JPS63162595A - Apparatus for crystal growth - Google Patents

Abstract

PURPOSE:To obtain uniform distribution of concn. of impurities and O2 in a grown single crystal, and to attain uniform and high rate of crystal growth even if the crystal to be grown is one having a large diameter in an apparatus for crystal growth, by pulling a crystal from melt by forming a bottom of a crucible facing oppositely to a pulling section of the crystal to a protruded shape. CONSTITUTION:For example, a trapezoidal protruded bottom 2a is provided to the center of the bottom facing oppositely to the pulling section of a crystal of a graphite external crucible 2A and graphite internal crucible 2B of a crucible 2. After allowing a seed crystal 8 to contact with melt 3, a crystal 10 is grown by pulling the seed crystal. Since, in this case, substantial depth of the melt in the crucible at the crystal growth section can be made shallower, so the generation of heat convection and turbulent flow are prevented more satisfactorily. Moreover, the thickness of a diffusion layer of impurities in the crystal pulling section is made more uniform, the ununiform distribution of concn. of impurities in the radial direction can be improved. Further, since the temp. distribution in the solid phase and liquid phase can be selected to a desired temp. with reference to the diametral direction, the crystal growth rate at each part in the diametral direction can be made more uniform and increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a crystal growth apparatus for pulling and growing a single crystal such as a silicon single crystal from a crystal material melt.

[Summary of the invention]

In the present invention, in order to grow a crystal by pulling it from a crystal material melt, the bottom of the crucible that accommodates the crystal material melt is formed into a convex shape that protrudes in a limited manner in the pulling direction, especially in the portion facing the crystal pulling part. This makes it possible to make the impurity concentration and oxygen concentration uniform in each part particularly in the diametrical direction of the crystal, to make the crystal growth rate uniform in each part, and to achieve a high growth rate and therefore a high pulling rate.

[Conventional technology]

For example, the Czochralski method (CZ method) is used as a method for obtaining silicon (Si) single crystals. This C
A crystal growth apparatus using the Z method, for example, as shown in FIG. is arranged on the axis of the jacket (11).

The crucible (2) has a structure in which an inner crucible (2B) made of quartz is placed within an outer crucible (2A) made of graphite, for example. This crucible (2) is supported by a support shaft (4) arranged on its axis. This support shaft (
4) The crucible (2) is rotatable about its axis and movable in the direction of its axis.

A melt heating means (5) made of, for example, a cylindrical graphite heating element is arranged coaxially around the outer periphery of the crucible (2). This melt heating means (5) is also driven up and down in the axial direction so as to barrel.

Further, (6) is a heat insulating body which enables the crucible (2) to be heated and maintained at a required temperature by the heating means (5).

A shaft (7) that can rotate and move in the axial direction is provided at the upper part of the salmon 7 (1), and a seed crystal (8) is held at the lower end by a chuck (9). Axis (7
) by pushing it downward, the seed crystal (
The crystal (10) is grown from the seed crystal (8) by bringing the seed crystal (8) into contact with the crystal material melt (3) and pulling it up from this state. At this time, the shaft (7) and the support shaft (4) are configured to rotate in opposite directions, for example, so that the crucible (2) and the seed crystal (8) are relatively rotated at the required rotational speed. It will be done. In addition, at this time, the crystal material melt (3) in the crucible (2) decreases due to the growth of the crystal (10), and the liquid level drops, so the crucible (2) follows this drop in the liquid level and supports it. The crystal material melt (3) is lifted up by the thrust of the shaft (4) so that the surface of the crystal material melt (3) is always at a predetermined position, and the surface of the material melt (3) is always maintained at a predetermined temperature. The heating means (5) is also adapted to be propelled in the axial direction so as to be held. Also, at this time, jacket (1)
An inert gas such as nitrogen gas is fed into the jacket (1) from above as shown by arrow a, and is discharged from an outlet (11) provided below the jacket (1). . (12) shows an observation window secretly provided on the shoulder of the jacket (1) to observe the crystal pulling state.

According to such a crystal growth apparatus, it is possible to carry out pulling growth of a crystal.

However, with this CZ method, crystal growth, for example S
When i-crystal growth is performed, the concentration of impurities taken into the crystal exhibits a distribution that is low at the top of the crystal and increases toward the bottom. That is, the concentration distribution in the case of this method corresponds to normal freezing in which the rod-shaped body is gradually solidified from one end to the other, and the impurity concentration Cs in the solid phase at this time is as follows.

Cs = kCo(1-G)''°-(1) where Co is the initial concentration, G is the solidification rate, and k is the segregation coefficient.

In addition, in the case of the above-mentioned configuration, since it is necessary to store the crystal material melt (3) in an amount necessary for crystal growth in the crucible (2) in advance, the depth of the crucible (2) is Generally, one that is as deep as the diameter of the crucible (2) is used. However, as the depth of the crucible (2) increases, thermal convection in the melt (3) becomes more intense.
This causes temperature fluctuations and irregular flows of the melt at the solid-liquid phase interface in the growing part of the crystal (10), which further causes non-uniformity in the impurity concentration in the crystal and also causes crystal defects. cause the occurrence of In addition, during the growth of the crystal (10), the crucible (2) is used to maintain the liquid level of the melt, which decreases as the crystal grows, at a constant position.
The mechanical structure and control means for pushing the support shaft (4) upward and pushing the heating means (5) together with it are complicated, and it is difficult to prevent the liquid level from fluctuating ( Furthermore, the position control of the heating means (5) for maintaining the temperature at a constant temperature is complicated, and there are also problems in that highly accurate control is difficult.

Further, a diffusion layer is generated due to impurity segregation at the solid phase-liquid phase interface in the crystal growth region, and this diffusion layer is thick at the center of the crystal and thin at the periphery. For this reason, the impurity concentration in the crystal forms a distribution that is high at the center and low at the periphery, and the impurity concentration also becomes non-uniform in the diametrical direction. In order to eliminate this non-uniformity of impurities in the diametrical direction, there is generally a method of increasing forced convection by increasing the crystal rotation speed and crucible rotation speed to agitate the melt (3) and flatten the diffusion layer. Be taken. However, in this case, as the rotation of the crystal or the rotation of the crucible increases, the shape of the grown crystal is deformed, making it difficult to obtain a good cylindrical shape with uniform diameters and a straight axis. This brings about the problem of becoming.

In addition, dissolved oxygen is introduced into the grown crystal from the inner crucible (2B) made of quartz of the crucible (2), and this oxygen allows the grown crystal to be used as a semiconductor material for various semiconductor devices. When using oxygen to manufacture various semiconductor devices, for example, this oxygen acts as a getter for impurity metals that are introduced during the manufacturing process and causes crystal defects.
). However, when the relative contact movement between the quartz crucible (2B) and the melt (3) becomes intense due to the forced convection described above, the solubility of oxygen changes, for example, becomes too large and exceeds the required oxygen concentration. This causes problems such as the inability to maintain necessary control of oxygen concentration.

For example, in the single crystal growth apparatus and method using the CZ technology disclosed in Japanese Patent Application Laid-Open No. 61-36197, the depth of the crucible is made shallow and the material is supplied while the crystal is pulled up. It is designed to suppress the occurrence of convection and turbulence. According to this, the various problems caused by heat convection and the like mentioned above have been considerably improved. However, even with such an apparatus and method, as the diameter of the pulled single crystal increases, the uniformity of the concentration distribution of impurities or oxygen as a dopant in the diametrical direction and the axial growth in each part of the pulled single crystal in the diametrical direction cannot be improved. There is a problem in that the uniformity of speed is not always satisfactory.

This non-uniform growth rate is due to the fact that the temperature at the center of the crystal is difficult to dissipate, so the temperature gradient near the solid-liquid interface in this center becomes gentle.

[Problem that the invention seeks to solve]

The present invention makes it possible to further improve the uniformity and acceleration of the growth rate of impurity or oxygen concentration distribution not only in the direction of the pulling axis but also in the diametrical direction even when the diameter of the crystal to be grown is increased as described above. The present invention provides a crystal growth apparatus.

[Means for solving problems]

As shown in FIG. 1, the present invention comprises a crucible (2) containing a crystalline material melt (3), a heating means (5) disposed around the crucible (2) for heating the melt, and a melt A crystal pulling means (15) for pulling a crystal, that is, a single crystal (10) from (3)
) and means for supplying crystal material into the melt (3), the bottom (2a) of the crucible (2) facing the crystal pulling part is made convex.

[Effect]

As described above, in the present invention, by making the bottom (2a) of the crucible (2) convex, the substantial depth of the melt storage area directly below the upper part for crystals becomes shallower, so that heat therein is reduced. Since the generation of convection and turbulence is further suppressed, crystal growth is performed stably, and disadvantages such as impurities as dopants, nonuniform oxygen concentration, and deformation of the pulled crystal are avoided.

Furthermore, due to the presence of the convex bottom (2a), that is, the heat dissipation path is present near the crystal pulling part, that is, near the solid-liquid phase interface, the temperature distribution at this solid-liquid phase interface is steep. As a result, the crystal growth rate and therefore the crystal pulling rate can be increased, and efficient crystal growth can be performed.

In addition, since the heat dissipation path by this convex bottom (2a) approaches the vicinity of the crystal pulling, heat dissipation can be particularly enhanced at the center of the crystal, and the crystal growth rate at each part in the radial direction can be made uniform. be able to.

In particular, by appropriately selecting the cross-sectional shape of this convex bottom (2a), it is possible to equalize the impurity diffusion layer near the solid phase-liquid phase interface in the diametrical direction of the crystal in the crystal growth section, and to achieve the required temperature distribution, etc. can be obtained, and the impurity concentration distribution and growth rate in the diametrical direction can be made more uniform.

〔Example〕

Further, an embodiment of the apparatus of the present invention will be described with reference to FIG. In FIG. 1, parts corresponding to those in FIG. 3 are given the same reference numerals and redundant explanations will be omitted. Consisted of. In this case as well, a water cooling pipe, for example, is inserted into the wall surface of the cooling jacket (1) by protruding inward on the central axis of the cover (IB) to circulate the cooling water and perform cooling. A cooling cylinder (13) is inserted into the cooling cylinder (13).
) A crystal pulling means (15) is disposed within.

The crystal pulling means (15) is similar to that explained in FIG.
A shaft (7) that rotates and moves in the axial direction is provided on its axis, and a seed crystal (8) is held at its tip by a chuck (9).

The lower end of the cooling cylinder (13) is adapted to fit into the opening of the crucible (2) while holding the crucible (2) in a predetermined position. The inner circumferential surface of the cooling cylinder (13), which faces the crystal (10) pulled and grown by the crystal pulling means (15), has heat resistance to prevent reflection of thermal radiation, that is, to absorb heat. A radiant heat reflection prevention surface (17) is formed by adhering a large black graphite coating, SiC coating, or black thin film. Also, this cooling cylinder (
13) from the outer peripheral surface of the cooling jacket (11)
B) and the jacket body (18) are each provided with a heat-resistant insulator (16) made of, for example, fibrous graphite on the inner peripheral surface.
). Further, on the lower end surface of the cooling cylinder (13), that is, on the end surface facing the liquid surface of the raw material melt in the crucible (2), a radiant heat reflecting surface (1) that effectively reflects radiant heat is provided.
8). This reflective surface (18) has a smooth surface, for example, and can be formed by applying a metal foil such as Mo, Ta, W, etc., or a metal foil having excellent heat resistance.

A crystal supply means (
20). The crystal supply means (20) is configured to melt and supply the crystal material to the vicinity of the peripheral side wall of the crucible (2) in the crucible (2), and therefore to the high temperature heating section by the heating means (4). For example, this means (20) has a holding means (22) for holding a crystal material body (21), for example, a columnar polycrystalline body of silicon, at its upper end, and by pushing down this holding means (22), Crystal material body (
The tip of the crucible (21) is constantly in contact with the melt (3) in the high temperature part of the crucible (2) so that the melt (3) is replenished in an amount corresponding to the amount of pulling growth of the crystal (10). controlled.

This control can be performed, for example, by detecting an increase in weight due to the grown crystal (10) and melting the crystal material (21) into the crucible (2) by the amount of this increase.

On the other hand, as shown in FIG. 1, for example, a trapezoidal convex bottom (
2a), or a conical convex bottom (2a) coaxial with the central axis of pulling the single crystal, as shown in the cross-sectional view of the crucible in Figure 2. A bottom portion (2a) is provided.

The support shaft (4) of the crucible (2) consists of a shaft having the required thermal conductivity such as a stainless steel shaft having a high heat resistant part (4A) made of carbon or the like at the tip, and is configured to be rotatable. The crucible (2) can be moved in the axial direction, that is, lifted up, but in this case, the axial movement does not need to be pulled up in accordance with the growth of the crystal, and is only needed to determine the initial position.

The cooling cylinder (13) also has a pulled crystal (10
) is provided with an observation window (19) through which the images can be observed.

In order to pull a crystal using a crystal growth apparatus having such a configuration, the seed crystal (8) is brought into contact with the melt (3), and then the crystal (10) to be pulled is grown.
In this case as well, the crystal is pulled and grown while relatively rotating the pulling means (15) and the crucible (2) about their respective axes (7) and (4). In this case, the cooling circle f
fi (13) Supply inert gas from the top to the bottom as shown by arrow a through the crucible (2
) from the inside to the outer periphery of the cooling cylinder (13) and then to the crucible (2)
Inert gas is passed outside and discharged from the outlet (11) provided at the lower end of the jacket body (IA) of the cooling jacket (1).

In this case, the inert gas flows through the melt (3) in the crucible (2).
However, since there is a heat insulator (16) on the outer circumferential surface of the cooling cylinder (13), the cooling cylinder (13) is prevented from being rapidly cooled. Even if SiO is generated by contacting the quartz crucible (2B), this S
Since iO is directly sent out as a gas, it is possible to avoid inconveniences such as solid-phase SiO precipitates entering the melt (3) and causing twins or dislocations in the pulled crystal (10).

In addition, in this example, a radiant heat reflection prevention surface (17) is formed on the inner peripheral surface of the cooling cylinder (13), so that radiant heat from other parts is reflected by this cooling cylinder (13) and crystallized. (10) is avoided, and in this example, by providing the reflective surface (18), the radiant heat from the melt (3) in the crucible f21 is effectively transferred to the melt. Since the temperature of the melt can be increased, the temperature gradient at the solid-liquid interface between the crystal (10) and the melt can be maintained steeply, further increasing crystal attraction. Top speed is increased.

In addition, if necessary, waves are generated on the melt surface (3) due to the crystal supply between the crystal material supply part and the crystal pulling part, and this gives a shadow to the solid phase-liquid phase surface of the crystal pulling part. A wall (32) can be provided to prevent this.

In addition, in the above-mentioned crystal supply means (20), the crystal material is supplied by the columnar crystal material body (21), and this crystal material is supplied in the form of grains or blocks. You can also use methods. In this case, a quartz pipe may be disposed as the crystal supply means (20), and granular or bulk crystal material may be loaded into the quartz vibe.

Furthermore, the apparatus of the present invention can be applied to a magnetic field application type crystal growth apparatus, and in this case, as shown by the chain line in FIG. It may be provided on the outer periphery of / (1).

〔Effect of the invention〕

As described above, the apparatus of the present invention has a structure in which the crystal supply means (20) supplies the crystal material to the melt (3) in the crucible (2) in an amount corresponding to the growth of the crystal (10) at one time. Therefore, the overall depth of the crucible (2) can be made shallow, and the liquid level of the melt (3) in the crucible (2) can be maintained at a constant position at all times, which in itself suppresses convection and turbulence. can be suppressed. Furthermore, since the control means for lifting the crucible (2) and maintaining the liquid level at a constant position can be avoided, the apparatus can be simplified and excellent crystallinity and impurity concentration crystallinity can be improved.

In addition, particularly in the present invention, by providing the convex bottom portion (2a) at a position opposite to the crystal pulling portion of the crucible (2), the depth of the crucible of the melt in the crystal growth portion can be made shallower ( The convex bottom (2a
), it is possible to make the thickness of the impurity diffusion layer in the crystal pulling part uniform, thereby improving the non-uniformity of the impurity concentration distribution in the radial direction. In addition, this convex bottom part (2a) allows the temperature distribution of the solid phase and liquid phase in the crystal pulling part to be selected to a desired temperature in the diametrical direction of the crystal, thereby making the crystal growth rate uniform and high at each part in the diametrical direction. can be converted into That is,
When pulling a crystal in the diametrical direction, especially a trapezoidal crystal, heat dissipation at the center is insufficient, and the temperature distribution at the solid-liquid interface tends to be gentle, and the crystal velocity at the center tends to be lower than that at the periphery. However, according to the present invention, due to the existence of the convex bottom part (2a) and by selecting the shape of the bottom part, the temperature distribution tends to be lower than that in the peripheral part. The crystallization speed can be accelerated.

As mentioned above, according to the apparatus of the present invention, excellent crystals (10
), it is possible to make the required impurity concentration distribution and crystal growth state uniform, especially in the diametrical direction, and the benefits are great in practical use.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an example of a crystal growth apparatus according to the present invention, FIG. 2 is a cross-sectional view of a main part of another example, and FIG. 3 is a cross-sectional view of a conventional crystal growth apparatus. (1) is a cooling jacket, (2) is a crucible, (3) is a crystal material melt, (5) is a heating means, (15) is a crystal pulling means, (20) is a crystal supply means, (2a) is Crucible (2)
It has a convex bottom. Hidemori Matsukuma 7-legged station / I#T side closed Figure 3

Claims (1)

[Scope of Claims] A crucible containing a melt of a crystal material, a melt heating means arranged around the crucible, a crystal pulling means for pulling a crystal from the melt, A crystal growth apparatus comprising a means for supplying a material, characterized in that the bottom of the crucible facing the crystal pulling part is convex.