JP5888203B2 - Manufacturing method of slurry for wire saw - Google Patents

Description

  The present invention relates to a slurry for a wire saw for slicing a workpiece using loose abrasive grains, and particularly to a slurry used for a wire saw for cutting a semiconductor material.

In recent years, wire saws are used for cutting workpieces such as semiconductor materials, magnetic materials, and ceramics in the manufacturing process of semiconductor wafers and solar cells for solar cells.
A wire saw is a device that moves a wire in a reciprocating direction and presses the workpiece against the wire while supplying slurry mixed with free abrasive grains such as silicon carbide to cut the workpiece. There are cases where oil-based coolant and water-soluble coolant are used for this slurry, but in recent years, water-soluble coolant has become the mainstream due to environmental load problems such as recycling after use and wastewater treatment. It has become.

  It is known that when a workpiece is cut with a wire saw in this way, the width obtained by adding approximately 2 to 3 times the wire diameter and the size of the loose abrasive grains becomes a raw material loss as kerf. ing. Therefore, in order to reduce kerf loss, thinning the wire diameter and reducing the particle diameter of loose abrasive grains are performed (for example, see Patent Document 1).

In general, the size of loose abrasive grains is often expressed in terms of grain size, and the classification is defined in, for example, R6002 of the JIS standard.
Conventionally, in the cutting of a semiconductor silicon wafer, for example, a piano wire having a diameter of 0.16 mm and a silicon carbide abrasive having a cumulative diameter of 50% and a particle diameter (hereinafter sometimes abbreviated as an abrasive particle diameter) of 11.5 μm. A slurry in which grains (abrasive grain number # 1000) were mixed was used. However, in recent years, as described above, in order to reduce kerf loss, wire thinning and loose abrasive grain refinement have been promoted. Piano wire with a diameter of 0.13 mm and silicon carbide with an abrasive grain size of 6.7 μm. Slurries in which abrasive grains (abrasive grain number # 2000) are mixed have come to be used.

  On the other hand, in recent years, as semiconductor integration progresses, the cleanliness required for the manufacturing process has become stricter. In particular, heavy metals such as Fe, Cu, Ni, and Cr have a great influence on the characteristics of the semiconductor, and when these are mixed into the semiconductor element as metal impurities, it is considered to cause defects such as pn junction leakage. Thus, in order not to deteriorate the electrical characteristics of the semiconductor element, it is required to suppress such metal contamination.

  Generally, a semiconductor material (silicon wafer) sliced with a wire saw has a damaged layer, that is, a work-affected layer, having a thickness equivalent to the abrasive grain size of the free abrasive grains used for slicing on the surface layer. This damaged layer has the ability to absorb metal impurities, that is, a gettering effect, and this gettering effect prevents diffusion of metal contamination into the wafer. Thereafter, the damaged layer is removed in the processing steps after slicing, that is, lapping or grinding, and the subsequent etching step, thereby manufacturing a wafer free from metal contamination.

  However, as described above, free abrasive grains have been refined to reduce kerf loss, and when wafers are sliced using fine free abrasive grains having an abrasive grain size of 6.7 μm or less, The thickness of the damage layer formed on the surface of the semiconductor becomes thinner, the ability to absorb metal impurities, that is, the gettering effect is lowered, and diffusion of metal contamination into the wafer has become a problem.

JP 2006-224266 A

  In order to solve the above problems, a slurry with a low metal concentration is required. However, in the wire saw processing of the loose abrasive method, brass plating (Cu + Zn) and wire scraps (Fe) on the wire surface are unavoidable due to wire wear. Mixing into the slurry. Circulating and recycling such a slurry increases the metal concentration in the slurry, so it is necessary to supply the slurry by throwing it away, which is not economical.

  As a method for preventing metal contamination of the wafer by the metal in the slurry, a method of adding a chelating agent to the polishing slurry (Japanese Patent Laid-Open No. 63-272460, etc.) is disclosed in the polishing process of the silicon wafer. According to this method, by adding the molar equivalent ratio of the chelating agent to the metal ions in the slurry to be 1 or more, the chelating agent captures and inactivates the metal ions, and the wafer is contaminated with the metal. Can be prevented. In the countermeasure against metal contamination in this silicon wafer polishing process, the amount of metal contained in the polishing slurry is very small. Therefore, the amount of the chelating agent added is very small as indicated by 0.002% by mass of ethylenediaminetetraacetic acid. However, a sufficient effect can be obtained. In addition, if the slurry is supplied by throwing it away or used after circulating for a certain period of time and then discarded and replaced with a new slurry, the metal trapped in the chelating agent is discharged out of the system together with the slurry. There was no need to consider the increase in the concentration of metals inside.

  On the other hand, in the wire abrasive slurry of the free abrasive method, the wire wears when the workpiece is processed, and this is mixed into the slurry as metal scrap. Therefore, when the slurry is circulated, the metal concentration in the slurry is To rise. For this reason, the chelating agent as described above does not have a sufficient effect of capturing the metal with respect to the increase in the metal concentration, and the metal contamination of the wafer occurs when the slurry is circulated.

  The present invention has been made in view of such problems, and in the case of slicing a workpiece with a wire saw, the workpiece is prevented from being contaminated with metal, and also when the slurry is repeatedly used by recycling the waste slurry. The present invention provides a wire saw slurry capable of preventing an increase in metal concentration in a slurry and preventing deterioration in slice quality.

In order to achieve the above object, the present invention provides:
A wire saw slurry that contains a dispersion medium and free abrasive grains dispersed in the dispersion medium, and recycles the waste slurry after cutting the work,
A phosphonic acid chelating agent that captures a metal is added to the dispersion medium, and a complex in which the metal contained in the waste slurry and the phosphonic acid chelating agent are bonded is separated from the waste slurry. Provided is a wire saw slurry characterized by being discharged.

  In such a wire saw slurry, the metal concentration in the slurry is reduced even when the slurry is repeatedly used by recycling the waste slurry while preventing the workpiece from being contaminated with metal in the work slicing with the wire saw. It is possible to prevent an increase in the slice quality and to prevent deterioration in slice quality while maintaining a low cost.

  At this time, it is preferable that the density | concentration in the said dispersion medium of the said phosphonic acid type chelating agent is 2 mass%-10 mass%.

  Thus, if the concentration of the phosphonic acid chelating agent is 2% by mass or more, a sufficient dispersion effect as a chelating agent can be obtained, and if it is 10% by mass or less, it is added without lowering the abrasive concentration. be able to.

  The phosphonic acid chelating agent preferably contains 1-hydroxyethylidene-1,1-diphosphonic acid.

  With such a phosphonic acid chelating agent, a high metal capture effect can be obtained even with a smaller addition amount.

  The dispersion medium is preferably a glycol-based dispersion medium.

  With such a dispersion medium, water can be added, so that the flash point of the slurry can be eliminated to make it a non-hazardous material, and the phosphonic acid chelating agent can be easily dissolved.

  Moreover, it is preferable that the said free abrasive grains consist of silicon carbide, and the particle diameter of the 50% cumulative height by the JIS R6002 electrical resistance test method is 5.5 μm or less.

  With such loose abrasive grains, the kerf loss of the workpiece can be further reduced.

  According to the present invention, in the slicing process of the workpiece by the wire saw, the metal concentration in the slurry increases even when the slurry is repeatedly used by recycling the waste slurry while preventing the workpiece from being contaminated with metal. , Preventing an increase in cost due to a decrease in the recycling rate of the slurry, and preventing deterioration in slice quality.

It is an example of the schematic of a common wire saw.

  The most problematic contaminant metal in semiconductor silicon wafers is Cu, but when a metal in a slurry is captured using a chelating agent, Cu can be completely captured even if only a molar equivalent of Cu is added. Can not. This is because the chelating agent also reacts with other metals present in the slurry. Since the regenerated slurry contains a high concentration of wire-derived Fe, for example, even if the purpose is to capture Cu, not only the amount that captures Cu but also the amount of chelate that captures Fe and the amount that captures Cu. It is necessary to add an agent. Therefore, the amount of addition of the chelating agent was calculated using as an example the case of using EDTA (ethylenediaminetetraacetic acid), which is widely used as a chelating agent.

  In this calculation, a wire having a diameter of φ0.13 mm and a length of 100 km was used, and the wire diameter after use was φ0.12 mm, that is, the amount of wear of the wire was 10 μm. When 44 g of Cu and 22 g of Zn are mixed into the slurry from the plated part and the mass of the slurry is 400 kg, the concentration after mixing of each metal becomes Fe 0.38%, Cu 0.011%, Zn 0.0055%. Assumed.

A wire saw slurry for slicing a workpiece made of a semiconductor material is usually weakly acidic. Therefore, when using EDTA as the chelating agent, for example, EDTA · 2H · 2Na · 2H 2 O to pH of the aqueous solution becomes 4.5 is selected. In the following, calculation was made using as an example the case of using EDTA · 2H · 2Na · 2H ₂ O (molecular weight: 372). In order to capture Fe (molecular weight: 55.85) present at a concentration of 0.38% in 400 kg of slurry, the molar equivalent of EDTA · 2H · 2Na · 2H ₂ O is added to 1.53 kg of Fe. The amount added was 10.1 kg.

  When the total amount of EDTA added to the slurry is coordinated with Fe in the slurry, 11.63 kg of complex is formed. This is 2.8% by mass with respect to 410.1 kg of the slurry.

  From this slurry, when recovering a part of the free abrasive grains and the dispersion medium and using it again, if the above complex cannot be separated and discharged, it is the same rate as the recovery ratio of the free abrasive grains and the dispersion medium, Alternatively, the complex remains in the slurry regenerated at a higher rate. That is, if the recovery rate of the free abrasive grains and the dispersion medium is 80%, 80% or more of the complex, that is, 9.3 kg or more remains in the slurry. Add a chelating agent corresponding to the amount of metal expected to be mixed in this slurry in the next workpiece processing and process the workpiece again. When recycled as described above, the concentration of the complex in the slurry further increases. .

  It is necessary to keep the viscosity of the slurry constant for the wire saw slurry to prevent the occurrence of defects such as cracking and dropping of the workpiece. In order to keep the viscosity constant, it is necessary to maintain the ratio of the dispersion medium to the solid content. If the complex cannot be separated and discharged, the free abrasive concentration in the slurry must be reduced by the increased amount, and the cutting ability Lowers and causes deterioration of slice quality.

  The present inventor has intensively studied in view of the above problems, and as long as the wire is a wire saw slurry in which a complex in which a metal and a phosphonic acid chelating agent are combined is separated and discharged, the workpiece is a metal. It has been found that even when the slurry is repeatedly used by recycling the waste slurry while preventing contamination, the increase in the metal concentration in the slurry can be prevented and the deterioration of the slice quality can be prevented. Completed the invention.

Here, the outline about the cutting | disconnection of the workpiece | work with a wire saw is demonstrated.
As shown in FIG. 1, the wire saw 1 mainly includes a wire 3 for cutting the workpiece 2, a wire guide 4 around which the wire 3 is wound, and a wire tension applying mechanism 5 or 5 for applying tension to the wire 3. ', A workpiece feeding mechanism 6 for feeding the workpiece 2 to be cut downward, a slurry supply mechanism 7 for supplying slurry at the time of cutting, and the like.

  The wire 3 is fed out from one wire reel 10 and passes through a traverser 11 to a wire guide 4 via a wire tension applying mechanism 5 including a powder clutch (torque motor 12), a dancer roller (dead weight) (not shown), and the like. In. The wire 3 is wound around the wire guide 4 about 300 to 400 times, and then wound around the wire reel 10 'through another wire tension applying mechanism 5' having a torque motor 12 'and a traverser 11'. Yes.

  When cutting a workpiece with such a wire saw 1, first, the workpiece 2 is held by the workpiece feeding mechanism 6. Further, an appropriate tension is applied to the wire 3 using the wire tension applying mechanism 5, and the wire 3 is caused to travel in the reciprocating direction by a drive motor (not shown). Next, while supplying slurry from a slurry supply mechanism 7 comprising a slurry tank 8 and a slurry chiller 9 that adjusts the temperature of the slurry, the workpiece 2 is fed to the wire 3 positioned below by the workpiece feeding mechanism 6. The work 2 is cut by pressing and feeding to.

  The relationship between the metal concentration and the metal ion concentration in the slurry, that is, what percentage of the metal present in the slurry is ionized cannot be uniquely determined because it varies depending on the pH of the slurry and the particle size of the metal powder. . However, in the case of a wire saw slurry for slicing silicon, which is a semiconductor material, the pH of the slurry is preferably weakly acidic, about 4-6, and the metal powder has a fine particle size of 1 μm or less, so that almost the entire amount is ionized. You can think of it.

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.
The metal in the slurry is fine particles having a particle size of 1 μm or less as described above. In the slurry, a part of the metal floats in the dispersion medium, and the majority exists in a state of adhering to the free abrasive grains. When the metal that remains attached to the free abrasive grains is combined with the chelating agent to form a complex, the complex remains attached to the surface of the free abrasive grains, and in the subsequent slurry regeneration treatment, only the complex can be separated and discharged. Can not.

  On the other hand, when a phosphonic acid chelating agent is added, the dispersibility of the phosphonic acid chelating agent causes the metal in the slurry to leave the free abrasive grains and then binds to the chelating agent to form a complex. In the slurry regeneration treatment, the complex can be easily separated and discharged from the slurry.

  Furthermore, phosphonic acid-based chelating agents have a threshold effect (a metal capture effect can be obtained in a smaller amount than the stoichiometric amount added to the metal in the slurry) due to the dispersibility effect, so a small amount of metal can be added. Capture effect can be obtained.

  The concentration of the phosphonic acid chelating agent in the dispersion medium is preferably 2% by mass to 10% by mass, more preferably 5% by mass to 10% by mass. If the concentration of the phosphonic acid chelating agent is 2% by mass or more, a sufficient dispersion effect can be obtained. Moreover, if it is 10 mass% or less, in order to make the slurry viscosity mentioned later constant, it is not necessary to reduce the abrasive concentration by the amount of the chelating agent added, and the productivity and slice quality (slicing quality ( Deterioration of TTV, Warp) can be prevented.

  Examples of such phosphonic acid chelating agents include HEDP (1-hydroxyethylidene-1,1-diphosphonic acid), NTMP (nitrilotrismethylenephosphonic acid), and PBTC (2-phosphonobutane-1,2,4-tricarboxylic acid). And alkali salts thereof. Among these, HEDP has the smallest molecular weight, can obtain a high metal capture effect with a smaller addition amount, and makes the slurry weakly acidic by dissolving HEDP · 2Na, which is a disodium salt of HEDP, in water. Further, it is preferable because there is little interference with other slurry-containing components.

  Although it does not specifically limit as a dispersion medium, It is preferable that it is a glycol type dispersion medium. In a glycol-based dispersion medium, generally about 15% by mass of water is added. By adding this water, the flash point of the slurry can be eliminated to make it a non-hazardous material and the viscosity can be adjusted, and the chelating agent can be easily dissolved in this water.

  The ratio of the dispersion medium in the slurry is preferably about 50% by mass, although it depends on the type of free abrasive grains and the abrasive grain size described later. For example, silicon carbide abrasive grains having an abrasive grain size of 6.7 μm as free abrasive grains When (SiC) is used, it is preferably 45 to 65 mass%, more preferably 50 to 60 mass%.

  The free abrasive grains are not particularly limited, but for example, silicon carbide abrasive grains (SiC) are preferably used.

The loose abrasive can reduce kerf loss by reducing the abrasive grain size. However, when the abrasive grain size is reduced, the gettering effect of the silicon wafer is lowered as described above, and metal contamination is easily diffused into the wafer. If the wire saw slurry of the present invention is used, the metal in the slurry can be separated and discharged, and the metal contamination of the silicon wafer can be prevented. Therefore, the particle size at a cumulative height of 50% according to the JIS R6002 electrical resistance test method is 5 Free abrasive grains of .5 μm (abrasive grain number # 2500) or less can be used.
With such free abrasive grains, it is possible to suppress the loss of cutting ability due to a decrease in the abrasive grain concentration, and thus the increase in cost due to the deterioration of cutting quality and the reduction of productivity, while sufficiently reducing kerf loss.

  As the abrasive concentration of the free abrasive grains, it is preferable that the abrasive concentration is high because the processing capacity of the slurry is proportional to the abrasive concentration. However, if the abrasive concentration, that is, the solid content concentration in the slurry is increased, the abrasive concentration is proportional to it. The slurry viscosity becomes high. Therefore, about 50 mass% is preferable, for example, when using SiC with an abrasive particle diameter of 6.7 μm as the free abrasive, it is preferably 35 to 55 mass%, more preferably 40 to 50 mass%.

  Moreover, in order to improve the washing | cleaning property at the time of washing | cleaning the wafer after slicing with water, you may further add surfactant to an appropriate density | concentration to the slurry for wire saws of this invention.

  In addition, the pH of the wire saw slurry of the present invention is weakly acidic such as about 4 to 6 in order to avoid generation of hydrogen due to reaction between silicon scrap generated by slicing and hydroxyl (OH) in the slurry. Is preferred.

  The slurry viscosity of the wire saw slurry of the present invention is preferably in the range of 100 mPa · s to 200 mPa · s, more preferably 100 to 150 mPa · s. Within such a range, it is possible to prevent the occurrence of defects such as cracking or dropping of the workpiece.

  The wire saw slurry of the present invention is recycled, and as a recycling method, for example, a slurry as shown in JP 2010-278327 A or JP 20115561 Centrifuge is centrifuged to obtain a solid content. An example of the method of recovery is illustrated. Specifically, the waste slurry after cutting the work is subjected to primary centrifugation to separate it into a solid content (primary solid content) containing free abrasive grains that can be recycled and the primary separation liquid. A part of the mixture is subjected to secondary centrifugation, and the complex (secondary solid content) is separated and discharged from the primary separation liquid to obtain a secondary separation liquid, and the secondary separation liquid and the primary solid content are prepared as a regenerated slurry. Can be mentioned. In this way, in the slurry regeneration process, if the complex in the slurry is separated and discharged, the increase in the metal concentration in the slurry can be suppressed, and metal contamination of the wafer can be prevented without having to replace the slurry with a new one each time it is used. , Can reduce costs.

  In such a wire saw slurry, the metal concentration in the slurry can be reduced even when the slurry is repeatedly used by recycling the waste slurry while preventing the workpiece from being contaminated with metal in the workpiece slicing step with the wire saw. Can be prevented, an increase in cost due to a decrease in the recycling rate of the slurry can be minimized, and deterioration in slice quality can be prevented.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.

[Experiment 1]
Using a saw wire with a diameter of 130 μm (a brass (CuZn) plating treatment on the surface), a cylindrical single crystal silicon ingot with a diameter of 300 mm was sliced while applying slurry.
As the slurry, a dispersion medium containing propylene glycol as a main component and SiC dispersed as free abrasive grains was used. From the waste slurry after cutting the silicon ingot, a part of the free abrasive grains and the dispersion medium is recovered as a primary solid (cake) and a primary separation liquid by the method disclosed in JP 2010-278327 A. A metal or complex was further separated and discharged from the primary separation liquid, and a recycled slurry was used. The abrasive grain size was 6.7 μm, the ratio of the dispersoid in the dispersion medium, that is, the free abrasive grain concentration was 46 mass%, the Fe concentration was 1.2%, and the Cu concentration was 0.015%.

  As the single crystal silicon ingot, an ingot having a resistivity of 0.01 Ω · cm, doped with boron at a high concentration and pulled up by the MCZ method, was used. Such a P-type low-resistance silicon single crystal is considered to be highly sensitive to metal contamination, and thus was used in this test for comparing metal contamination concentrations.

To the recycled slurry, EDTA · 2H · 2Na · 2H ₂ O and HEDP · 2Na are added as chelating agents so as to be 1 to 10% by mass of the dispersion medium amount, and the silicon single crystal ingot is sliced to obtain a wafer. Got.

The first sliced wafer is Comparative Example 1, EDTA · 2H · 2Na · 2H ₂ O is added at each concentration, and the sliced wafer is Comparative Examples 2 to 5, and the HEDP · 2Na is added at each concentration and sliced. The metal concentration was compared as 1-4.

  The measurement of the metal concentration of a wafer is performed by cleaning a chip obtained by cleaving a wafer with a cleaning liquid in which hydrofluoric acid, hydrochloric acid, hydrogen peroxide and pure water are mixed, and rinsing with pure water in Japanese Patent Laid-Open No. 2002-368052. The sample solution obtained by dissolving the entire amount by the indicated method was subjected to ICP-MS.

  As shown in Table 1, the concentration of the metal detected from the wafer became lower as the addition ratio of the chelating agent was increased.

Further, HEDP · 2Na has a smaller molecular weight than EDTA · 2H · 2Na · 2H ₂ O, so when the same amount is added in mass ratio, the addition amount in molar equivalent ratio increases, and further, dispersion The effect of lowering the concentration of metal detected from the wafer was significant due to the properties and the threshold effect.

[Experiment 2]
Similarly to Experiment 1, a cylindrical single crystal silicon ingot having a diameter of 300 mm was sliced using a saw wire having a diameter of 130 μm (a brass (CuZn) plating treatment on the surface). As in Experiment 1, an ingot having a resistivity of 0.01 Ω · cm prepared by MCZ method by doping boron at a high concentration was used.
As the slurry, a glycol-based dispersion medium mainly composed of propylene glycol was used, and a slurry was prepared by dispersing SiC having an abrasive particle size of 5.5 μm. The ratio of the dispersoid in the dispersion medium, the Fe concentration, and the Cu concentration were adjusted to be equivalent to those in Experiment 1.
The wafer thus obtained was processed and removed 60 μm on both sides by 30 μm on one side by lapping, and then removed by 20 μm on both sides by 10 μm on one side by etching to produce a wafer without a surface damage layer.

  Further, a wafer sliced by adding HEDP · 2Na at a concentration of 2% by mass with respect to the mass of the dispersion medium to the recycled slurry having an abrasive grain size of 5.5 μm was similarly lapped.

  Comparative Example 6, a wafer obtained by using 5.5 μm SiC without adding a chelating agent, and Example 5 in which a wafer obtained by adding HEDP · 2Na and using 5.5 μm SiC was tested. The metal concentration was measured by the same method.

  As shown in Table 2, the wafer sliced with the slurry to which no chelating agent was added had a Cu concentration five times higher than the wafer sliced with the slurry to which HEDP · 2Na was added.

  As described above, a silicon wafer sliced with a wire saw has a damage layer having a thickness equivalent to the abrasive grain size of the free abrasive grains used for slicing on the surface layer. The metal contamination of the silicon wafer is gettered by the gettering effect of the damaged layer and is prevented from diffusing into the wafer. Therefore, if the damaged layer is removed by slicing, the metal gettered to the damaged layer is also removed. However, if the abrasive grain size of the free abrasive grains of the wire saw slurry is small, the thickness of the damage layer on the surface formed by slicing is also reduced, the gettering effect is reduced, and the metal diffuses into the wafer. In Comparative Example 6 (abrasive grain size 5.5 μm), the gettering effect was low, so that a high concentration of metal was detected from the wafer from which the surface layer portion of the silicon wafer was removed.

  On the other hand, when the chelating agent HEDP · 2Na is added to a slurry having an abrasive grain size of 5.5 μm at a concentration of 2% by mass with respect to the mass of the dispersion medium, the metal in the slurry is added by the chelating agent. It became clear that the metal contamination does not diffuse into the wafer beyond the damaged layer on the surface because ions are trapped and the metal contamination level of the silicon wafer is reduced.

[Experiment 3]
In order to confirm how the metal concentration in the slurry changes when the free abrasive grains and the dispersion medium are recovered from the waste slurry discharged in the work slice and repeatedly used, the work is sliced once. The waste slurry after use and the recycled slurry obtained by adding a chelating agent to the waste slurry were centrifuged by a decanter (continuous centrifuge), and the Fe concentration of the obtained solid content (cake) was measured. The Fe concentration in the slurry before separation of the waste slurry after being used once was 1.5%.

  As a centrifuge, HS-205L made by Ishikawajima General-Purpose Machine Service Co., Ltd. was used. The operating conditions of the centrifuge were adjusted so that the solid content recovered from the waste slurry by centrifugation was 80%.

  Table 3 shows the solid Fe concentration obtained by centrifuging each slurry.

Waste slurry after being used once (Comparative Example 7) has an Fe concentration of 2% in the solid content, and EDTA · 2H · 2Na · 2H ₂ O is added to the slurry (Comparative Examples 8 and 9). Then, the Fe concentration in the solid content exceeded 2%. On the other hand, in the case of the slurry recycled by adding HEDP · 2Na, the Fe concentration is 1.9% at the addition concentration of 0.5% by mass (Example 6), and 1 at the addition concentration of 1% by mass (Example 7). .8%, 1.5% at an addition concentration of 2% by mass (Example 8) and 1.4% at an addition concentration of 5% by mass (Example 9), the higher the addition concentration, the higher the Fe concentration in the recovered solid content. Became low concentration.

In this way, when HEDP · 2Na is added to the wire saw slurry, when the waste slurry obtained by slicing the workpiece is regenerated and repeatedly used, the Fe concentration in the waste slurry is added to EDTA · 2H · 2Na · 2H ₂ O. It is possible to make the concentration lower than that of the method.

When HEDP · 2Na is added to the slurry, the Fe concentration in the centrifuged solid is lowered for the following reason.
The sedimentation velocity V of the solid particles in the liquid is expressed by the following Stokes equation (Equation 1). In the slurry of this test, the diameter of the SiC abrasive grains is 6.7 μm, the diameter of the Fe powder is 1 μm or less, the density of the SiC abrasive grains is 3.16 g / cm ³ , and the density of Fe is 7.85 g / cm ³ . Since the sedimentation rate of the particles is proportional to the density and proportional to the square of the abrasive particle size, when the slurry of this test is allowed to stand and the solid content is allowed to settle, the free abrasive particles first settle, Fe precipitates.

  In the process of recovering and reclaiming free abrasive grains from the used slurry after use, such a slurry is centrifuged so that the solids recovery rate is 80%. Fe should not be contained, but actually Fe is contained at a concentration of 2% higher than the Fe concentration of 1.5% in the waste slurry.

  This is because Fe is not dispersed alone in the waste slurry, and a part or most of it is present in a state of adhering to the free abrasive grains. Since the centrifugal separation process is performed with Fe adhering to the loose abrasive grains, the recovered solid content contains Fe.

  On the other hand, when HEDP · 2Na is added to the slurry, due to the dispersibility of HEDP, the FeDP is separated from the free abrasive grains and dispersed alone, and then HEDP and metal are combined to form a complex. Therefore, the Fe concentration contained in the solid content after centrifugation can be reduced.

  From the above results, the wire saw slurry of the present invention increases the metal concentration in the slurry even when the slurry is repeatedly used by recycling the waste slurry while preventing the workpiece from being contaminated with metal. It became clear that this could prevent the deterioration of slice quality.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

1 ... Wire saw, 2 ... Workpiece, 3 ... Wire, 4 ... Wire guide,
5, 5 '... wire tension applying mechanism, 6 ... work feeding mechanism, 7 ... slurry supply mechanism,
8 ... Slurry tank, 9 ... Slurry chiller, 10, 10 '... Wire reel,
11, 11 '... traverser, 12, 12' ... torque motor.

Claims (5)

Free abrasive grains and a including dispersed in a dispersion medium and the dispersion medium, a method for producing a wire saw slurries recycled waste slurry after work cutting,
Aforementioned added pressure to the phosphonic acid chelating agent to trap the metal in the dispersion medium separation, after work cutting, complexes with metal contained in the waste slurry and the phosphonic acid chelating agent bound, from the waste slurry A method for producing a slurry for a wire saw, characterized by being discharged. The manufacturing method of the slurry for wire saws of Claim 1 whose density | concentration in the said dispersion medium of the said phosphonic acid type chelating agent is 2 mass%-10 mass%. The method for producing a wire saw slurry according to claim 1 or 2, wherein the phosphonic acid-based chelating agent contains 1-hydroxyethylidene-1,1-diphosphonic acid. The said dispersion medium is a glycol type dispersion medium, The manufacturing method of the slurry for wire saws as described in any one of Claim 1 thru | or 3 characterized by the above-mentioned. The free abrasive grains are made of silicon carbide, and the particle diameter at the 50% cumulative height according to JIS R6002 electrical resistance test method is 5.5 μm or less. A method for producing a wire saw slurry according to claim 1.

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