Processing methods for a wafer

Abstract

A processing method for a wafer (44) by which a wafer (44) having several components (48) formed on a surface (44a) thereof and divided in a grid pattern by planned division lines (46) formed in a first direction (D1) and planned division lines (46) formed in a second direction (D2) orthogonal to the first direction (D1), is divided into individual component chips by a cutting blade (63), the processing method comprising: a crack detection step (66) for illuminating light of a wavelength for which the wafer (44) is transparent from a side face of the wafer (44), taking an image of the wafer (44) by an image acquisition means (7) positioned with respect to the wafer (44), and detecting whether a crack (66) has been generated in the interior of the wafer (44) or not;a verification step for a crack direction (L) to verify, if in the detection step for a crack (66) it was detected that a crack (66) was generated in the interior of the wafer (44), to which direction (L) in which the crack (66) extends is closer to the first direction (D1) or the second direction (D2); a first cutting step to position the cutting blade (63) at a planned division line (46) of a direction which was determined in the verification step for a crack (66) as a direction further away from the direction (L) in which the crack (66) extends from the first direction (D1) and the second direction (D2), and to cut the planned division line (46);and a second cutting step to position, after the first cutting step has been completed, the cutting blade (63) at a planned division line (46) in a direction determined to be closer to the direction (L) in which the crack (66) extends, and cutting the planned division line (46).

Description

Technical FieldThe present invention relates to a processing method for dividing a wafer having a plurality of devices formed on a surface thereof and divided by planned dividing lines into individual devices.Description of the Prior ArtA wafer having a plurality of devices such as integrated circuits (ICs) or Largescale Integration (LSIs) formed on a surface thereof and divided by a dicing plan line is divided into individual device chips by a dicing apparatus. The divided device chips are used in electronic devices such as mobile phones or personal computers.The dividing device may be configured of a cutting device that positions a cutting blade on a scheduled division line of a wafer held on a chuck table, rotates the cutting blade, and supplies the chuck table for processing to cut the scheduled division line with high accuracy (see, for example, Japanese Patent Application Laid-Open JP H11-176 771 A).US 2017 / 0 045 448 A1 discloses a device for detecting a light transmission of an incision. The incision is arranged on an infrared-transmissive material, which may be a wafer. The device includes a light source that emits visible light and infrared light.SUMMARY OF THE INVENTIONAccording to the cutting apparatus, although it is possible to cut a scheduled division line with high accuracy, there is a problem that while performing cutting processing along a scheduled division line, a crack sometimes occurs in a processing area by the cutting blade and damages multiple components.As a result of detailed examination performed by the applicant to solve the problem just described, it has been found that the problem is caused by the fact that where a crack potentially exists in the inside of a wafer beforehand, when processing by a cutting blade comes to the crack at an angle in the vicinity of a direction in which the crack extends, the crack grows by the processing, and when the grown crack reaches a device in an adjacent region, damage to the device is increased.Therefore, it is an object of the present invention to provide a processing method for a wafer by which, when a wafer is cut by a cutting blade of a cutting apparatus to divide the wafer into individual device chips, even if a crack potentially exists in the inside of the wafer beforehand, multiple devices are suppressed from being damaged by further growth of the crack.According to an aspect of the present invention, there is provided a processing method for a wafer by which a wafer having a plurality of devices formed on a surface thereof and divided in a lattice pattern by planned dividing lines formed in a first direction and planned dividing lines formed in a second direction orthogonal to the first direction is divided into individual device chips by a cutting blade. The processing method includes a crack detection step of irradiating light of a wavelength to which the wafer is transparent from a side surface of the wafer, capturing an image of the wafer by image capturing means positioned with respect to the wafer, and detecting whether or not a crack has been generated in the inside of the wafer, a crack direction verification step of verifying, when it has been detected in the crack detection step that a crack is generated in the inside of the wafer to which direction of the first direction or the second direction a direction in which the crack extends is closer, a first cutting step of positioning the cutting blade on a scheduled division line of a direction, which is determined from the first direction and the second direction by the crack direction verification step as a direction farther from the direction in which the crack extends, and cutting the scheduled division line, and a second cutting step of, after the first cutting step is completed, positioning the cutting blade at a scheduled division line of a direction determined as being closer to the direction in which the crack extends, and cutting the scheduled division line.According to a processing method for a wafer of the present invention, if a crack potentially exists in the inside of a wafer beforehand, if the scheduled division line is cut first in the direction farther from the direction in which a crack extends, then the crack is divided in the direction in which the crack extends, and thereafter the cutting blade is positioned on the scheduled division line of the direction closer to the direction in which the crack extends, and the scheduled division line is cut. Therefore, even if the processing by the cutting blade comes to the crack from the direction closer to the direction in which the crack extends, since the crack is already divided, growth of the crack at the division location is blocked and further damage to the device is suppressed.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 best be understood by studying the following description and appended claims with reference to the appended drawings which show a preferred embodiment of the invention.BRIEF DESCRIPTION OF THE FIGURESFIG. 1 is a general perspective view of a cutting apparatus suitable for performing a machining method of the present invention; FIG. 2 is a schematic view illustrating a crack detection step performed by the cutting device illustrated in FIG. 1 ; and FIGS. 3A to 3C are perspective views illustrating a first cutting step and a second cutting step in the processing method for a wafer of the present invention.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTIn the following, an embodiment of a processing method for a wafer configured on the basis of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 illustrates a general perspective view of a cutting apparatus that can perform a processing method for a wafer configured in accordance with the present invention. A cutting device 1 of the present embodiment includes a device housing 2 of a substantially rectangular parallelepiped. In the apparatus housing 2, a cover table 3 and a chuck table 4 for holding a workpiece thereon are arranged for movement in a direction indicated by an arrow with the mark X, which is a cutting feed direction. The cover table 3 includes bellows 31 in the X direction and has an opening 32 at a central location thereof. The chuck table 4 is fitted in the opening 32 and configured to rotate by a rotating mechanism that is not illustrated. Four clamps 42 are disposed at 90° intervals on the chuck table 4 so as to surround the chuck table 4, and are rotated integrally with the chuck table 4. The chuck table 4 has a suction jig 41 disposed on an upper surface thereof, so that when a suction means, not illustrated, is operated, a workpiece is held by or sucked by a holding surface that is an upper surface of the suction jig 41. The cover table 3 and the chuck table 4 configured in such a manner as described above are moved in the cutting feed direction indicated by the arrow with the mark X by a cutting feed means that is not illustrated. On an upper surface of the device case 2, display means 9 is uprightly provided so that various kinds of information are displayed thereon on the basis of a signal from control means described below, and work information, image and position information of a potential crack described below, etc. are displayed on the display means 9.The cutting device 1 in the present embodiment includes a spindle unit 6 as a cutting means. The spindle unit 6 is mounted on the apparatus housing 2 and includes a spindle housing 61 that can be moved and adjusted in a direction represented by an arrow with the mark Y being an index direction and another arrow with the mark Z being a cutting direction, a rotating spindle 62 rotatably supported on the spindle housing 61, and a cutting blade 63 mounted on a front end portion of the rotating spindle 62. As the cutting blade 63, an electroplated cutting blade formed by coupling abrasive grains to a side surface of a base formed of aluminum or the like by metal plating of nickel or the like is used. The spindle unit 26 as the cutting means configured in this manner is moved in the index feeding direction represented by the arrow with the mark Y in FIG. 1 by an unillustrated index feeding means, and is moved in the cut-in feeding direction represented by an arrow with the mark Z in FIG. 1 by the cut-in feeding means which is not illustrated.The cutting apparatus 1 in the present embodiment includes image capturing means 7 for capturing an image of the surface of a workpiece, for example, of a wafer, held on the chuck table 4 to detect an area to be cut by the cutting blade 63 and capture an image of the inside of the wafer. The image pickup means 7 is constituted of an ordinal image pickup element (charge coupled device (CCD)) that captures an image of the surface of the wafer using visible rays, an optical system for capturing infrared rays, and another image pickup element (infrared CCD) for outputting an electric signal corresponding to the infrared rays captured by the optical system. Captured image information is sent to the control means 58 described below (see FIG. 2 ). As shown in FIG. 2, the control means 58 is connected at least to the image capturing means 7 and the display means 9. Further, the control means 58 is also connected to moving means (cutting feed means, index feed means, cut-in feed means, etc.) for moving the chuck table 4 and the spindle unit 6, which is not illustrated. The control means 58 is configured of a computer and includes a central processing unit (CPU) 60 that performs arithmetic processing in accordance with a control program, a read only memory (ROM) 65 in which the control program, etc., is stored, a readable writable random access memory (RAM) 64 for temporarily storing detected information, a result of arithmetic processing, etc., an input interface, and an output interface. In a part of a storage area of the work memory 64, an image storage area 64 afor storing images captured by the image capturing means 7 and a crack storage area 64 bfor storing crack information such as a position of a crack detected in the captured image, a direction in which the crack extends, etc. are set (a detailed illustration thereof is omitted). Note that the control means 58 also executes control programs for operating the moving means (cutting feed means, index feed means, cutting feed means, etc.) configuring the cutting apparatus 1 and other operation units.In a cassette placing area 11 aof the apparatus housing 2, a cassette placing table 11 is disposed which receives a cassette in which a wafer is accommodated, which is placed thereon. The cassette placing table 11 is configured to move in an upward and a downward direction by a lifting means not illustrated. A cassette 12 in which wafers are accommodated is accommodated on the cassette placing table 11. The apparatus housing 2 further includes a supply means 14 for supplying a wafer accommodated in the cassette 12 placed on the cassette placing table 11 to a temporary placing table 13, a first transfer means 15 for transferring the wafer supplied to the temporary placing table 13 to the chuck table 4, a cleaning means 16 for washing the wafer cut and processed on the chuck table 4, and a second transfer means 17 for transferring the wafer cut and processed on the chuck table 4 to the cleaning means 16.FIG. 1 further illustrates a wafer 44 to be processed by the cutting apparatus 1 described above, and an illumination means 20 is used when it is to be determined whether or not a crack is generated in the inside of the wafer 44. A front surface 44 aof the wafer 44 of a disc shape, which may be formed of Si (silicon) or the like, is divided into a plurality of rectangular regions by a lattice-like division planned line 46, and a device 48 is formed in each of the plurality of rectangular regions. A notch n indicating the crystal orientation of the wafer 44 is formed at an outer circumferential portion of the wafer 44, and the planned dividing lines 46 are set in one direction (first direction) D 1 orthogonal to a straight line connecting the center of the wafer 44 and the notch n and another direction (second direction) D 2 orthogonal to the first direction D 1. The front surface 44 aof the wafer 44 is divided in a grid pattern by the planned dividing lines 46, and a device 48 is formed in each of the divided regions. In the present embodiment, the wafer 44 adheres at a rear surface thereof to an adhesive tape 52n fixed at a circumferential edge thereof to an annular frame 50. Note that the illumination means 20 includes an annular plate 54 having an inner diameter larger than the diameter of the wafer 44, and a plurality (four in the present embodiment) of light sources 56 arranged at intervals in a circumferential direction on the upper surface of the annular plate 54. It is preferable that the outer diameter of the annular plate 54 is smaller than the inner diameter of the annular frame 50. The light sources 56 for radiating light toward the inner side in a diametrical direction of the annular plate 54 radiate light of a wavelength to which the wafer 44 is transparent. For example, when the wafer 44 is formed of Si (silicon), light to be radiated from the light sources 56 is selected to have a wavelength of 1064-3000 nm to which Si (silicon) is transparent. The cutting apparatus 1 of the present embodiment generally has the above-described configuration, and the processing method for a wafer implemented by the cutting apparatus 1 will be described below.When the cutting apparatus 1 is used to process a wafer 44, a crack detection step is first performed. In order to perform the crack detection step, a wafer 44 to be a processing target is transported from the cassette 12 to the transport means 14 and 15 described above. Thereafter, the wafer 44 is placed on the upper surface of the chuck table 44 with the back side of the wafer 44 facing downward, one adhering to the adhesive tape. Thereafter, the suction means, not shown, is operated to cause the suction chuck 41 of the chuck table 4 to generate a suction force to suck the wafer 44 to the suction chuck 41. Further, the annular frame 50 is fixed to a circumferential edge portion thereof by the clamps 42. Thereafter, as illustrated in FIG. 1, the illumination means 20 is disposed between the outer periphery of the wafer 44 and the inner periphery of the annular frame 50 such that light of a wavelength (for example, 1064 nm) for which the wafer 44 is transparent is radiated from the outer peripheral side of the wafer 44 from the light sources 56 of the illumination means 20. Thereafter, in order for the wafer 44 to be opposite to the image pickup means 7, the chuck table 4 is moved by the moving means, which is not illustrated. Thereafter, while the chuck table 4 is moved by the moving means, an image of the entire wafer 44 is captured by the image capturing means 7. In this manner, while light of a wavelength for which the wafer 44 is transparent is radiated from the outer circumferential side of the wafer 44, an image of the wafer 44 is captured by the image capturing means 7 disposed in an opposing relationship to the wafer 44. Thereby, an image of the crack existing in the wafer 44 can be captured.Since an image captured by the image capturing means 7 is displayed on the display means 9 as illustrated in FIG. 2, if a crack exists, the crack (denoted by reference numeral 66) of the wafer 44 can be detected on the basis of the image display on the display means 9. When the crack 66 is detected, image information captured by the image of the region in which the crack 66 is included is stored in the image storage region 64 aof the working memory 64 of the control means 58, and position information of the crack 66 and information of a direction (angle) L in which the crack 66 extends are stored in a linked relationship with the image information in the crack storage region 64 b. Note that, regarding a specific method of the direction L in which the crack 66 extends, the direction L is preferably specified by an angle at a position (indicated by a point P) at which the direction L crosses a scheduled division line 46 to be cut by the cutting blade 63, for example. However, the present invention is not limited thereto, and the direction L may be specified with respect to an average direction (angle) of the entire crack 66.After the position of the crack 66 described above and the direction L in which the crack 66 extends are specified, a crack direction verification step for performing comparison between the direction L and the first direction D 1 defined on the wafer 44 and between the direction L and the second direction D 2 is performed to determine which of the first direction D 1 and the second direction D 2 are closer to the direction L in which the crack 66 extends. Specifically, an angle (θ 1) formed by the first direction D 1 and the direction L in which the crack 66 extends and another angle (θ 2) formed by the second direction D 2 and the direction L in which the crack 66 extends are specified as illustrated on the display means 9 in FIG. 2. As a result of the comparison between the angles θ 1 and θ 2 (in the present embodiment, θ 1<θ 2), it is confirmed that the first direction D 1 is closer to the direction L in which the crack 66 extends and the second direction D 2 is farther from the direction L in which the crack 66 extends. Thereafter, the verification result is stored in the crack storage area 64 bof the control means 58 together with the information of the crack 66 described above. The verification result for a crack direction is completed in this manner.After the crack direction verification step is completed, a cutting step for cutting the wafer 44 is performed. If no crack is found in the above-described crack detection step, it is free to determine in which of the first direction D 1 and the second direction D 2 the planned dividing lines 66 are cut first, and the chuck table 4 is moved in the X direction represented by the arrow with the mark X in FIG. 1, namely, in the cutting feed direction to cut the planned dividing line 46 using the cutting blade 63, and while an index feed means is being operated, the spindle unit 6 is inserted in the Y direction, all the dividing lines 46 formed along the first direction D 1 on the wafer 44 are cut. Thereafter, the chuck table is rotated by 90° so that the scheduled division lines 46 formed along the second direction D 2 of the wafer 44 are aligned in the direction represented by X in FIG. 1, and thereafter a cutting operation similar to that described above is performed to cut all the scheduled division lines 46. The cutting step for the wafer 44 is thereby completed.As described above, if, unlike the cutting step, if a crack 66 was found in the wafer 44 in the crack detection step, when no crack was found in the wafer 44, then the cutting step is divided into a first cutting step and a second cutting step, which are performed sequentially. The "first cutting step" and the "second grinding step" are referred to as a "first cutting step of positioning the cutting blade on a scheduled division line of a direction determined as a direction farther from the direction L in which the crack extends from the first direction D 1 and the second direction D 2 and cutting the scheduled division line", and a "second cutting step of positioning, after the first cutting step is completed, the cutting blade on a scheduled division line of a direction determined as being closer to the direction L in which the crack extends". In the present embodiment, as the direction farther from the direction L in which the crack 66 extends, in the crack direction verification step described above, the second direction D 2 has been determined and the first direction D 1 has been determined and stored as a direction closer to the direction L in which the crack 66 extends. Therefore, in the cutting step of the present embodiment, cutting is performed first for the planned dividing lines 46 formed along the second direction D 2 (first cutting step) as in FIG. 3A, and thereafter, all the planned dividing lines 46 formed in the second direction D 2 are cut.Thereafter, after the first cutting step is performed, cutting of the scheduled division line 46 formed along the first direction D 1 orthogonal to the second direction D 2 is performed (second cutting step) as illustrated in FIG. 3B, and by performing cutting along other scheduled division lines 46, the cutting step is completed (see FIG. 3C ). If a crack 66 has been found in the crack verification step, by successively performing such a first cutting step and a second cutting step as described above, the planned dividing lines are cut first in a direction farther from a direction in which a crack extends. Consequently, the crack is cut by being cut from a direction in which a crack is less likely to propagate, and even if the cutting blade is positioned on a scheduled division line of a direction defining an angle closer to the direction in which the crack extends, and the scheduled division line is cut, since the crack 66 is already divided, the growth of the crack at the division location is blocked and further increase in damage to the device is suppressed.The present invention is not limited to the embodiment described above, and various modifications are possible without departing from the technical scope of the present invention. For example, while in the above-described embodiment, the illumination means 20 in which the light sources 56 are disposed on the annular frame 50 is used to detect a crack, the present invention is not limited thereto, and illumination means may be disposed on the cutting apparatus 1 such that light of a wavelength to which the wafer 44 is transparent is radiated from the side.Further, while in the embodiment described above, the back surface side of the wafer 44 is bonded to the adhesive tape 42 and held on the chuck table 4 with the front side 44 aof the wafer 44 facing upward to perform cutting, the present invention is not limited thereto and can be applied to a case where the wafer 44 is bonded on the front surface 44 ato an adhesive tape 52 and held on a chuck table 4 with the back surface side thereof facing upward to perform cutting.Further, while it has been described in the above description that in the above-described embodiment, a wafer 44 made of Si (silicon) is presented as a workpiece and the detection step for a crack for irradiating infrared rays to detect a crack is performed using an infrared CCD, the present invention is not limited thereto, and it is also possible to apply the present invention to a workpiece made of other materials. Consequently, if visible rays can pass through the wafer, it is not necessary to arrange an infrared CCD, and an image pickup means that can be used for alignment or the like can be adapted to carry out the crack detection step.

Claims

A processing method for a wafer (44) by which a wafer (44) having a plurality of devices (48) formed on a surface (44a) thereof and divided in a lattice pattern by planned dividing lines (46) formed in a first direction (D1) and planned dividing lines (46) formed in a second direction (D2) orthogonal to the first direction (D1) is divided into individual device chips by a cutting blade (63), the processing method comprising: a crack detection step (66) of irradiating light of a wavelength to which the wafer (44) is transparent from a side surface of the wafer (44), capturing an image of the wafer (44) by an image capturing means (7) positioned with respect to the wafer (44), and detecting, whether or not a crack (66) has been generated in the inside of the wafer (44); a crack direction (L) verifying step for verifying when it has been detected in the crack (66) detecting step that a crack (66) has been generated in the inside of the wafer (44), to which a direction (L) in which the crack (66) extends is closer to the first direction (D 1) or the second direction (D 2); a first cutting step of positioning the cutting blade (63) on a scheduled division line (46) of a direction determined as one of the first direction (D 1) and the second direction (D 2) farther from the direction (L) in which the crack (66) extends in the crack verification step (66), and cutting the scheduled division line (46); and a second cutting step of positioning, after the first cutting step is completed, the cutting blade (63) on a scheduled division line (46) of a direction determined as being closer to the direction (L) in which the crack (66) extends, and cutting the scheduled division line (46).

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