JP2005088072A - Laser beam machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machine capable of consistently and correctly controlling the focusing position of laser beam for machining. <P>SOLUTION: In the laser beam machine having a lens 1 to focus laser beam 8 on a work 2 and at least two lasers, the work 2 is machined by controlling the focusing position of the laser beam 8 for machining to be at a predetermined position to the work 2. The frequency band when the distance between the lens 1 and the work 2 is controlled to be constant is different for each laser beam, and the distance between the lens 1 and the work 2 is controlled by simultaneously controlling these laser beams. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laser processing apparatus that forms an image of laser light on a workpiece and performs processing such as ablation, latent image formation, crystal structure change, magnetic structure change, material curing, and material dissolution on the workpiece. In particular, the present invention relates to a laser processing apparatus equipped with a mechanism for holding the imaging position of the laser beam at a fixed distance with respect to the workpiece.

The laser processing apparatus has a control system that uses light having a wavelength different from that for processing in order to control the distance between the workpiece and the laser imaging position. Of these control methods, a processing apparatus based on exposure uses light of a wavelength that does not contribute to exposure, in addition to exposure light, for contactless control of the distance between the apparatus and the workpiece. In particular, in the case of a master exposure apparatus for optical disc mastering, conventionally, an ultraviolet light laser having a wavelength of about 350 nm (hereinafter referred to as an exposure laser) for exposure and a red or infrared laser (hereinafter simply referred to as an exposure laser) for distance control. Red laser) is used.
Image position can be controlled by a skew method (a method in which a red laser is incident with a shift from the center of the objective lens and the distance between the workpiece and the objective lens is taken as a displacement perpendicular to the optical axis of the reflected light) or astigmatism Aberration method (A beam that gives astigmatism to the reflected light from the work piece and reflects the minimum confusion circle of reflected light reflecting the distance between the work piece and the objective lens in the direction of the optical axis. In many cases, a method of capturing as a change in shape is employed.

  Both systems use a red laser incident on the objective lens in parallel. Since the conventional objective lens is an achromatic lens and has the same focal length for the two wavelengths of the exposure laser and the red laser, both the exposure laser and the red laser are processed by the above-mentioned distance control method (this is the work piece). In this case, the image is formed at the same location on the master plate coated with resist. The red laser reflected from the workpiece detects the beam position or beam shape in the direction perpendicular to the optical axis with a detector (detector) in both the skew method and the astigmatism method.

  An objective lens is mounted on an actuator that can move toward and away from the direction of the workpiece by current, and the polarity and magnitude of the current are adjusted according to the output of the detector by the reflected light, and the reflected light on the detector Feedback is performed so that is at a predetermined position. Thereby, the distance between the objective lens and the workpiece is kept at a predetermined value.

  For this type of technology, for example, a proposal as described in Patent Document 1 below has been made.

JP 2003-45094 A

  As a means for creating a finer structure, the wavelength of an exposure laser is generally shortened. However, if the wavelength is shorter than 300 nm, the material of the condensing lens is limited, making it difficult to produce an achromatic lens. Therefore, it is necessary to master lenses that are not achromatic.

  When the exposure laser and the red laser are incident on an objective lens that is not achromatic with parallel light as usual, the red laser having a smaller refractive index usually forms an image farther from the lens. Therefore, when the exposure laser is imaged on the workpiece, the red laser is not imaged on the workpiece, and is irradiated onto the workpiece with a certain geometric optical area. If the workpiece is completely flat and has no tilt, there is no problem. However, if the workpiece is distorted or tilted, the direction of the reflected light is shifted. In the method in which the distance between the workpiece and the lens is detected at a position perpendicular to the optical axis of the reflected light or a beam shape in the vertical direction, this becomes an error and a deviation occurs in the distance to be controlled. As a result, the image forming point of the exposure laser is separated from the work piece, resulting in a so-called defocused state.

  In order to avoid this, it is necessary to bring the imaging position of the red laser closer to the imaging position of the exposure laser. For this purpose, a red laser beam may be used as a convergent beam and incident on an objective lens that is not achromatic.

  The above is a conventional technique that eliminates blurring that occurs in principle due to distortion or inclination of a workpiece with respect to a lens that is not achromatic (see Patent Document 1).

  However, according to this prior art, if the objective lens is displaced from the initial position due to distortion of the structure supporting the optical system of the red laser, as described above, the red laser is incident on the objective lens with a convergent beam as described above. The exposure laser is defocused.

  An object of the present invention is to provide a laser processing apparatus that can eliminate the drawbacks of the prior art and can stably and accurately control the imaging position of a processing laser.

In order to achieve the above object, the first means of the present invention comprises a lens for forming an image of a laser on a workpiece and at least two lasers, and the imaging position of a processing laser among them is defined as the workpiece. In a laser processing apparatus that processes a workpiece by controlling the workpiece at a fixed position,
The frequency band when the distance between the lens and the workpiece is controlled to be constant is different for each laser, and these lasers are simultaneously controlled to control the distance between the lens and the workpiece. .

  According to a second means of the present invention, in the first means, the processing laser is used for control of a low frequency band, and a laser other than the processing laser is used for control of a high frequency band. The error signals in the low frequency band and the high frequency band indicating the above are superimposed.

  According to a third means of the present invention, in the second means, when a shift in a low frequency band from a predetermined position using the processing laser is processed by exciting the optical axis of the processing laser. It is characterized in that it can be detected without being affected by vibration.

  According to a fourth means of the present invention, in the third means, the low-frequency band shift from a predetermined position using the processing laser is partly reflected in the optical path of the reflected light from the workpiece of the processing laser. It is cut off and imaged on a plurality of divided photodetectors for detection.

As described above, the present invention includes a lens that forms an image of a laser on a workpiece and at least two lasers, and the imaging position of the machining laser is controlled at a fixed position with respect to the workpiece. In the laser processing apparatus for processing the workpiece, the frequency band when the distance between the lens and the workpiece is controlled to be constant is different for each laser, and these lasers are controlled simultaneously to control the lens and the workpiece. It is characterized by controlling the distance of an object.

  By comprising in this way, the laser processing apparatus which can control the imaging position of the processing laser stably and correctly can be provided.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical disc master exposure apparatus that controls (autofocus) the imaging position of an exposure laser with two laser apparatuses according to the first embodiment.

  The objective lens 1 that is not achromatic is mounted on the actuator 3 so that the distance from the master 2 coated with a resist that is an exposure target (workpiece) can be adjusted.

  The red laser 5 is formed as a condensing beam 7 by a convex lens 6, passes through the wavelength-selective mirror 4, and then is incident with a shift from the optical axis of the objective lens 1. Here, the position of the convex lens 6 in the optical axis direction is such that when the exposure laser 8 enters the objective lens 1 as parallel light and forms an image on the surface of the master 2, the red laser also forms an image on the surface of the master 2. Are adjusted in advance.

  The reflected light from the master 2 of the red laser passes through the objective lens 1 again and becomes diffused light 9. The diffused light 9 is incident on the two-divided detector 12 as a condensed beam 11 by a converging optical system 10 such as a convex lens.

  When the distance between the objective lens 1 and the master 2 changes, the condensed beam 11 moves on the two-divided detector 12, and the positional information thereof passes through the high-pass filter 14 as the error signal 13 and the objective lens position control circuit 15 Is input. The position of the two-divided detector 12 is adjusted so that the output of the two-divided detector 12 is 0, that is, the error signal is 0, when the red laser forms an image on the surface of the master 2.

  The high-pass filter 14 is set so as to transmit a frequency band cut by a low-pass filter 16 on the exposure laser side described later, that is, both do not interfere with each other.

  Next, the optical system of the exposure laser will be described.

  The exposure laser 8 incident on the objective lens 1 with parallel light is reflected by the surface of the master 2 and enters the imaging position detection optical system 17. Since the light intensity of the beam incident on the imaging position detection optical system 17 is generally weak, the S / N (ratio of signal to noise) of the error signal 18 is very small. Since the ratio of noise is usually large at high frequencies, the error signal 18 becomes an error signal 19 from which noise components have been cut by the low-pass filter 16, and is added after appropriate weighting by the error signal 13 and the addition circuit 26. The new error signal 27 is input to the feedback circuit 15 for driving the actuator of the objective lens 1. The feedback circuit 15 drives the actuator 3 to perform feedback so that the exposure laser 8 forms an image on the surface of the master 2.

  In the case of the master exposure apparatus in which the autofocus optical system is configured using two lasers in this way, the error signal 13 obtained from the red laser optical system contains a high-frequency component detected when the master 2 rotates. Since the signal is included, this signal can be used for distance control (autofocus) between the master 2 and the laser imaging position. However, since the red laser is incident on the objective lens 1 as convergent light, if the structure supporting the optical system of the red laser is distorted due to the ambient temperature or the like, it is easily affected and the correct autofocus signal is obtained. In other words, there is a possibility that the imaging point of the exposure laser 8 is out of focus from the surface of the master 2.

  On the other hand, the exposure laser 8 is not affected even if the position of the objective lens 1 in the optical axis direction changes because the exposure laser 8 is incident on the objective lens 1 as parallel light. The error signal 18 obtained from 8 is a signal from the exposure laser itself that causes the original image point to coincide with the surface of the master 2. For this reason, it is convenient if the autofocus function can be achieved with only the exposure laser 8. However, since the reflected light from the master 2 of the exposure laser 8 has a small amount of reflected light as described above and the sensitivity of the detector 12 to the deep ultraviolet light is low, the high frequency component of the error signal 18 is buried in noise and cannot be used. Therefore, when only the low frequency component is used as an error signal in the low-pass filter 16, a low frequency phenomenon caused by the distortion of the structure supporting the optical system of the red laser described above is corrected on the exposure laser side. Can do.

  In this way, when the high frequency component of the error signal 13 from the red laser and the low frequency component of the error signal 18 from the exposure laser 8 are added together by the adding circuit 26, all frequency bands necessary for control can be obtained correctly. Since the error signal 18 of the exposure laser 8 is corrected even when the objective lens is displaced from the initial position due to distortion of the structure supporting the optical system of the red laser as in the prior art (see Patent Document 1), The imaging point of the exposure laser 8 can be kept cheap and accurate with respect to the master 2 for a long time.

  FIG. 2 is a schematic configuration diagram of a laser processing apparatus according to the second embodiment of the present invention. This embodiment specifically shows the imaging position detection optical system 17 in the first embodiment.

  The reflected light from the master 2 of the exposure laser 8 is reflected by the splitter 20, the beam diameter is halved by the knife edge 21, and then condensed by the convex lens 22 onto the two-divided detector 23. The position of the two-divided detector 23 is adjusted so that the error signal 18 is minimized when the exposure laser 8 forms an image on the surface of the master 2.

  In general, the exposure apparatus has a function of monitoring the imaging state of the exposure laser 8 on the surface of the master disk with an image sensor, and the monitor image also becomes out of focus when the imaging point deviates from the master disk 2. This monitoring may be available for the error signal 18. However, as one method of using the master exposure apparatus, there is a case where the exposure locus on the master 2 is shaken (wobbled) with respect to the optical axis of the exposure laser 8 for the purpose of making the exposure locus a sine wave or the like. At this time, the wobble frequency is generally a high band, and cannot be followed by the above-described monitoring image sensor.

  In this embodiment, the deviation of the imaging point of the exposure laser 8 is detected by the knife edge 21, the convex lens 22, and the two-divided detector 23. In this method, even in the case of the wobble described above, it is possible to detect the deviation of the imaging point of the exposure laser 8 by considering the installation direction of the knife edge 21 and the two-divided detector 23. That is, in FIG. 2, when the exposure laser 8 is wobbled in the direction perpendicular to the paper surface, if the knife edge 21 and the two-divided detector 23 are installed as shown in the figure, the deviation of the imaging point is the result on the two-divided detector 23. This is the direction of the arrow of the image point, and can be detected regardless of the wobble direction (broken arrow). High bandwidth wobble can also be detected without problems.

  The other parts of the present embodiment are the same as those in the first embodiment, and a description thereof will be omitted.

  FIG. 3 is a schematic configuration diagram of a laser processing apparatus according to the third embodiment of the present invention, in which a switch circuit 25 is added to the optical system of the exposure laser 8 of the second embodiment.

  In the case of the master exposure apparatus, after the master 2 is set on the exposure apparatus as an exposure procedure, the head portion on which the autofocus optical system of FIG. 3 is set is set, the autofocus is applied, and then the exposure laser 8 Open the shutter for exposure. In the case of the present invention, when the autofocus is applied by the exposure laser after setting the head portion, the autofocused portion of the master 2 is exposed. It is desirable to do it simultaneously.

  In the present embodiment, the first autofocus is performed with a red laser, and an object is to achieve an autofocus function with the exposure laser 8 simultaneously with exposure.

  In FIG. 3, the error signal 18 (hereinafter referred to as difference signal) of the two-divided detector 23 on the exposure laser side is input to the switch circuit 25 after the high-frequency component is removed by the low-pass filter 16. The other sum signal 24 of the two-divided detector 23 is input to the control terminal of the switch circuit 25 so that when the voltage of the sum signal 24 exceeds a predetermined threshold, the switch of the switch circuit 25 is connected. .

  With such a configuration, the procedure of the conventional master exposure apparatus described above, that is, the head unit is set, the autofocus is applied with the red laser, the exposure is started, and the autofocus on the exposure laser side is simultaneously started. The function works and a series of operations can be performed automatically.

  The other parts of the present embodiment are the same as those in the first embodiment, and a description thereof will be omitted.

FIG. 4 is a schematic configuration diagram of a laser processing apparatus according to the fourth embodiment of the present invention. The two-divided detector shown in FIG. 3 is changed to a four-divided detector 28 to measure the wobble amount.
The beam spot moving in the direction of the solid arrow (left and right direction) on the quadrant detector 28 gives the autofocus signal (low frequency band) information, and the direction of the broken arrow (vertical direction) on the quadrant detector 28. The beam spot moving to () gives information on the amount of wobble displacement.

  Assuming that each light receiving surface of the quadrant detector 28 is a, b, c, d as shown in FIG. 4, the output of each light receiving surface enters the branch circuit 29. The branch circuit 29 branches the output of each light receiving surface into a difference signal for autofocus, a sum signal, and a difference signal for wobble measurement. That is, for the autofocus signal, the output of each light receiving surface is input to the low-pass filter 16 as a difference signal of (a + c) − (b + d). The sum signal is input to the switch circuit 25 as (a + c) + (b + d), and the same operation as in the embodiment of FIG. 3 is performed.

  On the other hand, the wobble displacement amount is measured by entering the wobble amount measurement system 30 using (a + b) − (c + d) as a difference signal and measuring the wobble amount.

  In this way, the quadrant detector 28 can be used for both the autofocus function and the wobble amount measurement function. As described in the second embodiment, the wobble frequency is generally a high band, and an image sensor cannot be added. However, according to the configuration of the present embodiment, the amount of displacement that wobbles in the direction of the dashed arrow during exposure can be measured. Can do.

  In addition, about the other part of this embodiment, it is the same as the said 3rd refreshing embodiment, and those description is abbreviate | omitted.

  In the above embodiment, the optical disk master exposure apparatus has been described as the laser processing apparatus. However, the present invention forms an image of a laser beam on an object as the laser processing apparatus, and ablation and latent image are formed on the object. The present invention can also be applied to a technical field that performs processing such as image formation, crystal structure change, magnetic structure change, substance curing, substance dissolution, and the like.

1 is a schematic configuration diagram of a laser processing apparatus according to a first embodiment of the present invention. It is a schematic block diagram of the laser processing apparatus which concerns on 2nd Embodiment of this invention. It is a schematic block diagram of the laser processing apparatus which concerns on 3rd Embodiment of this invention. It is a schematic block diagram of the laser processing apparatus which concerns on 4th Embodiment of this invention.

Explanation of symbols

1: objective lens that is not achromatic, 2: master 3: actuator, 4: wavelength selective mirror, 5: red semiconductor laser, 6: convex lens, 7: focused beam, 8: exposure laser, 9: diffused light 10: convergent optical system, 11: focused beam, 12: split detector, 13: error signal, 14: high-pass filter, 15: objective lens position control circuit, 16: low-pass filter, 17: imaging position detection optics System: 18: Error signal (difference signal), 19: Error signal, 20: Splitter, 21: Knife edge, 22: Convex lens, 23: Divided detector, 24: Sum signal, 25: Switch circuit, 26: Adder circuit, 27: New error signal, 28: 40% detector, 29: Branch circuit, 30: Wobble amount measurement system.

Claims (6)

A lens for imaging the laser beam on the workpiece and at least two lasers are provided, and the machining position of the machining laser is controlled at a fixed position with respect to the workpiece to process the workpiece. In the laser processing device to perform,
The laser processing apparatus characterized in that the frequency band when the distance between the lens and the workpiece is controlled to be constant is different for each laser, and the distance between the lens and the workpiece is controlled by simultaneously controlling these lasers. .   2. The laser processing apparatus according to claim 1, wherein the processing laser is used for controlling a low frequency band, a laser other than the processing laser is used for controlling a high frequency band, and the low frequency indicating deviation from a predetermined position is used. A laser processing apparatus characterized by superposing error signals in a band and a high frequency band.   3. The laser processing apparatus according to claim 2, wherein a shift in a low frequency band from a predetermined position using the processing laser affects the vibration even when processing the optical axis of the processing laser. A laser processing device characterized in that it can be detected without receiving.   4. The laser processing apparatus according to claim 3, wherein a shift of a low frequency band from a predetermined position using the processing laser is partially cut off by dividing a part of an optical path of reflected light from a workpiece of the processing laser. A laser processing apparatus characterized in that an image is formed on a photo detector and detected.   5. The laser processing apparatus according to claim 4, wherein a function of detecting a shift in a low frequency band by the processing laser is switched by inputting a sum signal of the two-divided detector on the processing laser side to a switch circuit. Laser processing equipment. The two-divided detector on the processing laser side according to claims 4 and 5 is a detector divided into four or more parts, and on the workpiece when the optical axis of the laser according to claim 3 is vibrated. A laser processing apparatus for detecting a movement amount of an imaging point of a processing laser.

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