JP2012015164A - Laser diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser diagnostic device at least capable of detecting a repetition frequency of laser beam oscillation means and the stability of output per pulse.SOLUTION: A laser diagnostic device at least detects a repetition frequency of a pulse laser beam oscillated by laser beam oscillation means and the stability of output per pulse. The laser diagnostic device comprises: a laser diagnostic unit including a reflector which reflects the pulse laser beam oscillated by the laser beam oscillation means, a diffuser which diffuses the pulse laser beam reflected on the reflector, a photodetector which receives light transmitted through the diffuser and converts the light into an electric signal, and moving means which moves the photodetector toward or away from the diffuser; and an oscilloscope which displays the electric signal output from the photodetector of the laser diagnostic unit.

Description

  The present invention relates to a laser diagnostic apparatus capable of detecting the repetition frequency of a pulse laser beam oscillated by a laser beam oscillation means and the stability of output per pulse.

  In recent years, as a method of dividing a plate-like workpiece such as a silicon wafer formed with IC, LSI or the like, or a sapphire wafer formed with LED or the like, a pulsed laser beam along a street formed on the workpiece. Has been proposed in which a laser processing groove is formed in a workpiece by cutting the workpiece, and the workpiece is cleaved by a mechanical braking device along the laser processing groove (for example, JP-A-10-305421). See the official gazette).

  The laser processing apparatus includes a chuck table that holds a wafer, and laser beam irradiation means that irradiates the wafer held on the chuck table with a laser beam. The laser beam irradiating means includes a laser beam oscillating means for oscillating a pulse laser beam, an optical system for adjusting the laser beam oscillated by the laser beam oscillating means, and a condenser (laser head) for positioning the condensing point of the laser beam on the wafer. The wafer can be processed with high accuracy by a laser processing apparatus.

Japanese Patent Laid-Open No. 10-305421 JP 2005-313182 A

  However, the laser beam oscillating means deteriorates with the passage of time, causing a problem that the repetition frequency changes, the output per pulse becomes unstable, and the wafer cannot be processed with high precision (patent) Reference 2).

  The present invention has been made in view of these points, and an object thereof is to provide a laser diagnostic apparatus capable of detecting the repetition frequency of laser beam oscillation means and the stability of output per pulse. It is.

  According to the present invention, the laser diagnostic apparatus detects at least the repetition frequency of the pulse laser beam oscillated by the laser beam oscillation means and the stability of the output per pulse, and reflects the pulse laser beam oscillated by the laser beam oscillation means. A reflecting plate, a diffusing plate for diffusing the pulsed laser beam reflected by the reflecting plate, a photodetector for receiving light transmitted through the diffusing plate and converting it into an electrical signal, and bringing the photodetector close to the diffusing plate A laser diagnostic apparatus comprising: a laser diagnostic unit having a moving means that moves in a direction away from each other; and an oscilloscope for displaying an electrical signal output from the photodetector of the laser diagnostic unit. Is done.

  Preferably, the laser diagnostic unit further includes a light absorbing plate disposed on the back of the reflecting plate that absorbs light transmitted through the reflecting plate.

  When diagnosing the laser beam oscillating means with the laser diagnostic apparatus of the present invention, the reflecting plate of the laser diagnostic unit is positioned so as to block the pulse laser beam oscillated by the laser beam oscillating means, an appropriate amount of laser beam is taken in, the repetition frequency, Since the stability and pulse width of the output per pulse can be detected, it is possible to determine whether the laser beam oscillation means needs to be repaired or when to replace it.

  In addition, the amount of light received by the photodetector is adjusted by operating the moving means, the amplitude displayed on the oscilloscope is set to a predetermined value, and the output stability per pulse is compared in time series. The necessity of repair of the laser beam oscillation means or the timing of replacement can be determined.

It is a perspective view of a laser processing apparatus. It is a side view of the laser beam irradiation mechanism which can mount | wear with a laser diagnostic unit. It is a perspective view of a laser diagnostic unit. It is a partially broken perspective view of a laser diagnostic unit. It is sectional drawing which shows the labyrinth structure of a laser diagnostic unit. It is a block diagram of a laser diagnostic apparatus. It is a block diagram of a laser beam oscillation means.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, an external perspective view of a laser processing apparatus that can be diagnosed by the laser diagnostic apparatus of the present invention is shown. The laser processing apparatus 2 includes a first slide block 6 mounted on a stationary base 4 so as to be movable in the X-axis direction.

  The first slide block 6 is moved in the machining feed direction, that is, the X-axis direction along the pair of guide rails 14 by the machining feed means 12 including the ball screw 8 and the pulse motor 10.

  A second slide block 16 is mounted on the first slide block 6 so as to be movable in the Y-axis direction. That is, the second slide block 16 is moved along the pair of guide rails 24 by the index feed means 22 constituted by the ball screw 18 and the pulse motor 20 in the index feed direction, that is, the Y-axis direction.

  A chuck table 28 is mounted on the second slide block 16 via a cylindrical support member 26, and the chuck table 28 can be moved in the X-axis direction and the Y-axis direction by the processing feed means 12 and the index feed means 22. At the same time, it is rotated by a motor accommodated in the cylindrical support member 26.

  The chuck table 28 is provided with a clamp 30 that clamps a frame that supports the semiconductor wafer sucked and held by the chuck table 28 via a tape. 32 is a cover, and a bellows (not shown) is connected to the cover 32 to protect the processing feed means 12 and the index feed means 22 from debris.

  A column 34 is erected on the stationary base 4, and a laser beam irradiation mechanism (laser beam irradiation means) 36 is attached to the column 34. The laser beam irradiation mechanism 36 includes a laser beam oscillation means 38 and an optical system 39 shown in FIG. 6 housed in a casing 40, and a condenser (laser head) 42 attached to the tip of the casing 40. .

  An imaging means 44 is attached to the tip of the casing 40 so as to align with the condenser 42 in the X-axis direction. As shown in FIG. 2, an opening (not shown) is formed on the side surface of the casing 40, and this opening is closed by fastening a cover plate 52 with screws 54.

  When processing the wafer W held on the chuck table 28, the pulse laser beam 81 emitted from the laser beam oscillation means 38 is adjusted in its power and the like by the optical system 39 shown in FIG. The light is condensed on the wafer W by the condenser 42 having the objective lens object 90, and a laser processing groove is formed along the street of the wafer W.

  When diagnosing the laser beam oscillation means with the laser diagnostic apparatus of the present invention, the cover plate 52 is removed and the laser diagnostic unit 46 is attached to the opening as shown in FIG.

  As shown in FIGS. 3 and 4, the laser diagnostic unit 46 includes a housing 48, and a pair of mounting brackets 50 are integrally formed on the front side of the housing 48. Each mounting bracket 50 is formed with a round hole 51 for mounting the laser diagnostic unit 46.

  A support plate 56 projects forward from the bottom plate 48 a of the housing 48. A quartz reflection plate 58 and a light absorption plate 60 are mounted on the support plate 56. The quartz reflection plate 58 has a property of reflecting 4% of incident light and transmitting others. The light absorbing plate 60 absorbs light transmitted through the quartz reflecting plate 58.

  On the bottom plate 48 a of the housing 48, a diffusion plate 62 that diffuses the light reflected by the quartz reflection plate 58 is provided. The diffusion plate 62 is, for example, sand number # 240, and diffuses incident light appropriately.

  A photodetector 64 for converting the light diffused by the diffusion plate 62 into an electric signal is disposed on the back surface of the diffusion plate 62. The photodetector 64 is mounted on a carriage 66, and the carriage 66 can move in a direction toward or away from the diffusion plate 62 along the guide groove 68 by engaging the thumbscrew 70. Reference numeral 72 denotes a wiring connected to the photodetector 64, and the other end is connected to an oscilloscope.

  Referring to FIG. 5, a cross-sectional view of a portion where the thumbscrew 70 engages with the carriage 66 is shown. The member 74 and the member 76 form a labyrinth structure, and light leaks from the inside of the housing 48. It prevents it from being put out.

  When diagnosing the laser beam oscillation means 38 of the laser beam irradiation mechanism 36, the cover plate 52 shown in FIG. 2 is removed, and screws 54 are inserted into the round holes 51 of the mounting bracket 50 as shown in FIG. Fastened to the side of the casing 40.

  As a result, as shown in FIG. 6, the quartz reflecting plate 58 and the light absorbing plate 60 are inserted into the optical path of the laser beam oscillated by the laser beam oscillation means 38. As shown in FIG. 7, the laser beam oscillating means 38 includes a laser oscillator 80, a repetition frequency setting means 82, and a pulse width adjusting means 84.

  The laser oscillator 80 emits a pulsed laser beam 81 obtained by converting a fundamental wave having a wavelength of 1064 nm oscillated by a YAG laser or a YVO4 laser into 355 nm by THG (third harmonic generation) using a nonlinear crystal.

  When the laser diagnostic unit 46 is mounted on the side surface of the casing 40, the quartz reflecting plate 58 is inserted into the optical path of the pulse laser beam 81 oscillated by the laser beam oscillation means 38, as shown in FIG. Since the quartz reflecting plate 58 has a reflectance of 4%, 4% of the pulse laser beam 81 is reflected and 96% is transmitted through the quartz reflecting plate 58 and absorbed by the light absorbing plate 60.

  The pulse laser beam 81 reflected by the quartz reflection plate 58 is incident on the diffusion plate 62 and diffused. This diffused light is detected by the photodetector 64 and converted into an electrical signal. This electrical signal is input to the oscilloscope 92 via the wiring 72 and displayed on the screen 93 in time series. The horizontal axis of the graph displayed on the screen 93 indicates a time scaled every 2 μs, for example, and the vertical axis indicates a voltage scaled every 10 mV, for example.

  In the present embodiment, the laser diagnostic device 45 includes a laser diagnostic unit 46 and an oscilloscope 92 electrically connected to the laser diagnostic unit 46. On the screen 93 of the oscilloscope 92, the repetition frequency, pulse width, and pulse intensity of the pulse laser beam 81 are displayed as voltages.

  Since the intensity of the pulse is displayed in time series, the output stability per pulse can be compared in time series. For example, when there is an output fluctuation of 20% or more, the laser beam oscillation means 38 It can be determined that it is time for repair or replacement.

  Since the repetition frequency and the pulse width can also be observed on the screen 93 of the oscilloscope 92, if the repetition frequency and / or the pulse width fluctuate more than a predetermined allowable value, it is necessary to repair or replace the laser beam oscillation means 38 as well. Judge that there is.

  The oscilloscope 92 incorporates a controller 94 having a CPU 96 and a memory 98, and the repetition frequency, pulse width and output intensity per pulse of the pulse laser beam 81 are stored in the memory 98 of the controller 94.

  In the laser diagnostic apparatus 45 of this embodiment, the output per pulse is not accurately detected, but the stability of the output per pulse is detected. 68, the light amount received by the photodetector 64 is adjusted so that the output per pulse is within the range of 30 to 40 mV on the screen 93 of the oscilloscope 92. Adjust to fit. After completion of the diagnosis, the laser diagnosis unit 46 is removed from the casing 40, and the cover plate 52 is attached so as to close the opening of the casing 40.

2 Laser processing device 28 Chuck table 36 Laser beam irradiation mechanism 38 Laser beam oscillation means 40 Casing 42 Condenser (laser head)
45 Laser diagnostic device 46 Laser diagnostic unit 58 Quartz reflector 60 Light absorption plate 62 Diffuser 64 Photo detector 66 Carriage 80 Laser oscillator 81 Pulse laser beam 82 Repetition frequency setting means 84 Pulse width adjusting means 92 Oscilloscope

Claims (2)

A laser diagnostic apparatus for detecting at least the repetition frequency of a pulse laser beam oscillated by a laser beam oscillation means and the stability of output per pulse,
A reflection plate that reflects the pulse laser beam oscillated by the laser beam oscillation means; a diffusion plate that diffuses the pulse laser beam reflected by the reflection plate; and a photo that receives the light transmitted through the diffusion plate and converts it into an electrical signal. A laser diagnostic unit having a detector and moving means for moving the photodetector in a direction approaching or moving away from the diffusion plate;
An oscilloscope for displaying an electrical signal output from the photodetector of the laser diagnostic unit;
A laser diagnostic apparatus comprising:   The laser diagnostic apparatus according to claim 1, wherein the laser diagnostic unit further includes a light absorption plate disposed on a back portion of the reflection plate that absorbs light transmitted through the reflection plate.

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