KR102488116B1 - Combining method of SiC and Carbon materials - Google Patents

Abstract

The present invention relates to a bonding method between silicon carbide and graphite material, and more particularly, a) applying a thermosetting resin chemical solution to silicon carbide or graphite; b) compressing silicon carbide and graphite; and c) heat-treating the compressed silicon carbide and graphite.

Description

Combining method of SiC and Carbon materials}

The present invention relates to a bonding method between silicon carbide and a graphite material, and more particularly, by first bonding silicon carbide and a graphite material using a thermosetting resin chemical solution and then performing heat treatment to firmly bond the silicon carbide and the graphite material, When crystal growth is performed by attaching a silicon carbide seed crystal to a graphite material, it is possible to solve the problem that the silicon carbide seed crystal is dropped due to a difference in thermal expansion coefficient between the silicon carbide seed crystal and the graphite material, the impression rod.

Methods for growing a single crystal of silicon carbide are generally a method of bonding a silicon carbide seed crystal to an impression bar of graphite material, and then growing the crystal using silicon in a liquid state and carbon melted from graphite to silicon in a liquid state as raw materials, respectively. is adopting

Here, in joining the silicon carbide seed crystal and the graphite rod, a carbon paste is usually used. Carbon material paste is a universal adhesive used in this case. However, when the carbon material paste is used to bond the impression rod and the silicon carbide seed crystal, the difference in thermal expansion coefficient between the impression rod and the paste material graphite and silicon carbide becomes a problem. A problem has been raised that the rod is detached from the impression rod during the impression process.

The thermal expansion coefficient of graphite is 6.1 to 6.6×10 ^-6 /°C in the temperature environment of 1900°C, the crystal growth temperature, and in the case of 4H-SiC, it is 4.6×10 ^-6 /°C, with a difference of more than 1.5×10 ^-6 /°C. exist.

That is, silicon carbide and graphite have a material-specific thermal expansion coefficient, and when the two materials are bonded due to different thermal expansion coefficients when heated to a high temperature, one side receives compressive stress and the other side receives tensile stress. Since the thermal expansion coefficient of graphite is usually greater than that of silicon carbide, silicon carbide seed crystals are subjected to tensile stress, and cracks occur when tensile stress accumulates, or when the bonding force is low, they are separated from graphite to relieve stress.

In this way, when the silicon carbide seed crystal is separated from the graphite rod, in particular, when this happens during crystal growth, the single crystal ingot cannot be completed and must be remanufactured from the beginning.

Therefore, it is necessary to introduce a bonding material between a silicon carbide seed crystal and a graphite material suitable for use in a high-temperature single crystal growth environment.

The present invention has been made to solve the above-described problems, and an object of the present invention is to use a thermosetting resin chemical solution as an adhesive instead of carbon paste, and to bond silicon carbide seed crystals and graphite rods using this as an adhesive, followed by a heat treatment process To provide a bonding method of silicon carbide and graphite material to increase bonding strength through the.

Another object of the present invention is not only the bonding strength, but also the silicon carbide seed crystal is not separated from the graphite impression rod despite the difference in thermal expansion coefficient between the silicon carbide seed crystal and the graphite impression rod by buffering the difference in thermal expansion coefficient at high temperature with the polymer adhesive. It is to provide a bonding method of silicon carbide and graphite material to prevent.

The present invention in order to achieve the above object, a) applying a thermosetting resin chemical solution to silicon carbide or graphite; b) compressing silicon carbide and graphite; and c) heat-treating the compressed silicon carbide and graphite.

It is preferable to further include a step of planarizing the thermosetting resin chemical solution on silicon carbide or graphite after step a).

It is preferable that the time from application to flattening is more than 0 minutes and less than 5 minutes.

This is because if flattening is not performed after application, the bonding surface is non-homogeneous, and as a result, unintended external stress is applied to the bonding materials (graphite and SiC) and there is room for damage. This is because if the flattening operation exceeds 5 minutes, the surface of the chemical solution in contact with air is hardened, resulting in a non-uniform bonding surface.

After step a), it is preferable to leave the silicon carbide or graphite coated with the thermosetting resin chemical solution in a vacuum environment.

The degree of vacuum is preferably 0.04 to 0.07 MPa.

This is because if the vacuum is maintained above 0.07 Mpa, bubbles are generated on the surface of the thermosetting resin chemical solution applied to the graphite, resulting in a deterioration in bonding properties. If the vacuum is maintained below 0.04 Mpa, the thermosetting resin chemical solution is too fast There is a problem in that the bonding properties are deteriorated due to curing at a high speed.

It is preferable to leave it for 5 to 7 hours in the vacuum state.

Since the thermosetting resin chemical solution immediately after application is in a liquid state, it is not easy to bond due to its low viscosity, so it was experimentally confirmed that the optimum condition for changing to a property having viscosity and elasticity suitable for bonding is set at 5 to 7 hours. .

It is left in the vacuum state for 6 hours, and at this time, it is preferable to hold at 0.04MPa for 2 hours, 0.05MPa for 2 hours, 0.06MPa for 1 hour, and 0.07MPa for 1 hour.

Compression in step b) is preferably performed at a pressure of 1.0 to 9.0 kgf/cm ² . If the compression pressure exceeds 9.0 kgf/cm ² , SiC may be damaged, and if the compression pressure is maintained below 1.0 kgf/cm ² , graphite and SiC may not be properly compressed, resulting in voids, and air bubbles in such voids. As a result of remaining, there is a problem in that the adhesive force is lowered.

In the step c), the heat treatment is preferably carried out by raising the temperature from room temperature to 45 ~ 55 ° C., maintaining the temperature at that temperature, then raising the temperature, maintaining the temperature at 500 ~ 600 ° C., and then cooling.

The reason for heat treatment at room temperature to 45~55℃ is that the rate of evaporation of moisture in the liquid thermosetting resin chemical solution at the initial stage is very slow at room temperature. This is because it is possible to maintain high adhesive properties inherent in materials during the curing process only when appropriately controlled so as not to be fast or slow. Afterwards, when the thermosetting resin chemical solution has an appropriate hardness, the thermosetting resin chemical solution should be distributed as evenly as possible in the transverse direction so that the pores remaining between the graphite and SiC junctions can be pushed out as much as possible. The temperature is 500~600℃.

The holding time at 45 to 55 ° C is 20 minutes to 1 hour, and the holding time at 500 to 600 ° C is preferably 1 hour 30 minutes to 2 hours 30 minutes.

It depends on the concentration of the thermosetting resin chemical solution and the appropriate time required for bonding.

A step of cooling after the step c) is included, and it is preferable to cool in a vacuum environment during the cooling.

The cooling step is preferably performed for 5 to 7 hours.

The above time range is required when the free temperature is lowered from a high temperature of 600 ° C to room temperature (assumed to be 25 ° C) without an additional peripheral cooling unit.

Preferably, the thermosetting resin chemical solution is a photoresist.

Preferably, the thermosetting resin chemical solution contains a phenol group.

The coating thickness of the thermosetting resin chemical solution is preferably 45 ~ 55㎛.

According to the present invention as described above, a thermosetting resin chemical solution was used as an adhesive instead of carbon paste, and after bonding silicon carbide seed crystals and graphite rods using this, an effect of increasing the bonding strength through a heat treatment process can be expected. there is.

In addition, the present invention provides not only bonding strength, but also the polymer adhesive buffers the difference in thermal expansion coefficient at high temperature, so that the silicon carbide seed crystal is not separated from the graphite impression rod despite the difference in thermal expansion coefficient between the silicon carbide seed crystal and the graphite impression rod. effect can be expected.

1 is a schematic diagram showing behavior according to a difference in thermal expansion coefficient between graphite and silicon carbide bonded to each other.
2 is a schematic view of a three-point bending strength test of graphite and silicon carbide in the form of a bonded bar according to an embodiment of the present invention.
Figure 3 is a photograph of the equipment that performed the test of Figure 2.
4 is a photograph showing that graphite is broken as a result of performing the test of FIG. 2 .
Figure 5 is a graph showing the strength test results of Figure 2.
Figure 6 is a graph showing the results of performing the test of Figure 2 using various adhesives.
7 is a heat treatment process diagram according to an embodiment of the present invention.
8 is a diagram showing a heat treatment schedule in the heat treatment process of FIG. 7 .

Hereinafter, the present invention will be described in more detail based on the accompanying drawings and preferred embodiments.

As an example, the present invention suggests bonding between silicon carbide seed crystals and graphite materials for growth of silicon carbide single crystals, but it should be understood that it can be further extended and applied to bonding between silicon carbide and graphite.

The 'thermosetting resin chemical solution containing a phenol group' presented as an example in the present invention cannot be changed again once its shape is fixed, but it is not a hard solid that cannot be moved due to its characteristics, but since it has elasticity like silicon, it is resistant to temperature. It may have an effect of relieving stress such as a whip phenomenon of an object caused by contraction expansion between graphite having a very high expansion / contraction rate according to temperature and SiC having a lower expansion / contraction rate according to temperature. The fact that the bonding strength is very high means that the critical point for the thermal expansion stress according to such temperature is high, so that it can be maintained without being easily detached from the bonding material.

1 is a schematic diagram showing the behavior according to the difference in thermal expansion coefficients of graphite and silicon carbide bonded to each other, and FIG. A schematic diagram, Figure 3 is a photograph of the equipment subjected to the test of Figure 2, Figure 4 is a photograph showing that graphite is broken as a result of the test of Figure 2, Figure 5 is a graph showing the results of the strength test of Figure 2 6 is a graph showing the results of the test of FIG. 2 using various adhesives, FIG. 7 is a heat treatment process diagram according to an embodiment of the present invention, and FIG. 8 is a heat treatment schedule in the heat treatment process of FIG. 7 It is a drawing showing

<Example>

The present invention comprises the steps of a) applying a thermosetting resin chemical solution to silicon carbide or graphite; b) compressing silicon carbide and graphite; and c) heat-treating the compressed silicon carbide and graphite.

The thermosetting resin chemical solution may include, for example, a photoresist that is pre-coated on a semiconductor substrate in order to perform exposure in a semiconductor process.

It is also possible to adopt a thermosetting resin chemical solution that does not have an intrinsic function of adhesion. In the present invention, only the adhesive strength of the thermosetting resin chemical solution needs to be present to some extent, and the adhesive strength can be strengthened by the subsequent heat treatment process.

During solution growth, since the graphite rod-SiC seed crystal is not directly heated, the temperature of the actual junction region is lower than the growth temperature. Assuming that the growth temperature is 1900 ° C, the temperature that the bonding surface receives is about 4 to 500 ° C lower than that. In addition, the remaining main component of the thermosetting resin chemical solution cured through the heat treatment process is a carbon polymer, and the carbon polymer generally has very strong characteristics against heat.

When heat treatment is performed, the thermosetting resin chemical solution is thermally cured to greatly improve bonding strength between graphite and silicon carbide. If this is reflected in the silicon carbide single crystal growth process, the silicon carbide growth process can proceed more stably.
The heat treatment process is as shown in FIGS. 7 and 8 . The heat treatment process will be described later.

Among the above processes, there are processes that can be added. For example, when a thermosetting resin chemical solution is applied on graphite, the graphite is tilted by hand at an angle of 15 to 20 degrees before performing the compression process so that the thickness of the coating solution is about 50 μm. At this time, the precautions are to limit the time taken from application to flattening to less than 5 minutes. This is because as time goes by, the polymer chemical solution hardens, and a situation in which planarization is difficult may occur. Here, the thickness of the above coating liquid is not limited to the above numerical value. This thickness is the thickness with appropriate application and curing times. If it is thicker, the coating and curing time increases inefficiently, and if it is thinner than this, there are problems in that bonding characteristics and elasticity are deteriorated. Preferably, a thickness of 45 to 55 μm is preferred.

In addition, when the coating and planarization process is completed, the graphite is left in a vacuum state. At this time, in the case of silicon carbide seed crystals, in the case of using a seeding machine (a device commonly used for bonding seed crystals for single crystal material growth) for bonding with the impression rod, the graphite impression rod is mounted on the seeding machine. After maintaining a pressure state (vacuum state) of 0.04 to 0.07 MPa using a rotary pump for 5 to 7 hours, it is left here.

Here, if the vacuum process is not performed, the surface of the thermosetting resin chemical solution is rapidly hardened in the air and loses bonding strength.

The drying process was performed by holding at 0.04 MPa for 2 hours, at 0.05 MPa for 2 hours, at 0.06 MPa for 1 hour, and at 0.07 MPa for 1 hour. This is because when the pressure is maintained above 0.07 Mpa, the gas remaining inside the solution is not discharged to the outside of the solution due to the surface tension of the thermosetting resin chemical solution and remains while forming microbubbles (causing a decrease in bonding properties), so the internal gas remains. This is because it is effective to raise while maintaining the pressure gradually at 0.04 Mpa so that all can be discharged without doing so.

Thereafter, the silicon carbide seed crystal and the graphite impression rod are combined, and when combined, they are combined by compressing at a pressure of 1.0 to 9.0 kgf/cm ² using a press. By compressing and bonding in this way, the silicon carbide seed crystal and the graphite rod are primarily maintained in a bonded state.

After that, while maintaining the compressed state, heat treatment is performed in a seeding machine, preferably for 3 hours. Specifically, the temperature is maintained at 45 to 55 ° C for 20 minutes to 1 hour, and then the temperature is raised and maintained at 500 to 600 ° C for 1 hour 30 minutes to 2 hours 30 minutes. In this example, the temperature was maintained at 50° C. for 30 minutes and the temperature was maintained at 550° C. for 2 hours (see FIGS. 7 and 8).

The thermosetting resin chemical solution that has undergone such a process is bonded to silicon carbide seed crystals and graphite in a cured state to maintain its shape. All of the moisture in the components of the solution evaporates and disappears, and the main raw material, the carbon polymer component, remains.

Thereafter, by releasing the heat treatment state and cooling, the procedure is terminated. The cooling time was maintained for 6 hours, but generally maintained in the range of 5 to 7 hours. This cooling process is performed while maintaining a vacuum of 0.07 MPa.

<Evaluation example>

In order to measure the bonding strength of silicon carbide and graphite bonded according to the present invention, a sample as shown in FIG. 2 was prepared. Here, graphite and silicon carbide were produced in the form of a bar, and the length of the graphite bar was longer than the length of the silicon carbide bar, but one end of the graphite bar and one end of the silicon carbide bar were matched, and the bonding was performed using three types of adhesives. performed.

The size of the sample was 4 × 40 × 5 mm, the initial crack size (a0) was 6 mm, and the length of the span (distance between working points) was 30 mm.

The load was applied to the center of the graphite bar, and a three-point bending strength test was performed by setting one of the points of action where the reaction to the load is made to the graphite bar and the other to the silicon carbide bar. In addition, a bonding strength value is determined at a point where the graphite bar and the silicon carbide bar are spaced apart from each other. 3 shows a photograph of the test equipment for measuring the three-point bending strength.

As shown in FIG. 5, when measuring the joint strength, the load value increases in proportion to the displacement value, and then the load value rapidly decreases and recovers again at the moment when the stress is relieved due to external changes. The time when this phenomenon occurs can be regarded as the time when the junction state is released. As can be confirmed from the table of FIG. 5, since the load at the 8th order is lower than that at the 7th order, this point is the point at which the bonding state is released. Relief of stress generally occurs when the object to be analyzed is damaged, and in the present invention, a phenomenon in which graphite having relatively weak physical properties is damaged occurs as the bonding interface is separated. This is as shown in FIG. 4 .

6 is a graph of bonding strength measured when a carbon paste is used, when a thermosetting resin chemical solution is used, and when a carbon paste and a thermosetting resin chemical solution are mixed.

The average bonding strength of 5.43 kgf was shown when using carbon paste, the average bonding strength of 5.43 kgf when using thermosetting resin chemical solution, and the average bonding strength of 6.91 kgf when mixing carbon paste and thermosetting resin chemical solution showed Thus, it was found that the use of the thermosetting resin chemical solution of the present invention gave the most desirable results.

As described above, the present invention has been described based on preferred embodiments, but the embodiments are representative examples for convenience of description, and the claims of the present invention are not limited to these embodiments.

Claims (15)

a) applying a thermosetting resin chemical solution on silicon carbide or graphite and then flattening the thermosetting resin chemical solution on silicon carbide or graphite;
b) compressing silicon carbide and graphite; and
c) heat-treating the compressed silicon carbide and graphite;
A bonding method of silicon carbide and graphite material comprising a. delete According to claim 1,
A method of bonding silicon carbide and graphite materials, characterized in that the time from application to flattening is greater than 0 minutes and less than 5 minutes. According to claim 1,
A method of bonding silicon carbide and graphite materials, characterized in that after step a), the silicon carbide or graphite coated with the thermosetting resin chemical solution is left in a vacuum environment. According to claim 4,
A method for bonding silicon carbide and graphite materials, characterized in that the degree of vacuum is 0.04 to 0.07 MPa. According to claim 5,
A bonding method of silicon carbide and graphite material, characterized in that left for 5 to 7 hours in the vacuum state. According to claim 6,
The bonding method of silicon carbide and graphite material, characterized in that it is left for 6 hours in the vacuum state, and at this time, held at 0.04 MPa for 2 hours, 0.05 MPa for 2 hours, 0.06 MPa for 1 hour, and 0.07 MPa for 1 hour. . According to claim 1,
In step b), the compression is performed at a pressure of 1.0 to 9.0 kgf/cm ² . Method for bonding silicon carbide and graphite material. According to claim 1,
In the step c), the heat treatment is performed by raising the temperature from room temperature to 45 ~ 55 ℃, maintaining it at that temperature, then raising the temperature, maintaining it at 500 ~ 600 ℃, and then cooling. bonding method. According to claim 9,
The holding time at 45 to 55 ° C is 20 minutes to 1 hour, and the holding time at 500 to 600 ° C is 1 hour 30 minutes to 2 hours 30 minutes. According to claim 1,
A method of bonding silicon carbide and a graphite material, comprising cooling after step c), wherein cooling is performed in a vacuum environment during the cooling. According to claim 11,
The cooling step is a bonding method of silicon carbide and graphite material, characterized in that carried out for 5 to 7 hours. According to claim 1,
The thermosetting resin chemical solution is a method of bonding silicon carbide and graphite material, characterized in that the photoresist (photoresist). According to claim 1,
The thermosetting resin chemical solution is a bonding method of silicon carbide and graphite material, characterized in that it contains a phenol group. According to claim 1,
The bonding method of silicon carbide and graphite material, characterized in that the coating thickness of the thermosetting resin chemical solution is 45 ~ 55㎛.

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