KR20050039042A - Method for surface modification of silicon carbide and silicon carbide resulted therefrom - Google Patents

Abstract

The present invention relates to a method for surface modification of silicon carbide and surface-modified silicon carbide used as heat-resistant parts, wear-resistant parts and components for semiconductor manufacturing equipment, and more particularly, through the surface modification, strength, thermal shock characteristics, wear resistance A method for surface modification of silicon carbide in the air and thereby surface modified silicon carbide to be improved.

Silicon carbide surface modification method of the present invention

Heat-treating the silicon carbide at a temperature of 900-1300 ° C., preferably 1050-1300 ° C., for several seconds to several tens of hours in air.

According to the silicon carbide surface modification method of the present invention, silicon carbide has the effect of improving the strength, heat shock resistance and wear resistance, and healing cracks generated during processing.

In addition, the surface modification method not only improves the properties of silicon carbide by a simple method, but also provides an advantageous processing process in terms of cost, and therefore, parts for heat-resistant parts, wear-resistant parts, and semiconductor manufacturing equipment that use silicon carbide. A great effect is expected in the industry.

Description

Surface Modification Method of Silicon Carbide and Surface Modified Silicon Carbide {METHOD FOR SURFACE MODIFICATION OF SILICON CARBIDE AND SILICON CARBIDE RESULTED THEREFROM}

The present invention is to improve the strength, heat shock characteristics, wear resistance through the surface modification method and the surface-modified silicon carbide, more particularly surface modification of silicon carbide used as heat-resistant parts, wear-resistant parts and components for semiconductor manufacturing equipment The present invention relates to a surface modification method of silicon carbide in the air and thereby silicon carbide surface modified.

Silicon carbide is a carbide of silicon and its chemical name is silicon carbide (SiC), which is not only heat resistant and chemically stable at high temperatures, but also has sufficient strength not to be damaged by thermal shock during heating and cooling. BACKGROUND ART It is widely used as a material for peripheral components such as a heater heating element, a wafer support, an edge ring, a heater inner wall, and the like, which are used in a heating apparatus for annealing, oxidizing, and diffusing a semiconductor wafer.

In addition, due to the high thermal conductivity, heat resistance, abrasion resistance, chemical stability and thermal shock resistance of silicon carbide, the mechanical seal and the high thermal conductivity, heat resistance and resistance to thermal shock of a rotating machine that serve to prevent mixing of two fluid materials are required. It is used as a material of the heat exchanger which is a device for obtaining heat that can be recycled from hot waste gas or waste water.

Typically, silicon carbide was prepared by sintering silicon carbide powder at about 2000 ° C. in a vacuum or by agglomeration of silicon carbide powder in a vacuum and then melting the silicon with a relatively low melting point and then mixing it with the powder.

The reason why these processes proceed in a vacuum state is that silicon carbide and silicon are oxidized to silicon dioxide (SiO ₂ ) having low strength and brittleness when advancing in air.

Such silicon carbide and silicon carbide parts have the following problems in industrial use.

   First, strength less than 350 MPa is not sufficient.

   Second, there is a high possibility of breakage if the heat shock temperature is not enough and the cooling is abruptly at 400 ~ 500 ℃.

   Third, there is a problem in the reliability of the product because the fragility of silicon carbide tends to cause cracks on the surface of the part when the part is manufactured and manufactured.

   Fourth, it is not suitable as a mechanical seal material to be used at higher load conditions due to insufficient wear resistance.

Efforts have been made to improve the high temperature strength to overcome the drawbacks of silicon carbide, for example, Korean Patent Registration No. 0395685, filed Aug. 12, 2003, discloses β-silicon carbide powder, the total weight of ceramic 0.5 to 10% by weight of α-silicon carbide powder, 1 to 12% by weight of aluminum nitride, 2 to 25% by weight of niobium oxide or 1 to 12% by weight of aluminum nitride, and 2 to 25% by weight of Mixing any one kind of sintering aid selected from ether oxide, and a solvent and an organic binder to obtain a raw material powder mixture; Compressing the raw powder mixture to obtain a molded body; And it is disclosed a method for producing a high toughness silicon carbide material having a high temperature strength including the step of sintering the molded body at 1800 ~ 1900 ℃, heat treatment at 1950 ~ 2100 ℃.

The present invention has been invented to improve the conventional problems as described above, and to provide a simple method for surface modification of silicon carbide to improve the strength, thermal shock characteristics, wear resistance of silicon carbide and to heal cracks generated during processing. .

Another object of the present invention is to provide a surface-modified silicon carbide with improved physical properties.

In order to achieve the object of the present invention, the present invention includes a step of heat-treating silicon carbide in air.

In more detail, the present invention,

Heat-treating the silicon carbide at a temperature of 900-1300 ° C., preferably 1050-1300 ° C., for several seconds to several tens of hours in air.

 In this case, the step of grinding silicon carbide to make a crack before the heat treatment step may be further included, in particular, it is preferable to create a crack by grinding using a diamond wheel 200. The strength can be further increased by grinding silicon carbide to create artificial cracks and then healing the cracks by heat treatment.

Since the heat treatment time depends on the size of the product and the shape heat treatment temperature, it is difficult to determine an appropriate time range, but it is preferably about several seconds to 10 hours.

The heat treatment apparatus uses a general electric furnace, and this heating process is for oxidation reaction of the material surface, and the reaction atmosphere may be air.

  In other words, by heat-treating silicon carbide produced in vacuum in the air, a silicon dioxide layer is formed on the surface to prevent oxygen diffusion, and silicon oxide fills the gap of silicon carbide to heal the cracks of silicon carbide and Due to the difference in thermal expansion coefficient with silicon carbide, the compressive stress remains, thereby improving physical properties including thermal shock resistance and strength. At this time, depending on the heat treatment temperature, the oxide due to the reaction is changed to an amorphous or crystalline phase and the physical properties also show a difference.

This is explained theoretically as follows.

: Residual stress, negative sign, compressive stress, positive sign, tensile stress

And : Coefficient of thermal expansion of silica and silicon carbide

: When silica is crystalline, heat treatment temperature, silica is amorphous, and when heat treatment temperature is higher than softening point of amorphous silica, softening point of amorphous silica, heat treatment temperature when silica is amorphous and heat treatment temperature is lower than softening point of silica

And : Modulus of elasticity of silica and silicon carbide, respectively

The coefficient of thermal expansion of silicon carbide is about 3.5 × 10 ⁻⁶ , the coefficient of thermal expansion of amorphous silica is about 0.2 × 10 ^−6, and the coefficient of thermal expansion of cristobalite varies greatly with temperature, but it is known to be significantly larger than that of silicon carbide.

Therefore, in the case of cracks treated with amorphous silica by heat treatment at a temperature of 1300 ° C. or less, the residual stress is a compressive component as shown in FIG. 1, and in the case of cracks healed with cristobalite, the residual stress is a tensile component as shown in FIG. 2. It can be seen that the strength is increased by compressive stress when healed with silica.

Indeed, when the silicon carbide was heat treated at a temperature of 900-1300 ° C., preferably 1050-1300 ° C., the cracks were healed and filled with amorphous silica, the coefficient of thermal expansion and the softening point of amorphous silica 1050 ° C., the elasticity of amorphous silica and silicon carbide Substituting the coefficients 75 GPa and 400 GPa into the above equation, it can be calculated that there will be a compressive stress of about 290 MPa in and around the crack.

In addition, in case that the silicon carbide is heat-treated at a temperature higher than 1300 ° C. and cristobalite is healed by cracks, the thermal expansion coefficient of cristobalite is greater than that of silicon carbide, so the stress generated inside the crack becomes a tensile component. It can be seen that it serves to reduce the strength of the healed cracks.

Therefore, in the present invention, it can be seen that the temperature of the heat treatment is most suitable 900-1300 ℃, preferably 1050-1300 ℃.

Korean Patent Publication No. 2003-0047799 discloses a technique for curing a crack by heat treating a composite of silicon nitride and silicon carbide at 800-1400 ° C., and describes that heat treatment is required at a high temperature of 1400 ° C. or higher when using only silicon carbide. However, in the present invention, it is an invention that can heal cracks or the like as a heat treatment of 1050 ° C to 1300 ° C without mixing silicon nitride.

Through the following examples will be described in detail the present invention.

Example 1

Crack Healing of Silicon Carbide

Mixing boron and carbon with a sintering aid to process atmospheric sintered silicon carbide to make a specimen 4 mm high, 3 mm wide and 40 mm long, press-fit the Vickers indenter with a force of 98 N, and then bridge loading As can be seen, a penetration crack was introduced at the center of the specimen.

Thereafter, the specimen was heat-treated for 50 hours at a temperature range of 1050 ℃ to 1300 ℃ in the air atmosphere.

As a result, the cracks healed, as shown in FIG. 4.

In other words, it can be seen that the crack was completely filled by the new material and healed.

FIG. 5 shows the results of elemental analysis (EDX analysis) on the new material filled with cracks. According to these results, it can be seen that the material filled with cracks contains more oxygen and contains less silicon than the surrounding silicon carbide. Therefore, it can be seen that the material filling the crack is silica.

As shown in the diffraction patterns of FIGS. 6 and 7, which are shown inside and after heat treatment at 1300 ° C. and heat treatment at 1400 ° C., when the heat treatment is performed at a temperature of 1300 ° C. or less, the amorphous silica fills cracks and heals 1300 ° C. It can be seen that when heat treated at a higher temperature, crystalline silica (cristobalite) fills the cracks and heals.

Example 2

 Strength recovery from crack healing 1

The bending strength was measured according to the ISO 14704 standard to show that the strength was restored as the crack healed.

The cracks were always tested to be tensile planes and FIG. 8 plots the strength data according to the heat treatment temperature.

According to the graph described above, the original strength of silicon carbide measured without making cracks was about 310 MPa, and the strength measured after artificially indenting diamond into the surface was 10 MPa. (Opened rhombus of Figure 8) After the heat treatment at 1000 ℃ or less after that the strength is 100 MPa or less, when the heat treatment above 1050 ℃ it can be seen that the recovery to 80% of the original strength, when the heat treatment above 1300 ℃ It was confirmed that the strength was lowered again.

Therefore, the heat treatment temperature was confirmed that the most suitable 1050 ℃ to 1300 ℃.

Example 3

Strength recovery by crack healing 2

The specimens of Examples 1 and 2 had a large uneven portion due to the indentation of the diamond particles for generating an artificial crack, and thus had an effect on the resulting strength decrease. The uneven part cannot be generated during the actual production and processing operation of the material. The defects on the surface were polished to remove the error of the reduced strength caused by the uneven part, and the heat treatment experiment was conducted to find the actual strength increase effect. .

Strength (MPa) Comparative example: silicon carbide original strength 310 ± 61 Comparative example: strength after introducing cracks 10 ± 2 Example: Strength after healing a crack 324 ± 34

As shown in Table 1, the original strength of silicon carbide measured without cracking was about 310 MPa, but the strength measured after cracking was 10 MPa, and the cracks were thermally treated at 900-1300 ° C. to form amorphous silica. The strength of the filled and cured specimens was approximately 324 MPa, indicating full recovery to original strength.

As a result of observing the broken specimen, it can be seen that the fracture did not occur through the cured crack but through the silicon carbide as a raw material. This means that the repaired crack is stronger than the raw material.

On the other hand, when the crack was healed by cristobalite by heat treatment at a temperature higher than 1300 ° C, the strength was about 260 MPa, which was restored to about 83% of the original strength of 310 MPa, which was not completely recovered. Happened along the cracks. This means that the strength of the cracks healed and filled with cristobalite is less than that of the underlying silicon carbide.

Example 4

Experimental proof of the reason for strength recovery following crack healing

The effect of residual stress inside the repaired crack in determining its strength was experimentally confirmed as follows.

From the bottom of the specimen to the dashed line, i.e. the outer edge of the crack was ground and removed, the strength was measured.

As a result, it could be confirmed that when the stress component of the opposite component is removed, the stress existing in and around the crack also disappears. In other words, it is possible to measure the strength of the crack, that is, the strength of the silica itself, in a state where no stress remains.

In the case of specimens that were cured with amorphous silica by heat treatment at 900-1300 ℃, the strength after grinding and removing the crack tip was only about 60 MPa, and the fracture of the specimen always occurred through the cured crack. . This means that the strength of amorphous silica itself is only about 60 MPa, and the strength of the cracks healed in specimens heat-treated at temperatures of 900-1300 ° C. is greater than the original strength of silicon carbide. It can be seen that.

On the other hand, in the case of specimens that were cured by cristobalite by heat treatment at a temperature higher than 1300 ° C., the strength after grinding off the outer edge of the crack was about 320 MPa, which was the same as that of silicon carbide, and the damaged specimen was observed. As a result, the fracture of the specimen did not occur along the crack but through the silicon carbide.

This means that the strength of cristobalite itself is greater than that of silicon carbide, and that the strength of the cracks healed in specimens heat-treated at temperatures above 1300 ° C. does not fully recover to the original strength of silicon carbide. It can be seen that the residual stress.

Example 5

Strength improvement by surface modification

When the silicon carbide is heat-treated at a temperature of 900-1300 ° C., the cracks are filled with amorphous silica and the compressive stress remains in and around the cracks to improve the mechanical properties of the silicon carbide.

10 is a conceptual diagram of silicon carbide surface modification for explaining this.

The compressive stress distribution that would be cured by filling a crack with amorphous silica becomes as shown in the left figure of FIG. 10, that is, the compressive stress is distributed in and around the crack. If numerous cracks are made on the surface and these cracks are filled with amorphous silica to heal, compressive stresses occur at all parts of the surface of the material, as shown in the figure on the right.

By this compressive stress, mechanical properties such as strength, thermal shock resistance, and wear resistance can be improved, and a surface modification method for improving the characteristics of silicon carbide is directed to this.

   In order to create numerous cracks on the surface, a method of grinding silicon carbide with a diamond wheel may be used. In this example, the diamond wheel 200 was used to grind perpendicularly to the longitudinal direction of the specimen. The cracks were then cured by heat treatment at 1200 ° C. for 50 hours in air, and then treated with amorphous silica, and the strengths of the heat treated specimens were measured and compared with those of the unheated specimens.

Table 2 below shows the intensity data.

Strength (MPa) Comparative example: silicon carbide original strength 310 ± 61 Comparative example: strength after grinding with wheel 200 167 ± 4 Example: Strength after Surface Modification 473 ± 25

The strength of the raw material measured according to the ISO 14704 standard was 310 MPa, and the strength when grinding with the diamond wheel 200 was about 167 MPa, which was significantly smaller than the strength of the raw material 310 MPa. This means that there are many cracks when grinding with the diamond wheel 200.

When the specimens were heat-treated, the strength was about 473 MPa, which was significantly higher than that of the raw material, indicating that the strength was improved when numerous cracks were made and then the cracks were filled with a material with a low coefficient of thermal expansion.

Example 6

Cost reduction by surface modification

Another usefulness of surface modification is that it saves processing costs and processing time, which is a large part of the production cost of ceramics.

 FIG. 11 is a result of measuring the bending strength of the processed material by processing the specimen with various diamond wheels (○ in FIG. 11). The rougher (smaller numbers) the diamond wheels are, the lower the strength is, and the actual machining of ceramic parts is slower with finer particles (larger numbers), which consumes a lot of processing time and time.

However, the surface strength of the material processed by the various wheels and then measuring the bending strength (● of Figure b), it can be seen that the strength is not only recovered, but rather improved. In other words, even if the machined parts quickly processed by the coarse wheel, the physical properties are improved when the surface is subjected to surface modification, which can be confirmed that it has the advantage of reducing the processing cost and time.

Example 7

Improvement of heat shock by surface modification

In order to show that the thermal shock resistance is improved by the surface modification method, a quenching experiment was performed.

In the same manner as in Example 5, a number of cracks were formed on the surface by grinding with a diamond wheel 200, and then the cracks were filled with amorphous silica to heal.

Then, the specimens were heated to 430 ℃ to 800 ℃ and then quenched with water at room temperature to observe the occurrence of cracks under a microscope.

Table 3 shows whether cracks occur with temperature.

       Temperature (℃) Specimen 430 440 450 460 470 480 500 590 600 650 700 750 800 Comparative Example: Unmodified Silicon Carbide ○ ○ × ○ ××× × × × ××× - - - - - - Example: Surface Modified Silicon Carbide - - - - - - - ○ ○ ○○○ ○○○ ○ × ×××

X: crack occurred

○: no cracking

As a result, in the case of silicon carbide without surface modification, cracking occurred without exception when quenched at a temperature above 450 ° C., but in the case of surface modified silicon carbide, when it was quenched at temperature below 700 ° C., no crack occurred. Cracking occurred only after quenching at the above temperature. Therefore, this result shows that the thermal shock resistance is remarkably improved by surface modification.

According to the silicon carbide surface modification method according to the present invention, silicon carbide has the effect of improving the strength, heat shock resistance, and abrasion resistance and healing cracks generated during processing.

In addition, the surface modification method not only improves the physical properties of silicon carbide by a simple method, but also provides an advantageous processing process in terms of cost, and therefore, parts for heat-resistant parts, wear-resistant parts, and semiconductor manufacturing equipment that use silicon carbide. A great effect is expected in the industry.

1 shows the stress when the silicon carbide is heat-treated at a temperature of 1300 ° C. or less, so that the crack is filled with amorphous silica.

Figure 2 shows the stress when the silicon carbide is heat-treated at a temperature of 1300 ℃ or more cracks filled with cristobalite.

3 shows through cracks introduced into silicon carbide specimens.

4 shows cracks before heat treatment and silicon carbide cracks after heat treatment.

5 is an elemental analysis result (EDX analysis) of a material filled with cracks of silicon carbide.

6 is a transmission electron micrograph when the specimen of silicon carbide heat-treated at 1300 ℃.

Figure 7 is a transmission electron microscope photograph taken around the crack when the specimen of silicon carbide heat-treated at 1400 ℃

8 is a graph showing the strength data according to the heat treatment temperature of the silicon carbide specimen.

9 is a photograph showing that destruction did not occur along the cured crack, but along the silicon carbide as a base material.

10 is a conceptual diagram of reinforcement through silicon carbide surface modification.

11 is a graph showing the bending strength (○) and the bending strength (●) after surface modification thereof according to the particle size of the abrasive wheel processing the surface of the silicon carbide specimen.

Claims (5)

Method for surface modification of silicon carbide comprising the step of heat-treating silicon carbide in the air at a temperature of 900-1300 ℃ several seconds to several tens of hours. The method of claim 1, wherein the heat treatment temperature is 1050-1300 ° C. The method for surface modification of silicon carbide according to claim 1 or 2, comprising the step of grinding the silicon carbide to form cracks on the surface as a step before the heat treatment process. 4. The method of claim 3, further comprising: grinding using a diamond wheel having a grit number of 200 or more; Method for surface modification of silicon carbide comprising the step of heat-treating silicon carbide for 50 hours at 1200 ℃ in air. Silicon carbide surface-modified by one of the methods of claims 1-4.