JPS61158888A - Production of single crystal - Google Patents

Abstract

PURPOSE:To obtain high-quality single crystal, by using an X-ray transmitting material as the material of heater, container, etc. of an apparatus for growing a single crystal by shifting a molten raw material from a high-temperature furnace to a low-temperature furnace, and inspecting the growing state of the single crystal by X-ray diffraction method. CONSTITUTION:The sealing tube 1, the heater 9, the furnace wall 8, etc. of a furnace having plural temperature zones having different temperatures are made of an X-ray transmitting material (e.g. carbon). The sealed tube 1 containing a molten raw material liquid 2 in vacuum is transferred from the high-temperatur side to the low-temperature side. X-ray 13 generated from the X-ray source 12 is passed through the slit 11 and radiated to the crystal plane at an angle alpha to a point (a) near the solid-liquid interface of the growing crystal, and the Bragg's reflection 13', 13'' scattered by the crystal surface (a) are detected by the X-ray detector 14 (e.g. scintillation counter). The detected intensity and the reflection pattern of X-ray are investigated to enable the instant, continuous and accurate judgement of the state of the growing crystal 4 and obtain a single crystal of a group III-V compound semiconductor (e.g. GaAs) having high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing single crystals. More specifically, the present invention relates to a method of manufacturing a high-quality semiconductor bulk crystal with few defects using the vertical Bridgman method or the horizontal Bridgman method.

BACKGROUND ART Remarkable progress has been made in material research on compound semiconductors, mainly III-V group compound semiconductors such as GaAs s I n P, and research on the practical application of devices. for example,
Compound semiconductor lasers in optical fiber communications, which have already been put into practical use, and photodiodes as their light receiving elements;
There are great expectations for products such as avalanche photodiodes (ADPs).

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

On the other hand, in a compound semiconductor manufacturing process, first of all, it is essential to form a highly pure single crystal.

Since these have different characteristics from conventional Si, their single crystal growth techniques are also completely different. For Si, etc., Czochralski method (CZ method), floating zone method (FZ method), etc. Although it is widely used, for example, Ga
Taking As as an example, strict control of the composition (Ga:^S ratio) is required, and there are also delicate technical problems such as the small critical shear stress at high temperatures and the tendency for dislocations 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 produced from the bulk crystal, and it is directly sent to the following processing process or used as an epitaxy substrate. . However, crystals grown by epitaxy are thin and have low mechanical strength, so they cannot be used as they are, and require a substrate.

Among them, the Bridgman method (vertical Bridgman method, horizontal Bridgman method) has been used since ancient times as a method for growing bulk crystals.
For example, in the vertical Bridgman method, crystals are grown by moving a quartz container 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. . Therefore, in order to prevent crystal nucleation from occurring in a disorderly manner, the diameter of the container is narrowed at the point where the melt starts to solidify, so that fewer nuclei are generated in this area, and those with orientations that grow faster than others. It plays the role of a seed crystal.

In addition, the current mainstream Bridgman method is the horizontal Bridgman method, in which the raw material melt is moved horizontally using a boat, and is used as a mass production method for single crystals such as GaAs.
Three-temperature method (3-degree HB method), two-temperature method (2-degree HB method)
etc. are known.

The HB method will be explained based on the attached Fig. 2. For example, a quartz boat 3 containing a GaAs melt 2 is placed in a quartz tube 1 having a high temperature region and a low temperature region, and this is placed on the high temperature side (T)I. )
The single crystal 4 is grown by moving the crystal to the low temperature side (TL). On the other hand, with the diffusion barrier 5 in between, the As solid 6
It is possible to control the steam pressure. It is also possible to place a seed crystal 7 on the low temperature side of the boat 3 to grow a single crystal having a predetermined growth orientation.

By the way, as mentioned above, in the production of semiconductor bulk crystals, the growth state is monitored during the crystal growth stage to confirm that stable crystal growth conditions are maintained in the furnace, and to produce high-quality products with fewer defects. It is important to obtain single crystals.

Conventionally, in the vertical and horizontal Bridgman methods, the crystal state was monitored through a peephole and the facets of the crystal were observed to determine the crystal state.

For example, in the horizontal Bridgman method, as shown in FIG. I was checking to see if it was polycrystalline.

Problems to be Solved by the Invention As mentioned above, there are extremely high expectations for compound semiconductor devices, and it is thought that their importance will increase even more in the future. By the way, in order to manufacture highly reliable and stable compound semiconductor devices, it is necessary to manufacture single crystals of each compound semiconductor with high purity and low defects, and various methods and devices have been proposed and utilized for this purpose. It has been.

Furthermore, in order to obtain uniform crystals, it is important to observe the growing single crystal by some means and, depending on the results, devise a monitoring mechanism to ensure that the optimum crystal growth conditions are always maintained. . It is therefore extremely desirable to obtain a single crystal with low defects, increase the manufacturing yield of semiconductor devices, and guarantee the reliability of the semiconductor devices.

However, the conventional monitors, particularly those using the Bridgman method, simply rely on monitoring through a viewing window provided through the furnace wall and heater.

In conventional monitoring mechanisms like this, the presence of the observation window causes the temperature distribution in the vicinity to be disturbed and unstable, and since the observation window is located near the solid-liquid interface, it is difficult to disturb the heat during crystal growth. However, it has been difficult to grow low-defect, high-quality single crystals.

Therefore, it is important to eliminate the instability of temperature distribution caused by the presence of such a viewing window, to guarantee an optimal stable temperature distribution, and to develop a highly accurate monitoring mechanism. It is of great significance in the fabrication of devices using this method, and has been strongly desired.

Therefore, an object of the present invention is to provide a method for manufacturing a single crystal using the Bridgman method that enables such monitoring, and also to provide a highly reliable semiconductor single crystal with low defects. There is one.

Means for Solving the Problems In view of the current state of conventional methods, the present inventors have conducted various studies to develop a new method for manufacturing semiconductor single crystals that meets the above objectives. We have discovered that monitoring the crystalline state of crystals using X-ray diffraction and forming the furnace material, heater, enclosure tube, etc. from X-ray transparent materials is extremely advantageous in achieving the above objectives. , completed the invention.

That is, the single crystal manufacturing method of the present invention involves moving a vacuum-sealed container containing a raw material melt from a high temperature side to a low temperature side in a furnace having a plurality of temperature zones with different temperatures. In the vertical Bridgman method or the horizontal Bridgman method, the furnace material, heater, and container are made of an X-ray transparent material, and the growing single crystal is irradiated with X-rays to determine the intensity of diffracted X-rays or reflected X-rays. The method is characterized by obtaining a pattern, determining the state of the crystal during growth based on the result, and growing the crystal while adjusting the growth conditions.

XI useful in the method of the invention! As the transparent material, materials made of substances with a small atomic weight generally have high permeability to XII, so for example, carbon, quartz, aluminum nitride, alumina, boron nitride, etc. can be advantageously used. .

In addition, to detect the diffraction intensity and pattern of X-rays, various known detectors are used, such as a scintillation counter set to detect characteristic X-rays, a proportional counter, or a photographic or image amplifier that detects Bragg reflection patterns. You can do it by doing this.

Hereinafter, the method of the present invention will be explained in more detail with reference to the attached FIG.

In FIG. 1, parts similar to those in FIGS. 2 and 3 are given the same numbers and their explanations will be omitted.

FIG. 1(a) is a schematic diagram showing a longitudinal section of the apparatus used in the horizontal Bridgman method, and FIG.
It also shows the monitoring mechanism using X-ray diffraction.

A point sleeve) 1 is placed at point a near the solid-liquid interface of the growing crystal 4.
X-rays 13 from an X-ray source 12 are irradiated through the X-ray source 12 at an angle α to the crystal surface, and the Bragg reflection 13°, 13” scattered at the crystal surface a is detected by the X-ray detector 14. Thus detected. By examining the X-ray intensity or reflection pattern, it is possible to determine the state of the growing crystal, for example, whether it is single crystal, twin crystal, or polycrystal.

The method for producing a single crystal of the present invention can be applied to single crystals of various materials, particularly compound semiconductors, GaAs5GaP, InAs, In
It can be advantageously used for the production of III-V group compound semiconductors such as P, and is especially advantageous for producing single crystals of compounds with high dissociation pressures that are difficult to control and handle using other methods.

Function: In the method of the present invention, by forming the furnace material, the heater material for realizing various temperature ranges of the furnace, and the vacuum sealing container from an X-ray transparent material, the presence of a viewing window, which was seen in the conventional method, can be avoided. It is possible to eliminate disturbances (instability) in the temperature distribution in the furnace due to the above, and to obtain a stable temperature distribution. Therefore, it is possible to prevent various crystal defects from occurring due to such instability of temperature distribution, and to obtain a high-quality single crystal.

Furthermore, it is now possible to use X-rays to monitor the growth state of the crystal, and therefore the state of the growing crystal can be tracked more closely, and the result can be used to grow the crystal with higher precision. Conditions can be controlled.

For example, if the growing crystal is twinned or polycrystalline, defects can be removed by returning a considerable portion of the grown crystal to the high temperature side, melting it, and growing the crystal again under sufficient growth conditions. can be kept to a minimum.

The structural integrity of the bulk crystal thus obtained can be evaluated, for example, by treating the surface of a wafer cut from the bulk crystal with an etching solution and from the density of etch bits formed at that time. Furthermore, more rigorous methods include X-ray diffraction, electron beam diffraction, and low-speed electron diffraction.

In this way, generally speaking, it is not possible to determine the completeness, single crystallinity, etc. of a crystal until after the crystal growth operation is completed, but according to the method of the present invention, the crystallinity can be observed at each moment during the crystal growth operation. This makes it possible to respond to defects as soon as they occur, shorten operating time, reduce labor, and significantly improve yields.As a result, high reliability of semiconductor devices, etc. can be ensured, and their manufacturing yields can be increased. becomes possible.

For example, when the grown crystal is polycrystalline, the X-ray intensity detected by a diffraction X-ray detector will greatly decrease or disappear, and there will be a shift in the growth direction. In some cases, the strength is non-uniform, so the growth condition of the growing single crystal can be determined from these results, and the growth conditions can be optimized.

The same applies when using a Bragg reflection pattern. In this case, if the angle of Bragg reflection with respect to the crystal plane is β, then the reflection angle 2θ (= α + β) can be 0 and 2θ < 180°, but in order to obtain a strong Bragg reflection, 2θ must be 1
It is desirable that the X-ray irradiation position a be within the range of 0" to 40°.
The position of the solid-liquid interface can be detected by the difference in the X-ray intensity or reflected X-ray pattern between when the X-rays hit the raw material melt surface and when they hit the crystal. , can be easily determined in this way.

In the method of the present invention, various conventionally employed means can be employed to produce a bulk single crystal with high purity. For example, as already mentioned, volatile components (
In the case of GaAs single crystal production, for example, solid As is placed in the low temperature side of a vacuum sealed container to adjust the vapor pressure.
Alternatively, there is a method of doping with 02 gas (without using AS203) to prevent contamination with residual impurities, such as Si.

In addition, a boat with shelves is used as a boat to store the raw material melt, seed crystals are placed on the shelves, and the solid-liquid interface is adjusted to be on the shelves to grow single crystals in a predetermined growth direction. You can also do it. In general, in the Bridgman method, among the naturally occurring nuclei, those with a plane with a high growth rate (<111> direction in the case of GaAs) serve as seed crystals, so a seed crystal ゛ is not necessarily required. When growing a crystal, if only naturally generated nuclei are used, the directions within the growing crystal will be uneven, and generally a single crystal will not be formed.

Therefore, in the latter case it is important to use seed crystals. Although the growth direction may be any direction, the direction with the fastest growth rate is generally selected.

It is also possible to add impurities during the crystal growth process in order to control the conductivity of the single crystal, and this is generally done by adding impurities to the raw material melt. For example, G
In the case of aAs, Si, Te5S are used to obtain an n-type crystal.
Doping is performed with ri, etc., and with Zn, etc. to obtain an n-type crystal. Furthermore, in some cases it is necessary to obtain a semi-insulating crystal, in which case it can be doped with Cr, O□, etc.

EXAMPLES Hereinafter, the method of the present invention will be explained in more detail using examples, and its effects will be demonstrated. However, the scope of the present invention is not limited in any way by the following examples.

Example 1 A GaAs single crystal was produced using a 3-temperature HB furnace (furnace walls made of carbon and quartz). The crystal growth state is 3
The growing crystal surface was irradiated with an X-ray beam through a point slit of +no+φ (α=12°). Here, first, the surface of the growing crystal, that is, the solid-liquid interface, is x! ! The source and the image amplifier for detecting reflected X-rays were moved to B-B° in Figure 1, and the intensity of the scattered X-rays detected at that time was determined, and the X-ray incident point a was determined based on this. . The black reflection X-ray pattern thus detected is shown in FIG. Here, Fig. 4 (a
) is a reflection pattern corresponding to a single crystal, and (b) is a reflection pattern corresponding to a polycrystal, making it possible to judge the crystallinity during growth and adjust the growth conditions accordingly.

Effects of the Invention As described in detail above, according to the method for producing a single crystal of the present invention, the furnace material, heater, container, etc. are made of an X-ray transparent material, and the crystal growth state is monitored using X-rays. By doing so, it became possible to achieve various effects as described below.

That is, first of all, since there is no longer a need for a peephole as in the conventional method, the temperature distribution near the peephole due to its presence is not disturbed and is therefore significantly affected by temperature changes (temperature distribution). It is possible to prevent fluctuations in the growth state of the crystal and to prevent the occurrence of various defects, and it is possible to obtain a high-quality bulk single crystal. In addition, since the growth state of the crystal is monitored using X-rays, it is possible to closely track the state at each moment at all times and make accurate judgments. The determination of crystallinity is not inaccurate, as is the case when it is determined by

[Brief explanation of the drawing]

FIG. 1(a) is a schematic cross-sectional view for explaining the horizontal Bridgman method, which is an embodiment of the method of the present invention; FIG. 2 is a diagram similar to FIG. 1(a) for explaining the two-temperature zone horizontal Bridgman method, and FIG. 3 is a diagram showing the conventional X-ray monitoring mechanism. FIG. 4 is a diagram for explaining a horizontal Bridgman single crystal manufacturing apparatus having a peephole;
Figures (a) and 3) are diagrams showing Bragg reflection X-ray patterns obtained in Examples of the present invention, in which (a) is a pattern corresponding to a single crystal, and (b) is a pattern corresponding to a polycrystal. (Main reference numbers) 1. Sealing tube, 2. Raw material melt, 3. Boat, 4. Single crystal, 5. Diffusion barrier, 6. As solid, 7. Seed crystal.
8. Furnace wall, 9. Heater, 10. Peephole,
11...Point slit, 12...X-ray source, 13...X
Ray beam, 14...X-ray detection device patent applicant Sumitomo Electric Industries-Co., Ltd. Agent
Patent Attorney Masahiko Arai Figure 1 (a) (b) 1... Keisuniri'! ' 11. 4 slit 2...raw material M demon 12. -0XAL source 9...Heater Fig. 2 7...Japanese crystal

Claims (3)

[Claims] (1) In a furnace with multiple temperature zones with different temperatures,
In the vertical Bridgman method or the horizontal Bridgman method in which a single crystal is formed by moving a vacuum-sealed container of raw material melt from a high temperature side to a low temperature side, the furnace material and the heater that forms each temperature zone in the furnace are used. The growth state of the single crystal can be determined by making the material and container made of an X-ray transparent material, continuously irradiating the growing single crystal with X-rays, and measuring the intensity of the diffracted X-rays or the reflected X-ray pattern. The method for producing a single crystal as described above, characterized in that the single crystal is formed while monitoring and controlling the growth conditions according to the result. (2) The method according to claim 1, wherein the X-ray transparent material is one selected from the group consisting of carbon, quartz, aluminum nitride, alumina, and boron nitride. (3) A scintillation counter detects the X-rays,
The method according to claim 1 or 2, characterized in that the method is carried out using a proportional counter, a photograph or an image amplifier. (4) The single crystal is III-V
4. The method according to claim 1, wherein the method is a single crystal of a group compound semiconductor.