Pulse width measurement jig

Abstract

To provide a pulse width measurement jig for a laser processing device.SOLUTION: A pulse width measurement jig includes: a light input portion 12 that accepts a pulsed laser beam; a beam splitter 13; a first mirror 15A that reflects a first laser beam LB1 toward the beam splitter 13; a second mirror 15B that reflects a second laser beam LB2 that is split into a second path L2 toward the beam splitter 13; a first and second quarter-wave plates 14A and 14B; an optical path length modification means 16 for varying an optical path length by moving either of the first and second mirrors 15A and 15B in an optical axis direction; and a photodetector 18 that measures the optical intensity of the composite laser beam LB4 that has passed through a nonlinear crystal body 17 that allows passage of a composite laser beam LB3 of return laser beams LB1' and LB2' of the first laser beam merged at the beam splitter 13. The optical components from the light input section 12 to the photodetector 18 are arranged on the same plane 11a.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a pulse width measurement jig that is composed of a plurality of optical components for measuring the pulse width of a pulse laser beam. [Background technology]

[0002] Wafers with multiple devices such as ICs and LSIs formed on their surfaces, partitioned by planned division lines, are separated into individual device chips by a laser processing machine and used in electrical equipment such as mobile phones and personal computers.

[0003] The laser processing device includes a chuck table that holds a wafer, a laser irradiation means that irradiates a pulsed laser beam onto the wafer held on the chuck table, and a moving means that moves the chuck table and the laser irradiation means relatively in the X-axis and Y-axis directions. The laser irradiation means includes an oscillator that oscillates a pulsed laser beam, a condenser that focuses the pulsed laser beam oscillated by the oscillator onto the wafer held on the chuck table, and an optical system disposed between the oscillator and the condenser (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-002604 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-described laser processing apparatus, in order to maintain the processing quality of the laser processing, maintenance of the optical system of the laser irradiation means is performed periodically or at any timing. During this maintenance, the pulse width of the pulse laser beam oscillated by the oscillator is measured and an inspection is performed to determine whether the pulse width is the desired pulse width.

[0006] However, conventional pulse width measuring devices used to measure pulse widths are large and complex, and require the device to be positioned near the laser processing device undergoing maintenance, and the pulse laser beam emitted from the laser irradiation means of the laser processing device is branched using a separate branching means and guided to the pulse width measuring device located adjacent to the laser processing device to measure the pulse width. This poses a problem in that the installation and adjustment of the device before measurement is cumbersome and troublesome.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and its main technical object is to provide a pulse width measurement jig that can efficiently measure the pulse width without branching the pulse laser beam outside the laser processing device. [Means for solving the problem]

[0008] In order to solve the above-mentioned main technical problem, according to the present invention, The laser beam is irradiated from the laser irradiation means provided in the laser processing device. A pulse width measurement jig that is configured with a plurality of optical components for measuring the pulse width of a pulse laser beam, The optical component comprises: a first mirror that reflects the first laser beam that has been split into the first path toward the beam splitter; a second mirror that reflects the second laser beam that has been split into the second path toward the beam splitter; a first quarter-wave plate that is disposed between the beam splitter and the first mirror; a second quarter-wave plate that is disposed between the beam splitter and the second mirror; an optical path length changing means that moves either the first mirror or the second mirror in the optical axis direction to change the optical path length; a nonlinear crystal that allows passage of a combined laser beam of return light of the first laser beam and return light of the second laser beam that have been reflected by the first mirror and the second mirror and joined at the beam splitter; and a photodetector that measures the light intensity of the combined laser beam that has passed through the nonlinear crystal. The incident pulsed laser beam passes through or is reflected To the photodetector arranged on the optical path leading to Optical components In the laser processing device, a substrate formed to a size that can be held on a chuck table that holds a workpiece is A coplanar pulse width measurement fixture is provided. [Effects of the Invention]

[0009] The pulse width measurement jig of the present invention comprises: The laser beam is irradiated from the laser irradiation means provided in the laser processing device. A pulse width measurement jig that is configured with a plurality of optical components for measuring the pulse width of a pulse laser beam, The optical component comprises: a first mirror that reflects the first laser beam that has been split into the first path toward the beam splitter; a second mirror that reflects the second laser beam that has been split into the second path toward the beam splitter; a first quarter-wave plate that is disposed between the beam splitter and the first mirror; a second quarter-wave plate that is disposed between the beam splitter and the second mirror; an optical path length changing means that moves either the first mirror or the second mirror in the optical axis direction to change the optical path length; a nonlinear crystal that allows passage of a combined laser beam of return light of the first laser beam and return light of the second laser beam that have been reflected by the first mirror and the second mirror and joined at the beam splitter; and a photodetector that measures the light intensity of the combined laser beam that has passed through the nonlinear crystal. The incident pulsed laser beam passes through or is reflected To the photodetector arranged on the optical path leading to Optical components In the laser processing device, a substrate formed to a size that can be held on a chuck table that holds a workpiece is Since they are arranged on the same plane, they can be placed on the chuck table of a flat laser processing device and the pulse width can be measured, which solves the problem of having to branch the laser beam from the optical system constituting the laser irradiation means to measure the pulse width, which is troublesome. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view of a pulse width measuring jig and a laser processing device according to an embodiment of the present invention. FIG. [Figure 2]2 is an enlarged perspective view of the pulse width measurement jig shown in FIG. 1. FIG. [Figure 3] 3 is a perspective view showing a manner in which a pulse width is measured using the pulse width measuring jig shown in FIG. 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a pulse width measurement jig configured based on the present invention will be described in detail with reference to the accompanying drawings.

[0012] FIG. 1 shows a pulse width measuring jig 10 of this embodiment and an overall perspective view of a laser processing device 1 in which the pulse width of a pulsed laser beam is measured using the pulse width measuring jig 10.

[0013] The laser processing device 1 is arranged on a base 2 and comprises a holding means 3 for holding a plate-shaped workpiece, a laser irradiation means 6 for irradiating a pulsed laser beam onto the plate-shaped workpiece, an alignment means 7 equipped with a camera 7a for capturing an image of the workpiece held by the holding means 3, a moving means 4 for relatively feeding the laser irradiation means 6 and the holding means 3 for processing and moving the alignment means 7 and the holding means 3 relatively, and a frame 5 consisting of a vertical wall portion 5a erected on the back side of the moving means 4 on the base 2 and a horizontal wall portion 5b extending horizontally from the upper end of the vertical wall portion 5a.

[0014] As shown in FIG. 1 , the holding means 3 includes a rectangular X-axis direction movable plate 31 mounted on the base 2 so as to be movable in the X-axis direction; a rectangular Y-axis direction movable plate 32 mounted on the X-axis direction movable plate 31 so as to be movable in the Y-axis direction perpendicular to the X-axis direction; a cylindrical support 33 fixed to the upper surface of the Y-axis direction movable plate 32; and a rectangular cover plate 34 fixed to the upper end of the support 33. A chuck table 35 extending upward through an elongated hole formed in the cover plate 34 is disposed on the cover plate 34. The chuck table 35 is rotatable by a rotation drive means (not shown) housed in the support 33. A circular suction chuck 35a made of a breathable porous material and extending substantially horizontally is disposed on the chuck table 35. The suction chuck 35a is connected to a suction means (not shown) by a flow path passing through the support 33.

[0015] The moving means 4 includes an X-axis feed means 42 and a Y-axis feed means 44. The X-axis feed means 42 converts the rotational motion of the motor 42a into linear motion via a ball screw 42b and transmits the linear motion to the X-axis movable plate 31, causing the X-axis movable plate 31 to advance and retreat in the X-axis direction along a pair of guide rails 2a, 2a arranged along the X-axis direction on the base 2. The Y-axis feed means 44 converts the rotational motion of the motor 44a into linear motion via a ball screw 44b and transmits the linear motion to the Y-axis movable plate 32, causing the Y-axis movable plate 32 to advance and retreat in the Y-axis direction along a pair of guide rails 36, 36 arranged along the Y-axis direction on the X-axis movable plate 31.

[0016] An optical system (not shown) that constitutes the laser irradiation means 6 is housed inside the horizontal wall 5b of the frame 5. A condenser 6a that constitutes part of the laser irradiation means 6 is disposed on the underside of the tip of the horizontal wall 5b. A camera 7a of the alignment means 7 is disposed adjacent to the condenser 6a in the X-axis direction indicated by the arrow X in the figure. The camera 7a includes a normal image pickup element (CCD) that captures images using visible light, infrared irradiation means that irradiates the workpiece with infrared rays, an optical system that captures the infrared rays irradiated by the infrared irradiation means, and an image pickup element (infrared CCD) that outputs an electrical signal corresponding to the infrared rays captured by the optical system.

[0017] A control means (not shown) is provided in the laser processing apparatus 1. The control means is configured by a computer, and in addition to the above-mentioned moving means 4, laser irradiation means 6, and alignment means 7, is also connected to a display means 8 provided on the top surface of the laser processing apparatus 1. The control means controls each operating unit, and can display processing conditions on the display means 8 and images captured by the camera 7a of the alignment means 7.

[0018] The laser irradiation means 6 of the above-mentioned laser processing device 1 is equipped with an optical system (not shown), in which an oscillator that emits a pulsed laser beam with a predetermined pulse width is disposed. During maintenance that is performed periodically or arbitrarily, the pulse width of the pulsed laser beam emitted from the oscillator is measured to determine whether it is the desired pulse width.

[0019] Fig. 2 is an enlarged perspective view of the pulse width measurement jig 10 shown in Fig. 1. The pulse width measurement jig 10 includes a plate-like circular substrate 11 having a flat lower surface, a light incident portion 12 that receives a pulse laser beam irradiated from above on a flat surface 11a of the circular substrate 11, a beam splitter 13 that is disposed in the center of the flat surface 11a and splits the pulse laser beam incident from the light incident portion 12 into a first path L1 and a second path L2 by a reflective surface 13a formed by a multilayer film coating, a first mirror 15A that reflects the first laser beam split into the first path L1 toward the beam splitter 13, a second mirror 15B that reflects the second laser beam split into the second path L2 toward the beam splitter 13, and a beam splitter 13. The optical components provided include at least a first quarter-wave plate 14A disposed between the beam splitter 13 and the first mirror 15A, a second quarter-wave plate 14B disposed between the beam splitter 13 and the second mirror 15B, an optical path length changing means 16 for varying the optical path length by moving the first mirror 15A in the optical axis direction, a nonlinear crystal 17 for allowing the passage of a combined laser beam of the return light of the first laser beam and the return light of the second laser beam reflected by the first mirror 15A and the second mirror 15B and joined at the beam splitter 13, and a photodetector 18 for measuring the light intensity of the combined laser beam after passing through the nonlinear crystal 17. In this embodiment, the first path L1 starts from the reflecting surface 13a of the beam splitter 13, is reflected by the first mirror 15A, and reaches the reflecting surface 13a of the beam splitter 13, and the second path L2 starts from the reflecting surface 13a of the beam splitter 13, is reflected by the second mirror 15B, and reaches the reflecting surface 13a of the beam splitter 13.

[0020] The light entrance section 12 has a reflecting surface 12a with an inclination angle of 45 degrees, and reflects the pulsed laser beam irradiated from vertically above the plane 11a horizontally and redirects the optical path toward a beam splitter 13 disposed in the center of the plane 11a of the circular substrate 11.

[0021] The optical path length changing means 16 includes a step motor 161, a male screw 162 connected to the output shaft of the step motor 161, and a nut portion 163 having a female threaded hole into which the male screw 162 is screwed. The nut portion 163 is formed integrally with the first mirror 15A, and by operating the step motor 161 to rotate the male screw 162, the first mirror 15A is moved in the direction indicated by arrow R, i.e., in the optical axis direction of the first path L1.

[0022] The step motor 161 and photodetector 18 are connected to a control means 100. The control means 100 stores the light intensity detected by the photodetector 18 as an electrical signal and is capable of controlling the step motor 161, so that the first mirror 15A can be precisely advanced and retreated along the optical axis direction of the pulsed laser beam passing through the first path L1 by an actuation signal sent from the control means 100 to the step motor 161. The control means 100 does not necessarily have to be disposed in the pulse width measuring jig 10; the step motor 161 and photodetector 18 can be electrically connected to a control means (not shown) provided in the laser processing apparatus 1, and the control means of the laser processing apparatus 1 can be used to measure the pulse width using the pulse width measuring jig 10.

[0023] 1 and 2, and also with reference to FIG. 3, the effects of applying the pulse width measuring jig 10 to the laser processing device 1 will be described.

[0024] The circular substrate 11 of the pulse width measurement jig 10 is set to a size that allows it to be sucked and held by the chuck table 35 of the laser processing device 1 described above, and is set to, for example, a size that corresponds to the suction chuck 35a or a larger size.

[0025] When measuring the pulse width, first, the pulse width measurement jig 10 is placed on the suction chuck 35a of the chuck table 35, and a suction means (not shown) is activated to generate a negative pressure in the suction chuck 35a to hold the jig by suction. Next, the moving means 4 is activated to move the pulse width measurement jig 10 together with the chuck table 35 until it is positioned directly below the camera 7a of the alignment means 7. Next, the camera 7a captures an image of the pulse width measurement jig 10, and the center position of the reflecting surface 12a of the light entrance part 12 disposed on the flat surface 11a of the circular substrate 11 is detected.

[0026] As described above, once the center position of the reflecting surface 12a of the light entrance portion 12 has been detected by the alignment means 7, the moving means 4 is operated to position the center position of the reflecting surface 12a of the light entrance portion 12 directly below the condenser 6a of the laser irradiation means 6. Next, the laser irradiation means 6 is operated to irradiate a pulsed laser beam LB0 from the condenser 6a. The pulsed laser beam LB0 has a wavelength of, for example, 355 nm, and its average output is set to a low level that does not cause laser processing of the above-mentioned optical components.

[0027] 3, the pulsed laser beam LB0 emitted from the condenser 6a is reflected by the reflecting surface 12a of the light entrance section 12 and enters the beam splitter 13. The reflecting surface 13a formed inside the beam splitter 13 transmits the P-polarized part of the pulsed laser beam LB0 entering from the light entrance section 12 to the first path L1 as the first laser beam LB1, and reflects the S-polarized part of the pulsed laser beam LB0 to the second path L2 as the second laser beam LB2, thereby splitting the beam.

[0028] The P-polarized first laser beam LB1 that passed through the reflecting surface 13a of the beam splitter 13 is converted into circularly polarized light when it passes through the first quarter-wave plate 14A disposed between the beam splitter 13 and the first mirror 15A, and is reflected by the first mirror 15A. When the first laser beam LB1 is reflected by the first mirror 15A, the direction of rotation of the circularly polarized light is reversed, and when it passes through the first quarter-wave plate 14A, it is converted into S-polarized light and enters the beam splitter 13 as the returned light LB1' of the first laser beam LB1. It is reflected by the reflecting surface 13a, is guided to the photodetector 18 side, and enters the nonlinear crystal 17.

[0029] On the other hand, the S-polarized second laser beam LB2 reflected by the reflecting surface 13a of the beam splitter 13 is converted into circularly polarized light when it passes through the second quarter-wave plate 14B disposed between the beam splitter 13 and the second mirror 15B, and is reflected by the second mirror 15B. When it is reflected by the second mirror 15B, the direction of rotation of the circularly polarized light is reversed, and when it passes through the second quarter-wave plate 14B, it is converted into P-polarized light and enters the beam splitter 13 as the returned light LB2' of the second laser beam LB2, passes through the reflecting surface 13a, is guided to the photodetector 18 side, and enters the nonlinear crystal 17.

[0030] As described above, the pulsed laser beam entering nonlinear crystal 17 is the combined laser beam LB3 formed after the return light LB1' of the first laser beam and the return light LB2' of the second laser beam are combined in beam splitter 13, and this combined laser beam LB3 is a combined laser beam of a P-polarized pulsed laser beam and an S-polarized pulsed laser beam. Here, nonlinear crystal 17 of this embodiment has the property that the transmittance ratio through nonlinear crystal 17 changes depending on the overlap rate of the waveforms of the P-polarized pulsed laser beam and the S-polarized pulsed laser beam that make up this combined laser beam LB3, thereby changing the light intensity of combined laser beam LB4.

[0031] Therefore, the control means 100 of this embodiment operates the step motor 161 of the optical path length changing means 16 to move the first mirror 15A in the optical axis direction, thereby changing the optical path length of the first path L1 that branches off from the beam splitter 13, is reflected by the first mirror 15A, and returns to the beam splitter 13, and detects the change in light intensity with the photodetector 18. The amount of change in the optical path length of the first path L1 corresponds to twice the movement distance of the first mirror 15A in the optical axis direction.

[0032] The lower part of Figure 3 shows a graph plotting the change in the transmittance ratio of light passing through nonlinear crystal 17 based on the light intensity detected by photodetector 18 as the optical path length of first path L1 is changed. The vertical axis of the graph represents the transmittance ratio, and the horizontal axis represents the time (picoseconds (ps)) obtained by dividing the change in optical path length of first path L1 by the speed of light. An approximation curve S created based on each plot point is also shown.

[0033] The point P0 in the graph is the point where the light intensity detected by photodetector 18 is at its maximum, and this is the state where the waveforms of the P-polarized pulsed laser beam and the S-polarized pulsed laser beam that make up combined laser beam LB3 do not overlap at all. The light intensity detected in this state is taken as the reference (0%) transmittance ratio for the transmission of combined laser beam LB3 through nonlinear crystal 17. That is, optical path length changing means 16 is operated to make the optical path length of first path L1 shorter than that of second path L2. Then, as the optical path length changing means 16 is operated to move first mirror 15A and extend the optical path length, the waveforms of the P-polarized pulsed laser beam and the S-polarized pulsed laser beam that make up combined laser beam LB3 begin to overlap. As the overlap rate increases, the light intensity of combined laser beam LB4 after combined laser beam LB3 passes through nonlinear crystal 17 decreases.

[0034] The minimum point P1 of the approximation curve S in the graph shown at the bottom of Figure 3 indicates the point where the P-polarized pulsed laser beam and the S-polarized pulsed laser beam that make up the combined laser beam LB3 completely overlap, i.e., the point where the optical path length of the first path L1 and the optical path length of the second path L2 match, and the optical intensity of the combined laser beam LB4 after passing through nonlinear crystal 17 is at its lowest. Further operating optical path length changing means 16 to move first mirror 15A and extend the optical path length reduces the overlap rate of the P-polarized pulsed laser beam and the S-polarized pulsed laser beam that make up the combined laser beam LB3, and the optical intensity of the combined laser beam LB4 detected by photodetector 18 increases. When the overlap ends, the detected optical intensity reaches its maximum, as shown at point P2, and the transmittance ratio becomes the same value as that at point P0. The waveform thus derived (approximate curve S) is highly correlated with the pulse waveform of the pulse laser beam LB0, and the pulse width of the pulse laser beam LB0 is calculated from the approximate curve S using the following calculation procedure.

[0035] In the above-described embodiment, the change X1 in the optical path length of the first path L1 from point P0 to point P2 on the approximation curve S is, for example, 12,000 μm. Dividing this 12,000 μm by the speed of light per picosecond (ps) (300 μm / ps) results in 40 ps. Furthermore, from the distribution of transmittance ratios corresponding to the change X1=12,000 μm shown in the graph of FIG. 3 , the change X2 in the optical path L1 corresponding to the pulse width W is calculated as the change in the optical path length from point P3 to point P4, where the transmittance ratio Q2 is half the transmittance ratio Q1 of the minimum point P1 on the approximation curve S. In this embodiment, the detected change X2 is 3,180 μm, and the measured pulse width W is determined based on the value obtained by dividing the change X2 by the speed of light (300 μm / ps). More specifically, the parameter 2 is calculated using 3180 μm ÷ 300 μm / ps = 10.6 ps as the reference value, assuming that the pulse waveform of the pulsed laser beam LB0 is a Gaussian waveform. 1 / 2The value obtained (=7.5 ps) is determined as the pulse width W, which is taken as the measured value and stored in the control means 100. Then, it is determined whether the measured pulse width W is the desired pulse width, and if it is determined that it is not the desired pulse width, the oscillator that oscillates the pulse laser beam is adjusted or replaced.

[0036] The above-described method for measuring pulse width is merely an example, and various other methods for calculating pulse width are known. The calculation method for actually determining pulse width using the pulse width measuring jig 10 of the present invention is not limited to the above-described embodiment.

[0037] According to the above-described embodiment, it is possible to measure the pulse width by placing a flat object on the chuck table of the laser processing device, which solves the problem of having to branch the laser beam from the optical system constituting the laser irradiation means to measure the pulse width, which is troublesome.

[0038] In the above embodiment, the optical path length changing means 16 is provided as a means for moving the first mirror 15A in the optical axis direction, but the present invention is not limited to this, and the optical path length changing means 16 may be provided as a means for moving the second mirror 15B in the optical axis direction. In this case, too, the same measurement results as those described with reference to FIG. 3 can be obtained. [Explanation of symbols]

[0039] 1: Laser processing equipment 2: Base 3: Holding means 31:X-axis movable plate 32: Y-axis direction movable plate 33: Prop 34: Cover plate 35: Chuck table 35a: Suction chuck 36: Guide rail 4. Transportation 42: X-axis feed means 42a: Motor 42b: Ball screw 44: Y-axis feed means 44a: Motor 44b: Ball screw 5:Frame body 6: Laser irradiation means 6a: Concentrator 7: Alignment method 7a: Camera 8:Display means 10: Pulse width measurement jig 11:Circular board 11a: Plane 12: Light receiving part 12a: Reflective surface 13: Beam splitter 13a: Reflective surface 14A: First quarter-wave plate 14B: Second quarter-wave plate 15A: First mirror 15B: Second Mirror 16: Optical path length changing means 161: Step motor 162: Male thread 163: Nut part 17: Nonlinear crystal 18: Photodetector L1: First Path L2: Second Path

Claims

[Claim 1] A pulse width measuring jig comprising a plurality of optical components for measuring the pulse width of a pulse laser beam irradiated from a laser irradiation means disposed in a laser processing device, the optical component includes a light input section that receives a pulsed laser beam, a beam splitter that splits the pulsed laser beam input from the light input section into a first path and a second path, a first mirror that reflects the first laser beam split into the first path toward the beam splitter, a second mirror that reflects the second laser beam split into the second path toward the beam splitter, a first quarter-wave plate that is disposed between the beam splitter and the first mirror, a second quarter-wave plate that is disposed between the beam splitter and the second mirror, an optical path length changing means that moves either the first mirror or the second mirror in the optical axis direction to change the optical path length, a nonlinear crystal that allows passage of a combined laser beam of return light of the first laser beam and return light of the second laser beam that are reflected by the first mirror and the second mirror and joined at the beam splitter, and a photodetector that measures the light intensity of the combined laser beam that has passed through the nonlinear crystal; A pulse width measuring jig in which optical components arranged on the optical path through which the pulse laser beam entering from the light entrance portion passes or is reflected and reaches the photodetector are arranged on the same plane as a substrate formed to a size that can be held on a chuck table that holds the workpiece in the laser processing device.

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