CN107796314B

CN107796314B - Measuring device

Info

Publication number: CN107796314B
Application number: CN201710749731.XA
Authority: CN
Inventors: 能丸圭司
Original assignee: Disco Corp
Current assignee: Disco Corp
Priority date: 2016-09-02
Filing date: 2017-08-28
Publication date: 2021-03-05
Anticipated expiration: 2037-08-28
Also published as: TW201812248A; KR102254616B1; CN107796314A; JP2018036213A; KR20180026345A; JP6802012B2; TWI734817B

Abstract

Provided is a measuring device for measuring the thickness or height of a plate-like object (wafer (10)), including: a pulsed broadband light source (82) that emits light; a fiber Bragg grating (83) for transmitting the pulse light, splitting the light according to different wavelengths and inverting the light; an optical fiber transmission member (83a) for branching the pulse light in the reverse direction and transmitting the pulse light to the optical fiber; a measurement terminal (81) which branches the end of the optical fiber into two, and which has a mirror (81c) disposed on one end surface thereof for generating a first return light that is reversed in the optical fiber, and an objective lens (81a) disposed on the other end surface thereof for converging the light on the plate-like object; a light branching member (84) that branches first return light and second return light that is reflected by the upper surface of the plate-like object and light that is transmitted through the plate-like object and reflected by the lower surface, and that is reversed in the optical fiber; a spectral interference waveform generating means for obtaining a wavelength from a time difference of one pulse of the first and second return lights, detecting light intensities at the respective wavelengths, and generating a spectral interference waveform of one pulse; and a calculating means for calculating the thickness or height of the plate-like object by analyzing the waveform.

Description

Measuring device

Technical Field

The present invention relates to a measuring device for measuring the thickness or height of a plate-like object.

Background

A wafer having a plurality of devices such as ICs and LSIs formed on its front surface by dividing a predetermined line is ground on its back surface by a grinding apparatus to a predetermined thickness, and then divided into individual devices by a dicing apparatus or a laser processing apparatus, and used in electrical equipment such as mobile phones and personal computers.

As a grinding device, there is proposed a technique by having: a chuck table for holding a wafer; a grinding member in which a grinding wheel for grinding the back surface of the wafer held by the chuck table is disposed in a ring shape; and a detection member that detects the thickness of the wafer in a non-contact manner by the spectroscopic interference waveform to grind the wafer to a desired thickness (see, for example, patent document 1).

Patent document 1: japanese patent laid-open publication No. 2011-143488

However, in the technique described in patent document 1, when the thickness or height is to be detected, it is necessary to branch reflected light reflected by the upper surface and the lower surface of the workpiece, diffract interference of the two reflected lights by a collimator lens or a diffraction grating which makes the reflected light parallel, transmit a diffraction signal corresponding to each wavelength to a line image sensor via a condenser lens, and detect light intensity at each wavelength of the reflected light detected by the line image sensor or the like to obtain a spectroscopic interference waveform. Therefore, there are problems in that the number of devices mounted for measuring the thickness or height is increased, the structure is complicated, and the whole device becomes expensive.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and a main technical object thereof is to provide a measuring apparatus having a simple structure and being inexpensive.

In order to solve the above-described main technical problem, according to the present invention, there is provided a measuring apparatus for measuring a thickness or a height of a plate-like object, the measuring apparatus including at least: a pulsed broadband light source that emits light in a wavelength band that is transmissive to a plate-like object in the form of pulsed light; the fiber Bragg grating is used for transmitting the pulse light emitted by the pulse broadband light source, splitting the pulse light according to different wavelengths according to the transmission distance and enabling the pulse light to be retrograde; an optical fiber transmission member which is disposed in the fiber Bragg grating, branches the pulse light in the reverse direction, and transmits the pulse light to an optical fiber; a measurement terminal that branches an end portion of the optical fiber into two end surfaces, the measurement terminal having a mirror that is disposed on one end surface and generates first return light that is in a reverse direction in the optical fiber, and an objective lens that is disposed on the other end surface and converges the pulsed light on the plate-like object; a light branching member that branches a second return light obtained by interfering the pulse light reflected on the upper surface of the plate-like object with the pulse light transmitted through the plate-like object and reflected on the lower surface of the plate-like object and causing the optical fiber to travel in the reverse direction; a spectral interference waveform generating means for obtaining a wavelength from a time difference of one pulse of the first return light and the second return light branched by the optical branching means, detecting an intensity of light of each wavelength, and generating a spectral interference waveform of one pulse; and a calculating means for calculating the thickness or height of the plate-like object by performing waveform analysis on the spectroscopic interference waveform generated by the spectroscopic interference waveform generating means.

The measuring apparatus of the present invention is configured as described above, and particularly includes: a pulsed broadband light source that emits light in a wavelength band that is transmissive to a plate-like object in the form of pulsed light; the fiber Bragg grating is used for transmitting the pulse light emitted by the pulse broadband light source, splitting the pulse light according to different wavelengths according to the transmission distance and enabling the pulse light to be retrograde; an optical fiber transmission member which is disposed in the fiber Bragg grating, branches the pulse light in the reverse direction, and transmits the pulse light to an optical fiber; a measurement terminal that branches an end portion of the optical fiber into two end surfaces, the measurement terminal having a mirror that is disposed on one end surface and generates first return light that is in a reverse direction in the optical fiber, and an objective lens that is disposed on the other end surface and converges the pulsed light on the plate-like object; a light branching member that branches second return light that is obtained by interfering the pulsed light reflected by the upper surface of the plate-like object and the pulsed light transmitted through the plate-like object and reflected by the lower surface and traveling in reverse in the optical fiber; a spectral interference waveform generating means for obtaining a wavelength from a time difference of one pulse of the first return light and the second return light branched by the optical branching means, detecting an intensity of light of each wavelength, and generating a spectral interference waveform of one pulse; and a calculating means for calculating the thickness or height of the plate-like object by waveform-analyzing the spectroscopic interference waveform generated by the spectroscopic interference waveform generating means, thereby providing a measuring apparatus capable of measuring thickness variation with a simple configuration and at low cost.

Drawings

Fig. 1 is a perspective view of a grinding apparatus to which a measuring apparatus constructed according to the present invention is applied.

Fig. 2 is an explanatory diagram for explaining the structure of the measuring apparatus configured according to the present invention.

Fig. 3 (a) and (b) are diagrams showing an example of a spectroscopic interference waveform generated by the measurement apparatus shown in fig. 2 and an example of an optical path length difference and a signal intensity obtained by waveform analysis of the spectroscopic interference waveform.

Description of the reference symbols

1: a grinding device; 2: a device housing; 3: a grinding unit; 4: a spindle unit; 5: grinding the grinding wheel; 7: a chuck table mechanism; 8: a measuring device; 10: a wafer; 80: a measurement housing; 81: a measurement terminal; 81 a: an objective lens; 81 c: a mirror; 82: a pulsed broadband light source; 83: a fiber bragg grating; 83 a: an optical fiber transfer member; 84: an optical branching member; 85: a light receiving element; k1 to k 17: a diffraction grating; f 1-f 5: an optical fiber.

Detailed Description

Hereinafter, the measuring apparatus of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 shows a perspective view of a grinding apparatus 1 having a measuring device according to the present invention as a whole, and a wafer 10 as a plate-like object whose thickness and height are to be measured by the measuring device according to the present invention. The grinding device 1 shown in the figure has a device housing which will be designated as a whole by reference numeral 2. The device case 2 has: a main portion 21 of a substantially rectangular parallelepiped shape; and an upright wall 22 provided at a rear end portion (upper right end in fig. 1) of the main portion 21 and extending upward. On the front surface of the upright wall 22, a grinding unit 3 as a grinding member is mounted movably in the up-down direction.

The grinding unit 3 includes a movable base 31 and a spindle unit 4 attached to the movable base 31. The moving base 31 is configured to slidably engage with a pair of guide rails disposed on the upright wall 22. The spindle unit 4 as a grinding member is attached to the front surface of the moving base 31 slidably attached to the pair of guide rails provided on the upright wall 22 via a support portion projecting forward.

The spindle unit 4 includes: a spindle case 41; a rotary spindle 42 rotatably disposed in the spindle housing 41; and a servo motor 43 as a driving source for rotationally driving the rotary spindle 42. The rotating spindle 42 rotatably supported by the spindle case 41 is disposed such that one end (lower end in fig. 1) thereof protrudes from the lower end of the spindle case 41 and a wheel base 44 is provided at the lower end thereof. A grinding wheel 5 is attached to the lower surface of the wheel holder 44. A grinding wheel 51 composed of a plurality of segments is disposed on the lower surface of the grinding wheel 5.

The illustrated grinding apparatus 1 includes a grinding unit feed mechanism 6 that moves the grinding unit 3 in the vertical direction (direction perpendicular to a holding surface of a chuck table, which will be described later) along the pair of guide rails. The grinding unit feed mechanism 6 includes: an externally threaded rod 61 disposed on the front side of the upright wall 22 and extending substantially vertically; and a pulse motor 62 as a driving source for rotationally driving the male screw rod 61, wherein the grinding unit feeding mechanism 6 includes a bearing member of the male screw rod 61, not shown, and the like, and is provided on the back surface of the movable base 31. When the pulse motor 62 rotates forward, the movable base 31, i.e., the polishing unit 3, moves downward, i.e., moves forward, and when the pulse motor 62 rotates backward, the movable base 31, i.e., the polishing unit 3, moves upward, i.e., moves backward.

A chuck table mechanism 7 as a holding member for holding a plate-like object (wafer 10) as a workpiece is disposed on the main portion 21 of the housing 2. The chuck table mechanism 7 includes: a chuck table 71; a cover member 72 covering the periphery of the chuck table 71; and

corrugated members

73 and 74 disposed in front and rear of the cover member 72. The chuck table 71 is configured to suck and hold the wafer 10 on its upper surface (holding surface) by operating a suction member (not shown). The chuck table 71 is configured to be rotatable by a rotation driving member (not shown) and movable by a chuck table moving member (not shown) between a workpiece placement region 70a shown in fig. 1 and a grinding region 70b facing the grinding wheel 5 (in the X-axis direction shown by the arrow X).

The servo motor 43, the pulse motor 62, the chuck table moving means not shown, and the like are controlled by the control means 20 described later. In the illustrated embodiment, a notch indicating a crystal orientation is formed in the outer peripheral portion of the wafer 10, a protective tape 12 as a protective member is bonded to the front surface thereof, and the protective tape 12 is held on the upper surface (holding surface) of the chuck table 71.

The illustrated grinding apparatus 1 includes a measuring device 8 for measuring the thickness and height of the wafer 10 held by the chuck table 71. The measuring device 8 includes a measuring housing 80, and the measuring device 8 is disposed on the upper surface of the main portion 21 having a rectangular parallelepiped shape constituting the device housing 2 on a side of a path for moving the chuck table 71 from the workpiece placement area 70a to the grinding area 70b as shown in the drawing, and is disposed so as to be able to measure the wafer 10 held on the chuck table 71 from above when the chuck table 71 moves between the workpiece placement area 70a and the grinding area 70 b. The measurement housing 80 has a measurement terminal 81 on a lower surface thereof facing the chuck table 71 positioned immediately below, and the measurement terminal 81 is configured to be capable of reciprocating in a direction (Y-axis direction) indicated by an arrow Y in the figure. The measuring device 8 is explained in more detail with reference to fig. 2.

The measuring device 8 in the illustrated embodiment includes: a broadband light source (hereinafter referred to as "pulsed broadband light source 82") that oscillates pulsed light having a predetermined wavelength (for example, a wavelength of 1100nm to 1900nm) that is transparent to the wafer 10 as a workpiece; an optical fiber transmission member 83a to which pulsed light LB1 from the pulsed broadband light source 82 is incident; a fiber bragg grating 83 to which the pulsed light LB1 is incident via a fiber transfer member 83 a; an optical fiber f2 through which the light reflected and traveling backward by the fiber bragg grating 83 is branched by an optical fiber transmission member 83a and transmitted to the optical fiber f 2; an optical fiber f3 connected to the optical fiber f 2; a measurement terminal 81 that branches the end of the optical fiber f3 into two optical paths, the measurement terminal 81 including a mirror 81c and an objective lens 81a, the mirror 81c being disposed on an end surface of the optical fiber f4 that forms one optical path, the mirror 81c generating the first return light that is reversed in the optical fiber f4, the objective lens 81a being disposed on an end surface of the optical path (optical fiber f3) that branches into the other of the two optical paths, the objective lens 81a converging the light transmitted to the optical fiber f3 on the wafer 10; a light branching member 84 that branches the first return light and the second return light, which are caused by interference of the reflected light reflected by the upper surface of the wafer 10 by the light LB2 irradiated from the objective lens 81a and the reflected light transmitted through the wafer 10 and reflected by the lower surface of the wafer 10, and which are caused to travel in reverse by the optical fiber f 3; a light receiving element 85 that detects the light intensity of the return light that has traveled through the optical fiber f5 by the interference of the first return light and the second return light branched by the light branching member 84; and a control means 20 for determining the wavelength of the return light received by the light receiving element 85 based on the time difference of one pulse, detecting the light intensity of each wavelength, and inputting and storing the light intensity of each wavelength detected by the light receiving element 85. The control member 20 includes: a spectral interference waveform generating means for generating a spectral interference waveform in one pulse based on a wavelength determined based on a time difference and the detected light intensity; and a calculating means for calculating the thickness of the wafer 10 and the heights of the front and back surfaces of the wafer 10 by waveform-analyzing the spectroscopic interference waveform generated by the spectroscopic interference waveform generating means. The pulsed broadband light source 82 may be selected from LED, LD, SLD (Super Luminescent Diode), ASE (Amplified Spontaneous Emission), SC (Super Continuum), halogen light source, and the like, and may be irradiated with a repetition frequency of 10kHz (pulse interval of 100 μ s) and a pulse width of 10ns, for example.

In the fiber bragg grating 83, the diffraction gratings k1 to k17 are formed in the optical fiber f1 constituting the fiber bragg grating 83, and when light having a broad band spectrum is incident, the diffraction gratings k1 to k17 reflect only a specific wavelength component of the incident light and transmit all wavelengths other than the specific wavelength. In the present embodiment, the length of the optical fiber f1 is about 8km, and the diffraction gratings k1 to k17 are arranged in order every 500m from the incident position. As shown in the figure, the diffraction grating k1 closest to the incident position reflects only light having a wavelength of 1100nm and transmits light having other wavelength components. The next diffraction grating k2 reflects only light of a wavelength component having a wavelength of 1150nm and transmits light of other wavelength components. Thus, the remaining diffraction gratings k3 to k17 sequentially reflect light having wavelength components of 1200nm, 1250nm, and … 1900nm set at 50 nm.

The optical fiber transmission member 83a that functions to branch the light reflected by the fiber bragg grating 83 and the optical branching member 84 that branches the return light reflected by the wafer 10 are appropriately selected from any one of a polarization maintaining fiber coupler, a polarization maintaining fiber circulator, a single-mode fiber coupler, and the like, for example. As the light receiving element 85 for detecting the light intensity, a generally known photodetector, line image sensor, or the like can be used.

The control means 20 is constituted by a computer, and includes: a Central Processing Unit (CPU) that performs arithmetic processing in accordance with a control program; a Read Only Memory (ROM) that stores a control program and the like; a read-write Random Access Memory (RAM) for temporarily storing detected detection values, calculation results, and the like; and an input interface and an output interface (illustration of detailed cases is omitted). The control means 20 in the present embodiment controls each driving portion of the grinding apparatus 1, and has a function of storing a program for executing the spectral interference waveform generation means for generating the spectral interference waveform and the calculation means for performing waveform analysis on the spectral interference waveform generated by the spectral interference waveform generation means to calculate the thickness and height of the wafer 10 in a Read Only Memory (ROM), driving the pulsed broadband light source 82, and storing the detection value of the light receiving element 85 in a Random Access Memory (RAM) to calculate the thickness and height of the wafer 10, as described above. The grinding apparatus 1 and the measuring apparatus 8 of the present embodiment are configured substantially as described above, and their operation will be described below with reference to fig. 2 and 3.

The thickness and height of the wafer 10 are measured by the measuring device 8 of the present invention, for example, when the wafer 10 placed on the chuck table 71 is ground by the grinding device 1, and then the wafer 10 is moved in the direction of the workpiece placement area 70a from the grinding area 70b so as to pass directly under the measuring terminals 81. As described above, pulsed light having a pulse width of 10ns and including a predetermined wavelength component (1100nm to 1900nm) that is transparent to the wafer 10 is irradiated from the pulsed broadband light source 82 at a repetition frequency of 10kHz (irradiation interval of 100 μ s). The pulsed light LB1 irradiated from the pulsed broadband light source 82 enters the optical fiber f1 through the optical fiber transmission member 83a disposed in the fiber bragg grating 83.

The pulse light incident on the optical fiber f1 is light having wavelength components of 1100 to 1900nm, and in the diffraction grating k1 closest to the incident position of the optical fiber f1, only the light of the wavelength component of 1100nm is reflected as shown by the arrow in the figure and travels backward in the optical fiber f1, while the light of the other wavelength components is transmitted. The light reflected by the diffraction grating k1 and traveling backward in the optical fiber f1 is branched to the optical fiber f2 by the optical fiber transmission member 83 a. The light branched to the optical fiber f2 is transmitted to the optical fiber f3 via the light branching member 84, and travels to the optical fiber f4, and the optical fiber f4 forms an optical path branched into one of two optical paths at the distal end portion of the optical fiber f 3. The light traveling to the optical fiber f4 is reflected by a mirror 81c formed on the end face of the optical fiber f4, and is reversed in the optical fiber f4, thereby forming first return light. At the same time, the light traveling in the other optical path (optical fiber f3) of the two optical paths branched from the distal end portion of the optical fiber f3 is irradiated to the measurement position of the wafer 10 positioned directly below via the objective lens 81a of the measurement terminal 81. The light having a wavelength of 1100nm irradiated to the predetermined measurement position of the wafer 10 is reflected on the upper surface and the lower surface of the wafer 10, and the two reflected lights interfere with each other to form a second return light which is reversed in the optical fiber f 3. The first return light and the second return light interfere with each other to become a single return light, go backward in the optical fiber f3, are branched by the optical branching member 84, go forward in the optical fiber f5, and reach the light receiving element 85. As a result, the light intensity of the return light having a wavelength of 1100nm at time t1 when one pulse light is incident on the optical fiber f1 is detected. The light intensity is stored in an arbitrary storage area of a Random Access Memory (RAM) of the control unit 20 in association with the time t1, and the positions of the X coordinate in the X-axis direction and the Y coordinate in the Y-axis direction of the wafer 10 to be irradiated.

Continuing with fig. 2, at time t1, after the pulse light LB1 enters the optical fiber f1 via the optical fiber transmission member 83a, the pulse light transmitted through the diffraction grating k1 reaches the next diffraction grating k2 with a time difference. The diffraction grating k2 reflects only light of 1150nm wavelength components and transmits light of other wavelength components. The 1150nm light reflected by the diffraction grating k2 as indicated by an arrow and traveling in reverse in the optical fiber f1 is transmitted to the optical fiber f3 via the light branching member 84, and is irradiated to the measurement position of the wafer 10 positioned directly below via the objective lens 81a of the measurement terminal 81, and is irradiated to the mirror 81c, similarly to the 1100nm light described above. The light reflected by the mirror 81c is reversed in the optical fiber f4 to form a first return light, the light reaching the wafer 10 is reflected on the upper and lower surfaces of the wafer 10 positioned directly below the measurement terminal 81a, and the two reflected lights interfere with each other to form a second return light reversed in the optical fiber f 3. The first return light and the second return light interfere with each other to form one return light, go in reverse in the optical fiber f3, are branched by the optical branching member 84, go in the optical fiber f5, and reach the light receiving element 85. Since the return light having the wavelength of 1150nm is reflected by the next diffraction grating k2 disposed at a position of 500m in the optical fiber f1 from the diffraction grating k1, the return light reaches the light receiving element 85 with a predetermined time difference from time t1 when the light is incident on the optical fiber f1 (time t 2). Thus, at time t2 determined by the time difference, the light intensity of return light having a wavelength of 1150nm reflected on the upper surface and the lower surface of the wafer 10 is determined. The light intensity is stored in an arbitrary storage area of a Random Access Memory (RAM) of the control means 20 in association with the wavelength determined according to the time t2, and the positions of the X coordinate in the X-axis direction and the Y coordinate in the Y-axis direction of the wafer 10 to be irradiated.

Similarly, light beams having different wavelength components (1200nm, 1250nm … 1900nm) set for each diffraction grating are reflected sequentially at predetermined time intervals by the diffraction gratings k3 to k17 on the optical fiber f1 of the fiber bragg grating 83 and are irradiated onto the mirror 81c and the wafer 10, so that first return light beams reflected by the mirror 81c and second return light beams formed by interference of the reflected light beams reflected on the upper surface and the lower surface of the wafer 10 are formed, and the light intensity is sequentially detected by the light receiving element 85. The light intensity is stored in an arbitrary storage area of a Random Access Memory (RAM) of the control unit 20 in association with the wavelength determined from the time t3 to t17, and the position of the X coordinate in the X axis direction and the Y coordinate in the Y axis direction of the wafer 10 to be irradiated. The reflection time difference of the light of each wavelength component generated by the fiber bragg grating 83 is extremely short compared to the pulse interval, one pulse light is irradiated, and the detection of the light intensity of the return light of all the wavelength components (1100 to 1900nm) is completed before the next pulse light is irradiated.

As described above, the control unit 20 stores the wavelength determined by the time difference from the start of irradiation of one pulse light from the pulsed broadband light source 82, the light intensity detected by the light receiving element 85, and the measurement coordinate position in association with each other, and can generate the spectroscopic interference waveform as shown in fig. 3 (a) for each predetermined coordinate position of the wafer 10. In fig. 3 (a), the horizontal axis represents the wavelength (λ) of the return light, and the vertical axis represents the light intensity of each wavelength detected by the light-receiving element 85.

An example in which the control means 20 calculates the thickness of the wafer 10 based on the waveform analysis performed based on the spectral interference waveform will be described below.

The optical path length from the upper end of the optical fiber f3 positioned at the measurement terminal 81 to the mirror 81c is (L1), the optical path length from the upper end of the optical fiber f3 to the upper surface of the wafer 10 held by the chuck table 71 is (L2), the optical path length from the upper end of the optical fiber f3 to the lower surface of the wafer 10 held by the chuck table 71 is (L3), the difference between the optical path length (L1) and the optical path length (L2) is a first optical path length difference (d1 is L1-L2), the difference between the optical path length (L1) and the optical path length (L3) is a second optical path length difference (d2 is L1-L3), and the difference between the optical path length (L3) and the optical path length (L2) is a third optical path length difference (d3 is L3-L2). The optical path length (L1) itself is not changed, and the length is set by assuming the distance from the upper end of the optical fiber f3 to the upper surface of the chuck table 71.

Next, the control unit 20 performs waveform analysis based on the spectroscopic interference waveform generated for each predetermined position of the wafer 10 as shown in fig. 3 (a). The waveform analysis can be performed, for example, according to the fourier transform theory or the wavelet transform theory, and in the embodiments described below, examples using the fourier transform expressions shown in the following

expressions

1, 2, and 3 will be described.

[ mathematical formula 1 ]

[ mathematical formula 2 ]

[ mathematical formula 3 ]

In the above formula, λ is a wavelength, d is the first optical path length difference (d 1-L1-L2), the second optical path length difference (d 2-L1-L3), and the third optical path length difference (d 3-L3-L2), and ω (λ n) is a window function. The above equation 1 obtains the optical path length difference (d) in which the cycle of the wave is closest (correlation is high) in the comparison between the theoretical waveform of cos and the spectral interference waveform (I (λ n)), that is, the correlation coefficient between the spectral interference waveform and the theoretical waveform function is high. In addition, the above equation 2 finds a first optical path length difference (d 1-L1-L2), a second optical path length difference (d 2-L1-L3), and a third optical path length difference (d 3-L3-L2) in which the cycle of the wave is closest (correlation is high) in the comparison between the sin theoretical waveform and the spectral interference waveform (I (λ n)), that is, the correlation coefficient between the spectral interference waveform and the theoretical waveform function is high. Then, the above equation 3 calculates an average value of the result of equation 1 and the result of equation 2.

The control means 20 can obtain a waveform of signal intensity shown in fig. 3 (b) from spectral interference due to the difference in optical path length between the return light included in the reflected light by performing the calculation based on the above-described

expressions

1, 2, and 3. In fig. 3 (b), the horizontal axis represents the optical path length difference (d) and the vertical axis represents the signal intensity. In the example shown in fig. 3 (b), the higher signal intensity was exhibited at the position (s1) where the optical path length difference (d) was 500 μm, the position (s2) 330 μm, and the position (s3) 180 μm. That is, the signal intensity s1 at the position where the optical path length difference (d) is 500 μm is the position of the first optical path length difference (d1 — L1-L2), and indicates the height of the back surface 10b of the wafer 10 positioned above the chuck table 71 from the upper surface of the chuck table 71. The signal intensity s2 at the position where the optical path length difference (d) is 300 μm is the position of the second optical path length difference (d2 is L1-L3), and indicates the height of the front surface 10a of the wafer 10 positioned below the chuck table 71 from the upper surface of the chuck table 71. The signal intensity s3 at the position where the optical path length difference (d) is 150 μm is the position of the third optical path length difference (d3 — L3-L2), and indicates the thickness of the wafer 10. Then, the height and thickness of the wafer 10 at the coordinates (X-coordinate, Y-coordinate) of the measurement position determined by the relative position of the measurement terminal 81 and the chuck table 71 in the X-axis direction and the position of the objective lens 81a positioned in the Y-axis direction are stored in a Random Access Memory (RAM) of the control unit 20.

In the present embodiment, the measurement terminal 81 is configured to be capable of reciprocating in the direction indicated by the arrow Y1 by the operation of the drive mechanism 81b that holds the measurement terminal 81, and the thickness measurement is performed on the entire surface of the wafer 10 by moving the measurement terminal 81 in the Y-axis direction with respect to the wafer 10 positioned directly below the measurement device 8 and moving the chuck table 71 in the X-axis direction.

According to the measuring apparatus 8 of the illustrated embodiment, the thickness of the wafer 10 can be easily determined with a simple configuration, and the thickness and height of the wafer 10 at the time of processing the wafer 10 are detected from the spectral interference waveform obtained by the optical path length difference of the reflected light, so that the thickness and height of the wafer 10 can be accurately measured without being affected by the change in the thickness of the protective tape 12 attached to the front surface of the wafer 10.

The measuring device 8 is configured as described above, and a procedure for grinding the wafer 10 to a predetermined thickness by using the grinding device 1 having the measuring device 8 will be described below.

The wafer 10 with the protective tape 12 bonded to the front surface thereof is placed on the chuck table 71 positioned in the workpiece placement region 70a in the grinding apparatus 1 shown in fig. 1 on the protective tape 12 side, and is sucked and held on the chuck table 71 by operating a suction member, not shown. Therefore, the back surface 10b of the wafer 10 held by the chuck table 71 is sucked upward.

Next, the control means 20 operates a moving means, not shown, of the chuck table 71 holding the wafer 10, moves the chuck table 71 to position the chuck table 71 in the grinding area 70b, and positions the outer peripheral edges of the plurality of grinding stones 51 for grinding the grinding wheel 5 so as to pass through the rotation center of the chuck table 71.

In this way, the grinding wheel 5 and the wafer 10 held by the chuck table 71 are set in a predetermined positional relationship, and the control means 20 drives the not-shown rotary driving means to rotate the chuck table 71 at a rotational speed of, for example, 300rpm, and drives the above-mentioned servo motor 43 to rotate the grinding wheel 5 at a rotational speed of, for example, 6000 rpm. Then, the wafer 10 is supplied with grinding water, and the pulse motor 62 of the grinding unit feed mechanism 6 is driven in the normal direction to lower (grind and feed) the grinding wheel 5, thereby pressing the plurality of grinding stones 51 against the ground surface, which is the upper surface (back surface 10b) of the wafer 10, at a predetermined pressure. As a result, the surface to be polished of the wafer 10 is ground (grinding step).

After the grinding process is completed, the chuck table 71 holding the ground wafer 10 is moved to the workpiece placement area 70a located in front in the X-axis direction, so that the wafer 10 is positioned directly below the measurement terminal 81 of the measurement device 8, and the measurement device 8 is operated as described above to obtain spectral interference waveforms corresponding to the respective coordinate positions on the wafer 10, and the thickness and height of the wafer 10 are measured and stored by performing waveform analysis. Such measurement is performed for each predetermined position of the wafer 10, the thickness and height of the front surface of the wafer 10 are stored, the thickness and height of the entire surface of the wafer 10 after grinding are checked, the quality of the grinding process is determined, and re-grinding is performed as necessary until the grinding process reaches a predetermined thickness.

In the above-described embodiment, the description has been made of the mode in which the measurement by the measurement device 8 is performed on the entire surface of the wafer having finished the grinding step, but the present invention is not limited to this, and for example, the installation position of the measurement housing 80 of the measurement device 8 may be set in the vicinity of the grinding region 70b shown in fig. 1. With this configuration, when the wafer held by the chuck table of the grinding apparatus is ground by the grinding wheel, the measurement terminal 81 is moved to face the exposed wafer and submerged in the grinding water supplied during grinding to be positioned, the thickness of the wafer during grinding can be measured, and the thickness of the wafer 10 during grinding can be fed back to the control member 20, whereby the wafer can be efficiently ground to a desired thickness and height.

The measuring device 8 according to the present invention is not necessarily provided in the grinding device 1 as in the present embodiment, and may be configured as a single device independent of the grinding device 1. The present invention may be applied to a laser processing apparatus that is provided separately from the grinding apparatus 1, and that performs processing for irradiating laser beams on planned dividing lines of a wafer divided by the planned dividing lines to form a plurality of devices on the front surface thereof to become starting points of the dividing, and divides the wafer into the devices. More specifically, a laser processing method is known in which a converging point of a laser beam having a wavelength that is transparent to a wafer is positioned inside a planned dividing line and irradiated to form a modified layer inside along the planned dividing line. In this way, the position of the focal point during laser processing can be positioned at a desired depth inside the wafer, and the wafer can be divided satisfactorily.

Further, according to the measuring apparatus of the present invention, the thickness and the height of the plate-like object to be measured can be obtained, and only one of the thickness and the height can be measured as necessary.

Claims

1. A measuring device for measuring the thickness or height of a plate, wherein,

the measuring device at least comprises:

a pulsed broadband light source that emits light in a wavelength band that is transmissive to a plate-like object in the form of pulsed light;

the fiber Bragg grating is used for transmitting the pulse light emitted by the pulse broadband light source, splitting the pulse light according to different wavelengths according to the transmission distance and enabling the pulse light to be retrograde;

an optical fiber transmission member which is disposed in the fiber Bragg grating, branches the pulse light in the reverse direction, and transmits the pulse light to an optical fiber;

a measurement terminal that branches an end portion of the optical fiber into two end surfaces, the measurement terminal having a mirror that is disposed on one end surface and generates first return light that is in a reverse direction in the optical fiber, and an objective lens that is disposed on the other end surface and converges the pulsed light on the plate-like object;

a light branching member that branches the first return light and a second return light obtained by interfering the pulsed light reflected by the upper surface of the plate-like object with the pulsed light transmitted through the plate-like object and reflected by the lower surface of the plate-like object and causing the optical fiber to travel in the reverse direction;

a spectral interference waveform generating means for obtaining wavelengths from a time difference between pulse light of each wavelength included in the one pulse light of the first return light and the second return light branched by the light branching means, and detecting intensities of light of the respective wavelengths to generate a spectral interference waveform; and

and a calculating means for calculating the thickness or height of the plate-like object by waveform-analyzing the spectroscopic interference waveform generated by the spectroscopic interference waveform generating means.