JPH07115986B2 - Crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to fabrication of electronic materials, and in particular, to a technique for growing a semiconductor crystal which is indispensable for fabrication of a semiconductor device.

[Problems to be Solved by Conventional Techniques and Inventions] Using an appropriate substance as a solvent, a semiconductor to be grown at a certain temperature is saturated and dissolved as a solute, and this solution is supersaturated by an appropriate method. The method of precipitating a single crystal of solute by so-called is called liquid phase growth method.

Although there are various conventional liquid phase growth methods, they can be roughly classified into a cooling method and a temperature difference method. Among them, the cooling method is to saturate and dissolve the semiconductor solute in the solvent at a predetermined temperature, contact this solution with the seed crystal substrate at the growth temperature, and cool the solute that becomes supersaturated on the seed crystal substrate. This is a method of precipitating and performing crystal growth. The cooling method is roughly classified into three types, that is, an equilibrium cooling method, a step cooling method, and a supercooling method, depending on the method of cooling the growth system and the method of contacting the solution with the seed crystal substrate. Although each of these growth methods belonging to cooling has its own characteristics, the amount of crystals that can be grown is limited because the amount of solute that can be dissolved in the solvent is limited by the solubility at the growth temperature. The problem was that I could not do it.

On the other hand, in the temperature difference method, a solution in which the crystal is saturated and dissolved is filled between the seed crystal substrate and the raw material crystal. Then, a temperature difference is made so that the seed crystal side becomes low temperature and the raw material crystal side becomes high temperature. As a result, a temperature gradient is also formed in the solution, and the saturated solubility with respect to the solute becomes high on the high temperature side adjacent to the raw material crystal of the solution, so that the raw material crystal is dissolved and supplied to the solution. On the other hand, the solution on the low temperature side adjacent to the seed crystal substrate has a lower saturated solubility than the solution on the high temperature side. Therefore, in addition to the temperature gradient, a concentration gradient due to this difference in solubility occurs in the solution. Therefore, the solute supplied to the solution by melting the raw material crystals on the high temperature side is transported to the low temperature side by thermal diffusion and density diffusion. Then, since the saturated solubility is low on the low temperature side as described above, the solute becomes supersaturated, and the supersaturated portion is deposited on the adjacent seed crystal surface to perform crystal growth. Therefore, if this temperature difference method is used, in principle, if the amount of raw material crystals is sufficiently large and the growth time is sufficiently long, the amount of growing crystals is sufficiently large and it is possible to obtain thick grown crystals.

However, in the conventional temperature difference method, since the low-melting-point metal used as a solvent has a large thermal conductivity, it is difficult to have a temperature gradient in the solution, and thus the transport rate of the solute from the raw material crystal side to the seed crystal side becomes slow. The problem is that it takes a long time to obtain thick crystals. A second problem is that it is difficult to make the temperature difference between the raw material crystal and the seed crystal uniform, and thus the thickness of the growth layer becomes uneven. Further, in the temperature difference method, since it is necessary to provide a temperature gradient between the seed crystal substrate and the raw material crystal, it is difficult to obtain a growth layer on several seed crystal substrates at the same time, which is a point of mass productivity. I had a problem with.

The present invention has been made for the purpose of solving these problems of the conventional growth method.

Specifically, the first purpose is to increase the growth rate.

Secondly, the purpose is to obtain a grown crystal of sufficient thickness.

Thirdly, the purpose is to obtain a growth layer having a uniform thickness.

Fourthly, the purpose is to simultaneously obtain a growth layer on a plurality of seed crystal substrates.

[Means for Solving Problems] When using a solution in which the specific gravity of the solution decreases as the concentration of the solute involved in crystal growth increases, the seed crystal is placed on the upper side in the direction of gravity and the raw material crystal is placed on the lower side. When the specific gravity of the solution is increased, the raw material crystal is placed on the upper side in the direction of gravity,
The seed crystal is arranged on the lower side, and the seed crystal and the raw material crystal are heated in a state of being filled with a solution of the raw material crystal as a solute,
By keeping the temperature of the seed crystal, the raw material crystal, and the solution at the same temperature or close to the same temperature, by repeatedly raising and lowering the temperature in a certain temperature range,
By transporting the solute that contributes to crystal growth from the raw material crystal to the seed crystal side, and growing the crystal on the seed crystal,
The conventional problems are solved.

For example, the higher the concentration of solute contained in the solution,
When the specific gravity of the solution decreases, the seed crystal is placed above the raw material crystal. The crystal growth system containing this seed crystal, solution, and raw material crystal is heated to reach the minimum temperature of the growth temperature cycle, and the temperature is maintained for a certain period of time, whereby the seed crystal, solution, and raw material crystal are in thermal equilibrium or It will be explained from the time when the state is close to that. Of course, at this time the solution is saturated at this lowest temperature. Starting from this minimum temperature, the temperature rise of the growth system is started. This is called a temperature raising process. The solution becomes unsaturated as the solubility increases with increasing temperature. Therefore, the raw material crystals and the seed crystals that are in contact with this solution are dissolved into the adjacent solutions from the solid-liquid interface with the solution.
For example, in this case, at the contact interface between the lower surface of the solution and the raw material crystal, the raw material crystal is dissolved in the solution in an amount corresponding to the unsaturation degree of the solution. As a result, the solution in the vicinity of the solid-liquid interface of the raw material crystals contains a high concentration of solute, and the specific gravity of that portion decreases. Therefore, that portion moves upward due to buoyancy. Then, thereafter, the unsaturated solution having a large specific gravity in the upper layer portion apart from the raw material crystal is replaced. Since the replaced solution is unsaturated, the raw material crystals are dissolved. Then, since the specific gravity decreases, buoyancy acts and this high-concentration solution rises and is replaced with an unsaturated solution having a large specific gravity in the upper layer. The buoyancy due to such a difference in specific gravity not only increases the supply rate of the solute from the raw material crystals to the solution, but also serves to transport the solute at a high speed to the seed crystal side placed above the solution.
On the other hand, at the solid-liquid interface between the seed crystal placed in contact with the upper surface of the solution and the solution, the temperature of the solution causes the solution to become unsaturated, so that the seed crystal dissolves in the solution in the same manner as the raw material crystal side. Then, a solution layer containing a solute with a small specific gravity in a high concentration is formed near the solid-liquid interface of the seed crystal. Since this highly concentrated saturated solution layer can stably exist on the lower unsaturated solution layer due to buoyancy, the surface of the seed crystal side is protected by this saturated solution layer, and further dissolution does not occur. . In addition, since the high-concentration solution that has floated from the raw material crystal side is added near the solid-liquid interface on the seed crystal side,
The solution layer containing the solute on the seed crystal side at a high concentration expands rapidly. In this way, almost all of the solute in the high-concentration solution layer formed near the solid-liquid interface on the seed crystal side is supplied from the raw material crystal side by the temperature raising process. By making the solid-liquid interface on the seed crystal side flat and keeping it horizontal, this high-concentration solution layer is uniformly formed near the solid-liquid interface on the seed crystal side by the action of buoyancy. When the temperature reaches a predetermined maximum temperature, the heating process ends. At this time, the saturated solution layer corresponding to the maximum temperature is formed in the upper layer portion of the solution as described above, but is in the unsaturated state in the lower layer portion of the solution.

Next, the temperature of the growth system is gradually lowered to start a temperature lowering process for crystal growth. Due to the decrease in temperature, the solubility decreases, the solute becomes supersaturated in the upper layer of the solution, and the supersaturated part precipitates on the seed crystal side, and crystal growth occurs, at this time, the solution near the solid-liquid interface on the seed crystal side. A concentration gradient is formed to promote diffusion of the solute to the seed crystal side and transport by buoyancy. Therefore, the solute supplied from the high-concentration solution layer is deposited at high speed. On the other hand, the lower layer of the solution, that is, the solution near the solid-liquid interface with the raw material crystal, has a low concentration of solute, so that it does not reach supersaturation until the end of the temperature lowering process, and due to diffusion in the direction opposite to buoyancy, Since solutes are transported, the amount of solutes deposited on the raw material crystal side is extremely small.
Therefore, most of the supersaturated portion of the solute generated in the solution by the temperature lowering process is deposited as a growing crystal on the seed crystal side.

After the crystals have been precipitated from the solution by this temperature decreasing process, the temperature increasing process is started again, solute is supplied from the raw material crystals to the solution, and then the solute is precipitated from the solution to the seed crystal side by the temperature decreasing process. A grown crystal having a predetermined thickness can be obtained by repeating the process periodically. It goes without saying that the temperature raising rate in the temperature raising process, the temperature lowering rate in the temperature lowering process, and the temperature amplitudes of the maximum temperature and the minimum temperature thereof are appropriately set. In addition, the temperature may be kept constant at an appropriate time interval when switching from temperature increase to temperature decrease and when switching from temperature decrease to temperature increase. In the present invention, a flat and uniform growth layer can be obtained by flattening the seed crystal substrate surface and setting it horizontally.

In the above, the case where the specific gravity of the solution decreases as the concentration of the solute dissolved in the solvent increases has been described as an example. Conversely, when the concentration of the solute increases, the specific gravity of the solution increases. The arrangement of the crystal and the seed crystal may be exchanged.
That is, a growth layer can be obtained on the seed crystal by placing the raw material crystal on the upper side of the solution in contact with the solution and placing the seed crystal on the lower side of the solution in contact with the solution.
This case will be described from the temperature raising process. Since the solubility increases as the temperature rises, the solute concentration and the specific gravity increase due to the dissolution of the raw material crystal in the solution near the raw material crystal arranged in contact with the upper surface of the solution. Therefore, this high-concentration solution sinks, and an unsaturated solution with a small specific gravity floats from the bottom to the trace. Since the raw material crystals are dissolved in this floating unsaturated solution to increase the specific gravity, this saturated solution sinks and replaces the unsaturated solution in the lower part. By repeating such a process, the solution solute is supplied from the raw material crystals by the temperature raising process. The supplied solute is immediately transported to the vicinity of the seed crystal arranged at the bottom by the action of gravity and forms a high concentration solution layer. On the other hand, in the vicinity of the seed crystal surface, even if the seed crystal dissolves due to temperature rise, the specific gravity increases, so the solution near the seed crystal surface is in a stable and stationary state, and the seed crystal surface is protected by this saturated solution layer. It Therefore, the amount of dissolution from the seed crystal side in the temperature raising process is negligibly small. The solute supplied from the raw material crystal by the temperature raising process forms a high-concentration solution layer in the portion adjacent to the seed crystal. This high-concentration solution layer is close to the saturated state at the maximum temperature of the temperature raising process, while the upper layer solution close to the raw material crystal is in the unsaturated state. Next, the temperature decreasing process for crystal growth is started. At this time, the lower layer solution close to the seed crystal becomes supersaturated, the supersaturated part of the solute in the solution is deposited on the surface of the seed crystal, and the crystal grows. Since the temperature of the growth system is gradually lowered, this precipitation is continuously performed until the temperature reduction process is completed. In this case as well, it goes without saying that the specific gravity difference, in other words, gravity acts in the direction of accelerating the transport of the precipitated solute. It goes without saying that the amount of solute precipitated on the raw material crystal side in this temperature decreasing process is so small that it can be ignored. As described above, a desired crystal can be grown on the seed crystal by alternately repeating the temperature raising process and the temperature lowering process.

In addition, in the present invention, when impurities need to be added, the solvent itself can be used as an impurity. Further, by adding a predetermined amount of impurities to at least one of the raw material crystal and the solution in advance, or mixing a predetermined amount of the impurity gas or the substance containing the impurities into the atmosphere gas, the p-type or n-type crystal is grown. Any desired amount of the desired impurities can be added to the mold.

The means for solving the problems in the present invention have been described above, and they are summarized as follows. First, a solution in which a raw material crystal is dissolved between a raw material crystal and a seed crystal is filled on a sadwich to form a growth system. As long as the solid-liquid interface between the seed crystal and the solution and the solid-liquid interface between the raw material crystals and the solution become flat, and as the two solid-liquid interfaces become perpendicular to the direction of gravity, in other words, horizontal. To place. Then, when the specific gravity of the solution increases as the concentration of the solute in the solution increases, the seed crystal is placed below the solution, and conversely, when the specific gravity of the solution decreases, the seed crystal is placed above the solution.
By periodically raising and lowering the temperature of such a growth system within a certain temperature range, a difference in specific gravity occurs in the solution, and the solute is transported from the raw material crystal side to the seed crystal side at high speed and uniformly. As a result, the conventional problems can be solved and a crystal having a uniform and desired thickness can be grown at high speed. Furthermore, in the method of the present invention, the temperature can be grown only by cyclically changing the temperature while keeping the temperature of the entire growth system isothermal,
Crystal growth can be performed simultaneously using a plurality of seed crystal substrates.

[Configuration of the Invention] The configuration of the present invention will be described below with reference to the drawings.

FIG. 1 is for explaining the principle of the crystal growth method of the present invention, and shows the case where the specific gravity of the solution decreases as the concentration of the solute dissolved in the solvent increases. FIGS. 1 (a), (b) and (c) schematically show seed crystals 1, raw material crystals 2 and seeds of solution 3 corresponding to respective stages of the temperature process of growth shown in FIG. 1 (d). It is shown. The solution 3 is sandwiched between the seed crystal 1 and the raw material crystal 2. The surfaces of the seed crystal 1 and the raw material crystal 2 which are in contact with the solution 3 are flat and sufficiently cleaned by polishing and chemical etching. In particular, the surface of the seed crystal 1 is sufficiently removed of the mechanically processed layer that causes lattice defects. Further, in FIG. 1, the solution 3 is placed in a crucible or boat made of an appropriate material so that the solution 3 does not flow between the seed crystal 1 and the raw material crystal, or the surface tension of the solution itself is used. is doing. The arrow g in the figure indicates the direction in which gravity acts. The seed crystal 1 is arranged on the upper side of the solution 3 such that the solid-liquid interface between the solution and the seed crystal is horizontal, and the raw material crystal 2 is arranged on the lower side of the solution 3. These crystal growth systems (hereinafter abbreviated as growth systems) composed of a seed crystal 1, a raw material crystal 2, a growth solution 3, and a crucible or a boat for installing them prevent contamination by oxidation or impurities. For this purpose, it is installed in a high vacuum or in an electric furnace through which a high-purity hydrogen gas, a high-purity inert gas such as nitrogen, argon, or helium is passed. FIG. 1 (d) shows an example of the temperature cycle applied to these growth systems. The horizontal axis t represents the time from the start of heating the growth system, and the vertical axis T represents the temperature of the growth system. Now, heating is started for this growth system at t = 0, and as shown in FIG. 1 (d), at time t ₁₁ ,
The minimum temperature of the temperature cycle in which the temperature of the growth system is added to this system
_Be at T _l . At this time, the solution 3 is kept at this temperature T ₁ for a certain period of time to be in a saturated solution containing the raw material crystal 2 as a solute or in a state close to saturation. As shown in FIG. 1 (d), the temperature cycle is started to increase from time t ₁₁ in the temperature cycle. The solution becomes unsaturated because the solubility increases with increasing temperature. Therefore, raw material crystal 2
And the part of the seed crystal 1 near the solid-liquid interface begins to dissolve in the solution. Then, as shown in FIG. 1B, a solution layer 5 containing a high concentration of solute in the solution 3 adjacent to the raw material crystal 2, and a high concentration solution layer 6 in the solution 3 adjacent to the seed crystal 1 as well. To form. In this case, the higher the concentration of the solute in the solution is, the smaller the specific gravity of the solution is, so that buoyancy is generated in each of the solution layers 5 and 6 by the action of gravity g. The high-concentration solution layer 6 floats on the unsaturated solution layer 7 in the solution 3 having a large specific gravity, and prevents direct contact between the seed crystal 1 and the unsaturated solution layer 7, so that the dissolution of the seed crystal is stopped. . On the other hand, since the public concentration solution layer 5 is below the unsaturated solution layer 7 having a large specific gravity, the solution constituting this layer rises by buoyancy as indicated by an arrow 8 in FIG. It is supplied to the high-concentration solution layer 6 formed near the crystal. Thus, the high-concentration solution layer rapidly enlarges due to the supply of the material from the raw material crystals. Then, after the high-concentration solution rises, the unsaturated solution having a large specific gravity descends from the unsaturated solution layer 7. Therefore, the high-concentration solution layer in the vicinity of the raw material crystal disappears immediately or becomes almost disappeared. Since the raw material crystals come into contact with the unsaturated solution that has descended in this way, they dissolve and form the high-concentration solution layer 5 again in the vicinity thereof. Then, buoyancy acts on this high-concentration solution layer, the solution constituting this layer rises, and the solute is supplied to the high-concentration solution layer 6. Then, after rising, the unsaturated solution descends from the unsaturated solution layer 7 and is replaced, which is repeated. As a result, it is possible to rapidly supply the solute from the raw material crystals to the high-concentration solution layer 6 formed near the seed crystals. Thus, as shown in FIG. 1 (d), the time t
_{After the} temperature of the growth system is raised from T ₁ by raising the temperature from ₁₁ to t ₂₁ , the temperature is kept constant from time t ₂₁ to t ₃₁ . The reason why the period of maintaining the temperature T _h is provided in this way is so that the solubility of the high-concentration solution layer 6 reaches a sufficient saturation solubility at the temperature T _h . The temperature rising period from time t ₁₁ to t ₂₁ ,
The temperature process during which the temperature T _h is maintained from time t ₂₁ to t ₃₁ , that is, during the period τ _h from time t ₁₁ to t ₃₁ in FIG. 1D, is called a temperature raising process. Maximum temperature T _h ,
Temperature range ΔT = T _h −T _l , effective heating rate V = (T _h ＝
T _l ) / (t ₂₁ −t ₁₁ ), holding time at maximum temperature T _h t ₃₁ −t ₂₁
It goes without saying that the total dissolved mass contained in the high-concentration solution layer 6 can be adjusted by appropriately setting Further, by keeping the contact surfaces of the seed crystal 1 and the raw material crystals 2 and the solution 3 horizontal, the thickness of the high-concentration liquid phase 6 can be made uniform by the action of gravity.

Thus, after the solution of the high-concentration solution layer 6 reaches the saturated solubility at the temperature T _h by the temperature raising process, the time shown in FIG.
Cool from t _{31 at an} appropriate rate. High-concentration solution layer 6
The solution becomes supersaturated by this cooling, and its substance begins to precipitate on the seed crystal 1. Then, as the cooling progresses, the precipitated solute forms an epitaxial growth layer 4 having the same plane orientation as the seed crystal on the lower surface of the seed crystal 1 as shown in FIG. 1 (c). Cooled to time _41, the temperature is held at constant temperature T _l in stopping the cooling when it reaches a minimum temperature T _l temperature cycle, sufficient solutes supersaturation contained in a high concentration solution layer 6 as an epitaxial growth layer 4 To precipitate. By this precipitation, the solution in the high-concentration solution layer 6 becomes saturated at or near the temperature T _l .
In this way, the temperature process of cooling from time t ₃₁ to t ₄₁ and the subsequent temperature process of maintaining the temperature T _l , that is, the temperature process performed within the period τ _c of FIG. To do.

As described above, one cycle of the growth temperature cycle is completed by the temperature raising process from the time t ₁₁ and the temperature lowering process performed subsequently. Then, starting again heating process from the time t ₁₂ as shown in FIG. 1 (d) into the second cycle of temperature cycle, and repeats the same and the first cycle, at the first cycle The growth layer of the second cycle is stacked on the obtained growth layer 4. By repeating such a temperature cycle of growth as many times as necessary, a crystal having a desired thickness can be grown. As described above, in the growth method of the present invention, the solute dissolved from the raw material crystal is transported to the seed crystal to be precipitated, and thus the crystal growth rate is governed by this transport rate. The rate depends on the cycle of the growth cycle, the temperature swing, the difference in solubility between the minimum temperature T _l and the maximum temperature T _h , and the specific gravity difference, and the distance between the seed crystal and the raw material crystal. The growth rate can be increased when the difference in solubility and the difference in specific gravity are large and the distance between the seed crystal and the raw material crystal is short. The accessible distance between the seed crystal and the raw material crystal depends on the flatness of the surfaces of the seed crystal and the raw material crystal. A sufficient growth rate can be obtained by setting the distance between the seed crystal and the raw material crystal, that is, the gap within 1 cm, but it is important to set it within 500 μm in order to further increase the growth rate. In particular, it is more effective if this gap is within the diffusion length of the solute in the solution. Of course, it goes without saying that artificially adding a gravitational field that is larger than the gravitational field of the earth may cause descent.

Contrary to the case of FIG. 1 described above, FIG. 2 shows a case where the specific gravity of the solution increases as the temperature of the solute in the solution increases. In this case, contrary to the case of FIG. 1, the raw material crystal 2 is placed on the solution 3 as shown in FIG.
The seed crystal 1 is placed below the solution 3. The reason why the arrangement of the raw material crystal 2 and the seed crystal 1 is opposite to that in the case of FIG. 1 is that the specific gravity increases as the concentration of the solute in the solution increases, and this high-concentration high-concentration solution becomes a solution. This is because it will sink to the bottom of 3. That is, when the temperature rising process as shown in FIG. 1 (d) is carried out after the solution 3 is saturated at the lowest temperature T _l of the temperature cycle, the dissolution of the raw material crystal 2 causes a change in FIG. 2 (b). As shown, the high concentration solution layer 5 is formed in the portion adjacent to the raw material crystal 2. However, this high-concentration solution has a large specific gravity, so it settles due to gravity,
Instead, an unsaturated solution with a small gravity floats from below and replaces it. Therefore, the high-concentration solution layer 5 disappears, but since the raw material crystals are dissolved in this replaced unsaturated solution, the high-concentration solution layer 5 is formed again. Then, as described above, the process of substituting with the unsaturated solution which settles and floats from below is repeated. Therefore, the solute is supplied from the raw material crystal 2 to the solution by the temperature raising process. Since the solute thus supplied increases the specific gravity of the solution, it precipitates as shown by an arrow 9 in FIG. 2 (b), forming a high-concentration solution layer 6 in a portion adjacent to the seed crystal 1. When the temperature rising process progresses and the temperature reaches the maximum temperature T _h , the high-concentration solution layer becomes a saturated solution at that temperature. Therefore, as in the case of FIG. 1, the high-concentration solution becomes supersaturated in the next high-temperature process. Then, this supersaturated portion is deposited on the seed crystal 1 to form the growth layer 4. On the other hand, on the raw material crystal side, in the temperature lowering process, the portion adjacent to it is occupied by an unsaturated solution having a small specific gravity, so that solute precipitation hardly occurs. Therefore, as shown in FIG. A growth temperature cycle in which the process and the subsequent temperature lowering process are set as one cycle is repeated in this growth system, and the growth is repeated periodically to grow a crystal layer having a desired thickness on the seed crystal 1.

As described above, the case where the specific gravity of the solution decreases as the concentration of the solute increases and the case where the specific gravity of the solution increases vice versa are described. This would make the gist of the present invention clearer.

Specific Example Example 1 FIG. 3 shows a specific example. Seed crystal 1,
The raw material crystal 2 and the solution 3 are installed in a vertical furnace.
10 is an electric furnace with a wide soaking zone. Reference numeral 11 denotes a seed crystal support rod, which is made of a suitable material, such as quartz glass, so that the seed crystal can be fixed to the tip. The support rod 11 and the flange 13 are hermetically sealed so that the support rod 11 can rotate and move in the vertical direction. Reference numeral 12 is a supporting rod of a raw material crystal, which is made of the same material as that of the supporting rod 11 of a seed crystal, and is worked so that the raw material crystal can be fixed to the tip. The support rod 12 can rotate and move in the vertical direction. 13 'is the lower flange. The arrangement of the seed crystal 1 and the raw material crystal 2 corresponds to the case where when the crystal to be grown is dissolved, the specific gravity of the solution decreases as the concentration of the solute increases,
Even when the specific gravity is increased, the present apparatus can be used by replacing the support rods 11 and 12 with the seed crystals 1 and the raw material crystals 2 arranged upside down. Reference numeral 16 is a quartz tube, and 15 is a baffle plate for shielding the heat radiation in the vertical direction of the electric furnace to keep the growth system at a uniform temperature. Further, 14 and 14 'are gas piping systems for introducing a high-purity atmosphere gas such as hydrogen, nitrogen, or argon gas into the quartz tube. With this crystal growth apparatus, various semiconductor crystals, for example, group IV element semiconductors such as Si, Ge, III-V group compound semiconductors such as InSb, GaSb, InAs, GaAs, InP, GaP, and mixed crystals thereof, such as AlGaSb. , InGaSb, AlGa
As, InGaAs, InGaP, GaAsP, etc., IV-VI group compounds, II-VI
Group compounds can also grow.

Now, the growth of Si will be described as an example. First, the solvent used for growth has a high Si solubility at the growth temperature, is convenient for adding impurities of desired conductivity type of n-type or p-type to the grown crystal, and is easy to handle. That is, it is required that a solution whose specific gravity changes depending on the concentration of Si can be formed. From the viewpoint of the solubility of Si, Al, Ga, In, Sn, Pb, Au, Ag, Cu, Ge can be mentioned.
Of these, the Group III elements Al and Ga act on Si as p-type impurities. In is also a group III element, but when added to Si, it may become p-type or n-type. Ge, Sn and Pb are the same group IV elements as Si, and are electrically inactive when mixed with Si. Au, Ag, and Cu also have a high solubility of Si and can be used as a solvent for use, but their drawback is that they form a deep impurity level in the grown crystal. Al, Ga, In, Sn were used for the growth of Si from the viewpoint of easy handling and irregular addition.
Is suitable as a solvent.

Here, the case where Al-Sn is used as the solvent will be described. The reason for using Al-Sn as the solvent is that Al has a high solubility of Si, but has a small difference in specific gravity in the liquid state. On the other hand, Sn has a smaller solubility of Si than Al, but has a large difference in specific gravity between Sn and Si in the liquid state. Therefore, by using Al-Sn as a solvent, the features of both Al and Sn can be utilized. When Si was dissolved in this Al-Sn solvent, the specific gravity of the solution decreased as the Si concentration increased, so seed crystals were placed on the solution.
First, a seed crystal having a desired plane orientation, for example, a (111) plane as a growth plane is prepared. Of course, the crystal growth surface is cleaned by a usual method by polishing and chemical etching.
The seed crystal used in this growth example has a size of 50 mmφ and a thickness of 15 mm.
Met. This seed crystal is fixed to the tip of the support rod 11 so that the growth surface becomes horizontal. Next, prepare a Si polycrystal as a raw material crystal, sufficiently flatten the surface facing the seed crystal, and then sufficiently clean it by an etching treatment, etc.
Fix at the tip of 12 so that the surface facing the seed crystal becomes horizontal. The specific dimensions of the seed crystal used in this growth example are
The thickness was 50 mm and the thickness was 40 mm. Next, as a growth solvent, Al
-Prepare Sn alloy. Specifically, high-purity Al-30 atom%
50mm after rolling Sn eutectic alloy to 100μm thickness to form plate
Prepare the one punched out in φ, degrease it by the usual method,
After washing, it was etched with 50% HF solution, washed with water and dried quickly. This is inserted between the seed crystal 1 and the raw material crystal 2. Then, the inside of the quartz tube 16 is evacuated to a vacuum, and further oxygen and moisture are almost eliminated from the growth system through the high-order hydrogen gas. Next, the temperature is raised to the minimum temperature T _l of the growth temperature cycle. In this growth example, T _l = 800 ° C. Therefore, the temperature cycle of growth is started after the solution 3 is sufficiently saturated by dissolving the seed solute and the Si solute from the raw material crystal in the Al—Sn solution while maintaining the temperature constant for about 2 hours. In this growth example, the temperature is raised at a heating rate of 0.5 ° C./min, the temperature is maintained at T _h = 810 ° C. for 10 minutes, then cooled at a rate of 0.5 ° C./minute, and the temperature is maintained at T _l for 10 minutes. It has grown. As a result, a growth layer 4 is formed on the lower surface of the seed crystal 1 as shown in FIG. 3, the thickness of this layer increases as the number of growth cycles increases, and the position of the solution 3 gradually moves downward. When the growth was performed for 100 cycles, that is, for 100 hours, a growth layer having a thickness of about 10 mm was obtained. In the above growth example, the plane direction of the seed crystal is set to (111), but it is of course possible to grow on other (100) planes. The composition of the Al-Sn alloy used as the growth solvent can of course be grown in any other composition.

Example 2 FIG. 4 shows III-V group compounds, II-VI group compounds and IV-V compounds.
This shows an example of the growth of a crystal that easily dissociates like a group I compound. To prevent dissociation, the growth system can be sealed as is well known. FIG. 4 shows an example for sealing the growth system. Further, FIG. 4 shows a case where the specific gravity of the solution increases as the solute concentration in the solution increases. Therefore, the seed crystal 1 is arranged below the solution 3. Support rod 1
A quartz container for sealing the growth system is attached to the upper part of 1 ', and the seed crystal 1 is fixed by a holder 17 installed in the container. On the other hand, a support for the closed container is attached to the lower part of the support rod 12 '. As shown in the figure, the closed container has a groove into which the lid is fitted, and since the liquid sealing agent such as B ₂ O ₃ is filled in the groove, it can be closed. A gas pressure equal to the dissociation pressure may be applied around this closed container during growth.

As an example, we will describe the growth of GaSb. A GaSb single crystal having a (111) B plane as a growth plane is prepared as a seed crystal. After cleaning the growth surface by a usual method, the seed crystal 1 is fixed to the holder 17 of the growth apparatus. A plate-shaped Ga-8 atomic% Sb alloy having a thickness of about 0.2 to 0.3 mm to be the growth solution 3 is cleaned and then inserted. On the other hand, the cleaned GaSb raw material crystal is fixed to the support rod 12 '. First, pull up the support rod 12 '. Then, the inside of the quartz tube 16 is evacuated, and then high-purity hydrogen is flowed to remove residual oxygen in the growth system. Then, heating is carried out, and when the sealing agent is melted, the supporting rod 12 'is lowered to seal the growth system and bring the raw material crystal 2 and the growth solution 3 into contact with each other. When the temperature of the growth system reaches T _l , the temperature rise is stopped. In this growth example, T _l = 595 ° C. was set. After holding at this temperature for 2 hours, the temperature was raised at a rate of 0.25 ° C./minute, and T _h
When the temperature reaches 600 ℃, hold for 10 minutes, and then 0.25 ℃ /
It was cooled at a rate of 10 minutes and held for 10 minutes when T ₁ = 595 ° C. was reached. As a result, the growth layer 4 can be obtained on the seed crystal 1. In this example, 50 cycles of growth were performed with the above temperature process as one cycle. As a result, a grown layer with a thickness of 15 mm could be obtained.

In the Ga—Sb solution, as the Sb concentration increases, the specific gravity of the solution increases. Therefore, in this example, seed crystals were arranged below the solution 3 as shown in FIG. If the seed crystal and the arrangement of the raw material crystals are exchanged, InP, InAs, InSb,
III-V group compound semiconductors such as GaP and GaAs and their mixed crystals such as InGaP, InGaAs, AlGaAs, GaAsP and PbS, PbSnTe, PbSe
IV-VI group compounds, and ZnS, ZnSe, CdS, CdSe, CdTe, etc.
Crystals of II-VI compounds can grow.

Example 3 FIG. 5 shows an example in which a piston is used to insert the solution 3 between the seed crystal 1 and the raw material crystal 2. Reference numeral 20 is a boat using an appropriate material, for example, high-purity carbon, a part of which is used. It is equipped with a cylinder that allows the piston 19 to be inserted.
Before starting the growth, the material for the solution used for the growth is charged in this cylinder. Since it is only necessary to inject through the small holes 21 after melting the material for the solution by raising the temperature of the electric furnace, it is not necessary to descend the material for the solution into a plate shape, because it is injected by pressurizing with a piston, seed crystals 1 and the raw material crystal 2 can be completely filled with the solution, and the seed crystal 1 and the raw material crystal 2 are prepared in advance in a cylinder so that the solution is saturated at the temperature T _l for starting the growth process.
Since it can be injected between the seed crystal and the raw material crystal, there is an advantage that the seed crystal and the raw material crystal can be prevented from being melted back. In FIG. 5, 24 is a lid for the terminal crystal holder / growth container, 22 is a vent for gas / excess solution escape, and 23 is a pan for the excess solution.

Example 4 According to the method of the present invention, the temperature of the entire growth system is kept spatially isothermal, and the growth can be performed only by periodically raising or lowering the temperature with respect to time. It is possible to grow crystals. FIG. 6 shows an example of a boat for carrying it out. This example shows a case where the specific gravity of the solution decreases as the solute concentration in the solution increases. Seed crystal 1 and raw material crystal 2 as shown in FIG.
And are alternately arranged in multiple stages like a bookshelf. In FIG. 6, except for the uppermost stage and the lowermost stage, the seed crystal 1 and the raw material crystal 2 are arranged back to back in contact with each other.
Of course, a suitable spacer may be inserted between the seed crystal 1 and the raw material crystal 2. As a method for injecting the solution 3, for example, a method using a piston as described in the third embodiment is effective.

Example 5 FIG. 7 shows an example using a slide boat. FIG. 7 (a) shows the entire growth system, and FIGS. 7 (b) to 7 (e) are for explaining the slide operation. Quartz tube
High-purity hydrogen or nitrogen gas is introduced into the interior of 16. Reference numeral 20 'is a holder for the slide boat, on which the raw material crystals 2 and the used solution tray 23 are provided. Tell me about how to grow. First, as shown in FIG. 7 (b), seed crystals 1, raw material crystals 2 and solution material 3'are charged. Next, after the high purity hydrogen is passed through the quartz tube 16 to sufficiently remove the residual oxygen in the growth system, the electric furnace 10 is used to raise the temperature to T ₁ . Then, after the growth system reaches equilibrium for a certain period of time, the slider 27 is moved by the slide operating rod 19 ', and the solution 3'is inserted into the hole 26 for moving the solution provided in the slider as shown in FIG. 7 (c). . Then, the slider is further moved, and the solution 3 is added to the seed crystal 1 as shown in FIG. 7 (d).
And the raw material crystal 2. Here, the growth temperature cycle is repeated to obtain the growth layer 4 having a predetermined thickness on the seed crystal 1. After that, with the operating rod 19 ', slide 25
And the container 25 of the solution 3 ′ are simultaneously moved to
The growth layer 4 and the solution 3 ″ are separated as shown in FIG.

Example 6 In the case of a III-V group compound or a mixed crystal of a III-V group compound having one group V element in common, a sealed tube is used, and crystal growth is performed while controlling the vapor pressure of the group V element. It is possible to obtain good quality crystals. FIG. 8 shows an embodiment using a sealed tube. Quartz sealed tube as shown in FIG.
A boat 20 'containing seed crystals 1, raw material crystals 2 and solution 3 in 28 is installed in the soaking zone of the electric furnace 10, and V is provided in the soaking zone of the electric furnace 10' for controlling the vapor pressure of V group elements. Family material 29
Is installed. The temperature distribution of this growth system is shown in FIG. 8 (b). The growth temperature cycle is carried out by raising or lowering the temperature of the soaking zone of the electric furnace 10 as shown in FIG. 8 (b). Taking the case of growing an In _0.3 Ga _0.7 P mixed crystal as an example, as the seed crystal 1, for example, Ga
In _0.3 Ga _0.7 P having a proper thickness of about 30 μm is used on the As _0.6 P _0.4 (100) surface by a normal liquid phase growth method. Raw crystal 2
A suitable method such as InP and GaP powder in atomic ratio
Sintered polycrystals that were mixed at 3: 7 and sufficiently heat-treated in a sealed tube were used. The composition of the growth solution 3 is 38 g of InP for 1 g of In.
What melt | dissolved g and GaP in the ratio of 17 mg was used. In addition, red phosphorus was used as a group V substance for controlling the vapor pressure. Each of these materials is placed at a predetermined position shown in FIG. 8 (a) and heated. The temperature of red phosphorus 29 is constant at 380 ° C, T _l = 850 ° C, T _h
= 860 ℃, the heating process is from 850 ℃ to 0.25 ℃
After raising the temperature at / min and maintaining a constant temperature at 860 ° C for 20 minutes, 0.2
Cool down to 850 ℃ at 5 ℃ / minute, hold at that temperature for 20 minutes, 2
When the cycle is grown for 100 cycles, the pressure is 12 mm.
In _0.3 Ga _0.7 P could be grown.

It goes without saying that this method can also grow InGaAs, GaAs, InP, GaP and the like.

Example 7 In all of the examples described above, the seed crystal 1 was used. By using the method of the present invention and the Bridgman method together, the present invention can be carried out if there is a place having the same effect as the seed crystal without using the seed crystal. FIG. 9 (a) shows an example thereof. Bottom of boat 20 '
As shown in FIG. 9 (a), 30 is sharpened to facilitate crystal nucleation. Since the specific gravity of the solution increases as the solute concentration increases like the Ga-Sb solution, the supersaturated portion first forms crystal nuclei at the lower end 30, and the grown crystals 4 are formed by using them as seeds.

[Crystal name to which the present invention can be applied] The present invention positively utilizes the difference in specific gravity of the solutions.
When the present invention is carried out, there are two cases, that is, the seed crystal substrate is arranged on the upper side and the lower side of the solution. The following table shows examples of crystals to which the present invention is applicable for these two cases, together with the solvent used for growth.

In Table (a), GeSi indicates a mixed crystal of Ge and Si. Further, x in parentheses in the column of solvent in the table indicates a mixed crystal composition range to which this table can be applied. It is needless to say that the crystal names listed in Table 1 are some of the crystals to which the present invention can be applied, and the present invention can be applied to other crystals.

[Effects of the Invention] As described above, in the present invention, the growth system is configured by sandwiching the growth solution between the raw material crystals and the seed crystals. At that time, the solid-liquid interface between the seed crystal and the solution and the solid-liquid interface between the raw material crystal and the solution are flattened, and the two solid-liquid interfaces are arranged horizontally with respect to the gravitational field. The specific gravity difference is generated in the solution by periodically raising and lowering the temperature of the growth system configured as described above within a predetermined temperature range. This difference in specific gravity acts to transport the solute supplied from the raw material crystal side to the seed crystal side at a high speed, and at the same time, to make the solution concentration uniform in the horizontal direction. This has made it possible to grow crystals that are uniform and have a desired thickness. Furthermore, it became possible to grow using multiple seed crystal substrates at the same time, and the problems of the conventional temperature difference method were solved.

[Brief description of drawings]

1 and 2 are explanatory views of the principle of the crystal growth method of the present invention. FIG. 1 shows the case where the specific gravity of the solution decreases with the increase of the solute concentration, and FIG. Fig. 3 shows an example using a vertical furnace, Fig. 4 shows an example using a closed rigid container for preventing dissociation, and Fig. 5 shows a solution injection using a piston. Example, FIG. 6 is an example in which crystal growth was performed using a plurality of seed crystal substrates, FIG. 7 is an example using a slide boat, FIG. 8 is an example using a sealed tube, FIG. 9 shows an example in which seed crystals are not used. 1 ... Seed crystal, 2 ... Raw material crystal, 3 ... Solution, 4 ...
Growth layer, 10 ... Electric furnace, 16 ... Quartz tube.

Claims (2)

[Claims] 1. In a crystal growth method using a solution in which the specific gravity of the solution decreases as the concentration of a solute involved in crystal growth increases, a seed crystal is placed on the upper side and a raw material crystal is placed on the lower side, And heating between the raw material crystal and a solution containing the element constituting the raw material crystal as a solute,
A crystal growth method characterized in that the solute is transported from the raw material crystal to the seed crystal side by causing the temperature of the seed crystal, the raw material crystal, and the solution to periodically rise and fall within a constant temperature range, and the solute is deposited on the seed crystal. . 2. In crystal growth using a solution in which the specific gravity of the solution increases as the concentration of solutes involved in crystal growth increases, seed crystals are placed on the lower side and raw material crystals are placed on the upper side.
Heating between the seed crystal and the raw material crystal in a state of being filled with a solution containing an element constituting the raw material crystal as a solute, and raising and lowering the temperature of the seed crystal, the raw material crystal and the solution periodically in a constant temperature range. The method for growing crystals is characterized in that the solute is transported from the raw material crystals to the seed crystal side, and the solute is deposited on the seed crystals.