JPS63206380A - Growing method of single crystal - Google Patents

Abstract

PURPOSE:To exactly carry out the temperature control on a single crystal growth solid-liquid interface in a crucible and obtain a single crystal being homogeneous also in fine structure and having high quality, by depositing the single crystal while always keeping the position of the above-mentioned solid- liquid interface in the crucible during pulling up of a seed crystal. CONSTITUTION:In a growing method of a single crystal which is further deposited around a seed crystal by pulling up the seed crystal immersed in a molten liquid from a molten liquid in a crucible, the position of the single crystal growth solid-liquid interface in the crucible is always kept constant. There is a method for forming compensational component with a substance not to react with the molten liquid, gradually immersing the component in the molten liquid and keeping the liquid face in the crucible constant as means for keeping the liquid face constant. A material which is not reacted with the molten liquid and cause no degradation by temperature is required as the compensational component. A material having properties as same as that of crucible is preferably used as the material of the compensational component in order to satisfy the above-mentioned conditions.

Description

[Detailed description of the invention] [! ! Field of Industrial Application] This invention is applicable to semiconductor manufacturing raw materials such as silicon, single crystals of gallium arsenide, indium phosphide, etc., oxide single crystals such as sapphire, and furthermore, lithium niobate, gadolinium, gallium, garnet, etc. , relates to a method for growing a single crystal suitable for producing a single crystal of a composite oxide such as yttrium, aluminum, garnet, etc.

[Prior Art] Figures 3 and 4 show a conventional method for growing single crystals using the so-called Czochralski method, in which a cylindrical protective tube 1 in which the composition and pressure of the air inside can be adjusted is shown. A rotatable support stand 2 is provided inside, a crucible 3 loaded with raw material is placed on this support stand 2, and an induced current is passed through the raw material by a high frequency induction coil 4 to heat and melt it. Alternatively, if the raw material is non-conductive, the crucible 3 is made conductive and an induced current is passed through the crucible 3 to heat it, and the raw material is melted by the radiation or conduction heat. Then, the seed crystal (seed) S attached to the tip of the holder 5 is brought into contact with this molten liquid from above, and the lifting device (the path shown in the figure) provided at the upper part of the heating furnace 1 is rotated as necessary. While rotating the holder 5, the holder 5 is gradually pulled up, a single crystal of the molten liquid is precipitated using the seed crystal S as a nucleus, the seed crystal S is enlarged, and a cylindrical single crystal C is obtained. In order to keep the temperature of the molten liquid constant during the crystal precipitation process, a thermocouple is embedded in the bottom of the crucible 3, and the current supplied to the induction coil is controlled based on the detected value.

In order to prevent cracks from occurring in the pulled single crystal C due to temperature differences, a cylindrical heating element (after heater) 6 is provided in the upper part of the crucible 3 to heat the single crystal C.

[Problems to be solved by the invention] By the way, in the method for growing a single crystal as described above,
It is important to strictly control the temperature of the molten liquid at the solid-liquid interface, which is the precipitation point of crystals, but in the above-mentioned induction heating furnace, even if the temperature of the entire molten liquid is controlled, It was difficult to prevent local temperature changes at the liquid level. For example, if the material is non-conductive and the crucible 3 is conductive, if the solid-liquid interface for single crystal growth in the crucible 3 decreases, the temperature of the upper edge of the crucible 3 (the part not in contact with the melt) will decrease. increases, and therefore, the portion of the melt near the single crystal growth solid-liquid interface becomes high temperature. Furthermore, even if the crucible 3 is non-conductive and the material is conductive, the density of the magnetic flux generated by the induction coil 4 is not uniformly distributed in the vertical direction, so when the solid-liquid interface for single crystal growth falls, the temperature also changes. It ends up. Therefore, it is difficult to strictly control the surface temperature of the molten liquid, and it is difficult to produce high-quality single crystals with uniform even minute structures.
There were problems such as a change in the diameter of the single crystal C and a decrease in yield. In addition, in order to improve the above drawbacks, crucible 3
One possible method is to bury a thermocouple at a position corresponding to the solid-liquid interface for single crystal growth, and control the amount of current supplied to the induction coil 4 based on this detected value to keep the temperature of the liquid surface constant.
There is a problem in that effective control is difficult when there is variation in the position of the solid-liquid interface during single crystal growth.

The object of the present invention is to keep the position of the solid-liquid interface for single crystal growth constant and to strictly control the temperature of the liquid surface by relatively simple means.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a solution to the surroundings of the seed crystal by pulling up the seed crystal immersed in the melt from the melt in the crucible. In a method for growing single crystals that further precipitates single crystals, the position of the solid-liquid interface for single crystal growth in the crucible is always kept constant during pulling of the single crystals, thereby making it possible to The temperature environment at the solid-liquid interface is kept constant to grow stable, high-quality single crystals.

As a means for keeping the liquid level constant, there is a method of forming a compensating member from a substance that does not react with the molten liquid and gradually immersing it in the molten liquid to keep the liquid level in the crucible constant. In addition, if the crucible is non-conductive, there is a method in which the crucible itself is raised relative to the heating furnace by raising the support stand; It is difficult to adopt this method because the edge (the part that is not in contact with the melt) expands and changes the temperature environment of the liquid surface.

When using a compensating member, it should be cylindrical to follow the shape of the crucible so as not to impair the symmetry within the crucible, and should be sufficiently preheated to equalize the predetermined temperature of the liquid surface before being immersed in the molten liquid. This will be more effective in keeping the temperature environment of the liquid level constant. The material of the compensating member needs to be one that does not react with the molten liquid or deteriorate due to temperature, and a material that satisfies these conditions is preferably the same material as the crucible.

As a detection means for controlling the liquid level position,
A method is to incorporate weight detection means such as a load cell into the lifting device that pulls up the seed crystal, and use this detection value to determine the liquid level position, or a method is to incorporate a weight scale into the support mechanism of the crucible, or a method is to attach a level to the top of the crucible. There is a method of directly detecting the liquid level using a sensor and performing feedback control. Additionally, a method is added in which a thermocouple is embedded in the crucible at a position corresponding to the solid-liquid interface for single crystal growth, and the amount of heating (for example, the amount of current supplied to the induction coil in the case of induction heating) is controlled based on the detected value. This allows for more effective liquid surface temperature control.

This invention is particularly suitable when induction heating is used as a mechanism for melting raw materials, but is also effective in other cases.

[Function] In this single crystal growth method, the liquid level of the melt is kept constant when pulling the single crystal, so
The temperature environment near the crystal precipitation point becomes constant, and the precipitation conditions become uniform. Therefore, it becomes easy to control the temperature, and it becomes possible to produce a single crystal of constant quality in which the microscopic conditions such as the crystal structure and the macroscopic conditions such as the cylinder diameter are the same.

[Example code] Hereinafter, the present invention will be described in detail with reference to the drawings.

In FIGS. 1 and 2, 11 is a heating furnace, the inside of which is kept airtight by a cylindrical protection tube 12 made of a non-conductive material, and a gas such as argon or nitrogen is supplied as needed. The internal atmosphere can be kept inert. An induction coil 13 is installed around the outer periphery of the protection tube 12, and a high frequency current is passed through the induction coil 13 to generate an alternating magnetic field inside the protection tube 12, and an induced current is generated in the material in the crucible 14 to cause the material to melt. It is heated and melted. In addition, if the material is non-conductive such as ferroelectric, a noble metal such as platinum or iridium may be used as the material for the crucible 14.
4 Heat itself. A support stand 15 on which the crucible 14 is placed is installed inside the protection tube 12 so as to be rotatable about a support shaft 16 by a rotation drive device (not shown) provided at the bottom of the heating furnace 11 . 41. A closed cylindrical heating element (after heater) 17 is fixed above the crucible 14 so as to cover the upper surface of the crucible 14 . This heating element 17 is
If the crucible 14 is made of a noble metal, a crucible made of the same material is used, and if it is non-conductive, a suitable conductive material such as metal or graphite is used.

The heating element 17 is formed to have the same diameter as the crucible 14, and the upper top plate 18 is formed with an opening 21 through which the holder 19 for the seed crystal S and the compensation member 20 are inserted.

This holder 19 is connected to an elevating mechanism (not shown) at the upper part of the protection tube 12, and this elevating mechanism lifts up the holder 19 and the seed crystal S while rotating at a slow speed. A load cell (not shown) is incorporated in a part of the holder 19, so that changes in weight due to crystal growth can be detected. The compensating member 20 is selected from a material that does not react with the molten liquid, and usually may be made of the same material as the crucible 14. In this case, if the crucible 14 is conductive, an induced current also flows through the compensating member 20 and heats the crucible 1.
This satisfies the same heating conditions as in No. 4. Of course, Crucible 14
A non-conductive compensation member 20 may be used when the crucible 14 is conductive, and a conductive compensation member 20 may be used when the crucible 14 is non-conductive.

Examples of crystal materials and corresponding materials are listed in the table below.

This compensating member 20 has a lower cylindrical portion 22 and an upper small-diameter gripping portion 23 that are integrally molded.
is connected to a lifting device (not shown) installed at the top of the protection tube 12. Further, this heating furnace 11 is equipped with a control device (not shown), into which the output of the load cell is input, the control device calculates the amount of crystal precipitation from this detected value, and furthermore, the compensation member 20 is immersed. The desired depth is calculated, and a command signal for appropriately driving the lifting device is output based on this value.

A thermocouple (shown in the diagram) is embedded in the bottom of the crucible 14, and in order to keep the detected value constant, the current supplied by the induction coil 13 is adjusted according to the decrease in the amount of molten liquid due to crystal precipitation. I try to control it.

A method for growing silicon single crystals using the apparatus configured as described above will be described. First, a compensating member 20 made of an appropriate material (quartz in the case of silicon) as described above is selected in accordance with the material of the single crystal to be grown, and is attached to the lifting device. Then, a polycrystalline silicon piece as a raw material and a dopant if necessary are charged into the crucible 14, and the protective tube 1
2. While controlling the gas composition or atmospheric pressure inside 2, the induction coil 13 is energized to melt the raw material. At this time, a part of the magnetic field acts on the heating element 17, causing the heating element 17 to rise in temperature, and at the same time, the compensation member 20 is heated by radiant heat from the heating element 17, and the temperature rises. The temperature of this compensation member 20 can be controlled by changing the length that the induction coil 13 extends over the heating element 17, and the temperature of the compensation member 20 can be controlled by changing the length that the induction coil 13 extends over the heating element 17. Set the value in advance to a temperature that will cause the device to heat up. As shown in FIG. 1, when the melting is completed, the rotation drive mechanism is activated to rotate the support base 15.
The elevating mechanism operates, and the holder 19 descends while rotating in the opposite direction to the support base 15, and after immersing the tip of the seed crystal S in the molten liquid, rises while rotating.

As a result, a single crystal C is precipitated at the tip of the seed crystal S, and as it rises, the single crystal C expands in diameter to become a cylinder with a constant diameter (see FIG. 2). The load cell attached to the holder 19 detects changes in the load applied to the lower end of the seed crystal S, but this change is caused by the weight of the precipitated single crystal C itself and the surface acting on the single crystal C and the melt surface. This is due to tension. The amount of change in surface tension is thought to be proportional to the diameter of the single crystal C, and can be calculated in advance or determined experimentally along the pulling process, so enter this value into the control device. . In the control device, the above-mentioned factor is subtracted from the detected value of the load cell to calculate the net amount of crystals, and the immersion length of the compensation member 20 is calculated by taking the specific gravity into consideration.Based on this, the compensation member 20 is raised and lowered. An activation signal is output to the device. As a result, the compensation member 2
0 is immersed in the molten liquid for an appropriate length from its lower end, the loss of the molten liquid is compensated for, and the liquid level is always kept constant with respect to the heating furnace 11. A high-frequency current is supplied based on the detection value of a thermocouple buried in the bottom of the coil 14, but the way the magnetic flux acts by the induction coil 13 does not change, and the temperature of the liquid surface, which is the point of crystal precipitation, remains constant. At this time, the temperature of the compensating member 20 has been raised to the temperature of the molten liquid in advance, and the temperature between the compensating member 20 and the molten liquid or the atmosphere between the compensating member 20 and the atmosphere above the liquid level increases. Since there is no heat transfer, temperature changes due to immersion are kept to a minimum. Also, since induction heating is used, there is no possibility that the molten liquid will solidify in the gap between the compensating member 20 and the crucible 14. There is no risk that the precipitated and enlarged single crystal C is gradually cooled by the heating element 17 and the compensating member 20, and then pulled up and taken out.

Note that the implementation of the present invention is not limited to the above example, but is also effective when the raw material is non-conductive and the crucible 3 is conductive. Further, as a detection means for controlling the liquid level, a method of incorporating a weight scale into the support mechanism of the crucible 14, or a method of directly detecting the liquid level with a level sensor attached to the heating furnace 11 and performing feedback control. and so on.

Furthermore, as the material of the compensation member 20, a noble metal such as platinum may be used instead of quartz in the above example, and in that case, an induced current is caused to flow through the compensation member 20 by the alternating magnetic field of the induction coil 13. This has the advantage of being able to control the temperature. We are also considering adding a method of embedding a thermocouple at a position corresponding to the liquid level of the crucible 3 and controlling the amount of current supplied to the induction coil 13 based on the detected value, to perform more direct control. It will be done.

[Effects of the Invention] As detailed above, the present invention provides a method for producing a single crystal in which further single crystals are precipitated around the seed crystal by pulling up the seed crystal immersed in the melt from the melt in the crucible. In this growing method, the position of the solid-liquid interface for single crystal growth in the crucible is always kept constant during pulling of the single crystal, and the temperature of the molten liquid is strictly controlled at the solid-liquid interface, which is the point at which the crystal is precipitated. It is possible to manufacture high-quality single crystals with uniform microstructures, and it also suppresses changes in diameter to improve yields, and does not require complicated equipment. It has excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one step of a method according to an embodiment of the present invention, FIG. 2 is a sectional view showing another step of the same embodiment, and FIG. 3 is a sectional view showing one step of a conventional method. 4 are sectional views showing other steps in the conventional example. 14... Crucible, 20... Compensation member, S... Melt, S... Seed crystal, C...
...Single crystal.

Claims (5)

[Claims] (1) In a method for growing a single crystal in which a seed crystal immersed in the melt is pulled up from a melt in a crucible to further precipitate a single crystal around the seed crystal, the Single crystal growth A method for growing a single crystal, characterized in that the position of the solid-liquid interface is always kept constant. (2) The single crystal according to claim 1, wherein the means for keeping the solid-liquid interface of the single crystal constant in the crucible is immersing a compensating member in the melt. Cultivation method. (3) The method for growing a single crystal according to claim 2, characterized in that the weight of the precipitated single crystal is measured, and the amount of immersion of the compensating member is controlled based on the measured value. (4) Provide a liquid level detector to detect the liquid level position in the crucible,
3. The method for growing a single crystal according to claim 1, wherein the position of the solid-liquid interface for single crystal growth is feedback-controlled based on the detected value of the liquid level detector. (5) A single crystal according to claim 1, characterized in that a temperature detection means is provided at a position corresponding to the solid-liquid interface for single crystal growth in the crucible, and the amount of heating of the melt is controlled based on the detected value. How to cultivate.