Measuring device

Abstract

To provide a measurement device that can shorten a computation time for calculating a value about a thickness direction of a workpiece.SOLUTION: A measurement device 6 is provided which includes: a light source 61; an irradiator 68 that irradiates a workpiece with light the light source 61 emits; a diffraction grating 73A that splits reflection light reflected on the workpiece; an image sensor 71 that converts light split into a plurality of different broad-band wavelengths by the diffraction grating 73A to an electric signal; and calculation means 80 that Fourier transforms an inference waveform converted to the electric signal by the image sensor 71 to calculate a value about a thickness direction of the workpiece, in which a prism body 100A is disposed that is adjusted so that a size of a wavenumber (1 / λ) in each wavelength (λ) and an area of the image sensor 71 having each wavelength (λ) detected correspond to each other, and the measurement device 6 is configured to, when calculating the value about the thickness direction of the workpiece by the Fourier transform in the calculation means 80, enable omitting the computation of the wavenumber (1 / λ) on the basis of the area of the image sensor 71 detecting the split light.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a measuring device including a calculating means for calculating a value related to the thickness direction of a workpiece.

Background Art

[0002] A wafer having a plurality of devices such as ICs and LSIs formed on a surface partitioned by a dividing line is processed by a laser processing apparatus along the dividing line, divided into individual device chips, and used in electric devices such as mobile phones and personal computers.

[0003] The laser processing apparatus includes a chuck table for holding a wafer, a laser beam irradiation means for irradiating the wafer held on the chuck table with a laser beam having a wavelength that is transmissive to the wafer, and a feeding means for relatively feeding the chuck table and the laser beam irradiation means, and can process the wafer with high precision (see, for example, Patent Document 1).

[0004] The laser beam irradiation means disclosed in the above Patent Document 1 accurately positions the focus point of the laser beam at a desired position inside the wafer. Therefore, the laser beam is irradiated onto the processing area of the wafer and reflected, and diffracted by a diffraction grating for spectral separation for each wavelength. The interference waveform of the separated light is Fourier-transformed to precisely calculate a value in the thickness direction including the position of the upper surface of the wafer, for example, the height position on the upper surface of the wafer, and store it in the control means. Based on the information on the height position of the upper surface of the processing area of the wafer stored in the control means, the focus point of the laser beam is positioned at a desired position inside the wafer to perform laser processing.

[0005] In addition, Patent Document 2 discloses a chuck table for holding a wafer, a laser beam irradiation means for irradiating a laser beam having a wavelength that is transmissive to the wafer held on the chuck table, a feed means for relatively feeding the chuck table and the laser beam irradiation means, a condensing point position adjusting means, and a height position detecting means for detecting the height position of the upper surface of the wafer based on the amount of light of the reflected light of the inspection laser beam received by a light receiving element. In the laser processing step, it is also proposed to irradiate a processing laser beam while detecting the height of the upper surface of the wafer by the height position detecting means and adjusting the height of the condensing point by the condensing point position adjusting means.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the laser processing apparatus described in Patent Document 2 mentioned above, since laser processing is performed while detecting the upper surface height of the wafer, even when the wafer has undulations and the upper surface height position changes depending on the processing position, laser processing can be performed following the undulations without separately performing the step of detecting the upper surface height of the wafer. However, in the calculation of the upper surface height of the wafer in the height position detection means, since the ratio between the amount of light passing through the one-dimensional mask (slit) and the reference amount of light not passing through the one-dimensional mask among the reflected light of the inspection laser beam is used, there is a problem in the accuracy when calculating the upper surface height of the wafer. On the other hand, when calculating the value related to the thickness direction of the wafer described in Patent Document 1 mentioned above, since the reflected light is dispersed into a plurality of different broadband wavelengths by a diffraction grating to generate an interference waveform and an operation including Fourier transform is used, the upper surface height of the wafer can be calculated with higher accuracy. Therefore, it is conceivable to apply the calculation means to the laser processing apparatus described in Patent Document 2 mentioned above. However, in the operation including Fourier transform performed in the calculation means described in Patent Document 1, since it is necessary to calculate the wave number (1 / λ) for each wavelength λ of the dispersed interference waveform, when applied to the laser processing apparatus described in Patent Document 2 mentioned above, the operation takes time, a deviation occurs in the timing of irradiating the laser beam, and there is a problem that laser processing cannot be appropriately performed.

[0008] The present invention has been made in view of the above facts, and its main technical problem is to provide a measuring apparatus capable of shortening the calculation time for calculating the value related to the thickness direction of the workpiece.

Means for Solving the Problems

[0009] In order to solve the above main technical problems, according to the present invention, there is provided a measuring apparatus including a light source, an irradiator that irradiates light emitted from the light source onto a workpiece, a diffraction grating that disperses reflected light reflected by the workpiece, an image sensor that converts light dispersed into a plurality of different broadband wavelengths by the diffraction grating into an electrical signal, and a calculating means that performs a Fourier transform on an interference waveform converted into an electrical signal by the image sensor to calculate a value related to the thickness direction of the workpiece. A prism body is disposed such that the magnitude of the wave number at each wavelength corresponds to the region of the image sensor at which each wavelength is detected. When the calculating means calculates a value related to the thickness direction of the workpiece by Fourier transform, a measuring apparatus is provided in which the calculation of the wave number can be omitted based on the region of the image sensor that detects the dispersed light.

[0010] The prism body includes a first prism and a second prism, and it is preferable that the direction in which the vertex forming the apex angle formed by the incident surface and the exit surface of the first prism points and the direction in which the vertex forming the apex angle formed by the incident surface and the exit surface of the second prism points are arranged to face each other. Further, it is preferable that the apex angle of the first prism is different from the apex angle of the second prism, or the optical material of the first prism is different from the optical material of the second prism.

[0011] The prism body may be disposed between the diffraction grating and the image sensor, or may be disposed on the side opposite to the image sensor with respect to the diffraction grating. The diffraction grating can be selected from either a transmission type or a reflection type. Further, it is preferable that the interval between the short wavelength and the long wavelength dispersed by the diffraction grating for the broadband wavelength is 200 nm to 500 nm. It is preferable that the short wavelength is 460 nm and the long wavelength is 900 nm. It is preferable that a long-pass filter is disposed on the long wavelength side dispersed by the diffraction grating to prevent the second-order diffracted light from reaching the image sensor. The value related to the thickness direction of the workpiece is preferably any one of the position of the upper surface of the workpiece, the position of the lower surface of the workpiece, and the thickness of the workpiece.

Advantages of the Invention

[0012] The measuring device of the present invention includes a light source, an irradiator that irradiates the light emitted from the light source onto a workpiece, a diffraction grating that disperses the reflected light reflected by the workpiece, an image sensor that converts the light dispersed into a plurality of different broadband wavelengths by the diffraction grating into an electrical signal, and a calculation means that performs a Fourier transform on the interference waveform converted into an electrical signal by the image sensor to calculate a value related to the thickness direction of the workpiece. A prism body is arranged such that the magnitude of the wave number at each wavelength corresponds to the region of the image sensor where each wavelength is detected. When the calculation means calculates a value related to the thickness direction of the workpiece by Fourier transform, the calculation of the wave number can be omitted based on the region of the image sensor that detects the dispersed light. Therefore, the calculation time for measuring the upper surface position of the wafer by Fourier-transforming the interference waveform is shortened, and the problem that proper processing cannot be performed due to a deviation in the timing of irradiating the laser beam is solved.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of a measuring device configured based on the present invention will be described in detail with reference to the accompanying drawings.

[0015] FIG. 1 shows a laser processing apparatus 2 to which a measuring apparatus 6 of the present embodiment is attached, and a wafer W to be processed as a workpiece of the present embodiment. The illustrated wafer W is held by an annular frame F via an adhesive tape T. Note that the measuring apparatus 6 disposed in the illustrated laser processing apparatus 2 also includes a laser beam irradiation unit 9 that performs laser processing on the wafer W in the laser processing apparatus 2 (see FIG. 2).

[0016] The laser processing apparatus 2 is disposed on a base 2a, and includes a measuring apparatus 6 that calculates a value in the thickness direction of the wafer W, a holding unit 20 that holds the wafer W, an alignment unit 4 that images the wafer W held by the holding unit 20 and performs alignment, a moving unit 30 that relatively moves the alignment unit 4 and the holding unit 20, and the measuring apparatus 6 and the holding unit 20, and a frame 8 including a vertical wall portion 8a erected on the side of the moving unit 30 on the base 2a and a horizontal wall portion 8b extending in the horizontal direction from the upper end portion of the vertical wall portion 8a.

[0017] Inside the horizontal wall portion 8b of the frame 8, an optical system (details will be described later) that constitutes the above-described measuring apparatus 6 is accommodated. On the lower surface side of the tip of the horizontal wall portion 8b, a condenser 68 that constitutes a part of the measuring apparatus 6 and functions as an irradiator that irradiates the wafer W with light emitted from a light source 61 described later is disposed. The alignment unit 4 is disposed at a position adjacent to the condenser 68 in the X-axis direction indicated by an arrow X in the drawing. Note that the plane defined by the X-axis direction and the Y-axis direction indicated by arrows in FIG. 1 is substantially horizontal.

[0018] As shown in FIG. 1, the holding means 20 includes a rectangular X-axis movable plate 21 mounted on the base 2a so as to be movable in the X-axis direction, a rectangular Y-axis movable plate 22 mounted on the X-axis movable plate 21 so as to be movable in the Y-axis direction, a cylindrical support column 23 fixed to the upper surface of the Y-axis movable plate 22, and a rectangular cover plate 24 fixed to the upper end of the support column 23. A chuck table 25 extending upward through a long hole formed on the cover plate 24 is disposed on the cover plate 24. The chuck table 25 is configured to be rotatable by a rotation driving means (not shown) housed in the support column 23. On the upper surface of the chuck table 25, a circular suction chuck 26 formed of a porous material having air permeability and extending substantially horizontally is disposed. The suction chuck 26 is connected to a suction means (not shown) by a flow path passing through the support column 23, and four clamps 27 are arranged around the suction chuck 26 at intervals. The clamp 27 fixes the frame F holding the wafer W when fixing the wafer W to the chuck table 25.

[0019] The moving means 30 includes an X-axis feed means 31 and a Y-axis feed means 32. The X-axis feed means 31 converts the rotational motion of the motor 33 into a linear motion via a ball screw 34 and transmits it to the X-axis movable plate 21, and advances and retracts the X-axis movable plate 21 in the X-axis direction along a pair of guide rails 2b, 2b arranged along the X-axis direction on the base 2a. The Y-axis feed means 32 converts the rotational motion of the motor 35 into a linear motion via a ball screw 36 and transmits it to the Y-axis movable plate 22, and advances and retracts the Y-axis movable plate 22 in the Y-axis direction along a pair of guide rails 28, 28 arranged along the Y-axis direction on the X-axis movable plate 21.

[0020] The measuring device 6 attached to the laser processing device 2 shown in FIG. 1 will be described more specifically with reference to FIG. 2.

[0021] FIG. 2 shows a block diagram showing an outline of the optical system of the above-described measuring device 6. The measuring device 6 in the illustrated embodiment includes a light source 61 that emits broadband light for measurement (for example, white light), and a first optical branching means 62 that guides the light from the light source 61 to a first path 6a and guides the reflected light that travels back along the first path 6a to a second path 6b, a collimation lens 63 that forms the light irradiated from the light source 61 and guided to the first path 6a into parallel light, and a second optical branching means 64 that branches the light formed into parallel light by the collimation lens 63 into a third path 6c and a fourth path 6d.

[0022] The light source 61 can be appropriately selected and used from, for example, an SLD light source, an ASE light source, a supercontinuum light source, an LED light source, a halogen light source, a xenon light source, a mercury light source, a metal halide light source, a laser light source, etc. that emit broadband light having a wavelength of 460 to 900 nm. The first optical branching means 62 can use a polarization-maintaining fiber coupler, a polarization-maintaining fiber circulator, a single-mode fiber coupler, a single-mode fiber coupler circulator, etc. The second optical branching means 64 is composed of a beam splitter 641 and a direction-changing mirror 642 in the illustrated embodiment. Note that the path from the light source 61 to the first optical branching means 62 and the first path 6a are constituted by optical fibers.

[0023] In the third path 6c, there is an objective lens 65 accommodated in a condenser 68 that guides the light guided to the third path 6c to the wafer W held on the chuck table 25, and a condenser lens 66 is disposed between the objective lens 65 and the second optical branching means 64. This condenser lens 66 condenses the parallel light guided from the second optical branching means 64 to the third path 6c, positions the condensing point within the objective lens 65, and generates parallel light from the light from the objective lens 65. By disposing the condenser lens 66 between the objective lens 65 and the second optical branching means 64 in this way to generate parallel light from the light from the objective lens 65, when the reflected light reflected by the wafer W held on the chuck table 25 travels back through the objective lens 65, the condenser lens 66, the second optical branching means 64, and the collimation lens 63, it can be converged onto the optical fiber constituting the first path 6a. The above-mentioned condenser 68 can be moved to a desired position in the vertical direction in FIG. 2, that is, in a direction perpendicular to the holding surface of the suction chuck 26 of the chuck table 25, by a condensing point position adjusting means 69 composed of a voice coil motor, a linear motor, or the like. This condensing point position adjusting means 69 is precisely controlled by a control means 80.

[0024] In the fourth path 6d, there is a reflection mirror 67 that reflects the parallel light guided to the fourth path 6d and causes the reflected light to travel back in the fourth path 6d. This reflection mirror 67 is fixed to the condenser 68 that houses the objective lens 65 in the illustrated embodiment.

[0025] In the second path 6b, an optical system constituting the main part 7 of the measuring device 6 is disposed. In the optical system of the main part 7, an image sensor 71 that receives the irradiated light for each wavelength and converts it into an electrical signal is disposed and is connected to the control means 80. The control means 80 stores an algorithm that functions as a calculating means in the present embodiment, and based on this algorithm, the interference waveform obtained by converting the electrical signal by the image sensor 71 is calculated by Fourier transform to calculate a value related to the thickness direction of the wafer W.

[0026] The main part 7A of the first embodiment related to the above-described main part 7 is shown in Fig. 3(a). The main part 7A includes at least a reflective diffraction grating 73A that disperses the reflected light reflected by the wafer W and branched in the first optical branching means 62, and a prism body 100A adjusted so that the magnitude of the wave number (1 / λ) at each wavelength (λ) of the light dispersed by the diffraction grating 73A corresponds to the size of the region of the image sensor that images the light of each wavelength. In the optical system of the main part 7A, if necessary, collimation lenses 72A and 74A that make the irradiated light parallel light, and condenser lenses 75A and 76A that condense the light incident on the light receiving element surface 71a of the image sensor 71 are disposed. In Fig. 3(a), the collimation lenses 72A and 74A and the condenser lenses 75A and 76A are simply shown for convenience of explanation, but they may be combined lenses composed of a plurality of lenses.

[0027] The prism body 100A disposed in the main part 7A of the present embodiment includes a first prism 110A and a second prism 120A. The light irradiated from the light source 61 is reflected by the wafer W and travels backward along the third path 6c, the fourth path 6d, and the first path 6a. The light P1 branched into the second path 6b by the first optical branching means 62 includes the reflected light reflected by the front surface Wa, the back surface Wb of the wafer W, and the reflection mirror 67 fixed to the condenser 68. As shown in FIG. 3(a), when the light P1 branched into the second path 6b is irradiated on the reflection type diffraction grating 73A and reflected, it is split into light of a plurality of different broadband wavelengths. Then, the light P1 guided to the prism body 100A is incident on the incident surface 112A of the first prism 110A, and the angle of travel within the first prism 110A is adjusted by the action of different refraction angles for each wavelength, and is emitted from the emission surface 114A. The light P1 emitted from the emission surface 114A further enters from the incident surface 122A of the second prism 120A disposed adjacent thereto, and the traveling direction of the light P1 is adjusted for each wavelength by the action of different refraction angles for each wavelength, and is emitted from the emission surface 124A. The light P1 emitted from the emission surface 124A passes through the collimation lens 74A, the condenser lenses 75A, 76A and is condensed, and is irradiated on the light receiving element surface 71a of the image sensor 71. In the first embodiment shown in FIG. 3(a), light of a long wavelength (900 nm) is guided to the upper side in the drawing of the light receiving element surface 71a of the image sensor 71, and light of a short wavelength (460 nm) is guided to the lower side.

[0028] Here, the arrangement and angle adjustment of the first prism 110A and the second prism 120A disposed in the prism body 100A are adjusted based on the following technical idea.

[0029] On the light-receiving element surface 71a of the image sensor 71, a plurality of light-receiving elements are arranged in series in the longitudinal direction, and the light received by each light-receiving element is converted into an electrical signal and sent to the control means 80. Conventionally, the light-receiving elements on the light-receiving element surface 71a are arranged such that the light-receiving elements of the image sensor 71 correspond to the wavelength (λ) when the wavelength interval is made uniform by a diffraction grating. For example, the length of the region where the light-receiving elements of the image sensor 71 that receive the spectral light of wavelengths from 400 nm to 500 nm are arranged is the same as the length of the region where the light-receiving elements of the image sensor 71 that receive the spectral light of wavelengths from 500 nm to 600 nm are arranged. In this case, in the calculation process of calculating the value related to the thickness direction of the wafer 10 by performing Fourier transform or the like on the interference waveform that can be converted into an electrical signal by the image sensor 71, it is necessary to calculate the wave number (1 / λ) for each wavelength (λ), resulting in a large calculation load on the control means 80 and the problem that the calculation cannot be completed in a short time.

[0030] Therefore, in the present embodiment, as shown on the right side of FIG. 4, a curve showing the magnitude of the wave number (1 / λ) at the wavelength (λ) is obtained in advance, and as shown on the left side of FIG. 4, the magnitude of the wave number (1 / λ) at each wavelength (λ) is made to correspond to the size of the region of the light-receiving element surface 71a of the image sensor 71 that images the light intensity of each wavelength. Then, the positions and relative angles of the first prism 110A and the second prism 120A are adjusted so that the wavelength of the light P1 incident on the image sensor 71 matches this. As a result, the light P1 that passes through the prism body 100A and is received by the image sensor 71 is in a state where the magnitude of the wave number (1 / λ) at each wavelength (λ) corresponds to the size of the region of the image sensor that images each wavelength. At this time, the first prism 110A and the second prism 120A that constitute the prism body 100A are arranged such that the direction R1 pointed to by the vertex 116A that forms the apex angle formed by the incident surface 112A and the exit surface 114A of the first prism 110A and the direction R2 pointed to by the vertex 126A that forms the apex angle formed by the incident surface 122A and the exit surface 124A of the second prism 120A face each other.

[0031] By arranging the first prism 110A and the second prism 120A as described above, it becomes possible to make the magnitude of the wave number (1 / λ) at each wavelength (λ) correspond to the size of the area of the light-receiving element surface 71a of the image sensor 71 that images the light of each wavelength. The electrical signal obtained by imaging the light spectroscopically for each wavelength (λ) by the diffraction grating 73A is sent to the control means 80. Here, due to being set as described above, when performing a Fourier transform to calculate a value regarding the thickness direction of the wafer W, it is no longer necessary to calculate the wave number (1 / λ) again. Note that a display means 81 is connected to the control means 80, and the processing conditions and image information in the laser processing apparatus 2 are appropriately displayed on the display means 81.

[0032] Returning to FIG. 2 and continuing the explanation, the laser beam irradiation means 9 disposed in the measurement apparatus 6 described above includes a pulse laser beam oscillation means 91 and a dichroic mirror 92 that converts the direction of the pulse laser beam LB oscillated from the pulse laser beam oscillation means 91 toward the objective lens 65 of the condenser 68 described above. The pulse laser beam oscillation means 91 is composed of a pulse laser beam oscillator 911 and a repetition frequency setting means 912 attached thereto, and oscillates, for example, a pulse laser beam LB having a wavelength of 1064 nm that is transmissive to the wafer W. The dichroic mirror 92 is disposed between the condenser lens 66 and the objective lens 65, has the characteristic of allowing the light from the condenser lens 66 to pass through, and reflecting the pulse laser beam LB oscillated from the pulse laser beam oscillation means 91 toward the objective lens 65. Therefore, the pulse laser beam LB oscillated from the pulse laser beam oscillation means 91 is directionally converted by 90 degrees by the dichroic mirror 92, enters the objective lens 65, is condensed by the objective lens 65, and irradiates the wafer W held on the chuck table 25.

[0033] In the laser processing apparatus 2 equipped with the measurement apparatus 6 of the present embodiment, an aspect of performing laser processing on the wafer W while calculating the value in the thickness direction of the wafer W by the measurement apparatus 6 will be described.

[0034] When performing laser processing by the laser processing apparatus 2 of the present embodiment, first, the wafer W is placed and suction-held on the chuck table 25 of the laser processing apparatus 2 shown in FIG. 1 above, and the chuck table 25 holding the wafer W by operating the moving means 30 is positioned directly below the alignment means 4.

[0035] When the chuck table 25 is positioned directly below the alignment means 4, the upper surface of the wafer W is imaged by the alignment means 4, and the control means 80 executes image processing such as pattern matching to detect the processing area to be laser-processed on the wafer W and perform alignment. When this alignment is performed, the X coordinate and Y coordinate of the processing area to be processed on the wafer W are detected and stored in the control means 80. Next, based on the position information of the processing area stored in the control means 80, the above-described moving means 30 is operated to position the processing start position of the processing area of the wafer W directly below the condenser 68.

[0036] Next, the above-described measuring device 6 is operated to emit measurement white light from the light source 61 and irradiate the wafer W through the condenser 68. In FIG. 2 above, when the condenser 68 movable in the vertical direction is set to the initial state, the optical path length from the beam splitter 641 of the second optical branching means 64 in the third path 6c to the surface of the suction chuck 26 of the chuck table 25 (the back surface of the wafer W) is defined as L1, the optical path length from the beam splitter 641 of the second optical branching means 64 to the upper surface of the wafer W held by the chuck table 25 is defined as L2, and the optical path length from the beam splitter 641 of the second optical branching means 64 in the fourth path 6d to the reflection mirror 67 is defined as L3.

[0037] By executing operations based on the above-described Fourier transform or the like, as shown in FIG. 5, waveforms (A) to (C) of signal intensities indicating the optical path length differences between the respective optical path lengths L1, L2, and L3 are calculated. In FIG. 5, the horizontal axis indicates the optical path length difference, and the vertical axis indicates the signal intensity. That is, when the calculation means of the control means 80 of the measuring apparatus 6 of the present embodiment is executed, the waveform shown in FIG. 5(A) indicates an optical path length difference of 620 μm between the optical path length L1 and the optical path length L3, and the waveform shown in FIG. 5(B) indicates an optical path length difference of 500 μm between the optical path length L2 and the optical path length L3. The waveform shown in FIG. 5(C) indicates an optical path length difference of 120 μm between the optical path length L1 and the optical path length L2. In this case, it is measured that the distance from the surface of the adsorption chuck 26 of the chuck table 25 to the surface Wa (upper surface) of the wafer W, that is, the thickness of the upper wafer W is 120 μm. In this way, by the measuring apparatus 6, waveform analysis including Fourier transform is executed, and the optical path length differences L1 to L3 are calculated, so that the height from the surface of the adsorption chuck 26 of the chuck table 25 to the upper surface of the wafer W can be obtained. As described above, in the present embodiment, the prism body 100A is adjusted so that the magnitude of the wave number (1 / λ) at each wavelength (λ) of the light split by the diffraction grating 73A corresponds to the size of the region of the image sensor that images the light of each wavelength. For each wavelength (λ), the calculation of the wave number (1 / λ) is omitted, and even if an operation involving Fourier transform is executed, the calculation time in the control means 80 is shortened.

[0038] If the height position of the upper surface of the wafer W is measured by the control means 80, a control signal is transmitted from the control means 80 to the condensing point position control means 69, and the condenser 68 is moved in the vertical direction so that the condensing point adjusted by the condenser 68 is positioned at a desired internal position from the upper surface of the wafer W.

[0039] Next, the control means 80 activates the laser beam irradiation means 9 to irradiate the pulsed laser beam LB for processing, moves the chuck table 25 at a predetermined processing feed rate, and forms a modified layer inside the wafer W. Then, when the irradiation position of the condenser 68 reaches the end position of the processing region of the wafer W, the irradiation of the pulsed laser beam LB is stopped and the movement of the chuck table 25 is stopped. In this processing step, the height position of the upper surface of the wafer W is constantly measured by the control means 80 of the measuring device 6 described above, and based on the measured value, the condensing point position adjusting means 69 is constantly controlled. As a result, the condensing point of the pulsed laser beam LB is always positioned at a desired depth inside the wafer W, and a modified layer is formed at the desired depth from the upper surface of the wafer W.

[0040] If the above-described processing step is executed along all the processing regions extending in the predetermined direction of the wafer W as described above, the chuck table 25 is rotated 90 degrees, and the above-described modified layer is formed along each processing region orthogonal to the predetermined direction. A processing step is executed. In this way, if the processing step of forming the above-described modified layer is executed along all the processing regions formed on the wafer W, the chuck table 25 holding the wafer W is first returned to the position where the wafer W was sucked and held, and the suction and holding of the wafer W are released. Then, the wafer W is transported to a cassette that houses the wafer W by a transport means (not shown) or to the next process (for example, a dicing process).

[0041] As described above, in the measuring device 6 provided in the laser processing apparatus 2 in the above embodiment, even when calculating a value related to the thickness direction of the wafer W (workpiece) by Fourier-transforming the interference waveform that can be converted into an electrical signal by the image sensor 71, for each wavelength (λ), the wavenumber (1 / λ) calculation is omitted, and since the arithmetic processing is completed promptly, the problem that a deviation occurs in the timing of positioning and irradiating the condensing point of the above-described pulsed laser beam LB at a desired position and proper processing cannot be performed is solved.

[0042] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the main part 7 constituting the above-described measuring device 6 is not limited to disposing the prism body 100A between the diffraction grating 73A and the image sensor 71 as in the main part 7A of the above-described first embodiment. Instead of the above-described main part 7A, it is also possible to configure it as the main part 7B shown as the second embodiment in FIG. 3(b). In the main part 7B of the measuring device 6 shown in FIG. 3(b), the prism body 100B is composed of a first prism 110B and a second prism 120B, and is disposed on the side opposite to the image sensor 71 with respect to the diffraction grating 73B, that is, on the side of the first optical branching means 62. Even in the main part 7B shown in the figure, if necessary, collimation lenses 72B and 74B for making the irradiated light parallel light, and condenser lenses 75B and 76B for condensing the light incident on the light receiving element surface 71a of the image sensor 71 are disposed. By disposing in this way, it is possible to obtain the same operational effects as the above-described main part 7A. Note that the first prism 110B and the second prism 120B constituting the prism body 100B are arranged such that the direction R3 in which the vertex 116B forming the apex angle formed by the incident surface 112B and the exit surface 114B of the first prism 110B points, and the direction R4 in which the vertex 126B forming the apex angle formed by the incident surface 122B and the exit surface 124B of the second prism 120B points, face each other, similar to the above-described main part 7A. Further, in the main part 7B of the second embodiment shown in FIG. 3(b), a long-pass filter 77B formed of synthetic quartz or the like is disposed on the long-wavelength side spectrally separated by the diffraction grating 73B. By disposing the long-pass filter 77B, the short-wavelength light of the secondary diffracted light mixed in the long-wavelength side of the primary diffracted light reflected by the diffraction grating 73B is cut, and the measurement accuracy when calculating the value regarding the thickness direction of the wafer W is improved. The long-pass filter 77B can also be disposed in the optical system of the main part 7A of the above-described first embodiment and the optical system of the main part 7C of the third embodiment described later.

[0043] The main part 7 disposed in the measuring device 6 of the present invention is not limited to the above-described first and second embodiments, and may be the main part 7C shown as the third embodiment in FIG. 3(c). The diffraction gratings 73A and 73B used in the above-described first and second embodiments are reflective diffraction gratings. However, in the main part 7C shown in FIG. 3(c), a transmissive diffraction grating 73C is adopted, and the light dispersed by the diffraction grating 73C is irradiated onto the prism body 100C. In the optical system of the main part 7C, collimation lenses 72C and 74C for making the irradiated light parallel light, and condenser lenses 75C and 76C for condensing the light incident on the light receiving element surface 71a of the image sensor 71 are also disposed as necessary. Further, the first prism 110C and the second prism 120C constituting the prism body 100C are arranged such that the direction R5 in which the vertex 116C forming the apex angle formed by the incident surface 112C and the exit surface 114C of the first prism 110C points, and the direction R6 in which the vertex 126C forming the apex angle formed by the incident surface 122C and the exit surface 124C of the second prism 120C points, face each other, similar to the main parts 7A and 7B described above. Even when such a configuration is adopted, the same operational effects as those of the above-described first and second embodiments can be obtained.

[0044] It is preferable that the first prism and the second prism adopted in the prism bodies 100A to 100C adopted in the optical systems of the main parts 7A to 7C shown in the above-described first to third embodiments are prisms of different materials or different apex angles. More specifically, by adopting S-TIH11 as the material of the first prism 110B of the main part 7B shown in FIG. 3(b) and synthetic quartz as the second prism 120B, the magnitude of the wave number (1 / λ) at each of the above-described wavelengths (λ) and the size of the region of the image sensor 71 that images each wavelength (λ) are adjusted to correspond to each other appropriately.

[0045] Also, it is preferable to employ a prism in which the vertex angle formed by the incident surface and the exit surface of the first prism employed in the prism bodies 100A to 100C of the optical systems of the main parts 7A to 7C shown in the above-described first to third embodiments is different from the vertex angle formed by the incident surface and the exit surface of the second prism. For example, as shown in FIG. 3(c), it is preferable that the vertex angle θ1 formed by the incident surface 112c and the exit surface 114c of the first prism 110c employed in the prism body 100C is different from the vertex angle θ2 formed by the incident surface 122c and the exit surface 124c of the second prism 120c. By selecting the first prism 110c and the second prism 120c in this way, similarly to the above, adjustment is appropriately performed so that the magnitude of the wave number (1 / λ) at each wavelength (λ) corresponds to the size of the region of the image sensor 71 that images each wavelength (λ).

[0046] In the above-described embodiment, the wavelength of the light irradiated from the light source 61 is set to be broadband light of 460 to 900 nm. However, the interval between the short wavelength and the long wavelength dispersed by the diffraction gratings 73A to 73C is preferably 200 nm to 500 nm. By setting it in this way, when performing Fourier transform based on the interference waveform converted into an electrical signal by the image sensor 71 and calculating a value related to the thickness direction of the workpiece, appropriate calculations can be performed.

[0047] Furthermore, in the above-described embodiment, when performing the laser processing step, as a value related to the thickness direction of the workpiece, the height position of the upper surface of the wafer was calculated and implemented. However, the present invention is not limited to this, and as a value related to the thickness direction of the workpiece, the position of the lower surface of the workpiece or the value of the thickness of the workpiece may be calculated and processing may be performed.

Explanation of Reference Numerals

[0048] 2: Laser processing apparatus 2a: Base 2b: Guide rail 4: Alignment means 6: Measuring device (laser beam irradiation means) 6a: First path 6b: Second path 6c: Third path 6d: Fourth path 61: Light source 62: First optical branching means 63: Collimation lens 64: Second optical branching means 641: Beam splitter 642: Direction-changing mirror 65: Objective lens 66: Condensing lens 67: Reflecting mirror 68: Condenser 69: Condensing point position adjustment means 7, 7A, 7B, 7C: Essential part 71: Image sensor 71a: Light-receiving element surface 73A, 73B: Diffraction grating (reflection type) 73C: Diffraction grating (transmission type) 8: Frame 8a: Vertical wall portion 8b: Horizontal wall portion 9: Laser beam irradiation means 91: Pulse laser beam oscillation means 911: Laser oscillator 912: Repetition frequency setting means 92: Dichroic mirror 20: Holding means 21: X-axis direction movable plate 22: Y-axis direction movable plate 23: Support column 24: Cover plate 25: Chuck table 26: Adsorption chuck 27: Clamp 28: Guide rail 30: Moving means 31: X-axis feed means 32: Y-axis feed means 33: Motor 34: Ball screw 35: Motor 36: Ball screw 80: Control means 81: Display means 100A, 100B, 100C: Prismatic body 110A, 110B, 110C: First prism 120A, 120B, 120C: Second prism

Claims

1. A measuring device comprising: a light source; an irradiator that irradiates a workpiece with the light emitted by the light source; a diffraction grating that disperses the reflected light reflected by the workpiece; an image sensor that converts the light dispersed into a plurality of different broadband wavelengths by the diffraction grating into an electrical signal; and a calculating means that performs a Fourier transform on the interference waveform converted into an electrical signal by the image sensor to calculate a value related to the thickness direction of the workpiece, a prism body is disposed such that the magnitude of the wave number at each wavelength corresponds to the region of the image sensor at which each wavelength is detected, a measuring device configured such that when calculating a value related to the thickness direction of the workpiece by Fourier transform in the calculating means, the calculation of the wave number can be omitted based on the region of the image sensor that detects the dispersed light.

2. The prism body includes a first prism and a second prism, and is disposed such that the direction in which the vertex forming the apex angle formed by the incident surface and the exit surface of the first prism points and the direction in which the vertex forming the apex angle formed by the incident surface and the exit surface of the second prism points face each other. The measuring device according to claim 1.

3. The measuring device according to claim 2, wherein the apex angle of the first prism is different from the apex angle of the second prism, or the optical material of the first prism is different from the optical material of the second prism.

4. The prism body is disposed between the diffraction grating and the image sensor, or is disposed on the side opposite to the image sensor with respect to the diffraction grating. The measuring device according to claim 1.

5. The diffraction grating is either a transmission type or a reflection type. The measuring device according to claim 1.

6. The broadband wavelength means that the interval between the short wavelength and the long wavelength dispersed by the diffraction grating is 200 nm to 500 nm. The measuring device according to claim 1.

7. The short wavelength is 460 nm and the long wavelength is 900 nm. The measuring device according to claim 6.

8. A long-pass filter is disposed on the long wavelength side of the light dispersed by the diffraction grating to prevent the second-order diffracted light from reaching the image sensor. The measuring device according to claim 1.

9. The value related to the thickness direction of the workpiece is any one of the position of the upper surface of the workpiece, the position of the lower surface of the workpiece, and the thickness of the workpiece. The measuring device according to claim 1.

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