JPS62138392A - Preparation of semiconductor single crystal - Google Patents

Abstract

PURPOSE:To obtain single crystal having uniform concentration of impurities when semiconductor single crystals are prepd. by the Czochralski method using a crucible having a double wall structure by holding the liquid level of the inside crucible at somewhat lower level than the liquid level of the outside crucible. CONSTITUTION:A crucible for melt for growing semiconductor single crystal by the liquid encapsulated Czochralski method is constructed to have a double wall structure constituted of an inside crucible 3a and an outside crucible 3b and both crucibles are communicated with a small hole 8, and the outside cru cible 3b is constructed so as to be moved rotationally and vertically. When a single crystal 2 is pulled from the melt 5a of the starting material in the inside crucible 3b, the melt 5b of the starting material 5b is supplied simultane ously from the outside crucible 3b to the inside crucible 3a. By holding the level of the melt in the inside crucible 3a at least several mm lower level than the level of the melt in the outer crucible 3b, the variation of concentration of impurities in the crystal 2 due to segregation is prevented, thus a uniform crystal 2 is grown.

Description

[Detailed Description of the Invention] [Background and Objectives of the Invention] The present invention is based on L E C (L iquid Enc
The present invention relates to a method for manufacturing a semiconductor single crystal using the apsulated Czochralski method.

The concentration of an additive impurity in crystal growth by the pulling method has a distribution determined by the segregation coefficient of the impurity, and the concentration of impurities with a segregation coefficient of 1 or less increases as the crystallization fraction increases. A known method for avoiding this is to use a double crucible, pull the crystals from the inner crucible, and replenish the lost amount of the inner solution from the outer crucible through minute through holes provided in the inner crucible. If the segregation coefficient of the impurity is N, the impurity concentration in the inner crucible liquid is N in, and that in the outer crucible is Nout, then N0ut=k ・
If it grows as a concentration of Nin, the concentration in the crystal will be -N
It is constant at in and is made uniform over the entire length.

The double crucible method is extremely effective in making the impurity concentration uniform, but in reality, this method pressurizes the liquid in the inner crucible via the outer liquid, so the inner and outer liquid levels are Since they are at the same height, it is difficult to bring the temperature distribution in the liquid inside the inner crucible into a state suitable for crystal pulling, which is why it is not generally put into practical use. The solution in the crucible has some degree of temperature distribution in the radial direction of the crucible, with the center being lower and the periphery being higher, and this helps control the crystal shape, but when using a double crucible, this temperature distribution It becomes difficult to realize this, and the crystal shape tends to change due to slight changes in liquid temperature. In addition, the practical pulling speed is 1! ? At a temperature of

In addition, in the conventional double crucible type, the inner crucible is supported by a jig with a fixed part in the furnace as a fulcrum, but the outer crucible is supported by a jig that is inserted into the outer crucible and held by buoyancy against the solution ( A mechanism for rotating and moving up and down is attached to the crucible.For this reason, the inner crucible is either fixed or rotates synchronously with the outer crucible, making it difficult to achieve a solution temperature distribution that facilitates crystal growth.

FIG. 3 is a longitudinal sectional view of an apparatus for carrying out a conventional semiconductor single crystal manufacturing method. In the figure, 1 is a crystal drive shaft, 2 is a pulled single crystal, 3 is a crucible, 4 is a liquid sealant, 5 is a Qa AS solution, 6 is a heater, and 7 is a crucible drive shaft. And PBN(pyrOIitiC30rOn
GaAs was dissolved in a crucible of N 1tride), the liquid surface was sealed with 8203 liquid sealant 4, and the melt was melted in a high-pressure inert gas atmosphere while suppressing decomposition of GaAs and TS generation of As. Pull up the single crystal. Figure 4 shows the case where this is made into a double crucible. In Figure 14, 3a is an inner crucible, 3b is an outer crucible, 4a is a liquid sealant in the inner crucible, 4b is a liquid sealant in the outer crucible, and 5a is a liquid sealant in the outer crucible. The GaAs solution in the inner crucible, 5b is the GaAs solution in the outer crucible, and 8 is a small hole. The outer crucible 3b is driven to rotate and also to move in the vertical direction. By using this double crucible, the solution is replenished from the outer crucible 3b to the inner crucible 3a, and changes in the concentration of impurities in the pulled crystal due to segregation can be reduced. It is difficult to make the temperature distribution suitable for crystal pulling, making it difficult to grow the crystal.

The present invention has been made in view of the above situation, and an object of the present invention is to provide a method for manufacturing a semiconductor single crystal that can easily grow a crystal with a uniform impurity concentration.

[Summary of the Invention] The method for producing a semiconductor single crystal of the present invention includes a liquid-sealed Czochralski method semiconductor crystal growth solution crucible formed into a dual structure of an inner crucible and an outer crucible, and the outer crucible being rotationally driven. The structure is configured such that the single crystal is pulled up from the solution in the inner crucible by being driven to move in the vertical direction, and the inner crucible and the outer crucible are connected through a small hole to replenish the solution from the outer crucible to the inner crucible, thereby preventing segregation. When growing uniform crystals by eliminating changes in the impurity concentration in the crystal due to oxidation, this method maintains the liquid level so that the solution level in the inner crucible is kept at least several mm lower than the solution level in the outer crucible.

As described above, the solution level in the inner crucible is made lower than the solution level in the outer crucible, and the inner crucible is rotated and vertically driven independently with respect to the outer crucible.

In the double crucible method, one way to adjust the temperature distribution of the solution in the inner crucible is to devise the structure and temperature distribution of the heater. For example, heating the bottom of the outer crucible to a high temperature, or vice versa. Increasing heating from above the liquid level is also somewhat effective. However, heating via the solution in the outer crucible causes heat loss, and it is difficult to create a temperature distribution in the solution in the inner crucible that facilitates crystal pulling.

If the temperature is lowered slightly to increase the crystal diameter, precipitation from the inner wall of the crucible is likely to occur, and to avoid this, increasing the heating at the top will heat the pulled crystal, making it difficult to control the crystal diameter. Put it away.

Changing the heights of the liquid levels in the inner and outer crucibles from the same level greatly increases the degree of freedom in the above points, and makes it possible to take advantage of the effects of changing the heater structure and temperature distribution, resulting in a uniform impurity concentration. can grow crystals.

The present invention is a Ga AS using the LEC method.

It is effective for the growth of compound crystals such as cap and rnp. For example, it is particularly effective for the growth of low dislocation crystals using impurity hardening by adding a large amount of In to GaAs. It can also be applied to the growth of compound crystals with a mixed crystal composition.

[Example] Hereinafter, the method for manufacturing a semiconductor single crystal of the present invention will be described.
An example will be described in which ln is added at a concentration of approximately 1 x 10 cm in the growth of an S single crystal.

FIG. 1 is a longitudinal cross-sectional view of an apparatus for carrying out the method of the present invention, and in the figure, 9 is an inner crucible drive support, so that the inner crucible 3a can be rotated and moved up and down independently of the outer crucible 3b. It has become. Inner crucible 3a diameter is 100mm
, the diameter of the outer 3b is 150m, and the GaAs is 3.5K.
rt charge, and then add B203 to the inner crucible 3a.
650! /Put 250 g into the outer crucible 3b.

When melted by heating, at the melting point of GaAs of 1238°C, the liquid thickness of 82034a in the inner crucible 3a is approximately 55 mm, and the thickness of B2034b in the outer crucible 3b is approximately 1 mm.
5mm, and the density of B203 liquid is 1.531/C.
+3, so the liquid level of the GaAS solution 5a in the inner crucible 3a is about '+' than the liquid level of the GaAS solution 5b in the outer crucible 3b.
It is kept 3mm lower.

By doing this, the temperature of the liquid near the inner wall of the inner crucible 3a is higher than that of the center, and even if the temperature of the center is lowered to a temperature that allows crystal growth, the solution will not solidify on the crucible wall.
It also becomes possible to control the crystal diameter.

The raw material GaAS may be in the form of GaAs polycrystals or
Although Ga and AS may be charged and synthesized directly, Ga
Of the above 3.5Kg as As, 1.2Ky was charged into the inner crucible 3a and 2.3Kg was charged into the outer crucible 3b.
, 1×10 20 cm° of In alone or as InAs is added to the outer cross-section 3b. GaA of ln
Since the segregation coefficient in s is about 0.1, the Irzl degree in the crystal grown by this method is given by taking the crystallization separation on the horizontal axis,
The second diagram shows the characteristic diagram with TrzlE1 degree taken on the vertical axis.
As shown by curve B of this example in the figure, the crystallization fraction:
Up to a=0.66, it is approximately constant at I x 102acm-'. Curve A is the In 1 degree distribution in a crystal that has been pulled by adding In to the initial crystal growth concentration of 1 x 10 "cm" using the conventional method. The di(1!-di) of raw materials and added impurities may be adjusted by the segregation coefficient of impurities, and in this example, the addition of other impurities to GaAs, the growth of other compound crystals, or the growth of crystals with a mixed crystal composition are used. It can also be applied to growth.

In this way, in the method for manufacturing a semiconductor single crystal of this example, the inner crucible solution surface is kept lower than the outer crucible solution surface, and the inner crucible is rotated independently of the outer crucible and driven to move up and down as desired. It is possible to easily grow crystals with a uniform impurity concentration with a high yield, and also to reduce the change in impurity concentration in the length direction of the crystal. Nonuniformity in impurity concentration is reduced, and wafers with uniform concentration can be manufactured.

In addition, instead of changing the amount of liquid sealant charged into the inner crucible and outer crucible, pressurize the solution surface by floating a donut-shaped object with a lower density than the sealant on top of the sealant. Similar effects can be obtained. Furthermore, similar effects can be obtained by using substances with different densities or whose densities are changed by additives as the liquid sealant.

[Advantageous Effects of the Invention 1] As described above, the method for manufacturing a semiconductor single crystal of the present invention has the effect of easily growing a uniform crystal with an impurity level of +1 degree.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of an apparatus for carrying out the method of manufacturing a semiconductor single crystal of the present invention, FIG. 2 is a characteristic diagram of the In concentration distribution in the crystal of the method using the apparatus of FIG. 4 are longitudinal cross-sectional views of an apparatus implementing the conventional method, respectively. 2: Pulled single crystal, 3a: Inner crucible, 3b: Outer crucible, 8: Small hole.

Claims (2)

[Claims] (1) A liquid-sealed Czochralski method A solution crucible for semiconductor crystal growth is formed into a double structure of an inner crucible and an outer crucible, and the outer crucible is driven to rotate and move in the vertical direction, and the solution in the inner crucible is removed from the solution in the inner crucible. The structure is configured so that the single crystal can be pulled up, and the inner crucible and the outer crucible are connected through a small hole to supply a solution from the outer crucible to the inner crucible, thereby eliminating changes in the impurity concentration in the crystal due to segregation and making it uniform. A method for producing a semiconductor single crystal, characterized in that the method for growing a crystal comprises maintaining the solution surface in the inner crucible at least several mm lower than the solution surface in the outer crucible. (2) The method for manufacturing a semiconductor single crystal according to claim 1, wherein the inner crucible is formed to be rotated and driven to move up and down independently of the outer crucible.