JPS62288186A - Production of compound semiconductor single crystal containing high vapor pressure component - Google Patents

Abstract

PURPOSE:In producing the titled single crystal by three temperature zone horizontal Bridgman method, the titled uniform single crystal free from variability of physical properties, is readily attained by using a device equipped with a vapor pressure controlling storage tank. CONSTITUTION:A quartz boat 10 packed with a raw material 16 for growing single crystal is put in a crystal growing chamber 11 of a reaction tube 14, a vapor pressure controlling element 17 is added to a vapor pressure controlling storage tank 13 and the quartz tube 14 is sealed. Heaters 15 are operated, a given temperature distribution shown by the figure is set in a growth furnace and the reaction tube 14 is placed in the furnace. The reaction tube 14 is transferred from a high-temperature side to a low-temperature side in the furnace kept at the given temperature gradient to grow single crystal. In the operation, temperature control can be automatically regulated in good precision by detecting the temperature of the storage tank by a temperature detecting means 18 such as thermocouple, etc., connected to the storage tank 13 and inputting a signal based on the information to the heaters 15. Even if the vapor pressure controlling component 17 is melted, it neither flows nor diffuses and high-precision vapor pressure control is made possible.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Field of Industrial Application The present invention relates to a method for manufacturing a compound semiconductor single crystal. More specifically, we improved the three-temperature horizontal Bridgman method,
The present invention relates to a method for producing a uniform single crystal of a compound semiconductor with no variation in properties by controlling the vapor pressure with high precision and strictly controlling the stoichiometric composition.

BACKGROUND OF THE INVENTION Although Si semiconductors still play a leading role in the modern semiconductor industry, there are problems that cannot be solved with Si. These are due to the band structure of Si. That is, since Si is an indirect transition type, it is difficult to make a highly efficient light emitting device with Si. Recently, compound semiconductors, especially ■-V group compound semiconductors, have been attracting attention because of their high electron mobility and high saturation drift velocity, and they have become a major player in realizing high-speed operation and high frequency of various semiconductor devices. Expectations are high. On the other hand, all I[-VI group compound semiconductors are of the direct transition type, and are known to produce highly efficient luminescence when excited by ultraviolet rays or electron beams, and have been the subject of numerous studies.

In addition, II-VI group compound semiconductors are particularly used in the field of optoelectronics to emit light in a wide wavelength range not found in the ■-■ group.
It has the potential to realize a light-receiving element, and generally has a wide forbidden band width (suitable as a material for window effects, and also
Since it is relatively easy to form thin films compared to group V compound semiconductors, various application fields are being considered. For example, CdTe, which is a group I[-VI compound semiconductor, can be used as a T-ray detector, an X-ray detector, or)Ig+-x(1:d
Infrared detector, CCD (Charg
e CoupledDev 1ce) etc. or C
CdS/CdTe combined with dS is being used as a thin film solar cell with little deterioration.

Incidentally, in order to manufacture the various compound semiconductor devices as described above, it is necessary to form a compound semiconductor single crystal or mixed crystal with low dislocation density and low defects. Since compound semiconductors have various properties different from those of Si, their crystal growth techniques are also completely different. For example, for St, Czochralski method (CZ method), floating zone method (FZ method), etc. are commonly used, but compound semiconductors require strict control of composition, and critical shear stress at high temperatures is small. Moreover, since it has various delicate technical problems such as the tendency for dislocations to occur due to thermal strain, it is necessary to take measures such as vapor pressure control.

Even if the atomic weight ratio of the component elements is accurately weighed and reacted in order to grow a highly pure single crystal, the resulting crystal does not necessarily have a stoichiometric composition. For this reason, it is not enough to simply question the stoichiometries (IJ-) from a chemical analysis;
This suggests that it is also necessary to take into account deviations from the tightest perfection.

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 can be used directly in the device fabrication process or as a substrate for epitaxy. used. On the other hand, the latter crystal grown by epitaxy is thin and has insufficient mechanical strength, so it cannot be used as is, and a substrate is required to support it. Therefore, bulk crystals are also of great importance in epitaxy.

Conventionally used methods for growing bulk crystals of compound semiconductors include, for example, the Bridgman method (horizontal and vertical Bridgman methods), liquid-filled Czochralski method (LEC method), FZ method, and the like.

The three-temperature Bridgman method, which is one of the Bridgman methods, controls the partial pressure of high dissociated equilibrium vapor pressure component elements in a heating furnace with plateau parts at three different temperatures and a predetermined temperature gradient. However, a single crystal is produced by moving a reaction tube containing raw material component elements at a predetermined speed.

A method for manufacturing a compound semiconductor single crystal by the conventional three-temperature horizontal Bridgman method will be explained in more detail with reference to FIG. 2 attached hereto. FIG. 2 shows the temperature distribution inside the furnace in which the reaction tube 21 is housed, and a schematic cross-sectional view of an apparatus for growing a single crystal. The plateau portion of the temperature distribution consists of the temperature T1 of the raw material melting zone, the vapor pressure control temperature T3, and the control temperature T2 for ripening of grown crystals and impurities.

The crystal growth apparatus using the horizontal Bridgman method shown in FIG.
1 and a heater 22 (heating furnace) provided so as to surround the side thereof.

When growing a compound semiconductor single crystal using this equipment,
First, a raw material 23 such as a polycrystalline compound semiconductor is put into a quartz boat 20, and is stored in a quartz tube 21.
A high vapor pressure component solid 24 for vapor pressure control is placed in the low temperature side end of the quartz tube 21 and sealed. On the other hand, the temperature distribution in the furnace as shown in FIG. 2 is set by operating the heater 22, and then the right end of the boat 20 is in the T1 region, and the high vapor pressure component solid 24 is in the T3 region. As it is,
After arranging the quartz tube and maintaining this state for a sufficient period of time for the raw material 23 to melt and for the melt to reach a uniform temperature, the furnace or quartz tube 21 is moved at a predetermined speed to grow crystals. . The temperature of the raw material melt-growing crystal interface during growth is approximately at the middle of the transition from the T1 region to the T2 region (m).

p, ) part.

Thus, by performing single crystal growth while controlling vapor pressure, low dislocation density and compositional stoichiometry can be achieved.
A compound semiconductor single crystal that is satisfactory in terms of these points can be obtained.

It should be noted that quartz tubes are also known that consist of a single crystal growth chamber divided into two by a partition wall equipped with a capillary and a high vapor pressure component storage chamber, which also achieves good vapor pressure control. be able to.

Problems to be Solved by the Invention As mentioned above, in order to manufacture various compound semiconductor devices, it is necessary to manufacture a single crystal that is uniform and has low defects with little deviation from perfection. Several methods have been proposed and used.

Among these, the three-temperature zone horizontal Bridgman method is a frequently used technique because it provides good controllability of composition. Moreover, it has been found from experience that good results can be obtained by setting T3 in the range of 760 to 850°C. However, when the Bridgman method is used to manufacture a single crystal of CdTe, which is a ■-■ group compound semiconductor,
Since the boiling point of d is 767°C (melting point = 324°C), it will reach a molten state or boil within the range of the vapor pressure control temperature T3. As a result, the Cd melt flows and diffuses in the vapor pressure control component solid within the quartz tube or the vapor pressure control chamber. Therefore, the vapor pressure control range, that is, the temperature (T3) control range, also extends over a wide range, and in such a case, it becomes extremely difficult to maintain a uniform temperature distribution. This means that the physical properties of the grown single crystal cannot be controlled to predetermined values.

As described above, in order to manufacture a compound semiconductor single crystal containing a component that melts or boils under vapor pressure controlled temperature, as seen in CdTe single crystal growth,
It is not possible to use the conventional apparatus as described above as is, and it is necessary to make some kind of improvement or devising to overcome the above-mentioned problems.

Therefore, the development of a new method for producing single crystals has been desperately desired. Therefore, the purpose of the present invention is to improve the conventional three-temperature zone horizontal Bridgman method and provide a method for producing a bulk single crystal with excellent stoichiometry and less deviation from perfection, with uniform properties. It's about doing.

Means for Solving the Problems In view of the current state of the method for producing bulk single crystals of compound semiconductors containing high vapor pressure components by the three-temperature horizontal Bridgman method, the present inventor proposed the above-mentioned conventional method. As a result of various studies and studies to develop new techniques to solve the problems presented by the above, it was discovered that it is effective to provide a storage tank for controlling steam pressure, and based on this knowledge, the present invention was completed.

That is, the method for manufacturing a compound semiconductor single crystal of the present invention uses a reaction tube equipped with a crystal growth chamber and a vapor pressure control storage tank that communicates with the crystal growth chamber through a communication means. A boat filled with raw materials for semiconductor single crystal growth is stored in the chamber, high vapor pressure component elements are stored in the vapor pressure control storage tank, and the sealed reaction tube is placed inside a furnace maintained at a predetermined temperature gradient. It is characterized by moving from the high temperature side to the low temperature side.

The method of the present invention is effective for single crystal growth of compound semiconductors having a high dissociation equilibrium vapor pressure, and is particularly effective for growing single crystals of compound semiconductors with high precision, such as CdTe, which melts or boils under vapor pressure controlled temperatures. It is useful in the single crystal growth of compound semiconductors, which have various difficulties in pressure control, and also their mixed crystals.

A single crystal growth apparatus suitable for use in the method of the present invention includes a crystal growth chamber 11 for accommodating a boat 10 for storing raw materials for single crystal growth (for example, a quartz boat), and a crystal growth chamber 11 for accommodating a boat 10 for storing raw materials for single crystal growth, and a communication means 12 connected thereto. It includes a reaction tube, for example, a quartz tube 14, which is configured with a connected vapor pressure control element storage tank 13, and a heater 15 disposed around the outer circumference of the quartz tube 14. Here, the vapor pressure control element storage tank 13 may have a concave portion of sufficient depth to hold the element within a specific narrow area even if the element becomes molten. Furthermore, in consideration of ease of manufacturing, etc., it is desirable that the growth chamber be made of the same material as the growth chamber.

The means of communication between this and the growth chamber so that the vapor from the former can freely move into the growth chamber is a capillary or a somewhat large diameter tube with pores provided inside the tube, preferably on the growth chamber side. It is preferable that the structure be constructed using a partition wall member having the following structure.

When carrying out the method of the present invention using the horizontal Bridgman method single crystal growth apparatus shown in FIG. The boat 10 is housed, while the vapor pressure control element 17 is put into the storage tank 13, and the quartz tube 14 is sealed. On the other hand, the heater 15 is operated to set a predetermined temperature distribution in the growth furnace as shown in the upper part of FIG. 1, and the reaction tube 14 is placed inside the growth furnace.

At this time, the right end of the boat 10 is included in the T1 area, while the storage tank 13 is placed in the temperature control area, and is maintained in this state for a sufficient period of time to equalize the temperature and steam. Achieve pressure equilibration.

Next, the furnace or quartz tube is moved at a predetermined speed, generally 0.01 to 1 cm/hour, inside the furnace where the temperature distribution as described above is maintained, and the melt in the quartz boat is moved from T1 to T2 direction. By doing so, crystal growth is caused near the melting point (m, p,) of a substantially intermediate portion of the transition region between the T1 portion and the T12 portion.

Temperature control of the vapor pressure control component is performed by detecting the temperature with a temperature detection means 18 such as a thermocouple connected to the storage tank 13, and inputting a signal based on the information to the heater to automatically and accurately adjust the temperature. Furthermore, even if the component 17 is melted into a liquid state as shown in FIG. 1, it will not flow or diffuse, making it possible to control the vapor pressure with high precision from this point of view as well.

The temperature adjustment section of this vapor pressure control component, that is, the T3 region, is adjusted to form an upwardly convex monotonically decreasing curve as shown in the temperature distribution in FIG. This is advantageous because the vapor of the pressure-controlled component can flow smoothly and the component can be prevented from flowing back from the growth chamber.

In the above-mentioned apparatus of the present invention, there is no particular restriction on the heating method, and various conventionally known methods such as resistance heating, induction heating, and radiation heating (lamp, arc, laser, etc.) can all be used, and direct heating is also possible. In cases where this poses a problem, it is of course possible to provide shielding with a heat soaking tube, liner tube, or the like.

The quartz reaction tube and the boat for crystal length are heated in advance at a high temperature (approximately 1100°C) in an inert gas or flashing gas for a long period of time (
You can expect good results if you use one that has been baked (about 8 hours or more). It is desirable that the crystal growth boat be made of a material that has characteristics such as low thermal conductivity, no "wetting," no contamination of the melt and crystals, and no change in shape.

Quartz glass has the above characteristics, but when quartz is used as a boat for crystal growth, adsorbed gases such as 02 gas and 820 remain on the inner wall of the quartz tube, and residual oxides in the raw materials may remain. Since the presence of a trace amount of carbon contaminates the single crystal, it is preferable to coat the quartz surface with carbon. Non-reactive materials such as pyrolytic boron nitride (PBN) tubes are also useful as crystal growth boats.

It is generally said that it is difficult to produce bulk single crystals of IF-VI group compound semiconductors among compound semiconductors, because they contain high vapor pressure components, and the components melt under controlled temperature conditions. This is due to the problem of boiling, which makes it difficult to control vapor pressure.

However, according to the method for manufacturing a compound semiconductor single crystal of the present invention, firstly, by using an apparatus provided with an elemental component storage tank for vapor pressure control, it becomes liquid under controlled temperature conditions and does not boil. Even if it contains components, it can be reliably held within a predetermined area, so that it can flow and diffuse into the vapor pressure control chamber or crystal growth chamber, as was the case with conventional equipment. There is no fear of making vapor pressure control difficult or deteriorating the quality of the grown sato crystals, and accurate and strict vapor pressure control can be realized.

Furthermore, by setting the temperature distribution (T3) in the vapor pressure control region to an upwardly convex single meter decreasing curve, it is possible to easily move the vapor of the vapor pressure control component, and moreover, the vapor pressure control component can be easily transferred from the crystal growth chamber. In this case, vapor pressure control can be performed with even higher accuracy since backflow of the vapor can be prevented.

Thus, according to the method of the present invention, even for materials that melt and flow under controlled temperature conditions, such as Cd in CdTe, which is a typical example, there is no composition shift and integrity can be maintained, which was difficult with conventional methods. Also, it is possible to advantageously obtain a good compound semiconductor single crystal.

However, the method of the present invention is not limited to these, and can of course be applied to any compound semiconductor containing a component that generally has a high dissociation equilibrium vapor pressure.

EXAMPLES Hereinafter, the single crystal manufacturing method 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 crystal growth chamber 11 is installed on the left side as shown in FIG.
A CtlTe wheel crystal was manufactured using a horizontal Bridgman type crystal growth apparatus equipped with a vapor pressure control storage tank 13 on the right side. In this case, partial pressure control was performed by charging Cd into the vapor pressure control storage tank 13 and adjusting its temperature. Cd and Te with a purity of 6 nines (99,9999%) were used as raw materials. CdTe as a raw material is placed in a carbon-coated quartz boat 10 and placed in the crystal growth chamber 11 inside the high-purity quartz tube 14, while Cd is placed in the vapor pressure control storage tank 13 as described above. The quartz tube was vacuum sealed at a vacuum level of I x 10-7 torr. Such a reaction tube 14 is preheated to T+=1130°C, '
r2 = t05Q °C and T, = 760-850 °C (
The reactor tube 14 is inserted into the furnace where the temperature is set by operating the heater so that the temperature decreases (monotonically decreasing), and when temperature equilibrium is sufficiently achieved, the reaction tube 14 is moved in the direction of crystal growth at a predetermined speed (3 mm/hr). A CdTe single crystal was grown (the obtained single crystal is designated as A).

On the other hand, we also fabricated single crystals using the conventional three-temperature zone horizontal Bridgman method.

In the conventional method, a temperature distribution and a reaction apparatus as shown in FIG. 2 were utilized. As in Example 1, the raw materials were placed in a reaction tube, which was evacuated and sealed.

Temperatures with three different plateau parts, respectively T, = 1
130℃,'r2=t050℃,'r,=820℃
When the raw material melt sufficiently reached temperature equilibrium, the reaction tube was moved at a predetermined speed (3 mm/hr) in the crystal growth direction to grow a CdTe single crystal (the obtained single crystal was B).

The two types of CdTe single crystals A and A thus obtained were sliced perpendicularly to the longitudinal direction of the crystal, the resistance of each crystal piece was measured, and the results were plotted in FIG. In FIG. 3, the horizontal axis represents the length along the longitudinal direction of the crystal, and the vertical axis represents the logarithm of the resistivity ρ of CdTe.

As is clear from the results in Figure 3, when comparing single crystals A and B, single crystal A obtained by the method of the present invention is a p-type crystal with high resistance and excellent stability of characteristics. It can be seen that the resistivity, which is one of the characteristics of the crystal, of single crystal B produced by the conventional method varies greatly depending on the position of the crystal. The reason for this is thought to be that in the conventional method, the Cd melt for vapor pressure control flows toward the high-temperature part of the reaction tube, resulting in a high Cd vapor pressure control area. A region is formed.

Effects of the Invention As explained in detail above, according to the method for manufacturing a compound semiconductor single crystal of the present invention, by providing a storage tank for vapor pressure control, precise and highly accurate production can be performed within a limited predetermined area. It has become possible to control the vapor pressure of high vapor pressure component elements. As a result, it is possible to obtain a uniform single crystal with few deviations from perfection, uniform characteristics, and low defects.

Therefore, the method of the present invention can control the vapor pressure with sufficient accuracy even for components that melt or even boil within the controlled temperature range, such as CdTe, and can control the vapor pressure within the same growing crystal. High-quality single crystals without characteristic distribution can be obtained. Since it has traditionally been difficult to obtain single crystals of this type, the ability to produce high quality single crystals of II-VI compound semiconductors is extremely significant for the future development of this field.

Furthermore, by adjusting the temperature distribution of the vapor pressure control section as described above, it becomes possible to control the vapor pressure with higher precision, and it becomes possible to further improve the quality of the obtained single crystal.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing a preferred embodiment of an apparatus useful for carrying out the method for manufacturing a compound semiconductor single crystal of the present invention, and also shows the temperature distribution of the apparatus. , FIG. 2 is a cross-sectional view schematically showing a conventional three-temperature zone horizontal Bridgman method crystal growth apparatus, and also shows the temperature distribution of the apparatus, and FIG. 3 is a graph showing the resistivity distribution in the longitudinal direction of C, dTe single crystals synthesized by the method described above and the conventional method. (Main reference symbols) 10, 20...Quartz boat, 11...Crystal growth chamber, 1
2...Communication means, 13...Storage tank, 14, 21...Quartz tube, 15.22...Heater, L6.23...Raw material,
17.24... High vapor pressure component, 18... Thermocouple patent applicant Masaru Mochizuki Mimasu Moto Tsuyoshi Sumitomo Electric Industries, Ltd.

Claims (3)

[Claims] (1) Using a reaction tube equipped with a crystal growth chamber and a vapor pressure control storage tank that communicates with the crystal growth chamber via a communication means, the crystal growth chamber is filled with raw materials for compound semiconductor single crystal growth. The reaction tube, which has been sealed with high vapor pressure component elements stored in the vapor pressure control storage tank, is moved from the high temperature side to the low temperature side in a furnace maintained at a predetermined temperature gradient. 1. A method for producing a semiconductor single crystal containing a high vapor pressure component, characterized in that single crystal growth is performed by: (2) A patent characterized in that, in the temperature distribution in the furnace, the temperature of the steam pressure control storage pipe and the communication means is adjusted so as to decrease along an upwardly convex monotonically decreasing curve. The manufacturing method according to claim 1. (3) The manufacturing method according to claim 1 or 2, wherein the compound semiconductor is CdTe.