Laser processing device

Abstract

The present application provides a laser processing apparatus which monitors a state of a laser beam irradiated to a workpiece. The laser processing apparatus performs laser processing on a workpiece, wherein the laser processing apparatus includes: a chuck table which holds the workpiece; a laser beam irradiation unit which irradiates a laser beam to the workpiece held by the chuck table; a photographing unit which photographs light generated when the laser beam is irradiated to the workpiece to form a photographed image; and a control unit, the laser beam irradiation unit having: a laser oscillator; and a condenser lens which condenses the laser beam emitted from the laser oscillator to be irradiated to the workpiece, the control unit having a determination section which determines a state of the laser beam irradiated to the workpiece in accordance with a shape of the light appearing in the photographed image.

Description

Technical Field

[0001] This invention relates to a laser processing apparatus for laser processing of workpieces such as semiconductor wafers. Background Technology

[0002] In the manufacturing process of device chips used in electronic devices such as mobile phones and personal computers, multiple intersecting dicing lines (spacers) are first formed on the front side of a wafer made of materials such as semiconductors. Then, devices such as ICs (Integrated Circuits) and LSIs (Large-scale Integrations) are formed within the areas defined by these dicing lines. Finally, individual device chips are formed by dicing the wafer along these dicing lines.

[0003] Wafer dicing can be performed, for example, using a laser processing apparatus capable of laser processing the wafer by irradiating it with a laser beam. The laser processing apparatus includes: a chuck stage for holding a workpiece such as a wafer; and a laser beam irradiation unit for irradiating the workpiece held by the chuck stage with a laser beam to perform laser processing on the workpiece.

[0004] The laser beam irradiation unit focuses a laser beam of wavelength that is absorbed by the workpiece (the wavelength absorbed by the workpiece) onto the upper surface of the workpiece to perform ablation processing (see Patent Document 1). Here, when the output of the laser beam changes during laser processing, processing defects sometimes occur. Therefore, in the laser processing apparatus, the output of the laser beam is periodically monitored using a power meter (see Patent Document 2).

[0005] However, in order to measure the output of the laser beam, it is necessary to use a power meter to block the optical path or to interrupt laser processing and illuminate the power meter with the laser beam. In either case, laser processing of the workpiece cannot be carried out while the laser beam output is being measured, thus resulting in a reduction in the processing efficiency of the workpiece in the laser processing device.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2003-320466

[0007] Patent Document 2: Japanese Patent Application Publication No. 2009-291818

[0008] Therefore, for example, one could consider assembling a mirror capable of transmitting a portion of the laser beam along the optical path of the laser beam inside the laser beam irradiation unit. For instance, a portion of the laser beam emitted from a laser oscillator could be used to irradiate the workpiece to perform laser processing, while another portion of the laser beam could be used to irradiate a power meter to monitor the laser beam output. In this case, both laser processing of the workpiece and monitoring of the laser beam output can be performed simultaneously, thus improving the processing efficiency of the workpiece.

[0009] However, this method cannot detect problems such as contaminants adhering to the outer surface of the focusing lens at the end of the laser beam irradiation unit's optical path, preventing the laser beam from irradiating the workpiece as intended. In other words, the laser processing apparatus faces the challenge of monitoring the state of the laser beam actually irradiating the workpiece, in addition to detecting problems inside the laser beam irradiation unit, in order to detect problems outside the laser beam irradiation unit. Summary of the Invention

[0010] The present invention was made in view of this problem and its object is to provide a laser processing apparatus capable of monitoring the state of a laser beam irradiating a workpiece.

[0011] According to one aspect of the present invention, a laser processing apparatus is provided, characterized in that the laser processing apparatus comprises: a chuck stage for holding a workpiece; a laser beam irradiation unit for irradiating the workpiece held by the chuck stage with a laser beam; an imaging unit for capturing an image of the light generated by the laser beam irradiating the workpiece; and a control unit, the laser beam irradiation unit comprising: a laser oscillator; and a focusing lens for converging the laser beam emitted from the laser oscillator to irradiate the workpiece, the control unit having a determination unit for determining the state of the laser beam irradiating the workpiece based on the shape of the light reflected in the captured image.

[0012] Preferably, the control unit further includes: a storage unit that stores in advance a reference image obtained by photographing the light generated when the laser beam is irradiated onto the workpiece under specified conditions; and a comparison unit that compares the reference image stored in the storage unit with the photographed image, and the determination unit performs a determination based on the result of the comparison between the reference image and the photographed image performed by the comparison unit.

[0013] In addition, the laser beam irradiation unit preferably has an attenuator disposed between the laser oscillator and the focusing lens, and the attenuator adjusts the output of the laser beam emitted from the laser oscillator. The determination unit evaluates the output of the laser beam irradiating the workpiece, and the control unit controls the attenuator to adjust the output of the laser beam by referring to the evaluation result of the laser beam output performed by the determination unit.

[0014] In addition, the laser beam irradiation unit preferably also has a dichroic mirror, which allows the laser beam emitted from the laser oscillator to pass through and be guided to the condenser lens, and the dichroic mirror reflects wavelengths other than the wavelength of the laser beam. The light captured by the imaging unit is generated by the laser beam propagating through the condenser lens and the dichroic mirror irradiating the workpiece. The light passes through the condenser lens and is reflected by the dichroic mirror to reach the imaging unit.

[0015] In addition, preferably, the determination unit can determine whether the optical system of the laser beam is abnormal based on whether the shape of the light reflected in the captured image is abnormally distorted, and can evaluate the output of the laser beam based on the size of the light reflected in the captured image.

[0016] In one aspect of the laser processing apparatus of the present invention, an imaging unit is included to capture an image of the light generated when a laser beam irradiates a workpiece. The shape of the light generated by the workpiece reflects the state of the laser beam. Therefore, the determination unit of the control unit can determine the state of the laser beam based on the shape of the light reflected in the captured image. Furthermore, the determination unit can detect any abnormality occurring at any location inside or outside the laser beam irradiation unit. Moreover, when an abnormality is detected, laser processing does not need to be stopped.

[0017] Therefore, according to one aspect of the present invention, a laser processing apparatus is provided that is capable of monitoring the state of a laser beam irradiating a workpiece. Attached Figure Description

[0018] Figure 1 It is a perspective view schematically showing an example of a workpiece.

[0019] Figure 2 This is a schematic three-dimensional view of a laser processing device.

[0020] Figure 3 This is a schematic side view of the optical system of the laser beam irradiation unit.

[0021] Figure 4 It is a top view schematically showing the trajectory of the laser beam on the irradiated part of the workpiece.

[0022] Figure 5 (A) to Figure 5 (D) is a schematic top view showing an image obtained by photographing the light obtained by irradiating the workpiece with a laser beam.

[0023] Figure 6 (A) to Figure 6 (C) is a top view schematically showing an image obtained by photographing the light obtained by irradiating the workpiece with a laser beam.

[0024] Figure 7 It is a top view that schematically shows the order of light reflected in a captured image.

[0025] Label Explanation

[0026] 1: Workpiece; 1a: Front; 1b: Back; 3: Pre-defined dividing line; 5: Device; 7: Frame; 7a: Opening; 9: Scribing strip; 11: Frame unit; 13: Track; 15: Shooting position; 17a, 17b, 17c, 17d, 17e, 17f, 17g, 17h: Shooting image; 19a, 19b, 19c, 19d, 19e, 19f, 19g, 19h: Light; 21: Center line; 23a, 23b, 25a, 25b, 27a, 27b: Width; 2: Laser processing device; 4: Base; 6, 16: Moving unit; 8, 18: Guide rail; 10, 20: Moving worktable; 12, 22: Ball screw; 14, 24: Pulse motor; 26: Power meter ; 28: Chuck worktable; 28a: Holding surface; 28b: Fixture; 32: Laser beam irradiation unit; 34: Z-axis movement unit; 36: Lifting body; 38: Arm; 40: Camera; 42: Control unit; 42a: Judgment unit; 42b: Storage unit; 42c: Comparison unit; 44: Display unit; 46: Laser oscillator; 48: Laser beam; 50: Output adjustment unit (attenuator); 52: Hollow motor; 54: Half-wave plate; 56: Beam splitter; 58: Beam damper; 60: Mask; 62: Mirror; 64: Focusing lens; 66: Light; 68: Dichroic mirror; 70: Imaging unit; 72: Imaging element; 74: Mirror; 76: Illumination light; 78: Illumination source; 80: Semi-reflecting mirror. Detailed Implementation

[0027] Referring to the accompanying drawings, a laser processing apparatus according to one aspect of the present invention will be described. First, the workpiece processed using the laser processing apparatus of this embodiment will be described. The workpiece is, for example, a wafer in the shape of a disc made of materials such as Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), or other semiconductors.

[0028] Alternatively, the workpiece may be a roughly disc-shaped substrate made of materials such as sapphire, glass, or quartz. Examples of glass include alkali glass, alkali-free glass, soda-lime glass, lead glass, borosilicate glass, and quartz glass. The workpiece may be a packaging substrate, a ceramic substrate, etc. The following explanation uses a disc-shaped wafer as an example, but the workpiece is not limited to this. Figure 1 This is a schematic perspective view showing a frame unit 11 containing the workpiece 1.

[0029] The front surface 1a of the workpiece 1 is divided by multiple predetermined dividing lines 3 arranged in a grid pattern. IC, LSI, and other devices 5 are formed in each area divided by the predetermined dividing lines 3 on the front surface 1a of the workpiece 1. The laser processing apparatus of this embodiment performs laser processing on the workpiece 1 along the predetermined dividing lines 3, forming dividing grooves on the workpiece 1, dividing the workpiece 1, and forming individual device chips.

[0030] The workpiece 1, such as a wafer, is fed into the laser processing apparatus while supported on the frame 7 by means of a dicing belt 9. That is, before the workpiece 1 is fed into the laser processing apparatus, the workpiece 1, the frame 7, and the dicing belt 9 are integrated to form a frame unit 11. The frame unit 11 has: an annular frame 7 having an opening 7a; a dicing belt 9 disposed on the frame 7 in a manner that seals the opening 7a; and the workpiece 1 attached to the dicing belt 9 on the inside of the opening 7a.

[0031] The individual device chips formed by dividing the workpiece 1 are supported on the dicing tape 9. Then, when the spacing between the device chips is increased by expanding the dicing tape 9, the picking up of the device chips becomes easier.

[0032] The frame 7 is formed of a material such as metal and has an opening 7a with a diameter larger than that of the workpiece 1. When the frame unit 11 is formed, the workpiece 1 is positioned inside the opening 7a of the frame 7 and housed within the opening 7a.

[0033] The scribe strip 9 has a diameter larger than the opening 7a of the frame 7. The scribe strip 9 has a substrate layer and an adhesive layer formed on the substrate layer. The scribe strip 9 is adhered to the frame 7 and the back surface 1b of the workpiece 1 by the adhesive force exhibited by the adhesive layer. When the scribe strip 9 is adhered to the back surface 1b of the workpiece 1, the front surface 1a of the workpiece 1 is exposed upwards. Alternatively, the scribe strip 9 can be adhered to the front surface 1a of the workpiece 1, in which case the back surface 1b of the workpiece 1 is exposed upwards.

[0034] Next, the laser processing apparatus of this embodiment will be described, which performs laser processing on the workpiece 1, such as the wafer, included in the frame unit 11. Figure 2This is a schematic perspective view of the laser processing apparatus 2 of this embodiment.

[0035] The laser processing apparatus 2 has a base 4 that supports all its components. A chuck table 28 is provided on the upper surface of the base 4 to hold the workpiece 1. A laser beam irradiation unit 32 is provided above the chuck table 28 to irradiate the workpiece 1 held by the chuck table 28 with a laser beam.

[0036] In addition, a Y-axis moving unit 6 is provided on the upper surface of the base 4 to move the chuck stage 28 and the laser beam irradiation unit 32 relative to each other in the Y-axis direction, and an X-axis moving unit 16 to move the chuck stage 28 and the laser beam irradiation unit 32 in the X-axis direction perpendicular to the Y-axis direction.

[0037] The Y-axis moving unit 6 has a pair of Y-axis guide rails 8 along the Y-axis direction on the upper surface of the base 4. The Y-axis moving table 10 is slidably mounted on the pair of Y-axis guide rails 8. A nut portion (not shown) is provided on the back side of the Y-axis moving table 10, in which a Y-axis ball screw 12, which is substantially parallel to the Y-axis guide rails 8, is screwed.

[0038] A Y-axis pulse motor 14 is connected to one end of the Y-axis ball screw 12. The Y-axis pulse motor 14 rotates the Y-axis ball screw 12, thereby moving the Y-axis moving table 10 along the Y-axis guide rail 8 in the Y-axis direction.

[0039] The X-axis moving unit 16 has a pair of X-axis guide rails 18 along the X-axis direction on the upper surface of the Y-axis moving stage 10. The X-axis moving stage 20 is slidably mounted on the pair of X-axis guide rails 18. A nut portion (not shown) is provided on the back side of the X-axis moving stage 20, in which an X-axis ball screw 22, which is substantially parallel to the X-axis guide rails 18, is screwed.

[0040] An X-axis pulse motor 24 is connected to one end of the X-axis ball screw 22. The X-axis pulse motor 24 rotates the X-axis ball screw 22, thereby moving the X-axis moving stage 20 along the X-axis guide rail 18 in the X-axis direction. A power meter 26 capable of measuring the output of the irradiated laser beam and a chuck stage 28 for holding the workpiece 1 are provided on the upper surface of the X-axis moving stage 20.

[0041] The chuck table 28 has: a porous component exposed on its upper surface; a suction path connected to one end of the porous component; and a suction source connected to the other end of the suction path. When the suction source is activated, the workpiece 1 placed on the chuck table 28 is attracted and held. That is, the upper surface of the chuck table 28 becomes a holding surface 28a. In addition, a plurality of clamps 28b are provided around the chuck table 28 to hold the frame 7 containing the frame unit 11 of the workpiece 1.

[0042] A laser beam irradiation unit 32 is provided above the chuck table 28 to perform laser processing on the workpiece 1 held by the chuck table 28. The laser beam irradiation unit 32 focuses a laser beam of wavelength that is absorbed by the workpiece 1 (a laser beam of wavelength that the workpiece 1 can absorb) into the interior of the workpiece 1 held by the chuck table 28 to perform laser processing (ablation processing) on ​​the workpiece 1.

[0043] The focusing point is positioned on the front surface 1a of the workpiece 1 at a location overlapping with the predetermined dividing line 3. While concentrating the laser beam at this focusing point, the chuck stage 28 and the laser beam irradiation unit 32 are moved relative to each other in a direction parallel to the holding surface 28a. Thus, the laser beam is irradiated onto the workpiece 1 along the predetermined dividing line 3, forming a dividing groove along the predetermined dividing line 3 in the workpiece 1, thereby dividing the workpiece 1.

[0044] A Z-axis moving unit 34 is provided on the rear side of the base 4 to support the laser beam irradiation unit 32 so that it can move in the Z-axis direction, which is perpendicular to the X-axis and Y-axis directions. The Z-axis moving unit 34 is, for example, a ball screw type moving mechanism configured in the same way as the Y-axis moving unit 6 and the X-axis moving unit 16, so that the lifting body 36 can be raised and lowered along the Z-axis direction.

[0045] An arm 38 extending upward toward the chuck table 28 is connected to the lifting body 36. A laser beam irradiation unit 32 is fixed at the front end of the arm 38. A camera 40 is provided at the front end of the arm 38, adjacent to the laser beam irradiation unit 32, to photograph the upper surface (front 1a) of the workpiece 1 held by the chuck table 28.

[0046] The camera 40 has an image sensor such as a CCD (Charge-Coupled Device) sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) sensor, and can capture light arriving at the camera 40 to form an image. Furthermore, based on the image obtained by capturing the upper surface of the workpiece 1 using the camera 40, the position of the predetermined dividing line 3 on the workpiece 1 is determined. Additionally, the camera 40 can also be used to confirm the processing results of the laser beam irradiation unit 32.

[0047] Furthermore, the laser processing apparatus 2 includes a control unit 42 that controls each component of the laser processing apparatus 2. The control unit 42 is configured as a computer and includes: a processing unit such as a CPU (Central Processing Unit); a main storage device such as DRAM (Dynamic Random Access Memory); and an auxiliary storage device such as flash memory. The control unit 42 functions as a specific component cooperating with the software and processing unit (hardware resources) by causing the processing unit to operate according to the software stored in the auxiliary storage device.

[0048] When processing the workpiece 1 along the predetermined dividing line 3, the control unit 42 controls the Y-axis moving unit 6 and the X-axis moving unit 16 to move the chuck table 28 relative to the laser beam irradiation unit 32 in a direction parallel to the holding surface 28a. That is, the control unit 42 moves the focusing point of the laser beam relative to the workpiece 1 along the predetermined dividing line 3.

[0049] Furthermore, while the control unit 42 moves the focal point of the laser beam relative to the workpiece 1, the laser beam is irradiated onto the workpiece 1 by the laser beam irradiation unit 32, and the workpiece 1 is laser-processed along the predetermined dividing line 3.

[0050] Furthermore, in the laser processing apparatus 2, one or both of the Y-axis moving unit 6 and the X-axis moving unit 16 can replace the chuck table 28 to move the laser beam irradiation unit 32. Additionally, if the laser beam irradiation unit 32 has a mechanism inside that adjusts the height of the focusing point by raising or lowering the focusing lens, the laser processing apparatus 2 may not have a Z-axis moving unit 34.

[0051] Furthermore, the laser processing apparatus 2 has a display unit 44 capable of displaying various information such as operating status or alarm messages. The display unit 44 is, for example, a liquid crystal display (LCD). Additionally, the laser processing apparatus 2 may have a touch panel that functions as an input interface for operators to input various commands. Furthermore, the display unit 44 may be, for example, a display with a touch panel.

[0052] Next, the laser beam irradiation unit 32 will be described in detail. Figure 3 This is a schematic side view illustrating the optical system of the laser beam irradiation unit 32. Figure 3 A sectional view including a portion of the constituent elements. Additionally, in Figure 3 Various housings and other components are omitted in this version. Furthermore, the configuration of the constituent elements of the laser beam irradiation unit 32 can be appropriately modified.

[0053] The laser beam irradiation unit 32 has a laser oscillator 46 that emits a laser beam 48. The laser oscillator 46 has a medium such as Nd;YAG or Nd;YVO4, and is capable of emitting a laser beam 48 of a wavelength absorbed by the workpiece 1.

[0054] The laser beam irradiation unit 32 also includes an output adjustment unit (attenuator) 50 for adjusting the output of the laser beam 48 emitted from the laser oscillator 46. The output adjustment unit 50 includes: a half-wave plate 54 supported by a hollow motor 52 for rotation; and a beam splitter 56 that reflects the S-polarized component of the laser beam 48 and transmits the P-polarized component. The output adjustment unit 50 also includes a beam damper 58 that absorbs the S-polarized component of the laser beam 48 reflected by the beam splitter 56.

[0055] The laser beam 48 arriving at the output adjustment unit 50 travels inside the hollow motor 52 and passes through the half-wave plate 54. At this time, the laser beam 48 rotates, changing the ratio of the P-polarized light component to the S-polarized light component of the laser beam 48 arriving at the beam splitter 56. The output adjustment unit 50 uses the hollow motor 52 to rotate the half-wave plate 54, thereby adjusting the amount of the P-polarized light component of the laser beam 48 arriving at the beam splitter 56.

[0056] Therefore, by rotating the half-wave plate, the output adjustment unit 50 can adjust the amount of the component of the beam splitter 56 that passes through the laser beam 48, that is, it can adjust the output of the laser beam 48 emitted from the output adjustment unit 50. However, the structure of the output adjustment unit 50 is not limited to this.

[0057] The laser beam irradiation unit 32 has a mask 60 with a transmission window of a predetermined shape, which shapes the output laser beam 48, which has been adjusted by the output adjustment unit 50, into the predetermined shape. However, other methods can also be used to shape the laser beam 48 in the laser beam irradiation unit 32.

[0058] Additionally, the laser beam irradiation unit 32 includes: a reflector 62 that reflects the laser beam 48, shaped by the mask 60, toward the chuck table 28; and a focusing lens 64 that focuses the laser beam 48 reflected by the reflector 62 onto the upper surface of the workpiece 1 held by the chuck table 28. The focusing point of the focusing lens 64 is positioned on the front surface 1a of the workpiece 1 held by the chuck table 28. The height of this focusing point can be adjusted by the Z-axis movement unit 34 or by other methods.

[0059] When laser processing the workpiece 1 using the laser processing device 2, the frame unit 11 is first held by the chuck stage 28, and the front side 1a of the workpiece 1 is observed by the camera 40 to detect the position and extension direction of the predetermined dividing line 3. Then, the chuck stage 28 is rotated about an axis perpendicular to the holding surface 28a so that the orientation of the predetermined dividing line 3 is aligned with the X-axis or Y-axis direction.

[0060] Next, the Y-axis moving unit 6 and the X-axis moving unit 16 are activated to position one end of a predetermined dividing line 3 below the laser beam irradiation unit 32. Then, while activating the laser oscillator 46 to focus the laser beam 48 onto the front surface 1a of the workpiece 1, the Y-axis moving unit 6 or the X-axis moving unit 16 is activated to feed the workpiece 1 into the workpiece. Thus, laser processing (ablation) is performed on the workpiece 1 along the predetermined dividing line 3, forming a dividing groove along the predetermined dividing line 3 in the workpiece 1.

[0061] After laser processing of the workpiece 1 along a predetermined dividing line 3, the Y-axis moving unit 6 or the X-axis moving unit 16 is activated to index and feed the workpiece 1, and laser processing is performed on the workpiece 1 along the next predetermined dividing line 3 in the same way. In this way, the workpiece 1 is laser processed sequentially along the predetermined dividing lines 3 in one direction.

[0062] Then, by rotating the chuck stage 28 or switching the operation of the Y-axis moving unit 6 and the X-axis moving unit 16, laser processing is performed on the workpiece 1 along the predetermined dividing lines 3 in the other direction. When the workpiece 1 is laser processed along all the predetermined dividing lines 3, it is divided along the dividing grooves to form individual chips.

[0063] In order to perform laser processing on multiple workpieces 1 in a homogeneous manner using the laser processing apparatus 2, it is necessary to irradiate each workpiece 1 with a laser beam 48 under homogeneous conditions. However, during the laser processing of the workpiece 1, there are cases where the state of the laser beam 48 changes.

[0064] For example, there may be situations where the laser oscillator 46 operates unstably, causing pointing shift, or where the energy distribution of the laser beam 48 changes. Additionally, there may be situations where the output of the laser beam 48 changes, preventing it from irradiating the workpiece 1 with the required output, or where the laser beam 48 is irradiated with an excessive output. In all these cases, poor processing results.

[0065] Therefore, it is considered to periodically monitor the output of the laser beam 48 using the power meter 26. However, in order to measure the output of the laser beam 48, the laser processing of the workpiece 1 needs to be interrupted and the power meter 26 needs to be irradiated with the laser beam 48. That is, the laser processing of the workpiece 1 cannot be carried out during the measurement of the output of the laser beam 48, thus resulting in a decrease in the processing efficiency of the workpiece 1 in the laser processing apparatus 2.

[0066] Additionally, the following situation exists: inside the output adjustment unit 50, tiny dust particles generated when the hollow motor 52 rotates the half-wave plate 54, or the lubricating grease used in the hollow motor 52, are stirred up, and some of these particles intrude into the optical path. Furthermore, the following situation exists: the position of the mask 60 changes in a plane perpendicular to the optical path, making it impossible to use the mask 60 to shape the laser beam 48 into a suitable shape.

[0067] As another possibility, there is the following situation: when laser processing is performed on the workpiece 1 by the laser beam 48, the processing debris generated adheres to the outer surface of the condenser lens 64, thus preventing the laser beam 48 from properly irradiating the workpiece 1.

[0068] In these situations, the laser beam 48 may be partially blocked or scattered by foreign objects, causing a change in its shape. That is, an anomaly may occur in the optical system, preventing the laser beam 48 from converging properly on the workpiece 1 and thus hindering proper laser processing of the workpiece 1.

[0069] Thus, due to various reasons, the laser beam 48 may not be able to be irradiated onto the workpiece 1 in the prescribed state, and the workpiece 1 may not be processed properly. Therefore, the laser processing apparatus 2 of this embodiment captures the light generated by the laser beam 48 irradiating the workpiece 1, and monitors the state of the laser beam 48 based on the shape of the light reflected in the captured image.

[0070] The position and shape of the light reflected in the captured image reflect the state of the laser beam 48, thus allowing the state of the laser beam 48 to be determined based on the shape of the light. Here, when the determination is performed by capturing the light, there is no need to interrupt the laser processing of the workpiece 1. Hereinafter, the laser processing apparatus 2 of this embodiment will be described focusing on its structure, which facilitates monitoring the state of the laser beam 48.

[0071] When the laser beam 48 irradiates the workpiece 1, a portion of the workpiece 1 undergoes plasmaization, generating light 66. The light 66 generated by the workpiece 1 reaches the focusing lens 64 and travels into the interior of the laser beam irradiation unit 32. The laser processing apparatus 2 of this embodiment has a mechanism for capturing this light 66.

[0072] More specifically, the laser beam irradiation unit 32 has a dichroic mirror 68 between the reflector 62 and the condenser lens 64. The dichroic mirror 68 allows the laser beam 48 emitted from the laser oscillator 46 to pass through and be guided to the condenser lens 64, and reflects wavelengths other than the wavelength of the laser beam 48. Furthermore, the dichroic mirror 68 reflects the light 66 generated from the workpiece 1 by the laser beam 48 toward the imaging unit 70, which will be described next.

[0073] That is, light 66 is generated by a laser beam 48 that propagates through a condenser lens 64 and a dichroic mirror 68 and is irradiated onto the workpiece 1, and reaches the imaging unit 70 by passing through the condenser lens 64 and being reflected by the dichroic mirror 68.

[0074] The imaging unit 70 captures the light 66 generated when the laser beam 48 irradiates the workpiece 1. The imaging unit 70 has a reflector 74 that reflects the light reflected by the dichroic mirror 68 towards the imaging element 72. The imaging element 72 is, for example, a CCD sensor or a CMOS sensor. The imaging unit 70 is connected to the control unit 42 and sends the captured image showing the light 66 to the control unit 42.

[0075] Additionally, the imaging unit 70 can also illuminate the front side 1a of the workpiece 1. For example, the imaging unit 70 may also include a semi-reflective mirror 80 disposed between the dichroic mirror 68 and the reflector 74, and an illumination source 78. The illumination source 78 is, for example, a xenon flash.

[0076] Illumination light 76 emitted from illumination source 78 is reflected by semi-reflective mirror 80 towards dichroic mirror 68, and then, after being reflected by dichroic mirror 68, is directed through condenser lens 64 to illuminate the front surface 1a of workpiece 1. When illumination light 76 illuminates the front surface 1a of workpiece 1, the front surface 1a of workpiece 1 is reflected along with the light 66 in the image captured by imaging unit 70. In this case, the irradiated area of ​​laser beam 48 on the front surface 1a of workpiece 1 can be identified, and therefore it can be determined whether the irradiation position of laser beam 48 is appropriate.

[0077] Furthermore, the acquisition of images can be repeatedly performed during the laser processing of the workpiece 1. In this case, when the state of the laser beam 48 changes, the change can be detected immediately; however, this places an excessive burden on the control unit 42 that determines the state of the laser beam 48. In cases where drastic changes in the state of the laser beam 48 cannot be anticipated, images can be acquired at predetermined intervals.

[0078] Figure 4 This is a top view schematically showing the trajectory 13 of the irradiated portion of the laser beam 48 on the workpiece 1. As described above, the laser beam 48 converges sequentially along the predetermined dividing line 3 onto the front surface 1a of the workpiece 1, thus the irradiated portion on the front surface 1a moves along the predetermined dividing line 3. Furthermore, for example, when the irradiated portion approaches a specific shooting position 15, the shooting unit 70 is activated to shoot the front surface 1a of the workpiece 1 and acquire an image. In this case, the load on the control unit 42 is reduced.

[0079] The determination of the state of the laser beam 48 based on the captured image formed by the imaging unit 70 is performed by the control unit 42 of the laser processing apparatus 2. The control unit 42 has a determination unit 42a that determines the state of the laser beam 48 irradiating the workpiece 1 based on the shape of the light 66 reflected in the captured image.

[0080] Next, the method for determining the state of the laser beam 48 performed by the determination unit 42a will be explained. Figure 5 (A) to Figure 5 (D) are schematic top views showing images 17a, 17b, 17c, and 17d obtained by photographing the light produced when the laser beam 48 is irradiated onto the workpiece 1 with different outputs. As shown in each figure, the images 17a, 17b, 17c, and 17d respectively depict the light produced when the laser beam 48 irradiates the workpiece 1.

[0081] The laser beam 48 emitted from the laser oscillator 46 is shaped into a predetermined shape by the mask 60 and irradiates the workpiece 1. The cross-sectional shape of the laser beam 48 (the shape in the plane perpendicular to the direction of travel) is, for example, shaped as an ellipse that is close to a rectangle. Furthermore, the irradiated area of ​​the laser beam 48 on the front surface 1a of the workpiece 1 is set to be an ellipse with its minor axis aligned with the extension direction (processing feed direction) of the predetermined dividing line 3 and its major axis aligned with the width direction of the predetermined dividing line 3.

[0082] When a laser beam 48 is irradiated onto the workpiece 1 in this state, light 66 is generated, the shape of which reflects the shape of the irradiated area. The shapes of the light 19a, 19b, 19c, and 19d reflected in each of the captured images 17a, 17b, 17c, and 17d also become elliptical.

[0083] Furthermore, with filming Figure 5 Compared to the output of the laser beam 48 irradiating the workpiece 1 when the image 17a shown in (A) was captured, the image 17a was captured using a different laser beam 48. Figure 5 In image 17b shown in (B), the output of the laser beam 48 illuminating the workpiece 1 is relatively large. Figure 5 When the image 17c shown in (C) is captured, the output of the laser beam 48 irradiating the workpiece 1 is larger, and the image capture... Figure 5 The output of the laser beam 48 irradiating the workpiece 1 is larger when the image 17d shown in (D) is captured.

[0084] Furthermore, the magnitudes of the lights 19a, 19b, 19c, and 19d reflected in each of the captured images 17a, 17b, 17c, and 17d are determined by the output of the laser beam 48 that contributes to its generation; the larger the output, the greater the light. Therefore, the output of the laser beam 48 can be evaluated based on the magnitude of the light reflected in the captured image generated by the laser beam illuminating the workpiece 1. The determination unit 42a of the control unit 42 can evaluate the output of the laser beam 48 based on the captured images acquired by the imaging unit 70.

[0085] The output of the laser beam 48 can be adjusted by the output adjustment unit (attenuator) 50. Therefore, the control unit 42 can adjust the output of the laser beam 48 by controlling the output adjustment unit (attenuator) 50, based on the evaluation result of the output of the laser beam 48 performed by the determination unit 42a. In this case, in the laser processing apparatus 2, the output of the laser beam 48 can be monitored during the laser processing of the workpiece 1, and if the output deviates from the specified value by an allowable amount, the output can be corrected immediately.

[0086] Furthermore, the determination unit 42a of the control unit 42 can determine states other than the output of the laser beam 48. For example, the state of the laser beam 48 can be used to determine whether there is an abnormality in the optical system. Figure 6 (A) to Figure 6 (C) is a top view schematically showing the captured images 17e, 17f, and 17g obtained by the imaging unit 70 in the event of an anomaly such as foreign matter being introduced into the optical system.

[0087] like Figure 6 (A) to Figure 6 As shown in (C), when an anomaly occurs in the optical system of laser beam 48, laser beam 48 irradiates workpiece 1 with a deformed cross-sectional shape. Simultaneously, light 66 with a deformed shape is generated on the front surface 1a of workpiece 1. Therefore, the abnormally deformed light 19e, 19f, and 19g are reflected in the captured images 17e, 17f, and 17g.

[0088] Therefore, by observing whether there is any abnormal distortion in the shape of the light 66 generated by the laser beam 48 irradiating the workpiece 1 as reflected in the captured image, it is possible to determine whether there is any abnormality in the optical system. The determination unit 42a of the control unit 42 can determine whether there is any abnormality in the optical system of the laser beam 48 based on whether there is any abnormal distortion in the shape of the light reflected in the captured image.

[0089] For example, consider installing a power meter inside the laser beam irradiation unit 32 to monitor the state of the laser beam 48. In this case, even if an anomaly occurs outside the laser beam irradiation unit 32, such as foreign matter getting mixed into the path of the laser beam 48, the anomaly of the laser beam 48 cannot be detected by the power meter.

[0090] In contrast, in the laser processing apparatus 2 of this embodiment, the state of the laser beam 48 is monitored based on the light 66 generated when the laser beam 48 is actually irradiated onto the workpiece 1. Therefore, even if foreign matter is mixed into the path of the laser beam 48 outside the laser beam irradiation unit 32, abnormalities in the laser beam 48 can be detected.

[0091] Furthermore, the determination unit 42a can determine whether the laser beam 48 is abnormal by comparing the captured image obtained by the imaging unit 70 with a pre-prepared reference image. In this case, such as Figure 2 As shown, the control unit 42 has a storage unit 42b, which stores one or more reference images obtained by taking pictures of the light generated when the laser beam 48 is irradiated onto the workpiece 1 under specified conditions.

[0092] Furthermore, the control unit 42 also includes a comparison unit 42c, which compares the reference image stored in the storage unit 42b with the captured image. The determination unit 42a performs a determination based on the comparison result between the reference image and the captured image obtained by the comparison unit 42c. For example, the storage unit 42b may contain a captured image obtained by capturing light 66 generated by the workpiece 1 using a laser beam 48 irradiated in a predetermined state by the imaging unit 70, which is stored as a reference image.

[0093] It is particularly preferable that the images captured by the imaging unit 70, which capture light 66 generated by the workpiece 1 by irradiating the workpiece 1 with laser beams 48 at multiple predetermined outputs, are stored in the storage unit 42b according to each output of the laser beams 48. In this case, the comparison unit 42c can perform a comparison using a reference image set to correspond to the output of the laser beams 48.

[0094] The comparison unit 42c processes, for example, an image showing the light 66 generated by the workpiece 1 irradiated by the laser beam 48, extracts the outline of the area showing the light 66, and determines the shape of that area. Additionally, the comparison unit 42c selects a reference image corresponding to the output of the laser beam 48 irradiated to the workpiece 1 and reads it from the storage unit 42b, similarly determining the shape of the light shown in the selected reference image.

[0095] Then, the comparison unit 42c compares the captured image taken by the imaging unit 70 with the reference image and calculates the degree of consistency of the area reflecting the light generated by the workpiece 1. Furthermore, the determination unit 42a determines that the state of the laser beam 48 is normal if the two are consistent to a degree above a predetermined threshold, and determines that the state of the laser beam 48 is abnormal if the degree of consistency between the two is below the threshold.

[0096] However, the determination method of the determination unit 42a based on the comparison result of the comparison unit 42c is not limited to this. Furthermore, the determination performed by the determination unit 42a is not limited to the method of comparing the captured image taken by the imaging unit 70 with the reference image. Next, other determination methods performed by the determination unit 42a will be described.

[0097] Figure 7 This is a schematic top view showing an image 17h obtained by capturing light 66 generated when a laser beam 48 is irradiated onto a workpiece 1 using an imaging unit 70. (As shown) Figure 7 As shown, the shape of the light reflected in image 17h is similar to that of image 19h. Figure 5 (A) to Figure 5 The light rays 19a, 19b, 19c, and 19d shown in (D) are different, becoming deformed elliptical shapes. The evaluation method for the shape of light 19h is as follows.

[0098] In the captured image 17h, a center line 21 is set, which passes through the center of the irradiated portion of the laser beam 48 on the front side 1a of the workpiece 1, along the minor axis direction (in Figure 7 (The transverse direction is shown in the middle) transverse cut light 19h. In the long axis direction of the center line 21 (in the middle) Figure 7 The width of light 19h is measured at equidistant points along the vertical direction (center to bottom), and the difference between the measured widths of light 19h is calculated. Furthermore, this difference in width is evaluated. For example, when the longitudinal length of light 19h is 35μm to 60μm, the width of light 19h can be measured at approximately 5μm to 10μm away from the center line 21.

[0099] For example, at a position above the center line 21, the width 23a of the light 19h near the center line 21 is measured; the width 25a of the light 19h slightly away from the center line 21 is measured; and the width 27a of the light 19h further away from the center line 21 is measured. Additionally, at a position below the center line 21 of the light 19h, the width 23b of the light 19h at the position corresponding to the measurement of width 23a is measured; the width 25b of the light 19h at the position corresponding to the measurement of width 25a is measured; and the width 27b of the light 19h at the position corresponding to the measurement of width 27a is measured.

[0100] Furthermore, the differences in widths of light 19h at equidistant locations above and below the center line 21 are calculated as the differences between widths 23a and 23b, 25a and 25b, and 27a and 27b. It is then determined whether each difference exceeds a predetermined threshold.

[0101] In the laser processing apparatus 2, the shape of the transmission window of the mask 60 and the arrangement of each optical component are determined such that the irradiated area of ​​the laser beam 48 on the front surface 1a of the workpiece 1 is a predetermined elliptical shape. Therefore, the predetermined threshold can be set based on the width of the predetermined irradiated area of ​​the laser beam 48 on the front surface 1a of the workpiece 1.

[0102] For example, the threshold can be set to 15% to 25% of the width of the irradiated area along the center line of the minor axis of the predetermined elliptical shape of the irradiated area, preferably around 20%. For example, if the width along the center line of the minor axis of the predetermined irradiated area is 10 μm, the threshold can be set to 2 μm.

[0103] Furthermore, if the difference in the width of the light 19h at locations equidistant from the center line 21 by the determination unit 42a is less than 2 μm, the laser beam 48 is determined to be in a normal state. On the other hand, if any of these differences is 2 μm or more, the laser beam 48 is determined to be in a normal state.

[0104] Furthermore, the specified threshold can be set based on the width along the center line of the light reflected in the aforementioned reference image. Alternatively, it can be set based on the width along the center line 21 of the light reflected in the captured image 17h.

[0105] If an abnormality is detected in the state of laser beam 48 using this method, one possible cause is a positional offset of mask 60. Therefore, the following countermeasures are considered: inspect the adjusting threaded components that fix mask 60 in a movable manner, and readjust the position of mask 60.

[0106] The control unit 42 can, for example, notify the user or manager of the laser processing apparatus 2 of the determination result by displaying the determination result of the determination unit 42a on the display unit 44. Furthermore, if the determination result of the state of the laser beam 48 indicates that a processing defect is inevitable, the control unit 42 can immediately interrupt the processing of the workpiece 1.

[0107] As explained above, in the laser processing apparatus of this embodiment, when laser processing is performed on the workpiece 1 using the laser beam 48, the state of the laser beam 48 is determined by the light generated by the workpiece 1 due to plasma or the like. Therefore, it is not necessary to stop the laser processing of the workpiece 1 in order to determine the state of the laser beam 48.

[0108] Furthermore, the present invention is not limited to the embodiments described above, and various modifications and implementations are possible. For example, in the above embodiments, the storage unit 42b of the control unit 42 can not only store reference images for comparison with the images captured by the imaging unit 70, but also store and accumulate the captured images. In this case, if an abnormality occurs in the state of the laser beam 48 or if a processing defect occurs in the workpiece 1, the captured images stored in the storage unit 42b can be used to determine the cause of the abnormality.

[0109] In addition, the structure and method of the above embodiments can be appropriately modified and implemented as long as they do not depart from the scope of the purpose of the present invention.

Claims

1. A laser processing apparatus, characterized in that, The laser processing device includes: A chuck table holds the workpiece in place; A laser beam irradiation unit irradiates the workpiece held by the chuck table with a laser beam to perform laser processing on the workpiece; The imaging unit captures images of the light generated when the laser beam strikes the workpiece, thereby forming an image; and Control unit The laser beam irradiation unit has the following features: Laser oscillator; as well as A focusing lens that converges the laser beam emitted from the laser oscillator onto the workpiece. The control unit has a determination unit that determines the state of the laser beam irradiating the workpiece based on the shape of the light reflected in the captured image. The determination unit evaluates the output of the laser beam based on the magnitude of the light reflected in the captured image. When the control unit performs laser processing on the workpiece using the laser beam irradiation unit, it adjusts the output of the laser beam by referring to the evaluation result of the laser beam output performed by the determination unit.

2. The laser processing apparatus according to claim 1, characterized in that, The control unit also has: The storage unit stores, in advance, a reference image obtained by photographing the light produced when the laser beam is irradiated onto the workpiece under specified conditions; and The comparison unit compares the reference image stored in the storage unit with the captured image. The determination unit makes a determination based on the result of the comparison between the reference image and the captured image performed by the comparison unit.

3. The laser processing apparatus according to claim 1 or 2, characterized in that, The laser beam irradiation unit includes an attenuator disposed between the laser oscillator and the focusing lens, and the attenuator adjusts the output of the laser beam emitted from the laser oscillator. The control unit controls the attenuator to adjust the output of the laser beam.

4. The laser processing apparatus according to claim 1 or 2, characterized in that, The laser beam irradiation unit also includes a dichroic mirror that allows the laser beam emitted from the laser oscillator to pass through and be guided toward the focusing lens, and that reflects wavelengths other than the wavelength of the laser beam. The light captured by the imaging unit is generated by the laser beam propagating through the condenser lens and the dichroic mirror and irradiating the workpiece. The light passes through the condenser lens and is reflected by the dichroic mirror to reach the imaging unit.

5. The laser processing apparatus according to claim 1 or 2, characterized in that, The determination unit can determine whether the optical system of the laser beam is abnormal based on whether there is abnormal deformation in the shape of the light reflected in the captured image.

Images