JPS6385082A - Method for growing single crystal and apparatus thereof - Google Patents

Abstract

PURPOSE:To enable the control of the form of interface between solid and liquid over the whole crystal ingot in a vertical temperature gradient coagulation method for the production of a single crystal by solidifying a molten liquid in a crucible, by constantly maintaining the temperature of peripheral part contacting with the inner wall of the crucible to a level higher than the temperature of the core part in a cross-section of the molten liquid in the crucible at a definite height. CONSTITUTION:A molten liquid (or solution) 2 of a raw material is formed in a crucible 1, which is placed in an environment having a vertical temperature gradient higher at the upper part and lower at the bottom part. The molten liquid is slowly cooled and solidified from an end of the crucible to effect the growth of a single crystal having a shape corresponding to the inner shape of the crucible 1. In the above procedure, the peripheral temperature of the molten liquid contacting with the inner wall of the crucible is constantly maintained at a higher level than the core part in a cross-section of the molten liquid 2 at a definite height. The growing interface of the crystal is shifted from the bottom upward to effect the crystallization of the material while keeping the interface to a flat form or slightly upwards convex. The crystallization is carried out by the use of an interface form controlling means (a plate member 11, etc.) which is rotatable or vertically movable in the molten liquid and effective in controlling the thermal flow or molten liquid flow.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a crystal growth method in which a melt is solidified as it is in a crucible to obtain a single crystal with a shape corresponding to the shape of the crucible.
For example, in the vertical bridge method and vertical temperature gradient solidification method,
The present invention relates to a single crystal growth method and a growth apparatus that enable control of the shape of the crystal growth interface (solid-liquid interface) throughout the ingot, which is essential for obtaining a high-quality single crystal.

(Prior Art and Problems to be Solved by the Invention) In bulk crystal growth from a melt, controlling the shape of the solid-liquid interface is one of the basic techniques essential for obtaining a high-quality single crystal. In the growth of semiobtainable crystals by the pulling method used as substrates for optical and electronic devices, the shape of the solid-liquid interface is generally controlled by a combination of controlling the melt flow by rotating the crucible and controlling the heat flow by devising the hot sea/structure. are under control. As is well known, the shape of the solid-liquid interface changes from time to time as crystal growth progresses, so for example, by continuously changing the crystal rotation speed as crystal growth progresses, A method of controlling the shape of the solid-liquid interface over the entire grown crystal ingot has also been proposed.

However, in addition to the pulling method, growth methods that obtain single crystals by solidifying a melt in a crucible, such as the vertical Bridgman method or the vertical temperature gradient solidification method, are promising methods for growing large-diameter bulk single crystals. Since this is a growth method that essentially does not use a rotating medium, it is impossible to control the melt flow by the crystal rotation described above, and it is difficult to improve the hot zone structure by changing the solid-liquid interface shape only in a part of the crystal ingot. The current situation is that it is under control. Figure 6 shows an example (W, A, Gaultet al, J,
C, G 74 (198sp491-506) o Holding the crucible 1 during crystal growth of a group IV compound semiconductor in which the melt 2 prepared in the crucible 1 is solidified upward from the seed crystal 3 This is an example in which an attempt was made to control the shape of the solid-liquid interface by forming concentric grooves 5' in the vertical direction in the susceptor 4' to control the dissipation of heat from the growing crystal. Fig. 7 schematically shows the effect in comparison with the case of using a susceptor without grooves (Fig. 8). In the figure, arrows indicate heat flow near the solid-liquid interface.

Figures 7(a) and 7(b) show the early stage and late stage of growth when using a grooved susceptor, respectively.
Figures (a) and (■) correspond to the early and late stages of growth, respectively, when using a susceptor without grooves.

As is clear from the comparison between the two sides, in the early stage of growth, the lateral dissipation of heat from the crystal can be controlled by using a grooved susceptor. That is, considering point A in Figure 6, the flow of heat in the horizontal direction (X) is affected by the adiabatic effect due to the void inside the groove, while the flow in the vertical direction (downward: y) is The heat flow is parallel to the groove, so it is not adiabatic.

Therefore, as shown in FIG. 7(a), only the dissipation of heat in the lateral direction can be suppressed. However, in the method of controlling the dissipation of heat from the crystal through such a susceptor provided with a void, the effect is naturally limited to the vicinity of the susceptor, and becomes significantly smaller at locations far away from the susceptor. As shown in Fig. 71) and Fig. 8), in the late stage of growth, the presence or absence of grooves has almost no effect on the dissipation of heat from the crystal; 7(a), Φ), a large amount of heat is dissipated laterally through the wall surface of the crucible. However, in such a crystal growth method, the upper Since the temperature is high and the temperature below is low, when a large amount of heat is dissipated laterally through the crucible wall when viewed from a certain height of the melt, the temperature of the melt at the center of the crucible rises. The shape of the crystal growth interface, where the temperature at the periphery is lower compared to As a result, the shape of the crystal growth interface becomes concave upward. Here, regarding the relationship between the shape of the growth interface and the crystal quality, it is well known from experience that when the growth interface is concave upward, polycrystallization tends to occur, and the stress strain is large and the quality deteriorates. The reason for this is thought to be that if the crystal has a concave shape, the tensile force generated when the crystal is slowly cooled from the outside increases, resulting in a deterioration in quality.

In general, growing crystals cool faster on the surface than on the inside, so near the solid-liquid interface they have a radial temperature distribution of high temperature at the center and low temperature at the periphery, with compressive stress at the center and tensile stress at the periphery. receive.

When such stress exceeds a certain critical value, subgrains are generated from the outer periphery to relieve the stress, leading to polycrystalization.

The radial temperature distribution of the crystal strongly depends on the shape of the solid-liquid interface. FIG. 9 schematically shows the isothermal part of the crystallite near the solid-liquid interface. (a) shows the case where the interface shape is concave toward the top of the melt, (b) shows the case where it is flat, and (C) shows the case where it becomes convex.

The temperature difference between the center and the outer periphery in a cross section perpendicular to the growth axis is greatest when the growth interface is concave (a);

It can be reduced by flattening or convexing the growth interface with (c). In other words, it can be seen that polycrystalization can be prevented.

Ninth, it is important to carry out the entire growth process while maintaining the shape of the crystal interface in a flat or slightly upwardly convex state.

Therefore, in the conventional technology having the grooves (voids) shown in FIG. 6, only the characteristics at the initial stage of growth shown in FIG. The drawback was that it was not possible.

Single crystal growth by the above method becomes more difficult as the ingot length increases. On the other hand, increasing the ingot length is an essential requirement in order to reduce crystal manufacturing costs, and makes it possible to control the solid-liquid interface shape not only in a part of the crystal ingot but also over the entire ingot. This is why the development of technology is strongly desired.0 (Objective of the Invention) The present invention has been proposed to improve the above-mentioned drawbacks. The purpose of this study is to provide a new growth method and growth apparatus that make it possible to control the solid-liquid interface shape over the entire crystal ingot, which has been difficult and rare in the past.

(Means for Solving the Problems) In order to achieve the above object, the present invention creates a heated melted raw material melt (or solution) in a crucible, and vertically places the crucible with a high temperature In this method, the melt is placed in an environment with a temperature gradient where the temperature is low at the bottom, and the melt is slowly solidified from one end of the crucible to grow a single crystal with a shape corresponding to the inner surface shape of the crucible. When viewed in cross section, the temperature of the peripheral area in contact with the inner wall of the crucible is always kept higher than that of the center, thereby maintaining the crystal growth interface in a flat or slightly convex state with the center facing upward. Tsutsu,
The gist of the invention is a method for growing a single crystal, characterized in that crystallization is carried out by moving the crystal growth interface downwardly and upwardly.

Further, the present invention provides a crucible having a small-diameter portion at the bottom in which a minute seed crystal is to be installed, a seed crystal provided in the crucible, and a raw material molten material filled in the crucible in a heated molten state. (-1st order is a solution); and a heating means for vertically imparting a temperature gradient such that the upper part is higher temperature and the lower part is lower temperature, and the crucible and the heating means are In an apparatus for growing a single crystal in a shape corresponding to the inner surface shape of the crucible by changing the relative positional relationship and slowly cooling and solidifying it from one end of the crucible, the device moves in conjunction with the movement of the crystal growth interface and is in a molten state. When placed in a raw material melt at The gist of the invention is a single-crystal growth apparatus characterized in that it has at least an interface shape control means so that the center portion thereof maintains an upwardly convex state.

Therefore, the growth apparatus according to the present invention can move up and down 9 in the melt.
The most significant feature is that it has an interface shape control means for heat flow control or melt flow control that can be turned off by rotational movement. From the start to the end of crystal growth, the position and rotational speed of the plate member included in the interface shape control means in the melt are continuously controlled. Control the liquid surface shape. As a result, it is possible to obtain crystals in which the solid-liquid interface shape is controlled over the entire ingot, which is different from the conventional growth force method, which uses devising a hot zone structure, which allows the interface shape to be controlled only in a part of the crystal ingot. Examples of the present invention will be described in detail, which differ greatly in effects.

It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements may be made without departing from the spirit of the present invention.

, 6 FIGS. 1 and 2 show 2 of the interface shape control method of the present invention.
FIG. 2 is a diagram explaining the basic principle of two methods.

Here, 1 is a crucible, 2 is a raw material melt of the crystal to be grown,
3 is a seed crystal, 4 is a crystal part that has already grown (solidified), and 5 is a crystal part that has already grown (solidified).
11 indicates a liquid sealant when a volatile element is used, and 11 indicates a plate-like member which is the main part of the interface shape control means.

Here, for the sake of the following explanation, FIG. 1 will be referred to as a heat flow control method, and FIG. 2 will be referred to as a melt flow control method. First, the heat flow control method shown in FIG. 1 will be explained.

(υMethod using heat flow control The arrows in the diagram indicate heat flow. The melt temperature is high in the upper part and low in the lower part, and has a vertical distribution in the radial direction from the top to the bottom. A heat flow distribution exists.A plate member 11 having a heat-insulating effect is placed in the melt above the crystal growth interface 40 via a support rod 12 connected to a support and drive mechanism. If so, the plate member 11
Above the position where the plate-like member 11 exists, the heat flow from above to the downward direction is constant, but the plate-like member 11 leaves a gap and blocks or reduces the heat flow in the central part. Below where 11 is located, the amount of heat flowing downward from the upper high temperature area is controlled so that it is large in the peripheral area near the crucible wall surface and small in the central area. the result,
When viewed in cross-section at the same height, the center part is lower in temperature than the peripheral part near the crucible wall surface, and the crystal growth interface has a flat or slightly upwardly convex shape.

This growth interface shape can be controlled by changing the distance between the interface 40 and the plate-like member 11, or by changing the thickness, diameter, and cross-sectional shape of the plate-like member 11.

Here, although not shown, if the plate member is raised while keeping the distance between the plate member 11 and the crystal growth interface 40 constant, and the lower end of the crucible is slowly cooled and solidified, the inner surface of the crucible High-quality single crystals that correspond to various shapes can be obtained.

Next, a melt flow control method will be explained.

α) Method using melt flow control In the method shown in FIG. 2, the plate member 11 may be a thin plate that basically does not have a heat insulating effect. When the plate-shaped member 11 provided in the melt on the crystal growth interface is rotated as shown in the figure, due to the magnitude relationship of the viscosity of the melt in each part, the lower surface of the plate-shaped member 11 and the plate-shaped member As the plate member 11 rotates, the melt located near the outer periphery of the plate member 11 begins to rotate in a horizontal plane. As a result, the pressure in this area decreases due to the Bernoulli effect, and the high temperature melt above is drawn in through the gap, as shown by the arrow in the figure.
A flow of melt occurs.

As a result, the melt temperature near the crucible wall increases, and the above (I
), the shape of the crystal growth interface can be flat or upwardly convex.

This shape can be controlled by the rotation speed of the plate member or the distance between the plate member 11 and the crystal growth interface 40. In addition, similarly to (1), if the plate-shaped member is raised while keeping the distance between the plate-shaped member 11 and the crystal growth interface 40 constant, and the lower end of the crucible is slowly cooled and solidified, the inner surface of the crucible High-quality single crystals that correspond to various shapes can be obtained.

Two methods for controlling the shape of the crystal growth interface have been described above, but a method that combines these two methods, that is, a method in which a plate having a heat insulating effect is used and the plate is rotated is also possible.

Note that in (I) and CI[) above, if the surface of the plate member is made of a material that is inert to the raw material melt, the purity of the melt will not be lowered, so that higher quality can be achieved.

Next, other embodiments of the present invention will be described with reference to the wJa diagram. In this case, as shown in FIGS. 3(a) to 3(d), when the plate member 11 constituting the interface shape control means has a downwardly convex cross-sectional shape and is located at the lowest position, the minute seed crystals There is no difference from the previous embodiment except that the small-diameter portion 3' that is filled is sealed. That is, the plate member 11 is required to move in the vertical direction as the crystal grows, but it may or may not have a rotation function. The unique effects of this embodiment are clear from the comparison between the conventional manufacturing method (Fig. 4(a) to (d)) and the present invention (Fig. 3) to (d). When the raw material is heated and melted, it has a function of preventing contact between the seed crystal 3 and the melt 2 until the composition of the melt becomes completely equal to the composition of the crystal (and seed crystal) to be grown. The point is that there is. For example, it is particularly effective in the case of a compound semiconductor such as GaAs and a composition in which the constituent elements have significantly different melting points. In FIG. 4(b), G
Since the melting point of a is 1240°C or higher, a melt of only Ga is formed first, and when this comes into contact with the seed crystal, the seed crystal melts and then becomes a single crystal. During the process, crystals with the desired crystallographic orientation cannot be obtained (FIG. 4(d)).

In order to solve this problem, the inventors previously proposed a technique of sealing the part containing the m-child crystal with a cylindrical rod (Method for Manufacturing Compound Semiconductor Single Crystal, filed on September 16, 1988). and its manufacturing device, inventors: Shintabe Miyazawa, Hideo Nakanishi, Keigo Senyo In the present invention, the cylindrical rod of the previous application is replaced with a downwardly convex plate-like member, and the function of sealing the seed crystal is @In the subsequent crystallization process (slow cooling and solidification process), the above-mentioned crystal interface shape control function is used in combination.From Fig. 3(d) onwards, the crystal growth interface is Needless to say, since the crystal can be grown while keeping it convex (or flat), high quality crystals can be obtained.

Here, the temperature T of the melt is detected with the thermocouple 12, and the temperature T of the GaAs
The voltage △V = V, -V, which corresponds to the difference between the melting point Tm and the voltage T = T - Tm. Since the mechanism is such that the vertical movement of the shaft 13 can be controlled as a total control signal, the growth interface (solid-liquid interface) 40 is maintained throughout the entire crystal growth process.
The distance between the ingot and the plate member 11 can be arbitrarily controlled, and it is possible to realize crystals with a controlled solid-liquid interface shape over the entire ingot.

When a growth apparatus having the above functions was used to grow a GaAs crystal, the expected effect of optimizing the interface shape and obtaining a single crystal over the entire ingot was confirmed.

(Effect of invention As explained above, the growth method according to the present invention.

The use of a crystal growth apparatus has the advantage that the shape of the solid-liquid interface can be controlled over the entire ingot in the vertical temperature gradient solidification method or the vertical Bridgman method, in which a melt is solidified in a crucible to obtain a single crystal. This makes it possible to solve the problem of polycrystalization that conventionally occurred due to insufficient control of the interface shape, and to obtain a single crystal having the same growth direction as the seed crystal throughout the ingot.

Naturally, if the present invention is applied to the growth of impurity-doped crystals, by flattening the interface shape over the entire ingot, a single crystal with a uniform doped impurity distribution in the radial direction can be realized. It is also possible.

Furthermore, regarding crystal growth, the position of the growth interface and its movement speed (crystal growth - long speed storage) can be known with high precision from the information obtained from the thermocouple installed in the control board according to the present invention. , which has the effect of enabling effective control.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the crystal growth method of the present invention, FIGS. 2 and 3 show other embodiments, and FIG. 4 shows an explanatory diagram. FIG. 5 shows an embodiment of the single crystal growth apparatus of the present invention, and FIGS. 6 to 9 show explanatory diagrams of conventional examples. 1... Crucible 2... QaAs melt 3... Seed crystal 4... GaAs single crystal 5... Liquid sealant (BtOa )6・・・・・・
Susceptor 7...Beticle 8...Heating element 9...Heat insulating material 10...High pressure vessel 11...Plate member... ...Thermocouple 13 ... Shaft 14 ... - Slip ring 15 ... Reference voltage generator 16 ... Arithmetic unit 17 ... Drive unit control mechanism 40...Growth interface 41...Void portion Patent applicant Nippon Telegraph 'IIC Co., Ltd. Figure 1
Figure 2 41- Vacancy

Claims (8)

[Claims] (1) Prepare a heated melted raw material melt (or solution) in a crucible, place the crucible vertically in an environment with a temperature gradient where the upper part is higher temperature and the lower part is lower temperature. In a method of growing a single crystal with a shape corresponding to the inner surface of a crucible by slow cooling and solidification from one end, when the melt is viewed in a cross section at a certain height, the peripheral part in contact with the inner wall surface of the crucible is smaller than the central part. The temperature of the crystal growth interface is kept at a high temperature at all times, and the crystal growth interface is moved from the bottom to the top while keeping the crystal growth interface in a flat or slightly convex state with the center facing upward to crystallize. A single crystal growth method characterized by: (2) A crucible having a small-diameter portion at the bottom in which a minute seed crystal is to be installed, a seed crystal provided in the crucible, and a raw material melt in a heated molten state filled in the crucible (
or a heating means for imparting a temperature gradient vertically to the crucible and the raw material melt such that the upper part is higher temperature and the lower part is lower temperature, and the relative positional relationship between the crucible and the heating means is controlled. In an apparatus for growing a single crystal with a shape corresponding to the inner surface shape of the crucible by slowly cooling and solidifying it from one end of the crucible, the raw material melt moves in conjunction with the movement of the crystal growth interface and is in a molten state. When the melt is placed in the center and viewed in a cross section at a certain height,
The peripheral area in contact with the inner wall of the crucible is always kept at a high temperature.
1. A single-crystal growth apparatus comprising at least an interface shape control means to maintain the crystal growth interface in a state in which the center thereof is convex upward. (3) When the interface shape control means looks at the cross section of the crucible,
a plate-like member that covers the center portion and has a gap between it and the inner wall surface of the crucible; and a plate-like member that is connected to the plate-like member and moves in the vertical direction in conjunction with the movement of the crystal growth interface. 3. The single crystal growth apparatus according to claim 2, further comprising a mechanism section. (4) The single crystal growth apparatus according to claim 3, wherein the thickness of the plate member is thick at the center and thin at the periphery. (5) The single crystal growth apparatus according to claim 4, wherein the plate member has a structure in which a heat insulating material is coated with a material inert to the raw material melt. (6) When the interface shape control means looks at the cross section of the crucible,
a plate-like member that covers the center and has a gap between it and the inner wall surface of the crucible; and a plate-like member that is connected to the plate-like member and moves the plate-like member in a vertical direction in conjunction with movement of a crystal growth interface. 3. The single crystal growth apparatus according to claim 2, further comprising: a mechanical section for rotating said plate-like member. (7) The plate member has a downwardly convex cross section and is configured to seal the small diameter portion filled with minute seed crystals when the interface shape control means is at the bottom. A single crystal growth apparatus according to any one of claims 3 to 6. (8) The interface shape control means is provided with temperature detection means for detecting the temperature of the raw material melt, as described in any one of claims 2 to 7. Single crystal growth equipment.