JP2016192463A - Abrasive grind stone, manufacturing method of the same, and device with grind stone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent environmental pollution by minimizing use of lubricant and cooling oil and to supply lubricant to a grinding point securely continuously, in grinding process for a wafer or the like using a grind stone in which abrasive grains are bonded together by a fluorine-based resin bond.SOLUTION: In an abrasive grind stone used by its being cooled with water in the process of beveling a semiconductor wafer, a grind stone part is formed from abrasive grains and resin-based bonding agent having a number of pores, and the pores are vacuum impregnated with fatty acid salt as a lubricant. The resin-based bonding agent is fluorine-based bonding agent. The pores are vacuum impregnated with fatty acid salt in the form of a solution of high temperature lower than boiling temperature, and then naturally dried to hold the fatty acid salt in the pores.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a grinding wheel impregnated with a lubricant used for ultra-precision finishing, a manufacturing method thereof, and an apparatus equipped with the grinding wheel, and more particularly, to a grinding wheel impregnated with a lubricant suitable for chamfering of a semiconductor wafer and the like The present invention relates to a manufacturing method and an apparatus including the grinding wheel.

  A wafer as a material for a semiconductor device or an electronic component is formed into a thin plate by slicing an ingot such as single crystal silicon with a slicing device such as an inner peripheral blade or a wire device. Thereafter, an orientation flat (hereinafter also referred to as orientation flat) showing the crystal axis direction is processed, and then the peripheral surface is ground in order to prevent cracks and chips at the periphery. This peripheral surface machining is called chamfering. In the final stage of chamfering, processing is performed at a low temperature with a fine grindstone to reduce wafer deformation and processing distortion.

  An example of a grinding wheel used for such chamfering is described in Patent Document 1. The lubricant-containing grinding wheel described in this publication is intended to exhibit a lubricating action by melting a solid lubricant contained in the grinding wheel in a grinding process at a relatively low grinding point temperature. Therefore, the solid fats and oils are filled in the pores of the abrasive layer matrix, the solid fats and oils are melted by the heat generated at the grinding point and supplied to the grinding surface, and the grinding waste is received in the pores after the solid fats and oils are melted. Yes. The melted oil / fat softens the friction between the abrasive grains and the workpiece at the grinding point as a lubricant, suppresses heat generation, and reduces the grinding resistance.

  Other examples of grinding wheels are described in Patent Documents 2 and 3. In the wafer chamfering grindstone applied to the wafer chamfering device described in Patent Document 2, the outer periphery of the wafer is ground with a rotating grindstone to form the wafer into a predetermined shape. At that time, as a dual-purpose grindstone that integrally forms a rough grinding wheel and truing grindstone for rough grinding of the outer periphery of the wafer, the mechanism of the chamfering device is simplified and highly accurate and stable chamfering is enabled. .

  Further, in Patent Document 3, the chamfering device includes a truing grindstone, and a peripheral processing grindstone formed by coaxially providing a peripheral rough grinding grindstone and a master grindstone. The truing grindstone is arranged coaxially with the rotation axis of a mounting table on which a plate-like object is mounted and rotated. The groove shape of the master grindstone is formed by transfer onto a chamfering grindstone, and a desired shape is accurately formed on-machine.

JP 2004-291114 A JP 2007-044817 A JP-A-2005-153085

  In chamfering of a semiconductor wafer, conventionally, a large amount of cooling medium is supplied to a grinding point to radiate heat generated between the grindstone and the workpiece. However, in order to prevent environmental pollution and facilitate waste liquid treatment, there is an increasing demand for reducing the cooling medium used in grinding operations as much as possible. In order to meet this requirement, it has been proposed to impregnate a grindstone with a lubricant and suppress the generation of frictional heat at the cutting point by the lubricating action of the lubricant, and dry grinding.

  In Patent Document 1, in a dry grinding type lubricant-containing grinding wheel that does not use a lubricant or a grinding fluid, a large number of abrasive grains are bonded to each other with a vitrified binder, and a melting point is formed in pores formed between the abrasive grains. However, oils such as saturated fatty acids and fatty acid amides that melt and liquefy at 60 ° C. or more and act as lubricants are filled in the pores of the grindstone by a vacuum impregnation method. Since the grindstone described in Patent Document 1 uses dry grinding, even if the pores of the grindstone are impregnated with a lubricant to suppress heat generation at the grinding point, the frictional heat generated is excessive depending on the grinding state. There is a risk that the heat dissipation will not be sufficient. Vitrified binder is used to impregnate the abrasive grains with vacuum impregnation, but fluorine-based resins are often used to bond abrasive grains, and fluorine-based resins are extremely water and oil repellent. In that case, it is difficult to vacuum impregnate the lubricant.

  In the wafer chamfering apparatus described in Patent Document 2, a rough grinding wheel for rough grinding a wafer outer peripheral portion and a tooling grindstone are integrated to simplify the mechanism. At the same time, since truing and rough grinding are mounted on the same shaft that can be rotated at high speed, the occurrence of machining distortion and the like due to changes in thermal conditions during truing and rough grinding is suppressed. However, since this wafer chamfering device is premised on high-speed rotation, a great amount of frictional heat is generated during chamfering, but the lubricant and coolant used for removing the frictional heat during chamfering are not fully considered. . That is, at present, it is required to reduce the use of lubricants and cooling oil as much as possible in consideration of the environment, but this point is not disclosed.

  In the chamfering grindstone described in Patent Document 3, when a resin bond grindstone is used from the advantage of the shape retainability of the grindstone, the shape of the truing grindstone is retained by transfer from the master grindstone to improve machining accuracy and workability. ing. However, even in this chamfering grindstone, no consideration is given to efficiently removing the heat generated during the chamfering process and reducing the use of lubricant and cooling oil as much as possible in consideration of the environment.

  The present invention has been made in view of the above-mentioned problems of the prior art, and in the grinding processing of wafers and the like with a grindstone in which abrasive grains are bonded with a fluorine-based resin bond, the use of a lubricant and cooling oil is reduced as much as possible. The purpose is to prevent contamination and ensure that the lubricant can be continuously supplied to the grinding point. Another object of the present invention is to realize a wafer chamfering apparatus and a grindstone used in the apparatus that can perform environmentally-friendly processing at a low water cooling temperature by using a grindstone capable of supplying a lubricant over a long period of time.

  A feature of the present invention that achieves the above object is that it is used by cooling with water when chamfering a semiconductor wafer, and a grindstone portion is formed with abrasive grains and a resin-based binder having a large number of pores, and the pores are used as a lubricant. In a grinding wheel impregnated with a fatty acid salt in a vacuum, the resin binder is a fluorine binder, and the pores are vacuum impregnated into the pores in the state of a high-temperature aqueous solution at 80 ° C. or higher and lower than the boiling temperature at atmospheric pressure. Then, it is naturally dried and the fatty acid salt is retained in the pores.

  In this feature, the resin binder is PTFE (tetrafluoroethylene resin), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether), FEP (tetrafluoroethylene / hexafluoropropylene copolymer (4.6 fluoropolymer)). )), ETFE (tetrafluoroethylene / ethylene copolymer), PVDF (polyvinylidene fluoride (difluoride)), PCTFE (polychlorotrifluoroethylene (trifluoride)), ECTFE (chlorotrifluoroethylene / ethylene) The fatty acid salt is preferably a potassium salt or sodium salt of at least one of lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid.

  In the above feature, the aqueous solution concentration of the fatty acid salt used during vacuum impregnation is preferably 5 to 40 wt%, more preferably 10 to 30 wt%, and still more preferably 15 to 20 wt%. Furthermore, the temperature of the aqueous solution of the fatty acid salt used during vacuum impregnation is preferably set to a Kraft temperature or higher, and the amount of vacuum impregnation of the fatty acid salt is desirably 30 to 50% of the volume of the pores.

  Another feature of the present invention that achieves the above object is that it is used by cooling with water during chamfering of a semiconductor wafer, and a grindstone is formed with abrasive grains and a resinous binder having a large number of pores, and the pores are lubricated. In a method for producing a grinding wheel in which a fatty acid salt is vacuum impregnated as an agent, the fatty acid salt aqueous solution having an evaporation temperature that is substantially lower than the evaporation temperature is prepared, and the grinding stone is immersed in the fatty acid salt aqueous solution. The air in the grinding wheel is replaced with the fatty acid salt aqueous solution in an environment reduced in pressure to 33 kPa, and is naturally dried in a normal temperature air environment.

  In this feature, the concentration of the aqueous fatty acid salt solution is 5 to 10 wt%, and the fatty acid salt is a potassium salt or a sodium salt of at least one of lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid. Desirably, the resin binder is PTFE (tetrafluoroethylene resin), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether), FEP (tetrafluoroethylene / hexafluoropropylene copolymer (4.6 fluoride)). ), ETFE (tetrafluoroethylene / ethylene copolymer), PVDF (polyvinylidene fluoride (difluoride)), PCTFE (polychlorotrifluoroethylene (trifluoride)), ECTFE (chlorotrifluoroethylene / ethylene copolymer) At least one of Ri, the temperature of the fatty acid salt solution is preferably 80-90 ° C..

  Further, the present invention that achieves the above object is characterized in that a wafer table for holding a wafer, a rough grinding wheel for grinding an outer peripheral portion of the wafer, a fine grinding wheel, and the rough grinding wheel and the fine grinding wheel for the wafer table. Moving means for moving in the X, Y, and Z directions so as to face each other, a truing wheel used for forming the shape of the rough grinding wheel and the fine grinding wheel, and a wafer during grinding with the rough grinding wheel and the fine grinding wheel A wafer chamfering apparatus including a water cooling unit that absorbs and dissipates heat generated on the contact surface with the surface includes a grinding wheel having any of the above characteristics.

  According to the present invention, a lubricant is supplied together with a saturated fatty acid salt solution to a chamfering grindstone material having a porous surface, the grindstone surface is dried to obtain a lubricant-impregnated grindstone, and the grindstone containing this lubricant is used by water cooling. Therefore, the lubricant can be reliably supplied to the cutting point of the grindstone, and the cutting point temperature can be set to a predetermined temperature or less. Moreover, since the coolant is water, it is possible to prevent environmental pollution due to the coolant. Further, in the wafer chamfering apparatus, since the grindstone is impregnated with the lubricant, the lubricant can be supplied to the cutting point for a long period of time, and since the coolant is water, the processing can be performed at low temperature and in consideration for the environment.

It is a front view of one Example of the chamfering device provided with the grindstone concerning the present invention. It is a figure which shows the outline manufacturing process of the grindstone concerning this invention. It is a figure explaining the principle of this invention, and is a figure of the state before improving the wettability of a fluorine resin. It is a figure explaining the principle of this invention, and is a figure of the state after improving the wettability of a fluorine resin. It is a figure explaining the lubricant impregnation method to the grindstone concerning the present invention. It is the surface enlarged photograph of the grindstone which does not impregnate a lubricant. It is the surface enlarged photograph of the grindstone impregnated with the lubricant concerning the present invention. It is a figure which shows the shape of the various grindstones used for the chamfering apparatus shown in FIG.

  Hereinafter, a grinding wheel according to the present invention, a manufacturing method thereof, and an apparatus including the grinding wheel will be described with reference to the drawings. In the following description, a chamfering device for a wafer (plate-like object) which is a component of a semiconductor device or an electronic device and a grindstone used therefor will be described as an example. However, the present invention is not limited to a wafer chamfering device. The present invention can be applied to various grinding apparatuses that require smooth grinding and are desired to be processed at a low temperature, and grindstones used therefor.

  FIG. 1 is a front view of an embodiment of a wafer chamfering apparatus 10 as a grinding apparatus according to the present invention. In the wafer chamfering apparatus 10, the wafer chamfering apparatus 10 roughly controls operations of the wafer feeding unit 20, the grindstone rotating unit 50, a wafer supply / storage unit (not shown), a wafer cleaning / drying unit, a wafer transfer unit, and each part of the chamfering device. The controller is not shown.

  The wafer feeding unit 20 includes an X-axis base 21 placed on a main body base 11 that forms a base portion, and two X-axis guide rails 22, 22 that extend horizontally on the X-axis base 21 and are arranged in parallel. , Two X-axis guide rails 22, a total of four X-axis linear guides 23, 23, slidably attached, an X table 24 with an X-axis linear guide 23 attached to the lower surface, and X X-axis driving means 25 for driving the table 24 is provided. The X-axis drive unit 25 includes a ball screw and a stepping motor (not shown), and drives the X table 24 in the X direction (the depth direction in FIG. 1) based on a control command from a control unit (not shown).

  On the upper surface of the X table 24, two Y-axis guide rails 26, 26 are arranged in parallel in a horizontal direction orthogonal to the X-axis (the left-right direction in FIG. 1). For each Y-axis guide rail 26, two Y-axis linear guides 27, 27,..., Are slidably attached to the Y-axis guide rail 26. The Y-axis linear guide 27 is attached to the lower surface of the Y table 28, and drives the Y table 28 in the Y direction (left and right in FIG. 1) by Y axis driving means (not shown) having a ball screw and a stepping motor. Acts as a guide.

  On the upper surface of the Y table 28, two Z-axis guide rails 29, 29 extending in the vertical direction are arranged in parallel with an interval in the Y direction. Four Z-axis linear guides (not shown) are slidably attached to the Z-axis guide rail 29. The Z-axis linear guide is attached to a Z table 31 that moves in the vertical direction, and acts as a guide when the Z-axis drive means 30 having a ball screw and a stepping motor drives the Z table 31 in the vertical direction.

  A θ spindle 33 for rotating a wafer table (mounting table) 34 in the θ direction within a horizontal plane is incorporated in the central portion of the Z table 31. The θ spindle 33 is driven by a θ axis motor 32. The wafer table 34 is attached to the upper end portion that is the shaft end portion of the θ spindle 33, and sucks and places the wafer W that is a plate-like object. The wafer table 34 rotates around the rotation axis CW of the wafer table 34 (in the θ direction in FIG. 1). On the lower surface of the wafer table 34, a truing grindstone 41 is attached concentrically to the rotational axis CW of the wafer table 34. The truing grindstone 41 is used for shaping an outer peripheral grinding grindstone for chamfering the peripheral edge of the wafer W placed on the wafer table 34, that is, truing.

  As described above, the wafer feeding unit 20 provided in the wafer chamfering apparatus 10 rotates the wafer W and the truing grindstone 41 in the θ direction in FIG. 1 and moves in the X, Y, and Z directions.

  Next, the grindstone rotating unit 50 provided on the side of the wafer feeding unit 20 will be described. In the grindstone rotating unit 50, a grindstone rotating unit base 63 is provided to extend in the vertical direction in order to align the height position with the wafer W mounted on the wafer feeding unit 20. An outer peripheral grindstone spindle 51 having a rotating shaft extending in the vertical direction is provided at the center of the grindstone rotating unit base 63.

  An outer peripheral processing grindstone 52 for grinding the outer peripheral portion of the wafer W is attached to the tip of the outer peripheral grindstone spindle 51. The outer peripheral processing grindstone 52 is rotationally driven in the horizontal direction around the outer peripheral processing grindstone axis CH by an outer peripheral grindstone motor built in the grindstone rotating unit base 63. A disc-shaped turntable 53 on which a plurality of grindstones are mounted is disposed above the outer peripheral processing grindstone 52 with a distance in the vertical direction from the outer peripheral processing grindstone 52.

  A plurality of through holes are formed near the outer periphery of the turntable 53, and a grindstone set for each application is attached to each hole. That is, an outer peripheral fine grinding set for fine grinding (finish grinding) of an arc-shaped outer peripheral surface or a flat orientation flat surface of the wafer W, or a notch rough grinding for showing a crystal axis of a wafer provided on a part of the wafer W A set and a notch precision grinding set are installed. The outer peripheral fine grinding set includes an outer peripheral fine spindle 54 having a rotating shaft extending in the vertical direction, an outer peripheral fine grinding wheel 55 attached to the lower end of the outer peripheral fine spindle 54, and an outer peripheral attached to the upper part of the outer peripheral fine spindle 54. An outer peripheral fine motor 56 that drives the fine spindle 54 is provided. The notch rough grinding set is attached to a notch rough grinding spindle 60 having a rotation axis extending in the vertical direction, a notch rough grinding wheel 61 attached to the lower end of the notch rough grinding spindle 60, and an upper part of the notch rough grinding spindle 60. And a notch roughing motor 62 that rotationally drives the notch roughing spindle 60. Similarly, the notch precision grinding set includes a notch precision spindle 57 having a rotating shaft extending in the vertical direction, a notch precision grinding wheel 58 attached to the lower end of the notch precision spindle 57, and an upper portion of the notch precision spindle 57. It has a notch fine motor 59 which is attached and drives a notch fine spindle 57.

  When the turntable 53 is rotated around the rotation shaft 64 by a predetermined amount according to the processing position and processing type of the wafer W, the grindstone corresponding to the processing can be positioned on the processing surface of the wafer W. That is, after the outer peripheral surface of the wafer W is roughly processed by the outer peripheral processing grindstone 52, the chamfering process for finish grinding of the outer periphery of the wafer W is performed by the outer peripheral fine grinding grindstone 55 attached to the peripheral peripheral grinding spindle 54. The notch provided on the outer periphery of the wafer W is roughly processed with a notch rough grinding wheel 61 attached to the notch rough spindle 60 and then subjected to finish grinding with a notch fine grinding wheel 58 attached to the notch fine spindle 57. Perform chamfering.

  As described above, a plurality of grindstones are used to grind the outer peripheral surface of the wafer W. The outer peripheral grindstone 52 used when roughly grinding the outer peripheral surface of the wafer W has the largest diameter and a flat disk shape. doing. The cross-sectional shape of the side surface of the peripheral processing grindstone 52 may be formed in a plurality of layers so as to correspond to the shape of each part of the wafer W. The outer peripheral grinding wheel 55 is a cylindrical grindstone and has a smaller diameter than the outer peripheral processing grindstone 52. The notch rough grinding wheel 61 and the notch fine grinding wheel 58 are formed in a rod shape with a small diameter because the notch portion may be small.

  By the way, the peripheral processing grindstone spindle 51 is a spindle driven by a built-in motor using a ball bearing, and the rotation speed thereof is 8,000 rpm. The outer peripheral spindle 54 is a built-in motor driven spindle using an air bearing and has a rotational speed of 35,000 rpm. The notch rough spindle 60 is an air turbine driven spindle using an air bearing and has a rotational speed of 80,000 rpm, and the notch precision spindle 57 is a built-in motor driven spindle using an air bearing and has a rotational speed of 150,000 rpm. It is.

  Here, when the outer peripheral processing grindstone 52 is formed in a plurality of layers, the outer peripheral rough grinding grindstone of the wafer W and the chamfering grindstone for finishing and grinding the orientation flat and the orientation flat corner of the wafer W are laminated. A plurality of grooves are formed on the surface of these grindstones formed in layers in order to cope with the deformation of the groove shape due to wear.

  The particle size of the truing grindstone 41 attached below the wafer table 34 is typically # 320. Moreover, as an outer periphery rough grinding wheel which comprises the outer periphery processing grindstone 52, the metal bond grindstone of a 202 mm diameter diamond abrasive grain is used, and the particle size is about # 800. As the orientation flat and orientation flat corner grinding wheel, a resin bond grindstone with a diamond abrasive having a diameter of 202 mm is used, and the typical grain size is # 3000. On the other hand, the fine outer peripheral grinding stone 55, which will be described in detail later, is a resin-bonded grinding stone of diamond abrasive grains having a diameter of 50 mm, and typically has a grain size of # 3000. The notch rough grinding wheel 61 has a small diameter of 1.8 mm to 2.4 mm, a diamond bond resin bond grindstone having a particle size of about # 800, and the notch fine grinding wheel 58 has a diameter of 1.8 mm to A resin bond grindstone with a small diameter of 2.4 mm and a diamond abrasive grain size of about # 4000 is used.

  As described above, since the outer peripheral grinding wheel 55 is rotationally driven at a high speed of 35,000 rpm as described above, frictional heat is generated on the processing surface where the outer peripheral grinding wheel 55 is in contact with the wafer W as the workpiece. To do. Conventionally, oil-based grinding fluid has been used also for lubrication, but since the environmental load is large, the use of grinding oil that also serves as lubrication is currently suppressed and dry machining may be performed. However, in the case of dry processing, there are problems such as reliably supplying the lubricant and efficiently removing the heat generated in the processed portion. Therefore, in the present invention, the environmental load is reduced by ensuring the grindability of the lubricant-impregnated grindstone used in dry processing, which should be referred to as semi-dry processing, and by using water as a coolant.

  For this reason, the wafer chamfering apparatus 10 has a nozzle 71 for supplying water to the processing surface disposed in the vicinity of the peripheral grinding wheel 55 and in the vicinity of the processing surface. The water supplied to the processing surface by the nozzle 71 is partially collected by the drainage collecting means 72 without being leaked out of the wafer chamfering device 10 and contains, for example, a tank 73 accommodated in the grindstone rotating unit base 63. Led to. Then, the water in the tank 73 is pumped up again by the pump 74, pressurized and supplied to the nozzle 71. As will be described later, the lubricant is water-soluble, and only needs to be treated with water after a predetermined period of use, thereby reducing the environmental burden. Further, the amount of water used is sufficient to dissipate heat generated in the grinding portion, and can be made as small as possible.

  Next, the grindstone used for the wafer chamfering apparatus 10 which is one of the features of the present invention will be described. FIG. 2 is a flowchart showing an outline of a method for manufacturing the outer peripheral fine grinding wheel 55 which is a kind of grindstone. The peripheral grinding wheel material is processed into a cylinder having a diameter of approximately 50 mm so that the material of the circumferential grinding wheel 55 can be attached to the shaft end of the grinding spindle 54 (step S100). In this embodiment, in order to adhere the grinding stone layer in which the diamond abrasive grains are bonded with the fluorine-based resin to the outer peripheral precision grinding stone material, the adhesion surface of the grinding stone layer is surface-treated as necessary (step S110). Next, a mixed liquid of fluorine resin and diamond abrasive grains is prepared (step S120). A liquid in which diamond abrasive grains are dispersed in a fluorine-based resin is applied to the surface of the outer peripheral grinding wheel material and sintered or bonded using an adhesive (step S130). In the case of sintering, when the sintering is completed, the void formed in the grindstone layer is vacuum impregnated with an aqueous solution of oil or fat as a lubricant (step S140). Next, the peripheral grinding wheel 55 formed by vacuum impregnation is dried at room temperature for several hours to form a gap holding oil and fat (step S150). The gap portion serves as a storage place for grinding waste generated during grinding. Finally, a truing process is performed according to the wafer shape (step S160). This truing process is performed using the truing grindstone 41 with the peripheral grinding grindstone 55 attached to the wafer chamfering apparatus 10.

  The oil and fat vacuum impregnation in the manufacturing process of the outer peripheral grinding wheel 55 will be described in detail with reference to FIGS. FIG. 3 is a diagram schematically showing the effect of vacuum impregnation, and is a diagram of a state before improving the wettability of the fluororesin, and FIG. 4 is a diagram after improving the wettability of the fluororesin. is there. FIG. 5 is a diagram for explaining a method of impregnating the grinding wheel layer formed on the circumferential surface side of the outer peripheral precision grinding wheel 55 with a lubricant.

  A lubricant-impregnated grindstone can be produced by impregnating the pores of the grindstone with liquid oil and then solidifying the oil and fat. However, since oils and fats have a higher viscosity and lower fluidity than water, it is difficult to impregnate fine pores formed inside the grindstone. Therefore, in the present invention, in order to impregnate the pores formed in the grindstone with the oil and fat, the oil and fat are made into an aqueous solution and the aqueous solution is heated to a temperature higher than the Kraft point to promote the dissolution of the oil and fat in water.

  FIG. 3A shows a state in which a grindstone is immersed in an aqueous solution 200 of a fatty acid salt (fatty acid sodium). Before the improvement of wettability, the surface of the fluororesin 203 in which the abrasive grains 204 are dispersed and the pores 205 are formed is in contact with the surface of the aqueous solution 200 of the fatty acid salt (fatty acid sodium), as shown in FIG. Thus, it does not penetrate into the grindstone due to surface tension. On the other hand, after the wettability is improved by increasing the aqueous solution temperature to about 80 to 90 ° C., the pore 205 formed in the grindstone layer is filled with the fatty acid salt aqueous solution 200 as shown in FIG. Whether the wettability of the fatty acid salt aqueous solution is 80-90 ° C., which improves the wettability with respect to the fluororesin 203 exhibiting such a strong water repellency and oil repellency, is unclear, Research has found that the wettability is improved under the temperature condition, and the aqueous solution 200 of the fatty acid salt can be introduced into the pores 205. Here, the temperature of the aqueous solution is more preferably 80 ° C. to 90 ° C., but the aqueous solution 200 of the fatty acid salt is infiltrated into the grindstone even when the temperature is lower than the boiling temperature at 80 ° C. or higher, and the fatty acid salt 202 is introduced into the pores of the grindstone. Confirmed that can be introduced.

  In addition, since fluorine resin is used as a binder for diamond abrasive grains, fluorine resin has poor wettability at room temperature compared to vitrified resin, and the pores formed with fluorine resin are vitrified. Therefore, even when oils and fats and fatty acid salts are emulsified and made into an aqueous solution, it is difficult to enter pores inside the grindstone at a low temperature of about room temperature. That is, even if the outer peripheral precision grinding stone 55 is immersed in an aqueous solution of fats and oils, fatty acid salts or the like and the numerous pores formed on the resin surface are impregnated by sintering, the fats and oils cannot be impregnated as they are.

  Here, in FIG. 3, PTFE (tetrafluoroethylene resin) is used as an example of the fluororesin, but other fluororesins such as PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether), FEP ( Tetrafluoroethylene / hexafluoropropylene copolymer (4.6 fluoro)), ETFE (tetrafluoroethylene / ethylene copolymer), PVDF (polyvinylidene fluoride (difluoride)), PCTFE (polychlorotrifluoro) Even when ethylene (trifluoride) or ECTFE (chlorotrifluoroethylene / ethylene copolymer) is used, there is a hydrophobic defect.

  What is impregnated is a fatty acid salt (surfactant). For example, sodium laurate, which is a soap material, or potassium salt or sodium salt such as myristic acid, palmitic acid, stearic acid, or oleic acid can be used. It is more impregnated when the vacuum impregnation method according to the present invention described later is used.

  When a grindstone having a large number of pores is formed using a fluororesin as a binder, the wettability of the fatty acid salt to the fluororesin is low even if the fatty acid salt is vacuumed, so that the grindstone is impregnated with the fatty acid salt in the aqueous solution. Is difficult. Therefore, in this embodiment, the aqueous solution temperature is increased to improve the wettability with respect to the fatty acid salt and the fluororesin. The present inventor has found that wettability to a fluorine-based resin is improved by increasing the temperature of the aqueous solution of the fatty acid salt.

  FIG. 5 is a schematic diagram showing one technique for improving wettability. A 20 wt% aqueous solution of a fatty acid salt (sodium laurate) is prepared. At that time, the temperature of the fatty acid salt 81 is set to 90 ° C., and the temperature of the water 82 is also set to 90 ° C. The prepared fatty acid salt aqueous solution 83 is placed in a sealable container (vacuum container) 84, and the outer peripheral grinding wheel 55 is immersed in the fatty acid salt aqueous solution 83. The soaked outer peripheral grinding wheel 55 is vacuumed using a vacuum pump 85. Due to the vacuum suction, the bubbles 86 come out from the pores of the outer peripheral grinding wheel 55, and the fatty acid salt aqueous solution 86 enters the pores that have become voids. In addition, the pressure in the vacuum vessel 84 at the time of vacuum suction is maintained at about 0.133 kPa to 1.33 kPa. After impregnating the outer peripheral fine grinding grindstone 55 with the fatty acid salt aqueous solution 83, the outer peripheral fine grinding grindstone 55 is taken out from the vacuum vessel 84 and dried at room temperature. As a result, moisture is evaporated from the fatty acid salt aqueous solution 86, and the pores replaced with the fatty acid salt aqueous solution 86 become pores having a smaller volume than the original pores in which the fatty acid salt 81 is retained.

  Here, by increasing the temperature of the fatty acid salt aqueous solution 83 to near the limit at which moisture evaporates, the permeability of the fatty acid salt aqueous solution 83 or the fluidity to the pores can be improved while maintaining the concentration of the aqueous solution. As a result, the substitution of the air in the pores formed in the fluororesin that is the binder of the fine grinding wheel 55 with the fatty acid salt aqueous solution 83 is promoted, and the fatty acid salt 81 that is the lubricant is made into a gap in the fluororesin. Can hold.

  In this embodiment, the concentration of the aqueous solution of the fatty acid salt is 20 wt%. However, if the concentration of the fatty acid salt is 5 to 40 wt%, it can be used practically. However, if the fatty acid salt aqueous solution concentration is 10 to 30 wt%, a good grindstone can be obtained, and if the fatty acid salt aqueous solution concentration is 15 to 20 wt%, a homogeneous best grindstone can be obtained. This is because the circle described below can be secured.

  When the fatty acid salt aqueous solution concentration is changed within the above range, the substitution rate can be adjusted or controlled according to the content of the grinding process. Here, the substitution rate is defined as the volume of all pores formed in the fluororesin during firing and the portion where only the fatty acid salt is retained in the pores by the above vacuum impregnation and drying, and as a result, only the water content portion remains as pores. Is a volume ratio.

  As described above, since the pores formed in the fluororesin act as a grinding waste container when used as a grindstone, it is preferable in terms of grinding performance to replace all pores formed during firing with a fatty acid salt. Absent. When all pores are actually replaced with a fatty acid salt, the grinding resistance increases and the lubricity deteriorates. Therefore, in this example, the fatty acid salt aqueous solution concentration and the vacuum impregnation time (5 minutes to 60 minutes: the density of the grindstone are set so that about 30 to 50% of the total pores formed by firing are replaced with the fatty acid salt. And the fatty acid salt aqueous solution temperature is set as described above.

  FIG. 6 shows an enlarged photograph of the surface of a grindstone layer obtained by vacuum impregnating a fluorine-based resin with a fatty acid salt and then drying it at room temperature and atmospheric conditions for about 1 day to 2 weeks. The photograph in FIG. 6 shows that the fatty acid salt covers the diamond abrasive grains by vacuum impregnation, making it difficult to understand the pores. Moreover, in FIG. 6, the blackish portions are diamond abrasive grains, and the others are the fluorine resin of the binder. By changing the concentration of the fatty acid salt aqueous solution, the ratio of the water impregnated in the pores during vacuum impregnation changes, and it can be easily understood that the amount of water finally remains as pores when naturally dried.

  FIG. 7 shows, as a comparative example, an enlarged view of the surface shape of a grindstone using a fluororesin as a binder before applying the vacuum impregnation of the present invention (before putting the fatty acid salt into the pores). The fatty acid salt which is a lubricant is not held in the pores of the grindstone, and the dark diamond abrasive grains are not covered with the fatty acid salt.

  FIG. 8 shows an example of a grindstone used when chamfering a wafer using the grindstone created by the above method, and an example of the shape of the wafer surface. Fig.8 (a) is an example of the cross-sectional shape of the grindstone used for grinding. The grindstone includes an orientation flat rough grinding grindstone 91 having a V groove (grinding groove 92) formed on the outer peripheral portion, and an outer peripheral rough grinding grindstone 93 similarly formed with a V groove (grinding groove 94) on the outer peripheral portion. It is the shape which piled up. In FIG. 8A, only one groove is shown for each of the grindstones 91 and 93, but a plurality of grooves are usually formed in order to reduce the grindstone replacement and truing frequency.

FIG. 8B to FIG. 8D show various chamfered shapes of the wafer W in a perspective view and a sectional view. FIG. 8B shows an example of the trimming process for forming the step W ₁ on the outer peripheral portion of the wafer W. FIG. 8C shows the chamfering process of the bonded wafer W, in which the groove W2 is formed at the peripheral edge of the wafer bonded in two steps. FIG. 8D shows an asymmetric wafer chamfering process in which an inclined processing surface W3 is formed from the upper surface to the lower surface of the peripheral edge of the wafer W. In order to process into a chamfered shape, the grindstone is processed into a desired shape by truing. The grindstone described in the above embodiment can be used for chamfering such various shapes.

  The chamfering process may be dry grinding, but it is desirable to use water as a coolant. Since the coolant is water, the lubricant can be expected to spread on the ground surface. Further, even when a fatty acid salt as a lubricant is mixed in water as a coolant, it is easily dissolved and there is no environmental pollution. Furthermore, by using water as a coolant, low-temperature grinding can be performed, and high-precision grinding of the wafer becomes possible. In addition, heat generated on the grinding surface can be absorbed by a phase change of water, and grinding can be performed with a small amount of cooling water, reducing the environmental load. Furthermore, since the fatty acid salt is also used as a soap, it can be expected to perform a cleaning action together with cooling water.

  As described above, according to this embodiment, since the surface of a grindstone formed by sintering using a fluororesin that is hydrophobic at room temperature as a binder can be reliably impregnated with a fatty acid salt as a lubricant, The processing accuracy with a grindstone can be improved. In addition, since the fatty acid salt to be impregnated is water-soluble, when processed with water as the coolant, low-temperature grinding is possible by water cooling, enabling high-precision grinding and reducing the environmental impact of the coolant. it can.

  In addition, since a grindstone is created by sintering a mixed solution of diamond abrasive grains and a fluorine-based resin to the grindstone material, it can be easily adapted to various chamfered shapes of the wafer simply by changing the grindstone shape. Wafer chamfering can be realized. Furthermore, by changing the concentration of the fatty acid salt aqueous solution within the allowable range at the time of vacuum impregnation, the substitution ratio of the pores formed in the fluororesin to the fatty acid salt can be changed. Can be realized. For example, in the above embodiment, the pore replacement ratio is set by taking a precision grinding wheel as an example, but the present invention is also applicable to a rough grinding wheel. In the case of a rough grinding wheel, the amount of grinding is increased by increasing the replacement ratio. It is also possible to increase.

DESCRIPTION OF SYMBOLS 10 ... Wafer chamfering apparatus, 11 ... Main body base, 20 ... Wafer feeding unit, 21 ... X-axis base, 22 ... X-axis guide rail, 23 ... X-axis linear guide, 24 ... X table, 25 ... X-axis drive means, 26 ... Y-axis guide rail, 27 ... Y-axis linear guide, 28 ... Y table, 29 ... Z-axis guide rail, 30 ... Z-axis drive means (ball screw), 31 ... Z table, 32 ... θ-axis motor, 33 ... θ Spindle, 34 ... wafer table, 41 ... truing grindstone, 50 ... grinding wheel rotating unit, 51 ... peripheral grindstone spindle, 52 ... peripheral processing grindstone, 53 ... turntable, 54 ... periphery precision spindle, 55 ... peripheral precision grinding wheel, 56 Peripheral precision motor, 57 ... Notch precision spindle, 58 ... Notch precision grinding wheel, 59 ... Notch precision motor, 60 ... Notch coarse spindle, 61 ... notch rough grinding wheel, 62 ... notch rough grinding motor, 63 ... grinding wheel rotating unit base, 64 ... (turntable) rotating shaft, 71 ... nozzle, 72 ... drainage collecting means, 73 ... tank, 74 ... pump, 81 ... Fatty acid salt, 82 ... Water, 83 ... Fatty acid salt aqueous solution, 84 ... Sealed container (vacuum container), 85 ... Vacuum pump, 86 ... Bubble, 91 ... Whetstone for Orifura grinding (straight and corner grinding wheel), 92 ... Grinding Groove for grinding, 93 ... Coarse grinding wheel, 94 ... Groove for grinding, 200 ... Aqueous fatty acid salt solution, 201 ... Water, 202 ... Fatty acid salt (fatty acid sodium), 203 ... Resin (PTFE), 204 ... Abrasive grain, 205 ... Pore , CH: (peripheral processing grindstone) axis, CW: (wafer table) rotation axis, W: wafer, θ: wafer table rotation direction.

Claims (12)

In a grinding wheel that is used by water cooling at the time of chamfering a semiconductor wafer, a grindstone is formed with abrasive grains and a resin-based binder having a large number of pores, and the pores are vacuum impregnated with a fatty acid salt as a lubricant.
The resin-based binder is a fluorine-based binder, and the fatty acid salt is vacuum-impregnated into the pores in an aqueous solution having a boiling temperature of 80 ° C. or higher and lower than the boiling temperature at atmospheric pressure, and then naturally dried to convert the fatty acid salt into the pores. A grinding wheel characterized in that it is held on the surface.   The resin binder is PTFE (tetrafluoroethylene resin), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether), FEP (tetrafluoroethylene / hexafluoropropylene copolymer (4.6 fluoride)), ETFE. (Tetrafluoroethylene / ethylene copolymer), PVDF (polyvinylidene fluoride (difluoride)), PCTFE (polychlorotrifluoroethylene (trifluoride)), ECTFE (chlorotrifluoroethylene / ethylene copolymer) The grinding wheel according to claim 1, which is at least one of them.   3. The grinding wheel according to claim 1, wherein the fatty acid salt is a potassium salt or sodium salt of at least one of lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid.   The grinding wheel according to claim 3, wherein the concentration of the aqueous solution of the fatty acid salt used during vacuum impregnation is 5 to 40 wt%.   The grinding wheel according to claim 3, wherein the concentration of the aqueous solution of the fatty acid salt used in vacuum impregnation is 10 to 30 wt%.   The grinding wheel according to claim 3, wherein the concentration of the aqueous solution of the fatty acid salt used in vacuum impregnation is 15 to 20 wt%.   The grinding wheel according to any one of claims 4 to 6, wherein the temperature of the aqueous solution of the fatty acid salt used at the time of vacuum impregnation is equal to or higher than the Kraft point temperature.   The grinding wheel according to any one of claims 1 to 7, wherein the amount of vacuum impregnation of the fatty acid salt is 30 to 50% of the volume of the pores. A method for producing a grinding wheel, which is used by cooling water during chamfering of a semiconductor wafer, forms a grindstone portion with abrasive grains and a resin-based binder having a large number of pores, and vacuum impregnates the pores with a fatty acid salt as a lubricant. In
The fatty acid salt aqueous solution at 80 ° C. to 90 ° C. is prepared, the grinding wheel is immersed in the fatty acid salt aqueous solution, and the air in the grinding wheel is changed to 0.13 to 1.33 kPa in the fatty acid salt aqueous solution. A method for producing a grinding wheel characterized by being substituted and naturally dried in a normal temperature air environment.   The concentration of the aqueous fatty acid salt solution is 5 to 10 wt%, and the fatty acid salt is a potassium salt or sodium salt of at least one of lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid. A method for manufacturing a grinding wheel according to claim 9.   The resin-based binder is PTFE (tetrafluoroethylene resin), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether), FEP (tetrafluoroethylene / hexafluoropropylene copolymer (4.6 fluoride)), ETFE ( Tetrafluoroethylene / ethylene copolymer), PVDF (polyvinylidene fluoride (difluoride)), PCTFE (polychlorotrifluoroethylene (trifluoride)), ECTFE (chlorotrifluoroethylene / ethylene copolymer) The method for producing a grinding wheel according to claim 9 or 10, which is any one of the above. A wafer table for holding a wafer, a rough grinding wheel for grinding the outer periphery of the wafer, a fine grinding wheel, and moving the wafer table in the X, Y, and Z directions to face the rough grinding wheel and the fine grinding wheel A moving means, a truing grindstone used for forming the shape of the rough grinding wheel and the fine grinding wheel, and heat generated on the contact surface with the wafer during grinding by the rough grinding wheel and the fine grinding wheel. In a wafer chamfering apparatus provided with water cooling means for radiating heat,
The wafer chamfering apparatus, wherein at least one of the rough grinding wheel and the fine grinding wheel is the grinding wheel according to any one of claims 1 to 8.