JP5101312B2 - Thickness measuring device and grinding device provided with the thickness measuring device - Google Patents

Description

  The present invention relates to a thickness measuring device that measures the thickness of a wafer and a grinding device including the thickness measuring device.

  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.

  The present invention has been made in view of these points, and the object of the present invention is to provide a thickness measuring device that measures the thickness of a wafer in a non-contact manner and a grinding device equipped with the thickness measuring device. is there.

  According to the first aspect of the present invention, there is provided a thickness measuring device for measuring the thickness of the wafer held on the chuck table, the laser beam oscillating means for oscillating a laser beam having a wavelength transmissive to the wafer, An optical element that receives the first reflected light reflected from the upper surface of the wafer and the second reflected light reflected from the lower surface when the laser beam oscillated by the laser beam oscillating means is applied to the wafer held by the chuck table. A scale, measuring means for measuring the thickness of the wafer based on the output of the optical element scale, and counting the maximum or minimum number of interference intensities of the first reflected light and the second reflected light. A counter for outputting to the measuring means; a switch for selectively inputting the output of the optical element scale to the measuring means or the counter; Control means for controlling the switching of the wafer, and when the first reflected light reflected by the upper surface of the wafer and the second reflected light reflected by the lower surface are thicker than a predetermined thickness and do not interfere with each other via the switch The optical element scale output is directly input to the measuring means, and the thickness of the wafer is measured by reading the optical element scale. When the wafer thickness is equal to or less than the predetermined thickness, the control means The switch is switched to input the output of the optical element scale to the counter, and the thickness of the wafer is measured by counting the maximum or minimum number of interference intensities of the first reflected light and the second reflected light. A characteristic thickness measuring device is provided.

  According to the second aspect of the present invention, the chuck table for holding the wafer, the thickness measuring device for measuring the thickness of the wafer held by the chuck table, and the wafer based on the thickness of the wafer measured by the thickness measuring device. The thickness measuring device includes a laser beam oscillating unit that oscillates a laser beam having a wavelength that is transparent to the wafer, and the laser beam oscillating unit oscillates. An optical element scale that receives first reflected light reflected by the upper surface of the wafer and second reflected light reflected by the lower surface when the laser beam is irradiated on the wafer held by the chuck table; and the optical element scale Measuring means for measuring the thickness of the wafer based on the output of the output, and the maximum or minimum interference intensity of the first reflected light and the second reflected light A counter that outputs the count value to the measuring unit, a switch that selectively inputs the output of the optical element scale to the measuring unit or the counter, and a control unit that controls switching of the switch, When the wafer is thicker than a predetermined thickness and the first reflected light reflected by the upper surface of the wafer and the second reflected light reflected by the lower surface do not interfere with each other, the output of the optical element scale is measured via the switch. The thickness of the wafer is measured by directly inputting to the means and reading the optical element scale. When the thickness of the wafer falls below the predetermined thickness, the control means switches the switch to switch the optical element scale. The output is input to the counter, and the thickness of the wafer is measured by counting the number of maximum or minimum interference intensity of the first reflected light and the second reflected light. Grinding apparatus is provided which is characterized in that.

  Preferably, the control means controls to stop the operation of the grinding means when the thickness of the wafer reaches a predetermined thickness.

  According to the thickness measuring apparatus of the present invention, when the wafer is relatively thick and the first reflected light reflected by the upper surface of the wafer and the second reflected light reflected by the lower surface do not interfere with each other, the thickness of the wafer is determined by reading the optical element scale. When the measured thickness of the wafer is below a predetermined thickness and the first reflected light reflected on the upper surface of the wafer interferes with the second reflected light reflected on the lower surface, the first reflected light detected on the optical element scale Since the wafer thickness is measured by counting the maximum value or the minimum value of the interference intensity with the second reflected light, the wafer thickness is reliably measured even when the wafer thickness is reduced. be able to.

  By applying the thickness measuring apparatus of the present invention to a grinding apparatus, the wafer can be ground to a predetermined desired thickness while reliably measuring the thickness of the wafer.

  Hereinafter, a wafer thickness measuring apparatus and a grinding apparatus including the thickness measuring apparatus according to an embodiment 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. A non-contact thickness measuring device 57 that measures the thickness of the wafer being ground without contact with the wafer is rotatably disposed on the cover 56.

  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.

  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 a non-contact thickness measuring device 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, with reference to FIG. 7 thru | or FIG. 10, the detail of the non-contact thickness measuring apparatus 57 which concerns on this invention embodiment is demonstrated. First, referring to FIG. 7, reference numeral 92 denotes a housing of the non-contact thickness measuring device 57, and a measurement chamber 95 is defined between the front end portion of the housing 92, the glass plate 96, and the upper surface of the wafer 11. Yes.

  The pipe line 102 is connected to a compressed air source, and compressed air is ejected from the tip 102a of the pipe line 102 to blow away contamination such as grinding water staying on the grinding surface of the wafer 11.

  A semiconductor laser (LD) 98 is attached to the partition wall 94, and a laser beam having a wavelength (for example, 1000 nm to 1500 nm) having transparency to the wafer 11 is emitted from the LD 98, and has a predetermined incident angle on the wafer 11. Incident at.

  Reference numeral 100 denotes a CCD scale in which a number of CCDs are arranged at a predetermined pitch. The CCD scale 100 is formed on the partition wall 94 so as to be perpendicular to the reflected light 101a, 101b from the upper surface and the lower surface of the wafer 11 of the laser beam 99. It is attached. Instead of the CCD scale 100, another optical element scale having a similar function may be adopted.

  The output of the CCD scale 100 is input to the measuring unit 104 via the switch 106, and the thickness of the wafer 11 is measured by the measuring unit 104 in accordance with the reading of the CCD scale 100.

  Reference numeral 108 denotes a case where the thickness of the wafer 11 becomes a predetermined thickness or less and the first reflected light 101a reflected by the upper surface 11b of the wafer 11 and the second reflected light 101b reflected by the lower surface 11a of the wafer 11 interfere with each other. , A counter that counts the maximum value or the minimum value of the interference intensity of the reflected light, and is selectively connected to the CCD scale 100 via the switch 106.

  The count value of the counter 108 is input to the measuring unit 104, and the thickness of the wafer 11 is measured based on a method described in detail below. The counter 108 may count both the maximum value and the minimum value.

  When the grinding is continued and the thickness of the wafer 11 reaches a predetermined thickness, a signal is input from the measuring unit 104 to the controller 110 of the grinding apparatus 2, and the controller 110 controls to stop grinding. .

  Hereinafter, a method for measuring the thickness of the wafer 11 according to the embodiment of the present invention will be described in detail. The laser beam 99 emitted from the LD 98 is transmitted through the glass plate 96 and is incident on the wafer 11 at a predetermined incident angle. A part of the laser beam 99 is reflected as the first reflected light 101a on the upper surface 11a of the wafer 11 and the rest. The laser beam is refracted by the wafer 11 (refractive index: 3.35), transmitted through the wafer 11, reflected by the lower surface 11a of the wafer 11 at a reflection angle θ, and received by the CCD scale 100 as second reflected light 101b.

  When the wafer 11 is relatively thick, for example, when the thickness of the wafer 11 is larger than 110 μm, the first reflected light 101a and the second reflected light 101b hardly interfere. Therefore, in this case, the thickness of the wafer 11 is measured by the measuring unit 104 from the reading of the CCD scale 100.

If the relative refractive index of the air and the Si wafer 11 is ignored, the optical path of the laser beam 99 emitted from the LD 98 is as shown in FIG. As shown in FIG. 8, when the reading of the CCD scale 100 is L,
L1 = L / sin2θ
Because
W = L1 cos θ
= Lcosθ / sin2θ
It becomes. Considering the relative refractive index of air (refractive index of about 1.0) and Si wafer (refractive index of 3.35), the correction coefficient based on the refractive index is k.
W = L × cos θ / sin 2θ × k (1)
Is obtained.

  L is detected from the reading of the CCD scale 100, the reflection angle θ on the lower surface 11a of the wafer 11 is an existing value, and the correction coefficient k is obtained in advance by experiments, so that the thickness W of the wafer 11 is determined by the measuring unit 104. Measurement is possible based on equation (1).

  When the grinding is continued and the thickness of the wafer 11 becomes a predetermined thickness or less, for example, 110 μm or less, the first reflected light 101a and the second reflected light 101b interfere with each other and are sine on the CCD scale 100. A wavy interference intensity is obtained. That is, when the wavelength of the laser beam 99 is λ, the first reflected light 101a and the second reflected light 101b interfere with each other and increase (or decrease) in intensity for each wavelength λ (2π).

Therefore, when the wavelength of the laser beam 99 emitted from the LD 98 is λ and n is the number of wavelengths, the relationship shown in FIG. 9 is obtained when the wafer 11 has a thickness of 110 μm. From FIG.
L2 = nλ × cos θ / sin θ
L3 = L2 × 1 / sin2θ = nλ × cosθ / sinθ × 1 / sin2θ
Therefore, W1 = L3 × cos θ = nλ × cos ² θ / (sin 2θ × sin θ)
It becomes. Considering the relative refractive index of air and Si wafer 11, if the correction coefficient is k,
W1 = cos ² θ × k / (sin 2θ × sin θ) × nλ = 110 μm (2)
Is obtained.

Grinding is continued, and the upper surface 11b of the wafer 11 is ground to 11b '. At this time, the distance between the first reflected light 101a' and the second reflected light 101b is set to L4, and the first reflected light 101a 'and the first reflected light 101a' If the maximum count of interference intensity with the two reflected light 101b is c, for example, the relationship shown in FIG. 10 is obtained. From FIG.
L4 = (n−c) λ × cos θ / sin θ
L5 = L4 × 1 / sin2θ = (n−c) λ × cosθ / sinθ × 1 / sin2θ
Therefore, W = L5 × cos θ = (n−c) λ × cos ² θ / (sin θ × sin θ)
= 110 μm-cos ² θ / (sin 2θ × sin θ) × cλ
Considering the refractive index of air and Si wafer 11, if the correction coefficient is k,
W = 110 μm−cos ² θ × k / (sin 2θ × sin θ) × cλ (3)
It becomes. If both the maximum value and the minimum value are counted, the count number is doubled and the resolution is doubled.

  Since θ and wavelength λ are already values, the counter 108 counts the number of times that the interference intensity between the first reflected light 101a ′ and the second reflected light 101b has increased, so that the measuring unit is based on the count value of the counter 108. At 104, the thickness of the wafer 11 can be measured.

  In this embodiment, at the moment when the wafer 11 is continuously ground and the thickness of the wafer 11 reaches 110 μm, the controller 110 switches the switch 106 and inputs the output of the CCD scale 100 to the counter 108.

  In this embodiment, when the thickness of the wafer 11 is continued while the thickness of the wafer 11 is measured by the measuring device by the method described above, and the thickness of the wafer 11 reaches a predetermined desired thickness (for example, 50 μm). In this case, a signal is output from the measuring unit 104 to the controller 110 of the grinding apparatus 2, and the controller 110 is controlled to stop grinding of the wafer 11.

  Thus, even when the thickness of the wafer 11 is reduced by grinding and the thickness of the wafer 11 cannot be measured from the reading of the CCD scale 100, the wafer 11 is finished to a desired thickness while accurately measuring the thickness of the wafer 11. Can do.

  In the above-described embodiment, compressed air is ejected from the tip of the pipe line 102 to remove contamination such as grinding water from the grinding surface 11b of the wafer 11, but compressed air is jetted from the pipe line 102. Instead, water is supplied into the measurement chamber 95 from the conduit 102, and water is filled between the front end portion of the housing 92, the glass plate 96, and the upper surface of the wafer 11, and the same as described above. Measurement may be executed.

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. It is explanatory drawing which shows the dimensional relationship in case the thickness of a wafer is larger than 110 micrometers. It is explanatory drawing which shows the dimensional relationship in case the thickness of a wafer is 110 micrometers. It is explanatory drawing which shows the dimensional relationship in case the thickness of a wafer is 110 micrometers or less.

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 57 non-contact thickness measuring device 98 laser diode (LD)
100 CCD scale 104 Measuring unit 106 Switch 108 Counter

Claims (3)

A thickness measuring device for measuring the thickness of a wafer held on a chuck table,
Laser beam oscillation means for oscillating a laser beam having a wavelength that is transparent to the wafer;
An optical system for receiving the first reflected light reflected by the upper surface of the wafer and the second reflected light reflected by the lower surface when the laser beam oscillated by the laser beam oscillating means is applied to the wafer held by the chuck table. Element scale,
Measuring means for measuring the thickness of the wafer based on the output of the optical element scale;
A counter that counts the maximum or minimum number of interference intensities of the first reflected light and the second reflected light, and outputs the count value to the measuring means;
A switch for selectively inputting the output of the optical element scale to the measuring means or the counter;
Control means for controlling the switching of the switch,
When the wafer is thicker than a predetermined thickness and the first reflected light reflected by the upper surface of the wafer and the second reflected light reflected by the lower surface do not interfere with each other, the output of the optical element scale is directly input to the measuring means via the switch. Then, the thickness of the wafer is measured by reading the optical element scale,
When the thickness of the wafer is equal to or less than the predetermined thickness, the control means switches the switch to input the output of the optical element scale to the counter, and the interference between the first reflected light and the second reflected light. A thickness measuring apparatus for measuring the thickness of a wafer by counting the number of maximum or minimum intensity values. A chuck table for holding a wafer, a thickness measuring device for measuring the thickness of the wafer held on the chuck table, and a grinding means for grinding the wafer based on the wafer thickness measured by the thickness measuring device. A grinding device,
The thickness measuring device is
Laser beam oscillation means for oscillating a laser beam having a wavelength that is transparent to the wafer;
An optical system for receiving the first reflected light reflected by the upper surface of the wafer and the second reflected light reflected by the lower surface when the laser beam oscillated by the laser beam oscillating means is applied to the wafer held by the chuck table. Element scale,
Measuring means for measuring the thickness of the wafer based on the output of the optical element scale;
A counter that counts the maximum or minimum number of interference intensities of the first reflected light and the second reflected light, and outputs the count value to the measuring means;
A switch for selectively inputting the output of the optical element scale to the measuring means or the counter;
Control means for controlling the switching of the switch,
When the wafer is thicker than a predetermined thickness and the first reflected light reflected by the upper surface of the wafer and the second reflected light reflected by the lower surface do not interfere with each other, the output of the optical element scale is directly input to the measuring means via the switch. Then, the thickness of the wafer is measured by reading the optical element scale,
When the thickness of the wafer is equal to or less than the predetermined thickness, the control means switches the switch to input the output of the optical element scale to the counter, and the interference between the first reflected light and the second reflected light. A grinding apparatus for measuring the thickness of a wafer by counting the maximum or minimum number of strengths.   3. The grinding apparatus according to claim 2, wherein when the thickness of the wafer measured by the thickness measuring apparatus reaches a predetermined thickness, the control means controls to stop the operation of the grinding means. .

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