workpiece cutting process

Abstract

Workpiece cutting method for cutting a workpiece (11) having a front face on which several intersecting parting lines (13) are formed to define several separate areas in each of which several components (15) are formed, the workpiece cutting method comprising: a workpiece holding step for holding the workpiece (11) on a first clamping table (6); a test wafer holding step for holding a test wafer (23) on a second clamping table (18) which is provided independently of the first clamping table (6); a workpiece cutting step for cutting the workpiece (11) held on the first clamping table (6) along the parting lines (13) by using a cutting blade; a test wafer cutting step for cutting the test wafer (23) held on the second clamping table (18) by using the cutting blade (50, 50a);a test wafer imaging step for imaging a cut groove (25, 25a) formed on the test wafer (23) in the test wafer cutting step by using an imaging agent in order to obtain a captured image (60, 70, 80, 90); and a determination step for determining the state of the cutting blade from the state of chips (27, 27a, 27b, 27c) formed on both sides of the cut groove (25, 25a) in the captured image;wherein, if in the determination step it is determined that the condition of the cutting blade (50, 50a) is normal, the workpiece cutting step is continued, whereas, if in the determination step it is determined that the condition of the cutting blade (50, 50a) is abnormal, the workpiece cutting step is stopped, and wherein the test wafer (23) has a polished surface and the test wafer (23) is held in the test wafer holding step on the second clamping table (18) in the state in which the polished surface of the test wafer (23) is exposed.

Description

BACKGROUND OF THE INVENTIONField of the InventionThe present invention relates to a workpiece cutting method for cutting a plate-shaped workpiece such as a semiconductor wafer by using a cutting blade.Description of the Prior ArtA cutting apparatus including a cutting blade is used for dividing a semiconductor wafer having a plurality of semiconductor devices formed on the front side, an optical device wafer having a plurality of optical devices formed on the front side, or a plate-shaped workpiece such as a glass substrate, a ceramic substrate, and a resin substrate having a plurality of devices formed on the front side, to thereby obtain a plurality of individual chips. The cutting blade included in the cutting device has a cutting edge formed by attaching abrasive grains of diamond or the like with a plating or by attaching the abrasive grains with a bond such as metal and resin. Self-sharpening of the cutting edge is accelerated by cutting a workpiece with the cutting edge, thereby maintaining constant sharpness. The cutting of the workpiece is effected by grinding the workpiece with the abrasive grains of the cutting edge.Thus, the cutting is effected by the grinding, so that chipping is caused by using the cutting blade on both sides of a cut groove formed on the workpiece. If the chippings have a size that extends beyond the parting line at which the cut groove is formed on the workpiece, defective devices can be produced. Accordingly, the cut groove is appropriately imaged and observed during the process of cutting the workpiece to check the size of chipping (see, for example, Japanese Patent Application Laid-Open JP 2009-246 015 A).Such observation of the cut groove is referred to as cut-line inspection, in which the size of chipping is measured. When the size of the chippings is out of tolerance, an error message is displayed and an operator can visually recognize the state of the cut groove (cut groove) formed on the workpiece (for example, a wafer). When it is determined that the chips do not reach the components, the components are used as usable products, while when it is determined that the chips reach the components, a step such as a step of removing an unusable portion from the workpiece is performed. Further, the cutting blade causing generation of chipping is replaced.JP 2007-96 091 A relates to a processing method for wafers.SUMMARY OF THE INVENTIONIn the cutting operation, the state of the cut groove varies according to the state of the cutting edge of the cutting blade and various cutting conditions (for example, the type of a layer formed on the workpiece, a feed speed, a rotation speed of the cutting blade, a depth of the cut, a size of the abrasive grains, and a type of the bond). For example, as compared with a so-called test wafer (mirror wafer) on which no devices are formed, a semiconductor wafer having a plurality of low-permittivity insulating layers (low-k layers) formed as layered layers on a substrate has such a property that the front side of the wafer is less liable to occurrence of chipping. In this case, even if chipping occurs on the front side of the wafer, these chippings are usually small chippings.However, an abnormality may arise that does not occur on the front side of the workpiece such as a wafer. For example, cracks may be generated on the side surfaces of the cut groove. It is difficult to detect these cracks by the kerf inspection during the cutting operation.It is therefore an object of the present invention to provide a workpiece cutting method that can quickly recognize an erroneous cutting state difficult to detect when cutting the workpiece.According to an aspect of the present invention, there is provided a workpiece cutting method for cutting a workpiece having a front side on which a plurality of crossing division lines are formed to define a plurality of divided regions in each of which a plurality of devices are formed, the workpiece cutting method including: a workpiece holding step of holding the workpiece on a first chuck table; a test wafer holding step of holding a test wafer on a second chuck table provided independently of the first chuck table; a workpiece cutting step of cutting the workpiece held on the first chuck table along the division lines by using a cutting blade; a test wafer cutting step of cutting the test wafer held on the second chuck table by using the cutting blade; a test wafer imaging step of imaging a cut groove formed on the test wafer in the test wafer cutting step by using imaging means to thereby obtain a captured image; and a determination step of determining the state of the cutting blade from the state of chippings formed on both sides of the cut groove in the captured image; wherein when it is determined in the determination step that the state of the cutting blade is normal, the workpiece cutting step is continued, while when it is determined in the determination step that the state of the cutting blade is abnormal, the workpiece cutting step is stopped. The test wafer has a polished surface and is held on the second chuck table in the test wafer holding step in the state where the polished surface of the test wafer is exposed.Preferably, the state of the cutting blade is determined in the determining step according to any one of factors including the length or width of each chipping, the number of chippings, and the area of each chipping.According to the present invention, a test wafer having a polished surface (mirror surface) is cut at an appropriate timing in cutting the workpiece. Thereafter, by checking the state of chippings generated on both sides of a cut groove formed on the test wafer, it is possible to quickly recognize an erroneous cutting state difficult to detect when cutting the workpiece.The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent and the invention itself will be best understood by studying the following description and appended claims with reference to the accompanying drawings showing a preferred embodiment of the invention.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a perspective view of a cutting apparatus suitable for use in performing the workpiece cutting method of the present invention; FIG. 2 is a perspective view of a wafer unit including a semiconductor wafer as a workpiece; FIG. 3 is a partially cut side view for illustrating a wafer cutting step for cutting the semiconductor wafer; FIG. 4 is a partially cut side view for illustrating a test wafer cutting step for cutting a test wafer; FIG. 5A is a view showing a captured image of the test wafer when it is determined that a cutting blade included in the cutting device does not have abnormality; FIG. 5B is a view showing a captured image of the semiconductor wafer when it is determined that the cutting blade does not have abnormality; FIG. 6A is a view showing a captured image of the test wafer when it is determined that the cutting blade has an abnormality; and FIG. 6B is a view showing a captured image of the semiconductor wafer when it is determined that the cutting blade has an abnormality.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTA preferred embodiment of the present invention will be described below in detail with reference to the drawings. Referring to Fig. 1, there is shown a perspective view of a cutting apparatus 2 suitable for use in performing the workpiece cutting method of the present invention. The cutting device 2 is a two-facing-spindle cutting device in which two cutting blades are provided so as to face each other.The cutting apparatus 2 includes a base 4. the base 4 is provided with a chuck table (first chuck table) 6 configured to be reciprocated in the X direction (shown by an arrow X) by a feed mechanism (not shown). The chuck table 6 includes a frame 8 and a suction holding portion 10 provided inside the frame 8, the frame 8 is formed of metal such as SUS, and the suction holding portion 10 is formed of porous ceramic or the like. A plurality of clamps 12 and a water cover 14 are provided around the chuck table 6. A pair of bellows 16 are provided so as to connect the water cover 14 and the base 4. A substrate chuck table (second chuck table) 18 for holding a test wafer is provided on the water cover 14 adjacent to the chuck table 6.Referring to FIG. 2, a perspective view of a wafer unit 17 is shown. The wafer unit 17 is composed of an annular frame F, a dicing tape T attached to the annular frame F at its peripheral portion, and a semiconductor wafer (hereinafter also referred to simply as a wafer) 11 whose back side is attached to a central portion of the dicing tape T. A plurality of crossing division lines 13 are formed on the front surface of the wafer 11 to thereby define a plurality of separate regions in each of which a plurality of devices 15 such as ICs and LSIs are formed. In the wafer unit 17 shown in FIG. 2, the semiconductor wafer 11 is used as a workpiece. However, the workpiece is not limited to the semiconductor wafer 11, but may include another wafer such as an optical device wafer having a plurality of optical devices formed on the front side, and also include a plate-shaped workpiece such as a ceramic substrate and a resin substrate having a plurality of devices formed on the front side.Referring again to Fig. 1, a plurality of such wafer units 17 are stored in a cassette 20, and this cassette 20, which stores the plurality of wafer units 17, is mounted on a vertically movable cassette elevator 22 disposed at a left front portion of the base 4. A gate-shaped support 24 having an inverted U-shape is provided at a rear portion of the base 4. A pair of guide rails 26 extending in the Y direction (shown by an arrow Y) are fixed to the bracket 24. A first Y moving block 28 is mounted on the bracket 24 so as to be movable in the Y direction by a first Y moving mechanism 34 while being guided by the guide rails 26. The first Y moving mechanism 34 is composed of a ball screw 30 and a pulse motor (not shown) for rotating the ball screw 30.A pair of guide rails 36 extending in the Z direction (shown by an arrow Z) are fixed to the first Y moving block 28. A first Z moving block 38 is attached to the first Y moving block 28 so as to be movable in the Z direction by a first Z moving mechanism 44 while being guided by the guide rails 36. The first Z moving mechanism 44 is composed of a ball screw 40 and a pulse motor 42 for rotating the ball screw 40 A first cutting unit 46 and a first imaging unit 52 are mounted on the first Z moving block 38. As shown in FIG. 3, the first cutting unit 46 includes a spindle 48 configured to be rotationally driven by a motor (not shown), and a first cutting blade 50 detachably attached to the front end portion of the spindle 48.Referring again to FIG. 1, a second Y moving block 28 ais also mounted on the bracket 24 so as to be movable in the Y direction by a second Y moving mechanism 34 awhile being guided by the guide rails 26. The second Y moving mechanism 34a is composed of a ball screw 30a and a pulse motor 32a for rotating the ball screw 30a. A pair of guide rails 36 aextending in the Z direction is fixed to the second Y moving block 28 a. A second Z moving block 38a is mounted on the second Y moving block 28a so as to be movable in the Z direction by a second Z moving mechanism 44a while being guided by the guide rails 36a. The second Z moving mechanism 44a is composed of a ball screw 40a and a pulse motor 42 for rotating the ball screw 40a.A second cutting unit 46 aand a second imaging unit 52 aare mounted on the second Z moving block 38 a. As shown in FIG. 3, the second cutting unit 46 aincludes a spindle 48 aconfigured to be rotationally driven by a motor (not shown), and a second cutting blade 50 adecommodatablely attached to the front end portion of the spindle 48 a. Referring back to FIG. 1, a centrifugal cleaning unit 54 having a centrifugal table 56 is provided at a right front portion of the base 4. In this spin cleaning unit 54, the wafer 11 after cutting is held on the spin table 56 under suction and then subjected to spin cleaning. After performing spin cleaning, the wafer 11 is spin dried in this spin cleaning unit 54.Next, a workpiece cutting method to be performed by using the cutting apparatus 2 will be described. First, a workpiece holding step is performed to hold the wafer 11 to the chuck table (first chuck table) 6 with the devices 15 formed on the front side of the wafer 11. Further, a test wafer holding step is performed to hold a test wafer having a polished surface on the substrate chuck table (second chuck table) 18. In the test wafer holding step, the polished surface of the test wafer is exposed.Thereafter, a workpiece cutting step is performed to cut the division lines 13 of the wafer 11 held on the chuck table 6 by using a cutting blade. That is, the wafer 11 is cut along the division lines 13. More specifically, the workpiece cutting step using the cutting apparatus 2 according to this preferred embodiment is performed by stepwise cutting, as shown in FIG. 3, wherein each division line 13 of the wafer 11 is first half-cut by the second cutting blade 50 ato form a cut groove 19 having a relatively large width, and the lower end of each cut groove 19 is subsequently fully cut by the first cutting blade 50 to form a cut groove 21 having a relatively small width. In this workpiece cutting step, the first cutting unit 46 and the second cutting unit 46 aare moved for division in the Y direction to successively perform stepwise cutting, thereby forming a plurality of cut grooves 21 along all division lines 13 extending in a first direction.With appropriate timing (for example, after cutting 20 division lines 13) in performing the workpiece cutting step, the cut grooves 19 or 21 are imaged by the first imaging unit 52 or the second imaging unit 52 ato perform a kerf check for checking the size (as an example) of chipping occurring at the periphery of the cut grooves 19 or 21. Therefore, all the division lines 13 extending in the first direction on the wafer 11 are cut sequentially while this dicing groove inspection is performed. After all the division lines 13 extending in the first direction are cut, the chuck table 6 is rotated 90 degrees to similarly perform the workpiece cutting step along the other division lines 13 extending in a second direction perpendicular to the first direction, thereby dividing the wafer 11 into individual device chips.The chippings occurring on the front side of the wafer 11 can be detected by performing the above-described dicing groove inspection. However, if the wafer 11 is a semiconductor wafer having a plurality of low-permittivity insulating layers (low-k layers) formed as layered layers on a substrate, the front surface of the wafer 11 is less prone to occurrence of chipping. In this case, even if chipping occurs on the front surface of the wafer 11, these chippings are usually small chippings. Accordingly, even if an abnormality does not occur on the front side of the wafer 11 arises, for example, even in the case where cracks are generated on the side surfaces of the cut grooves 19 or 21, the detection of these cracks by the usual kerf inspection is difficult.To solve this problem, the workpiece cutting method of the present invention includes a test wafer cutting step of cutting a test wafer at a predetermined timing, for example, by stopping the cutting step after cutting a predetermined number of wafers 11 or after continuing the cutting for a predetermined period of time. Alternatively, the test wafer cutting step may be performed before performing the cutting step for cutting the wafer 11. As shown in FIG. 4, the test wafer cutting step in this preferred embodiment includes the steps of cutting a test wafer 23 held on the substrate chuck table 18 by using the first cutting blade 50 to form a cut groove 25, and also cutting the test wafer 23 by using the second cutting blade 50 ato form another cut groove 25 a.Thereafter, a test wafer imaging step is performed to image the cut grooves 25 and 25a by using either the first imaging unit 52 or the second imaging unit 52a. Referring to FIG. 5A, there is shown a captured image 60 of the cut groove 25 obtained by the test wafer imaging step. As can be seen from the captured image 60, relatively small chips 27 occur at the periphery of the cut groove 25. However, in these relatively small chips 27, the length or width of each chip 27, the number of these chips 27 and the area of each chip 27 are each within the tolerance. Accordingly, in a determination step, as the next step, it is determined that the first cutting blade 50 does not have abnormality.FIG. 5B shows a captured image 70 obtained by performing the kerf inspection for the wafer 11 in the case where it is determined in the above determination step that the first cutting blade 50 does not have abnormality. As can be seen from the captured image 70, relatively small chips 27 aoccur at the periphery of the cut groove 21 formed on the parting line 13.In contrast, FIG. 6A shows a captured image 80 of the cut groove 25 formed on the test wafer 23 in the case where it is determined in the determination step that the first cutting blade 50 has an abnormality. As can be seen from the captured image 80, relatively large chips 27b occur on the periphery of the cut groove 25, and the length or width of each chip 27b, the number of these chips 27b, or the area of each chip 27b is out of tolerance (i.e., exceeds a tolerance limit). That is, if the cutting edge of the first cutting blade 50 has an abnormality such as a clog, these chips 27b tend to occur in cutting the test wafer 23 by using the first cutting blade 50, with the length or width of each chip 27b, the number of these chips 27b, or the area of each chip 27b being out of tolerance.FIG. 6B shows a captured image 90 obtained by performing the kerf inspection for the wafer in the case where it is determined in the above determination step that the first cutting blade 50 has an abnormality. As can be seen from the captured image 90, relatively small chips 27c occur on both sides of the cut groove 21. That is, although the kerf inspection is performed for the wafer 11, the abnormality of the first cutting blade 50 cannot be detected. To solve this problem, the cutting method of the present invention includes the test wafer cutting step, the test wafer imaging step, and the determining step to detect abnormality of the first cutting blade 50.Similarly to the case of the first cutting blade 50, it can be determined in the determination step whether or not the second cutting blade 50 acomprises an abnormality by imaging the cut groove 25 aformed on the test wafer 23 in the test wafer imaging step.When it is determined in the determination step that both the first and second cutting blades 50 and 50 ado not have abnormality, the cutting step for the wafer 11 is started again. On the other hand, when it is determined in the determination step that either the first cutting blade 50 or the second cutting blade 50 ahas an abnormality, the cutting step for the wafer 11 is stopped (remains stopped).Although in this preferred embodiment the cutting apparatus 2 is a two-faced spindle cutting apparatus for performing stepwise cutting of the wafer 11, the workpiece cutting method of the present invention is not limited to the above preferred embodiment, but can be similarly applied to the case of cutting the wafer 11 by using a cutting apparatus including a single cutting unit.The cutting of the test wafer 23 is preferably performed under conditions similar to those of the cutting step for the wafer 11. However, the cutting conditions for the test wafer 23 can be independently set so that chipping or abnormality can be easily detected, such as by increasing the moving speed of the substrate chuck table 18 to increase the feeding speed in cutting the test wafer 23.Further, although in the above preferred embodiment, the stepwise cutting of the wafer 11 is performed by using the first and second cutting blades 50 and 50 a, a single cutting blade may be used to perform full cutting of the wafer 11 or half cutting of the wafer 11. Further, the area of each chipping refers to the area of one chipping or the total area of a plurality of chippings generated in a measurement region.

Claims

A workpiece cutting method for cutting a workpiece (11) having a front side on which a plurality of crossing division lines (13) are formed to define a plurality of divided regions in each of which a plurality of devices (15) are formed, the workpiece cutting method comprising: a workpiece holding step of holding the workpiece (11) on a first chuck table (6); a test wafer holding step of holding a test wafer (23) on a second chuck table (18) provided independently of the first chuck table (6); a workpiece cutting step of cutting the workpiece (11) held on the first chuck table (6) along the division lines (13) by using a cutting blade; a test wafer cutting step of cutting the test wafer (23) held on the second chuck table (18) by using the cutting blade (50, 50a); a test wafer imaging step of imaging a cut groove (25, 25a) formed on the test wafer (23) in the test wafer cutting step by using imaging means to thereby obtain a captured image (60, 70, 80, 90); and a determination step of determining the state of the cutting blade from the state of chips (27, 27a, 27b, 27c) formed on both sides of the cut groove (25, 25a) in the captured image; wherein, when it is determined in the determining step that the state of the cutting blade (50, 50a) is normal, the workpiece cutting step is continued, while when it is determined in the determining step that the state of the cutting blade (50, 50a) is abnormal, the workpiece cutting step is stopped and in which the test wafer (23) has a polished surface, and the test wafer (23) is held on the second chuck table (18) in the test wafer holding step in the state in which the polished surface of the test wafer (23) is exposed.The workpiece cutting method according to claim 1, wherein the state of the cutting blade in the determining step is determined according to one of factors including the length or the width of each chipping (27, 27a, 27b, 27c), the number of chippings, and the area of each chipping (27, 27a, 27b, 27c).

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