurity concentration of the grown GaP epitaxial layer decreases. When the heat treatment time exceeds 3 hours, the donor impurity concentration decreases to a low concentration (2×10 ¹⁶ cm ⁻³ ) necessary to obtain high luminous output. That is, the carbon boat is treated to a high degree of purity through the heat treatment for 3 hours.

Figure 3 shows a carbon boat heat-treated for 3 hours in a vacuum of 5 x 10 ^-3 Torr at a temperature of 1500℃ using the purification treatment equipment shown in Figure 1 based on the above study results, and a conventional carbon boat. 1100℃ using resistance heating furnace
The following is a comparison result of the impurity concentration distribution when a GaP epitaxial layer was grown in liquid phase using a carbon boat heat-treated at a temperature of , the same degree of vacuum, and for the same time as above. In the figure, the impurity concentration distribution of A was grown using a boat that underwent the purification treatment of the present invention.
Shows the impurity concentration distribution of the GaP epitaxial layer,
Furthermore, the impurity concentration distribution of B is shown as the impurity concentration distribution of a GaP epitaxial layer grown using a carbon boat that has been purified using a resistance heating furnace.

According to the method of the present invention, not only the purification effect is greatly increased, but also the silicon contamination from the quartz tube is greatly reduced, so that the donor impurity concentration of the GaP epitaxial layer grown as shown in the figure is lower than that of the conventional method. This is about one-fourth of the GaP epitaxial layer grown using carbon boats purified by this method.

Furthermore, if a nitrogen-doped GaP (green) LED is formed by liquid-phase epitaxial growth using a carbon boat that has been purified using the method of the present invention, it becomes possible to reduce the donor concentration of the n-layer, making it possible to seal the n-layer with resin. The luminous efficiency of the nitrogen-doped GaP (green) LED was approximately 50% compared to the conventional efficiency (0.3%).
It was confirmed that there was an improvement.

Effects of the Invention As is clear from the above explanation, according to the purification treatment method of the present invention, all impurities adsorbed on the carbon member can be removed in a short time, and silicon contamination from quartz is also eliminated. By treating a carbon boat for epitaxial growth with the method of the present invention, it becomes possible to grow a highly pure epitaxial layer.

According to the method of the present invention, it is possible to produce highly efficient light emitting diodes and other semiconductor devices having highly pure epitaxial layers.

[Brief explanation of drawings]

Figure 1 is a diagram showing an outline of a purification treatment apparatus that enables the purification treatment method of the present invention, and Figure 2 is a diagram showing a GaP epitaxy grown using a carbon boat that has been purified with the purification treatment apparatus shown in Figure 1. Figure 3 shows the dependence of the impurity concentration of the layer on the purification treatment time. FIG. 4 is a diagram showing a comparison of impurity concentration distributions when double growth is performed. 1...Quartz tube, 2...High frequency coil, 3
...Flange, 4...Exhaust pipe, 5...Vacuum pump, 6...3-way socket, 7...Carbon member,
8...Insulator.

Claims (1)

[Claims] 1. A carbon member used in liquid phase epitaxial growth is placed in a quartz tube kept in a vacuum or reduced pressure state, and then heat treatment is performed once in which only the carbon member is heated to a temperature equal to or higher than the melting point of quartz using high-frequency heating. A method for purifying a carbon member, which comprises removing impurities adsorbed therein in a process.