JP5465120B2 - Optical axis adjustment method and laser processing apparatus - Google Patents

Description

  The present invention relates to a method for adjusting the optical axis of a laser beam emitted from a laser light source, and a laser processing apparatus having a function of adjusting the optical axis of a laser beam emitted from a laser light source.

  In a laser processing apparatus equipped with a transfer mold optical system that splits and superimposes a laser beam, if the optical axis adjustment is incomplete, the beam does not travel a predetermined optical path in the transfer mold optical system, and There is a problem that the energy fluctuation of the main component becomes large.

  An invention of a laser processing apparatus that includes an optical axis position detector that monitors the position of the optical axis of a laser beam and that can correct the deviation of the optical axis is disclosed (for example, see Patent Document 1). In the laser processing apparatus described in Patent Document 1, the direction of the reflecting surface of the reflecting mirror is adjusted using fuzzy inference based on the light intensity of the laser beam received by the light receiving element of the optical axis position detector. However, Patent Document 1 does not mention a transfer mold optical system.

JP 2006-289443 A

  An object of the present invention is to provide a laser beam optical axis adjustment method and a laser processing apparatus that enable high-quality laser processing.

  According to one aspect of the present invention, (a) a laser beam is spatially divided into a plurality of laser beams, the divided laser beams are superimposed, and the light intensity distribution of the laser beam at the position where the laser beams are superimposed And (b) adjusting the optical axis of the laser beam emitted from the laser light source based on the light intensity distribution of the laser beam detected in the step (a). In a), the light intensities of the first and second sub beams formed separately on both sides of the main beam having the highest light intensity are detected, and in the step (b), the first and second sub beams are detected. There is provided an optical axis adjustment method for adjusting an optical axis of a laser beam emitted from a laser light source so that a difference in light intensity is reduced.

  According to another aspect of the present invention, a laser light source that emits a laser beam, a stage that holds the workpiece, and a propagation that propagates the laser beam emitted from the laser light source to the workpiece that is held by the stage. An optical system and a split superposition optical system that is included in or not included in the propagation optical system, wherein at least a part of the laser beam emitted from the laser light source is spatially divided into a plurality of laser beams and split A split superposition optical system that superimposes the laser light on the superposition position, and a light intensity detector that detects the light intensity distribution of the laser beam at the superposition position, and the main beam having the highest light intensity. A light intensity detector for detecting the light intensity of the first and second sub-beams formed separately on both sides, and the first and second light beams detected by the light intensity detector; As the difference in the light intensity of the sub beam is small, the laser processing apparatus is provided with a control device to adjust the optical axis of the laser beam exiting the laser light source.

  ADVANTAGE OF THE INVENTION According to this invention, the optical axis adjustment method of a laser beam and the laser processing apparatus which enable high quality laser processing can be provided.

It is the schematic which shows the laser annealing apparatus which is a laser processing apparatus by an Example. (A)-(C) are the schematic which shows the laser beam in the cylindrical lens array group 47. FIG. (A)-(C) are the schematic which shows the light intensity distribution of the laser beam 70 detected with the CCD camera 51 arrange | positioned on the overlapping surface of the divided | segmented laser beam. (A) And (B) is a figure for demonstrating the optical axis adjustment method by an Example. It is the schematic which shows the laser annealing apparatus which is the laser processing apparatus by a modification. (A) And (B) is a figure for demonstrating the laser beam optical axis adjustment method by a comparative example.

  With reference to FIGS. 6A and 6B, a laser beam optical axis adjustment method according to a comparative example will be described. FIG. 6A is a schematic diagram illustrating a laser oscillator and a portion where an optical axis of a laser beam emitted from the laser oscillator is adjusted.

  For example, a laser beam 20 is emitted from a laser oscillator 10 which is an excimer laser oscillator. The laser beam 20 is folded back by 90 ° by the first mirror 11, the second mirror 12, and the third mirror 13 which are total reflection mirrors. A CCD camera 14 is disposed on the back surface of the second mirror 12, and a CCD camera 15 is disposed on the back surface of the third mirror 13.

  In the optical axis adjustment method according to the comparative example, first, the first mirror 11 is swung while the image of the transmitted light of the laser beam 20 reflected on the CCD camera 14 disposed on the back surface of the second mirror 12 is monitored. Is adjusted to align the optical axis of the laser beam 20.

  FIG. 6B is a photograph showing an image of the transmitted light of the laser beam 20 reflected on the CCD camera 14. The white part of the photograph shows the transmitted light of the laser beam 20. The transmitted light of the laser beam 20 is incident on the CCD camera 14 through a target having a cross-shaped portion with a round hole in the center. The adjustment of the optical axis of the laser beam 20 is performed by, for example, reflecting the surface of the first mirror 11 so that the length and width of the four regions of the transmitted light of the laser beam 20 defined by the cruciform portion of the target are equal to each other. This is done by adjusting the direction of the.

  Next, while monitoring the transmitted light image of the laser beam 20 reflected on the CCD camera 15 disposed on the back surface of the third mirror 13, the second mirror 12 is swung and the same operation is performed. Align the optical axis. In this way, the optical axis of the laser beam 20 emitted from the second mirror 12 is made constant.

  However, a laser beam emitted from a high-power laser such as an excimer laser oscillator has a large beam size, and the cross-sectional shape of the beam is not necessarily symmetrical. For this reason, in the optical axis adjustment performed based on the image displayed on the camera arranged behind the mirror, it is difficult to determine the center of the beam cross section, and fine adjustment may be difficult.

  The inventor of the present application diligently studied a method for adjusting the optical axis of a laser beam with higher accuracy than the optical axis adjustment method according to the comparative example.

  FIG. 1 is a schematic diagram showing a laser annealing apparatus which is a laser processing apparatus according to an embodiment. The laser annealing apparatus includes a laser oscillator 40, a first mirror 41, a second mirror 42, a third mirror 43, CCD cameras 44 and 45, a cylindrical lens array group 47, a folding mirror 48, a cylindrical lens 49, a stage 50, and a CCD camera 51. And the control device 52. The control device 52 includes a storage device 53. The laser oscillator 40, the first mirror 41, and the second mirror 42 constitute the laser light source 30. The cylindrical lens array group 47, the folding mirror 48, and the cylindrical lens 49 constitute a transfer molding optical system (divided superposition optical system) 46. For example, laser annealing of the semiconductor substrate 60 is performed using the laser annealing apparatus shown in FIG.

  For example, a pulse laser beam 70 is emitted from a laser oscillator 40 which is an excimer laser oscillator. The laser beam 70 is folded back by 90 ° by the first mirror 41, the second mirror 42, and the third mirror 43, which are total reflection mirrors. A CCD camera 44 is disposed on the back surface of the second mirror 42, and a CCD camera 45 is disposed on the back surface of the third mirror 43.

  The first mirror 41 and the second mirror 42 are swung by a driving device such as a motor, for example, and can change the direction of the reflecting surface. The CCD cameras 44 and 45 image the laser beam 70 that passes through the second mirror 42 and the third mirror 43, respectively.

  For example, prior to the laser annealing process, while monitoring the image of the transmitted light of the laser beam 70 reflected on the CCD camera 44, the first mirror 41 is swung to adjust the direction of the reflecting surface, and the optical axis of the laser beam 70 is adjusted. Alignment can be performed. Subsequently, similarly, while monitoring the transmitted light image of the laser beam 70 reflected on the CCD camera 45, the second mirror 42 can be swung to align the optical axis of the laser beam 70. . By operating the first mirror 41 and the second mirror 42, the optical axis of the laser beam 70 emitted from the laser light source 30 (second mirror 42) can be made constant.

  The laser beam 70 turned back by the third mirror 43 is incident on a semiconductor substrate 60, for example, a silicon wafer, which is a processing target (annealing target) held on the stage 50, via the transfer mold optical system 46. To do. The stage 50 is an XY stage, for example, and can move the semiconductor substrate 60 in a two-dimensional direction. By the operation of the stage 50, the laser beam 70 is scanned on the semiconductor substrate 60, and laser annealing of the semiconductor substrate 60 is performed.

  The transfer mold optical system 46 spatially divides the laser beam 70 into a plurality of laser beams at the dividing surface (dividing position) of the cylindrical lens array group 47, and superimposes the divided laser light on the overlapping surface (overlapping position). ). Thereby, the cross-sectional shape of the laser beam 70 can be formed, for example, in a rectangular shape on the overlapping surface, and the light intensity in the beam cross-section can be made uniform. The cylindrical lens 49 of the transfer mold optical system 46 is a condensing lens. The stage 50 holds the semiconductor substrate 60 such that the surface of the semiconductor substrate 60 is disposed on the overlapping surface. That is, the processed surface matches the superimposed surface.

  A CCD camera 51 is installed on the stage 50 so as to be movable in a two-dimensional direction. The CCD camera 51 is a light intensity detector that can detect the light intensity of incident light. Prior to processing or during processing, the light receiving surface of the CCD camera 51 can be arranged on the overlapping surface of the divided laser beams by the operation of the stage 50.

  The CCD camera 51 detects the light intensity distribution of the laser beam 70 on the overlapping surface. The detection result is transmitted to the control device 52. The control device 52 oscillates the first mirror 41 and the second mirror 42 based on the detected light intensity distribution, and sends a signal for changing the direction of the reflecting surface to the laser light source 30 (the first mirror 41 and the second mirror 42). To the driving device that drives the mirror 42).

  The correspondence relationship between the light intensity distribution on the superposed surface and the amount of swing of each of the mirrors 41 and 42 (the amount of change in the direction of the reflecting surface) is stored in a storage device 53 included in the control device 52, for example, a memory. The control device 52 refers to the stored contents of the storage device 53 and determines the swing amount of the mirrors 41 and 42 based on the detected light intensity distribution.

  According to the control signal transmitted from the control device 52, the directions of the reflecting surfaces of the first mirror 41 and the second mirror 42 are changed, and the emission direction (light) of the laser beam 70 emitted from the laser light source 30 (second mirror 42). Axis) is adjusted.

  The control device 52 controls the emission direction (adjustment of the optical axis) of the laser beam 70 emitted from the laser light source 30 based on the light intensity distribution on the overlapping surface, and also performs the CCD camera 51 and the semiconductor by the stage 50. The movement of the substrate 60 is controlled. Further, a control signal is transmitted to the laser oscillator 40 to control the emission of the laser beam 70 by the laser oscillator 40.

  2A to 2C are schematic views showing laser light in the cylindrical lens array group 47. FIG. The cylindrical lens array group 47 includes a first cylindrical lens array 47a, a second cylindrical lens array 47b, and a third cylindrical lens array 47c.

  The first cylindrical lens array 47a is a lens array having a convex surface on the side on which the laser beam 70 is incident, and spatially divides and condenses the incident laser light. The second and third cylindrical lens arrays 47b and 47c can determine the beam size on the overlapping surface depending on the configuration.

  The laser beam 70 is spatially divided into a plurality of laser beams by each cylindrical lens of the first cylindrical lens array 47a arranged at the division position. The plurality of divided laser beams are incident on the corresponding cylindrical lenses of the third cylindrical lens array 47c via the corresponding cylindrical lenses of the second cylindrical lens array 47b.

  As shown in FIG. 2A, when the optical axis adjustment is insufficient and the laser beam 70 is incident on the first cylindrical lens array 47a from an oblique direction, each cylindrical beam of the first cylindrical lens array 47a is obtained. The plurality of laser beams divided by the lens cannot be accommodated by the corresponding cylindrical lens of the third cylindrical lens array 47c, and a part of the laser light is incident on the adjacent cylindrical lens.

  As shown in FIG. 2B, when the laser beam 70 is incident on the first cylindrical lens array 47a, for example, from the vertical direction, a plurality of lasers divided by the respective cylindrical lenses of the first cylindrical lens array 47a. The light is incident on the corresponding cylindrical lenses of the second and third cylindrical lens arrays 47b and 47c.

  FIG. 2C shows a case where the laser beam 70 is incident on the first cylindrical lens array 47a from an oblique direction opposite to that shown in FIG. 2A due to insufficient optical axis adjustment. A plurality of laser beams divided by the respective cylindrical lenses of the first cylindrical lens array 47a cannot be accommodated by the corresponding cylindrical lenses of the third cylindrical lens array 47c, and a part of them is shown in FIG. It enters the adjacent cylindrical lens on the opposite side.

  3A to 3C are schematic views showing the light intensity distribution of the laser beam 70 detected by the CCD camera 51 arranged on the overlapping surface of the divided laser beams. 3A to 3C show the light intensity distribution when the laser beam 70 is incident on the first cylindrical lens array 47a in the incident mode shown in FIGS. 2A to 2C in order. Show.

  Reference is made to FIG. On the superposed surface, out of the components of the respective laser beams divided by the first cylindrical lens array 47a, the components transmitted through the corresponding cylindrical lenses of the second and third cylindrical lens arrays 47b and 47c are the center. The light intensity of the main beam formed by superimposing and the sub beam formed at a position away from the main beam is detected. Laser annealing is performed using a main beam. The sub beam is formed by, for example, a component that has not transmitted through the corresponding cylindrical lens of the third cylindrical lens array 47c among the components of the respective laser beams divided by the first cylindrical lens array 47a.

  Reference is made to FIG. Even when the plurality of laser beams divided by the respective cylindrical lenses of the first cylindrical lens array 47a are incident on the corresponding cylindrical lenses of the second and third cylindrical lens arrays 47b and 47c, the optical axis A sub beam may be formed by the component of the laser beam deviating from the above. The sub beam is formed on both sides of the main beam, for example, separately from the main beam.

  Reference is made to FIG. In the incident mode of FIG. 2C in which the laser beam 70 is incident on the first cylindrical lens array 47a from an oblique direction opposite to that shown in FIG. It is formed on the opposite side to the example shown in FIG.

  3A and 3C, for example, the light intensity of the sub beam formed by the component of the laser beam deviated from the optical axis is large. For this reason, if the optical axis adjustment is performed with an optical axis adjustment method that is not highly accurate, for example, the fluctuation of the light intensity of the main beam for each laser pulse increases, which adversely affects processing quality.

  As in the example shown in FIG. 3B, for example, when a sub beam having the same light intensity is formed on both sides of the main beam by the component of the laser beam deviated from the optical axis, the light intensity of the sub beam is minimized. . The fluctuation of the light intensity of the main beam is also small. For this reason, laser processing with reduced irradiation unevenness is possible. As for the light intensity distribution of the laser beam 70 on the overlapping surface, it is desirable that the light intensity of the sub beams formed on both sides of the main beam be equal.

  With reference to FIGS. 4A and 4B, an optical axis adjustment method according to the embodiment will be described.

  In the optical axis adjustment method according to the embodiment, first, the transmitted light image of the laser beam 70 reflected on the CCD camera 44 is monitored, the first mirror 41 is swung to adjust the direction of the reflecting surface, and the laser beam 70 Align the optical axis. Subsequently, the transmitted light image of the laser beam 70 reflected on the CCD camera 45 is monitored, the second mirror 42 is swung to adjust the direction of the reflecting surface, and the optical axis of the laser beam 70 is aligned.

  Further, the CCD camera 51 is arranged on the overlapping surface to detect the light intensity distribution of the laser beam 70. FIG. 4A shows a general light intensity distribution on the overlapping surface detected by the CCD camera 51. On the overlapping surface, a main beam having the highest light intensity and a sub beam are formed on both sides of the main beam at positions away from the main beam. In FIG. 4A, the two sub beams are denoted as sub beam A and sub beam B. The light intensity of the main beam, the sub beam A, and the sub beam B can be changed by swinging the first mirror 41 and the second mirror 42 and changing the direction of the reflecting surface.

  Reference is made to FIG. Based on the light intensity distribution detected by the CCD camera 51, the control device 52 desirably makes the light intensities of both sub-beams equal so that the difference in light intensity between the sub-beam A and the sub-beam B is reduced. Then, a signal for swinging the first mirror 41 and the second mirror 42 and changing the direction of the reflecting surface is transmitted to the laser light source 30 (a driving device for driving the first mirror 41 and the second mirror 42).

  According to the control signal transmitted from the control device 52, the directions of the reflecting surfaces of the first mirror 41 and the second mirror 42 are changed, and the emission direction (light) of the laser beam 70 emitted from the laser light source 30 (second mirror 42). Axis) is adjusted.

  When the laser beam 70 that has passed through the transfer molding optical system 46 is monitored on the overlapping surface, the component of the laser beam that is off the optical axis is separated on both sides of the main beam and shaped as a sub-beam, so that quantification Is possible.

  The reflection surfaces of the first mirror 41 and the second mirror 42 are preferably made so that the difference in light intensity between the two sub beams formed on both sides of the main beam is small, and preferably the light intensities of both sub beams are equal. By changing the direction, the accuracy of optical axis adjustment of the laser beam 70 emitted from the laser light source 30 can be improved. For this reason, higher quality laser processing can be performed.

  Furthermore, in the optical axis adjustment method according to the embodiment, the light intensity of the main beam and the sub beam is measured at the processing position. At the machining position away from the laser light source 30, the deviation amount of the component of the laser beam 70 deviated from the optical axis becomes obvious. Therefore, finer adjustment of the optical axis can be performed. Further, since the optical axis is adjusted based on the light intensity at the processing position of the laser beam 70, a direct improvement in processing quality can be expected as compared with the case based on the results measured at other positions.

  FIG. 5 is a schematic diagram showing a laser annealing apparatus which is a laser processing apparatus according to a modification. In the modification, a branching optical system 80 is disposed on the optical path of the laser beam 70 emitted from the laser light source 30. The branching optical system 80 branches a part of the laser beam 70 from the optical path traveling to the stage 50 (processing position).

  A part of the branched laser beam 70 enters a CCD camera 85 via a transfer mold optical system (divided superposition optical system) 81. The transfer mold optical system 81 includes a cylindrical lens array group 82, a folding mirror 83, and a cylindrical lens 84, and the function thereof is the same as that of the transfer mold optical system 46. That is, also in the transfer mold optical system 81, a branched part of the laser beam 70 is spatially divided into a plurality of laser beams on the dividing surface (dividing position) of the cylindrical lens array group 82, and the divided laser beams are divided. Are superimposed on the overlapping surface (overlapping position). A part of the branched laser beam 70 is formed into a rectangular cross-sectional shape on the overlapping surface, and the light intensity in the beam cross-section is made uniform.

  The CCD camera 85 is a light intensity detector that can detect the light intensity of incident light, and is disposed, for example, such that its light receiving surface coincides with the overlapping surface.

  Similarly to the embodiment, the CCD camera 85 detects the light intensity distribution on the overlapping surface of the branched laser beam 70. The detection result is transmitted to the control device 52, and the control device 52 determines the swing amount (change amount of the direction of the reflecting surface) of the first mirror 41 and the second mirror 42 based on the detected light intensity distribution, Control the behavior. The operation control of both mirrors 41 and 42 is the same as in the embodiment, and preferably the light intensity of both sub-beams is made equal so that the difference in light intensity between the sub-beams formed separately on both sides of the main beam becomes small. To be done.

  Also in the laser processing apparatus according to the modified example, the emission direction (optical axis) of the laser beam 70 emitted from the laser light source 30 (second mirror 42) can be adjusted with high accuracy, and the processing quality can be improved.

  The branching optical system 80 can be installed at an arbitrary position on the optical path of the laser beam 70 between the laser light source 30 and the transfer mold optical system 46.

  FIG. 5 illustrates a modification of the configuration in which the transfer optical system 46 is also included in the propagation optical system that propagates the laser beam 70 emitted from the laser light source 30 to the semiconductor substrate 60 on the stage 50. It is also possible to adopt a configuration in which the propagation optical system does not include the transfer mold optical system.

  Although the present invention has been described with reference to the embodiments and the modifications, the present invention is not limited to these.

  For example, the operator of the apparatus can perform all or part of the optical axis adjustment process performed by the control device 52.

  It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like are possible.

  For example, it can be suitably used for laser processing using a transfer mold optical system, for example, laser annealing.

DESCRIPTION OF SYMBOLS 10 Laser oscillator 11 1st mirror 12 2nd mirror 13 3rd mirror 14, 15 CCD camera 20 Laser beam 30 Laser light source 40 Laser oscillator 41 1st mirror 42 2nd mirror 43 3rd mirror 44, 45 CCD camera 46 Transfer molding type Optical system (split superposition optical system)
47 Cylindrical Lens Array Group 47a First Cylindrical Lens Array 47b Second Cylindrical Lens Array 47c Third Cylindrical Lens Array 48 Folding Mirror 49 Cylindrical Lens 50 Stage 51 CCD Camera 52 Controller 53 Storage Device 60 Semiconductor Substrate 70 Laser Beam 80 Branch optical system 81 Transfer molding optical system (split superposition optical system)
82 Cylindrical lens array group 83 Folding mirror 84 Cylindrical lens 85 CCD camera

Claims (7)

(A) spatially dividing the laser beam into a plurality of laser beams, superimposing the divided laser beams, and detecting a light intensity distribution of the laser beam at a position where the laser beams are superimposed;
(B) adjusting the optical axis of the laser beam emitted from the laser light source based on the light intensity distribution of the laser beam detected in the step (a),
In the step (a), the light intensity of the first and second sub-beams formed separately on both sides of the main beam having the highest light intensity is detected,
In the step (b), an optical axis adjustment method for adjusting an optical axis of a laser beam emitted from a laser light source so that a difference in light intensity between the first and second sub beams is reduced.   2. The optical axis adjustment method according to claim 1, wherein in the step (b), the optical axis of the laser beam emitted from the laser light source is adjusted so that the light intensities of the first and second sub beams are equal. A laser light source for emitting a laser beam;
A stage for holding the workpiece,
A propagation optical system for propagating a laser beam emitted from the laser light source to an object to be processed held by the stage;
A split superposition optical system that is included or not included in the propagation optical system, wherein at least a part of a laser beam emitted from the laser light source is spatially divided into a plurality of laser beams, and the divided laser A split superposition optical system that superimposes light at a superposition position;
A light intensity detector for detecting a light intensity distribution of a laser beam at the overlapping position, wherein the light intensity of first and second sub beams formed separately on both sides of a main beam having the highest light intensity is detected. A light intensity detector;
A laser processing unit that adjusts an optical axis of a laser beam emitted from the laser light source so that a difference in light intensity between the first and second sub-beams detected by the light intensity detector is reduced; apparatus.   The laser processing apparatus according to claim 3, wherein the control device adjusts an optical axis of a laser beam emitted from the laser light source so that light intensities of the first and second sub beams are equal. The propagation optical system includes the split superposition optical system,
The laser processing apparatus according to claim 3, wherein the stage holds a processing target such that the overlapping position becomes a processing position. The laser light source includes a laser oscillator that emits a laser beam, a first reflecting mirror that reflects the laser beam emitted from the laser oscillator, and a second that reflects the laser beam reflected by the first reflecting mirror. Including reflectors,
The said control apparatus adjusts the optical axis of the laser beam radiate | emitted from the said laser light source by changing the direction of the reflective surface of the said 1st and 2nd reflective mirror. The laser processing apparatus as described.   The control device includes a storage device that stores a correspondence relationship between the light intensity distribution of the laser beam at the overlapping position and the amount of change in the direction of the reflection surface of the first and second reflecting mirrors, and the storage device 7. The direction of the reflecting surfaces of the first and second reflecting mirrors is changed so that the difference in light intensity between the first and second sub-beams is reduced with reference to the stored contents. Laser processing equipment.