CN111195991A

CN111195991A - Method for manufacturing wafer, method for evaluating quality of reusable slurry for wire saw, and method for evaluating quality of used slurry for wire saw

Info

Publication number: CN111195991A
Application number: CN201911119131.0A
Authority: CN
Inventors: 利根俊辅; 铃木一彦; 南畑祐司; 舟山诚
Original assignee: Sumco Corp
Current assignee: Sumco Corp
Priority date: 2018-11-16
Filing date: 2019-11-15
Publication date: 2020-05-26
Also published as: TW202037775A; TWI731428B; JP7003897B2; JP2020082224A

Abstract

The present invention relates to a method for manufacturing a wafer, a method for evaluating the quality of a reusable slurry for a wire saw, and a method for evaluating the quality of a used slurry for a wire saw. Provided is a method for manufacturing a wafer, wherein the flatness of the wafer can be stably improved by suppressing deterioration of the processing quality due to the quality of a reuse slurry supplied to slicing processing by a wire saw. By supplying with abrasive particlesAnd a slurry of coolant to slice the ingot. The used slurry is recovered and after separating and removing the small particles, the mixed abrasive particles and the coolant are newly added to make a reused slurry. The reuse slurry is supplied to a wire saw when a new ingot is sliced. The invention is characterized in that the volume fraction R of the recycled pulp is reduced to a small particle size defined as follows_ALess than 5.0%, small particle volume fraction R_A: the average particle diameter in the volume particle size distribution of the particles in the reuse slurry is defined as R_A1Will have as R_A1A reference particle diameter R of_A2The particles of the following particle size are defined as small particles, and are the volume ratio occupied by the small particles among the particles in the recycled slurry.

Description

Method for manufacturing wafer, method for evaluating quality of reusable slurry for wire saw, and method for evaluating quality of used slurry for wire saw

Technical Field

The present invention relates to a method for manufacturing a wafer, in which a step of slicing an ingot by a wire saw supplied with slurry including abrasive grains and a coolant to obtain a plurality of wafers is repeated. The present invention also relates to a method for evaluating the quality of the reusable slurry for wire saw and a method for evaluating the quality of the used slurry for wire saw.

Background

A wafer to be a substrate of a semiconductor device is manufactured by cutting an ingot made of silicon, a compound semiconductor, or the like. In recent years, as a method for slicing an ingot, a free abrasive method has become mainstream, in which a slurry including abrasive grains and a coolant is supplied to a wire saw to slice an ingot and simultaneously obtain a plurality of wafers.

Here, the following were performed: the used slurry used in slicing is collected, and after separating and removing small particles, a reusable slurry is prepared by adding mixed abrasive grains and a coolant, and the reusable slurry is supplied to a wire saw during slicing of a new ingot. Here, the small particles are mainly composed of silicon chips generated from an ingot in association with slicing processing, and also include wire chips generated by cutting wires or abrasive grains reduced in diameter by abrasion.

For example, patent document 1 describes: in a method for regenerating a slurry by recovering effective abrasive grains from a used slurry, removing worn abrasive grains, and adding new abrasive grains in an amount corresponding to the removed abrasive grains, the average circularity of the new abrasive grains is set to a range of 0.855 to 0.875, the weight ratio of the new abrasive grains is set to about 20%, and the average circularity of the abrasive grains included in the regenerated slurry is set to a range of 0.870 to 0.915.

Further, patent document 2 describes: an additional abrasive grain group is prepared, a predetermined amount of the additional abrasive grain group is added to and mixed with the abrasive grain group for the cutting process, and the mixed abrasive grain group is classified so that the size of the abrasive grains is not less than 1 st abrasive grain diameter and not more than 2 nd abrasive grain diameter. According to this method, the amount of the waste abrasive grains can be reduced, and the polishing process having the same quality as that of the new abrasive grain group can be performed.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2004-255534;

patent document 2: japanese patent laid-open publication No. 2011-218516.

Problems to be solved by the invention

The small particles included in the slurry not only do not contribute to ingot cutting but also hinder cutting mainly by medium diameter (median diameter) abrasive particles contributing to cutting. Therefore, when the amount of small particles in the reuse slurry is large, the flatness of a wafer manufactured by slicing using the reuse slurry tends to be deteriorated. Conventionally, in the regeneration treatment of used pulp, small particles are separated and removed from the used pulp by a classification treatment of a centrifugal separation system. However, the present inventors have recognized that there are cases where small particles cannot be sufficiently removed depending on the amount of the collected small particles in the used slurry, and in such cases, the amount of the small particles in the reused slurry also increases, and as a result, the slicing quality (i.e., the flatness of the wafer) deteriorates. Accordingly, the present inventors have come to recognize that the amount of small particles in used pulp or recycled pulp needs to be properly evaluated and managed.

Disclosure of Invention

In view of the above-described problems, an object of the present invention is to provide a method for manufacturing a wafer, which can stably improve the flatness of the wafer by suppressing deterioration of the processing quality due to the quality of the reuse slurry supplied to the slicing processing by the wire saw. Further, an object of the present invention is to provide a quality evaluation method capable of appropriately evaluating the quality of used pulp and recycled pulp.

Means for solving the problems

In order to solve the above problems, the present inventors have conducted intensive studies and obtained the following findings. That is, it is effective to evaluate and manage the quality of used pulp and recycled pulp using a parameter such as "small particle volume fraction" according to a predetermined definition. Then, it is known that: by reliably setting the volume fraction of small particles in the reusable slurry supplied to the wire saw to 5.0% or less, the flatness of the wafer manufactured by slicing can be stably improved.

The main structure of the present invention completed based on the above-described findings is as follows.

(1) A method for manufacturing a wafer, by repeating a step of slicing an ingot by a wire saw supplied with a slurry including abrasive grains and a coolant to obtain a plurality of wafers, the method comprising:

a step 1 of recovering used slurry used for the slicing process into a 1 st tank;

a 2 nd step of supplying the used slurry from the 1 st tank to a regeneration unit, and separating and removing small particles from the used slurry in the regeneration unit to obtain a regenerated slurry;

a 3 rd step of supplying the regenerated slurry from the regeneration unit to a 2 nd tank, and adding and mixing abrasive grains and a coolant to the regenerated slurry in the 2 nd tank to prepare a reuse slurry;

a 4 th step of supplying the reuse slurry from the 2 nd tank to the 3 rd tank; and

a 5 th step of supplying the reuse slurry from the 3 rd tank to the wire saw to slice a new ingot,

subjecting the recycled slurry supplied to the wire saw to a small particle volume fraction R defined as follows_AIs 5.0% or moreIn the following, the first and second parts of the material,

small particle volume fraction R_A: the average particle diameter in the volume particle size distribution of the particles in the reuse slurry is defined as R_A1Will have as R_A1A reference particle diameter R of_A2The particles of the following particle size are defined as small particles, and are the volume ratio occupied by the small particles among the particles in the recycled slurry.

(2) The method for producing a wafer according to the above (1), wherein a volume fraction R of small particles in accordance with the following definition is supplied to a used slurry for slicing_BIf the concentration exceeds 10.0%, the used slurry is discarded without being recovered in the 1 st tank,

small particle volume fraction R_B: the average particle diameter in the volume particle size distribution of the particles in the used slurry is defined as R_B1Will have as R_B1A reference particle diameter R of_B2The particles of the following particle size are defined as small particles, and are the volume ratio occupied by the small particles among the particles in the used slurry.

(3) The method for manufacturing a wafer according to the above (1) or (2), wherein in the 3 rd step, the amounts of the abrasive grains and the coolant to be added are set so that the specific gravity of the reuse slurry becomes a predetermined target value.

(4) The method for manufacturing a wafer according to the above (3), wherein,

determining a small particle volume fraction R of the recycled slurry taken from the 3 rd tank_A，

At the measured R_AWhen the concentration of the reusable slurry is 5.0% or less, the reusable slurry is supplied directly from the 3 rd bath to the wire saw to perform slicing of a new ingot,

at the measured R_AIf the amount exceeds 5.0%, abrasive grains and a coolant are added and mixed again to the regenerated slurry in the 2 nd tank to prepare additional recycled slurry, and the additional recycled slurry is supplied to the 3 rd tank, whereby the volume fraction of small particles in the recycled slurry in the 3 rd tank is 5.0% or less, and thereafter the volume fraction of small particles in the recycled slurry in the 3 rd tank is adjusted to 5.0% or lessAnd supplying the reuse slurry to the wire saw to perform slicing of a new ingot.

(5) The method for manufacturing a wafer according to the above (4), wherein in the re-preparation, the amounts of the added abrasive grains and the coolant are set so that the mass ratios of the added abrasive grains and the added coolant in the additional reused slurry in the 2 nd tank are 35% to 55%, respectively.

(6) A method for evaluating the quality of a reusable slurry for a wire saw prepared by separating and removing small particles from a used slurry containing abrasive grains and a coolant, and then adding and mixing new abrasive grains and a coolant, the method being used for slicing an ingot using a wire saw,

based on the volume fraction R of small particles according to the definition below_ATo evaluate the quality of the recycled pulp,

(7) The method for evaluating the quality of a reusable slurry for wire saw according to the above (6), wherein if the small particle volume fraction R_AWhen the content is 5.0% or less, the reusable slurry is evaluated as being reusable for slicing a new ingot, and if the small particle volume fraction R is less than the predetermined value_AIf the amount exceeds 5.0%, the reuse slurry is evaluated as not being reusable for slicing a new ingot.

(8) A method for evaluating the quality of a used slurry for a wire saw, the used slurry including abrasive grains and a coolant, the method being used for slicing an ingot by the wire saw, the method being characterized in that,

based on the volume fraction R of small particles according to the definition below_BTo evaluate the quality of the used pulp,

(9) The method for evaluating the quality of a used slurry for a wire saw according to the above (8), wherein if the small particle volume fraction R_BIs 10.0% or less, the used slurry is evaluated as being capable of being provided for a regeneration treatment if the small particle volume fraction R_BIf the slurry content exceeds 10.0%, the used slurry is evaluated as not being available for the regeneration treatment.

Effects of the invention

According to the method for manufacturing a wafer of the present invention, the flatness of the wafer can be stably improved by suppressing deterioration of the processing quality due to the quality of the reuse slurry supplied to the slicing processing by the wire saw. Further, according to the method for evaluating the quality of recycled slurry for wire saw and the method for evaluating the quality of used slurry for wire saw of the present invention, the quality of used slurry and recycled slurry can be appropriately evaluated.

Drawings

Fig. 1 is a schematic view showing a general wire saw (wire saw) 60.

Fig. 2 is a schematic diagram showing the structure of a wire saw system 100 used in one embodiment of the present invention.

FIG. 3 is a small particle volume fraction (R) for recycled slurry (slurry)_AThe method of calculating (2) is explained.

FIG. 4 is a graph showing the small particle volume fraction R of the reuse slurry in example 1_AGraph of the effect on the thickness distribution of a wafer.

FIG. 5 is a graph showing the small particle volume fraction R of the recycled slurry in example 2_AGraph of GBIR versus wafer.

FIG. 6 is a graph showing the small particle volume fraction R of the used slurry in example 3_BWith small particle volume fraction R of the recycled pulp_AA graph of the relationship of (a).

Detailed Description

(method for manufacturing wafer)

Hereinafter, a method for manufacturing a wafer according to an embodiment of the present invention will be described with reference to fig. 1 to 3. The method for manufacturing a wafer according to the present embodiment relates to a free-abrasive method in which a step of slicing an ingot by a wire saw supplied with slurry including abrasive grains and coolant (coolant) to obtain a plurality of wafers is repeated. Silicon single crystal can be used as a material of the ingot. After the silicon wafer obtained in the slicing step is supplied with an ingot of a silicon single crystal, the ingot is subjected to polishing (lapping), etching, double-side polishing (rough polishing), single-side polishing (mirror polishing), cleaning, and the like in this order to obtain a silicon wafer as a product.

First, a general wire saw 60 that can be used in the present embodiment will be described with reference to fig. 1. The wire saw 60 includes: a line group 64 for drawing a line so as to be able to run in parallel and reciprocally between the plurality of

rollers

62A, 62B, 62C, an ingot holding mechanism 66 for holding the ingot W, and a nozzle 68 for supplying the line group 64 with a slurry. In the free abrasive mode, the line group 64 is reciprocated at a high speed along the extending direction Z while continuously supplying slurry including abrasive particles and coolant from the nozzle 68 to the line group 64. At the same time, the spindle W is moved in the stuffing direction with respect to the wire group 64 by the spindle holding mechanism 66. The ingot W can be simultaneously sliced into a plurality of wafers by the cutting action of the abrasive grains. Further, fig. 1 depicts a state where the wire group 64 is shifted from the left to the right in the drawing.

The slurry is obtained by dispersing abrasive grains in a water-soluble or oil-soluble coolant. The material of the abrasive grains may be one or more selected from silicon carbide, silicon nitride, boron carbide, alumina, diamond, and the like, and it is particularly preferable to use free abrasive grains containing silicon carbide as a main component. As the coolant, it is preferable to use an ethylene glycol-based organic solvent such as propylene glycol or diethylene glycol as a main component. Typically, a water-soluble coolant based on propylene glycol can be used. Further, water was included in the coolant at around 5 mass%.

The structure of the wire saw system 100 used in the present embodiment and the respective steps of the wafer manufacturing method of the present embodiment using the same will be described with reference to fig. 2. Wire saw system 100 includes: the wire saw device 10, the recovery tank 20 as the 1 st tank, the regeneration treatment unit 30, the conditioning tank 40 as the 2 nd tank, the new coolant tank 42, the new abrasive grain tank 44, and the supply tank 50 as the 3 rd tank.

The wire saw system 100 generally includes about 10 to 20 wire saw devices 10. Each wire saw device 10 includes a slurry tank 12 and a processing chamber 14. A wire saw 60 described in fig. 1 is disposed in the processing chamber 14. The slurry tank 12 accommodates slurry. A pipe is provided between the slurry tank 12 and the nozzle 68 shown in fig. 1, and slurry is supplied from the slurry tank 12 to the nozzle 68 through the pipe. The slurry used for the slicing process is recovered and returned to the slurry tank 12. In slicing of 1 ingot, slurry circulates between the slurry tank 12 and the processing chamber 14, and no new slurry is supplied to the slurry tank 12 of the wire saw device 10.

[ step 1 ]

When slicing of 1 ingot is completed in each wire saw device 10, the used slurry used for the slicing is collected into the collection tank 20 through a pipe connecting each wire saw device 10 and the collection tank 20. The recovery tank 20 can usually contain about 1000 to 2000L of slurry.

[ 2 nd step ]

The used slurry collected in the collection tank 20 is supplied from the collection tank 20 to the regeneration unit 30. In the regeneration treatment unit 30, small particles are separated and removed from the used pulp to obtain regenerated pulp.

The regeneration unit 30 includes at least a primary separation decanter (decanter) 32, a separation tank 34, a secondary separation decanter 36, and a secondary light liquid tank 38. First, the used slurry stored in the recovery tank 20 is supplied to the primary separation decanter 32 through a pipe connecting the recovery tank 20 and the primary separation decanter 32, and is supplied to the primary separation step. The primary separation step is mainly intended to recover reusable abrasive grains. The primary separation decanter 32 is composed of a normal decanter centrifugal separator (decanter centrifuge), and the used slurry is separated into a primary heavy liquid and a primary light liquid by applying a predetermined centrifugal force thereto. The primary heavy liquid mainly comprises reusable abrasive particles (regenerated abrasive particles) including a trace amount of coolant. The primary light liquid consists mainly of small particles and most of the coolant, which are not suitable for reuse. That is, in the primary separation step, with respect to the particles in the used slurry, small particles are separated on the primary light liquid side, the regenerated abrasive particles other than the small particles are separated on the primary heavy liquid side, and the coolant in the used slurry is mainly separated on the primary light liquid side. As described above, the small particles are mainly composed of silicon chips generated from an ingot in accordance with slicing processing, and also include chips generated by cutting of wires or abrasive grains reduced in diameter by abrasion.

The primary heavy liquid is supplied to the separation tank 34 through a pipe connecting the primary separation decanter 32 and the separation tank 34. The separation tank 34 can contain about 500 to 2000L of primary heavy liquid.

The primary light liquid is supplied to the secondary separation decanter 36 through a pipe connecting the primary separation decanter 32 and the secondary separation decanter 36, and is supplied to the secondary separation step. The secondary separation step is mainly intended to recover a reusable coolant. The secondary separation decanter 36 is composed of a general decanter-type centrifugal separation device, and here, the primary light liquid is given a predetermined centrifugal force larger than that at the time of the primary separation step, and is separated into a secondary heavy liquid and a secondary light liquid. The secondary light liquid mainly comprises a reusable coolant (regenerative coolant). The secondary heavy liquid mainly comprises small particles which are not suitable for reuse and a coolant which is not suitable for reuse. That is, in the secondary separation step, the coolant component in the primary light liquid, which contains impurities such as small particles and has an increased specific gravity, is separated to the secondary heavy liquid side, the regenerated coolant other than the impurities is separated to the secondary light liquid side, and the small particles in the primary light liquid are separated to the secondary heavy liquid side.

The secondary light liquid is supplied to the secondary light liquid tank 38 via a pipe connecting the secondary separation decanter 36 and the secondary light liquid tank 38, and then is supplied to the separation tank 34 via a pipe connecting the secondary light liquid tank 38 and the separation tank 34. The secondary light liquid tank 38 can contain about 200 to 800L of secondary light liquid. However, the secondary light liquid may be directly supplied to the separation tank 34 without passing through the secondary light liquid tank 38.

The secondary heavy liquid mainly includes small particles unsuitable for reuse and a coolant unsuitable for reuse, and is therefore discarded through a pipe extending from the secondary separation decanter 36. In this manner, the regenerated slurry obtained by separating and removing the small particles from the used slurry is stored in the separation tank 34.

[ 3 rd step ]

After that, the regeneration slurry is supplied from the regeneration unit 30 to the conditioning tank 40. Specifically, the regenerated slurry is supplied to the conditioning tank 40 through a pipe connecting the separation tank 34 and the conditioning tank 40. In the tempering tank 40, new abrasive grains and coolant are added to and mixed with the regenerated slurry to prepare a reuse slurry. The new coolant is stored in the new coolant tank 42, and is supplied to the tempering tank 40 through a pipe connecting the new coolant tank 42 and the tempering tank 40. The new abrasive grains are accommodated in the new abrasive grain tank 44, and are supplied to the conditioning tank 40 through a pipe connecting the new abrasive grain tank 44 and the conditioning tank 40. The mixing tank 40 can accommodate about 1000 to 2000L of recycled slurry.

In the 3 rd step, the amounts of the abrasive grains and the coolant to be added are preferably set so that the specific gravity of the prepared reusable slurry becomes a predetermined target value. Specifically, it is preferable to set the specific gravity of the unused slurry to a range of 1.500 to 1.600 as a target value.

In this case, the mass ratio of the fresh abrasive grains to the fresh coolant in the reused slurry in the tempering tank 40 also varies within a range of about 20 to 50%. The reason for this is the non-uniform amount of regenerable abrasive particles and coolant in the used slurry. The mass ratio of fresh abrasive grains to fresh coolant in the conditioning tank 40 is defined as follows.

Mass ratio of new abrasive grain = new abrasive grain input amount/(new abrasive grain input amount + abrasive grain amount in regenerated slurry)

The input ratio of the new coolant = the input amount of the new coolant/(the input amount of the new coolant + the amount of the coolant in the regeneration slurry).

[ 4 th step ]

The recycled slurry prepared in the preparation tank 40 is supplied to the supply tank 50 through a pipe connecting the preparation tank 40 and the supply tank 50. The supply tank 50 can accommodate about 2000 to 8000L of recycled slurry.

[ 5 th Process ]

The reused slurry stored in the supply tank 50 is supplied to each slurry tank 12 via a pipe connecting the supply tank 50 and the slurry tank 12 of each wire saw device 10, and then supplied to the wire saw 60 to be used for slicing a new ingot.

[ volume fraction of small particles of recycled slurry ]

In the present embodiment, the volume fraction R of the small particles of the reused slurry supplied to the wire saw, which is defined as follows, is made small_AIt is important that the content is 5.0% or less.

Small particle volume fraction R_A: the average particle diameter in the volume particle size distribution of the particles in the reuse slurry is defined as R_A1Will have as R_A1A reference particle diameter R of_A2The particles having the following particle diameters are defined as small particles, and are volume ratios occupied by the small particles among the particles in the reuse slurry.

"Small particle volume fraction R of recycled pulp_A"is an index showing the proportion of small particles in all particles such as abrasive grains, silicon chips, and string chips in the recycled slurry, and has not been measured as a quantitative index before. In the present embodiment, by making the small particle volume fraction R_ABeing 5.0% or less, deterioration of processing quality due to the quality of the recycled slurry can be suppressed, and as a result, the flatness of the wafer can be stably improved. That is, the flatness indexes such as GBIR (Global Backside Ideal Range), warpage (Warp), nanotopography (Nano topography) and the like are stably improved. Furthermore, from the viewpoint of improving the flatness, the volume fraction R of the small particles of the recycled slurry_AThe smaller the amount of the abrasive grains or the coolant, the more preferable the amount is, from the viewpoint of suppressing the amount of the abrasive grains or the coolant (that is, cost), the more preferable the amount is 3.0% or more.

Fig. 3 is a graph showing the particle size distribution of particles in the reuse slurry for explaining the calculation method of the small particle volume fraction. First, the particle size (area equivalent diameter) of each particle in a sample of the reuse slurry was measured, and a particle size distribution D was obtained by volume counting of the particles in the reuse slurry as shown in fig. 3. The method of measuring the particle diameter of each particle is not particularly limited, but the particle diameter of each particle can be measured by, for example, imaging the particles one by one with a camera while flowing the recycled slurry through a flow path between cells (cells) of fine glass, and performing image processing. From the viewpoint of measurement accuracy, the amount of the reusable slurry to be supplied to the measurement is preferably 2mL or more.

Next, the average particle diameter R of the particle size distribution D is determined_A1R is to be_A1[ 2 ] is set as a reference particle diameter R_A2. Small particles are defined as having this reference particle diameter R_A2Particles having the following particle diameters. Then, the volume ratio occupied by small particles among the particles in the reuse slurry is calculated based on the particle size distribution D. Further, "average particle diameter R_A1"is defined as the particle size at 50% of the particle size distribution D.

Even when the amounts of abrasive grains and coolant to be added are set so that the specific gravity of the reused slurry prepared in the 3 rd step is a predetermined target value as described above, the volume fraction R of small particles of the reused slurry may be small_AAnd the fluctuation exceeds 5.0%. Specifically, when the reuse treatment of the used pulp is repeated 10 times or more, the small particles continue to accumulate in the used pulp recovered later in the slicing process, and as a result, the small particles also increase in the regenerated pulp after the regeneration treatment. In such a case, there is a small particle volume fraction R of the recycled pulp_AMore than 5.0%. When the reusable slurry is directly supplied to the wire saw device 10 in such a case, the slicing process quality (i.e., the flatness of the wafer) is impaired. Therefore, as a method for reliably making the volume fraction of small particles in the recycled slurry supplied to the wire saw 5.0% or less, there can be mentionedThe following.

First, the small particle volume fraction R of the reuse slurry collected from the supply tank 50 is measured_A. Here, R is measured_AWhen the concentration is 5.0% or less, the reusable slurry is directly supplied from the supply tank 50 to the wire saw apparatus 10, and a new ingot is sliced.

On the other hand, in the measurement of R_AWhen the amount exceeds 5.0%, new abrasive grains and coolant are added to and mixed with the regenerated slurry again in the preparation tank 40 to prepare additional recycled slurry. By supplying the additional reuse slurry to the supply tank 50, the volume fraction of the small particles of the reuse slurry in the supply tank 50 is set to 5.0% or less, and then the reuse slurry is supplied to the wire saw apparatus 10, and a new ingot is sliced. Further, after additional reuse slurry is supplied to the supply tank 50, the small particle volume fraction R is measured again_AIt was found to be 5.0% or less. According to this method, the volume fraction of small particles in the reusable slurry supplied to the wire saw can be reliably set to 5.0% or less.

In this case, in the reconstitution, the amounts of the abrasive grains and the coolant to be added are preferably set so that the mass ratios of the fresh abrasive grains and the fresh coolant in the additional reused slurry in the preparation tank 40 are 35% to 55%, respectively. This makes it possible to reliably set the volume fraction of small particles in the reused slurry to 5.0% or less without excessively increasing the amount of abrasive grains or coolant used.

In the above embodiment, the case where the silicon single crystal ingot is sliced is exemplified, but the present invention is not limited thereto, and an ingot of an arbitrary material can be used as a target of processing.

[ volume fraction of small particles of used pulp ]

Referring to fig. 2, in the present embodiment, it is also preferable to consider the small particle volume fraction of the used slurry to be subjected to slicing. I.e. the small particle volume fraction R according to the following definition, in the used slurry supplied to the slicing process_BWhen the concentration exceeds 10.0%, the used slurry is preferably discarded without being collected in the collection vessel 20.

Volume fraction of small particlesNumber R_B: the average particle diameter in the volume particle size distribution of the particles in the used slurry is defined as R_B1Will have as R_B1A reference particle diameter R of_B2The particles having the following particle diameters are defined as small particles, and are volume ratios occupied by the small particles among the particles in the used slurry.

"Small particle volume fraction R of used pulp_B"is an index showing the proportion of small particles in all particles such as abrasive grains, silicon chips, and string chips in the used slurry, and is not measured as a quantitative index. At the small particle volume fraction R_BWhen the content exceeds 10.0%, when the regeneration treatment is performed thereafter, it is difficult to reliably reduce the volume fraction R of the small particles in the reused slurry_A5.0% or less, or the amount of abrasive grains or coolant used needs to be excessive. Thus, at a small particle volume fraction R_BIf the concentration exceeds 10.0%, the used slurry is discarded without being collected in the collection vessel 20. At small particle volume fraction R_BWhen the concentration is 10.0% or less, the used slurry is collected in the collection vessel 20. Thus, the volume fraction R of the recycled slurry can be reliably reduced without excessively increasing the amount of abrasive grains or coolant used_AIs 5.0% or less. Furthermore, the "small particle volume fraction R_B"calculation method of and Small particle volume fraction R of recycled slurry_AThe same is true.

The following are examples of the embodiment of the method. First, after slicing of 1 ingot is completed in each wire saw device 10, the volume fraction R of small particles of the used slurry collected from the slurry tank 12 can be measured_BThe discarding or the collection is determined based on the measured value.

In addition, as the second mode, the small particle volume fraction may not necessarily be measured. As already described, in the slicing process of 1 ingot, slurry circulates between the slurry tank 12 and the process chamber 14. Thus, the small particle volume fraction of the used slurry has a generally positive correlation with the size (length and diameter) of the ingot provided for slicing. Therefore, if the correlation between the size of the ingot and the volume fraction of the small particles in the used slurry is obtained in advance when slicing is performed using the slurry having the volume fraction of the small particles of 5.0% or less, the discard or recovery can be determined based on the size of the ingot supplied to the slicing.

(method of evaluating quality of recycled slurry for wire saw)

A method for evaluating the quality of a reusable slurry for a wire saw according to an embodiment of the present invention will be described. The present embodiment is a method for evaluating the quality of a reuse slurry prepared by separating and removing small particles from a used slurry containing abrasive grains and a coolant, which is used for slicing an ingot by a wire saw, and then adding and mixing new abrasive grains and a coolant.

Then, characterized in that it is based on a small particle volume fraction R according to the definition already stated_AThe quality of the recycled pulp was evaluated. This enables the quality of the recycled pulp to be appropriately evaluated.

For example, if the small particle volume fraction R_AWhen the content is 5.0% or less, the reusable slurry can be evaluated as reusable for slicing a new ingot, and if the small particle volume fraction R is small_AIf the amount exceeds 5.0%, the reusable slurry can be evaluated as not being reusable for slicing a new ingot.

(method of evaluating quality of used slurry for wire saw)

A method for evaluating the quality of a used slurry for a wire saw according to an embodiment of the present invention will be described. The present embodiment is a method for evaluating the quality of a used slurry containing abrasive grains and a coolant, which is used for slicing an ingot by a wire saw.

Then, characterized in that it is based on a small particle volume fraction R according to the definition already stated_BThe quality of the used pulp was evaluated. Thus, the quality of the used pulp can be appropriately evaluated.

For example, if the small particle volume fraction R_BWhen the content is 10.0% or less, the used slurry can be evaluated as being capable of being subjected to the regeneration treatment, and when the volume fraction R of the small particles is small_BIf the amount exceeds 10.0%, the used slurry can be evaluated as not being available for the regeneration treatment.

[ examples ] A method for producing a compound

The process of slicing a silicon ingot using the wire saw system shown in fig. 2 including the wire saw shown in fig. 1 was repeated. As the abrasive grains, free abrasive grains containing # 2000 grit number silicon carbide as a main component were used. As the coolant, a water-soluble glycol coolant was used. The abrasive grains were added to the water-soluble coolant to prepare a slurry having a specific gravity of 1.570, and the operation was started as an unused slurry. The used slurry used for slicing is recovered and regenerated by the above-described method to form a reused slurry, and is used for slicing a new ingot. The amounts of abrasive grains and coolant added were set so that the specific gravity of the prepared recycled slurry was 1.570.

The volume fraction R of small particles in the used slurry was measured by the method described above using a particle diameter/shape analyzer FPIA-3000 manufactured by sysmex_BAnd a small particle volume fraction R of the recycled pulp_A。

(example 1)

Small particle volume fraction R of recycled pulp used in slicing process_AIn the case of 5.23% and the case of 3.73%, the flatness of the (As-sliced) wafer after the slicing process was compared. Fig. 4 shows the result of obtaining the thickness of 1 wafer sliced from the central portion of the ingot by an electrostatic capacitance method (electrostatic capacitance method) at each level.

As is apparent from FIG. 4, a small particle volume fraction R is used_AThe thickness of the wafer processed with 5.23% recycled slurry locally fluctuates in the center portion, and the flatness is deteriorated. In contrast, a small particle volume fraction R is used_AThe wafer processed with the reuse slurry of 3.73% had little local variation in thickness and had good flatness.

(example 2)

Using various small particle volume fractions R_AThe slurry was repeatedly subjected to dicing, and GBIR, which is a flatness index of the obtained wafer, was measured. GBIR is an overall flatness index of the back side reference, defined as the crystal relative to the back side of the wafer when the back side is the reference planeThe deviation of the maximum thickness from the minimum thickness of the surface of the sheet. The small particle volume fraction R is shown in FIG. 5_AThe GBIR of the wafer. Furthermore, each plot in FIG. 5 shows the use of a certain R_AAverage GBIR of all wafers obtained from 1 ingot by slurry reuse.

As is apparent from fig. 5, by using a small particle volume fraction R_AThe GBIR can be reliably controlled to 10.0 μm or less by reusing the slurry at 5.0% or less.

(example 3)

Small particle volume fraction R of the used slurry after slicing_BFor various values, the small particle volume fraction R of the prepared recycled slurry was measured_A. As described above, in the preparation of the reuse slurry, the amounts of the abrasive grains and the coolant to be added were set so that the specific gravity of the reuse slurry became 1.570. The results are shown in fig. 6.

As is apparent from FIG. 6, the small particle volume fraction R in the used slurry_BWhen the content is 10.0% or less, the volume fraction of small particles in the reuse slurry can be reliably set to 5.0% or less.

Industrial applicability

According to the method for manufacturing a wafer of the present invention, deterioration in processing quality due to the quality of the reuse slurry supplied to slicing processing by the wire saw is suppressed, whereby the flatness of the wafer can be stably improved.

Description of reference numerals

100 wire saw system

10 wire saw device

12 stock trough

14 processing chamber

20 recovery groove (1 st groove)

30 regeneration processing unit

32 one-step separation decanter

34 separating tank

36 secondary separation decanter

38 secondary light liquid tank

40 mixing groove (2 nd groove)

42 new coolant tank

44 new abrasive grain groove

50 feed tank (3 rd tank)

60 wire saw

62A, 62B, 62C roller

64 line group

66 ingot holding mechanism

68 nozzle

And (5) ingot W.

Claims

1. A method for manufacturing a wafer, by repeating a step of slicing an ingot by a wire saw supplied with a slurry including abrasive grains and a coolant to obtain a plurality of wafers, the method comprising:

subjecting the recycled slurry supplied to the wire saw to a small particle volume fraction R defined as follows_AThe content of the organic acid is less than 5.0%,

small particle volume fraction R_A: the average particle diameter in the volume particle size distribution of the particles in the reuse slurry is defined as R_A1Will have as R_A1A reference particle diameter R of_A2The following particles of a particle size are defined as small particles, and are referred to asAnd then the volume ratio occupied by the small particles among the particles in the slurry is utilized.

2. The method for manufacturing a wafer according to claim 1, wherein a volume fraction R of small particles in accordance with the following definition is provided in a used slurry for the slicing process_BIf the concentration exceeds 10.0%, the used slurry is discarded without being recovered in the 1 st tank,

3. The method for manufacturing a wafer according to claim 1 or 2, wherein in the 3 rd step, the amounts of the abrasive grains and the coolant to be added are set so that the specific gravity of the reuse slurry becomes a predetermined target value.

4. The method of manufacturing a wafer according to claim 3,

at the measured R_AIf the amount exceeds 5.0%, an additional reused slurry is prepared by adding and mixing abrasive grains and a coolant to the regenerated slurry again in the 2 nd tank, and the additional reused slurry is supplied to the 3 rd tank, whereby the volume fraction of small particles in the reused slurry in the 3 rd tank is set to 5.0% or less, and then the reused slurry is supplied to the wire saw, and a new ingot is sliced.

5. The method of manufacturing a wafer according to claim 4, wherein in the re-preparation, the amounts of the added abrasive grains and the coolant are set so that the mass ratios of the added abrasive grains and the added coolant in the additional reused slurry in the 2 nd tank are 35% to 55%, respectively.

6. A method for evaluating the quality of a reusable slurry for a wire saw prepared by separating and removing small particles from a used slurry containing abrasive grains and a coolant, and then adding and mixing new abrasive grains and a coolant, the method being used for slicing an ingot using a wire saw,

7. The method for evaluating the quality of a reusable slurry for wire saw according to claim 6, wherein if the small particle volume fraction R_AWhen the content is 5.0% or less, the reusable slurry is evaluated as being reusable for slicing a new ingot, and if the small particle volume fraction R is less than the predetermined value_AIf the amount exceeds 5.0%, the reuse slurry is evaluated as not being reusable for slicing a new ingot.

8. A method for evaluating the quality of a used slurry for a wire saw, the used slurry including abrasive grains and a coolant, the method being used for slicing an ingot by the wire saw, the method being characterized in that,

9. The method for evaluating the quality of a used slurry for a wire saw according to claim 8, wherein if the small particle volume fraction R is small_BIs 10.0% or less, the used slurry is evaluated as being capable of being provided for a regeneration treatment if the small particle volume fraction R_BIf the slurry content exceeds 10.0%, the used slurry is evaluated as not being available for the regeneration treatment.