JP2011146568A - Method and device for detecting cracking of wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for detecting cracking of a wafer in which the cracking of the wafer can be confirmed before the wafer is diced. <P>SOLUTION: The method for detecting the cracking of the wafer having a plurality of devices formed on a surface includes an ultrasonic wave applying step of bringing an ultrasonic wave applicator into contact with the wafer and applying an ultrasonic wave to the wafer, an ultrasonic wave detecting step of bringing an ultrasonic wave detector into contact with the wafer at a position apart from the position where the ultrasonic wave applicator is brought into contact and detecting the ultrasonic wave propagated in the wafer, and a determination step of determining that the wafer cracks when the state of the ultrasonic wave detected by the ultrasonic wave detector in the ultrasonic wave detecting step is abnormal or that the wafer does not crack when not. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wafer crack detection method and a detection apparatus capable of detecting fine cracks generated in a wafer after grinding or polishing the wafer.

  A semiconductor wafer in which a number of devices such as IC and LSI are formed on the surface, and each device is partitioned by a line to be divided (street), the back surface is ground by a grinding machine and processed to a predetermined thickness. A division line is cut by a dicing apparatus to be divided into individual devices, and the divided devices are used for electric devices such as mobile phones and personal computers.

  The grinding apparatus includes a chuck table for holding a wafer, a grinding means for rotatably supporting a grinding wheel in which a grinding wheel for grinding the wafer held on the chuck table is annularly arranged, and a wafer to the chuck table. Loading means, unloading means for unloading the wafer from the chuck table, cleaning means for cleaning the unloaded wafer, wafer transporting means for unloading the wafer before grinding from the cassette and storing the cleaned wafer in the cassette The wafer can be ground to a desired thickness.

JP 2005-153090 A

  However, when grinding the wafer, or when polishing the wafer dry or wet, clogging occurs in the grinding wheel and polishing cloth, or a lump containing abrasive grains constituting the grinding wheel is removed from the grinding wheel. There is a problem that the wafer is subjected to an unpredictable load due to falling off or the degree of application of grinding water or polishing liquid, and fine cracks that cannot be confirmed with the naked eye occur inside or outside the wafer. Yes (for example, see Patent Document 1).

  When fine cracks occur in the wafer, when the wafer is attached to the dicing tape and supported by the annular frame, the wafer is completely broken to reduce the work efficiency, or the wafer is supported by the annular frame via the dicing tape. There is a problem that the wafer is cracked when the wafer is diced, and as a result, a shift occurs in the line to be divided and a large number of defective devices are generated.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a wafer crack detection method and a detection apparatus capable of confirming minute cracks in a wafer before dicing the wafer. It is.

  According to the first aspect of the present invention, there is provided a wafer crack detection method for detecting a crack in a wafer having a plurality of devices formed on the surface, wherein the ultrasonic wave is applied to the wafer by contacting the wafer with an ultrasonic wave applying means. An ultrasonic wave application step, an ultrasonic wave detection step for detecting an ultrasonic wave propagating through the wafer by bringing the ultrasonic wave detection unit into contact with a wafer at a position separated from the position where the ultrasonic wave application unit is brought into contact, and the ultrasonic wave detection In the process, there is a determination step of determining that there is a crack in the wafer when there is an abnormality in the state of the ultrasonic wave detected by the ultrasonic detection means, and that there is no crack when there is no abnormality. A method for detecting cracks in a wafer is provided.

  Preferably, the change in the ultrasonic state includes any of a change in the frequency of the ultrasonic wave, a difference in the propagation speed of the ultrasonic wave, a change in the volume of the ultrasonic wave, and a change in the interference wave of the ultrasonic wave.

  According to a third aspect of the present invention, there is provided a wafer crack detection device for detecting a crack in a wafer having a plurality of devices formed on the surface, the ultrasonic wave applying means for applying ultrasonic waves to the wafer in contact with the wafer; An ultrasonic detection means for detecting an ultrasonic wave applied by the ultrasonic wave application means and propagating through the wafer by contacting a wafer at a position separated from a position where the ultrasonic wave application means is in contact with the ultrasonic detection means; Provided is a wafer crack detection device comprising: a determination unit that determines that a crack exists in a wafer when there is an abnormality in the detected ultrasonic state, and no crack exists when there is no abnormality. Is done.

  In the present invention, ultrasonic waves are applied to a wafer and ultrasonic waves are detected at a position apart from the position where the ultrasonic waves are applied, so that cracks in the wafer can be confirmed depending on whether or not the detected ultrasonic waves are abnormal. Therefore, even fine cracks that cannot be confirmed with the naked eye can be reliably detected, and when a crack is found, the wafer is excluded from the production line, thereby improving productivity and suppressing the occurrence of defective devices.

It is a surface side perspective view of a semiconductor wafer. It is a back surface side perspective view of a semiconductor wafer in the state where a protective tape was stuck on the surface. It is a perspective view of a grinding device provided with a crack detection device of a wafer of an embodiment of the present invention. It is a perspective view of a chuck table unit and a chuck table feed mechanism. It is a longitudinal cross-sectional view of the grinding wheel with which the wheel mount and the wheel mount were mounted | worn. 1 is a perspective view of a wafer crack detection device according to an embodiment of the present invention. It is a side view of a wafer crack detection device. It is a block diagram of a crack detection apparatus and a detection method. FIG. 9A is a graph showing the relationship between frequency and amplitude when there is no crack, and FIG. 9B is a graph showing the relationship between frequency and amplitude when there is a crack.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a perspective view of a semiconductor wafer before being processed to a predetermined thickness. A semiconductor wafer 11 shown in FIG. 1 is made of, for example, a silicon wafer having a thickness of 700 μm, and a plurality of streets 13 are formed in a lattice shape on the surface 11a, and a plurality of streets partitioned by the plurality of streets 13 are formed. A device 15 such as an IC or LSI is formed in the region.

  The thus configured silicon wafer 11 includes a device region 17 in which the device 15 is formed and an outer peripheral surplus region 19 that surrounds the device region 17. A notch 21 is formed on the outer periphery of the wafer 11 as a mark indicating the crystal orientation of the silicon wafer.

  A protective tape 23 is attached to the surface 11a of the wafer 11 by a protective tape attaching process. Therefore, the front surface 11a of the wafer 11 is protected by the protective tape 23, and the back surface 11b is exposed as shown in FIG.

  Hereinafter, the grinding apparatus 2 for grinding the back surface 11b of the wafer 11 thus configured to a predetermined thickness will be described with reference to FIG. The housing 4 of the grinding device 2 is composed of a horizontal housing part 6 and a vertical housing part 8.

  A pair of guide rails 12 and 14 extending in the vertical direction are fixed to the vertical housing portion 8. A grinding means (grinding unit) 16 is mounted along the pair of guide rails 12 and 14 so as to be movable in the vertical direction. The grinding unit 16 is attached to a moving base 18 that moves up and down along a pair of guide rails 12 and 14 via a support portion 20.

  The grinding unit 16 includes a spindle housing 22 attached to the support portion 20, a spindle 24 rotatably accommodated in the spindle housing 22, and a servo motor 26 that rotationally drives the spindle 24.

  As best shown in FIG. 5, a wheel mount 28 is fixed to the tip of the spindle 24, and a grinding wheel 30 is screwed to the wheel mount 28. The grinding wheel 30 is configured by adhering a plurality of grinding wheels 34 in which diamond abrasive grains or the like are hardened with an appropriate bonding agent such as resin bond or vitrified bond to a free end portion of a wheel base 32.

  Grinding water is supplied to the grinding means (grinding unit) 16 via a hose 36. Preferably, pure water is used as the grinding water. As shown in FIG. 5, the grinding water supplied from the hose 36 is formed in the grinding water supply hole 38 formed in the spindle 24, the space 40 formed in the wheel mount 28, and the wheel base 32 of the grinding wheel 30. Then, it is supplied to the wafer W held on the grinding wheel 34 and the chuck table 54 via a plurality of grinding water supply nozzles 42.

  Referring back to FIG. 3, the grinding apparatus 2 includes a grinding unit feed mechanism 44 that moves the grinding unit 16 in the vertical direction along the pair of guide rails 12 and 14. The grinding unit feed mechanism 44 includes a ball screw 46 and a pulse motor 48 fixed to one end of the ball screw 46. When the pulse motor 48 is pulse-driven, the ball screw 46 rotates and the moving base 18 is moved in the vertical direction via the nut of the ball screw 46 fixed inside the moving base 18.

  A chuck table unit 50 is disposed in the recess 10 of the horizontal housing portion 6. As shown in FIG. 4, the chuck table unit 50 includes a support base 52 and a chuck table 54 that is rotatably disposed on the support base 52. The chuck table unit 50 further includes a cover 56 having a hole through which the chuck table 54 is inserted.

  The chuck table unit 50 is moved in the front-rear direction of the grinding apparatus 2 by the chuck table moving mechanism 58. The chuck table moving mechanism 58 includes a ball screw 60 and a pulse motor 64 connected to one end of a screw shaft 62 of the ball screw 60.

  When the pulse motor 64 is pulse-driven, the screw shaft 62 of the ball screw 60 rotates, and the support base 52 having a nut screwed to the screw shaft 62 moves in the front-rear direction of the grinding device 2. Therefore, the chuck table 54 also moves in the front-rear direction according to the rotation direction of the pulse motor 64.

  As shown in FIG. 3, the pair of guide rails 66 and 68 and the chuck table moving mechanism 58 shown in FIG. 4 are covered with bellows 70 and 72. That is, the front end portion of the bellows 70 is fixed to the front wall that defines the recess 10, and the rear end portion is fixed to the front end surface of the cover 56. The rear end of the bellows 72 is fixed to the vertical housing portion 8, and the front end thereof is fixed to the rear end surface of the cover 56.

  The horizontal housing portion 6 of the housing 4 includes a first wafer cassette 74, a second wafer cassette 76, a wafer transfer means (wafer transfer robot) 78, a wafer temporary mounting means 80, and a wafer carry-in means (loading). Arm) 82, wafer unloading means (unloading arm) 84, and spinner cleaning device 86. The spinner cleaning device 86 is provided with a wafer crack detection device 88 according to an embodiment of the present invention.

  In front of the housing 4 is provided operating means 89 for an operator to input grinding conditions and the like. Further, a cleaning water spray nozzle 90 for cleaning the chuck table 54 is provided at the approximate center of the horizontal housing portion 6.

  The cleaning water jet nozzle 90 ejects cleaning water toward the wafer after grinding held by the chuck table 54 in a state where the chuck table unit 54 is positioned in the wafer carry-in / carry-out region. The recess 10 of the housing 4 is provided with a discharge port 92 for draining the grinding water containing the grinding scraps of the wafer 11 ground by the grinding wheel 34.

  As shown in FIG. 6, the wafer crack detection device 88 includes a table 96 having a center hole 97, and a spinner table 94 that rotates while sucking and holding the wafer 11 in the center hole 97 when the wafer 11 is cleaned. Has been inserted.

  Four vacuum pads 98 are mounted on the table 96, and piezoelectric vibrators (PZT) 100 a to 100 d are inserted into the vacuum pads 98. In the present embodiment, as shown in FIG. 8, the piezoelectric vibrator 100a is connected to the high frequency power supply 108 to act as an ultrasonic wave generating element that generates ultrasonic waves, and the piezoelectric vibrators 100b to 100d receive ultrasonic waves. Acts as a receiving element.

  The table 96 is supported by the piston rods 104 of the four air cylinders 102. By driving the air cylinder 102, the table 96 is moved in the vertical direction (up and down direction).

  When the ground wafer 11 is attracted to the unloading arm 84 and conveyed to the spinner cleaning device 86, the spinner table 94 sucks and holds the wafer 11. While rotating the spinner table 94, cleaning water such as pure water is sprayed from the cleaning water spray nozzle to clean the wafer 11. After the cleaning is completed, the spinner table 94 is rotated at a high speed to spin dry the wafer 11.

  After cleaning and drying of the wafer 11, the negative pressure of the spinner table 94 is released, and then the air cylinder 102 is driven to extend the piston rod 104 as shown in FIG. As a result, the table 96 is raised and the wafer 11 on the spinner table 94 is pushed up by the table 96, the protective tape 23 side of the wafer 11 is sucked and held by the vacuum pad 98, and the piezoelectric vibrators 100 a to 100 d are protected by the protective tape of the wafer 11. 23.

  With the wafer 11 sucked and held in this way, a high frequency power having a predetermined frequency is applied to the piezoelectric vibrator 100a by the high frequency power supply 108 set to a predetermined frequency by the frequency setting unit 106 of the ultrasonic wave applying means 105 as shown in FIG. To do. As a result, an ultrasonic wave having a predetermined frequency is generated from the piezoelectric vibrator 100 a, and this ultrasonic wave propagates through the wafer 11 sucked and held by the vacuum pad 98.

  The ultrasonic waves propagated through the wafer 11 are received by the piezoelectric vibrators 100b to 100d acting as ultrasonic receiving elements, and the frequency of the ultrasonic waves received by the frequency detecting unit 110 of the ultrasonic detecting means 109 is detected.

  The frequency set by the frequency setting unit 106 and the frequency detected by the frequency detection unit 110 of the ultrasonic detection unit 109 are input to the determination unit 112. In the determination means 112, it is determined whether or not there is an abnormality in the state of the ultrasonic waves detected by the ultrasonic detection means 109 (step S10). If there is no abnormality, it is determined in step S11 that the wafer 11 is not cracked, If there is an abnormality, it is determined in step S12 that the wafer 11 is cracked.

  FIG. 9A shows the relationship between frequency and amplitude when the wafer 11 is not cracked, and FIG. 9B shows the relationship between frequency and amplitude when the wafer 11 is cracked. As is apparent from the comparison between the two graphs, when the wafer 11 has a crack, the amplitude at the corresponding frequency is smaller than when there is no crack. Therefore, by detecting a waveform as shown in FIG. 9B, it can be determined that there is a small crack that cannot be confirmed with the naked eye on the wafer 11 after grinding.

  In the embodiment described above, the determination unit 112 determines whether or not there is an abnormality in the amplitude of the frequency detected by the ultrasonic detection unit 109. The detection of the abnormality is a change in the volume (amplitude) of the ultrasonic wave. In addition, any of a change in the frequency of the received ultrasonic wave, a difference in the propagation speed of the ultrasonic wave, and a change in the interference wave of the ultrasonic wave may be detected.

  In the embodiment described above, the detection of cracks after wafer grinding is performed by disposing the wafer crack detection device 88 in the spinner cleaning device 86, but detection of cracks in the wafer 11 is limited to the grinding device 2. Instead of using a dicing machine, the wafer may be diced along the street.

  In this case, as is well known, it is preferable that the wafer 11 is supported by an annular frame via a dicing tape, and the ultrasonic wave application step, the ultrasonic detection step, and the determination step are performed in this state. This is because cracks may occur during the operation of supporting the wafer 11 with the annular frame via the dicing tape.

2 Grinding device 11 Semiconductor wafer 16 Grinding unit 30 Grinding wheel 54 Chuck table 86 Spinner cleaning device 88 Wafer crack detection device 94 Spinner table 98 Vacuum pads 100a to 100d Piezoelectric vibrator 102 Air cylinder 105 Ultrasonic wave application means 109 Ultrasonic detection means

Claims (3)

A method for detecting cracks in a wafer that detects cracks in a wafer having a plurality of devices formed on the surface,
An ultrasonic wave application step of contacting the wafer with ultrasonic wave application means to apply ultrasonic waves to the wafer; and
An ultrasonic detection step of detecting an ultrasonic wave propagating through the wafer by bringing the ultrasonic detection means into contact with a wafer at a position separated from the position where the ultrasonic wave application means is contacted;
In the ultrasonic detection step, if there is an abnormality in the state of the ultrasonic wave detected by the ultrasonic detection means, there is a crack in the wafer, and if there is no abnormality, a determination step for determining that there is no crack,
A method for detecting cracks in a wafer, comprising:   2. The wafer crack detection method according to claim 1, wherein the anomaly includes any one of a change in ultrasonic frequency, a difference in propagation speed of ultrasonic waves, a change in volume of ultrasonic waves, and a change in interference waves of ultrasonic waves. A wafer crack detection device for detecting a wafer crack having a plurality of devices formed on a surface thereof,
Ultrasonic application means for applying ultrasonic waves to the wafer in contact with the wafer;
An ultrasonic detection means for detecting an ultrasonic wave which is applied by the ultrasonic wave application means and propagates through the wafer by contacting a wafer at a position apart from a position where the ultrasonic wave application means is contacted;
If there is an abnormality in the state of the ultrasonic wave detected by the ultrasonic detection means, there is a crack in the wafer, and if there is no abnormality, a determination means that determines that there is no crack,
A wafer crack detection apparatus comprising:

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