KR20210004736A - Manufacturing methode for siliconcarbide single crystal - Google Patents

Abstract

The present invention relates to a manufacturing method of silicon carbide single crystal, comprising: an input step of inputting an initial raw material containing silicon and metal in a crucible; a melting step of heating the crucible to melt the initial raw material; a depressurization step of depressurizing the process atmosphere to less than 1 atm after the initial raw material is completely melted; and a touching step of returning the process atmosphere to an atmospheric pressure in the range of 1 ± 0.1 atm and providing a seed crystal in the crucible.

Description

Manufacturing method of silicon carbide single crystal {MANUFACTURING METHODE FOR SILICONCARBIDE SINGLE CRYSTAL}

The present invention relates to a method for producing a silicon carbide single crystal.

Silicon carbide (SiC) single crystal has excellent mechanical strength such as abrasion resistance, heat resistance, and corrosion resistance, so it is widely used as a component material for semiconductors, electronics, automobiles, and machinery.

For the growth of silicon carbide single crystals, for example, the Acheson method in which carbon and silica are reacted in a high-temperature electric furnace of 2000 degrees Celsius or higher, and sublimation of growing single crystals by sublimating silicon carbide as a raw material at a high temperature of 2000 degrees Celsius or higher. Method, a solution growth method using a crystal pulling method, and the like. In addition, a method of chemical vapor deposition using a gas source has been used.

However, the Acheson method is very difficult to obtain a high-purity silicon carbide single crystal, and the chemical vapor deposition method may be able to grow only to a limited level of the thickness of a thin film. Accordingly, research on a sublimation method for growing crystals by sublimating silicon carbide at high temperatures has been focused. However, the sublimation method is also generally performed at a high temperature of 2400°C or higher, and there is a high possibility of occurrence of various defects such as micro-pipes and lamination defects, and thus there is a limitation in terms of production cost.

Accordingly, there is active research on a solution growth method in which metals as raw materials including Si are put in a graphite crucible, the crucible is heated through induction heating to form a metal melt, and a SiC single crystal is grown on the surface of the seed crystal.

Among them, there is a Top Seeded Solution Growth (TSSG) method in which SiC seed crystals are grown by contacting SiC seed crystals on the upper surface of the melt.

In the above method, crystal growth proceeds through selective precipitation of SiC while the seed crystals are in contact with the melt. First, SiC is supplied from the melt only when the seed crystals are touched with the melt to proceed, and after the touch is made, the crystal growth is continuously supplied and precipitated from the melt to the seed crystals as the crystal growth plant proceeds.

However, if bubbles are caught on the surface of the seed crystal during such a process, SiC precipitation is prevented, and the space in which the bubbles exist will remain as voids after the final crystal growth, thereby deteriorating the quality of the SiC single crystal.

Thus, in order to remove this, the temperature of the melt is raised and lowered, the He atmosphere gas is used, or the ratio (Sc/Ss) of the surface area (Sc) of the SiC seed crystal to the area (Ss) of the solution interface is adjusted. Attempts have been made to introduce process parameters to eliminate air bubbles inside the melt.

However, it is not easy to clearly remove air bubbles only by the above method.

Therefore, in the crystal growth process using the SiC solution growth method by solving this problem, there is an urgent need for a technology that enables high-quality SiC single crystal growth by preventing voids on the crystal growth surface.

An object of the present invention is to provide a method of manufacturing a high-quality SiC single crystal with minimized voids on the crystal growth surface by introducing a decompression process before touching the melt liquid of the seed crystal to remove air bubbles in the melt.

In addition, it is intended to provide a method for producing a high-quality SiC single crystal by returning to normal pressure during crystal growth to prevent a rapid change in composition due to evaporation of the melt and to prevent impurities from being incorporated.

On the other hand, the technical problem to be solved by the present invention is not limited to the technical problems mentioned above, and other technical problems that are not mentioned are clearly to those of ordinary skill in the technical field to which the present invention belongs from the following description. It will be understandable.

In the method of manufacturing a silicon carbide single crystal according to an embodiment of the present invention, an input step of introducing an initial raw material including silicon and a metal into a crucible,

A melting step of heating the crucible to melt the initial raw material,

After the initial raw material is completely melted, a decompression step of reducing the process atmosphere to less than 1 atm; And

And a touching step of returning the process atmosphere to an atmospheric pressure in the range of 1 ± 0.1 atm and providing a seed crystal in the crucible.

It may further include a pre-treatment step of reducing the process atmosphere to a vacuum atmosphere before the melting step and returning to normal pressure.

Specifically, the pretreatment step before the melting step may be a process of reducing pressure in a vacuum atmosphere, filling an inert gas, and returning to normal pressure.

Meanwhile, the decompression step before the touching step may be sequentially decompressed for 1 minute to 1 hour.

Here, the crucible is located in the chamber, and the change of the process atmosphere in the depressurization step and the pretreatment step may be performed by adjusting the atmosphere in the chamber.

The crucible may be a graphite crucible.

The initial raw material may further include a carbon material.

Heating in the melting step may be performed by an induction heating type heating element.

The heating in the melting step may be specifically performed at 1700°C to 2100°C.

The method of manufacturing a silicon carbide single crystal of the present invention may further include a rotating step of rotating the seed crystal after the touching step.

According to the method for producing a silicon carbide single crystal according to the present invention, in the case of forming a melt and introducing a decompression process before touching the seed crystal to the melt, most of the bubbles in the melt can be removed, so that the crystal growth process is performed. In this regard, the pores in the grown SiC single crystal can be minimized by removing bubbles that may intervene in the crystal growth surface in advance, and the quality of the SiC single crystal can be further improved.

1 is a schematic diagram showing the types of voids generated during crystal growth;
2 is a photograph of a large void;
3 is a graph showing a method of manufacturing a silicon carbide single crystal according to an embodiment of the present invention according to processing time;
4 is a microscopic photograph of a surface and a cross section of a crucible after growth of SiC crystals prepared according to Comparative Example 1 proceeds, and a SEM photograph of the inside of the melt;
5 is a microscopic photograph of a surface and a cross section of a crucible after growth of SiC crystals prepared according to Comparative Example 2 proceeds, and an SEM photograph of the inside of the melt;
6 are SEM photographs of a SiC single crystal according to growth time after growth of SiC crystals prepared according to Example 1 proceeds;
7 are SEM photographs of a SiC single crystal according to growth time after growth of a SiC crystal prepared according to Comparative Example 3 proceeds.

Hereinafter, embodiments of the present invention will be described in detail. However, in describing the present description, descriptions of functions or configurations that are already known will be omitted in order to clarify the gist of the present description.

According to an embodiment of the present invention,

An input step of introducing an initial raw material including silicon and metal into the crucible,

A melting step of heating the crucible to melt the initial raw material,

After the initial raw material is completely melted, a decompression step of reducing the process atmosphere to less than 1 atm; And,

There is provided a method for producing a silicon carbide single crystal comprising a; touching step of returning the process atmosphere to an atmospheric pressure in the range of 1 ± 0.1 atm and providing a seed crystal in a crucible.

That is, according to the present invention, a process of depressurizing the process atmosphere before the step of touching the melt liquid by the seed crystal in the existing process and returning to normal pressure is included.

In general, in a method of manufacturing a silicon carbide single crystal, in order to form a molten liquid in a crucible, raw materials are put in a crucible and the temperature is increased to melt it. However, at this time, it is impossible to pack 100% of the solid raw materials, and when the solid raw materials become liquid, the atmospheric gas existing in the voids between the solid raw materials is entrained into the molten liquid to form bubbles. In addition, when the gas adsorbed to the raw material or the natural oxide film is melted, it is dissolved in the molten liquid, and when buoyancy is generated to some extent through the agglomeration process, it acts as a bubble. Furthermore, when the crucible is used as a carbon feedstock, a graphite crucible having a porosity is used. As the gas in the pores in the closed cell existing in the crucible flows into the melt as the graphite melts, bubbles are generated. It may be incorporated into the melt.

FIG. 1 schematically shows the types of voids occurring in the above case, and FIG. 2 shows a photograph of a large void among the voids.

During the growth process, the bubbles generated by the etching of the graphite crucible are very small in size, and then, through the rotation of the melt, they are moved to the surface of the melt where growth does not proceed, so that the bubbles do not move to the seed crystals. It is not a problem, but bubbles in the melt resulting from the solid raw material increase in volume and generate buoyancy, and if this process occurs before touching the seed crystal, it is possible to remove the bubbles by bursting from the surface, but after touching the seed crystal When the bubble rises due to buoyancy, the bubble adheres to the seed crystal and is formed into a large void later. These voids are formed as shown in FIG. 2 later, and become a factor of deteriorating quality as impurities in the SiC single crystal.

Accordingly, after the inventors of the present application have conducted in-depth research, when the air bubbles existing in the melt are first removed before touching the seed crystal by performing a decompression process before touching the seed crystal, crystal growth according to the colon growth process As a result, it was confirmed that the voids in the grown SiC single crystal were significantly reduced, and the present invention was completed.

Here, the decompression process may be to reduce the pressure to less than 1 atm, and in detail, it may be to reduce the pressure to a range of 0.01 atm to 0.5 atm.

In addition, according to the confirmation of the inventors of the present application, it was confirmed that the desired result of the present invention can be derived only after performing the decompression process as described above and then returning to normal pressure.

Specifically, when the seed crystals are touched under reduced pressure without returning to normal pressure, and crystal growth proceeds, the evaporation of the high-temperature melt occurs very well, and the composition of the melt continues to rapidly increase as the crystal growth proceeds. It is not desirable because it will change. Moreover, when the evaporated melt solidifies in the atmosphere and falls back onto the surface of the melt, the solidified evaporated product acts as an impurity, which is not only disadvantageous in the process, but also in the resulting composition, a SiC single crystal containing impurities. As this can be obtained, there is a problem that the quality may be lowered.

On the other hand, in order to prevent the evaporation, when the pressure is added during crystal growth and pressurization is performed, the bubbles remaining inside the melt increase, even if it can prevent the evaporation of the melt. It is not preferable because it can cause a large amount of voids.

Therefore, after the depressurization step and before the seed crystal is touched, the pressure must be returned to the normal pressure within the above range to obtain a SiC single crystal of excellent quality as desired by the present invention.

Meanwhile, the method of manufacturing a silicon carbide single crystal according to the present invention may include a pretreatment step of reducing a process atmosphere to a vacuum atmosphere before the melting step and returning to normal pressure. Specifically, in the pretreatment step, the pressure is reduced in a vacuum atmosphere, and an inert gas is filled to return to normal pressure.

Here, the decompression in the decompression step and the repression before the seed crystal touch, and the decompression and the recompression before the melting step of the pretreatment step may be sequentially performed. I can.

If the above process takes place in less than 1 minute, there is not enough time to reduce the pressure, and if it proceeds beyond 1 hour, it is not preferable because evaporation of the raw material melt occurs a lot.

In addition, the change of the process atmosphere in the decompression step and the pretreatment step may be performed by adjusting the atmosphere in the chamber by the crucible being located in the chamber.

Accordingly, the chamber is a closed form including an empty inner space, and an atmosphere such as pressure may be adjusted inside the chamber. That is, although not shown, a vacuum pump and a gas tank for controlling an atmosphere may be connected to the chamber. For example, in the pretreatment step, an inert gas such as argon gas may be filled (restored pressure) after making the inside of the chamber into a vacuum state using a vacuum pump and a gas tank for atmosphere control (reduced pressure). In addition, in the depressurization step, the inert gas may be removed (reduced pressure) to a certain portion inside the reaction chamber using a pump and a gas tank for atmosphere control, and then charged (restored pressure).

In order to show the overall process flow of the present invention, FIG. 3 is a graph showing a method of manufacturing a silicon carbide single crystal according to an embodiment of the present invention according to process time.

Referring to FIG. 3, in a method of manufacturing a silicon carbide single crystal according to an embodiment of the present invention, first, after evacuating the interior of the chamber, filling an inert gas to restore pressure to normal pressure, and then heating the crucible (heating). Thus, after melting the initial raw material, the inside of the chamber is decompressed to a certain portion before touching the seed crystal and then returned to normal pressure, and then the seed crystal is touched and crystal growth is performed.

When the above-described process is passed, crystal growth can proceed in a state where bubbles in parts that are difficult to remove during actual crystal growth are removed, and thus, the resulting SiC single crystal not only significantly reduces voids, but also has a rapid melt composition. There is no change, so it is possible to obtain a SiC single crystal of uniform composition and excellent quality.

Hereinafter, another method of manufacturing a silicon carbide single crystal and a manufacturing apparatus used therein will be described.

First, in the initial raw material input step, an initial raw material including silicon and a metal, for example, a metal such as Cr, Ti, Fe, or Al, is introduced into the crucible. The initial raw material may be in a powder form or in a chunk form, but is not limited thereto.

Thereafter, the chamber containing the crucible is adjusted to an inert atmosphere such as argon or helium gas, and heated in an inert atmosphere using a heating member. With this heating, the initial raw material in the crucible turns into a molten liquid containing silicon and metal.

Here, the heating member may be located spaced apart from the crucible, for example, may have a shape surrounding the crucible in a spaced state.

In addition, the heating member may be an induction heating type heating member, and specifically, the heating member may be an induction heating method in which the crucible is heated by heat generation by an eddy current by allowing a high frequency current to flow through the induction coil.

The heating may be performed at 1700°C to 2100°C in consideration of melting even the metal.

Outside the above range, at a low temperature, the initial raw materials may not be completely melted, a high temperature is inefficient, and due to rapid evaporation of the melt, the composition may change rapidly, which is not preferable.

On the other hand, the crucible is provided inside the chamber and may be any form in which a melt for forming a silicon carbide single crystal may be charged, and may also include a cover that covers the upper surface according to the manufacturing process.

In addition, the crucible may be made of a material containing carbon such as graphite, graphite, or SiC, or a ceramic crucible may be used without being limited thereto. However, the molten liquid contains carbon in order to produce a SiC single crystal. It should further include, and therefore, for this purpose, the crucible may be a graphite crucible.

If the crucible is a crucible made of a ceramic material that cannot be a carbon supplier, a material or source to provide carbon may be separately provided. Therefore, in this case, the initial raw material may further include a carbon material.

Due to such a process, carbon introduced separately from the crucible may be included in the final molten melt.

When the melting is complete, the temperature of the crucible is maintained, and then, a decompression process according to an embodiment of the present invention is performed, and after returning to normal pressure, a seed crystal is provided in the crucible to touch the seed crystal in the melt.

From this, a silicon carbide single crystal can be deposited on the surface of the seed crystal.

For this, the temperature of the seed crystal is lower than the temperature of the melt inside the crucible. When a silicon carbide supersaturation state is reached near the seed crystal, a silicon carbide single crystal grows on the seed crystal using this supersaturation degree as a driving force. The temperature of the crucible is not limited thereto, and crystal growth may be performed while gradually lowering the temperature of the crucible.

In addition, as the silicon carbide single crystal grows, conditions for depositing silicon carbide from the melt may change. At this time, by adding silicon, metal, and carbon to suit the composition of the melt over time, the melt can be maintained in a composition within a certain range. The raw materials to be added may be added continuously or discontinuously.

Meanwhile, the method of manufacturing a silicon carbide single crystal of the present invention may further include a rotating step of rotating the seed crystal immediately after the touching step.

This can be performed by rotation of the support member supporting the seed crystal, and the seed crystal support member is a member that allows the seed crystal to be moved in a direction not touching or touching the melt. The seed crystal can also rotate, and thus, the SiC single crystal can be evenly grown on the surface of the seed crystal.

Hereinafter, FIGS. 4 to 7 are photographs according to examples and comparative examples according to the present invention. Specifically, FIG. 4 is a micrograph of the surface and cross section of the crucible after growth of SiC crystals prepared according to Comparative Example 1 and an SEM image of the inside of the melt, and FIG. 5 is a view after growth of SiC crystals prepared according to Comparative Example 2 proceeds. It is a microscopic photograph of the crucible surface and cross section, and an SEM photograph of the inside of the melt. In addition, FIG. 6 is an SEM photograph of a SiC single crystal according to the growth time after the SiC crystal growth proceeds according to Example 1, and FIG. 7 shows the SiC crystal growth according to Comparative Example 3 after progression. These are the SEM pictures of SiC single crystals.

In Comparative Example 1, as initial raw materials, silicon, chromium (Cr), and aluminum (Al) were used as Si _{0 . 56} Cr _{0 . 4} Al _{0 . 04} , the crucible was a graphite crucible, the atmosphere in the chamber was evacuated and then filled with argon gas to adjust to normal pressure, and the crucible was gradually heated up to 1900°C to melt the initial raw material. Thereafter, the melt was maintained at the above temperature for 2 hours at normal pressure, cooled to room temperature, and the surface of the crucible and the cross section of the crucible were photographed with a microscope, and the portion of the solidified melt was taken as a SEM photograph and observed. Shown in.

Comparative Example 2, as the initial raw material, silicon, chromium (Cr), and aluminum (Al) Si _{0 . 56} Cr _{0 . 4} Al _{0 . 04} , the crucible was a graphite crucible, the atmosphere in the chamber was evacuated and then filled with argon gas to adjust to normal pressure, and the crucible was gradually heated up to 1900°C to melt the initial raw material. Thereafter, the melt was maintained at the temperature for 2 hours by pressing at 8 atm, cooled to room temperature, the surface of the crucible and the cross section of the crucible were photographed with a microscope, and the portion of the solidified melt was taken with a SEM photograph and observed. It is shown in Figure 5.

Referring to Figures 4 and 5, it can be seen that bubbles are generated in the melt when the decompression process is not introduced (black part), especially, when the pressure is performed as shown in FIG. 5, more bubbles are generated. Then, it can be expected that a large number of voids will be generated during seed crystal growth.

Meanwhile, in Example 1, a single crystal was grown in the same manner as in FIG. 3 using an apparatus for manufacturing a silicon carbide single crystal. Specifically, as an initial raw material, silicon, chromium (Cr), and aluminum (Al) were Si _{0 . 56} Cr _{0 . 4} Al _{0 . 04} , the crucible was a graphite crucible, the atmosphere in the chamber was evacuated and then filled with argon gas to adjust to normal pressure, and the crucible was gradually heated up to 1900°C to melt the initial raw material. Thereafter, the argon gas was partially exhausted to reduce the pressure in the chamber to 0.15 atm for 3 minutes, and then returned to 1 atm for 15 minutes. Thereafter, the seed crystal was touched and rotated in the melt to proceed with SiC single crystal growth.

Meanwhile, after touching the seed crystal according to Example 1, growth of the single crystal was performed for 8 hours, and the grown single crystal including the seed crystal was divided into three parts in the longitudinal direction, and SEM photographs of the cross section of the seed crystal were taken, respectively, and the results were shown. It is shown in 6.

Comparative Example 3 proceeds in the same manner as in Example 1, but without performing the decompression and pressure reduction process after initial melting of the raw material, the seed crystal was immediately touched and rotated in the melt to grow a SiC single crystal for 8 hours, and then, the grown single crystal In the longitudinal direction, including the seed crystal, by dividing into three, SEM photographs of the cross section of the seed crystal were respectively taken, and the results are shown in FIG. 7.

Referring to FIGS. 6 and 7, when the decompression process is not performed (Fig. 7), it can be confirmed that a large number of spherical pores are found on the surface of the seed crystal, and a number of pores are also found in the middle and late stages, whereas the decompression process In the case of performing (FIG. 6), it can be seen that the void formation is significantly reduced.

Therefore, it can be seen from this that when the production method of the present invention is performed, a SiC single crystal of excellent quality can be obtained.

In the above, although specific embodiments of the present invention have been described and illustrated, the present invention is not limited to the described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. It is self-evident to those who have. Therefore, such modifications or variations should not be individually understood from the technical spirit or point of view of the present invention, and the modified embodiments should be said to belong to the claims of the present invention.

Claims (10)

An input step of introducing an initial raw material including silicon and metal into the crucible,
A melting step of heating the crucible to melt the initial raw material,
After the initial raw material is completely melted, a decompression step of reducing the process atmosphere to less than 1 atm; And
A method for producing a silicon carbide single crystal comprising; a touching step of returning the process atmosphere to an atmospheric pressure in the range of 1 ± 0.1 atm and providing a seed crystal in a crucible. The method of claim 1,
A method for producing a silicon carbide single crystal comprising a pretreatment step of reducing a process atmosphere to a vacuum atmosphere before the melting step and returning to normal pressure. The method of claim 2,
The pretreatment step prior to the melting step is a method for producing a silicon carbide single crystal in which the pressure is reduced to a vacuum atmosphere and returned to normal pressure by filling an inert gas. The method of claim 1, wherein the depressurization step is sequentially depressurized for 1 minute to 1 hour. The method of claim 1 or 2, wherein the crucible is located in a chamber, and in the depressurization step and the pretreatment step, the process atmosphere is changed by adjusting the atmosphere in the chamber. The method of claim 1,
The crucible is a graphite crucible, a method of manufacturing a silicon carbide single crystal. The method of claim 1,
The initial raw material is a method of manufacturing a silicon carbide single crystal further comprising a carbon material. The method of claim 1,
The heating of the melting step is performed by an induction heating type heating member. The method of claim 1,
The heating in the melting step is performed at 1700°C to 2100°C. The method of claim 1,
The method of manufacturing a silicon carbide single crystal further comprising a rotating step of rotating the seed crystal after the touching step.

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