JP2005254343A - Notch wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a notch wheel, preventing heavy metal contamination to a wafer and keeping good working accuracy. <P>SOLUTION: The notch wheel 1 is composed of an abrasive grain layer 2 having a groove 4 for machining a notch part of the wafer; and a metallic support 3 to which the abrasive grain layer 2 is fixed to form a fitting part to a machine tool. The abrasive grain layer 2 of the notch wheel 1 is formed by binding diamond abrasive grain with grading of #1500 to #4000 (mean particle diameter of 2 to 12 μm) with resin. The abrasive grain layer 2 may contain SiC. The bending strength of the abrasive grain layer 2 is set to 60 to 150 MPa, the longitudinal elastic modulus is set to 10 to 40 GPa, the hardness is set to HRf 70 or higher, and the degree of concentration is set ranging from 75 to 150. The SiC as filler is added in a suitable quantity depending on the physical property of the abrasive grain layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a notch wheel used for processing a notch formed in a silicon wafer.

  A silicon wafer (hereinafter sometimes abbreviated as “wafer”) is provided with a notch notched in a V shape as a mark indicating the direction of the crystal axis. This notch is used when aligning the position and crystal orientation of the wafer in a photolithography process for forming a semiconductor integrated circuit pattern on the wafer.

  Positioning is performed by bringing a positioning pin into contact with the notch. At this time, if the notch has an edge or the surface is rough, particles (fine dust) are generated due to the contact of the pins and may adhere to the wafer surface and hinder fine processing in the photolithography process. Therefore, for the purpose of suppressing particle generation, the notch is ground by the notch wheel.

  Since the notch processing is performed by transferring the shape of the notch wheel to the wafer, the notch wheel is required to maintain the shape. Therefore, a metal bond wheel having high strength is mainly used in notching. In addition, there are rough grinding and finish grinding in notching, and diamond abrasive grains having a grain size of about # 1500 to # 4000 are used in rough grinding and # 800 to 1200 in finish grinding.

  However, in metal bonds, metals such as Cu, Ni, and Fe that cause heavy metal contamination on the wafer are used as abrasive layer components. This metal component adheres to the wafer surface during notching and diffuses inward to cause crystal defects. As a result, there has been a problem that the operation, performance, and reliability of a device manufactured on a wafer are greatly affected, which causes a defect.

As a means for solving this problem, there is a method of adopting a notch wheel made of a resin bond in finish grinding. A resin bond containing a resin as a main component can suppress heavy metal contamination on a wafer as compared with a metal bond. However, since resin bonds are inferior in wear resistance compared to metal bonds, wear progresses during use is extremely fast. Therefore, there is a problem that a wafer dimensional accuracy defect occurs due to the wheel shape collapse.
Resin bonds have a lower modulus of longitudinal elasticity than metal bonds. Therefore, when the abrasive grains escape to the bond side with respect to the notch during notching, the wafer surface comes into contact with the bond and the grinding resistance increases, resulting in surface roughness failure and wafer surface burning failure due to peeling of the processed surface. There is a problem that occurs.

Regarding the notch wheel, Patent Document 1 describes a wafer in which Cu and Fe contamination on a wafer is prevented by using a metal bond wheel mainly composed of Co and Sn in wafer chamfering and planar processing.
Patent Document 2 describes a rubber wheel as a polishing notch wheel used after rough and finish grinding with a diamond wheel.
Patent Document 3 describes a notch wheel using a resin bond as well as rough / finish grinding.

JP 2003-39328 A JP 2001-300837 A Japanese translation of PCT publication No. 2003-521816

  However, in the metal bond wheel described in Patent Document 1, the bond is made of Co and Sn, and Cu, Ni, and Fe are not included. However, metal powders such as Co and Sn used for industrial use contain about 100 to 1000 ppm of Cu, Ni, and Fe as impurities. The allowable residual concentration in the wafer after final finishing is several ppt for Cu, Ni, and Fe. Therefore, when notches are machined with a metal bond wheel containing Cu, Ni, and Fe, which is 100,000,000 times the allowable concentration, the residual concentration may exceed the allowable value, and the metal contamination to the wafer is sufficient. There is a problem that cannot be prevented. In addition, these metal components adhere to the wafer surface during notching and cause crystal defects by diffusing into the inside of the wafer. This significantly affects the electrical characteristics of the wafer and causes defects.

  Since the rubber wheel described in Patent Document 2 does not use the above metal, metal contamination can be prevented, but the elastic modulus is lower than that of a metal bond or a resin bond. Therefore, since the abrasive grains escape to the bond side with respect to the incision during processing, the wafer surface comes into contact with the rubber surface, increasing the frictional resistance, resulting in a defective processing surface. It cannot be applied to the wheel.

  Further, in the notch wheel using the resin bond described in Patent Document 3, unlike the metal bond, it is possible to suppress heavy metal contamination on the wafer. In addition, since the change-over cycle of the abrasive grains is fast, clogging is unlikely to occur even in fine abrasive grains of # 1500 to # 4000 applied to finish grinding, the work surface roughness is kept good, and the work-affected layer is made small. It becomes possible to do.

  However, since the resin bond has a lower strength than the metal bond, the wear progress during use is extremely fast. Therefore, there is a problem that the tool life is extremely shortened due to the wheel shape collapse and the production efficiency is poor. In addition, the resin bond has a lower elastic modulus than the metal bond, and the abrasive grains escape to the bond side when cutting, causing the wafer surface to come into contact with the bond, resulting in frictional resistance, and processing surface defects are likely to occur. is there.

Patent Document 3 does not describe any means for solving these problems in the resin bond wheel, and the above problems for the resin bond wheel remain unsolved.
The present invention has been made to solve the above-described problems, and an object thereof is to provide a notch wheel capable of maintaining good processing accuracy while preventing heavy metal contamination on a wafer.

  In order to solve the above-described problems, the present invention provides a notch wheel used for processing a notch formed in a silicon wafer, and has an abrasive layer in which diamond abrasive grains are bonded with a resin, and the abrasive layer The notch wheel has a bending strength of 60 MPa or more and 150 MPa or less.

Since Cu, Ni, and Fe that cause heavy metal contamination to the wafer are not included, heavy metal contamination to the wafer can be prevented. The abrasive layer can also contain SiC.
In the present invention, the bending strength of the abrasive layer is preferably 60 MPa or more and 150 MPa or less. By setting the bending strength of the abrasive grain layer to 60 MPa or more and 150 MPa or less, the deformation of the wheel can be reduced and good dimensional accuracy can be obtained. When the strength is less than 60 MPa, the abrasive grains fall off due to insufficient abrasive grain holding force, and the shape of the abrasive grain layer is rapidly deformed, resulting in poor wafer dimensional accuracy. On the other hand, if the strength exceeds 150 MPa, the abrasive grains are worn away due to excessive holding power of the abrasive grains, resulting in clogging, resulting in surface roughness failure due to peeling of the wafer processing surface and wafer surface burning failure due to heat generation.

  In the present invention, the longitudinal elastic modulus of the abrasive layer is preferably 10 GPa or more and 40 GPa or less. By setting the longitudinal elastic modulus of the abrasive layer in the range of 10 to 40 GPa, it is possible to maintain an appropriate abrasive cutting depth and obtain a good processed surface. If the longitudinal elastic modulus is less than 10 GPa, abrasive grains are pushed into the bond side when the wafer is cut, and the grinding resistance increases when the bond surface comes into contact with the wafer. To do. On the other hand, when the longitudinal elastic modulus exceeds 40 GPa, since the amount of abrasive grains pushed into the bond side when the wafer is cut is small, the amount of abrasive grain cut becomes excessive and surface roughness defects occur.

In the present invention, the hardness of the abrasive layer is preferably HRf 70 or more. By setting the hardness of the abrasive layer to HRf 70 or more, the wheel is less deformed and good dimensional accuracy can be obtained.
When the hardness of the abrasive layer is smaller than HRf70, the shape collapse due to the abrasion of the abrasive layer progresses quickly, resulting in poor wafer dimensional accuracy.

  In the present invention, the concentration of the abrasive layer is preferably 75 or more and 150 or less. By making the concentration of the abrasive layer 75 or more and 150 or less, there is little deformation of the wheel shape, good dimensional accuracy can be obtained, and an appropriate cutting amount of the abrasive grain can be maintained and good cutting can be achieved. The taste can be sustained. If the degree of concentration is less than 75, the number of working abrasive grains is too small, so that the shape of the abrasive grain layer is rapidly deformed, resulting in poor wafer dimensional accuracy. In addition, since the number of working abrasive grains is too small, the abrasive cutting depth becomes excessive and surface roughness defects occur. On the other hand, when the degree of concentration exceeds 150, the number of working abrasive grains is excessive, so that the abrasive cutting depth becomes excessive and the sharpness is lowered. As a result, the bond surface comes into contact with the wafer, the grinding resistance increases, and the wafer surface is burnt due to heat generation.

  According to the present invention, it is possible to realize a notch wheel capable of maintaining good processing accuracy while preventing heavy metal contamination on a wafer.

Below, the notch wheel of this invention is demonstrated based on the embodiment.
FIG. 1 shows the configuration of the notch wheel. 2 and 3 show grinding using a notch wheel.
The notch wheel 1 is composed of an abrasive grain layer 2 having a groove 4 for machining a notch portion 6 of a wafer 5 and a base metal 3 that adheres the abrasive grain layer 2 and serves as an attachment portion to a notch processing machine. The base metal 3 is attached to the notch processing machine, and the notch wheel 1 is rotated and brought into contact with the wafer 5 for processing. As shown in FIG. 2, the notch wheel 11 performs processing while moving along the shape of the notch portion 6 of the wafer 5.

  The abrasive grain layer 2 of the notch wheel 1 is constituted by bonding diamond abrasive grains having a grain size of # 1500 to # 4000 (average grain size of 2 to 12 μm) with a resin. The abrasive layer 2 can also contain SiC. The abrasive grain layer 2 has a bending strength of 60 to 150 MPa, a longitudinal elastic modulus of 10 to 40 GPa, a hardness of HRf 70 or more, and a concentration degree of 75 to 150. An appropriate amount of SiC, which is a filler, is added according to the physical properties of the abrasive layer. Further, SiC having a particle size smaller than that of diamond abrasive grains is used. This is because when the SiC grain size is larger than the diamond abrasive grains, the SiC as the filler acts on the wafer as a cutting edge, so that a predetermined processed surface roughness cannot be obtained. At the time of notching, the surface roughness and dimensional accuracy of the processed surface change by changing the bending strength, longitudinal elastic modulus, hardness, and concentration of the abrasive layer 2.

  Polishing is performed after the processing by the notch wheel. Polishing is performed for the purpose of mirror-finishing the notch, but at the same time, the work-affected layer generated by finish grinding is also removed. This is done to eliminate the cause of defects such as deformation and cracking of the wafer during heat treatment if a work-affected layer remains on the wafer. As the surface roughness after finish grinding increases, the work-affected layer also increases. If the work-affected layer is large, the machining allowance in the polishing process increases. Since the polishing efficiency is low, the production efficiency is remarkably lowered by increasing the machining allowance. Therefore, in consideration of the production efficiency of the polishing process, it is necessary that the processed surface roughness in finish grinding be Ra 0.05 μm or less.

  In the present invention, the following test results are based on the fact that the strength of the abrasive layer is 60 MPa to 150 MPa, the elastic modulus is 10 GPa to 40 GPa, the hardness is HRf 70 or more, and the concentration is 75 to 150. This will be explained based on.

(Example)
Specific examples are shown below.
In the following examples, the optimum configuration of the abrasive layer is verified based on the measurement results of the surface roughness when the bending strength, longitudinal elastic modulus, hardness, and concentration of the abrasive layer are changed.
Table 1 shows the configuration of the notch wheel used in the test.

Processing conditions are shown below.
Work material: 8inch single crystal silicon wafer Wheel rotation speed: 100,000min ^-1
Toray allowance: 50μm
Number of processing: 500 sheets

(Example 1)
In Example 1, notch wheels in which the bending strength of the abrasive layer was changed at a predetermined ratio were manufactured, and the wafer surface roughness after processing was measured. FIG. 4 is a graph showing the measurement results of surface roughness.
The bending strength is a physical property value indicating the holding force (caulking force) of the abrasive grains by the bond, and as the bending strength increases, the abrasive holding force increases, the abrasive shedding decreases, and the abrasive layer wears. It is suppressed.

  In the range where the bending strength is less than 60 MPa, abrasive dropout due to lack of abrasive grain holding force is frequent, so that the shape of the abrasive layer is rapidly deformed, and the wafer dimensional accuracy is deteriorated before processing 500 sheets, resulting in defects. On the other hand, in the range where the bending strength is greater than 150 MPa, the abrasive grain retention force becomes excessive, causing the abrasive grains to wear out and causing clogging. It became rougher than Ra0.05micrometer. On the other hand, when the bending strength is in the range of 60 to 150 MPa, the surface roughness is Ra 0.05 μm or less, and there is no problem in dimensional accuracy.

(Example 2)
In Example 2, a notch wheel was manufactured in which the longitudinal elastic modulus of the abrasive layer was changed within a predetermined range, and the wafer surface roughness after processing was measured. FIG. 5 is a graph showing the measurement results of surface roughness.
The longitudinal elastic modulus is a physical property value indicating the support force (back-up force) of the abrasive grains by the bond. As the longitudinal elastic modulus increases, the amount of abrasive grains pushed into the bond side at the time of cutting decreases, and the abrasive on the wafer. Increases the amount of grain cut.

  When the longitudinal elastic modulus is less than 10 GPa, abrasive grains are pushed into the bond side when the wafer is cut, and the grinding resistance increases when the bond surface comes into contact with the wafer. There has occurred. On the other hand, in the range where the longitudinal elastic modulus is larger than 40 GPa, since the amount of abrasive grains pushed into the bond side when the wafer is cut is small, the amount of abrasive grain cut becomes excessive, resulting in surface roughness. Became rougher than Ra0.05micrometer. On the other hand, when the longitudinal elastic modulus is in the range of 10 to 40 GPa, the surface roughness is Ra 0.05 μm or less, and there is no problem in dimensional accuracy.

(Example 3)
In Example 3, a notch wheel was manufactured in which the hardness of the abrasive layer was changed within a predetermined range, and the wafer surface roughness after processing was measured. FIG. 6 is a graph showing the measurement results of surface roughness.
Hardness is a physical property value indicating the wear resistance of the abrasive layer. As the hardness increases, the wear resistance of the abrasive layer increases, the progress of wear of the abrasive layer slows down, and the groove shape collapses less. .
When the hardness was less than HRf70, the shape collapse due to the abrasion of the abrasive layer progressed rapidly, and the wafer dimensional accuracy defect occurred before processing 500 sheets. On the other hand, when the hardness is in the range of 70 HRf or more, the surface roughness is Ra 0.05 μm or less, and there is no problem in dimensional accuracy.

Example 4
In Example 4, a notch wheel having an abrasive layer concentration degree varied within a predetermined range was manufactured, and the wafer surface roughness after processing was measured. FIG. 7 is a graph showing the measurement results of surface roughness.
Concentration is a parameter indicating the density of abrasive grains acting on the wafer during processing. As the concentration increases, the number of abrasive grains acting on the wafer increases, and the grinding load applied to each abrasive grain decreases. For this reason, the progress of wear of the abrasive layer is slowed, and the groove shape collapse is reduced. Further, as the degree of concentration increases, the number of abrasive grains acting on the wafer processing increases, and the cutting amount per abrasive grain decreases, so that the processed surface roughness decreases.

  When the concentration level is less than 75, since the number of working abrasive grains is too small, the shape collapse due to wear of the abrasive grain layer proceeds rapidly, and a wafer dimension accuracy defect occurs before processing 500 sheets. Further, since the number of working abrasive grains was too small, the abrasive grain cutting amount was excessive, and the surface roughness became rougher than Ra 0.05 μm. On the other hand, in the range where the degree of concentration is greater than 150, the number of working abrasive grains is excessive, so that the abrasive cutting depth becomes excessive and the sharpness decreases. As a result, the bonding surface was in contact with the wafer and the grinding resistance was increased. On the other hand, when the degree of concentration is in the range of 75 to 150, the surface roughness is Ra 0.05 μm or less, and there is no problem in dimensional accuracy.

  The present invention can be used as a notch wheel used for processing a notch formed in a silicon wafer.

It is a figure which shows the structure of a notch wheel. It is a figure which shows the use condition of a notch wheel. It is a figure which shows the use condition of a notch wheel. It is a figure which shows the test result about the notch wheel manufactured by changing the bending strength of an abrasive grain layer. It is a figure which shows the test result about the notch wheel manufactured by changing the longitudinal elastic modulus of an abrasive grain layer. It is a figure which shows the test result about the notch wheel manufactured by changing the hardness of an abrasive grain layer. It is a figure which shows the test result about the notch wheel manufactured by changing the concentration degree of an abrasive grain layer.

Explanation of symbols

1 Notch Wheel 2 Abrasive Grain Layer 3 Base Metal 4 Groove 5 Wafer 6 Notch

Claims (4)

  A notch wheel used for processing a notch formed in a silicon wafer has an abrasive layer in which diamond abrasive grains are bonded with a resin, and the bending strength of the abrasive grain layer is 60 MPa or more and 150 MPa or less. And notch wheel.   The notch wheel according to claim 1, wherein the abrasive grain layer has a longitudinal elastic modulus of 10 GPa or more and 40 GPa or less.   The notch wheel according to claim 1, wherein the abrasive layer has a hardness of HRf 70 or more.   The notch wheel according to any one of claims 1 to 3, wherein the concentration of the abrasive layer is 75 or more and 150 or less.

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