JP5357477B2 - Grinding method and grinding apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To grind a workpiece to a target finishing thickness with high accuracy without being influenced by an elastic change caused during grinding. <P>SOLUTION: A grinding means grinds the workpiece till measured data obtained by a thickness measuring means shows a target thickness set to become the target finish thickness of the workpiece while measuring the thickness of the workpiece by the thickness measuring means. After termination of a grinding process, the thickness measuring means measures the real thickness of the workpiece in a state that the grinding means is retracted from the workpiece after grinding, the real thickness is compared with a target finish thickness, and the target thickness is corrected. Thereafter, the workpiece is ground according to the corrected target thickness. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a grinding method and a grinding apparatus for grinding a thin plate-like workpiece such as a semiconductor wafer to a predetermined thickness.

  In the semiconductor device manufacturing process, a large number of rectangular areas are defined on the surface of a disk-shaped semiconductor wafer (hereinafter referred to as a wafer) by grid-like division lines, and electronic circuits such as ICs and LSIs are formed on the surface of these rectangular areas. After the formation, all the dividing lines are cut, that is, diced to obtain a large number of semiconductor chips from one wafer. The semiconductor chip thus obtained is packaged by resin sealing and widely used in various electric / electronic devices such as mobile phones and PCs (personal computers).

  In such a manufacturing process, prior to dicing into a large number of semiconductor chips, the back surface opposite to the surface on which the electronic circuit is formed is ground and thinned to a predetermined thickness. Thinning of the wafer is performed for the purpose of further reducing the size and weight of the equipment and improving heat dissipation. For example, the thickness of the wafer is reduced from about 700 μm to about 50 to 100 μm. It is done.

  The backside grinding of the wafer is usually performed by using a grinding device that is configured to press the grinding wheel against the backside of the wafer held on the chuck table while rotating it. Measurement is performed by a measuring means, and when the measured value reaches a desired value, the grinding wheel is separated from the wafer (see Patent Document 1).

JP 2000-6018 A

  Therefore, even when the thickness measured by the thickness measuring means reaches the desired value, the actual thickness differs from the desired value, and an error may occur in the finished thickness. It was speculated that the thickness error after grinding was mainly caused by elastic fluctuations that occurred when grinding while pressing a rotating grinding wheel against a wafer and applying a load.

  In other words, when grinding the wafer back surface, the back surface to be ground is exposed, so the front side of the wafer is aligned with the chuck table. The surface is protected with a protective tape. The measured value by the thickness measuring means is the total thickness of the protective tape and the wafer, and the value obtained by subtracting the known thickness of the protective tape from the measured value is the thickness of the wafer during grinding. Is done.

  However, during the grinding of the wafer, the protective tape may be elastically deformed and thinned by receiving the above load, and even if the measured value of the thickness measuring means reaches the desired thickness, the actual thickness of the wafer is reduced. This means that it is thicker than desired. In addition, the wafer itself is slightly crushed by receiving the load of the grinding wheel, and when the grinding is finished and the load is released, a springback phenomenon occurs and the wafer thickness returns to the original state. Also in this case, the grinding is finished while the thickness of the wafer is thicker than the actual thickness.

  In FIG. 9, the wafer 1 with the protective tape 5 attached to the surface is held on the chuck table 110 with the protective tape 5 side down, and the grinding wheel 120 is pressed against the back surface (upper surface in the figure) of the wafer 1 for grinding. Then, when the grinding wheel 120 is separated from the wafer 1, a state in which the wafer 1 and the protective tape 5 are spring-backed is schematically shown. Conventionally, the thickness is measured in the grinding state on the left side of FIG. 9, but the actual thickness is thicker than that in the grinding state as shown on the right side.

  In addition to elastic deformation of materials such as protective tape and wafers, the chuck table slightly sinks due to the load of the grinding wheel, and conversely, the grinding wheel side receives a repulsive force from the chuck table side and moves upward. An error may occur in the wafer measurement value by the thickness measurement means due to the occurrence of a behavior such as slightly lifting.

  The present invention has been made in view of the above circumstances, and a grinding method and grinding capable of grinding a workpiece to a target finish thickness with high accuracy without being affected by the elastic fluctuation as described above. The object is to provide a device.

The grinding method of the present invention includes a holding means having a holding surface for holding a work to which a protective tape is attached, a grinding means for grinding the work held by the holding means, and a thickness of the work held by the holding means. A grinding method comprising grinding a workpiece to reduce the thickness by a grinding device comprising thickness measuring means for detecting thickness, wherein the workpiece is held on the holding surface of the holding means via a protective tape , While measuring the thickness of the work held on the holding surface with the thickness measuring means, until the measurement data by the thickness measuring means reaches the target thickness set to the target finish thickness of the work A grinding process for grinding the workpiece by the grinding means, and after the grinding process is finished, the actual thickness of the workpiece is measured by the thickness measuring means in a state where the grinding means is retracted from the ground workpiece and no grinding load is applied. Reality A measurement step, by comparing the actual thickness and the target finished thickness, is characterized by comprising at least a correction step of correcting the target thickness.

According to the grinding method of the present invention, the target thickness corresponding to the target finish thickness of the workpiece is set, and the grinding means grinds the workpiece until the measurement data of the thickness measuring means reaches the target thickness ( Grinding process). Subsequently, the thickness of the workpiece is measured in a state where the grinding means is retracted from the workpiece and no grinding load is applied (actual thickness measurement step). In this actual thickness measurement process, the grinding means is retracted from the workpiece so that no grinding load is applied. Therefore, the measured value is not affected by the elastic fluctuation caused by the load from the grinding means. The thickness, that is, the actual thickness. Next, the actual thickness is compared with the target finish thickness, a correction value that is the difference between the actual thickness and the target thickness is obtained. This is the pre-grinding for obtaining data to obtain the correction value and correct the target thickness. After that, the workpiece is ground again according to the corrected target thickness. To be ground. Therefore, it is possible to grind the workpiece to the target finish thickness with high accuracy without being affected by the elastic fluctuation caused by the load from the grinding means.

Next, the grinding apparatus of the present invention can suitably carry out the above grinding method, and has a holding means having a holding surface for holding the workpiece with the protective tape attached thereto via the protective tape , Grinding means for grinding the work held by the holding means, grinding feed means for reducing the thickness of the work by grinding and feeding the grinding means in a direction perpendicular to the holding surface, and thickness of the work held by the holding means In a grinding apparatus, comprising: a thickness measuring means for detecting the measurement data; and a control means for controlling the grinding means and the grinding feed means based on the measurement data supplied with the measurement data measured by the thickness measurement means, control means includes a first data storage unit for storing the set target thickness data so the work becomes the target finished thickness, after grinding completion to the work, the grinding load is either grinding means from the workpiece is retracted A second data storage unit for storing real thickness data of the workpiece thickness measuring means has measured at al absence, and a calculation unit that compares with the target finished thickness real thickness data for calculating a correction value And feeding means is controlled based on the corrected target thickness data in which the correction value is reflected in the target thickness data.

  In the grinding apparatus according to the present invention, the grinding means includes a roughing portion for rough grinding and a finishing portion for finish grinding, and the holding means is sequentially sent to the roughing portion and the finishing portion. The thickness measuring means is held by the first thickness measuring section for measuring the thickness of the work held by the holding means positioned at the rough machining section and the holding means positioned at the finishing section. A second thickness measuring unit for measuring the thickness of the workpiece, and the second data storage unit includes a configuration for storing actual thickness data measured by the second thickness measuring unit.

According to the present invention, since the measured actual thickness of the workpiece after grinding is measured in a state where the grinding means is retracted and no grinding load is applied, it is affected by the elastic fluctuation caused by the load from the grinding means. The actual thickness is compared with the target finish thickness, and the target thickness is set and ground again. Therefore, the target is accurately affected without being affected by the elastic fluctuations described above. There is an effect that the workpiece can be ground to the finished thickness.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[1] Semiconductor wafer First, the semiconductor wafer shown in FIG. 1 will be described. This semiconductor wafer 1 (hereinafter referred to as wafer 1) is a workpiece in one embodiment, and is made of a single crystal material such as silicon, and has a thickness before grinding of, for example, about 700 μm. A plurality of rectangular chips 3 are partitioned on the surface of the wafer 1 by grid-like division lines 2. Electronic circuits (not shown) such as ICs and LSIs are formed on the surfaces of these chips 3. A V-shaped notch 4 indicating a semiconductor crystal orientation is formed at a predetermined location on the peripheral surface of the wafer 1.

  The back surface of the wafer 1 is ground by the wafer grinding apparatus 10 shown in FIG. 2 and thinned to a thickness of about 50 to 100 μm, for example. A protective tape 5 is attached to the entire surface of the wafer 1 provided to the wafer grinding apparatus 10 for protecting the electronic circuit. As the protective tape 5, for example, one having a configuration in which an adhesive of about 5 to 20 μm is applied to one side of a soft resin base sheet such as polyolefin having a thickness of about 70 to 200 μm is used, and the adhesive is applied to the surface of the wafer 1. Attached together.

[2] Wafer Grinding Device A wafer grinding device 10 shown in FIG. 2 sucks and holds the wafer 1 on a vacuum suction chuck table (holding means) 30 and holds two grinding units (for rough grinding and finish grinding). 40A and 40B are used to sequentially perform rough grinding and finish grinding on the back surface of the wafer 1. Hereinafter, the configuration and basic operation of the wafer grinding apparatus 10 will be described.

  Reference numeral 11 in FIG. 2 denotes a processing stage for grinding the wafer 1. The wafer 1 before grinding is supplied to the processing stage 11 on the front side in the Y direction of the processing stage 11, and the wafer 1 after grinding is supplied. A supply / recovery stage 12 is also provided.

Two elevators 13A and 13B arranged in the X direction are installed at the end of the supply / collection stage 12 on the front side in the Y direction. These elevators 13A, among 13B, the X-direction front side of the elevator 13A, supply cassette 14A for accommodating the wafer 1 of multiple previous back grinding is set. Further, a recovery cassette 14B for storing the wafer 1 after back surface grinding is set in the elevator 13B on the back side in the X direction. These cassettes 14A and 14B have the same configuration and are provided with trays for storing wafers 1 in a stacked state.

  The wafer 1 stored in the supply cassette 14A is positioned at a predetermined extraction height position by raising and lowering the elevator 13A. Then, the wafer 1 is taken out from the supply cassette 14A by the transfer robot 15 and temporarily placed on the temporary placement table 16 provided on the supply / recovery stage 12 with the back surface of the wafer 1 facing upward. The The wafer 1 placed on the temporary placement table 16 is positioned at a certain transfer start position.

  A turntable 17 that is rotationally driven in the R direction is provided on the processing stage 11. A plurality of (in this case, three) disk-shaped chuck tables 30 are arranged on the outer peripheral portion of the turntable 17 at equal intervals in the circumferential direction. As shown in FIG. 4, the chuck table 30 has a top surface 31 a of a frame 31 fitted with a suction portion 32 made of a porous material. ) 32a is formed on the same horizontal plane. When the chuck table 30 is operated in vacuum, the air above the suction unit 32 is sucked, whereby the wafer 1 is sucked and held on the upper surface 32 a of the suction unit 32. Each chuck table 30 is rotatably supported by the turntable 17 and is rotated in one direction or both directions by a rotation driving mechanism (not shown).

  The wafer 1 positioned on the temporary placement table 16 is picked up from the temporary placement table 16 by the supply means 20 and is transported to above the one chuck table 30 in the vacuum operation state positioned at the wafer attachment / detachment position. The wafer 1 is placed and held concentrically on the chuck table 30 with the back surface of the wafer 1 facing up. The wafer 1 held on the chuck table 30 is protected from the electronic circuit formed on the surface because the protective tape 5 adhered to the surface contacts the chuck table 30.

  The wafer attachment / detachment position is a position where the chuck table 30 is closest to the supply / collection stage 12, and the chuck table 30 is positioned at the wafer attachment / detachment position by the rotation of the turntable 17. The supply means 20 is provided at a position of the supply / collection stage 12 close to the wafer attachment / detachment position.

  The supply means 20 has a horizontally extending arm 22 fixed to a rotary shaft 21 extending in the Z direction that is rotatable and vertically movable, and a vacuum suction type suction pad 23 is attached to the tip of the arm 22. It is provided. According to this supply means 20, the suction shaft 23 is positioned above the wafer 1 on the temporary placement table 16 by rotating the rotary shaft 21 and turning the arm 22, and then the rotary shaft 21 is lowered and moved downward. By performing a vacuum operation in which air is sucked from the suction surface of the suction pad 23 facing, the wafer 1 is sucked and held on the suction surface. When the wafer 1 on the temporary placement table 16 is held by the suction pad 23, the rotating shaft 21 is raised, the arm 22 is rotated, and the wafer 1 is transported to the wafer attaching / detaching position, where the rotating shaft 21 is lowered, The vacuum operation is stopped. Thus, the wafer 1 is placed on the chuck table 30 that is operated in vacuum.

  The wafer 1 held on the chuck table 30 is sent to a primary processing position (rough processing portion) below the rough grinding unit 40A when the turntable 17 rotates by a predetermined angle in the R direction. The back surface of the wafer 1 is roughly ground by the grinding unit 40A. Next, the turntable 17 is again rotated by a predetermined angle in the R direction to feed the wafer 1 to a secondary processing position (finishing portion) below the finishing grinding unit 40B. At this position, the grinding unit 40B The back surface of the wafer 1 is finish ground.

  Two columns 50A and 50B arranged in the X direction are erected at the end of the processing stage 11 on the back side in the Y direction, and the grinding units 40A and 40B are respectively Z in front of the columns 50A and 50B. It can be moved up and down in the direction (vertical direction). Each grinding unit 40A, 40B is slidably mounted via a slider 52 on a guide 51 extending in the Z direction provided on the front surface of each column 50A, 50B, and is driven by a servo motor 53. The feed mechanism (grind feed means) 54 moves up and down in the Z direction via the slider 52.

  Each of the grinding units 40A and 40B has the same configuration, and is distinguished by the fact that the grindstones to be mounted are different for rough grinding and finish grinding. The grinding units 40A and 40B have a cylindrical spindle housing 41 whose axial direction extends in the Z direction, and a spindle shaft (not shown) that is rotationally driven by a spindle motor 42 is supported in the spindle housing 41. ing. A grindstone wheel 44 is attached to the lower end of the spindle shaft via a flange 43.

  On the lower surface of the grindstone wheel 44, a plurality of grindstones 45 are arranged in an annular shape. The grinding surface formed by the lower surfaces of these grinding wheels 45 is set to be horizontal and orthogonal to the axial direction of the spindle shaft. Therefore, the ground surface is parallel to the upper surface of the chuck table 30. As the grindstone 45, for example, a glass-bonded material mixed with diamond abrasive grains, molded, and sintered is used.

  As the grindstone 45 attached to the grinding unit 40A for rough grinding, for example, a grindstone containing relatively coarse abrasive grains of about # 330 to # 400 is used. Further, as the grindstone 45 attached to the grinding unit 40B for finish grinding, for example, a grindstone containing relatively fine abrasive grains of about # 3000 to # 8000 is used. Each of the grinding units 40A and 40B is provided with a grinding water supply mechanism (not shown) for supplying grinding water for cooling and lubrication of the surface to be ground or discharging grinding waste.

  The grindstone wheel 44 rotates integrally with the spindle shaft, and the grinding outer diameter of the rotating grindstone 45 is set larger than the diameter of the wafer 1. Further, the processing position of the wafer 1 determined by rotating the turntable 17 by a predetermined angle is that the cutting edge, which is the lower surface of the grindstone 45, passes through the rotation center of the wafer 1 and the wafer 1 that rotates as the chuck table 30 rotates. It is set at a position where the entire back surface can be ground.

  The back surface of the wafer 1 is ground by each grinding unit 40A, 40B at each processing position of rough grinding and finish grinding. In the backside grinding, the chuck table 30 rotates to rotate the wafer 1 and the feed mechanism 54 grinds and feeds the grinding unit 40A (40B) downward while the grinding wheel 45 of the rotating grinding wheel 44 is exposed to the wafer 1. It is done by pressing against the back side.

  The wafer 1 is thinned to a target finish thickness through rough grinding and finish grinding. In rough grinding, the thickness after finish grinding is ground to, for example, 30 to 40 μm before, and the rest is ground by finish grinding. The thickness of the wafer 1 includes a first thickness measurement gauge (thickness measurement means, first thickness measurement unit) 60A and a second thickness measurement gauge (which are provided near the primary processing position and the secondary processing position, respectively). (Thickness measuring means, second thickness measuring section) 60B. The back surface grinding of the wafer 1 is performed while measuring the thickness of the wafer 1 with the thickness measurement gauges 60A and 60B, and the grinding feed amount by the feed mechanism 54 based on the measurement values of the thickness measurement gauges 60A and 60B. Is controlled by the control means 100. The control method relates to the present invention and will be described later.

  When the wafer 1 is thinned from rough grinding to finish grinding to the target finish, the wafer 1 is recovered as follows. First, the finish grinding unit 40B is raised and retracted from the wafer 1, and then the turntable 17 is rotated by a predetermined angle in the R direction, whereby the wafer 1 is returned to the wafer attaching / detaching position. Next, the vacuum operation of the chuck table 30 is stopped, and then the wafer 1 is transferred to the spinner type cleaning device 80 by the recovery means 70 provided in the supply / recovery stage 12.

  The collecting means 70 is disposed adjacent to the back side of the supply means 20 in the X direction. The recovery means 70 has the same configuration as the supply means 20, and includes a rotary shaft 71 that can be moved up and down, a horizontal arm 72 fixed to the rotary shaft 71, and a vacuum provided at the tip of the arm 72. The wafer 1 is sucked and held by the suction pad 73, and is transported to the spinner cleaning device 80 as the arm 73 rotates.

  In the spinner type cleaning device 80, the cleaning water is supplied to the wafer 1 held and rotated by the vacuum suction type spinner table 81 to clean the wafer 1, and then the cleaning water is supplied while the spinner table 81 is rotated. Processing such as stopping and drying the wafer 1 is performed.

  The above process is continuously repeated on the wafer 1 in the supply cassette 14A, and a plurality of wafers 1 whose back surface is ground and thinned to the target finish thickness are stored in the recovery cassette 14B. Is done. Thereafter, the thinned wafer 1 is transported to the next process together with the collection cassette 14B, and finally the division planned line 2 is cut and diced into a plurality of chips 3.

[3] Wafer Thickness Measuring Means and Grinding Feed Control Means The first thickness measuring gauge 60A and the second thickness measuring gauge 60B have the same configuration as shown in FIGS. Shows a second thickness measurement gauge 60B), a post 63 erected on the processing stage 12, and two probes 61 and 62 extending from the upper end of the post 63 toward the upper side of the chuck table 30. Is. The two probes 61 and 62 are a reference probe 61 and a variable probe 62, respectively, and are attached to the post 63 so as to be swingable up and down.

  As shown in FIG. 4, the reference probe 61 is brought into contact with the upper surface 31 a of the chuck table frame 31 whose tip is not covered with the wafer 1. On the other hand, the variable probe 62 is brought into contact with the upper surface of the wafer 1 held on the chuck table 20, that is, the surface to be ground. In each of the thickness measurement gauges 60A and 60B, the height position of the chuck table 30 is detected by the reference probe 61, and the height position of the upper surface of the wafer 1 is detected by the variable probe 62. Then, the thickness of the wafer 1 is calculated based on the difference between the two detection data. In this case, since the protective tape 5 is stuck on the surface of the wafer 1, the thickness of the wafer 1 is calculated in consideration of the thickness of the protective tape 5. That is, “(detection data of fluctuation probe 62−detection data of reference probe 61) −thickness of protective tape” is the thickness of wafer 1.

  Although the first thickness measurement gauge 60A and the second thickness measurement gauge 60B are described as having the same configuration, in general, the second thickness measurement gauge 60B on the finish grinding side is the first thickness measurement on the rough grinding side. What can be measured more precisely than the gauge 60A is used. In this case, the value measured by the second thickness measurement gauge 60B is the actual thickness after finish grinding and is substantially equal to the target finish thickness.

  The feed mechanisms 54 of the rough grinding unit 40A and the finish grinding unit 40B are controlled by the control means 100. The control means 100 includes a first data storage unit 101 and a second data storage unit 102 as shown in FIG. In the first data storage unit 101, target thickness data T1 respectively set for the feed mechanism 54 of each grinding unit 40A, 40B (T1a on the rough grinding unit 40A side, T1b on the finish grinding unit 40B side). Is input and stored. The target thickness data T1 means that the feed mechanism 54 including the servo motor 53 causes the wafer 1 to have a target finish thickness T (Ta on the rough grinding grinding unit 40A side and Tb on the finishing grinding unit 40B side). The control element is, for example, data based on the distance between the cutting edge of the grindstone 45 and the chuck table 30, the rotational speed of the drive shaft of the servo motor 53, and the like.

  Each feed mechanism 54 is ground and fed in accordance with the target thickness data T1 (T1a, T1b), and the wafer 1 is set to a target finish thickness T corresponding to the target thickness data T1 (T1a, T1b). It will be ground to (Ta, Tb). In the second data storage unit 102, the wafer measured by the second thickness measurement gauge 60B after being ground by the rough grinding unit 40A and before being ground by the finishing grinding unit 40B. One actual thickness data T2b is supplied and stored. The actual thickness data T2b is thickness data in a state where the grinding unit 40B is retracted upward and the grindstone 45 is separated from the wafer 1 and no grinding load is applied to the wafer 1.

  In addition, the control unit 100 includes a calculation unit 103 and a correction unit 104. The target finish thickness Ta on the rough grinding side is input to the calculation unit 103, and the actual thickness data T2b (finishing data) of the wafer 1 measured from the second data storage unit 102 by the second thickness measurement gauge 60B. The actual thickness data before being ground by the grinding unit 40B) is supplied and stored. Then, the calculation unit 103 calculates “target finished thickness Ta−actual thickness data T2b” and sets the value as a correction value t. The correction value t is supplied to the correction unit 104, and the correction unit 104 calculates “correction value t + target thickness data T1a on the rough grinding side” to calculate corrected target thickness data T1a ′. Thereafter, the control unit 100 controls the feed mechanism 54 and the servo motor 53 of the rough grinding unit 40A according to the corrected target thickness data T1a 'calculated by the correction unit 104.

[4] Grinding Feed Control Method by Control Unit Next, the operation of the grinding process controlled by the control unit 100 will be described.
First, in the primary processing position, while the thickness of the wafer 1 is measured by the first thickness measurement gauge 60A by the rough grinding unit 40A, the grinding feed is performed according to the target thickness data T1a corresponding to the target finish thickness Ta. The When the measurement value of the first thickness measurement gauge 60A reaches the target thickness data T1a, the rough grinding is finished. Here, the description will be made assuming that the target finish thickness Ta after rough grinding is specifically 100 μm.

  Subsequently, the wafer 1 is moved to the secondary processing position. First, the grinding unit 40B is retracted upward from the wafer 1 and the grindstone 45 is separated from the wafer 1, and the wafer 1 is moved by the second thickness measuring gauge 60B. Actual thickness data T2b is measured. The measured actual thickness data T2b should match the target finish thickness Ta, but may actually differ due to the effect of elastic fluctuations that occur during rough grinding. Here, it is assumed that the actual thickness measured by the second thickness measurement gauge 60B is 105 μm.

  Next, “target finish thickness Ta (100 μm) −actual thickness data T2b (105 μm)” is calculated by the calculation unit 103, and a correction value t: −5 μm is calculated. Subsequently, “correction value t (−5 μm) + target thickness data T1a (100 μm)” is calculated by the correction unit 104, and corrected target thickness data T1a ′: 95 μm is calculated.

  This is the so-called preliminary grinding for obtaining data to obtain the true target thickness data T1a 'by obtaining the correction value t on the rough grinding side and correcting the target thickness data T1a. The pre-ground wafer 1 is collected and then ground from the wafer 1 waiting for processing in the rough grinding unit 40A according to the target thickness data T1a '. That is, the target thickness data (T1a) is corrected to 95 μm, and a new wafer 1 is roughly ground with the target of 95 μm. Although 95 μm is 5 μm thinner than the target finish thickness of 100 μm, the actual thickness is 105 μm, which is 5 μm thick. Therefore, 5 μm is actually added to 95 μm, and this is ground to the target finish thickness of 100 μm.

  After the rough grinding, the wafer 1 is finish-ground to the target thickness finish thickness Tb in accordance with the target thickness data T1b by the finish grinding grinding unit 40B at the secondary processing position.

[5] Effect of Grinding Feed Control Method According to the grinding feed control method, the thickness of the wafer 1 measured by the second thickness measurement gauge 60B at the secondary machining position on the finish grinding side in the first preliminary grinding ( (Actual thickness data) is measured in a state where the grinding unit 40B is retracted and no grinding load is applied. Therefore , the measured value is an elastic fluctuation caused in the protective tape 5, the wafer 1 or the like due to the load from the grinding unit 40B. The actual thickness of the actual wafer 1 that is not affected, that is, the actual thickness. The actual thickness data T2b after the rough grinding is compared with the target finish thickness Ta in the rough grinding, and the difference is an error on the rough grinding side due to the influence of the elastic fluctuation, that is, a value to be corrected. (Correction value t). Thus, by obtaining the correction value and correcting the target thickness data T1a on the rough grinding side, the wafer 1 after the rough grinding can be ground to the target finish thickness Ta.

  As described above, the second thickness measurement gauge 60B on the finish grinding side is more precise than the first thickness measurement gauge 60A on the rough grinding side, and the second thickness measurement gauge 60B allows the grinding unit 40B to be used. The actual thickness data T2b of the wafer 1 measured in the retracted state can be said to be a highly accurate measurement value. Therefore, the target thickness data T1a on the rough grinding side is corrected based on the actual thickness data T2b, and the thickness of the wafer 1 after rough grinding ground according to the target thickness data T1a is the target with high accuracy. It becomes the value of the finished thickness Ta. Then, by performing rough grinding precisely in this way, the wafer 1 after finish grinding also shows the value of the target finish thickness Tb with high accuracy.

  In the above embodiment, the first wafer is roughly ground to obtain the correction value t. However, the first wafer has an error after the rough grinding, and the second and subsequent wafers are non-defective. Therefore, if the first wafer to be ground satisfies the condition that the protective tape 5 is adhered with the same material and thickness, the chip 3 does not need to be formed, and the data collected in advance is not necessary. A wafer may be used.

[6] Other Grinding Feed Control Method by Control Unit In the above embodiment, the correction value t obtained by rough grinding the first wafer is reflected in the rough grinding of all the second and subsequent wafers. The correction value t is immovable. In addition to this control method, also for the third and subsequent wafer grinding, feedback control is performed in which correction values after rough grinding are calculated one by one and the correction values are sequentially used as correction values for the next rough grinding. You may go.

  That is, if the correction value obtained by roughly grinding the first wafer 1 as described above is reflected at the time of rough grinding of the second wafer, the second wafer at the time of rough grinding of the third wafer. This is a control method in which a correction value obtained by rough grinding the wafer is reflected. FIG. 6 shows the process. For example, when the second and subsequent wafers are ground, the actual thickness “T2b” of the second wafer 1 after the rough grinding is obtained at the secondary processing position. Measured with the grinding unit 40B retracted from the wafer 1 <Step S1>, and then the “target finish thickness Ta after rough grinding—actual thickness data T2b (n)” is calculated by the calculation unit 103 to obtain three sheets. A correction value t3 for the first wafer 1 is calculated <step S2>.

  Subsequently, the correction unit 104 calculates “correction value t (n + 1) + previous (n-th) target thickness data T1a” to calculate the next target thickness data T1a (n + 1) <step S3>. The third wafer 1 is roughly ground by a grinding unit 40A that operates according to the next target thickness data T1a (n + 1). Next, it is determined whether or not the number of processed wafers 1 has reached the target number <step S4>. If not reached, the process returns to the next wafer 1, and if it has reached, the grinding process is finished. Move on to processing.

  According to this control method, the correction value given at the time of rough grinding is renewed for each rough grinding, so that there is an advantage that the accuracy of the final thickness after final finish grinding can be further increased. .

[7] Other Embodiments of Thickness Measuring Means In the above embodiment, the second thickness measuring gauge 60B on the finish grinding side brings the probe into contact with the object in the same manner as the first thickness measuring gauge 60A on the rough grinding side. Although it is a contact type, a non-contact type is more preferable as the thickness measuring means on the finish grinding side where precise thickness measurement is required. 7 and 8 show a state in which the non-contact type second thickness measurement gauge 90 is provided at the secondary machining position on the finish grinding side.

  Examples of the non-contact type thickness measuring means include those using ultrasonic waves and those using laser light. In the ultrasonic method, an ultrasonic wave with a predetermined frequency is emitted toward one side of the wafer, and the thickness is measured from the waveform of the interference wave between the reflected wave from the wafer surface and the reflected wave from the back surface. (See JP-A-8-210833, JP-A-2006-38744, etc.). The laser beam method is based on the same principle as the ultrasonic method, and a laser beam with a predetermined frequency is irradiated toward one surface of the wafer, and the reflected wave from the front surface of the wafer and the reflection from the back surface. The thickness can be measured from the waveform of the interference wave with the wave (see JP-A-9-36093, etc.). In addition to these, an electric type using a differential transformer can also be used (see Japanese Patent No. 2999381).

  According to the non-contact type thickness measuring means, since the thickness of only the wafer can be measured without including the protective tape 5, the thickness of the wafer after finish grinding can be set to a target finish thickness with higher accuracy. Can be finished. In the contact-type thickness measuring means, the probe is still in contact with the back surface of the wafer even after finish grinding, and the probe may be damaged. However, in the non-contact type, such a scratch is applied to the wafer. There is an advantage that there is no fear.

It is a perspective view of the semiconductor wafer ground back by the wafer grinding device concerning one embodiment of the present invention. It is a perspective view of a wafer grinding device concerning one embodiment of the present invention. It is a perspective view which is a part of the wafer grinding apparatus and shows a thickness measuring means. It is a side view which shows the chuck table, thickness measurement means, and grinding means of the wafer grinding apparatus. It is a block diagram which shows the structure of the control means with which the wafer grinding device is provided. It is a flowchart which shows the control process at the time of rough grinding by another control method (feedback control) in one Embodiment. It is a perspective view of the wafer grinding device concerning other embodiments of the present invention. It is a perspective view which shows the thickness measurement means of other embodiment. It is a figure which shows typically the phenomenon which an error produces by the elastic fluctuation | variation of a protective tape and a wafer in the thickness measurement of a wafer.

Explanation of symbols

1 ... wafer (work)
DESCRIPTION OF SYMBOLS 10 ... Wafer grinding apparatus 30 ... Chuck table (holding means)
32a ... Upper surface (holding surface) of adsorption part
40A ... rough grinding unit (grinding means)
40B ... Grinding unit for finish grinding (grinding means)
54 ... Feed mechanism (grind feed means)
60A ... 1st thickness measurement gauge (thickness measurement means, 1st thickness measurement part)
60B ... Second thickness measurement gauge (thickness measurement means, second thickness measurement section)
DESCRIPTION OF SYMBOLS 100 ... Control means 101 ... 1st data storage part 102 ... 2nd data storage part 103 ... Operation part 104 ... Correction | amendment part

Claims (3)

Holding means having a holding surface for holding a workpiece to which a protective tape is attached ;
Grinding means for grinding the workpiece held by the holding means;
A grinding method comprising a grinding device comprising a thickness measuring means for detecting the thickness of the work held by the holding means, and grinding the work to reduce the thickness;
A workpiece holding step of holding the workpiece on the holding surface of the holding means via the protective tape ;
While measuring the thickness of the workpiece held on the holding surface by the thickness measuring means, the target thickness set so that the measurement data by the thickness measuring means becomes the target finish thickness of the workpiece. A grinding step of grinding the workpiece with the grinding means until
After the grinding step, the actual thickness measuring step of measuring the actual thickness of the workpiece by the thickness measuring unit in a state where the grinding unit is retracted from the ground workpiece and no grinding load is applied ;
A grinding method comprising at least a correction step of correcting the target thickness by comparing the actual thickness with the target finish thickness. Holding means having a holding surface for holding the work with the protective tape attached thereto via the protective tape ;
Grinding means for grinding the workpiece held by the holding means;
Grinding feed means for reducing the thickness of the workpiece by grinding the grinding means in a direction perpendicular to the holding surface;
A thickness measuring means for detecting the thickness of the workpiece held by the holding means;
In a grinding apparatus provided with measurement data measured by the thickness measurement means, and a control means for controlling the grinding means and the grinding feed means based on the measurement data,
The control means includes
A first data storage unit for storing target thickness data set so that the workpiece has a target finish thickness;
A second data storage unit for storing the actual thickness data of the workpiece measured by the thickness measuring unit in a state where the grinding unit is retracted from the workpiece and no grinding load is applied after the grinding of the workpiece;
A calculation unit that compares the actual thickness data with the target finish thickness to calculate a correction value;
A grinding apparatus, wherein the feeding means is controlled based on corrected target thickness data in which the correction value is reflected in the target thickness data. The grinding means has a roughing part for rough grinding and a finishing part for finish grinding,
The holding means is sequentially sent to the roughing portion and the finishing portion,
The thickness measuring unit includes a first thickness measuring unit that measures the thickness of the workpiece held by the holding unit positioned at the roughing unit, and a holding unit positioned at the finishing unit. A second thickness measuring unit for measuring the thickness of the held workpiece,
The grinding apparatus according to claim 2, wherein the second data storage unit stores the actual thickness data measured by the second thickness measurement unit.

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