JP2977297B2 - Crystal manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a single crystal,
In particular, use the vertical Bridgman method of solidifying the melt as it is in a vertically placed crucible to ensure that the molten raw material and the seed crystal are brought into contact, and that the change in the growth interface position is precisely controlled. The present invention relates to a method for producing a single crystal that can be used.

[0002]

2. Description of the Related Art Single crystals of inorganic compound semiconductors (hereinafter referred to as "III-V compound semiconductors") comprising elements of groups IIIb and Vb of the periodic table, particularly gallium arsenide (GaAs) and gallium phosphide (GaP) Single crystals are field-effect transistors (FETs), Schottky barrier diodes, and integrated circuits (I
It is widely used for manufacturing various semiconductor devices such as C).

[0003] III- used for the substrate of these semiconductor elements
As a method for producing a group V compound semiconductor, particularly a single crystal of GaAs, a crystal growth method from a melt is mainly used.

The pulling method, which is one of the methods for growing crystals from a melt, is suitable for increasing the diameter of crystals, and has the advantage that a circular (100) wafer can be obtained. On the other hand, since crystal growth is performed under a large temperature gradient, there is a problem that the dislocation density of the manufactured crystal is increased.

As another method for growing a crystal from a melt, a vertical boat method for solidifying the melt in a crucible as it is to obtain a single crystal is effective. The vertical boat growth method includes a vertical Bridgman method (VB method) and a vertical temperature gradient solidification method (VGF method). According to the VB method or the VGF method, since a crystal can be grown under a low temperature gradient, a single crystal having good crystallinity can be obtained. Moreover, these methods have an advantage that they are suitable for manufacturing circular (100) wafers.

[0006] Incidentally, a single crystal to be a product must have a desired crystallographic orientation. For this purpose, a raw material melt is brought into contact with a seed crystal at the start of crystal growth (hereinafter referred to as "seed"). A predetermined crystal orientation must be determined. However, in the method in which the crucible is arranged vertically and the raw material is filled above the crucible as in the vertical boat method, the seed crystal is not movable, and precise control of the seeding position, the crystal growth rate, and the like is impossible.

FIG. 6 is a schematic sectional view for explaining GaAs single crystal growth by the conventional liquid-sealed vertical Bridgman method.

In FIG. 6, 1 is a seed crystal and 2 is a grown crystal.
GaAs crystal, 3 is a GaAs melt, 4 is a liquid sealant, 5 is a crucible having a circular cross-sectional shape, 6 is a crucible holder, 7 is a crucible shaft supporting this holder 6, and 8 is a shaft A crucible driving mechanism for rotating and moving the crucible 5;
9 is a heating element, 10 is a heat insulating material, 11 is an airtight container, 21 is a heating element 9
This is a control device for changing the heat generation power of the crucible 5 and the rotation and position of the crucible 5. (21 is not shown)

In such an apparatus configuration, the conventional technique is as follows. First, a crucible 5 is filled with a seed crystal 1, a polycrystalline GaAs material, and a solid liquid sealing agent 4. To melt the liquid sealant 4 and the GaAs polycrystal, seeding is performed while grasping the temperature condition with a thermocouple installed in the vicinity, and crystal growth is started. As shown in FIG. I was going.

However, in the above-mentioned conventional method, the seeding operation is very difficult because the seed crystal is not movable and observation from the outside is difficult. Furthermore, since the conventional method cannot detect the crystal growth speed, that is, the moving speed of the growth interface 12, accurate control of the growth speed and control of the interface shape have not been performed.

[0011]

The liquid sealing pulling method (LEC method) or the horizontal Bridgman (HB method) which is currently in practical use as a method for manufacturing compound semiconductor crystals such as GaAs single crystals. In the case of crystal growth, a viewing window is provided in an airtight container or a furnace body, a growth state is observed, and crystal growth conditions in the furnace are controlled.

On the other hand, in the case of the crystal growth method such as the vertical Bridgman method according to the present invention, the control of the crystal growth conditions such as the growth interface position, the growth rate, and the interface shape has not been performed.

Incidentally, since the growth rate of a crystal has a significant effect on the quality of a crystal to be a product, it is one of the basic techniques for crystal growth to precisely control the crystal growth rate. In crystal growth from a melt, it is essential to precisely control the growth surface of the crystal over the entire length of the grown crystal from the time of seeding to obtain a uniform and high-quality crystal.

[0014] However, it is difficult to solve the above problem by the conventional method. An object of the present invention is to provide a single crystal manufacturing method for manufacturing a uniform and high quality single crystal.

[0015]

The above object is achieved by placing a seed crystal in the bottom of a vertically arranged crucible, filling a raw material above the seed crystal, and heating and melting the raw material to form a melt. And
In a crystal manufacturing method using a vertical Bridgman method of solidifying the melt to obtain a single crystal, heating and melting of the raw material are performed using a main heating element and an auxiliary heating element, and the heat generation power of the main heating element and A method for producing a crystal according to the present invention, comprising: maintaining a constant ratio with the heat generation power of the auxiliary heating element; controlling the temperature of the main heating element; It is solved by 1).

In the above method of the present invention, in order to secure a temperature gradient so that the seeding operation can be reliably performed, the value of the ratio of the heat generation power of the main heat generation element to the heat generation power of the auxiliary heat generation element is set to 0.1. It is preferably from 5 to 0.7.

[0017] Further, the above-mentioned problem is that a seed crystal is accommodated in the bottom of a vertically arranged crucible, a raw material is filled above the crucible, and the raw material is heated and melted to form a melt, and the melt is solidified. In the crystal manufacturing method using the vertical Bridgman method for obtaining a single crystal, heating and melting of the raw material are performed using a main heating element and an auxiliary heating element, and the heat generation power of the main heating element and the heat generation of the auxiliary heating element The value of the ratio to the power is set to 0.5 to 0.7 during the seeding operation of bringing the seed crystal and the melt into contact with each other, and is gradually increased after the seeding operation to control the temperature of the main heating element to control the crystal growth. The crystal production method (2) of the present invention is characterized in that at the end, the ratio of the heat generation power of the main heat generation element to the heat generation power of the auxiliary heat generation element is set to 1.0 to 1.2. You.

[0018]

[0019]

[0020]

According to the present invention, at least one or more auxiliary heating elements are provided in addition to the main heating element for melting the raw material, and the main heating element and the auxiliary heating element are maintained at a constant heating power while maintaining a constant ratio. By changing the temperature of the body, the temperature gradient in the furnace can be precisely controlled. Therefore, the seeding operation is facilitated, and the shape of the crystal growth surface and the crystal growth rate can be precisely controlled over the entire length of the crystal to be grown.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic sectional view of an apparatus used in the single crystal manufacturing method according to the present invention. In FIG. 1, 19 is a main heating element, and 20a and 20b are auxiliary heating elements according to the present invention. 13 is a thermocouple for measuring the temperature at the lower end of the crucible.

As shown in FIG. 1, the apparatus for producing a single crystal of the present invention has an outer shape of 80 mm in an isotropic graphite susceptor 6 provided in an airtight container 11 having a heat insulating material 10 such as graphite felt. 150mm high рBN crucible 5
And the susceptor 6 and the crucible 5 are held by the support shaft 7. The heating element was made of isotropic graphite, the main heating element (main heater) 19 was 20 cm in height, and the auxiliary heating elements (sub-heaters) 20a and 20b were 10 cm in height.

FIG. 2 shows a representative example of the temperature distribution on the center axis of the hot zone. Insert a thermocouple from the top of the airtight container,
The measurement was performed by heating the heater and changing the position of the thermocouple when the inside of the airtight container became a steady state. Note that the inside of the airtight container is filled with an argon atmosphere controlled to 7 atm.

FIG. 3 shows that the temperature gradient at the center of the furnace is the ratio of the heating power of the main heating element and the auxiliary heating element (the heating power of the auxiliary heating element /
It is a graph showing how it changes with the heat generation power of the main heating element). From FIG. 3, it can be seen that the temperature gradient of the hot zone is determined by the ratio of the heating power of the main heating element to that of the auxiliary heating element.

The temperature gradient at the center of the furnace can be derived from the following equation. (Temperature gradient at the center of the furnace) = -17 x (calorific value of auxiliary heating element / calorific value of main heating element) + 24.5 A thermocouple is installed at the lower end of the crucible (= seed crystal end). Since the temperature at the lower end of the crucible can be measured, the temperature distribution in the furnace can be accurately grasped from this temperature and the temperature gradient in the furnace determined by the ratio of the heating power of the main heating element and the auxiliary heating element. . As a result, the growth rate and the interface shape can be precisely controlled.

Crystal growth was performed using the above hot zone. The raw materials used were 1.5 kg of high-purity GaAs polycrystal and 300 g of B ₂ O ₃ .

The cross section of the seed crystal perpendicular to the growth direction has a side of 5
mm square and 5 cm long were used.

After melting the raw materials, a crystal having a diameter of 3 inches could be grown at a growth rate of 3 mm / h in an argon atmosphere at 7 atm.

At the start of crystal growth, a seeding operation must be performed. In order to perform seeding, it is sufficient that one point of the region where the seed crystal is set has a melting point.

FIG. 4 is a graph showing the ratio between the temperature of the lower end of the crucible for enabling seeding and the heat generation amount of the main heating element and the auxiliary heating element. The shaded area in the figure is a condition that enables seeding. After seeding under the conditions of the points (x marks) shown in FIG. 4, the temperature distribution inside the crucible and the position of the growth interface were controlled, and as a result, the crystal growth rate and the crystal shape were controlled.

COMPARATIVE EXAMPLE Hereinafter, comparative data with the above embodiment of the present invention will be described using a case where there is no auxiliary heating element in the above embodiment as a comparative example.

(1) Reproducibility of Seeding (Seeding) Comparative Example: No reproducibility was obtained after 10 runs. That is, the seeding position changed by ± 5 mm. 3 out of 10 runs failed to seed. This Example: Reproducibility was obtained after 10 runs. That is, the seeding position was changed by only ± 1.5 mm. There were no seeding failures during 10 runs.

[Table 1]

(2) Dislocation density of crystal (EPD, unit: cm / cm ² ) Next, as a comparative example, the case where the power ratio (power consumption ratio) of the auxiliary heating element / main heating element deviates from the present invention (power ratio) It is.

[Table 2]

It can be seen that the dislocation density is smaller in the case of the present invention. FIG. 5 is an example showing a change in the power ratio of the auxiliary heating element / main heating element from seeding (seed) to completion of crystal growth (growing). This is an example of increasing the value to 1.2. As a result, the dislocation density was 1 × 10 ⁴ / cm ² or less over the entire length, which was good.

[0035]

As described above, according to the present invention, the seeding operation and the control of the position of the growth interface, which have been difficult in the past, can be accurately performed. As a result, the growth rate and the shape of the growth interface can be controlled, and the single crystallization ratio can be greatly improved. Further, the temperature distribution inside the crystal during and after the crystal growth can be controlled, and dislocations and defects generated in the crystal can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of an apparatus used for a method for producing a single crystal of the present invention.

FIG. 2 is a temperature distribution diagram inside an apparatus used in the method for producing a single crystal of the present invention.

FIG. 3 is a diagram showing how the temperature gradient inside the apparatus used in the single crystal manufacturing method of the present invention changes depending on the ratio of the amount of heat generated between the main heating element and the auxiliary heating element.

FIG. 4 is a diagram showing a temperature of a lower end of a crucible enabling seeding and a ratio of heat generation power of a main heating element and an auxiliary heating element.

FIG. 5: Seeding and crystal growth (growing)
It is a figure which shows the power ratio change of the main heating element and an auxiliary heating element until completion | finish.

FIG. 6 is a schematic longitudinal sectional view of a conventional single crystal manufacturing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Seed crystal 2 ... Grown GaAs crystal 3 ... GaAs melt 4 ... Liquid sealant 5 ... Crucible 6 ... Crucible holder 9 ... Heating element 10 ... Heat insulating material 19 ... Main heating element 20a, 20b ... Auxiliary heating element

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shinichiro Kawabata 1000, Higashikiana-cho, Ushiku City, Ibaraki Prefecture Mitsubishi Kasei Polytech Co., Ltd. (56) References JP-A-3-80181 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C30B 1/00-35/00

Claims (3)

(57) [Claims] 1. A crucible vertically arranged to receive a seed crystal at a bottom thereof, filling a raw material above the seed crystal, heating and melting the raw material to form a melt, and solidifying the melt. In a crystal manufacturing method using a vertical Bridgman method for obtaining a single crystal, heating and melting of the raw material are performed using a main heating element and an auxiliary heating element, and heat generation power of the main heating element and heat generation of the auxiliary heating element A method for producing a crystal, comprising maintaining a constant ratio with power, controlling the temperature of the main heating element, and bringing a seed crystal into contact with a melt to perform a seeding operation. 2. The method according to claim 1, wherein a value of a ratio of a heat generation power of the main heat generation element to a heat generation power of the auxiliary heat generation element is 0.5 to 0.7. 3. A crucible vertically arranged to accommodate a seed crystal at the bottom, filling a raw material above the seed crystal, heating and melting the raw material to form a melt, and solidifying the melt to form a single crystal In the crystal manufacturing method using the vertical Bridgman method, heating and melting of the raw material are performed using a main heating element and an auxiliary heating element, and a heating power of the main heating element and a heating power of the auxiliary heating element are obtained. The value of the ratio is set to 0.5 to 0.7 during the seeding operation of bringing the seed crystal into contact with the melt, and is gradually increased after the seeding operation to control the temperature of the main heating element. A crystal manufacturing method, wherein a value of a ratio of a heating power of the main heating element to a heating power of the auxiliary heating element is 1.0 to 1.2.