JP2002255532A - Method for producing silicon carbide and method for disposing waste silicon sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing SiC by which high purity SiC can be obtained from waste silicon sludge and which enables effective utilization of waste silicon sludge, and to provide a method for disposing waste silicon sludge. SOLUTION: Carbon black powder in an amount of 1.5 mol is added to 1 mol of waste silicon sludge in terms of slid part, pressure formed and externally heated by an electric furnace at 950 deg.C for 2 hours in the atmosphere. From the XRD pattern of the sample, it is observed that peaks of Si and C are large before heating while they both decrease and a peak of SiC increase after heating, which proves that SiC can be produced from waste silicon sludge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silicon carbide (hereinafter referred to as "silicon carbide").
More specifically, the present invention relates to a method for producing silicon carbide (hereinafter referred to as “SiC”) and a method for treating waste silicon sludge, and more specifically, to obtain high-purity and high-quality SiC from waste silicon sludge that has been conventionally disposed of by a special method, The present invention relates to a method for producing SiC and a method for treating waste silicon sludge that enable effective use of waste silicon sludge treated as waste.

[0002]

2. Description of the Related Art In recent years, with the development of the information communication and semiconductor industries, the demand for silicon single crystal wafers is increasing year by year. Generally, a silicon single crystal wafer is cut by a wire saw while supplying a mixture of cutting oil and an abrasive (generally, hard free abrasive grains such as SiC) to a silicon single crystal ingot, and then polished by a polishing machine. It is manufactured by In this process, silicon scrap is generally generated in an amount of about 20 to 30% of the silicon single crystal ingot. Then, abrasives such as silicon dust and SiC generated during the production of the silicon single crystal wafer are usually washed away together with the cutting oil and removed from the silicon single crystal wafer. As a result, waste silicon sludge in which silicon chips and abrasives such as SiC are dispersed in used cutting oil is generated in the process of manufacturing a silicon single crystal wafer.

[0003] Conventionally, the waste silicon sludge has been treated as industrial waste without any particular use. However, since such waste silicon sludge contains silicon waste and cutting oil, it is simply incinerated. In addition, simply reclaiming may cause soil contamination by cutting oil. Therefore, at present, such waste silicon sludge is treated by a special treatment method of hardening it with cement and then performing landfill treatment.

[0004] However, the above-described processing method is special, and has a problem that the cost and labor are further increased. And
As a result of such processing costs rebounding to semiconductor manufacturing costs,
This also leads to a rise in the price of the semiconductor itself. In addition, with the demand for silicon single crystal wafers growing with the recent development of the information and communication and semiconductor industries, while the amount of waste silicon sludge has increased, the disposal of waste silicon sludge has been There are limits to disposal. Therefore, conventionally, effective use of waste silicon sludge has been desired in terms of environment and effective use of resources.
Since waste silicon sludge contains SiC and cutting oil components as impurities, it is difficult in terms of cost to treat and reuse the waste silicon sludge. The fact is that research has not progressed.

On the other hand, SiC has good strength, heat resistance, thermal shock resistance, and abrasion resistance even at a high temperature exceeding 1000 ° C., so that not only abrasives but also parts for semiconductor manufacturing equipment, It is widely used as components for information equipment and structural components such as vacuum equipment. As a general method for producing SiC, there is known an Acheson method in which silicon dioxide and carbon are heated to 2500 to 3000 K in an electric furnace in the presence of an inert gas to cause a reaction. However, this method requires a long-term reaction at a high temperature in a special environment under a reducing atmosphere with an inert gas such as nitrogen gas, so that the production cost is high and the obtained SiC
Also has a problem that it is difficult to obtain sufficient crystallinity due to its particle size distribution, purity, crystallinity and the like.

As another manufacturing method, for example, a high-purity SiO2 fine powder and a carbon fine powder are mixed and then mixed in an electric furnace.
There are a silicification method of carbon synthesized by heating to 00 to 2100K, and an evaporation-condensation method of synthesizing SiC by heating and evaporating a solid of Si or SiC to cool and condense the solid. However, even though these production methods can lower the reaction temperature as compared with the Acheson method, they still have high production costs and have the same problems as the Acheson method, such as the problem of impurities. On the other hand, CV in which silane gas (SiH ₄ , SiHCl ₃ etc.) and methane gas (acetylene gas etc.) react directly
Method D has the advantage that the obtained SiC has high purity, uniform particle size, and good crystallinity, but is suitable for mass production because silane gas as a raw material gas is expensive and dangerous. There is no problem. Therefore, conventionally, there has been a demand for the development of a method for producing high-purity SiC that is inexpensive, safe and uniform in particle size.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and obtains high-purity SiC from waste silicon sludge that has been conventionally disposed of and treats it as industrial waste. An object of the present invention is to provide a method for producing SiC and a method for treating waste silicon sludge that enable effective utilization of waste silicon sludge.

[0008]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventor has found that by adding carbon to waste silicon sludge and heating it, it is possible to produce high quality SiC from waste silicon sludge. The inventors have found that the present invention can be performed, and have completed the present invention.

The method for producing SiC according to the first aspect is characterized in that a mixture obtained by adding and mixing carbon to waste silicon sludge is heated.

The above-mentioned "waste silicon sludge" is not particularly limited as long as it contains Si, and in general, silicon waste is dispersed as Si component together with an abrasive such as SiC in used cutting oil. Is mentioned. In the present invention, the cutting oil constituting the “waste silicon sludge” functions as a binder when mixing Si components such as silicon chips and carbon, thereby further promoting the reaction between the two. The type of the above cutting oil is not limited as long as it is generally used in the production of silicon single crystal wafers, and generally includes oil-based cutting oil.

The amount of solids in the above-mentioned "waste silicon sludge" is not particularly limited, and can be varied as required. However, when the amount of solids is increased, the cutting oil in the waste silicon sludge is reduced. This is preferred because the pretreatment is simplified, the throughput is reduced, the transportation is facilitated, and the mixture obtained by adding and mixing carbon maintains its form, so that briquetting becomes possible. The solid content is usually 10% or more, preferably 20 to 90%, and more preferably 25 to 80%. Therefore, the Si of the present invention
In the method for producing C, the "waste silicon sludge" or the "mixture" obtained by adding carbon thereto may be appropriately subjected to a filtration treatment as needed. By performing such a filtration treatment, the solid content in the waste silicon sludge can be increased, which is preferable.

As the "carbon", any carbon source may be used as long as it is a powdered carbon source, but usually, carbon black is preferably used. In this case, it may be added before heating, or may be added while heating. In the method for producing SiC according to the present invention, the "carbon"
The addition amount of carbon is not particularly limited, but as shown in claim 2, the addition amount of the carbon is 0.7 to 3.0 mol, more preferably 1 to 2.0 mol per mol of Si in the waste silicon sludge. 0 mol, particularly preferably 1 to 1.5
It can be mol. By setting the amount of carbon added to the above range, the particle size of the obtained SiC can be increased, and high quality and high purity SiC having a uniform particle size can be obtained.
Is preferred because

In the method for producing SiC according to the present invention, the "mixture" obtained by adding and mixing the carbon to the waste silicon sludge is heated. Accordingly, SiC can be produced by directly reacting Si and carbon in the waste silicon sludge. Moreover, since this reaction is thermodynamically negative in Gibbs free energy, it is possible to spontaneously react even at a low temperature by providing only activation energy. Therefore, it can be performed at a lower temperature than before. In addition, if the oil-based cutting oil is used, it is burned by heating and solves the problem of impurities of SiC contained as impurities, so that waste silicon sludge can be efficiently disposed.

In the method for producing SiC of the present invention, the heating conditions and method are not particularly limited as long as the mixture can be heated. For example, the heating temperature in the method for producing SiC of the present invention is not particularly limited as long as SiC can be produced, but is usually 1100 to 2500K, preferably 1200C to 1800K, and more preferably 12C to 1800K.
50 to 1500K. By setting the heating temperature within the above range, it is possible to further select the heating material when external heating is performed, since metal can be used. In addition, a wide variety of heat insulating materials, furnace materials, and the like can be selected, and it can be synthesized at a lower temperature than conventional methods, so that SiC can be efficiently produced, which is preferable.

In the method for producing SiC according to the present invention, the heating may be performed in an inert gas atmosphere such as nitrogen as in the conventional method. Under an atmosphere in which heating is performed. Generally, Si is oxidized to silicon dioxide (SiO ₂ ) in an oxidizing atmosphere such as the air. And the conventional SiC
In the production method of the present invention, since it is necessary to carry out in an inert gas atmosphere, it has to be electrically heated by an electric furnace, resulting in a high production cost. Since it can be performed not only in an inert gas atmosphere but also in an oxidizing atmosphere, it is also possible to directly heat using a fossil fuel or the like under normal atmospheric pressure, and as a result, when using an electric furnace Si compared to
C is preferable because C can be efficiently obtained at low cost.

In the method for producing SiC of the present invention, the heating means is not particularly limited as long as it can be heated. As described above, the method for producing SiC of the present invention can be carried out at a lower temperature and in an oxidizing atmosphere than the conventional method for producing SiC, so that not only electric furnaces but also fossil fuels and combustion gases can be burned. Then, a heating furnace for heating can be used. For example, as shown in FIG.
An external heating furnace for heating the mixture by heating the reaction furnace from the outside of the reaction furnace, or an inside for heating by directing hot air generated by combustion into the reaction furnace as shown in FIG. A heating-type heating furnace can be used.

Further, since the cutting oil component contained in the waste silicon sludge has a binder-like property and the carbon to be added is electrically conductive, the waste silicon sludge and the carbon are combined with each other. Mixing to form a mixture (in this case, it can be formed into a predetermined shape such as a rod or plate using the properties of a binder), and then combustible materials (fossil fuel, combustible gas, etc.) While heating the mixture under an oxidizing atmosphere, the mixture is heated by direct current flow, or as described in claim 5, mixed with waste silicon sludge and carbon to form a mixture,
The mixture can be heated in an oxidizing atmosphere by burning the combustibles, and then the mixture can be heated by direct current flow (see FIGS. 1B and 2B). In this case, there is no particular limitation on the electrodes for energizing the sample as long as the electrodes can be energized. For example, materials having high temperature resistance such as graphite, tungsten, and TiN are preferable. The current may be direct current or alternating current. According to this method, heating is performed in an oxidizing atmosphere in a low temperature range up to about 1000 ° C., and thereafter, the temperature is further increased by electric resistance heating, so that the direct reaction between Si and carbon can be promoted. SiC is preferred because it can be efficiently obtained at low cost.

Generally, when producing a silicon single crystal wafer, since SiC is used as an abrasive, fine SiC is usually mixed in the waste silicon sludge in the present invention. And this fine SiC
When the grains grow as seed crystals, it is possible to efficiently obtain particulate SiC having a more uniform grain size. In this case, as described in claim 6, SiC can be added to the waste silicon sludge or the mixture. This allows
It is preferable because the grain growth of SiC can be promoted more reliably even at a low heating temperature, and the waste silicon sludge containing Si but not containing SiC can be effectively used. In this case, the particle size of the SiC to be added is not particularly limited. However, it is preferable that the particle size be fine, since the grain growth can be further promoted, and is usually 10 μm or less. Also, the amount of addition is not particularly limited, and is usually about 20% or less, preferably about 15% or less, more preferably about 10% or less based on the waste silicon sludge. Furthermore, there is no particular limitation on the method of addition, and it may be simply added to waste silicon sludge or the above mixture, or may be added to waste silicon sludge together with the above carbon.
Further, it may be added before heating, or may be added while heating.

As described above, the process for producing SiC using waste silicon sludge in the method for producing SiC of the present invention generally includes (1) waste silicon sludge stored in a storage unit such as a container. (2) mixing by a mixing means, (3) molding by a molding device, and (4) heating by a heating reaction device. And according to the method for producing SiC of the present invention,
Conventionally, high-quality SiC can be obtained from silicon waste contained in waste silicon sludge that has only been disposed of by a special method. In addition, cutting oil components, which are problematic during disposal, can also be removed by heating. Therefore, the method for producing SiC of the present invention can be effectively used as a method for treating waste silicon sludge, as described in claim 7. By this, waste silicon sludge, which was difficult to treat conventionally,
This is preferable because it can be processed easily and at low cost. In this case, when SiC is added to the waste silicon sludge or the mixture, the grain growth of the SiC proceeds more reliably even at a low heating temperature.
It is preferable because waste silicon sludge containing i but not containing SiC can be treated.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be specifically described with reference to examples. <Example 1> (1) Waste silicon sludge Waste silicon sludge used in Example 1 is generally generated by cutting a silicon single crystal ingot using an oil-based cutting oil and SiC as an abrasive. Derived from typical waste silicon sludge. The solid content in this waste silicon sludge is 55% by mass. Next, the waste silicon sludge was filtered to obtain waste silicon sludge having a solid content of 70% by mass, which was used as waste silicon sludge used in Example 1.

(2) Manufacture of SiC The waste silicon sludge of the above (1) has a solid content of 1 mol (4
(0 g / mol), 1.5 mol of carbon black powder (particle size: 5 μm) was added, and pressure molding was performed to prepare a rod-shaped sample. This sample was heated at 950 ° C. for 2 hours by external heating with an electric furnace in the atmosphere. Further, the above sample was subjected to 9
External heating was performed at 50 ° C. for 1 hour, and then heating was performed by electric resistance heating (voltage: 10 to 20 V) for 1 hour. FIG. 3 shows an XRD pattern of the sample after heating, and FIG. 4 (with electric resistance heating) shows an SEM photograph. Further, 1.5 mol of carbon black powder was added to 1 mol of Si in the waste silicon sludge of the above (1), and a sample was prepared in the same manner as described above. Then, it was heated at 1000 ° C. for 4 hours. FIG. 5 shows the XRD pattern of the sample after heating.

(3) Effect of Embodiment 1 From the XRD pattern of FIG. 3, the peak of SiC increases after heating. In particular, comparing the case of only external heating and the case of using both external heating and electric resistance heating, in the latter XRD pattern after heating, the peaks of Si and C almost disappeared, and the peak of SiC appeared strongly. From that
It turns out that SiC can be produced more efficiently by heating using both external heating and electric resistance heating in an oxidizing atmosphere. From the SEM photograph of FIG. 4, when the external heating and the electric resistance heating are used together,
This indicates that SiC having a large particle diameter can be obtained. Furthermore, FIG. 5 shows that when nitrogen atmosphere and air atmosphere are compared, under nitrogen atmosphere, peaks of Si and C are still large even after elapse of 4 hours.
Since this peak has already disappeared after 4 hours in the atmosphere, it can be seen that unlike the conventional method, SiC can be sufficiently produced even in the atmosphere.

<Example 2> (Effect of adding SiC as seed crystal) (1) Production of SiC Si1 in waste silicon sludge of (1) of Example 1 above
A sample was prepared in the same manner as in Example 1 except that 1 mol of carbon black powder was added to the mol, and SiC as a seed crystal was further added to 20%.
At the same time, a sample containing no seed crystal SiC was prepared.
Then, both of them were heated in an electric furnace at 1,000 ° C. for 2 hours in the atmosphere by external heating in the same manner as in Example 1 above. The XRD patterns of the sample after heating are shown in FIGS. 6A (without seed crystal) and (B) (with seed crystal).

(2) Effect of Embodiment 2 From the XRD pattern of FIG.
It can be seen that the peaks of Si and C decrease after heating and the peaks of SiC increase after heating. From these results, it is understood that SiC can be produced from waste silicon sludge by the method for producing SiC of the present invention. 6 (A) and 6 (B), when SiC as a seed crystal was not added (A), 2
The peak of SiC is not recognized only by heat treatment for a period of time, whereas when SiC as a seed crystal is added (B), the peak intensity of SiC is increased only by heat treatment for 2 hours, and the Si and C It can be seen that the peak has decreased. From these results, by adding SiC as a seed crystal to waste silicon sludge, silicon dust and C directly react with each other to form SiC even in a short time. Therefore, it is necessary to add SiC as a seed crystal to waste silicon sludge. As a result, it can be understood that SiC can be manufactured more efficiently.

Example 3 (Reaction Temperature and Molar Ratio of Si and Carbon) (1) Production of SiC The waste silicon sludge described in Example 1 was used as waste silicon sludge. A sample was prepared by adding carbon black powder so that 1.5 mol of carbon was added to 1 mol of Si in the waste silicon sludge, and mixing in the same manner as in Example 1 above. Then, in the same manner as in Example 1, by external heating in an electric furnace, 950
Heating was performed at 〜１０1050 ° C. for 4 hours. 950, 1000
The XRD pattern of the sample after heating at 1050 ° C. and FIG.
Shown in Further, a mixture in which the molar ratio of Si in the waste silicon sludge to the added carbon was 1: 0.7, and a mixture of 1: 1.
In the same manner as in Example 1 above, the mixture obtained in Example 5 was externally heated in an electric furnace, and was heated to 950 to 1 under the atmosphere.
Heating was performed at 050 ° C. for 2 hours and 8 hours. 950, 1
SiC obtained when heated at 000 and 1050 ° C.
Graphs of the crystal size of are shown in FIGS. 8 (A) and (B).
The crystal size was calculated from the half-width of the XRD peak by Scher.
It was determined using the rr equation.

(2) Effect of Example 3 FIG. 7 shows that the peak intensity of SiC is increased and the peak intensity of Si and carbon is decreased by increasing the reaction temperature. FIGS. 8A and 8B
By increasing the reaction temperature, the resulting SiC
Crystal size can be increased. In particular, in heating for a short time of 2 hours, the growth of the crystal size of SiC due to an increase in the reaction temperature (particularly 1000 ° C. to 1050 ° C.) is remarkable as compared with heating for 8 hours. It can be seen that SiC having a large crystal size can be obtained in a short time. On the other hand, FIG. 7 shows that the peak intensity of SiO ₂ tends to increase as the reaction temperature increases. That is, it is understood that when the temperature is too high, SiO ₂ tends to be generated as an impurity. Therefore, from these results, 950 to 1050
By heating the mixture of waste silicon sludge and carbon in the range of ℃, SiC can be produced by reacting Si and carbon in waste silicon sludge, and reducing the amount of by-product silicon dioxide. It can be seen that SiC having high purity, large particle size and excellent quality can be efficiently obtained.

8 (A) and 8 (B), when the molar ratio of Si to carbon in the waste silicon sludge is 1: 1.5, the molar ratio is 1: 1.5. It turns out that the crystal size of SiC obtained at the same heating time and heating temperature is large. That is, it is understood that SiC having a large crystal size can be efficiently obtained by increasing the amount of carbon. In particular, when the heating time is set to 8 hours, the crystal size of the obtained SiC is set to 1: 1.5 from the case where the molar ratio of Si to carbon in the waste silicon sludge is set to 1: 0.7. It can be seen that the effect when the amount of carbon is increased is more prominent by increasing the heating time.

Example 4 (Reaction Time) (1) Production of SiC The waste silicon sludge described in Example 1 was used as waste silicon sludge. Carbon black powder was added so that carbon became 0.7 mol with respect to 1 mol of Si in the waste silicon sludge, and a sample was prepared in the same manner as in Example 1 above. Then, in the same manner as in Example 1 above, by external heating in an electric furnace, at 1000 ° C. in air.
For 2 to 8 hours. The XRD patterns of the samples after 2, 4 and 8 hours have passed are shown in FIG.
FIG. 9B shows the relative peak intensity ratio to the starting SiC peak intensity in the RD pattern.

(2) Effect of Embodiment 4 FIGS. 9A and 9B show that the peak intensity of SiC is increased by increasing the heating time.
It turns out that the production amount of SiC increases. On the other hand, it can be seen that the longer the heating time, the higher the peak intensity of SiO ₂ tends to be. From these results, the heating time was 2 to 8
By heating the mixture of waste silicon sludge and carbon within the time range, Si and carbon in the waste silicon sludge can be reacted to produce SiC, and the amount of silicon dioxide as a by-product is reduced. It can be seen that high purity and high quality SiC can be efficiently obtained.

It should be noted that the present invention is not limited to the specific embodiments described above, but can be variously modified according to the purpose and application.

[0031]

According to the method for producing SiC of the present invention, high-purity SiC is obtained from waste silicon sludge that has been conventionally disposed of, and waste silicon sludge that has been treated as industrial waste is effectively used. can do.
Further, the method for producing SiC of the present invention comprises the steps of:
Since it can be performed at a lower temperature than the conventional method for producing SiC, high-quality SiC having a uniform particle diameter can be efficiently obtained at low cost as compared with the conventional method for producing SiC. Furthermore, according to the method for treating waste silicon sludge of the present invention, waste silicon sludge, which has conventionally been difficult to treat, can be treated simply and at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a reaction system of the present invention.

FIG. 2 is a schematic diagram of another reaction system of the present invention.

FIG. 3 is an XRD pattern of the sample of Example 1.

FIG. 4 is an SEM photograph of a sample of Example 1.

FIG. 5 shows the X of the sample when the atmosphere was changed in Example 1.
This is an RD pattern.

FIG. 6 is an XRD pattern of the sample of Example 2.

FIG. 7 is an XRD pattern of a sample when the heating temperature is changed in Example 3.

FIG. 8 is an XRD pattern of a sample when the molar ratio of carbon is changed in Example 3.

9 shows an XRD pattern (A) and X of the sample of Example 4. FIG.
It is a relative peak intensity ratio (B) to the peak intensity of the starting stage SiC in the RD pattern.

[Explanation of symbols]

1A, 1B, 1C, 1D; reactor 2, sample 3,
Sample holder, 4; electrode, 5; power supply, 6; heater.

Claims (8)

[Claims] 1. A method for producing silicon carbide, comprising heating a mixture obtained by adding and mixing carbon to waste silicon sludge. 2. 1 mol of silicon in said waste silicon sludge
2. The method for producing silicon carbide according to claim 1, wherein the amount of the carbon added is 0.7 to 3.0 mol based on 1. 3. The method according to claim 1, wherein the heating is performed in an oxidizing atmosphere.
Or the method for producing silicon carbide according to 2. 4. Mixing waste silicon sludge and carbon to form a mixture, and then heating the mixture under an oxidizing atmosphere by burning a combustible to heat the mixture by passing electricity through the mixture. A method for producing silicon carbide. 5. A method in which waste silicon sludge and carbon are mixed to form a mixture, and then the mixture is heated in an oxidizing atmosphere by burning a combustible material, and thereafter, the mixture is heated by direct current flow. Method for producing silicon carbide. 6. The method for producing silicon carbide according to claim 1, wherein silicon carbide is added to said waste silicon sludge or said mixture. 7. A method for treating waste silicon sludge, comprising heating a mixture obtained by adding and mixing carbon to waste silicon sludge. 8. The method for treating waste silicon sludge according to claim 7, wherein silicon carbide is added to said waste silicon sludge or said mixture.