JPS62158187A - Method and device for producing single crystal of semiconductor - Google Patents

Abstract

PURPOSE:To maintain concn. of a component having high dissociation pressure in the growth direction to the prescribed uniform value and to obtain single crystal or mixed crystal having strict stoichiometric composition by controlling independently the vapor pressure of plural components having high dissociation pressure respectively in the production of single crystal or mixed crystal of a semiconductor of multi-elemental compd. by a natural solidification method. CONSTITUTION:Single crystal or mixed crystal of a semiconductor of a multi- elemental compd. is produced by a natural solidification method. In this produc tion, both a boat 16 housing melt of a raw material and the componental elements (e.g. A and B) having high dissociation equibrium vapor pressure are arranged respectively at the inside of a reaction pipe 10. Also the temp. distribution of the inside of a furnace housing the reaction pipe 10 is regulated so that at least four-plateau parts having different temp. are formed. The vapor pressure in a growth chamber 12 of at least two kinds of componental elements (e.g. A and B) having high dissociation equibrium vapor pressure is indepenetally controlled, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for manufacturing compound semiconductor single crystals or mixed crystals. More specifically, by improving the natural U solid state, controlling the vapor pressure with high precision, and strictly controlling the stoichiometric composition, we can create a uniform compound semiconductor single crystal or compound semiconductor with no variation in properties. The present invention relates to a method for forming mixed crystals with good productivity and an apparatus therefor.

BACKGROUND OF THE INVENTION Remarkable progress has been made in material research on compound semiconductors, centering on ■-■ group compound semiconductors such as GaAsXInP, and research on the practical application of devices. For example, compound semiconductor lasers, photodiodes as light-receiving elements for optical fiber communications, avalanche photodiodes, and the like have already been put into practical use, and great expectations are placed on them.

In addition, recent trends include faster operation and faster operation of semiconductor devices.
Higher frequencies are required, and in order to achieve such improvements, compound semiconductors such as GaAs of the ■-■ group, which have high electron mobility and high saturation drift velocity, are attracting attention.

Furthermore, in the case of compound semiconductors of the ■-■ group, it is possible to obtain mixed crystals relatively freely while maintaining good semiconductor properties. For example, a ternary mixed crystal of GaAs and InAs (I
A semiconductor crystal having intermediate physical properties (such as forbidden band width) between GaAs and 1nAs can be obtained by producing 1nAs. Such mixed crystals can be expected to realize semiconductor devices with interesting physical properties that cannot be realized with conventional single semiconductors or binary compound semiconductors, and are useful for light-emitting devices such as visible light laser diodes, P
Light-receiving devices such as IN diodes, as well as heterojunction devices and superlattice devices (HEMT), which have been attracting attention recently.
, multi-quantum well laser, etc.).

By the way, in the manufacturing process of various compound semiconductor devices as described above, first of all, it is essential to form a highly pure single crystal or liquid crystal.

However, since these have various characteristics different from conventional 31, their crystal growth techniques are also completely different.
For Si, etc., the Czochralski method (CZ method), floating zone method (FZ method), etc. are widely used, but when using GaAs as an example, strict control of the composition (Ga:As ratio) is required. Furthermore, there are subtle technical problems such as the fact that the critical shear stress at high temperatures is small, and dislocations are likely to occur due to thermal strain.

Crystal growth of compound semiconductors can be broadly divided into bulk crystal growth and epitaxy. A plate-shaped crystal called a wafer is cut from the bulk crystal, and this is either directly sent to the following processing process or used as a substrate for epitaxy. It will be used as. On the other hand, the latter crystal grown by epitaxy is thin and therefore has insufficient mechanical strength, so it cannot be used as is and requires the use of a substrate.

The Bridgman method (vertical Bridgman method, horizontal Bridgman method), pulling method (LEC method), FZ method, etc. have been used for a long time as methods for growing bulk crystals of the above-mentioned compound semiconductors, and the principles thereof are, for example, The vertical Bridgman method involves growing crystals by moving a quartz container or the like containing a raw material melt into the low temperature section of a heating furnace, which consists of a high temperature section and a low temperature section. In addition, in order to prevent the formation of disordered crystal nuclei, the diameter of the container is narrowed at the point where the melt starts to solidify.In this area, fewer nuclei are formed, and within this area, the orientation in which they grow faster than in other areas. The one with this functions as a seed crystal.

The current mainstream Bridgman method is the horizontal Bridgman method, in which the raw material melt is moved horizontally using a boat.It is used as a mass production method for single crystals such as GaAs, and is called the three-temperature method (three-temperature HB). method), two-temperature method (two-temperature HB method), etc. However, the latter two-temperature method has inherent problems such as insufficient reproducibility of the characteristics of GaAs grown, such as electron density, and a low proportion of solidified GaAs that becomes a single crystal. and
The former three-temperature method was mainly used.

The conventional three-temperature method will be explained in more detail with reference to the attached FIG. 3. As is clear from the figure, this method has three plateau portions in the temperature distribution. Each temperature T7, T2 and T
3 is adjusted to a constant value so that the relationship T + > T 2 > T 3 holds. These temperatures are controlled by a plurality of heaters (not shown) provided on the outer periphery of the reaction tube 1 made of a quartz tube or the like. The reaction tube 1 is divided into two by a partition wall 3 provided with a capillary 2 for preventing gas diffusion, for example, and a quartz boat 4 is sealed in a growth chamber on the left side of the reaction tube 1. - In the compartment on the Mangoku side, there is a high dissociation pressure component (for example, B
) is housed therein, and by controlling the vapor pressure, it is possible to control the dissociation of the crystal growth raw material melt and, in turn, the stoichiometry of the resulting crystal composition.

A raw material melt (AB) L is stored in the quartz boat 4, and by moving the boat 4 to the low temperature side (T2), a single crystal (AB) is produced.

grows.

In the actual three-temperature HB method, a quartz boat called a shelf boat is used. In this figure, the solid-liquid interface is approximately T+
The melting point (m, p,
) part.

The methods for producing bulk crystals of compound semiconductors as described above are used appropriately depending on the physical properties of the crystal to be grown, its type, etc. Recently, there has been a need for semiconductor materials with low defects, especially due to demands for improving device characteristics.
-The dislocation density has already reached 10 in the pulling method using methods such as In doping and applying a magnetic field, which are found in group V GaAs.
A high dislocation-free state of 0/C1'11 or less has been achieved. On the other hand, in the ■-■ group compound semiconductor, Zn5e
Development and research on SCdTe etc. is actively progressing.
For example, it is known that it is possible to reduce defects in CdTe by doping Zn at a high concentration to form a mixed crystal.

However, as mentioned above, when a third additive element such as In or Zn is used for the purpose of reducing defects in the bulk crystal, a concentration distribution occurs within the crystal, especially for elements whose segregation coefficient deviates by more than 1. It is known. This point will be explained in more detail with reference to FIGS. 4a and 4b. That is, for example, in the case of a substance shown in the phase diagram shown in Figure 4a (
When the segregation coefficient is 1), when a liquid with a liquid phase composition of C8 is solidified, a solid with a composition of a is precipitated when the point p (temperature T) is reached, and when the temperature is further lowered (T2), The composition becomes b, and when it is further cooled, it changes to composition C and completely solidifies. When a solid of composition a is precipitated at the above point p, component X (for example, an impurity) is expelled from the solid, and as a result, the concentration of component A concentration gradient will be formed.

As explained in detail above, even though dopants were originally used for the purpose of reducing defects, there is a concentration distribution along the growth direction in the resulting crystal, making it difficult to obtain a homogeneous product with a predetermined composition. Can not.

Furthermore, attempts have been made to grow crystals by providing a high temperature gradient in order to solve the problem of concentration distribution, but this resulted in an increase in defect density.

It seems that the above problem can be solved by the three-temperature HB method as shown in Figure 3, but it is also possible to create a mixed crystal containing two or more components with high dissociation pressure, or to create a mixed crystal containing two or more components with high dissociation pressure. This is ineffective when attempting to add a high concentration of a dopant with a high dissociation pressure to the crystal, and it is impossible to obtain the desired bulk crystal with few defects and sufficient stoichiometry.

Problems that the original S
It is becoming difficult to meet these requirements using only single-element semiconductors such as i. Therefore, compound semiconductors that can operate at high speeds and operate at high frequencies, have high mobility, saturation drift speed, etc. are attracting attention, and are expected to become even more important in the future.

In order to fabricate various devices using such compound semiconductors, it is necessary to obtain compound semiconductor crystals or mixed crystals with high purity and low defects, but unlike Si, etc., these require special care when growing single crystals. There are some technical issues that require this. Among these, it is particularly important to perform strict vapor pressure control and to stably obtain bulk single crystals and mixed crystals with chemical composition and uniform characteristics.

In this regard, the conventional method described above is particularly effective when using an element whose segregation coefficient deviates widely from 1, such as when using a third additive element, or when using an element whose segregation coefficient deviates widely from 1, or when using an element that contains two or more components with a high dissociation pressure. This method is completely ineffective for the production of bulk mixed crystals, and the development of new bulk crystal production techniques is strongly desired. In addition, in order to eliminate the drawbacks regarding the segregation coefficient,
Growth methods with a high temperature gradient have also been proposed, but only negative results have been achieved in that the defect density increases.

Therefore, the purpose of the present invention is to use the natural coagulation method (normalfr).
eezing method) and the growth direction (D
The object of the present invention is to provide a method for manufacturing a bulk single crystal of a multi-element compound semiconductor that maintains the concentration of a high dissociation pressure component at a predetermined uniform value, has excellent stoichiometry, and has uniform properties.

Another object of the present invention is to provide a bulk single crystal manufacturing apparatus for carrying out the above method.

Means for Solving the Problems The present inventor has developed the above-mentioned method and apparatus for producing bulk single crystals or mixed crystals of multi-element compound semiconductors, particularly multi-element compound semiconductors containing elements having high dissociation pressure as components. In view of the current situation, we have conducted various studies and research to develop a new technology that solves the drawbacks of the conventional methods mentioned above.
We have found that it is effective to separately control the vapor pressures of at least two high dissociation equilibrium vapor pressure components, and have completed the present invention based on this knowledge.

That is, the present invention has 1. First, it relates to a method for manufacturing semiconductor single crystals (hereinafter the term "single crystal" is used to include mixed crystals and dopants), and this method involves moving a boat containing a raw material melt to a predetermined temperature gradient. A method for producing a multi-element compound semiconductor single crystal by a natural solidification method in which crystal growth is performed by moving the crystal from a high temperature side to a low temperature side in a furnace maintained at The method is characterized in that the temperature is adjusted to form a plateau portion, the vapor pressures of at least two high dissociation equilibrium vapor pressure component elements are controlled, and the vapor pressure control is performed for each high dissociation pressure component.

The present invention also relates to an apparatus for carrying out the above method, the apparatus comprising a growth chamber and at least two storage chambers for high vapor pressure components, each separated by a partition wall, and a storage chamber and the growth chamber. The reactor tube is characterized by comprising a reaction tube equipped with a capillary that communicates with each other independently, and a furnace equipped with a heating means for forming at least four plateau portions with different temperatures.

The method and apparatus for producing multi-element compound semiconductor crystals of the present invention are related to improvements in the natural solidification method, and in particular are multi-element compound semiconductors containing two or more high vapor pressure (or dissociation pressure) components. The present invention can be advantageously applied to cases where the segregation coefficient deviates widely from 1, but is of course not limited to these.

Therefore, the present invention is applicable to, for example, a mixed system of CdTe and ZnTe, a system in which CdTe is doped with Se, a mixed crystal of a II-VI group compound semiconductor or a ■-■ group compound semiconductor, an I-
It can be advantageously applied to the production of III-VI type compound semiconductors, II-IV-V type compound semiconductor single crystals, etc.

FIG. 1 is a schematic cross-sectional view of the apparatus of the present invention, and the apparatus of the present invention will be explained in more detail below based on this figure. That is, the device of the present invention has T.

(raw material melt zone), T2 (crystallization zone), T3 (heating zone of the first high vapor pressure component, e.g. A) and T,
The reaction tubes 10, e.g. , Pyrex, Vycor pipes, etc. will be installed. This reaction tube has a growth chamber 12 separated by melting walls 111, 112, and at least two high vapor pressure component storage chambers 13, 14, and a growth chamber 12 and each storage chamber 13.
．． Capillary 15 that independently communicates with 14...
．． ．． It consists of 15□...

By configuring the reaction tube 10 as described above and independently controlling the temperature of each component in the storage chamber, which is independently communicated with the reaction chamber 2 by each capillary, the corresponding high vapor pressure component in the reaction chamber 12 can be controlled. The vapor pressure can be sufficiently adjusted, and a uniform single crystal with a predetermined composition and excellent stoichiometry can be obtained.

In the apparatus of the present invention, the number of storage chambers 13, 14, etc. is not particularly limited and can be adjusted as appropriate depending on the number of high vapor pressure components in the single crystal to be formed. Therefore, for example, four storage chambers can be prepared in advance, and 1, 2, 3 or 4 storage chambers can be used as needed, and of course each storage chamber has the number of storage chambers that match the composition of each species. It can be used selectively depending on the case.

According to another aspect of the present invention, as shown in FIG. 2, it can also be of a vertical type, the structure of which is similar to the horizontal type device shown in FIG. Therefore, the same numbers will be given and the explanation will be omitted.

In the apparatus of the present invention, there is no particular restriction on the heating format;
Various conventionally known methods such as resistance heating, induction heating, and radiation heating (lamp, arc, laser, etc.) can all be used, and in cases where direct heating would be a problem, soaking tubes, liner tubes, etc. can be used. Of course, it is also possible to perform shielding.

In particular, when it is necessary to provide a considerable temperature difference along the growth direction as in the present invention, divided heating by heaters, various baths (air bath, molten metal bath, etc.), and even heat pipes may be used. It is valid.

According to the present invention, it is an object of the present invention to obtain a single crystal of a multi-element compound semiconductor in which the concentration distribution of high vapor pressure components in the crystal growth direction is uniform. Therefore, in order to achieve this, a storage chamber for high vapor pressure components is provided in the conventional three-temperature HB, etc., so that the vapor pressure in each reaction chamber can be independently controlled.

This vapor pressure control is performed by controlling the temperature of each storage chamber, and in the early stage of growth, that region is maintained at a relatively high temperature so as to increase the vapor pressure of the high vapor pressure component in the reaction chamber, while in the late stage of growth, On the contrary, it is preferable to lower the vapor pressure in the growth chamber. The reason for this is already explained with reference to FIGS. 4a and 4b.

As stated above, no growth method or apparatus has been developed that is advantageous for the synthesis of single crystals of multi-element compound semiconductors, especially when obtaining single crystals containing multiple high vapor pressure components. Or, when trying to obtain a single crystal of a two-element compound semiconductor that contains components whose segregation coefficient deviates significantly from 1, or is doped with such impurities, the various methods and devices that have been proposed in the past are ineffective. there were.

By the way, by independently controlling the vapor pressures of a plurality of high vapor pressure components according to the present invention, it is possible to advantageously produce a single crystal of the multi-element compound semiconductor with excellent stoichiometry and low defects. became. Set this point to group a A
The production of a single crystal of a ternary compound semiconductor having l-MB-C will be described in detail below as an example.

For example, according to the horizontal Bridgman method shown in FIG. 1, this example involves mixing a BC compound semiconductor with an AC compound semiconductor having different dissociation pressures to form a mixed crystal with the above composition. This corresponds to manufacturing a multi-element compound semiconductor single crystal having a uniform concentration distribution over the growth direction.

Here, assuming that the dissociation equilibrium vapor pressure is in the relationship PR>PA>PC, component A is stored in the higher temperature zone T3, while component B is stored in the lower temperature zone T.

A quartz boat 16 is housed in the growth chamber 12, into which AC and BC polycrystals are charged as raw materials, and as already mentioned, the A component is placed in the storage chamber 151, and the A component is placed in the storage chamber 15°. The B components are placed in boats 170 and 172, respectively. In this state, the quartz tube 10 is sealed,
A single crystal is grown by operating a heater in a split heater furnace or the like so that the temperature distribution as shown in FIG. 1 is achieved, and by moving the reaction tube in the direction of crystal growth. In this case, the temperature T of the heater is related to the temperature of the growth chamber that controls crystal growth.

and T2 are always adjusted to be constant.

On the other hand, the heaters for the T3 zone and the T4 zone are each adjusted to vary according to a predetermined temperature program. This temperature program can be determined in advance by performing preliminary experiments. Furthermore, it can be combined with a combinator or the like so that the heater can be automatically controlled according to such a temperature program. At this time, under the situation where T 4 > T 3 must be satisfied in order to achieve the required vapor pressure in the growth chamber, the heater can be controlled in this way, but this low temperature region (T4) Care must be taken not to affect the growth boat 16.

Such operations and temperature control are the same when a vertical device as shown in FIG. 2 is used.

As described above, by producing a multi-element compound semiconductor single crystal according to the method and apparatus of the present invention, a high-quality product with a uniform concentration of each component along the crystal growth direction and a low defect density can be obtained. I can do it.

Furthermore, by separately and independently controlling the equilibrium vapor pressures of a plurality of high dissociation pressure components in the reaction chamber as in the present invention,
Formation of mixed crystals containing multiple high vapor pressure element components, which was previously impossible, and also in the case of containing components with segregation coefficients that deviate widely from 1, or when such dopants are added, the total length of the growing crystal can be reduced. This means that it is possible to advantageously obtain a product with a uniform concentration distribution over the entire range.

Therefore, even when cutting wafers from the obtained bulk crystal (ingot), wafers with uniform properties can be mass-produced with a high yield, which is economically advantageous, and can be said to be an extremely advantageous method from an industrial perspective.

EXAMPLES Hereinafter, the method and apparatus of the present invention will be explained in more detail according to examples, and the effects thereof will be demonstrated.
The present invention is not limited to these in any way.

Example 1 In this example, a single crystal (mixed crystal: [:d + - xZn,Te
) was created. In this case, vapor pressure control is controlled by Cd and Zn
However, since Cd requires higher temperature, Cd was used.
d was stored in the T3 zone, and Zn was stored in the T zone.

To, T2 and T3 zones are respectively 1150℃, 103
By setting the temperature at 0° C. and 820° C. and appropriately controlling the temperature of the T4 zone, the concentration within the ln crystal was adjusted.

In this example, the target Zn composition X was set to 0.045. CdTe and ZnTe were charged into the boat 16 at a ratio corresponding to this, and single Zn and CdTe were added for steam pressure control.
were placed in storage chambers 13 and 14, respectively. In this state, the reaction tube is sealed and placed in a furnace adjusted to the above temperature, and when temperature equilibrium has been sufficiently achieved, the reaction tube is heated at a predetermined speed (0.3 cm/
Cdo, 5ss2no, and o4sTe mixed crystals were grown by moving the reaction tube 10 in the growth direction (direction of T2).

At this time, the temperature of the T3 zone, that is, the temperature of simple Zn, was set to 650°C at the initial stage of growth (Zn vapor pressure in the reaction chamber: 0.045 atm).
), and in the late stage of growth, the temperature was controlled at 612°C (Zn vapor pressure in the reaction chamber = 0,021'atm).

On the other hand, the same mixed crystal was grown by a conventional method (three-temperature HB method) under similar conditions but with vapor pressure control only for Cd.

Two types of mixed crystals thus obtained, Cdo, 5ssZno,
A wafer of an appropriate thickness was cut from o+sTe along the crystal growth direction, and the Zna degree at each position was measured according to the X-ray microanalyzer method, and the results were plotted in FIG. In FIG. 5, the horizontal axis represents the extra length from the direction of crystal growth or the position of the wafer, and the vertical axis represents the Zn concentration.

As is clear from the results in Figure 5, CdTe and 2n
Comparing Te, the segregation coefficient of 2nTe is 0.7, and according to the conventional method, as seen in Figures i4a and 4b, most of it is expelled from the crystal at the early stage of growth, and Z is removed at the end of growth.
It can be seen that n is concentrated (see solid line in Figure 5).
. On the other hand, according to the method and apparatus of the present invention, it can be seen that Zn is distributed almost uniformly over the entire crystal growth direction (see the dotted line in FIG. 5). That is, according to the present invention,
It can be easily understood that by controlling the vapor pressure of a plurality of components, a crystal ingot having extremely uniform concentrations of each component element can be formed.

Effects of the Invention As explained in detail above, according to the method and apparatus for producing a single crystal of a multi-element compound semiconductor of the present invention, the vapor pressure of a plurality of high dissociation pressure components can be controlled. The composition of a crystal containing a high dissociation pressure element or a mixed crystal containing a component whose segregation coefficient greatly deviates from 1,
It becomes possible to uniformly maintain a predetermined level over the entire produced crystal.

Therefore, according to the present invention, it is possible to cut out wafers with uniform characteristics at a high yield from a produced single crystal ingot, resulting in significant improvements in terms of productivity and economy.

[Brief explanation of drawings]

Attached FIG. 1 is a cross-sectional view schematically showing a preferred embodiment of the apparatus for producing a multi-element compound semiconductor single crystal of the present invention, and also shows the temperature distribution of the apparatus. 1 is a diagram similar to FIG. 1 showing another preferred embodiment of the device of the present invention, and FIG. 3 is a diagram similar to FIG.
This is a schematic cross-sectional view similar to FIG. 1 for explaining the apparatus in method B, FIGS. 4a and 4b are diagrams for explaining the drawbacks of the conventional method, and FIG. 5 is a sectional view similar to FIG. Cd synthesized by the method of the present invention and conventional method
3 is a graph showing the concentration distribution of Znt in the length direction in the o, 5ssZno, and a4sTe mixed crystals. (main reference number)

Claims (10)

[Claims] (1) Crystal growth of single crystals or mixed crystals is achieved by moving the boat placed in the reaction tube, which houses the raw material melt, from the high temperature side to the low temperature side in a furnace maintained at a predetermined temperature gradient. A method for producing a multi-element compound semiconductor single crystal or mixed crystal by a natural solidification method, the temperature distribution in the furnace being adjusted to form at least four plateau portions of different temperatures, and at least two high temperature The method for producing a multi-element compound semiconductor single crystal or mixed crystal as described above, characterized in that the vapor pressures of dissociated equilibrium vapor pressure component elements in a growth chamber are controlled, and the vapor pressures are controlled independently of each other. (2) The vapor pressure in the reaction chamber is controlled so that at least the component exhibiting the maximum dissociation equilibrium vapor pressure has a high vapor pressure in the early stage of growth and a low vapor pressure in the late stage of growth. A method for producing a multi-element compound semiconductor single crystal or mixed crystal according to claim 1, characterized in that: (3) The vapor pressure control of the component element having a high dissociation equilibrium vapor pressure is carried out by operating a heater according to a predetermined temperature program. A method for producing a multi-element compound semiconductor single crystal or mixed crystal. (4) The above-mentioned single crystal or mixed crystal is a II-VI group or III-V group compound semiconductor single crystal or mixed crystal, I-III-VI type or II-IV-V type compound semiconductor, which may contain a dopant. Claims 1 to 3 are characterized in that:
A method for producing a multi-element compound semiconductor single crystal or mixed crystal according to any one of Items 1 to 9. (5) A reaction tube comprising a single crystal or mixed crystal growth chamber and at least two storage chambers for high vapor pressure component elements, each separated by a partition wall, and a capillary that communicates each storage chamber with the growth chamber. , a furnace equipped with heating means for forming at least four plateau portions of different temperatures, the reaction tube being accommodated in the furnace, and the reaction tube being moved within the furnace at a predetermined speed. Equipment for producing single crystals or mixed crystals of multi-element compound semiconductors. (6) An apparatus for producing a multi-element compound semiconductor single crystal or mixed crystal according to claim 5, wherein the apparatus is of a horizontal type. (7) An apparatus for producing a multi-element compound semiconductor single crystal or mixed crystal according to claim 5, wherein the apparatus is of a vertical type. (8) An apparatus for producing a multi-element compound semiconductor single crystal or mixed crystal according to claim 6 or 7, characterized in that the reaction tube has two storage chambers. . (9) The heating means is divided into four parts by a divided furnace,
9. The apparatus for producing a multi-element compound semiconductor single crystal or mixed crystal according to claim 8, wherein the temperature of each of the heating means for the storage chamber is independently controlled. (10) An apparatus for producing a multi-element compound semiconductor single crystal or mixed crystal according to claim 9, wherein the storage chamber heating means operates according to a predetermined program.