JPH0411520B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a GaAs single crystal growth technique, and relates to a technique that is most effective when used, for example, in heat treatment after GaAs single crystal growth. In the growth of compound semiconductor single crystals, low-resistance crystal portions (10 ⁷ Ωcm or less) that cannot be used for electronic devices are often formed, which is one of the major causes of reduced yields. The present invention solves this problem. [Conventional technology] Conventionally, single crystals were grown using the single crystal pulling method.
For example, the following methods have been proposed as techniques for increasing the resistivity of GaAs single crystals or decreasing the concentration of EL2, which is an inherent defect in the crystal. (1) A heat treatment method in which resistivity is increased by thermally controlling a GaAs single crystal grown by the single crystal pulling method at 950°C and then rapidly cooling it (W.Ford and G.Mathur, “ Thermal Cycling
of Electrical Properties in GaAs”Semi−
Insulating Materials, Hakone (1986)
P227 Ohmsha Ltd.) (2) Pulled by single crystal pulling method
A heat treatment method in which the GaAs single crystal is thermally controlled at 1200℃ for 8 to 16 hours and then rapidly cooled to room temperature in a few seconds to decrease the EL2 concentration and increase the resistivity. (J.
Lagowski et al., “Inverted Thermal
Conversion-GaAs, a New Alternative
Ma terial for Integrated Circuits”Appl.
Phys., Lett, 49, (1986) 892) [Problems to be Solved by the Invention] Among the above heat treatment methods, method (1) of rapidly cooling after heat treatment at 950°C increases the resistivity, but There is a problem in that the concentration of EL2, which is an inherent defect in EL2, is also increased. Also, among the above heat treatment methods, after heat treatment at 1200℃
Cooling is performed at exceedingly high speeds such as 10,000℃/min (2)
The problem with this method is that although the EL2 concentration is low, the dislocation density increases by more than two orders of magnitude from the order of 10 ⁴ cm ^-2 to the order of 10 ⁶ cm ^-2 as shown in Figure 9c. was discovered through experiments. Moreover, none of the above conventional heat treatment methods takes into account in-plane variations in resistivity, mobility, and EL2 concentration when the crystal is cut into wafers. This invention was made in view of the above-mentioned problems, and its purpose is to increase the resistivity of a compound semiconductor single crystal with low resistance (10 ⁷ Ωcm or less).
The object of the present invention is to provide a heat treatment method that can increase the LE2 concentration to 10 ⁷ Ωcm or more, reduce the LE2 concentration, and make the electrical and optical characteristics uniform over the entire crystal. [Means for solving the problem] The present inventors have solved the problem by
It is speculated that the increase in concentration is due to the relatively low heat treatment temperature of 950°C, and that the increase in dislocation density in conventional technology (2) is due to the rate of cooling down after heat treatment being too fast. Under the assumption of
Through repeated experiments, we obtained proof that the above assumption was correct. This invention is based on the above-mentioned demonstration,
Heat treatment of the single crystal is performed at a temperature range of 1000℃ or higher and lower than the melting point for 1 to 24 hours, and the cooling rate is 20 to 250℃.
It is suggested that the temperature be within the range of °C/min. [Function] According to the above means, heat treatment is performed at a relatively high temperature of 1000°C or higher, which increases the resistivity and increases the EL.
2 concentration can be reduced, and the temperature does not fall extremely quickly, so there is little possibility that the unit density will increase. Furthermore, variations in resistivity, mobility, and EL2 concentration are reduced, making it possible to achieve the above-mentioned objective of making the electrical and optical characteristics of the entire crystal uniform. [Example] In proposing the present invention, the present inventor heat-treated a single crystal ingot of GaAs, which is a compound semiconductor, under various temperature conditions and cooling rates, and then degree, EL2 concentration,
The dislocation density was measured. Specifically, a GaAs single-crystal ingot grown by the LEC method (liquid-enclosed Czochralski method) is cylindrically ground, cut into blocks with a thickness of 17 to 27 mm, degreased, and then etched. and washed. After that, the blocks were vacuum sealed in a high-purity quartz ampoule (2×10 ^-6 Torr).
The ampoule was then heated to a suitable temperature between 700° C. and the melting point over 1 to 2 hours. Then about 5
After keeping the temperature constant for a certain period of time, it was cooled to room temperature at an appropriate cooling rate. The above heat treatment was carried out at various cooling rates, and the crystals after the heat treatment were taken out from the ampoules and cut into wafers to examine the in-plane distribution of resistivity, migration, EL2 concentration, and dislocation density. The resistivity and mobility were measured by the Van der Pauw type Hall measurement method, and the EL2 concentration was determined by measuring the absorption rate of light at a wavelength of 1 μm. Also,
Dislocation density was determined by measuring the number of etched pits created by molten KOH. Table 1 shows some of the above measurement results. In the same table, Z indicates the average value of each measurement item, and V indicates the variation range (standard deviation divided by the average value and expressed as a percentage). Temperature cooling rate is A: 23℃/min, B: 171℃/min.
min, C: 167°C/min, D: 3.1°C/min.

【table】

[Table] Furthermore, Fig. 1 shows the resistivity distribution in the wafer plane before and after the heat treatment of the crystal heat-treated under the conditions shown in column A of Table 1, and Figs. 2 to 4 also show the same. 1 shows the resistivity distribution in the wafer plane before and after the heat treatment of the crystal that was heat treated under the conditions shown in columns B to D of No. 1. In Figures 1 to 4, the ● marks are plots of the measured values for the crystal before heat treatment, and the circles mark are the plots of the measured values for the crystal after heat treatment. This is what I did. In addition, Fig. 5a, Fig. 6a, Fig. 7a, and Fig. 8a show the results obtained by heat treatment under the above conditions A, B, C, and D.
The changes in the distribution of EL2 concentration are shown in Figure 5b, Figure 6b,
Figures 7b and 8b show the above conditions A, B, and CD.
Figure 2 shows changes in mobility distribution due to heat treatment. Low resistance (10 ⁷ Ωcm or less) from Table 1 and Figure 1
The dangling crystals have a high resistance (=4.79×
10 ⁷ Ωcm). Similarly, in FIG. 2, it can be seen that the low resistance (3×10 ⁵ Ωcm) at the wafer edge became high resistance (=7.95×10 ⁷ Ωcm) by heat treatment. In Figure 3, the resistance is even higher (=
1.08×10 ⁸ Ωcm), and the variation has decreased to 4.8%. In FIG. 4, even after heat treatment, the resistivity is as low as 7.91×10 ⁶ Ωcm, and the variation is 25.8%, which is hardly improved. On the other hand, the EL2 concentration is determined under conditions A, B, as shown in Fig. 5a, Fig. 6a, Fig. 7a, and Fig. 8a.
Although the in-plane uniformity improves in both C and D, the EL2 concentration also increases under condition B, and under conditions A, C,
In D, the EL2 concentration has decreased. That is,
Heat treatment below 1000℃ increases the EL2 concentration;
Heat treatment at 1000°C or higher reduces the EL2 concentration. From Table 1 and Figures 1 to 8, it can be seen that Condition C: temperature 1052°C, duration 5 hours, cooling rate 167
It was found that when the heat treatment was performed at a rate of .degree. C./min, the resistivity was highest, the EL2 concentration was decreased, and the variations in resistivity, mobility, and EL2 concentration were also the smallest. Furthermore, Figure 9a shows the in-plane distribution of etch pit density measured for a crystal that was heat treated at a temperature of 1052°C for 5 hours and then cooled at a cooling rate of 167°C/min. Figure 9b shows the in-plane distribution of the etch pit density measured for the crystal cooled at a cooling rate of 171°C/min after heat treatment for 5 hours. From Figures 9a and b, the etching pit density due to the difference between the two conditions does not differ much, but 1200
As is clear from the comparison with Figure 9c, which shows the etchipite density distribution measured for a crystal to which the method of prior art (2) is applied, in which cooling is performed at an ultra-high speed of 10,000°C/min after heat treatment at 10,000°C/min, the present invention By following this method, the increase in dislocation density can be significantly reduced. From the above measurement results and the measured values of the crystals after heat treatment under various conditions at the same time, when heat treatment is performed, the temperature range is from 1000℃ to the melting point, and the cooling rate is from 20℃ to 250℃ per minute to prevent dislocations. It was concluded that it is possible to increase the resistivity of a low-resistance crystal, reduce the EL2 concentration, and reduce the variations in resistivity, mobility, and EL2 concentration without significantly increasing the density. As described above, by applying the heat treatment of the present invention, it is possible to increase the resistivity of a low-resistance crystal, reduce variations in resistivity and mobility, and make the electrical characteristics of the crystal uniform. In addition, it reduces the EL2 concentration, which is an inherent defect in GaAs crystal, and further
Since EL2 serves as an absorption source for light with a wavelength of around 1 μm, the optical characteristics of the crystal are also made uniform by reducing the variation in EL2 concentration. In the above example, the heat treatment time was around 5 hours, but the heat treatment time is not limited to this, and the same effect can be obtained as long as the heat treatment time is in the range of 1 to 24 hours. Needless to say, the effect is even more remarkable when applied to high-resistance crystals. In addition, in the above example, the crystal is placed in an ampoule and heated to perform heat treatment.
Instead of using an ampoule, it is also possible to pull the grown crystal from the sealing material in a crystal growth apparatus and heat-treat it as it is. However, since crystal growth equipment is large and expensive, if it is used for heat treatment, the equipment will be occupied for a long time, resulting in high costs.
On the other hand, the use of ampoules is economically advantageous, and various parameters as heat treatment conditions can be controlled accurately and easily. [Effects of the Invention] As explained above, the present invention heat-treats a GaAs single crystal in a temperature range of 1000°C or higher and lower than the melting point.
Run for 24 hours and reduce the temperature at a rate of 20 to 250℃/min.
range, and the resistivity of the low-resistance crystal can be increased to 10 ⁷ Ωcm or more, making it possible to use crystals that normally cannot be used in electronic devices. Furthermore, since the concentration of EL2, which is an inherent defect, can be reduced and the rate of temperature drop is not extremely fast, there is little possibility that the dislocation density will increase. Furthermore, variations in resistivity, mobility, and EL2 concentration are reduced, and the electrical and optical characteristics of the entire crystal can be made uniform.

[Brief explanation of drawings]

Figures 1, 2, 3 and 4 are shown in Table 1.
Graphs showing changes in the in-plane resistivity distribution of GaAs single crystals heat-treated under the four conditions A, B, C, and D shown in Figure 5a, Figure 6a, and Figure 6a. Figures 7a and 8a also show conditions A in Table 1,
Graphs showing changes in EL2 concentration distribution due to heat treatment of B, C, and D, Figure 5b, Figure 6b, Figure 7b
And FIG. 8b also shows conditions A, B in Table 1,
Graphs C and D show changes in mobility distribution due to heat treatment; FIGS. 9a and b are graphs showing changes in etching pit density due to heat treatment under conditions B and C in Table 1; FIG. 3 is a graph showing changes in etch pit density due to the proposed ultra-fast cooling heat treatment method.

Claims (1)

[Claims] 1 After growing a GaAs single crystal, maintain a constant temperature in a temperature range of 1000°C or higher and below the melting point in a vacuum or gas atmosphere, and then lower the crystal temperature at a rate of 20°C to 250°C per minute. A heat treatment method for GaAs single crystal characterized by: