JPH0411518B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Application This invention relates to a method for producing gallium arsenide crystals with controlled electrical properties.

(b) Prior Art Conventionally, the following manufacturing methods have been used to obtain GaAs crystals with uniform electrical characteristics, such as high resistance, in gallium arsenide (GaAs) crystals.

() Ga and As are doped with impurities that form electrically active deep levels such as Gr and Fe to create semi-insulating
A method of manufacturing GaAs crystals.

() By controlling the molar ratio (As/Ga) or composition ratio of Ga and As during crystal growth, semi-insulating
How to obtain GaAs crystals.

() A method of making electrical characteristics uniform by performing heat treatment after crystal growth.

The manufacturing method of () and () above focuses only on the crystal growth process and obtains the final electrical characteristics by changing the growth conditions.
The manufacturing method involves heat-treating the obtained crystal to obtain electrical properties.

(c) Problems to be solved by this invention The manufacturing method described in () above has a difficulty in controlling the impurity concentration, and as a result, the obtained GaAs
The disadvantage is that each crystal has a different resistance, and there is also a difference in the concentration of the solidified portion at the early and late stages of the crystal growth process, which causes problems in crystal reproducibility and uniformity of properties. For this reason, there was a drawback that adversely affected devices using the obtained GaAs crystal as a substrate and the device manufacturing process.

In the case of the method () mentioned above, the resistivity differs greatly between the obtained crystals and within the plane of the wafer,
Furthermore, within the crystal, there is a difference in specific resistance between the early and late stages of solidification. That is, in the same crystal, the specific resistance differs by one order of magnitude or more depending on the location. For this reason, the reliability of the crystal was low and the yield was low.

The above-mentioned method () is carried out for the purpose of improving the characteristics of () (), and it is difficult to obtain uniform resistivity due to the disadvantage of () (), that is, the non-uniformity of resistivity. It was hot.

Furthermore, the above-mentioned methods () to () are used as a method for obtaining a GaAs crystal that is semi-insulating, that is, has a resistivity of 10 ⁷ Ωcm or more, and cannot be used to control the resistivity over a wide range.

Note that when growing GaAs crystals using the methods () to (), the molar ratio of Ga and As is generally kept as close to 1:1 as possible, or the excess of As is 1% or less. This is because if the amount of Ga is too large, a P ^- type crystal with non-reproducible electrical properties, for example, whose resistivity varies greatly between and within crystals, is obtained. Furthermore, even if the amount of As is excessive, an N ^- type crystal whose electrical characteristics are not reproducible will be obtained.

The object of the present invention is to provide a method for manufacturing a gallium arsenide crystal that can obtain uniformity in electrical properties represented by resistivity and can control resistivity over a wide range of orders.

(d) Means for solving the problem The present invention provides a means for solving the problems by reducing the molar ratio of arsenic and gallium to As/
A crystal growth step in which a gallium arsenide crystal is grown with a Ga concentration of 1.02 to 1.5, and the obtained gallium arsenide crystal is heat-treated in an arsenic-containing atmosphere, an inert gas, or a vacuum in a temperature range of 450°C to 650°C. reducing the resistivity of the gallium arsenide crystal;
and a reduction control step.

In addition, this invention allows gallium arsenide crystals to be heated to 700°C
An increase control step of increasing the resistivity of the gallium arsenide crystal by heat treatment in an arsenic-containing atmosphere, inert gas, or vacuum in a temperature range of 1100° C. is added after the crystal growth step or the decrease control step. be done.

(e) Effect This invention intentionally makes the amount of As more than the amount of Ga, and the electrical characteristics of the obtained N ^- type GaAs crystal are in a thermally unstable state. The resistance can be controlled by subsequent heat treatment. The GaAs crystal obtained through this manufacturing process has a uniform resistivity value that varies depending on the temperature range of the heat treatment.

(f) Examples First, the outline of the process of this invention will be explained.

() The molar ratio of As and Ga is 1.02 (50.5%)
As vs. 49.5% Ga) to 1.5 (60.0% As vs. 40%
A crystal growth process that grows gallium arsenide crystals as a range of Ga).

This process is performed using N ^- type GaAs with a specific resistance in the range of 0.1 to 5 x 10 ⁷ Ωcm at room temperature after crystal growth.
It is used to obtain crystals, and its electrical properties are obtained by controlling the subsequent heat treatment process. This process is based on the premise that the resistivity is controlled by a control process. The reason for setting the molar ratio As/Ga to 1.02 or more is that the ratio process can be easily controlled in the subsequent control process, and the electrical characteristics between the crystals and within the crystal can be easily made uniform. Another reason is that when used as a semi-insulating substrate, the resistivity can be kept lower than that of conventional products. By the way, if the molar ratio As/Ga is 1.5 or more, more precisely 1.22 or more, As will precipitate, causing problems in terms of crystal growth. It should be noted that the process () is different in nature from conventional techniques for controlling the concentration of levels due to electrically active intrinsic defects or impurities.

() The GaAs crystal obtained in step () is heated at 700℃ in an As atmosphere, inert gas, or vacuum.
Heat treated in a temperature range of 1100℃,
A control process that increases the resistivity of GaAs crystals.

This step (a) increases the resistivity if it is small, (b) equalizes the electrical properties within the crystal, and (c) thermally stabilizes the electrical properties, if necessary. It is something to do. In order to thermally stabilize the electrical properties, a longer heat treatment time is required than the heat treatment time required to increase the resistivity in (a). This treatment time varies depending on the molar ratio of As and Ga in step (2), the heat treatment temperature, etc., but in general, the characteristics are stable within 100 hours of heat treatment. In addition, (b) and (c) above
In order to obtain these characteristics, a heat treatment temperature of 700°C or higher is required. However, temperatures of 1100°C or higher complicate the process, but we do not see a need for this. Note that it is necessary to perform the heat treatment in an As atmosphere or an inert gas vacuum in order to prevent separation and deterioration of GaAs.

() The GaAs crystal obtained in step () is heated from 450℃ to 650℃ in an As atmosphere, inert gas, or vacuum.
A controlled process that reduces the resistivity of GaAs crystal by performing heat treatment in the temperature range of ℃.

This step () is a step to reduce the resistivity of the GaAs crystal, and the characteristics are manipulated in the opposite direction to step (). At temperatures above 650℃, the phenomenon seen in process () occurs; on the other hand, at 450℃
Below this, a long time heat treatment is required, which is not practical for specific resistance reduction control. Further, since the heat treatment effect is saturated in about 300 hours, no further treatment time is required.

Further, the present invention has the following aspects.

A method of performing step () after the step ().
It is significant to control the increase in resistivity.

A method of performing step () after the step ().
There is significance in controlling the decrease in resistivity.

A method of performing step () after the step (), and then performing step (). It is meaningful to control the specific resistance by increasing it and then decreasing it appropriately. However, after long-term heat treatment is performed in step () and the electrical characteristics are stabilized, there is no effect.

A method of performing step () after the step (), and then performing step (). It is meaningful to control the resistivity to increase it appropriately after decreasing it.

Specific example 1 A GaAs single crystal with a diameter of 55 mm ± 2 mm and a length of 10 cm was made using the high-pressure LEC (liquid encapsulation Czyochralski) method.
PBN using 99.9999% purity As and Ga as raw materials
It was grown using a crucible (a crucible made of pyrolytic boron nitride). At this time, the amounts of As and Ga are determined by the molar ratio As/
Ga was set at 1.2, and no impurity doping was performed. The ingots obtained as a result of the above growth were sliced to obtain 0.55 mm thick wafers. The resistivity distribution of the wafers cut out from the seed (seed crystal) side and tail side of the ingot was measured.
The measurements were carried out in the direction perpendicular to the orientation flatness using a 3 x 3 mm ^square sample.

FIG. 2 shows a plane perpendicular to the orientation flatness OF of the wafer 1 used in the measurement. In Fig. 2, the left half shows measurements on a wafer in an as-grown state, that is, a GaAs single crystal has been grown before heat treatment, and the numbers 1 to 8 in the figure indicate the measurement positions. ing. On the other hand, in Figure 2, the wafer on the right half has been cut.
It was heat treated at 800°C for 1 hour in an N ₂ atmosphere. The measurement positions are shown as 1' to 8' in correspondence with the measurement positions in the as-grown state.

FIG. 1 is a diagram showing the above measurement results. In Fig. 1, the resistivity Pa of the GaAs single crystal in the as-grown state varies depending on the position;
The specific resistance Pb after heat treatment increases and becomes uniform regardless of the position.

Specific Example 2 Figure 3 shows GaAs grown by the method of the present invention.
This shows an example in which the resistivity of a single crystal is controlled by heat treatment. In the as-grown state shown in Figure 3
The resistivity Po, which was on the order of 10 ⁶ Ωcm, was heat treated at 500°C for 20 hours (step ()) to reduce the resistivity to the order of 10 ⁴ Ωcm. After further heat treatment at 500℃ for 20 hours,
It has been shown that although the specific resistance decreases, the rate is small.

On the other hand, in the as-grown state of the above resistivity Po,
When the GaAs single crystal was heat-treated at 785°C for 1 hour (step ()), the specific process increased to the order of 10 ⁷ Ωcm.
After this, when heat treatment is performed at 500° C. for 20 hours (step ()), the resistivity decreases, but the decrease in resistivity is smaller than when step () is performed directly from the as-grown state. This is because heat treatment at 785°C has the effect of increasing the specific resistance to a certain value, and also has the effect of maintaining the specific resistance in a more stable state against subsequent heat treatments. If heat treatment is performed at 785°C for different times from the as-grown state, and then heat treatment is performed at 500°C for 20 hours, the resistivity will be controlled as shown by the broken line in Figure 3. In addition, as-grown GaAs
When the single crystal was heat-treated at 785° C. for a long time, in this example for about 15 hours, the specific resistance became thermally stable at about 3×10 ⁷ Ωcm.

Specific Example 3 A GaAs single crystal grown under the same conditions as in Specific Example 1 was vacuum-substituted in an ingot state, sealed together with As, and heat-treated at 950° C. for 15 hours (step ()). After that, as a result of measuring the resistivity of each wafer sliced from the ingot, the resistivity of each wafer (shown as wafer number) was 3 (±1) × 10 ⁷ Ωcm, as shown in Figure 4, and the entire crystal was A GaAs single crystal with uniformity was obtained.

Further, the wafer was heat treated at 850° C. for 0.5 hours. As a result, as shown in FIG. 5, the resistivity of each wafer is almost unchanged from that in FIG. 4, indicating that it is thermally stable.

FIG. 6A shows a GaAs single crystal wafer manufactured by the above steps () and () according to the present invention by AB etching (MSAbrahams et al.
This is a photograph taken under a microscope after etching (see Journal of Applied Physics, Vol _{. 35} , p. ₂₈₅₅ ). . On the other hand, FIG. 6B is a micrograph after the AB etching, obtained by a combination of a conventional crystal growth method and heat treatment. Generally, AB etching is
It is known that it can not only reveal the presence of dislocations, but also the non-uniformity of electrical properties. Therefore, by observing the crystal pattern obtained by AB etching, the uniformity of the electrical characteristics can be determined. In Fig. 6B, there is non-uniformity near the dislocations distributed in a network, whereas in Fig. 6A, the non-uniformity is significantly reduced, and the electrical characteristics are uniform due to the present invention. This indicates that

FIG. 7 shows the hole mobility distribution of a GaAs wafer manufactured according to the present invention. That is.
The absolute value of the Hall mobility of the present invention is 8000 to 8300 cm ² /
While the mobility of conventional GaAs is uniform in VS, it is non-uniform in the range of 5000 to 7000 cm ² /VS, indicating that the electrical characteristics are improved by the present invention.

Note that the present invention can also be applied to polycrystalline GaAs.

(G) Effects The method for producing gallium arsenide crystals of the present invention has the following effects, as represented by () specific resistance.
It is possible to control the electrical properties of GaAs crystals. That is, the present invention adjusts the value of specific resistance through three aspects of electrical property control: a crystal growth process and a decrease control process, a crystal growth process and a decrease control process and an increase control process, and a crystal growth process and an increase control process and a decrease control process. can be controlled to a large extent as needed. ()GaAs
It is possible to obtain a uniform resistivity of the crystal and to lower the resistivity than before. () A GaAs crystal with thermally stable resistivity can be obtained.
() Since the specific resistance can be kept relatively low, the problem of so-called thermal transformation, in which the GaAs substrate surface characteristics become P-type, which has conventionally been a problem in the device manufacturing process, is greatly alleviated.

() The crystal uniformity of the GaAs crystal wafer is obtained, and the non-uniformity of electrical properties, especially near dislocations, is significantly reduced. () Hole mobility is increased and made uniform.

[Brief explanation of drawings]

Figure 1 is a diagram showing a specific example of the as-grown state of GaAs single crystal and the distribution of resistivity after heat treatment, Figure 2 is a diagram showing the cutout position of the sample used for the resistivity measurement in Figure 1, and Figure 3 Figure 4 shows the resistivity distribution of the GaAs single crystal after heat treatment at 950°C according to the present invention. FIG. 5 is a diagram showing the distribution state of resistivity after further heat treatment after the treatment shown in FIG. 4, and FIGS.
FIG. 7 is a micrograph showing the crystal structure of a GaAs crystal wafer after AB etching, and FIG. 7 is a diagram showing the hole mobility distribution of the GaAs crystal of the present invention.

Claims (1)

[Claims] 1 (a) The molar ratio of arsenic and gallium As/Ga is 1.02.
(b) a crystal growth process of growing a gallium arsenide crystal as a temperature ranging from 450 to 650 °C;
A method for producing a gallium arsenide crystal, comprising: a step of controlling electrical properties to reduce the resistivity of the gallium arsenide crystal by performing a heat treatment in an arsenic-containing atmosphere, an inert gas, or a vacuum in a temperature range of . 2 (a) The molar ratio of arsenic and gallium As/Ga is 1.02
(b) a crystal growth process of growing a gallium arsenide crystal as a temperature ranging from 450 to 650 °C;
(c) the process of (b) above, in which the specific resistance of the gallium arsenide crystal is reduced by heat treatment in an arsenic-containing atmosphere, inert gas, or vacuum in a temperature range of The obtained gallium arsenide crystal is heat treated in a temperature range of 700°C to 1100°C in an atmosphere containing arsenic, in an inert gas, or in a vacuum to increase the specific resistance of the gallium arsenide crystal and increase its electrical properties. A method for producing a gallium arsenide crystal, comprising: a controlled process; 3 (a) The molar ratio of arsenic and gallium As/Ga is 1.02.
(b) a crystal growth process of growing a gallium arsenide crystal as a temperature ranging from 700℃ to 1100℃;
(c) a step of controlling the increase in electrical properties of increasing the specific resistance of the gallium arsenide crystal by performing heat treatment in an arsenic-containing atmosphere, an inert gas, or a vacuum in a temperature range of (c) the step of (b) above; The gallium arsenide crystal obtained is heat treated in a temperature range of 450°C to 650°C in an arsenic-containing atmosphere or in an inert gas or in vacuum to reduce the specific resistance of the gallium arsenide crystal and reduce its electrical properties. A method for producing a gallium arsenide crystal, comprising: a controlled process;