KR950007600B1 - Method for decreasing dislocation of gaas single crystal by vertical temperature zone control method - Google Patents

Abstract

The decreasing method of a dislocation of a GaAs single crystal by the vertical temperature gradient method is characterized by (a) inserting 600g undopped polycrystal GaAs into the quartz boat of the modified vertical gradient furnace, (b) maintaining the high temp. part and the low temp. part of the furnace to be at most 1250≰C and at least 1215≰C respectively, and stabilizing it, and (c) maintaining 2 mm/hr back melting speed and 2 mm back melting distance, 5 ≰C/cm temp. slope of the solid part and 1≰C/cm temp. slope of the molten part, and 2 mm/hr growth speed.

Description

Potential Reduction Method of GaAs Single Crystal by Vertical Temperature Reduction Method

1 is a schematic diagram showing the initial GaAs polycrystal and seed size during GaAs single crystal growth by the vertical temperature reduction method of the present invention.

FIG. 2 is a schematic diagram showing a stabilized state of a GaAs single crystal grown by the vertical temperature reduction method of the present invention, seeded at 1238 ° C, which is a melting point of GaAs, to maintain thermodynamic equilibrium.

3 is a schematic diagram showing a state in which the thermally impacted portion of the seed is backmelted by 2 mm at a speed of 2 mm / hr during the growth of GaAs single crystal by the vertical temperature reduction method of the present invention.

FIG. 4 is a micrograph showing lineage defects occurring in the shoulder portion during GaAs single crystal growth by a conventional vertical temperature reduction method.

5 is a microscope top view showing the edge cone cavity during GaAs single crystal growth by the vertical temperature reduction method.

* Explanation of symbols for main parts of the drawings

1: Quartz Boat 2: Polycrystalline GaAs

3: GaAs melt 4: seed

5: Line defect (Lineage) 6: Enicon cavity

The present invention relates to a method for reducing the potential of a GaAs single crystal by the vertical temperature reduction method. More specifically, in order to use a GaAs single crystal grown by the vertical temperature reduction method for an optical device, the number of potentials to be improved first is 500. It relates to a method of decreasing to cm ^-2 or less.

In the conventional liquid encapsulated Czochralski method, the dislocation is mainly generated by thermal stress because the temperature gradient in the solid portion is very high, such as 200 ° C./cm, immediately after the GaAs melt solidifies. Seed necking, high concentration doping of Si, solid-liquid interfacial shape control, cooling rate control, etc. are used, but in most cases, the dislocation density (EPD) is very high above 10,000 cm ^-2 , requiring low dislocation density. It is not suitable for optical devices.

In addition, in the conventional horizontal Bridgman method, dislocation propagation from seeding point, which is the cause of dislocation generation, dislocation propagation from local wlettin g point, solid-liquid interface shape Solid-liquid inter face shape induced grown-in dislocation, defect collapse dislocation during post-cooling process, misfit dislocation by dopant segregation, thermoelastic strain induction It is known as thermoelastic deformation induced moving dislocation and sometimes sells single crystal with zero dislocation density, but no detailed reduction method is disclosed.

In recent years, the Vertical Bridgman method, which combines the advantages of the liquid cap shoul method and the horizontal Bridman method, is essentially flat in the solid-liquid interface shape due to the intrinsic growth effect, and has a solid phase portion. Since the temperature gradient of is small, crystals of low defect density can be produced. However, in order to manufacture high-quality GaAs wafers, that is, GaAs wafers having a dislocation density of 5000 cm ^-2 or less (EPD ≤ 500 cm ^-2 ), There is a problem that a potential reduction method should be used.

The present invention provides a method for fabricating high quality GaAs wafers by reducing the potential during seeding, by reducing the potential by eliminating partial chemical fusion, or by reducing the potential by reducing edge concavity. To provide.

Now, the present invention will be described in detail.

The present invention uses the following method during the growth of GaAs single crystals using the vertical Bridgman method to produce high quality GaAs crystals having a dislocation density of 500 cm ^-2 or less.

In the first method, since the diameter of the seed portion is small and the surface tension of the GaAs melt is large when the GaAs melt is initially in contact with the seed, such a large interfacial energy causes supercooling to increase the growth rate. Results in an increase in dislocation.

In addition, under the influence of the upper melt, the portion below the freezing point is instantaneously subjected to thermal shock in which the melt is formed, the solid-liquid interfacial shape is very concave, and local fusion is also severely caused, resulting in a very high dislocation density.

Usually, the GaAs crystals are subjected to thermal shock because they are once cooled to 1250 ° C after being raised to 1260 ° C or more. However, the present invention, in order to reduce dislocation density during seeding, first of all, as shown in FIG. The temperature of the melt is maintained at 1250 ° C. or less so that the temperature is gradually raised to not fully form the GaAs melt.

Subsequently, as shown in FIG. 2, after seeding, a sufficient stabilization time is maintained so that the portion where subcooling has occurred remains in equilibrium, and then, after sufficient stabilization time has passed, as shown in FIG. Back melting is applied to the side about 2mm at the speed of hr, and the part subjected to thermal shock is made into a melt and then grown again.

In the second method, in particular, local fusion, which occurs mainly in the shoulder section, is produced by the chemical reaction between the quartz bout and the GaAs melt, in which the line as shown in FIG. Defects (lineage) 5 and low angle boundary occur, and the dislocation density is also partly high, such as 20,000 cm ^-2 , and these dislocations propagate into the crystal and gradually decrease. have.

Therefore, in order to eliminate local fusion, 1) sandblasting the inner wall of the boat prevents local fusion by uniform α-crystobilite production and 2) lowers the growth rate in the shoulder area. It is a method to reduce dislocation density by removing fusion.

The GaAs melt, which explains the third method, and the solid phase meet the inner wall of the boat, creating a facet, which is a big feature of GaAs. The facet is layered and grows very fast. The sheet size becomes uneven.

The partial solid-liquid interface shape at the point where this facet and the overall solid-liquid interface meet is defined as an edge cone cavity and is shown in FIG. 5, immediately after the melt solidifies when this edge cone cavity 6 is severe. When the stress caused by the expansion stop is exceeded and the stress caused by the expansion stop exceeds the critical stress value, the generation of dislocation is caused, and the dislocation propagates inside the crystal.

Therefore, 1) the edge cavity is reduced, and 2) the facet size is kept small and uniform to suppress the generation of dislocations.

According to the vertical Bridgman method of the present invention, the potential increase / decrease effect due to public collapse during post-cooling, which is important for the HB method, does not have a significant effect, and the thermoelastic potential, which is important for the liquid cap shoal method, is a DSL (dilute sirtlewith light). It was found when observing by photo etching, but the number was very small, and the effect of dislocation generation due to the overall solid-liquid interface shape also had little effect.

EXAMPLE

Charge 600 g of undoped polycrystalline GaAs into a two-diameter quartz boat in a modified vertical gradient furnace using a separate 12 temperature zone control method, and the furnace temperature is 1250. The temperature is kept below 1215 ° C., the temperature gradient is 5 ° C./cm for the solid phase, the melt part is kept at 1 ° C./cm, stabilized for 8 hours, and the backmelting speed is 2 mm / hr. The GaAs single crystal was prepared by setting the back melting distance to 2 mm, the temperature gradient of 5 ° C./cm for the solid phase part, and the melting part of 1 ° C./cm for the growth rate of 2 mm / hr. The dislocation density of the GaAs single crystal was 5000 cm ^-2 or less.

The present invention achieves the effect of suppressing the generation of dislocations in the seed by seeding at a temperature of 1250 ° C. or less, adjusting the stabilization time, and performing back melting.

Claims (1)

In the method of decreasing the potential of GaAs single crystal by the vertical temperature reduction method, the temperature of the furnace at the time of seeding is maintained at 1250 ° C. or less at the high temperature part and maintained at 1215 ° C. or more at the low temperature part. The potential reduction of GaAs single crystal by the vertical temperature reduction method is characterized in that the temperature gradient is 5 ℃ / ㎝ and the melt portion is maintained at 1 ℃ / ㎝ and the growth rate is 2 mm / hr. Way.