JP2008062353A - Grinding method and grinding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely grind the surface of a workpiece evenly without having any influence on machining accuracy of a grinding device while a grinding stock is reduced as small as possible; and to reduce costs of a substrate material or the like. <P>SOLUTION: The surface of a wafer 1 is ground by a cup wheel 35 of a grinding unit 30 while the thickness of the wafer 1 adsorbed and retained on a chuck table 20 is measured by a thickness measuring gauge 50, and grinding of the wafer 1 is controlled to stop when fluctuation in thickness (maximum measuring value minus minimum measuring value) recognized on a recognition section 61 reaches a predesignated target value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a grinding method and a grinding apparatus for grinding a surface of a thin plate-like substrate such as a semiconductor wafer to process the surface flatly.

  Thin semiconductor substrates used as materials for semiconductors and electronic components include, for example, those made of a single crystal material such as silicon and those made of a compound having a plurality of elements. These substrates slice raw material ingots. Then, after chamfering, lapping, and etching, grinding is performed to make one side flat and parallel (see Patent Document 1, etc.). This type of substrate grinding process is performed by adsorbing and holding the substrate on a vacuum chuck type chuck table having a holding surface made of porous ceramics, and grinding by pressing a grindstone on the exposed surface opposite the adsorption surface. How to do is known. According to this method, since the exposed surface is ground by adsorbing the substrate to the holding surface of the chuck table that has been flattened, even if the flatness and parallelism of both surfaces deteriorate due to pre-processing such as etching, these surface characteristics There is an advantage that can be improved.

  By the way, in such a grinding process, by reducing the grinding allowance (the thickness to be removed by grinding, the processing amount) as much as possible, the basic unit is reduced and the cost is reduced. In addition, even when grinding is performed again for the purpose of reuse after being used for a certain purpose after grinding, it is possible to increase the number of reuses by suppressing the grinding cost.

JP 2002-25950 A

  As described above, it is preferable to minimize the grinding allowance due to the grinding process in order to improve the flatness of the substrate surface and the parallelism of both surfaces. At present, for example, 5 μm or more is required due to the limit. Specifically, the mechanical accuracy is the accuracy of the thickness measurement gauge that measures the thickness of the substrate being ground, and the porous ceramic holding surface of the chuck table sinks when receiving a high pressing load from the grinding wheel. Is mentioned.

  For example, the surface of the substrate after grinding is usually subjected to a polishing process in order to remove mechanical damage that remains due to grinding and loses strength, but when the polishing allowance at this time is large, the substrate surface is finished flat. The accuracy of the ground surface will be inferior. Therefore, in order to minimize the amount of polishing during the polishing process, finish grinding is performed with a grindstone containing fine abrasive grains of, for example, # 2000 or more in the final stage of the grinding process. When grinding with a grindstone with a high count, the grinding force is low, so the grinding stone is pressed against the substrate surface by such an operation. In the initial stage, the grinding process does not start, and a phenomenon occurs in which the substrate is ground at a time when a necessary load is applied.

  For this reason, if the displacement of the thickness of the substrate being ground is monitored by a thickness measurement gauge, for example, the grinding allowance is set to 3 μm, and it is confirmed that the substrate surface has been cut by 3 μm by the thickness measurement gauge. Even if the feeding operation of the grinding device that supports the grindstone is stopped after that, the pressing operation toward the substrate still remains on the grindstone side, so that the cutting operation does not stop immediately. As a result, the cutting is finally stopped when, for example, 2 to 3 μm deeper than the set 3 μm is ground, resulting in an increase in the grinding allowance.

  In addition, when the grinding processing allowance is set to about 3 μm, the accurate thickness cannot be measured due to variations in the measurement accuracy of the thickness measurement gauge or the sinking of the holding surface of the chuck table that receives the pressing load of the grindstone as described above. As a result, if the thickness is already reduced by 3 μm, it is erroneously recognized, and a problem such that the grinding process does not proceed occurs. These harmful effects do not occur if the grinding allowance is about 20 to 30 μm or more, for example.

  Therefore, the present invention can surely grind the surface of the workpiece flatly while reducing the grinding allowance as much as possible without being affected by the mechanical accuracy of the grinding apparatus, thereby reducing the cost of the substrate material and the like. It aims at providing the grinding method and grinding device which can contribute to reduction.

  The grinding method of the present invention holds a plate-like workpiece on a rotatable holding table, and grinds the surface of the workpiece to a predetermined thickness with a grinding tool while rotating the workpiece together with the holding table. A grinding method, wherein the surface position of the workpiece held on the holding table is measured over the entire circumference by the surface position measuring means before grinding, and the surface is the difference between the maximum measured value and the minimum measured value at this time. When the position variation value exceeds a preset target surface position variation value, start grinding the surface of the workpiece with a grinding tool while measuring the surface position of the workpiece by the surface position measuring means, Along with grinding, when the surface position variation value measured by the surface position measuring means reaches the target surface position variation value, the grinding of the workpiece is stopped.

  The grinding method of the present invention is not a method of grinding the surface until the target machining allowance is reached while detecting the thickness of the workpiece as in the prior art, but the target value is set in the workpiece. The surface position variation value is the difference between the maximum measurement value and the minimum measurement value of the surface position (surface height position). The surface position variation value is larger before and after the grinding process than before and after the grinding process, and becomes smaller as the grinding is performed, that is, the variation becomes smaller. The present invention utilizes this principle, and sets a predetermined target value for the surface position variation value, measures the surface position by the surface position measuring means, and obtains the surface position variation value one by one. When the calculated surface position variation value reaches the target value, the grinding is stopped.

  The surface position variation value according to the present invention can always be reliably and accurately obtained as a value for setting the grinding allowance without being affected by the mechanical accuracy of the grinding apparatus as described above. Therefore, it is possible to reliably grind the surface of the workpiece to a state extremely close to flatness while minimizing the grinding allowance.

  Next, a grinding apparatus of the present invention is an apparatus that can suitably carry out the grinding method of the present invention, a rotatable holding table having a holding surface for adsorbing and holding a plate-like workpiece, Grinding means for grinding a workpiece with a grinding tool that is disposed opposite to the holding table and has a tool rotation axis parallel to the rotation axis of the holding table and is concentric with the tool rotation axis, and the grinding In a grinding apparatus comprising a feed means for pressing a grinding tool against a work piece held on a holding table by a feed operation for moving the means closer to and away from the holding table, and the workpiece held on the holding table. It has surface position measuring means for measuring the surface position of the work piece, and the maximum when the surface position of the work piece held while rotating the holding table is measured over the entire circumference by the surface position measuring means. When the difference between the constant value and the minimum measured value is the surface position variation value, the storage means for storing the target surface position variation value as the target surface position variation value and the surface position variation value before and during grinding are recognized. The recognition unit and the surface position variation value recognized by the recognition unit before grinding are compared with the target surface position variation value stored by the storage unit, and the storage unit stores the surface position variation value recognized by the recognition unit. When the target surface position variation value is exceeded, the feed means is operated to start grinding the surface of the work piece by the grinding tool, and the surface position variation value recognized by the recognition means becomes the target surface position variation value. And a control means for stopping the feeding operation of the feeding means when it arrives.

  According to the present invention, it is possible to reliably grind the surface of a workpiece flatly while being as small as possible without being affected by the mechanical accuracy of the grinding apparatus. There exists an effect that it can contribute to cost reduction.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[1] Configuration and Schematic Operation of Grinding Apparatus FIG. 1 shows a grinding apparatus that uses a semiconductor wafer such as a silicon wafer (hereinafter abbreviated as a wafer) as a workpiece and grinds the surface of the wafer. FIG. 2 shows an example of a wafer to be ground. This wafer 1 is obtained by slicing an ingot of a raw material, adjusted in thickness by lapping, and then mechanical damage on both sides formed by lapping. The material stage is the layer removed by etching. A V-shaped notch 2 indicating a crystal orientation is formed on the outer peripheral edge of the wafer 1. The thickness of the wafer 1 is, for example, about 700 μm, but the in-plane thickness is not uniform, and there is unevenness of about 2 to 3 μm by etching.

  The grinding apparatus 10 shown in FIG. 1 includes a rectangular parallelepiped base 11 whose upper surface is horizontal. In FIG. 1, the longitudinal direction, the width direction, and the vertical direction of the base 11 are shown by the Y direction, the X direction, and the Z direction, respectively. At one end portion of the base 11 in the Y direction, a column 12 arranged in the X direction is erected in a pair. On the base 11, a processing area 11A for grinding the wafer 1 is provided on the column 12 side in the Y direction, and the wafer 1 before processing is supplied to the processing area 11A on the side opposite to the column 12, and An attachment / detachment area 11B for collecting the processed wafer 1 is provided.

  In the processing area 11A, a disk-shaped turntable 13 whose rotation axis is parallel to the Z direction and whose upper surface is horizontal is rotatably provided. The turntable 13 is rotated in the direction of arrow R by a rotation drive mechanism (not shown). A plurality of (in this case, three) disk-shaped chuck tables (holding tables) 20 whose rotation axis is parallel to the Z direction and whose upper surface is horizontal are equidistantly spaced in the circumferential direction on the outer periphery of the turntable 13. It is arranged so that it can rotate freely.

  These chuck tables 20 are of a generally known vacuum chuck type and suck and hold the wafer 1 placed on the upper surface. As shown in FIG. 3, most of the chuck table 20 excluding the outer peripheral portion of the upper surface 20 a that is a wafer holding surface is formed as a suction area 21 formed of a porous member. The wafer 1 is adsorbed and held on the surface. Each chuck table 20 is independently rotated or rotated in one direction or both directions by a rotation drive mechanism (not shown) provided in the turntable 13, and revolves when the turntable 13 rotates. It becomes a state.

  As shown in FIG. 1, in a state where two chuck tables 20 are arranged in the X direction on the column 12 side, a grinding unit (grinding means) 30 is disposed immediately above the chuck tables 20. Each chuck table 20 is positioned at three positions, that is, a grinding position below each grinding unit 30 and an attachment / detachment position closest to the attachment / detachment area 11 </ b> B by rotation of the turntable 13. There are two grinding positions, and a grinding unit 30 is provided for each of these grinding positions. In this case, the grinding position on the upstream side (back side in FIG. 1) in the transfer direction indicated by the arrow R of the chuck table 20 by the rotation of the turntable 13 is the primary grinding position, and the downstream grinding position is the secondary grinding position. .

  Each grinding unit 30 is fixed to a slider 40 attached to the column 12 so as to be movable up and down. The slider 40 is slidably mounted on a guide rail 41 extending in the Z direction, and can be moved in the Z direction by a ball screw type feed mechanism (feed means) 43 driven by a servo motor 42. Each grinding unit 30 is moved up and down in the Z direction by the feed mechanism 43 and lowered to grind the exposed surface of the wafer 1 held by the chuck table 20 by a feed operation that approaches the chuck table 20.

  As shown in FIG. 3, the grinding unit 30 includes a cylindrical spindle housing 31 whose axial direction extends in the Z direction, and a spindle shaft portion (tool rotation axis) that is coaxially and rotatably supported in the spindle housing 31. ) 32, a motor 33 that is fixed to the upper end portion of the spindle housing 31 and rotationally drives the spindle shaft portion 32, and a disk-like flange 34 that is coaxially fixed to the lower end of the spindle shaft portion 32. . A cup wheel (grinding tool) 35 is detachably attached to the flange 34 by attachment means such as screwing.

  The cup wheel 35 is configured such that a plurality of grindstones 37 are annularly arranged and fixed to the lower end surface of a disk-shaped frame 36 over the entire outer periphery of the lower end surface. A cup wheel 35 including a grindstone 37 containing abrasive grains # 2000 to # 8000 is attached to the flange 34 of the grinding unit 30 for primary grinding disposed above the primary grinding position. Further, a cup wheel 35 having a grinding wheel 37 containing abrasive grains of, for example, # 10000 or more is attached to the flange 34 of the grinding unit 30 for secondary grinding disposed above the secondary grinding position. The flange 34 and the cup wheel 35 are provided with a grinding water supply mechanism (not shown) for supplying grinding water for cooling and lubrication of the grinding surface or discharging grinding scraps, and a water supply line is connected to the mechanism. Yes. The grinding outer diameter of the cup wheel 35, that is, the diameter of the outer peripheral edge of the plurality of grindstones 37 is set to be approximately equal to or slightly larger than the radius of the wafer 1.

  Reference numeral 50 in FIG. 3 denotes a thickness measurement gauge (surface position measuring means) configured by a combination of a reference side height gauge 51 and a variable side height gauge 52. The reference-side height gauge 51 detects the height position of the upper surface 20a when the tip of the swinging probe 51a contacts the upper surface 20a of the chuck table 20. The variation-side height gauge 52 detects the height position of the upper surface of the wafer 1 when the tip of the oscillating probe 52 a comes into contact with the upper surface of the wafer 1 held by the chuck table 20, that is, the surface to be ground.

  As shown in FIG. 1, a measurement signal indicating the height position measured by each of the height gauges 51 and 52 of the thickness measurement gauge 50 is supplied to a recognition unit (recognition means) 61. The recognition unit 61 calculates a thickness variation value (surface position variation value) that is a difference between the maximum measurement value and the minimum measurement value in each thickness measurement gauge 50 on the primary grinding side and the secondary grinding side, and the thickness. The variation value is supplied to the control unit (control unit) 62 and processed. The control unit 62 controls the servo motor 42 of the feed mechanism 43. Furthermore, the control unit 62 is connected to a storage unit (storage unit) 63 that stores predetermined information and is supplied with the stored information.

  The grinding unit 30 moves down at a predetermined speed (for example, about 0.3 μm / second) while the cup wheel 35 rotates at, for example, 3000 to 5000 rpm, so that the grindstone 37 of the cup wheel 35 presses the surface of the wafer 1, As a result, the surface is ground. During grinding, the wafer 1 is rotated together with the chuck table 20 in the same direction as the cup wheel 35 at about 10 rpm, for example.

  As shown in FIG. 4, the cup wheel 35 is positioned facing the wafer 1 so that the grindstone 37 passes through the center of the wafer 1. Due to this positional relationship, the entire surface of the wafer 1 is uniformly ground by the grindstone 37 of the cup wheel 35. The thickness of the wafer 1 before and during grinding is monitored in real time by the thickness measurement gauge 50, and the thickness variation value is calculated by the recognition unit 61.

  The wafer 1 is first ground by the grinding unit 30 at the primary grinding position, and then transferred to the secondary grinding position by the turntable 13 rotating in the R direction shown in FIG. Is subjected to secondary grinding.

  In the center of the detachable area 11B, a two-bar link pickup robot 70 that moves up and down is installed. Around the pickup robot 70, a supply cassette 71, an alignment table 72, a supply arm 73, a recovery arm 74, a spinner type cleaning device 75, and a recovery cassette 76 are arranged counterclockwise as viewed from above. ing. The cassettes 71 and 76 accommodate the plurality of wafers 1 in a horizontal posture and in a stacked state at regular intervals in the vertical direction, and are set at predetermined positions on the base 11.

  The wafer 1 to be ground is first taken out from the supply cassette 71 by the pickup robot 70, placed on the alignment table 72, and determined at a certain position. Next, the wafer 1 is picked up from the alignment table 72 by the supply arm 73 and placed on the chuck table 20 waiting at the attachment / detachment position with the surface to be ground facing up. The wafer 1 is transferred to the primary grinding position and the secondary grinding position in this order by the rotation of the turntable 13 in the R direction, and the surface is ground as described above by the grinding unit 30 at these grinding positions.

  The wafer 1 for which the secondary grinding has been completed is returned to the attaching / detaching position by further rotating the turntable 13 in the R direction. The wafer 1 on the chuck table 20 returned to the attachment / detachment position is picked up by the recovery arm 74, transferred to the cleaning device 75, washed with water and dried. The wafer 1 cleaned by the cleaning device 75 is transferred and accommodated in the collection cassette 76 by the pickup robot 70.

[2] Control operation of grinding unit by control unit Next, the operation of the grinding unit 30 controlled by the control unit 62 in primary grinding and secondary grinding will be described.
Before and during wafer grinding by the grinding unit 30, the thickness of the wafer 1 measured by the thickness measurement gauge 50 is supplied to the recognition unit 61. First, when the wafer 1 held on the chuck table 20 is transferred to each grinding position, the chuck table 20 rotates at the number of rotations during grinding, and the thickness of the wafer 1 before grinding is measured over the entire circumference. It is supplied to the recognition unit 61. The thickness measurement point of the wafer 1 is preferably an outer peripheral portion close to the outer peripheral edge as shown by a broken line in FIG.

  In the recognizing unit 61, as shown in FIG. 4A, a thickness variation value: t2-t1 that is a difference between the maximum measurement value t2 and the minimum measurement value t1 by the thickness measurement gauge 50 is calculated, and the thickness is calculated. The variation value (t2-t1) is supplied to the control unit 62. On the other hand, a target value (for example, an arbitrary value of 1 μm or less) of the thickness variation value is stored in the storage unit 63, and the control unit 62 and the thickness variation value calculated by the recognition unit 61 ( t2-t1) are compared one by one. Here, when the thickness variation value measured before grinding is equal to or less than the target value, it is determined that the surface need not be ground and grinding is avoided. When the thickness variation value measured before grinding exceeds the target value, the following grinding operation is started.

  From the state where the wafer 1 is continuously rotated together with the chuck table 20, the grinding unit 30 is lowered while the cup wheel 35 is rotating, and the grindstone 37 of the cup wheel 35 is pressed against the surface of the wafer 1 for grinding. Is started. Even during grinding of the wafer 1, the thickness of the wafer 1 is measured, and a thickness variation value is calculated and supplied to the controller 62. The thickness variation value gradually decreases with grinding, and when the thickness variation value reaches the target value stored in the storage unit 63 (FIG. 4B shows the state), the feed mechanism 43 The servo motor 42 is stopped and the feeding operation of the grinding unit 30 is stopped. Thereafter, after a certain amount of time has elapsed for the rotation of the cup wheel 35, the servo motor 42 is rotated in the reverse direction to retract the grinding unit 30 upward and finish the grinding.

  The thickness measurement of the wafer 1 by the thickness measuring gauge 50 is performed over the entire circumference of the rotating wafer 1, and the maximum measurement value t2 and the minimum measurement value t1 during one rotation are measured. For example, assuming that the rotation speed of the chuck table 20 is 10 rpm and the measurement timing is every 50 milliseconds, the number of measurements during one rotation of the wafer 1 is set to 120 times. The recognition unit 61 calculates a thickness variation value at each measurement timing and supplies the thickness variation value to the control unit 62. The control unit 62 always compares the thickness variation value sent from the recognition unit 61 with the target thickness variation value stored in the storage unit 63, and the thickness variation value being measured is the target thickness variation. The servo motor 42 is controlled so that the grinding unit 30 descends at a predetermined feed rate (for example, 0.3 views / second) until the value is reached.

  According to the control operation of the present embodiment, the grinding target end value is not the thickness of the wafer 1 as in the prior art, but is a thickness variation value representing the thickness unevenness of the wafer 1. This thickness variation value is obtained reliably and accurately without being affected by the mechanical accuracy of the grinding apparatus 10. For example, when grinding is performed with thickness control, when the suction area 21 of the chuck table 20 slightly sinks due to the pressing load of the cup wheel 35, the thickness of the wafer 1 is measured as a value reduced by the sinking amount. Grinding stops even if there is still an amount to be ground.

  However, in the present embodiment, the above (t2-t1) is always measured and calculated as a value equal to or greater than a certain value, so that the grinding reliably proceeds until the value reaches the target thickness variation value. Further, since the feeding operation of the grinding unit 30 is stopped when the target thickness variation value is reached, even if the grinding is further performed by 2 to 3 μm by the pressure of the grindstone 37 from the stopped state, the grinding total amount is very small (for example, About 3 μm).

  In this way, by controlling the feeding operation of the grinding unit 30 based on the thickness variation value, the wafer surface can be surely made while being as small as possible without being affected by the mechanical accuracy of the grinding apparatus 10. Can be ground flat. As a result, for example, the number of wafers cut from an ingot can be increased, or the number of times that a used wafer can be ground again and reused can be increased, thereby reducing the cost of wafer materials, etc. Is planned.

  In the control of this embodiment, an upper limit value (for example, 20 to 30 μm) of the grinding amount is set in order to prevent the grinding from proceeding even when the actual grinding amount becomes larger than expected. When the value is exceeded, it is preferable to provide an interlock function that interrupts grinding even if the measured thickness variation value does not reach the target thickness variation value. This is useful as a safety measure when a failure occurs in the thickness measurement gauge 50 or the feed mechanism 43 of the grinding unit 30.

  The thickness measuring gauge 50 for measuring the thickness of the wafer 1 is a contact type, but an optical type using a laser beam or the like or a non-contact type thickness measuring unit using an ultrasonic wave may be used. .

1 is a perspective view of a grinding apparatus according to an embodiment of the present invention. It is the (a) perspective view of the wafer ground with the grinding device concerning one embodiment, and (b) the side view. It is the (a) perspective view and (b) side view which show the state which grinds the wafer surface with the grinding unit with which the grinding-work apparatus of one Embodiment comprises. It is a figure which shows operation | movement of the grinding processing apparatus of one Embodiment, Comprising: It is a side view which shows the state in which the wafer surface is ground in order of (a), (b).

Explanation of symbols

1 ... Semiconductor wafer (workpiece)
10 ... Grinding device 20 ... Chuck table (holding table)
20a ... Holding surface of chuck table 30 ... Grinding unit (grinding means)
32 ... Spindle shaft (tool rotation axis)
35 ... Cup wheel (grinding tool)
43 ... Feeding mechanism (feeding means)
50 ... Thickness measuring gauge (surface position measuring means)
61 ... Recognition unit (recognition means)
62 ... Control section (control means)
63: Storage section (storage means)

Claims (2)

A grinding method for holding a plate-like workpiece on a rotatable holding table and grinding the surface of the workpiece with a predetermined thickness by a grinding tool while rotating the workpiece together with the holding table,
Before grinding, the surface position of the workpiece held on the holding table is measured over the entire circumference by the surface position measuring means, and the surface position variation value, which is the difference between the maximum measured value and the minimum measured value at this time, is preliminarily determined. When the set target surface position variation value is exceeded, the grinding of the surface of the workpiece by the grinding tool is started while measuring the surface position of the workpiece by the surface position measuring means,
A grinding method characterized by stopping grinding of a workpiece when the surface position variation value measured by the surface position measurement means reaches the target surface position variation value during grinding. A rotatable holding table having a holding surface for adsorbing and holding a plate-like workpiece;
A grinding means disposed to face the holding table, having a tool rotation axis parallel to the rotation axis of the holding table, and grinding a workpiece by a grinding tool provided concentrically with the tool rotation axis;
In a grinding apparatus comprising: a feed unit that presses the grinding tool against a workpiece held on the holding table by a feed operation that causes the grinding unit to approach / separate the holding table;
It has surface position measuring means for measuring the surface position of the workpiece held on the holding table, and the surface position of the workpiece held while rotating the holding table is measured over the entire circumference by the surface position measuring means. When the difference between the maximum measured value and the minimum measured value is the surface position variation value,
Storage means for storing a target surface position variation value as a target surface position variation value;
A recognition means for recognizing surface position variation values before and during grinding;
Before grinding, the surface position variation value recognized by the recognition unit and the target surface position variation value stored by the storage unit are compared, and the surface position variation value recognized by the recognition unit is the target surface stored by the storage unit. When the position variation value is exceeded, the feed means is fed to start grinding the surface of the workpiece by the grinding tool, and the surface position variation value recognized by the recognition means becomes the target surface position variation value. And a control means for stopping the feeding operation of the feeding means when it arrives.

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