JP4369054B2 - Separation, regeneration and reuse of spent glycol slurry - Google Patents

Description

【００３２】
どのような特定の理論にも縛られるものではないが、この場合は炭化珪素である「再生」砥粒の粒子寸法の分布が、より平滑な、より均質な表面を与えるのに適している故に、本発明の方法が、新しいスラリーと比較して、シリコンインゴットのスライス用の向上したスラリーの製造を可能にすると一般に考えられる。特に、再生砥粒は、約５０ミクロン以上の砥粒が本質的に存在しない粒子寸法分布を有し、これに対して、新しいスラリーの砥粒の約２％以上が約５０ミクロン以上である（６０、７０、８０ミクロンまたはそれ以上の粒子寸法を有する砥粒もある）。
【００３３】
前記に鑑みて、本発明の目的が達成され、他の有利な結果が得られることが理解される。前記説明における全ての内容は、例示的なものであり、限定することを意図するものではない。
【図面の簡単な説明】
【図１】 シリコンインゴットをスライスするのに使用されるスラリーに再使用するのに好適な成分を単離する、本発明によって使用される工程（そのいくつかは任意工程である）の例を示すフローチャートである。[0001]
(Technical field)
The present invention generally relates to a method for reclaiming a polishing slurry used in the manufacture of silicon wafers. In particular, the present invention provides a spent slurry (exhausted slurry) used to slice a wafer from a single crystal or polycrystalline silicon ingot so that the desired abrasive and lubricating or cooling liquid therein can be reused. slurry).
[0002]
(Background technology)
A silicon wafer is obtained from a monocrystalline or polycrystalline silicon ingot by first slicing the ingot in a direction perpendicular to its axis. The slicing operation is generally performed by a wire saw. In this case, a silicon ingot is brought into contact with a reciprocating wire, and an abrasive-containing slurry is supplied to a contact area between the ingot and the wire. Conventional wire saw slurries typically include a lubricating or cooling liquid such as mineral oil or some water soluble liquid (eg, polyethylene glycol (PEG)) and abrasive grains such as silicon carbide.
[0003]
During the slicing operation, silicon particles are formed and mixed with the slurry. As the concentration of silicon particles in the slurry increases, the efficiency of the slicing operation decreases. As a result, the slurry becomes ineffective or “exhausted” and must be discarded. Generally, spent slurry is discarded by incineration or processed in a wastewater treatment facility. However, incineration of this slurry generates carbon dioxide, while transport of this slurry to a wastewater facility generally forms sludge that must be discarded in landfills. Therefore, both disposal methods are environmentally undesirable. It is therefore preferable to eliminate or significantly reduce this waste generated.
[0004]
In addition to the negative impact on the environment and the cost of disposal of used slurry, the disposal of the slurry in general also increases the cost of manufacturing silicon wafers. In particular, the rate at which the slicing operation consumes abrasive grains in the slurry (ie, wears to a size that is too small to effectively slice) is generally much slower than the rate at which the slurry is contaminated with silicon particles. Furthermore, the general lubrication or coolant pot life is governed almost entirely by the accumulation of silicon particles, i.e., if the concentration of silicon particles in the slurry does not increase, the lubrication or coolant will be considerably longer. It can be used for hours. As a result, the slurry is generally discarded when the concentration of silicon particles in the slurry becomes too high, even if most of the abrasive grains and lubrication or cooling liquid are still usable.
[0005]
In view of the foregoing, there remains a need for a method that separates silicon particles from a slurry, thereby allowing reuse of abrasive grains and lubrication or coolant. Such a method reduces the manufacturing costs required for slicing silicon ingots. In addition, such methods also reduce the amount of waste and / or waste by-products that are discharged into the environment.
[0006]
(Disclosure of the Invention)
Objects and features of the present invention provide a method for extending the pot life of slurry components used to slice silicon ingots; such components are regenerated by separating them from spent slurry. Providing a method; efficiently regenerating the lubricant or cooling liquid by separating it from the solids in the slurry; and providing the abrasive grains with silicon particles, used abrasive grains in the slurry providing such a method of regenerating by separating from grains) and other particle contaminants; such a method of reintroducing the regenerated lubricating or cooling liquid and regenerated abrasive grains into the silicon wafer manufacturing process Providing such a method that reduces the amount of waste that must be disposed of; and so reducing the cost of manufacturing silicon It is to provide a method.
[0007]
Briefly, therefore, the present invention treats a spent slurry comprising an abrasive component and a lubricant component used to slice a silicon wafer from a silicon ingot to recover at least one component. Relates to a method for re-use in the production of new slurries. The method comprises heating the spent slurry to reduce the viscosity and then separating the heated slurry into a liquid portion and a solid portion. The liquid portion containing the lubricating liquid component is collected and reused in the production of a new slurry without further separation.
[0008]
The present invention treats a used slurry comprising an abrasive component and a lubricant component used to slice a silicon wafer from a silicon ingot to recover at least one component and produce a new slurry. Also relates to how to reuse. The method comprises heating the spent slurry to reduce viscosity, and then separating the heated slurry into a liquid portion and a solid portion, the solid portion comprising silicon particles and abrasive components, The abrasive component further includes a spent abrasive component portion and an unspent abrasive component portion. The solid component is mixed with water to produce a solid / liquid mixture, and then the mixture is separated into a waste portion and a circulation portion, the waste portion comprising silicon particles and a consumable abrasive component portion, The circulation portion includes a non-consumable abrasive component portion. The non-consumable abrasive component portion is then separated from the circulating portion for reuse in the production of a new slurry.
[0009]
Other objects and features of the invention will be apparent in part and will be set forth in part below.
[0010]
Recycle the consumable abrasive slurry used to slice the silicon ingot from which the silicon wafer is derived in order to reduce the amount of waste generated by the general silicon wafer manufacturing process and to reduce the cost of manufacturing the silicon wafer. Or circulating. In particular, it is preferred that the slurry components that are still suitable for slicing the ingot (ie, cooling or lubricating liquid and non-consumable abrasive grains) are isolated from the remainder of the slurry and used in the production of a new slurry.
[0011]
It should be noted that the following phrases or terms used herein have a specific meaning: “used slurry” is a consequence of an unacceptably high viscosity or concentration of silicon particles. Means a slurry that is essentially unsuitable for slicing a silicon wafer from a silicon ingot; “consumable abrasive” refers to slicing a silicon wafer from a silicon ingot as a result of wear by the slicing process Means non-consumable abrasive grains, which are not generally suitable for use in the past; “non-consumable abrasive grains” means abrasive grains in the used slurry that are still suitable for slicing silicon from silicon ingots; "Viscosity" is a slurry that is evaluated or measured while the slurry is flowing by methods common in the art The viscosity means a kinetic viscosity of the slurry.
[0012]
As noted above, the viscosity of the slice slurry increases during use and generally reaches a viscosity of about 700 cps (centipoise) or higher at 20 ° C. due to at least a portion of the accumulation of particulate matter such as silicon particles in the slurry. . The high viscosity of the spent slurry hinders the separation of particulate contaminants from the underlying lubricating or cooling liquid and abrasives not used by the slicing process, and thus the separation, recovery, and recovery of these slurry components. Make reuse difficult.
[0013]
The method of the present invention solves these problems, from reusable slurry components (ie, lubrication or coolant and non-consumable abrasive) to waste solids (ie, silicon particles and consumable abrasive). Provide a simple and efficient method of separation. With reference to FIG. 1, the method of the present invention provides a spent slurry to a level that allows for the separation of essentially all solids (ie, waste solids and non-consumable abrasive grains) from the lubricating or cooling liquid. The viscosity of is first reduced. The viscosity of the spent slurry is reduced by heating the slurry, and the exact temperature at which the slurry is heated is related, at least in part, to the composition of the slurry. For example, a lubricating or cooling liquid based on polyethylene glycol is commonly used as the “suspension medium” for the slurry. In such cases, the consumable “glycol” slurry is generally heated to a temperature of at least about 50 ° C., more preferably at least about 75 ° C., and even more preferably at least about 100 ° C. Most preferably, the slurry is heated to a temperature just below the boiling point or at which decomposition of the glycol-based liquid begins. After reaching the desired temperature, the slurry can be further processed, but generally the temperature is maintained for a period of about 10 minutes, 20 minutes, 30 minutes or more. Furthermore, in order to assist the heat transfer, the heating process can be accelerated by arbitrarily stirring.
[0014]
It should be noted that the temperature at which the slurry is heated does not depart from the method of the present invention and may be other than the above. For example, generally speaking, the slurry is heated to a temperature just below the boiling point or decomposition temperature of a given lubrication or coolant that allows the most efficient and essentially complete separation of the liquid from the solids. Most preferably. However, devices that contain, transfer, and separate from solids (or vice versa) may not be able to withstand such temperatures, in which case the temperature may be reduced or another device may be used. Need to use.
[0015]
It should also be noted that in a preferred embodiment, the slurry is heated directly, ie, the slurry is not diluted with water or other solvents prior to heating. The liquid underlying when separated from the solids, the liquid is further due to separation or is suitable for re-use in ingot slicing slurry without processing, such a method is preferable. However, the viscosity of the slurry can be reduced, for example, by adding water or other suitable solvent (eg, methanol for glycol-based slurries). When the slurry is diluted in this manner to reduce the viscosity, the diluted slurry can be heated directly or by first heating the solvent to be added. However, if a solvent is used, generally the resulting lubricating or cooling liquid must be concentrated (eg, by distillation) before being reused in the ingot slice slurry.
[0016]
When the viscosity of the used slurry is reduced to about 200 cps or less (viscosity at about 50 ° C. to about 80 ° C. as measured by dynamic viscosity measurement methods common in the art), the underlying lubrication or Previous experience has shown that solids can be separated from the coolant. It is preferred to reduce the viscosity of the used slurry to about 50 to about 200 cps. More preferably, the viscosity of the used slurry is reduced to about 55 to about 150 cps. More preferably, the viscosity of the used slurry is reduced to about 60 to about 100 cps, and more preferably, the viscosity is reduced to about 70 to about 80 cps. Most preferably, the viscosity is reduced to a level that allows for the most efficient and essentially complete separation of the liquid from the solids.
[0017]
After the slurry viscosity is reduced, the solids in the slurry are separated from the lubricating or cooling liquid. Any method of separating solids of very small diameter (ie about 5 microns, 3 microns, 1 micron or less) can be used provided that the slurry can withstand the heated temperature. To do. However, it is preferred that the method used is a method that results in a substantially dry solid, i.e. a method that does not require further separation to remove essentially all of the liquid. Filtration of a hot slurry, more preferably vacuum filtration, is an example of a method used to separate solids from the underlying liquid.
[0018]
Filtration generally involves passing the hot slurry through liquid at least one sieve, such as a polypropylene sieve having sufficient pores or mesh size to remove substantially all solids from the liquid. Separating into components and solid components. For example, sieves having pores or mesh sizes less than about 5 microns, preferably less than about 3 microns, more preferably less than about 1 micron are commonly used for vacuum filtration.
[0019]
In accordance with the method of the present invention, the filtrate or liquid portion obtained by separation is directly circulated through the silicon wafer manufacturing process without additional separation or processing steps to lubricate or cool the silicon ingot slice slurry. Can be used as However, additional steps can be used when the filtrate viscosity is not in the preferred range of about 80 cps to about 100 cps at about 25 ° C. For example, if necessary, an optional “polishing” or “clearing” step can be performed in which the liquid portion can be subjected to an additional separation step to remove very small or fine particles. Further, when the solvent is added to reduce the viscosity of the used slurry as described above, it is necessary to concentrate the liquid component, for example, by distillation, before reuse, in order to obtain a lubricating or cooling liquid.
[0020]
The solid portion obtained by separation is further processed to remove non-consumable abrasive grains (ie, slicing process) from silicon particles and consumable abrasive grains (ie, abrasive grains that have been worn to a diameter that is too small for further use by the slicing process). Abrasive grains having a diameter not significantly reduced by In order to aid in the isolation of the abrasive suitable for reuse, the solid portion from the initial separation is diluted in a liquid such as water that allows the formation of two solid suspensions. In particular, the solid portion is mixed with a liquid such as water, for example, one suspension containing non-consumable abrasive grains of silicon carbide, and silicon particles and consumable abrasive grains and other particulate contaminants that may be present. A second suspension containing is formed.
[0021]
Generally, water is added to the solid portion until the solid content is about 10 to about 100 g / L (grams / liter), preferably about 15 to about 50 g / L, and most preferably about 20 to about 30 g / L. In addition, the solid / liquid mixture is agitated by means common in the art (eg, rotating blade mixer, ultrasonic, circulating, or gas bubbling / jetting) to produce undesired solids (ie, silicon particles and Separation of the desired solids (ie abrasive grains) from the consumable abrasive grains) and the formation of each of the two types of suspensions can be assisted.
[0022]
This solid / liquid mixture is then divided into two suspensions, a first suspension containing relatively heavy or large particles and a second suspension containing relatively light or small particles. Separate into liquid. Common means in the art that can separate particles based on weight or size, such as cyclone separators, sedimentation centrifuges, filtration centrifuges, or filters (filters with pore sizes suitable for the required selection). In combination with a cloth). However, it is preferred to perform this separation with a cyclone separator that is preferred because of its relatively low cost and durability (eg, model number RWK810 by AKW, Germany).
[0023]
Generally speaking, in a cyclone separator, and discharging a liquid containing lighter solid particles from the predetermined weight from the upper exit, while the liquid containing the same or heavier particles with a predetermined weight from the lower exit Discharge . In the present invention, the predetermined weight corresponds to a particle size that allows reusable abrasive grains to be separated from silicon particles and consumable abrasive grains that have a much smaller diameter compared to the abrasive grains. Thus, after separating the solid / liquid mixture, two types of suspension remain. The first suspension contains abrasive grains suitable for reuse in the silicon ingot slice slurry, while the second suspension contains silicon particles and consumable abrasive grains.
[0024]
The first suspension is subjected to the next treatment, and the liquid is removed to obtain abrasive grains that are reused in the wafer manufacturing process. The abrasive grains can be isolated from this first suspension by means common in the art such as filtration or centrifugation. This further concentration is preferred because, for example, if the abrasive grains must be dried, the removal of excess liquid reduces the drying time. Drying can be done by means common in the art, for example by placing the filtered solid in a vacuum oven. However, since the silicon carbide abrasive grains tend to form a relatively large mass of solidified material, it is preferable to move the collected abrasive grains periodically during the drying process.
[0025]
When heating and drying the abrasive grains, it is preferable to use as high a temperature as possible (ie, the temperature at which the solid is dried as fast as possible) so that the reaction between the residual silicon particles and oxygen does not occur to form silicon oxide. It should be noted. Accordingly, it is preferable to dry the abrasive grains at a temperature of preferably about 75 ° C to about 200 ° C, particularly about 100 ° C to about 150 ° C. The drying time can vary depending on, for example, the liquid to be removed and the drying method, but generally continues to dry until only a trace or less liquid remains. For example, when water is used to form a solid / liquid mixture, the water content is generally less than about 5000 ppm (parts per million) as measured by means common in the art (eg, Karl Fischer), The abrasive solid is dried until it is preferably less than about 1000 ppm, and most preferably less than about 500 ppm.
[0026]
Low water content is preferred because the presence of water acts to reduce the viscosity of the resulting slurry (in which the recovered abrasive is used). Water also acts to inhibit the slurry's ability to maintain solids in suspension. The presence of water in the slurry further causes abrasive grains such as silicon carbide to stick together, resulting in the formation of large abrasive grains that can damage the surface of the wafer during the slicing process.
[0027]
When separating the solid / liquid mixture into two types of suspension, some silicon particles may remain in the first suspension, i.e., a small amount of silicon particles are present with the circulating abrasive grains. It should also be noted that there are. Without being bound to any particular theory, the presence of silicon particles depends on the type of separation means used (eg when cyclone separation is used), This is considered to be due to at least the same weight as the predetermined separation weight. Alternatively, it is considered that some silicon particles were attached to the surface of the large abrasive grains. However, the amount of silicon particles in an abrasive such as silicon carbide is generally less than about 2% by weight , preferably less than about 1% by weight , and most preferably less than about 0.5% by weight .
[0028]
The second suspension (ie, the suspension containing silicon particles and consumable abrasive grains) is discarded. However, it is preferred to concentrate the suspension, collect a liquid such as water, and reuse it to separate other solid / liquid mixtures to reduce the amount of waste generated. The suspended solids can optionally be collected and dried.
[0029]
The method of the present invention isolates the components of the slurry used to slice the silicon wafer from the silicon ingot (ie, abrasive grains and lubricating or cooling fluid) so that they can be used to make a new slurry. Give a means to do. In other words, the method of the present invention allows the regeneration of the slurry used for slicing silicon ingots. Thus, the present invention is advantageous because it limits the amount of waste that would otherwise be generated, thereby limiting the total cost of manufacturing silicon wafers. Such benefits are obtained because the recovered lubricant and non-consumable abrasive are reused and the liquid (eg, water) used to separate the solids is circulated and used repeatedly. Thus, basically only consumable abrasive and silicon particles are discarded if, of course, these other uses are not found.
[0030]
Furthermore, the process of the present invention yields components that can be used to produce a slurry that produces the same or better results than a slurry made from fresh components. Referring to Table I below, the results of warp measurements for silicon carbide and polyethylene glycol “regenerated” slurries and new slurries of the same composition are about the same, while total thickness variation (TTV) and It should be noted that the surface roughness measurement results show that the “regenerated” slurry is better (microns recorded for the same number of wafer slices using the same process parameters for each slurry ( Average results in μm)).
[0031]
[Table 1]

[0032]
Without being bound to any particular theory, in this case the particle size distribution of the “regenerated” abrasive grain, which is silicon carbide, is suitable to give a smoother, more homogeneous surface It is generally believed that the method of the present invention enables the production of improved slurries for slicing silicon ingots compared to fresh slurries. In particular, reclaimed abrasive grains have a particle size distribution that is essentially free of abrasive grains of about 50 microns or greater, whereas about 2% or more of the new slurry abrasive grains are about 50 microns or greater ( Some abrasives have a particle size of 60, 70, 80 microns or more).
[0033]
In view of the above, it will be seen that the objects of the invention are achieved and other advantageous results are obtained. All content in the foregoing description is exemplary and not intended to be limiting.
[Brief description of the drawings]
FIG. 1 shows an example of the steps used by the present invention, some of which are optional steps, to isolate components suitable for reuse in a slurry used to slice a silicon ingot. It is a flowchart.

Claims (20)

Treat the spent slurry comprising the abrasive and lubricant components used to slice the silicon wafer from the silicon ingot so that at least one component can be recovered and reused in the production of a new slurry. A method comprising the steps of:
Heating the used slurry to reduce the viscosity;
The heated slurry is separated into a liquid portion and a solid portion, the liquid portion includes a lubricating liquid component; and the separated liquid portion is collected and reused in the production of a new slurry without further separation. sell;
A method comprising that.   The method of claim 1, wherein the spent slurry is heated to reduce the viscosity from about 55 cps to about 150 cps.   The method according to claim 1, wherein the lubricating liquid component is polyethylene glycol.   The method of claim 1, wherein the heated slurry is separated into a liquid portion and a solid portion by filtration.   Adding water to the solid portion to form a solid / liquid mixture, the solid portion comprising silicon particles and an abrasive component, the abrasive component further comprising a consumable abrasive component portion and a non-consumable abrasive component portion. Item 2. The method according to Item 1.   6. The method of claim 5, wherein water is added to the solid portion to form a solid / liquid mixture having a total solids content of about 20 to about 30 g / L.   6. The method of claim 5, wherein the solid / liquid mixture is separated into waste and circulation, the waste comprising the silicon particles and the consumable abrasive component portion, and the circulation portion comprising the non-consumable abrasive component portion. .   8. The method of claim 7, wherein a cyclone separator is used to separate the solid / liquid mixture.   8. The method of claim 7, wherein water is removed from the circulation to collect the non-consumable abrasive component portion, and the non-consumable abrasive component portion can be reused to produce a new slurry. The method of claim 9, wherein the non-consumable abrasive component portion has a silicon particle content of less than about 2% by weight . Treat the spent slurry comprising the abrasive and lubricant components used to slice the silicon wafer from the silicon ingot so that at least one component can be recovered and reused in the production of a new slurry. A method comprising the steps of:
Heating the used slurry to reduce the viscosity;
Separating the heated slurry into a liquid portion and a solid portion, the solid portion comprising silicon particles and an abrasive component, the abrasive component further comprising a consumable abrasive component portion and a non-consumable abrasive component portion;
Mixing the solid components with water to form a solid / liquid mixture;
The solid / liquid mixture is separated into waste portion and the circulating portion, said waste portion comprises the silicon particles and the consumable abrasive component parts, the circulating unit content comprises non-consumable abrasive component parts; and The non-consumable abrasive component portion is isolated from the circulation portion and reused to produce a new slurry;
A method comprising that.   The method of claim 11, wherein the spent slurry is heated to reduce the viscosity of the slurry from about 55 cps to about 150 cps.   The method according to claim 11, wherein the lubricating liquid component is polyethylene glycol.   The method of claim 11, wherein the solid / liquid mixture has a solids content of from about 20 to about 30 g / L.   The method of claim 11, wherein the solid / liquid mixture is separated using a cyclone separator.   The method of claim 11, wherein the non-consumable abrasive component portion is isolated from the circulating portion by separating the abrasive component portion from the water in the circulating portion.   The method of claim 16, wherein after separation, the non-consumable abrasive component portion is dried to have a residual moisture of less than about 1000 ppm. 18. The method of claim 17, wherein the non-consumable abrasive component portion contains less than about 2% by weight silicon particles.   17. The method of claim 16, wherein after separation, the non-consumable abrasive component portion is dried to have a residual moisture of less than about 500 ppm. 20. The method of claim 19, wherein the non-consumable abrasive component portion contains less than about 2% by weight silicon particles.

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