JP2008212975A - Laser machining method and laser machining apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser machining apparatus capable of preventing a change in the waveform of a laser beam to perform stable machining even if a disturbance, such as existence of a reflected beam from a workpiece, occurs in machining. <P>SOLUTION: A laser machining apparatus is provided with a laser beam oscillator 1 for emitting a laser beam by using a nonlinear optical crystal 3, a temperature measuring element 5 for adjusting the temperature of the nonlinear optical crystal 3, a heater 4, and a temperature controller 6, and performs machining of a workpiece 9 by irradiating the workpiece 9 with the laser beam. Further, the laser machining apparatus is provided with: a partially transparent mirror 7 for measuring the waveform of the laser beam; a focusing lens 11; a photodetector 12; an AD converter 13; and a controller 14, which compares a reference waveform, as a reference for a measured laser beam, with a monitored waveform of the laser beam during machining of the workpiece 9, and controls the temperature controller 6 so that the monitored waveform approximates the reference waveform. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser processing method and a laser processing apparatus using a laser oscillator that converts a wavelength using a nonlinear optical crystal, and in particular, can prevent a change in the waveform of laser light and perform stable processing.

  In a laser processing apparatus equipped with a conventional pulse laser oscillator that performs wavelength conversion using a nonlinear optical crystal, the temperature of the nonlinear optical crystal is set so that the wavelength conversion efficiency is maximized, that is, the laser output is maximized. The stability of the laser output is ensured by controlling to be constant with a heater or the like. However, immediately after the laser light is generated or immediately after the reflected light from the processed part is generated, a part of the laser light is absorbed by the nonlinear optical crystal itself, and the crystal temperature changes transiently. There is a problem that it becomes difficult to maintain and the laser output fluctuates. To solve this problem, two temperature controllers are attached to the nonlinear optical crystal, and the crystal temperatures are maintained at different temperatures. Even if a transient temperature change occurs inside the crystal due to laser light, the laser output fluctuates. (For example, refer to Patent Document 1).

Japanese Patent Laid-Open No. 2001-42371 (page 3, lines 44 to 48, FIG. 1)

  Conventional laser processing equipment keeps the laser output constant even if the temperature inside the nonlinear optical crystal changes due to the influence of the reflected light from the work piece immediately after the laser light is generated. There is a problem that the pulse waveform of light changes, and the maximum temperature and the cooling rate of the processing part such as heat treatment greatly affect the processing result, resulting in non-uniform processing.

  The present invention has been made to solve the above-described problems, and prevents changes in the waveform of the laser beam even when there is a disturbance during processing, such as the presence or absence of reflected light from the workpiece. An object of the present invention is to provide a laser processing method and a laser processing apparatus capable of performing stable processing.

  In the laser processing method for processing a workpiece by oscillating a laser beam using a nonlinear optical crystal and irradiating the workpiece with the laser beam, a reference waveform serving as a reference for the laser beam is acquired. Monitor the monitor waveform during processing of the laser beam workpiece, compare the monitor waveform with the reference waveform, and control the temperature of the nonlinear optical crystal so that the monitor waveform approximates the reference waveform. Is what you do.

  The present invention also includes laser oscillation means for oscillating laser light using a nonlinear optical crystal and temperature adjusting means for adjusting the temperature of the nonlinear optical crystal, and irradiates the workpiece with the laser light. In the laser processing apparatus for processing the above, the measuring means for measuring the waveform of the laser light, the reference waveform that becomes the reference of the laser light measured by the measuring means, and the monitor waveform of the laser light being processed into the workpiece of the laser light And a control means for controlling the temperature adjusting means so that the monitor waveform approximates the reference waveform.

  The laser processing method of the present invention is a laser processing method for processing a workpiece by oscillating a laser beam using a nonlinear optical crystal and irradiating the workpiece with the laser beam. And monitor the monitor waveform being processed on the workpiece of the laser beam, compare the monitor waveform with the reference waveform, and control the temperature of the nonlinear optical crystal so that the monitor waveform approximates the reference waveform Since the workpiece is processed, even if there is a disturbance during the processing such as the presence or absence of reflected light from the workpiece, a change in the waveform of the laser beam can be prevented and stable processing can be performed.

  The laser processing apparatus according to the present invention further includes laser oscillation means for oscillating laser light using a nonlinear optical crystal and temperature adjusting means for adjusting the temperature of the nonlinear optical crystal, and irradiates the workpiece with the laser light. In the laser processing apparatus for processing the workpiece, the measuring means for measuring the waveform of the laser beam, the reference waveform serving as the reference of the laser beam measured by the measuring means, and the laser being processed into the workpiece of the laser beam Control means that controls the temperature adjustment means so that the monitor waveform is compared with the reference waveform by comparing with the monitor waveform of light, so even if there is a disturbance during processing, such as the presence or absence of reflected light from the workpiece Thus, it is possible to prevent a change in the waveform of the laser beam and perform stable processing.

Embodiment 1 FIG.
Embodiments of the present invention will be described below. FIG. 1 is a diagram showing a configuration of a laser processing apparatus according to Embodiment 1 of the present invention. FIG. 2 is a diagram showing a relationship between an average output, a pulse width, and a peak output with respect to a temperature change of a nonlinear optical crystal. FIG. 3 is a diagram showing a laser beam irradiation method according to Embodiment 1 of the present invention, FIG. 4 is a diagram showing changes in pulse waveforms in the laser processing method according to Embodiment 1 of the present invention, and FIG. 5 is shown in FIG. 6 is a flowchart for explaining a laser processing method using the laser processing apparatus. In the figure, a laser processing apparatus measures a laser oscillator 1 as a laser oscillation means for oscillating infrared laser light 2, a nonlinear optical crystal 3 for converting the wavelength of infrared laser light 2, and the temperature of the nonlinear optical crystal 3. The temperature measuring element 5 for heating, the heater 4 for heating the nonlinear optical crystal 3, and the temperature of the nonlinear optical crystal 3 by turning the heater 4 on and off based on the temperature of the nonlinear optical crystal 3 measured by the temperature measuring element 5. And a temperature controller 6 to be adjusted.

  Furthermore, a part of the visible or ultraviolet irradiation laser beam 15 whose wavelength is converted by the nonlinear optical crystal 3 is transmitted, and the partial transmission mirror 7 that reflects most of the irradiation laser beam 15 and the irradiation laser beam 15 are collected and processed. An irradiation-side condenser lens 8 for irradiating the object 9, an XY stage 10 for moving the workpiece 9, a photodetector 12 for monitoring the pulse waveform of the measurement laser beam 16 transmitted through the partial transmission mirror 7, and a measurement A measuring-side condensing lens 11 for making the laser beam 16 incident on the photodetector 12, an AD converter 13 for changing the output signal of the photodetector 12 from analog to digital, and a peak output of the pulse waveform of the laser beam from the output of the AD converter 13; A control device 14 is provided as control means for calculating the pulse width and controlling the temperature controller 6 based on the change in the calculation result. The infrared laser light 2 emitted from the laser oscillator 1 passes through the nonlinear optical crystal 3 and is converted into a laser beam 15 for irradiation as laser light. The temperature measuring element 5, the heater 4, and the temperature controller 6 constitute a temperature adjusting means, and the partial transmission mirror 7, the measurement-side condensing lens 11, the photodetector 12, and the AD converter 13 measure the measuring means. Will be constructed.

  Next, a laser processing method of the laser processing apparatus according to the first embodiment configured as described above will be described. First, before performing laser processing on the workpiece 9, the irradiation laser beam 15 is blocked by a shutter or the like not shown in the figure, and only the laser beam is oscillated to irradiate the workpiece 9 with the laser beam. When not, a predetermined temperature at which the conversion efficiency from the infrared laser beam 2 to the visible or ultraviolet laser beam is highest is determined. Then, the temperature controller 6 adjusts the heater 4 while measuring the temperature of the nonlinear optical crystal 3 with the temperature measuring element 5 so that the predetermined temperature is obtained. When the temperature of the nonlinear optical crystal 3 is changed, as shown in FIG. 2, the average output, the peak output, and the pulse width of the irradiation laser light 15 change. As apparent from FIG. 2, the average output is almost constant over a relatively wide temperature range, whereas there is almost no temperature range in which the pulse width and peak output are constant, and the temperature of the nonlinear optical crystal 3 If a slight change occurs, a change occurs.

  As a specific laser processing method, for example, a second harmonic of an Nd: YLF laser having a wavelength of 537 nm is used as the irradiation laser beam 15, and a size in which an impurity element such as phosphorus or boron is ion-implanted as the workpiece 9 is used. A silicon wafer 19 of about 5 inches was used, and an impurity element activation heat treatment was performed using the laser processing apparatus shown in FIG. The irradiation of the irradiation laser beam 15 on the wafer 19 is performed by scanning the irradiation laser beam 15 so that the irradiation laser beam 15 is irradiated to the entire wafer 19 as shown in FIG. At this time, the reflected light returns from the wafer 19 to the nonlinear optical crystal 3 while the irradiation laser beam 15 is irradiated on the wafer 19.

  FIG. 4 is an example of the monitor waveform 18 and the reference waveform 17 monitored by the photodetector 12. The reference waveform 17 before irradiating the wafer 19 with the irradiation laser beam 15 has a pulse width W0 and a peak output P0. When temperature adjustment is not performed as in the present invention, the irradiation laser beam 15 is irradiated onto the wafer 19. As a result, the temperature of the nonlinear optical crystal 3 rises due to the reflected light, and the average output corresponding to the area of the monitor waveform 18 does not change, but the pulse width changes from W1 and the peak output changes from P1 and the reference waveform 17. This change increases as the ratio of reflected light generation increases. That is, in FIG. 3, the change is small when the edge of the wafer 19 is irradiated, but the change increases as it goes to the center of the wafer 19 and then decreases again.

  Therefore, in the present invention, the reference waveform 17 serving as a reference before irradiating the wafer 19 with the irradiation laser beam 15 is measured. The monitor waveform during processing of the irradiation laser beam 15 is converted into an electric signal by the photodetector 12 (step S1 in FIG. 5), and A / D conversion is performed by the AD converter 13 (step S2 in FIG. 5). Next, the control device 14 calculates the peak output and pulse width of the monitor waveform (step S3 in FIG. 5). Next, it is determined whether the reference waveform and the monitor waveform are approximated by comparing the pulse width and peak output (step S4 in FIG. 5). Next, if it is not approximate, that is, if the peak output increases and the pulse width decreases, the temperature of the nonlinear optical crystal is decreased by a predetermined temperature to increase the peak output or the pulse The decrease in width is reduced, and the monitor waveform is brought close to the reference waveform (step S5 in FIG. 5). If approximate, the temperature of the nonlinear optical crystal is kept at a predetermined temperature (step S6 in FIG. 5). The operations from step S1 to step S6 are repeated until the processing of the workpiece is completed.

  Here, the appropriate value for changing the temperature of the nonlinear optical crystal 3 varies depending on the workpiece and irradiation conditions, but in the case of the specific example of the laser processing method described above, the temperature is set to 0.2 ° C. from the predetermined temperature. Lowered and controlled. Then, in the activation heat treatment that does not use the laser processing method of the present invention, the monitor waveform of the laser light changes due to the reflected light from the workpiece, so that the activated state varies greatly. The laser processing method of the present invention As compared with the case where the laser processing method of the present invention was not used, the variation in the activated state could be reduced to about 1/10.

  According to the laser processing method and the laser processing apparatus according to Embodiment 1 configured as described above, it is possible to prevent a change in waveform due to the reflected light of the laser beam during processing of the workpiece. Even if the maximum temperature and cooling rate of a workpiece greatly affect the processing result, even if the waveform has a large effect on the processing state, it is possible to suppress processing variations due to reflected light, so stable processing is performed. be able to. In addition, since the control is performed by comparing the peak output and the pulse width of the monitor waveform and the reference waveform, it can be performed only by comparing two points in the waveform, so that the control is performed efficiently. be able to. Further, when the monitor waveform and the reference waveform are approximate, the laser processing can be performed efficiently because the preset predetermined temperature at which the processing can be performed efficiently is set.

  In the first embodiment, the monitor waveform and the reference waveform are compared by comparing the peak output and the pulse width, but the method of comparing the monitor waveform and the reference waveform as a whole, Needless to say, the comparison between the monitor waveform and the reference waveform may be made by comparing the peak output or the pulse width in order to perform more efficiently, and the same effects as in the above embodiment can be obtained. . In the above-described embodiment, a wafer that easily generates reflected light has been described as an example of the workpiece. However, the present invention is not limited to this, and for example, a workpiece that does not easily generate reflected light is used. Even if it is, reflected light may be generated by a jig or the like that supports the workpiece. Also in that case, the monitor waveform of the laser light changes as in the first embodiment. Therefore, it is necessary to adjust the temperature of the nonlinear optical crystal. In this case, the temperature of the nonlinear optical crystal is raised. In the first embodiment, an example is shown in which the reference waveform is acquired before the workpiece is irradiated. However, the present invention is not limited to this. For example, the waveform of the laser beam immediately after irradiation of the workpiece is used as a reference. Needless to say, it can also be set as a waveform.

It is a figure which shows the structure of the laser processing apparatus of Embodiment 1 of this invention. It is a figure which shows the relationship of an average output, a pulse width, and a peak output with respect to the temperature change of a nonlinear optical crystal, respectively. It is a schematic diagram which shows the irradiation method of the laser beam by Embodiment 1 of this invention. It is a figure which shows the change of the pulse waveform in the laser processing method by Embodiment 1 of this invention. It is a flowchart for demonstrating the laser processing method using the laser processing apparatus shown in FIG.

Explanation of symbols

1 laser oscillator, 3 nonlinear optical crystal, 4 heater, 5 temperature measuring element,
6 Temperature controller, 9 Work piece, 11 Measuring side condenser lens, 12 Photo detector,
13 AD converter, 14 controller, 15 laser beam for irradiation, 16 laser beam for measurement, 19 wafer.

Claims (6)

In a laser processing method for processing a workpiece by oscillating a laser beam using a nonlinear optical crystal and irradiating the workpiece with the laser beam, obtaining a reference waveform serving as a reference for the laser beam, Monitor the monitor waveform during processing on the workpiece of the laser light, compare the monitor waveform with the reference waveform, and control the temperature of the nonlinear optical crystal so that the monitor waveform approximates the reference waveform. A laser processing method characterized by processing a workpiece. The comparison between the monitor waveform and the reference waveform is performed by comparing at least one of the peak output or the pulse width of each of the monitor waveform and the reference waveform, and the temperature of the nonlinear optical crystal is controlled by the peak of the monitor waveform. 2. The laser processing method according to claim 1, wherein at least one of output and pulse width is approximated to at least one of peak output and pulse width of the reference waveform. 2. The monitor waveform and the reference waveform are compared, and if the monitor waveform approximates the reference waveform, control is performed to keep the temperature of the nonlinear optical crystal at a predetermined temperature. Item 3. The laser processing method according to Item 2. Laser oscillating means for oscillating laser light using a nonlinear optical crystal and temperature adjusting means for adjusting the temperature of the nonlinear optical crystal are provided, and the workpiece is irradiated with the laser light to process the workpiece. In the laser processing apparatus to be performed, a measuring means for measuring the waveform of the laser light, a reference waveform serving as a reference of the laser light measured by the measuring means, and the laser light being processed on the workpiece of the laser light A laser processing apparatus comprising: a control means for comparing the monitor waveform and controlling the temperature adjusting means so that the monitor waveform approximates the reference waveform. The control means compares at least one of the peak output or pulse width of each of the monitor waveform and the reference waveform, and at least one of the peak output or pulse width of the monitor waveform is at least the peak output or pulse width of the reference waveform. The laser processing apparatus according to claim 4, wherein the temperature adjusting unit is controlled to approximate one. The control means compares the monitor waveform with the reference waveform, and controls the temperature adjusting means to keep the temperature of the nonlinear optical crystal at a predetermined temperature when the monitor waveform approximates the reference waveform. The laser processing apparatus according to claim 4 or 5, wherein

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