JPH0784360B2 - Method for manufacturing semi-insulating GaAs substrate - Google Patents

Description

The present invention relates to a method for manufacturing an impurity-free semi-insulating GaAs substrate having a specific resistance of 10 ⁷ Ωcm or more, which is used as a substrate for LSIs and ICs.

[Conventional technology]

Since GaAs has a higher electron mobility than Si, it is used as a substrate for microwave communication devices, and is expanding its application as a substrate for next-generation ultra-high speed integrated circuit devices. This GaAs substrate is usually manufactured from an ingot obtained by a liquid sealing pulling method (hereinafter abbreviated as LEC method) or a horizontal Bridgman method in which chromium is added (hereinafter abbreviated as HB method). However, in an element manufactured by growing an epitaxial film on a GaAs substrate, the GaAs substrate obtained by the HB method has a low dislocation density, but has a bad influence on the epitaxial film of chromium added to the substrate, Additive-free semi-insulating Ga
Supply of As substrate is desired. Further, the GaAs substrate obtained by the LEC method is not used because of its high dislocation density, although it has no additive semi-insulating property.

In order to solve these problems, the vertical temperature gradient method (hereinafter VGF
Method is abbreviated), but GaAs obtained by VGF method
Although the substrate has the same dislocation density as the GaAs substrate obtained by the HB method, the specific resistance remains in the 10 ⁵ Ωcm range.

For LSI and IC substrates, it is important that the electrical resistance between the elements is good, and that high specific resistance is possible in order to enable high integration. Generally, it is required to be 10 ⁷ Ωcm or more. There is. However, the specific resistance of the substrate obtained by the VGF method is too low as described above, so that the electrical isolation between the elements is incomplete and the leakage current through the substrate becomes a problem.

[Problems to be Solved by the Invention]

An object of the present invention is to provide a method for obtaining a semi-insulating GaAs substrate having no impurities added, a low dislocation density, and a specific resistance of 10 ⁷ Ωcm or more.

[Means for Solving the Problems]

In order to achieve the above object, the first aspect of the present invention is to use a VGF method to obtain Ga with a carbon atom concentration of less than 1 × 10 ¹⁵ cm ^{−3 and} no impurities.
Characteristic in that As crystals are grown and then gradually cooled to 650 to 800 ° C., then cooled to 450 ° C. or less at a rate of 10 to 1000 ° C. per minute from the temperature, and the obtained crystals are cut into wafers. There is.

The second aspect of the present invention is that the carbon atom concentration is 1 × 10 ¹⁵ by the VGF method.
Cultivate GaAs crystal with less than ³ cm ^-3 without impurities at 450 ℃
After gradual cooling to the following, followed by heat treatment at 800 to 1200 ° C. and holding at this temperature for 1 to 100 hours, gradual cooling from that temperature to 650 to 800 ° C. and 10 to every minute from that temperature 1000
It is characterized in that it is cooled to 450 ° C or lower at a rate of ℃ and the obtained crystal is cut into a wafer.

The third aspect of the present invention is that the carbon atom concentration is 1 × 10 ¹⁵ by the VGF method.
Cultivate GaAs crystal with less than ³ cm ^-3 without impurities at 450 ℃
After gradual cooling to the temperature below, continue heating at 650 to 800 ° C and maintain this temperature for 1 minute to 10 hours, then 10 to 10 minutes per minute from the temperature.
It is characterized in that it is cooled to 450 ° C. or less at a rate of 00 ° C. and the obtained crystal is cut into a wafer.

In the fourth aspect of the present invention, a GaAs crystal obtained by the VGF method having a carbon atom concentration of 1 × 10 ¹⁵ pieces / cm ^{−3 and} containing no impurities is 10 ^−6.
In vacuum evacuated to less than torr, or in an inert gas or hydrogen gas stream, heat to 800-1200 ° C and keep this temperature at 1-1.
After heat treatment for 00 hours, 650-800 ℃
It is characterized in that it is gradually cooled to 450 ° C. or less at a rate of 10 to 1000 ° C./min and the obtained crystal is cut into a wafer.

Further, the fifth is GaAs crystal undoped below the obtained carbon atom concentration 1 × 10 ¹⁵ atoms cm ^-3 by the VGF method of the present invention, 10 ^-6
After heating to 650 to 800 ° C and maintaining this temperature for 1 minute to 10 hours in a vacuum depressurized to torr or less, or in an inert gas or hydrogen gas stream, a rate of 10 to 1000 ° C per minute from the temperature. so
It is characterized in that it is cooled to 450 ° C or less and cut into wafers.

Further, the sixth invention after cutting the GaAs crystal of undoped obtained fewer carbon atom concentration 1 × 10 ¹⁵ atoms cm ^-3 by the VGF method the wafer shape and vacuum below 10 ^-6 torr vacuum After performing a heat treatment in which it is heated to 800 to 1200 ° C. and kept at this temperature for 1 to 100 hours in an inert gas or hydrogen gas stream, the temperature is gradually cooled to 650 to 800 ° C. From every minute
It is characterized in that it is cooled to 450 ° C or less at a rate of 10 to 1000 ° C.

In the seventh aspect of the present invention, a GaAs crystal having a carbon atom concentration of less than 1 × 10 ¹⁵ cm ^-3 obtained by the VGF method and containing no impurities is cut into a wafer, and then the vacuum is reduced to 10 ^-6 torr or less. After heating to 650 to 800 ° C in an inert gas or hydrogen gas stream and maintaining this temperature for 1 minute to 10 hours, cool it to 450 ° C or less at a rate of 10 to 1000 ° C per minute. There is a feature in doing it.

[Action]

In the GaAs crystal obtained by the LEC method, the concentration of residual carbon atoms that are acceptors is rarely lower than 1 × 10 ¹⁵ cm ^-3 . In that case, as shown in FIG.
When heat-treated in the temperature range of up to 650 ℃, a donor level located below 0.43 eV in the conduction band (hereinafter abbreviated as a deep donor level) is generated and the specific resistance is reduced to 10 ⁷ Ωcm or less. It has been confirmed by the present inventors that the deep donor level disappears and the specific resistance is restored to 10 ⁷ Ωcm or more by heat treatment at 450 ° C. and rapid cooling to 450 ° C. or less.

The present invention is based on the above findings. That is, in the GaAs crystal obtained by the VGF method, since the carbon member is not contained in the crystal growing tube, the carbon atom concentration is always 1 × 10 ¹⁵ cm 2.
^Since it is ^-3 or less and the cooling after growth is gradual cooling, the deep donor level as described above is generated, and the specific resistance decreases to the order of 10 ⁵ Ωcm. When this crystal is given a thermal history of quenching in the temperature range from 650 to 800 ℃ to 450 ℃ or less, the deep donor level disappears and the specific resistance becomes 10 ⁷ Ωcm or more.

The upper limit of the temperature at the start of quenching is 800 ° C, because the crystal may be destroyed by thermal strain above this, and the lower limit is 650 ° C. This is because it does not rise effectively. The upper limit of the cooling rate is 1000 ° C per minute because practically no further rapid cooling is necessary, and the lower limit of 10 ° C per minute is effective to increase the specific resistance below this. Because not.

This can be applied to a cooling process after the growth of a single crystal or a heat treatment that is performed after the cooling after the growth of a single crystal. First, a GaAs crystal without impurities was grown by the VGF method and then gradually cooled to 650 to 800 ° C.
By quenching to 450 ° C or less, the deep donor level is extinguished and a specific resistance of 10 ⁷ Ωcm or more can be obtained.

In addition, a GaAs crystal containing no impurities was grown by the VGF method, and was gradually cooled to 450 ° C or less, then heated to 800 to 1200 ° C and kept at this temperature for 1 to 100 hours to make the structure uniform. After that, the temperature may be gradually cooled to 650 to 800 ° C. and then to 450 ° C. or lower to extinguish the deep donor level and make the specific resistance 10 ⁷ Ωcm or more. Furthermore, according to a method in which after gradually cooling to 450 ° C. or lower, it is subsequently heated to 650 to 800 ° C. and kept at this temperature for 1 minute to 10 hours for homogenization, and then rapidly cooled from that temperature to 450 ° C. or lower. It is possible to eliminate the deep donor level and obtain a specific resistance of 10 ⁷ Ωcm or more.

In these methods, as compared with the method of taking out the ingot after the crystal production from the quartz sealed tube and subjecting it to heat treatment, the deep donor level can be eliminated in a part of the cooling process after the crystal growth, so that the productivity is improved. There are also advantages.

Eliminating the deep donor level and setting the specific resistance to 10 ⁷ Ωcm or more can be applied to a crystal subjected to heat treatment for homogenization after the crystal is manufactured.

800 to 12 GaAs crystal without impurities added by VGF method
After performing a heat treatment of holding at 00 ° C. for 1 to 100 hours, gradually cooling from the temperature to 650 to 800 ° C., and then rapidly cooling from the temperature to 450 ° C. or less to eliminate the deep donor level 10 ⁷ Ωc
Obtain a specific resistance of m or more. In addition, a GaAs crystal obtained by the VGF method with a carbon atom concentration of 1 × 10 ¹⁵ pieces / cm ^{-3 and} no impurities added
A method of heating to 650 to 800 ° C. and maintaining at this temperature for 1 minute to 10 hours and then rapidly cooling from that temperature to 450 ° C. or less can also eliminate the deep donor level and obtain a pulling resistance of 10 ⁷ Ωcm or more. With such heat treatment, the same effect can be expected even if the GaAs crystal is in the form of a wafer.

If it is cut into a wafer before obtaining this heat treatment, the thermal strain introduced into the crystal by quenching can be somewhat reduced, so a higher cooling rate can be applied as compared with the case of the ingot. . The preferred cooling intensity is 10 to 50 ° C per minute for ingots and 10 to 150 for wafers.
℃. Further, by heat-treating in a vacuum, in an inert gas or hydrogen gas stream, surface oxidation can be prevented and substrates can be manufactured with good yield.

〔Example〕

Example 1 700 g of GaAs raw material was placed on a GaAs single crystal as a seed crystal in a pyrolytic boron nitride crucible having an inner diameter of 52 mm, and 15 g of metal As for pressure control was provided, and another As reservoir was provided. , 1
The quartz sealed tube, which was vacuum-sealed under 0 ^-6 torr, was set in a VGF furnace. The As reservoir was heated to 615 ° C., the upper end of the seed crystal and the raw material crystal portion thereon were heated to 1238 to 1350 ° C., melted, and then cooled to 0.6 ° C./hour. After the crystal growth is completed, the whole crucible is continuously cooled to 700 ° C at a cooling rate of 1.0 to 1.5 ° C per minute, and a single crystal is obtained by cooling the temperature from room temperature to 15 ° C per minute. Natsuta. A GaAs crystal having a carbon atom concentration of 1 × 10 ¹⁵ cm ^{-3 or} less obtained by the VGF method was cut into a wafer having a thickness of 0.6 mm, and the wafer was shaped into a chip of 4 mm square to measure the specific resistance. The resistivity measurement was performed using the Hall coefficient measurement method. In order to clarify the effect of the present invention, as shown in FIG. 2, no addition was obtained by the conventional method of cooling to room temperature at 1.0 to 1.5 ° C. per minute.
FIG. 3 shows the result of comparison between the specific resistance of the GaAs crystal and the specific resistance of the one obtained by the method of the present invention. As is clear from FIG. 3, the conventional cooling method had a resistivity of the order of 10 ⁵ Ωcm, but after the heat treatment, the wafer showed a resistivity of 10 ⁷ Ωcm or more and was semi-insulating.

Example 2 By the same VGF method as in Example 1, the carbon atom concentration was 1 × 10 ¹⁵ c
After growing a GaAs crystal of less than m ^{-3 with} no impurities added, annealed to 450 ° C, heated to 950 ° C and held at this temperature for 100 hours, then annealed from this temperature to 700 ° C. After cooling and cooling from the temperature to room temperature at a rate of 15 ° C./min, the obtained crystal was cut into a wafer and the specific resistance was measured. The crystals produced by this method are the same as in Example 1, and
It exhibited a specific resistance of 10 ⁷ Ωcm or more and was semi-insulating.

Example 3 By the same VGF method as in Example 1, the carbon atom concentration was 1 × 10 ¹⁵ c
After growing an impurity-free GaAs crystal of less than m ^-3 and slowly cooling it to 450 ° C, it was heated to 800 ° C and kept at this temperature for 10 minutes, and then at room temperature at a rate of 15 ° C / min. The obtained crystal was cut into a wafer and the specific resistance was measured. Also in this case, as in Example 1, the entire crystal exhibited a semi-insulating property of 10 ⁷ Ωcm or more.

Example 4 Carbon atom concentration 1 obtained by the same VGF method as in Example 1
× 10 ¹⁵ cm ^-3 undoped GaAs crystals are heat-treated at 950 ° C for 100 hours in a high-purity hydrogen stream, then gradually cooled to 700 ° C, and then 15 ° C / min. The resulting crystal was cut into a wafer and the specific resistance was measured. As-grown had a resistivity of the order of 10 ⁵ Ωcm, but after heat treatment, it showed a semi-insulating property of 10 ⁷ Ωcm or more over the entire crystal.

Example 5 Carbon atom concentration 1 obtained by the same VGF method as in Example 1
× 10 ¹⁵ cm ^-3 non-impurity-doped GaAs crystal is heated to 800 ° C in a high-purity hydrogen stream and kept at this temperature for 10 minutes, then from that temperature to room temperature at a rate of 15 ° C per minute It was cooled, cut into wafers, and the specific resistance was measured. Also in this case, as in Example 4, a semi-insulating property of 10 ⁷ Ωcm or more was exhibited over the entire crystal.

Example 6 Carbon atom concentration 1 obtained by the same VGF method as in Example 1
After cutting 10 × 10 ¹⁵ cm ^-3 less impurity-free GaAs crystal into a wafer, it was heated to 950 ° C in a vacuum reduced to 10 ^-6 torr and heat-treated at this temperature for 10 hours. Gradually cool from temperature to 700 ℃, and from that temperature to 450 ℃ at a rate of 100 ℃ per minute.
Cooled to below ℃. After etching the surface of 50 μm to remove the influence of surface deterioration due to heat treatment, the specific resistance was measured. The resistivity was 10 ⁵ Ωcm before the heat treatment, and after the heat treatment, all the wafers showed a semi-insulating property of 10 ⁷ Ωcm or more.

Example 7 Carbon atom concentration 1 obtained by VGF method similar to Example 1
× 10 ¹⁵ cm ^-3 less impurity-free GaAs crystal was cut into a wafer, heated to 800 ° C in a high-purity hydrogen stream and kept at this temperature for 10 minutes, then 100 minutes per minute from that temperature. It was cooled to 450 ° C or lower at a rate of ° C. After etching the surface of 50 μm to remove the influence of surface deterioration due to heat treatment, the specific resistance was measured. In this case as well, all the wafers exhibited an insulating property of 10 ⁷ Ωcm or more, as in Example 6.

〔The invention's effect〕

As described above, according to the present invention, a semi-insulating GaAs substrate having a low dislocation density can be obtained without adding impurities.
It can make a great contribution to I It goes without saying that the present invention can also be applied to the vertical Britzmann method having the same principle as the VGF method.

[Brief description of drawings]

FIG. 1 is a diagram showing temperature dependence of resistivity change due to generation and disappearance of deep donor level which is the basis of the present invention, and FIG. 2 is a temperature program for cooling after crystal growth according to one embodiment of the present invention, FIG. 3 is an actual measurement diagram showing the cooling rate dependence of the specific resistance distribution in the ingot according to the embodiment of the present invention.

Claims (7)

[Claims] 1. A carbon atom concentration of 1 × 10 5 by a vertical temperature gradient method.
^Fifteen cm ^{−3 or} less of impurity-free GaAs crystal was grown, and then gradually cooled to 650 to 800 ° C.
A method for producing a semi-insulating GaAs substrate, which comprises cooling the obtained crystal to a wafer shape at a temperature of 1000 ° C to 450 ° C or lower. 2. A carbon atom concentration of 1 × 10 5 by a vertical temperature gradient method.
Growing up to ¹⁵ cm ^-3 undoped GaAs crystal,
After gradual cooling to ℃ or less, subsequently heat-treated at 800 to 1200 ℃ and kept at this temperature for 1 to 100 hours, then gradually cooled to 650 to 800 ℃ from the temperature, 10 minutes per minute from the temperature. ~Ten
A method for producing a semi-insulating GaAs substrate, which comprises cooling at a temperature of 00 ° C to 450 ° C or less and cutting the obtained crystal into a wafer. 3. A carbon atom concentration of 1 × 10 5 by a vertical temperature gradient method.
Growing up to ¹⁵ cm ^-3 undoped GaAs crystal,
After gradual cooling to below ℃, it is heated to 650 to 800 ℃ and kept at this temperature for 1 minute to 10 hours.
A method for producing a semi-insulating GaAs substrate, which comprises cooling the obtained crystal at a temperature of 1000 ° C to 450 ° C or lower and cutting the obtained crystal into a wafer. 4. An impurity-free GaAs crystal having a carbon atom concentration of 1 × 10 ¹⁵ cm ⁻³ obtained by a vertical temperature gradient method is
^In a vacuum reduced to ^-6 torr or less, or in an inert gas or hydrogen gas stream, heat to 800-1200 ° C to bring this temperature to 1
After heat treatment for ~ 100 hours, 650 ~ 80
Slowly cool to 0 ° C, and then 450 at a rate of 10 to 1000 ° C per minute from that temperature.
A method for producing a semi-insulating GaAs substrate, which comprises cooling the obtained crystal to a temperature of ℃ or less and cutting the obtained crystal into a wafer. 5. A GaAs crystal free from impurities, which has a carbon atom concentration of 1 × 10 ¹⁵ cm ^{-3 and is} obtained by a vertical temperature gradient method.
Heat to 650-800 ℃ in a vacuum reduced to ^-6 torr or less, or in an inert gas or hydrogen gas stream,
A method for manufacturing a semi-insulating GaAs substrate, which comprises holding the material for 10 minutes to 10 hours, then cooling from the temperature to 450 ° C. or less at a rate of 10 to 1000 ° C. per minute, and cutting into a wafer. 6. After cutting the GaAs crystal of the obtained carbon atom concentration 1 × 10 ¹⁵ atoms cm ^-3 less than undoped by the vertical temperature gradient method to the wafer-shaped, vacuum pressure was reduced below 10 ^-6 torr ,
Alternatively, after performing a heat treatment of heating to 800 to 1200 ° C in an inert gas or hydrogen gas stream and maintaining this temperature for 1 to 100 hours, the temperature is gradually cooled to 650 to 800 ° C, and the temperature is changed every minute.
A method of manufacturing a semi-insulating GaAs substrate, which comprises cooling to 450 ° C or less at a rate of 10 to 1000 ° C. 7. A GaAs crystal having a carbon atom concentration of 1 × 10 ¹⁵ cm ^-3 less than an impurity-free GaAs crystal obtained by a vertical temperature gradient method is cut into a wafer and then depressurized to 10 ^-6 torr or less in a vacuum. ,
Alternatively, in an inert gas or hydrogen gas stream, heating to 650 to 800 ° C., maintaining this temperature for 1 minute to 10 hours, and then cooling from that temperature to 450 ° C. or less at a rate of 10 to 1000 ° C. per minute. A method of manufacturing a characteristic semi-insulating GaAs substrate.