JP2011025279A - Optical system and laser machining device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical system for laser machining capable of efficiently carrying out uniform machining along each machining line and of improving machining quality, and also to provide a laser machining device having the same. <P>SOLUTION: The optical system includes: a pair of prisms 132 for converting laser beam irradiated from a laser light source 11 into elliptic laser beam having an elliptic cross section; prism rotating mechanisms 133a, 133b for changing length in a long axis direction in the elliptic cross section of the elliptic laser beam converted by the pair of the prisms 132; a prism moving mechanism 14 for moving the pair of the prisms 132 in parallel along the long axis direction in the elliptic cross section of the elliptic laser beam converted by the pair of the prisms 132; and a condenser lens 16 for condensing the elliptic laser beam toward a workpiece. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical system used when laser processing a workpiece (workpiece) such as a semiconductor wafer and a laser processing apparatus including the optical system.

  In recent years, as a method of dividing a workpiece (workpiece) such as a semiconductor wafer, a plurality of regions are defined by providing division lines called streets arranged in a grid on the surface of the workpiece, and lasers are divided along the streets. There has been proposed a method in which a laser processing groove is formed by irradiating a beam of light, and a mechanical breaking device cuts along the laser processing groove (Patent Document 1).

  Laser processing can increase the processing speed as compared with cutting processing, and can relatively easily process a workpiece made of a material having high hardness such as sapphire. In laser processing, it is very difficult to form a uniform laser processing groove at a desired depth along each processing line. In other words, even if the laser beam output is increased above a certain level to increase the depth of the laser processing groove formed on the workpiece, the laser beam energy is not sufficiently absorbed, and a laser processing groove with a desired depth is formed. Can not do it. If the output of the laser beam is too high, the processing quality may deteriorate.

  In order to solve these problems, the present applicant has proposed a laser processing apparatus that forms a spot diameter of a laser beam in an elliptical shape using a cylindrical lens (Patent Document 2). By shaping the spot shape of the focused laser beam into an ellipse and positioning the long axis of the shaped spot in the processing feed direction, the energy per unit time can be dispersed in the long axis direction. Now, processing can be performed efficiently along the processing line.

JP-A-10-305420 JP 2006-289388 A

  However, when a beam is formed into an elliptical shape by a cylindrical lens in a laser processing apparatus, the angle of incidence on the objective lens differs between the minor axis direction and the major axis direction of the elliptical spot. As a result, the minor axis of the elliptical spot is changed. The focal point is formed at different positions in the direction and the major axis direction. For this reason, about the laser processing apparatus mentioned above, the further improvement is calculated | required in processing quality.

  The present invention has been made in view of such circumstances, can form an elliptical spot having the same focal point in the minor axis direction and the major axis direction, and can efficiently perform uniform machining along the machining line. An object of the present invention is to provide an optical system for laser processing capable of improving the processing quality and a laser processing apparatus including the same.

  The optical system of the present invention is disposed on an optical path of the laser beam emitted from the laser light source and the laser beam emitted from the laser light source, and converts the laser beam into an elliptical laser beam having an elliptical cross section. A pair of prisms, and the ellipse that is converted by the pair of prisms by rotating the pair of prisms in a reverse direction with a direction perpendicular to the optical axis direction of the laser beam incident on the pair of prisms as a rotation axis. A prism rotation mechanism that changes the length in the major axis direction of the elliptical cross section of the laser beam, and the pair of prisms in parallel along the major axis direction in the elliptical section of the elliptical laser beam converted by the pair of prisms A prism moving mechanism for moving, and a condensing lens for condensing the elliptical laser beam toward a workpiece. It is characterized in.

  According to this configuration, the laser beam incident on the incident-side prism from the laser light source is refracted and shaped into an elliptical shape while maintaining the parallel light flux. The direction of the outgoing light of the elliptical laser beam that has passed through the incident-side prism changes, but the elliptical laser beam emitted from the incident-side prism enters the outgoing-side prism and is refracted and emitted while holding the parallel light beam. Finally, the optical axis of the elliptical laser beam is directed in a direction (fixed) that coincides with the optical axis direction of the condenser lens. The incident angle of the laser beam to the incident side prism and the incident angle of the elliptical laser beam to the output side prism are adjusted by the prism rotation mechanism. As a result of changing the incident angle of the laser beam to the pair of prisms, the optical axis position of the elliptical laser beam emitted from the prism on the emission side moves in the major axis direction of the elliptical spot and deviates from the optical axis of the condenser lens. The prism moving mechanism can move the pair of prisms in a direction to absorb this optical axis deviation, and it is not necessary to move the optical components arranged in the subsequent stage. Since the elliptical laser beam emitted from the exit-side prism enters the condenser lens in the form of a parallel beam, the incident angle to the condenser lens can be the same, and the minor axis direction and major axis of the elliptical spot It is possible to focus at the same position in the direction. Further, since the pair of prisms are aspherical optical elements, the optical axes can be easily aligned as compared with the cylindrical lenses, and the optical axes can be accurately aligned with simple control.

  The optical system of the present invention includes a diffractive optical element disposed between the pair of prisms and the condensing lens, and the diffractive optical element includes the elliptical laser beam incident on the diffractive optical element. The elliptical laser beam is preferably dispersed into a plurality of elliptical laser beams each having a predetermined angle with respect to the major axis direction of the elliptical cross section.

  According to this configuration, even with a laser having high energy, the energy can be divided into a plurality of parts, and the energy can be efficiently used for processing.

  A laser processing apparatus of the present invention includes the optical system and a holding table that holds a workpiece, and processes the workpiece by irradiating the workpiece with an elliptical laser beam generated by the optical system. And

  According to this configuration, the angle incident on the objective lens can be the same in the minor axis direction and the major axis direction of the elliptical spot, and the same position can be obtained in the minor axis direction and the major axis direction of the elliptical spot. It can be focused. As a result, the processing quality in laser processing can be improved.

  According to the present invention, an elliptical spot having the same focal point in the minor axis direction and the major axis direction can be formed, the machining can be efficiently performed along each machining line, and the machining quality can be improved. .

1 is an overall configuration diagram showing an optical system according to an embodiment of the present invention. It is a figure which shows the laser cross section in the optical system of FIG. It is an external view which shows the laser processing apparatus which concerns on one embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is an overall configuration diagram showing an optical system according to an embodiment of the present invention. The optical system shown in FIG. 1 includes a laser light source 11 that emits a laser beam, and a pair of prisms 132 that convert a laser beam of parallel light beams emitted from the laser light source 11 into an elliptical laser beam having an elliptical cross-sectional shape. The conversion unit 13, the prism moving mechanism 14 that translates the pair of prisms 132, the diffractive optical element 15 that splits the elliptical laser beam emitted from the beam conversion unit 13 to form a plurality of elliptical laser beams, and the plurality of ellipses A condensing lens 16 that mainly condenses the laser beam and forms a plurality of elliptical spots on a workpiece (work) 18 placed on the holding table 17 is mainly configured. Each of the prisms 132a and 132b of the pair of prisms 132 is provided with prism rotation mechanisms 133a and 133b that rotate each other in the reverse direction. The optical system also includes a control circuit 19 that controls the oscillator of the laser light source 11, controls the prism moving mechanism, and controls the prism rotating mechanisms 133a and 133b.

  The laser light source 11 has an oscillator that oscillates a short pulse laser having a laser wavelength of 100 nm to 1500 nm. The short pulse laser oscillated by the oscillator is emitted as a laser beam having a circular cross section and a parallel light beam. A mirror 12 is disposed on the optical path of the laser beam emitted from the laser light source 11, and the laser beam is reflected by the mirror 12 in the same direction as the movement direction of a beam conversion unit 13 to be described later. It is made incident on. Further, the oscillator of the laser light source 11 is electrically connected to the control circuit 19, and the oscillation of the short pulse laser is controlled by the control circuit 19.

  In the beam conversion unit 13, a laser beam whose optical path is changed from the mirror 12 is incident, a mirror 131 that reflects the laser beam vertically downward and enters the upper prism 132a of the pair of prisms 132 (prism 132a). It is arranged. Accordingly, the mirror 12 disposed outside the beam conversion unit 13 receives the laser beam emitted from the laser light source 11, reflects it in the same direction as the movement direction of the beam conversion unit 13, and fixes it in the beam conversion unit 13. Since the light is incident on the mirror 131, the laser beam oscillated from the laser light source 11 can be guided to the beam conversion unit 13 even if the beam conversion unit 13 moves.

  In the beam conversion unit 13, a pair of prisms 132 for converting the laser beam into an elliptical laser beam having an elliptical cross-sectional shape is disposed in the subsequent stage on the optical path of the laser beam. The pair of prisms 132 includes an upper prism 132a and a lower prism 132b. When the laser beam passes through the pair of prisms 132, the laser beam having a circular cross-sectional shape is converted into an elliptical beam shape expanded in one axial direction orthogonal to the optical axis. Therefore, in the cross-sectional view of the elliptical beam (elliptical laser beam), the major axis direction is orthogonal to the optical axis of the laser beam.

  The upper prism 132a is rotatably attached by the upper prism rotation mechanism 133a. Further, the lower prism 132b is rotatably attached by the lower prism rotation mechanism 133b. The upper prism rotation mechanism 133a and the lower prism rotation mechanism 133b are electrically connected to the control circuit 19, and the control circuit 19 rotates the upper prism rotation mechanism 133a and the lower prism rotation mechanism 133b, respectively. Be controlled.

  When a circular laser beam having a circular cross-section with respect to the upper prism 132a is incident on the incident surface at a predetermined incident angle, it is refracted while maintaining the parallel light beam and expanded in one direction perpendicular to the optical axis. It is converted into an elliptical cross section. The direction of the emitted light from the upper prism 132a changes in accordance with the incident angle of the elliptical laser beam that has been transmitted through the upper prism 132a and expanded in one direction in the form of a parallel light beam. A lower prism 132b is provided in order to always match the optical axis of the elliptical laser beam emitted from the beam conversion unit 13 with the optical axis of the fixed optical component arranged at the subsequent stage of the condenser lens 16 and the like. The lower prism 132 b functions to refract the elliptical laser beam and maintain the optical axis of the elliptical laser beam parallel to the optical axis of the condenser lens 16. Therefore, the lower prism 132b adjusts the direction of refraction at the lower prism 132b by rotating in the direction opposite to the rotation direction of the upper prism 132a. As a result, the angle of incidence on the condenser lens in the short axis direction and the long axis direction of the elliptical spot can be made the same, and as a result, the same position in the short axis direction and the long axis direction of the elliptical spot. To focus on. In this way, the upper prism 132a and the lower prism 132b cooperate to adjust the size of the elliptical laser beam in the major axis direction and adjust the direction of the emitted light, and thus rotate in conjunction with the control circuit 19. Controlled.

  The control circuit 19 causes the upper prism 132a and the lower prism 132b to rotate reversely with respect to each other about a direction perpendicular to the optical axis direction of the incident laser beam (front side to the back side as viewed in the drawing). The upper prism rotation mechanism 133a and the lower prism rotation mechanism 133b are controlled. By controlling the amount of rotation of the upper prism rotation mechanism 133a and the lower prism rotation mechanism 133b, the length in the major axis direction of the elliptical cross section of the elliptical laser beam can be changed.

  A prism moving mechanism 14 is attached to the beam conversion unit 13 described above, and the beam conversion unit 13 is moved in parallel along the long axis direction in the elliptical cross section of the elliptical laser beam. As the beam conversion unit 13 translates along the long axis direction, the pair of prisms 132 translate. As described above, when the pair of prisms 132 is rotated, the optical axis of the elliptical laser beam that is transmitted through the pair of prisms 132 and emitted from the lower prism 132b is in the major axis direction of the elliptical cross section with respect to the condenser lens 16. Shift. The prism moving mechanism 14 corrects an optical axis shift that deviates in the major axis direction of the elliptical section with respect to the condenser lens 16. That is, the prism moving mechanism 14 is configured so that the optical axis of the elliptical laser beam transmitted through the pair of prisms 132 is always aligned with the diffractive optical element 15 and the condenser lens 16. ) In parallel. Thus, even if the pair of prisms 132 are rotated to change the length of the elliptical laser beam in the elliptical cross section, the optical axis of the elliptical laser beam is always directed to the diffractive optical element 15 and the condenser lens 16. The workpiece 18 can be irradiated with an elliptical laser beam while being aligned with respect to the workpiece 18.

  The prism moving mechanism 14 is electrically connected to a control circuit 19, and the parallel movement of the beam conversion unit 13 is controlled by the control circuit 19. Specifically, the amount of deviation of the optical axis between the outgoing light of the beam conversion unit 13 and the optical axis of the condenser lens 16 is determined according to the rotational position of the pair of prisms 132. Therefore, the control circuit 19 determines the position of the beam conversion unit 13 in the parallel direction corresponding to the rotational position of the pair of prisms 132, and translates the beam conversion unit 13 to the target position that eliminates the optical axis deviation.

  A diffractive optical element 15 is disposed on the optical path of the elliptical laser beam emitted from the beam conversion unit 13, that is, between the pair of prisms 132 and the condenser lens 16. The diffractive optical element 15 splits the elliptical laser beam into a plurality of elliptical laser beams each having a predetermined angle with respect to the major axis direction of the elliptical cross section of the elliptical laser beam incident on the diffractive optical element 15. In the case of a laser having a high energy, if it is used for laser processing as it is, all the high energy does not contribute to the processing, and the energy may be wasted. By splitting into a plurality of elliptical laser beams in this manner, even a laser having high energy can divide the energy into a plurality of energy, and the energy can be efficiently used for processing.

  A condenser lens 16 that condenses the elliptical laser beam toward the workpiece 18 is disposed in the subsequent stage of the optical path of the elliptical laser beam that has passed through the diffractive optical element 15. The elliptical laser beam transmitted through the condenser lens 16 is condensed on the workpiece 18 held on the holding table 17. Thus, in the laser processing apparatus provided with the present optical system, the workpiece 18 is processed by irradiating the workpiece 18 with the generated elliptical laser beam.

  Next, an operation when the laser beam is condensed on the workpiece (work) using the optical system configured as described above will be described.

  The parallel light beam generated by the laser light source 11 and having a circular cross section is incident on the beam conversion unit 13 after the optical path is changed by the mirror 12. In the beam conversion unit 13, the optical path of the laser beam is changed by the mirror 13 and directed to the upper prism 132a. At this time, the cross-sectional shape of the laser beam (laser beam at the portion X shown in FIG. 2) is circular as shown in FIG. 2 (circular laser beam).

  This circular laser beam is incident on the pair of prisms 132 and converted into an elliptical beam shape expanded in one axial direction orthogonal to the optical axis. That is, the circular laser beam is incident on the incident surface of the upper prism 132a at a predetermined incident angle, is refracted while maintaining a parallel light beam, and is converted into an elliptical cross section that is expanded in one direction perpendicular to the optical axis. The light exits from the exit surface at an exit angle corresponding to the incident angle. The elliptical laser beam emitted from the upper prism 132a enters the lower prism 132b, is refracted while maintaining a parallel light beam, and is emitted at an emission angle parallel to the optical axis of the condenser lens 16. When the circular laser beam passes through the pair of prisms 132 in this way, the cross-sectional shape is shaped into an ellipse as shown in FIG. 2 (the elliptical laser beam in the Y portion shown in FIG. 2) and emitted. The light is always emitted in a direction parallel to the optical axis of the condenser lens 16 regardless of the angle of incidence on the upper prism 132a.

  In this case, when the circular laser beam passes through the pair of prisms 132, the circular laser beam is converted into an elliptical cross-sectional shape expanded in one direction orthogonal to the optical axis while maintaining the parallel light flux. The angle of incidence on the condensing lens 16 can be the same in the minor axis direction and the major axis direction of the cross section, and the focal point is formed at the same position in the minor axis direction and the major axis direction of the elliptical spot be able to. As a result, the processing quality in laser processing can be improved. Further, since the pair of prisms 132 are aspherical optical elements, the optical axes can be easily aligned as compared with the cylindrical lens, and the optical axes can be accurately aligned with simple control.

  In this configuration, the control circuit 19 drives the upper prism rotating mechanism 133a and the lower prism rotating mechanism 133b to change the upper prism 132a and the lower prism rotating mechanism 133b when the length of the elliptical laser beam in the elliptical cross section is changed. The rotational position of the lower prism 132b is controlled. For example, when the dimension in the major axis direction of the elliptical cross section of the elliptical laser beam is increased, the angle formed by the line perpendicular to the incident surface of the prism 132a and the circular laser beam incident on the prism 132a approaches 90 degrees. The longer the dimension in the long axis direction, the longer. As described above, when the pair of prisms 132 are rotated, the optical axis is shifted with respect to the diffractive optical element 15 and the condenser lens 16, so that the optical axis shift is corrected by the prism moving mechanism 14. That is, the control circuit 19 determines a target position to which the beam conversion unit 13 should be translated based on the rotational position of the pair of prisms 132, and translates the beam conversion unit 13 by the amount of translation to the target position. . Thereby, the optical axis shift with respect to the diffractive optical element 15 and the condensing lens 16 can be corrected.

  The elliptical laser beam is incident on the diffractive optical element 15 and splits the elliptical laser beam into a plurality of elliptical laser beams each having a predetermined angle with respect to the major axis direction in the elliptical cross section of the elliptical laser beam (FIG. 2). A plurality of elliptical laser beams in the Z section shown in FIG. By splitting into a plurality of elliptical laser beams in this manner, even a laser having high energy can divide the energy into a plurality of energy, and the energy can be efficiently used for processing.

  The plurality of elliptical laser beams are focused on the workpiece 18 by passing through the condenser lens 16, and the workpiece 18 is laser processed.

Next, a laser processing apparatus using the above-described optical system will be described.
FIG. 3 shows a configuration example of a laser processing apparatus using a multi-beam optical system.
The semiconductor wafer W is formed in a substantially disc shape, and is partitioned into a plurality of regions by division lines arranged on the surface in a grid pattern, and devices 42 such as IC and LSI are formed in the partitioned regions. ing. Further, the semiconductor wafer W is supported by the annular frame 41 via the sticking tape 43.

In the present embodiment, a semiconductor wafer such as a silicon wafer will be described as an example of the workpiece. However, the present invention is not limited to this configuration, and a DAF (Die Attach Film) attached to the semiconductor wafer W is not limited thereto. The workpiece may be an adhesive member such as a semiconductor product package, ceramic, glass, sapphire (Al ₂ O ₃ ) inorganic material substrate, various electrical components, or various processing materials that require micron-order processing position accuracy.

  In the laser processing apparatus 20, Y-axis guide rails 22a and 22b are disposed on a pair of processing tables 21 formed in the Y-axis direction. The Y-axis table 23 is mounted so as to be movable in the Y-axis direction along the Y-axis guide rails 22a and 22b. A nut portion (not shown) is formed on the back side of the Y-axis table 23, and a ball screw 24 is screwed into the nut portion. A drive motor 25 is connected to the end of the ball screw 24, and the ball screw 24 is rotationally driven by the drive motor 25.

  On the Y-axis table 23, a pair of X-axis guide rails 26a and 26b formed in the X-axis direction orthogonal to the Y-axis direction are disposed. The X-axis table 27 is placed so as to be movable in the X-axis direction along the X-axis guide rails 26a and 26b. A nut portion (not shown) is formed on the back side of the X-axis table 27, and a ball screw 28 is screwed into the nut portion. A drive motor 29 is connected to the end of the ball screw 28, and the ball screw 28 is rotationally driven by the drive motor 29.

  A chuck table 30 is installed on the X-axis table 27. The chuck table 30 includes a table support unit 31, a wafer holding unit 32 that sucks and holds a semiconductor wafer W having a street that is a processing scheduled line provided above the table support unit 31, and a frame holding that holds an annular frame 41. Part 33. Inside the table support portion 31, a suction source that causes the wafer holding portion 32 to suck and hold the semiconductor wafer W is provided.

  Further, a column 34 is erected on the processing table 21, and a laser irradiation unit 36 is supported by an arm 35 extending from the upper end of the column 34 above the chuck table 30. The laser irradiation unit 36 houses the optical system described above.

  In the laser processing apparatus 20 configured as described above, the semiconductor wafer W is placed on the chuck table 30. Then, the semiconductor wafer W is attracted to the wafer holder 32 by a suction source (not shown).

  Next, the laser beam irradiation unit 36 is driven, the position is adjusted by the X-axis table 27 and the Y-axis table 23, and laser processing is started. The laser beam irradiation unit 36 irradiates the street with a laser beam. At this time, the optical system of the laser beam irradiation unit 36 forms a plurality of elliptical spots in one line as shown in FIG. 2, and the machining progress direction and the major axis direction of the elliptical cross section coincide with each other. Yes. Further, laser processing is performed on the workpiece in a state where the focal point is focused at the same position in the short axis direction and the long axis direction of the elliptical spot. The X-axis table 27 and the Y-axis table 23 move the laser processing position along the street of the semiconductor wafer W, and the energy is divided by the divided elliptical spots, and each spot has a long axis with an elliptical cross section. Processed with energy dispersed in the direction.

  In such a laser processing apparatus, in the optical system, the angle of incidence on the objective lens can be the same in the minor axis direction and the major axis direction of the elliptical spot, and the minor axis direction of the elliptical spot And the focal point at the same position in the long axis direction. As a result, uniform processing can be efficiently performed along each processing line, and processing quality can be improved.

  Further, the laser processing apparatus of this configuration can be applied not only to the above-described line processing, but also to a hole processing such as a via hole processing and a surface processing such that a part of a wafer is depressed.

  The embodiment disclosed this time is illustrative in all respects and is not limited to this embodiment. The scope of the present invention is shown not by the above description of the embodiments but by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

  The present invention can be applied to a laser processing apparatus for laser processing a workpiece such as a semiconductor wafer using an elliptical beam.

DESCRIPTION OF SYMBOLS 11 Laser light source 12 Mirror 13 Beam conversion unit 14 Prism moving mechanism 15 Diffractive optical element 16 Condensing lens 17 Holding table 18 Workpiece (workpiece)
DESCRIPTION OF SYMBOLS 19 Control circuit 20 Laser processing apparatus 30 Chuck table W Semiconductor wafer

Claims (3)

A laser light source emitting a laser beam;
A pair of prisms arranged on an optical path of the laser beam emitted from the laser light source and converting the laser beam into an elliptical laser beam having an elliptical cross-sectional shape;
An elliptical cross-section of the elliptical laser beam converted by the pair of prisms by rotating the pair of prisms in reverse directions with a direction perpendicular to the optical axis direction of the laser beam incident on the pair of prisms as a rotation axis A prism rotation mechanism that changes the length in the long axis direction at
A prism moving mechanism that translates the pair of prisms along a major axis direction in an elliptical cross section of the elliptical laser beam converted by the pair of prisms;
A condensing lens for condensing the elliptical laser beam toward the workpiece;
An optical system comprising: Including a diffractive optical element disposed between the pair of prisms and the condenser lens;
The diffractive optical element is
The elliptical laser beam is split into a plurality of elliptical laser beams each having a predetermined angle with respect to a major axis direction of an elliptical cross section of the elliptical laser beam incident on the diffractive optical element. The optical system according to 1. The optical system according to claim 1 or 2, and a holding table for holding a workpiece,
A laser processing apparatus for processing an object by irradiating the workpiece with an elliptical laser beam converted by the optical system.

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