JP5160190B2 - Grinding apparatus and grinding method - Google Patents

Description

  The present invention relates to a grinding method and a grinding apparatus for grinding a wafer while measuring the thickness of the wafer.

  A semiconductor wafer in which a large 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) is processed by a grinding machine to have a predetermined thickness after the back surface is ground. A division line is cut by a dicing machine (cutting machine) and divided into individual devices, which are used for electric devices such as mobile phones and personal computers.

A grinding apparatus for grinding a back surface of a wafer includes a chuck table for holding a wafer, a grinding means for rotatably supporting a grinding wheel provided with a grinding wheel for grinding a wafer held by the chuck table, and a chuck table And a thickness measuring means for measuring the thickness of the wafer held on the wafer, the wafer can be processed to a desired thickness while constantly detecting the thickness of the wafer (see Japanese Patent No. 2999381).
Japanese Patent No. 2993821

  However, since the conventional thickness measuring means performs grinding while bringing a measuring needle into contact with the grinding surface of the wafer, there is a problem that a ring-shaped scratch is generated on the wafer, causing distortion and the like, leading to a decrease in quality. .

  In particular, when a base wafer for forming a circuit is formed by grinding the front and back surfaces of a wafer cut out from an ingot, this scratch becomes a cause of hindering subsequent mirror surface processing.

  This invention is made | formed in view of such a point, The place made into the objective is providing the grinding apparatus and grinding method which have a non-contact thickness measurement means using an ultrasonic wave.

According to the first aspect of the present invention, there is provided a grinding apparatus comprising a chuck table unit including a chuck table for holding a wafer, a grinding means having a grinding wheel for grinding the wafer held by the chuck table , and the chuck table. An actual thickness measuring means rotatably arranged on the chuck table unit for measuring the actual thickness of the wafer held on the wafer, and emitting ultrasonic waves toward one surface of the wafer and reflecting it on the one surface A non-contact thickness measuring means rotatably disposed on the chuck table unit for measuring the thickness of the wafer in a non-contact manner by a time difference between the ultrasonic wave transmitted through the wafer and reflected by the other surface. and, the non-contact thickness measuring means, and ultrasonic device that emits ultrasonic waves, the time to receive the ultrasonic wave reflected by the one surface and the other surface of the wafer A time difference measuring unit for measuring the thickness of the wafer based on the time difference and the measurement reference value, and measuring the thickness of the wafer before grinding by the actual thickness measuring means. Assuming that the time difference measured by the time difference measurement unit for the wafer having the initial thickness W1 is T1, W1 / T1 is set as the measurement reference value used by the calculation unit, and W1 / A grinding apparatus is provided in which the thickness W of the wafer is calculated by (W1 / T1) · T by multiplying T1 by the time difference T during grinding measured by the time difference measuring unit .

According to the second aspect of the present invention, there is provided a chuck table unit including a chuck table for holding a wafer, a grinding means having a grinding wheel for grinding the wafer held on the chuck table, and a wafer held on the chuck table . The actual thickness measuring means rotatably arranged on the chuck table unit for measuring the actual thickness, and the ultrasonic wave is emitted to one surface of the wafer, and the ultrasonic wave reflected on the one surface and the wafer are transmitted. The thickness of the wafer is measured in a non-contact manner by the time difference from the ultrasonic wave reflected by the other surface, and the ultrasonic element that emits ultrasonic waves and the ultrasonic wave reflected by one surface and the other surface of the wafer are received and the time difference is received. The chuck table unit includes a time difference measuring unit for measuring, and an arithmetic unit for calculating the thickness of the wafer based on the time difference and the measurement reference value. A contactless thickness measuring means Tsu pivotally disposed bets, a wafer grinding method of by grinding apparatus having a, a initial thickness measured by the actual thickness measurement means W1, initial thickness When the time difference measured by the time difference measuring unit with respect to the wafer having a thickness W1 is T1, the calculation unit of the non-contact thickness measuring unit uses the initial thickness W1 of the wafer obtained by the actual thickness measuring unit. The measurement standard value is set to W1 / T1 , and the thickness W of the wafer is calculated by (W1 / T1) · T by multiplying the time difference T during grinding measured by the time difference measurement unit by W1 / T1 by the calculation unit. , grinding method of a wafer, characterized by performing the grinding of the wafer while measuring the thickness W of the wafer by the non-contact thickness measurement means.

  Since the grinding apparatus of the present invention includes the actual thickness measuring means and the non-contact thickness measuring means using ultrasonic waves, the non-contact thickness measuring means calculates based on the initial thickness of the wafer measured by the actual thickness measuring means. The measurement reference value used in the wafer can be set, and grinding is performed while constantly measuring the thickness of the wafer with a non-contact thickness measuring means, and the wafer is brought to a desired thickness without damaging the ground surface of the wafer. Can be finished.

  Hereinafter, a wafer grinding method and a grinding apparatus according to embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is 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 semiconductor wafer 11 configured as described above 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 semiconductor 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 semiconductor wafer 11 by a protective tape attaching process. Therefore, the front surface 11a of the semiconductor wafer 11 is protected by the protective tape 23, and the back surface 11b is exposed as shown in FIG.

  Hereinafter, a grinding apparatus 2 for grinding the back surface 11b of the semiconductor 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. 6, a mounter 28 is fixed to the tip of the spindle 24, and a grinding wheel 30 is screwed to the mounter 28. For example, the grinding wheel 30 is configured by affixing a plurality of grinding wheels 34 in which diamond abrasive grains having a grain size of 0.3 to 1.0 μm are hardened by vitrified bonds to a free end portion of a wheel base 32. Therefore, the grinding surface is a mirror surface.

  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. 6, 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 mounter 28, and the wheel base 32 of the grinding wheel 30. It is supplied to the wafer 11 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.

  An actual thickness measuring means 55 for measuring the actual thickness of the wafer in contact with the wafer to be ground and a non-contact thickness measuring means 57 for measuring the thickness of the wafer being ground without contacting the wafer are rotatable on the cover 56. It is arranged.

  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.

  In the horizontal housing portion 6 of the housing 4, a first wafer cassette 74, a second wafer cassette 76, a wafer transport means 78, a wafer temporary mounting means 80, a wafer carry-in means 82, and a wafer carry-out means 84 are provided. A cleaning means 86 is provided. Further, an operation means 88 is provided in front of the housing 4 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 chuck table unit 50 pulse-drives the pulse motor 64 of the chuck table moving mechanism 58 to receive the wafer from the grinding area on the back side of the apparatus and the wafer carry-in means 82 shown in FIG. It is moved to and from the wafer loading / unloading area on the near side.

  The grinding operation of the grinding device 2 configured as described above will be described below. The wafer housed in the first wafer cassette 74 is a semiconductor wafer having a protective tape mounted on the front surface side (surface on which the circuit is formed), and therefore the wafer is positioned with the back surface positioned on the upper side. Housed in the first cassette 74. As described above, the first wafer cassette 74 that accommodates a plurality of semiconductor wafers is mounted with a predetermined cassette of the housing 4 in the carry-in area.

  When all of the unprocessed semiconductor wafers contained in the first wafer cassette 74 placed in the cassette carry-in area are carried out, a plurality of semiconductor wafers are accommodated in place of the empty wafer cassette 74. A new first wafer cassette 74 is manually placed in the cassette loading area.

  On the other hand, when a predetermined number of ground semiconductor wafers are loaded into the second wafer cassette 76 placed in the predetermined cassette unloading area of the housing 4, the second wafer cassette 76 is manually unloaded. A new empty second wafer cassette 76 is placed in the cassette unloading area.

  The semiconductor wafer accommodated in the first wafer cassette 74 is conveyed by the vertical movement and forward / backward movement of the wafer conveyance means 78 and is placed on the wafer temporary placement means 80. The wafer placed on the temporary wafer placement means 80 is centered here, and then the chuck table of the chuck table unit 50 positioned in the wafer carry-in / out area by the turning operation of the wafer carry-in means 82. 54 and is sucked and held by the chuck table 54.

  When the chuck table 54 sucks and holds the wafer in this way, the chuck table moving mechanism 58 is operated to move the chuck table unit 50 and position it in the grinding area behind the apparatus. Then, the actual thickness measuring means 55 measures the initial thickness of the wafer before grinding.

  When the chuck table unit 50 is positioned in the grinding area, the center of the wafer held by the chuck table 54 is positioned slightly beyond the outer circumference circle of the grinding wheel 30.

  Next, the chuck table 54 is rotated at, for example, about 100 to 300 rpm, the servo motor 26 is driven to rotate the grinding wheel 30 at 4000 to 7000 rpm, and the pulse motor 48 of the grinding unit feed mechanism 44 is driven to rotate forward. The grinding unit 16 is lowered.

  Then, as shown in FIG. 6, the back surface of the wafer 11 is ground by pressing the grinding wheel 34 of the grinding wheel 30 against the back surface (surface to be ground) of the wafer 11 on the chuck table 54 with a predetermined load.

  By grinding in this way for a predetermined time, the wafer 11 is ground to a predetermined thickness. During the grinding of the wafer, the wafer is ground while the thickness of the wafer is measured by the non-contact thickness measuring means 57 described later in detail.

  When grinding is completed, the chuck table moving mechanism 58 is driven to position the chuck table 54 in the wafer loading / unloading area on the front side of the apparatus. If the chuck table 54 is positioned in the wafer loading / unloading area, the cleaning water is sprayed from the cleaning water spray nozzle 90 and the ground surface (back surface) of the ground wafer 11 held by the chuck table 54 is held. Wash.

  After the suction and holding of the wafer 11 held on the chuck table 54 is released, the wafer 11 is transferred to the cleaning means 86 by the wafer unloading means 84. The wafer 11 conveyed to the cleaning means 86 is cleaned here and spin-dried. Next, the wafer 11 is stored in a predetermined position of the second wafer cassette 76 by the wafer transport means 78.

  Next, the details of the non-contact thickness measuring means 57 according to the embodiment of the present invention will be described with reference to FIG. Reference numeral 92 denotes a housing of the non-contact thickness measuring means 57, and a water filling chamber 96 is defined between the front end portion of the housing 92, the partition wall 94, and the upper surface of the wafer 11.

  One end 98 a of the pipe line 98 is connected to the water source 100, and the other end 98 b opens to the water filling chamber 96. Reference numeral 102 denotes a switching valve. The distance between the tip 92a of the housing 92 and the wafer 11 is preferably maintained at about 0.5 to 1 mm.

  Reference numeral 104 denotes an ultrasonic transmission rod, which is attached to the partition wall 94 so that its lower end protrudes into the water filling chamber 96. The ultrasonic transmission rod 104 is made of a resin such as quartz or acrylic resin.

An ultrasonic element 106 is mounted and fixed on the upper end of the ultrasonic transmission rod 104. The ultrasonic element 106 is made of, for example, lead zirconate titanate (PB (Zi, Ti) O ₃ ), barium titanate (BaTiO ₃ ), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or the like. ing. Lead zirconate titanate is sometimes referred to as PZT.

  The ultrasonic element 106 generates ultrasonic waves of 6 MHz to 20 MHz, for example. The ultrasonic waves generated by the ultrasonic element 106 are transmitted through the ultrasonic transmission rod 104 and emitted toward the back surface 11b of the wafer 11 facing upward.

  The pulse voltage generator 108 drives the ultrasonic element 106 by oscillating a pulse voltage of, for example, 250 V about 1000 times per second. The time difference measuring unit 110 receives the ultrasonic wave R1 reflected by the one surface 11b of the wafer 11 and the ultrasonic wave R2 transmitted through the wafer 11 and reflected by the other surface 11a, and measures the time difference T between the arrival times of R1 and R2. .

  The calculation unit 112 calculates the thickness of the wafer 11 based on the time difference T measured by the time difference measurement unit 100 and the measurement reference value. This measurement reference value is set as follows. That is, the actual thickness measuring means 55 measures the thickness W1 of the wafer 11 before grinding.

  Next, the pulse voltage generator 108 generates a pulse voltage to drive the ultrasonic element 106, and the time difference measuring unit 110 reflects the ultrasonic wave R1 reflected from the one surface 11b and the ultrasonic wave R2 reflected from the other surface 11a. The time difference T1 of the arrival times is measured. In the calculation unit 112, W1 / T1 is set as a measurement reference value.

  In the present embodiment, the measurement of the thickness of the wafer 11 by the actual thickness measuring means 55 is used only for the measurement of the initial thickness W1. During grinding by the grinding wheel 30, the actual thickness measuring means 55 is retracted from the wafer 11, and the wafer is ground while the thickness of the wafer 11 is measured by the non-contact thickness measuring means 57.

  That is, the pulse voltage generator 108 generates a pulse voltage to drive the ultrasonic element 106, and the ultrasonic wave R 1 reflected by the one surface 11 b of the wafer 11 and the ultrasonic wave reflected by the other surface 11 a of the wafer 11. The time difference measuring unit 110 measures the difference T in arrival time of R2.

  The computing unit 112 can calculate the thickness W of the wafer 11 during grinding by multiplying the measurement reference value (W1 / T1) by the time difference T. That is, the calculation unit 112 performs a calculation of W = (W1 / T1) × T.

The thickness W of the wafer 11 obtained by calculating in the calculating portion 112 is inputted to the controller 114 of Grinding apparatus 2 ends the grinding of the wafer 11 by the grinding apparatus 2 if desired thickness of the wafer 11 is obtained .

  During grinding of the wafer 11, water is constantly supplied from the water source 100 into the water filling chamber 96 to fill the water filling chamber 96, and in this state, the wafer 11 is ground and the thickness of the wafer 11 by the non-contact thickness measuring means 57 is filled. Perform the measurement. The supplied water is preferably pure water. The reason why the water filling chamber 96 is filled with water is to stabilize the emitted ultrasonic waves.

  According to this embodiment described above, the grinding apparatus includes the actual thickness measuring means 55 for measuring the actual thickness of the wafer 11 and the non-contact thickness measuring means 57 using ultrasonic waves. Based on the measured initial thickness W 1 of the wafer 11, a measurement reference value (W 1 / T 1) used by the calculation unit 112 of the non-contact thickness measuring unit 57 can be set, and the thickness of the wafer 11 can be set by the non-contact thickness measuring unit 57. The wafer 11 can be finished to a desired thickness without grinding the surface of the wafer by scratching the surface of the wafer without being damaged.

It is a front side perspective view of a semiconductor wafer. It is a back surface side perspective view of the semiconductor wafer where the protective tape was stuck. 1 is an external perspective view of a grinding apparatus according to 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 perspective view of the grinding wheel seen from the lower side. It is a longitudinal cross-sectional view of a grinding wheel. It is a partial cross section block diagram which shows the principal part of this invention.

Explanation of symbols

2 Grinding machine 11 Semiconductor wafer 16 Grinding means (grinding unit)
24 Spindle 26 Servo motor 30 Grinding wheel 34 Grinding wheel 50 Chuck table unit 54 Chuck table 55 Actual thickness measuring means 57 Non-contact thickness measuring means 104 Ultrasonic transmission rod 106 Ultrasonic element 108 Pulse voltage generating part 110 Time difference measuring part 112 Calculation part

Claims (2)

A grinding device,
A chuck table unit including a chuck table for holding a wafer;
Grinding means having a grinding wheel for grinding the wafer held on the chuck table;
An actual thickness measuring means rotatably disposed on the chuck table unit for measuring the actual thickness of the wafer held on the chuck table ;
Toward one side of the wafer to emit ultrasonic waves, measures the thickness of the wafer by the time difference between the ultrasonic waves transmitted through the ultrasonic wave and the wafer that is reflected by one surface the reflected on the other surface without contact the A non-contact thickness measuring means rotatably disposed on the chuck table unit ,
The non-contact thickness measuring means includes an ultrasonic element that emits ultrasonic waves, a time difference measuring unit that receives ultrasonic waves reflected from one surface and the other surface of the wafer, and measures a time difference, and the time difference and the measurement reference value. And a calculation unit that calculates the thickness of the wafer based on the
When the thickness of the wafer before grinding is measured by the actual thickness measuring means to obtain an initial thickness W1, and the time difference measured by the time difference measuring unit with respect to the wafer having the initial thickness W1 is T1, W1 / T1 Is set as the measurement reference value used in the calculation unit, and W1 / T1 is multiplied by the grinding time difference T measured by the time difference measurement unit in the calculation unit, and the wafer thickness W is (W1 / T1) · T. A grinding apparatus characterized by calculating A chuck table unit including a chuck table for holding a wafer, a grinding means having a grinding wheel for grinding a wafer held by the chuck table, and the chuck table unit for measuring an actual thickness of the wafer held by the chuck table An actual thickness measuring means rotatably disposed on the surface, an ultrasonic wave emitted to one surface of the wafer, an ultrasonic wave reflected on the one surface, an ultrasonic wave transmitted through the wafer and reflected on the other surface, and Measuring the thickness of the wafer in a non-contact manner according to the time difference between the ultrasonic element that emits ultrasonic waves, the time difference measuring unit that receives the ultrasonic waves reflected from one surface and the other surface of the wafer, and measures the time difference, and the time difference. and it is composed of an arithmetic unit for calculating the thickness of the wafer on the basis of the measurement reference value, which is disposed so as to be rotatable on the chuck table unit A contact thickness measurement means, a wafer grinding method of by grinding device provided with,
When the initial thickness measured by the actual thickness measuring means is W1, and the time difference measured by the time difference measuring unit with respect to the wafer having the initial thickness W1 is T1, the wafer obtained by the actual thickness measuring means is Based on the initial thickness W1 , the measurement reference value used in the calculation unit of the non-contact thickness measuring means is set to W1 / T1 ,
Multiplying the time difference T during grinding measured by the time difference measurement unit by W1 / T1 by the calculation unit, the wafer thickness W is calculated by (W1 / T1) · T,
Grinding method of the wafer, which comprises performing the grinding of the wafer while measuring the thickness W of the wafer by the non-contact thickness measurement means.

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