Laser processing method and chip manufacturing method

Abstract

The present invention provides a laser processing method and a chip manufacturing method that can suppress the accumulation of heat in the workpiece during laser processing, thereby preventing deterioration of processing quality. [Solution] The present invention relates to a laser processing method for irradiating a workpiece with a laser beam, comprising: a first processing step in which a laser beam is incident on the reflective surface of a rotating polygon mirror, and the laser beam reflected from the reflective surface is irradiated onto the workpiece to form a plurality of first processing marks on the workpiece that are aligned along the processing feed direction and do not overlap with each other; and a second processing step in which, after the first processing step, a laser beam is incident on the reflective surface of a rotating polygon mirror, and the laser beam reflected from the reflective surface is irradiated onto the workpiece to form a plurality of second processing marks on the workpiece that are aligned along the processing feed direction and do not overlap with each other.

Description

Technical Field

[0001] The present invention relates to a method for processing a workpiece containing a semiconductor or the like as a material by irradiating the workpiece with a laser beam. The present invention also relates to a method for dividing a workpiece containing a semiconductor or the like as a material by irradiating the workpiece with a laser beam to manufacture chips.

Background Art

[0002] Device chips such as ICs (Integrated Circuits) are essential components for electronic devices such as mobile phones and personal computers. In the manufacturing process of device chips, a plurality of streets (division planned lines) are set in a grid pattern on the surface of a wafer, and after devices are formed in a plurality of regions partitioned thereby, the wafer is divided along the streets to obtain individual device chips.

[0003] For example, a method called laser ablation processing is used for dividing the wafer. In laser ablation processing, a laser beam having a wavelength absorbed by the material of the workpiece is irradiated onto the workpiece, and the material of the irradiated portion is removed by evaporation due to its energy, thereby forming a groove on the surface of the workpiece or cutting the workpiece.

[0004] As prior art documents describing techniques related to such laser ablation processing, for example, there are Patent Documents 1, 2, and the like.

[0005] In the laser ablation process described above, a pulsed laser that emits a laser beam at a constant interval is generally used. When laser ablation is performed linearly on a workpiece, for example, the first pulse briefly irradiates the workpiece with a laser beam, forming a dot-like processing mark. Then, the second pulse forms the next processing mark adjacent to the first processing mark. The first and second processing marks partially overlap, and this is repeated, resulting in the formation of a linear processing mark on the workpiece consisting of numerous spot-like processing marks.

[0006] In processes using laser ablation, one way to improve productivity is to increase the repetition frequency of the laser beam used for irradiation, thereby increasing the number of laser beam irradiations per unit time and thus increasing the speed of formation of the processed marks.

[0007] However, as the repetition frequency of the laser beam increases, the effect of residual heat after laser beam irradiation becomes significant. A higher laser beam repetition frequency means that the time between the first laser beam irradiating the workpiece and the next laser beam irradiating the adjacent area becomes shorter. As a result, heat remains around the first processed area when the next laser beam irradiates it, and consequently, the condition of the workpiece around the processed area deteriorates. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2003-320466 [Patent Document 2] Japanese Patent Publication No. 2024-16594 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The present invention provides a laser processing method and a chip manufacturing method that can suppress the accumulation of heat in the workpiece during laser processing and prevent deterioration of processing quality. [Means for solving the problem]

[0010] According to one aspect of the present invention, a laser processing method is provided for irradiating a workpiece with a laser beam, comprising: a first processing step of irradiating the workpiece with the workpiece by irradiating the workpiece with the reflective surface of a rotating polygon mirror and the laser beam reflected from the reflective surface, thereby forming a plurality of first processing marks on the workpiece that are aligned along the processing feed direction and do not overlap with each other; and a second processing step of irradiating the workpiece with the workpiece by irradiating the workpiece with the workpiece after the first processing step and the laser beam reflected from the reflective surface, thereby forming a plurality of second processing marks on the workpiece that are aligned along the processing feed direction and do not overlap with each other.

[0011] Preferably, each of the plurality of second processing marks overlaps with at least a portion of any of the plurality of first processing marks.

[0012] Preferably, when one processing mark and another processing mark overlap or are adjacent in at least part, the irradiation of the laser beam that forms the other processing mark is not performed at an interval of less than 100 microseconds from the irradiation of the laser beam that forms the first processing mark.

[0013] Preferably, the width of the plurality of first machining marks in the machining feed direction is equal to the distance between the centers of the plurality of first machining marks in the machining feed direction.

[0014] Preferably, the laser processing method further comprises: a pre-processing mark forming step of irradiating a workpiece with the laser beam to form a pre-processing mark before the first processing step; a measurement step of measuring the width of the pre-processing mark in the processing feed direction after the pre-processing mark forming step and before the first processing step; and a setting step of setting, after the measurement step and before the first processing step, at least one of the values ​​relating to the repetition frequency of the laser beam in the first and second processing steps, the rotation speed of the polygon mirror, or the relative moving speed of the workpiece and the polygon mirror along the processing feed direction, based on the width of the pre-processing mark in the processing feed direction, wherein if the value relating to the relative moving speed of the workpiece and the polygon mirror along the processing feed direction is set, the workpiece and the polygon mirror are moved relative to each other along the processing feed direction during the first processing step, during the second processing step, or at least between the first and second processing steps.

[0015] Preferably, grooves are formed on the workpiece by ablation of the workpiece with the laser beam.

[0016] Preferably, the workpiece contains gallium arsenide.

[0017] Furthermore, according to another aspect of the present invention, a method for manufacturing chips is provided, which divides a workpiece into a plurality of chips using the laser processing method described above. [Effects of the Invention]

[0018] According to the laser processing method and chip manufacturing method relating to each aspect of the present invention, during laser processing, the irradiation position of the laser beam on the workpiece is moved by a polygon mirror, thereby forming multiple non-overlapping first processing marks on the workpiece, and subsequently forming multiple non-overlapping second processing marks on the workpiece. This suppresses the accumulation of heat in the workpiece and prevents deterioration of processing quality. [Brief explanation of the drawing]

[0019] [Figure 1] FIG. 1 is a perspective view schematically showing an example of the overall configuration of a laser processing apparatus. [Figure 2] FIG. 2 is a perspective view showing an example of the form of a workpiece. [Figure 3] FIG. 3 is a schematic diagram showing an example of the configuration of a laser irradiation unit. [Figure 4] FIG. 4 is a schematic diagram showing, as a reference example, an example of the movement of the position of an irradiation spot along a street of a workpiece in laser processing. [Figure 5] FIG. 5 is a schematic diagram showing an example of the relationship between the angle of the reflecting surface of a polygon mirror and the traveling direction of a laser beam. [Figure 6] FIG. 6(A) is a schematic diagram showing, as an example, the movement of the position of an irradiation spot along a street of a workpiece in laser processing, and shows the position of the irradiation spot due to reflection on one surface (the first surface) of the reflecting surface of the polygon mirror. FIG. 6(B) is a schematic diagram showing, as an example, the movement of the position of an irradiation spot along a street of a workpiece in laser processing, and shows the position of the irradiation spot due to reflection on the second surface adjacent to the first surface of the reflecting surface of the polygon mirror. [Figure 7] FIG. 7 is a flowchart for explaining an example of a procedure related to a laser processing method and a method for manufacturing a chip.

Embodiments for Carrying Out the Invention

[0020] Embodiments of the present invention will be described with reference to the accompanying drawings. First, an example of the configuration of a laser processing apparatus according to the present embodiment will be described. FIG. 1 is a perspective view schematically showing an example of the overall configuration of the laser processing apparatus 2.

[0021] In Figure 1, the X, Y, and Z directions represent the orientations of three mutually orthogonal axes in three-dimensional space. The X direction (left-right direction) and the Y direction (front-back direction) are mutually orthogonal horizontal directions. The Z direction (up-down direction) is orthogonal to the X and Y directions and is the vertical direction. Furthermore, in the laser processing apparatus 2 of this first embodiment, the direction along the X direction is the processing feed direction, and the direction along the Y direction is the indexing feed direction.

[0022] In this specification, expressions such as "along the X direction" or "along the XY plane" are used, but these do not necessarily mean that the orientation or movement of the components or light strictly coincides with or is parallel to these axes or planes. For example, they also include cases where they are at a slightly oblique angle to each other but are generally facing the same direction, or where the angle or movement includes a component in that direction.

[0023] The laser processing apparatus 2 comprises a base 4 that supports each element constituting the laser processing apparatus 2, and each of the elements (moving mechanism (Y-axis moving unit 6, X-axis moving unit 16), holding table (chuck table) 26, laser irradiation unit 40) supported on the base 4.

[0024] The upper surface 4a of the base 4 is a surface that aligns with the horizontal plane (XY plane), and the Y-axis movement unit 6 and the X-axis movement unit 16, which serve as movement units, are attached to this upper surface 4a.

[0025] The Y-axis movement unit 6 includes a Y-axis guide rail 8, a ball screw 10, a Y-axis movement table 12, and a rotary drive source 14.

[0026] The Y-axis guide rails 8 are a pair of rod-shaped members arranged parallel to each other along the Y-direction on the upper surface 4a of the base 4. A ball screw 10 is positioned between the pair of Y-axis guide rails 8 along the longitudinal direction of the Y-axis guide rails 8. A flat Y-axis moving table 12 is mounted on the upper part of the pair of Y-axis guide rails 8 so as to be slidable along the Y-axis guide rails 8.

[0027] A nut (not shown) is provided on the underside (bottom) of the Y-axis moving table 12, and the ball screw 10 passes through this nut. A rotational drive source 14, such as a pulse motor, is connected to the end of the ball screw 10, and the operation of the rotational drive source 14 causes the ball screw 10 to rotate around its axis, and the Y-axis moving table 12 moves along the Y-axis guide rail 8.

[0028] The X-axis movement unit 16 includes an X-axis guide rail 18, a ball screw 20, an X-axis movement table 22, and a rotary drive source 24.

[0029] The X-axis guide rails 18 are a pair of rod-shaped members arranged parallel to each other along the X-direction on the Y-axis moving table 12. A ball screw 20 is positioned between the pair of X-axis guide rails 18 along the longitudinal direction of the X-axis guide rails 18. A flat X-axis moving table 22 is mounted on the upper part of the pair of X-axis guide rails 18 so as to be slidable along the X-axis guide rails 18.

[0030] A nut (not shown) is provided on the underside (bottom) of the X-axis moving table 22, and a ball screw 20 passes through this nut. A rotational drive source 24, such as a pulse motor, is connected to the end of the ball screw 20, and the ball screw 20 rotates about its axis as the rotational drive source 24 operates, causing the X-axis moving table 22 to move along the X-axis guide rail 18.

[0031] A chuck table 26, which is a holding table, is mounted on the X-axis moving table 22. The chuck table 26 is a table that holds the workpiece 28, which is the object to be laser processed by the laser processing device 2.

[0032] Here, the workpiece 28 will be described. Figure 2 is a perspective view showing an example of the form of the workpiece 28. The workpiece 28 is a disc-shaped wafer made of a semiconductor material such as gallium arsenide or single-crystal silicon.

[0033] The disc-shaped workpiece 28 is divided into multiple rectangular regions by a grid of streets (planned division lines) 30 that intersect each other. Devices such as ICs (Integrated Circuits), LSIs (Large Scale Integrations), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) devices are formed on the surface 28a side of each region divided by the streets 30.

[0034] However, there are no restrictions on the type, material, shape, structure, size, etc., of the workpiece 28. For example, the workpiece 28 may be formed from a substrate (wafer) made of gallium arsenide or a semiconductor other than silicon (InP, GaN, SiC, etc.), sapphire, glass, ceramics, resin, metal, etc. There are also no restrictions on the type, number, shape, structure, size, arrangement, etc., of devices formed on the surface 28a of the workpiece 28, and the workpiece 28 may not even have devices formed on it.

[0035] When the workpiece 28 is handled by a laser processing device 2 (see Figure 1) or the like, the workpiece 28 is supported by a frame 32 as shown in Figure 2 for convenience in transport and holding. The frame 32 is a plate-shaped member made of metal such as SUS (stainless steel), and a circular opening is provided in the center of the frame 32 that penetrates the frame 32 in the thickness direction. The diameter of this opening is set to be larger than the diameter of the workpiece 28.

[0036] A sheet 34 is attached to the workpiece 28 and the frame 32. The sheet 34 may be, for example, a tape comprising a circularly formed film-like base material and an adhesive layer (glue layer) provided on the base material. The base material is made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate. The adhesive layer is made of an epoxy, acrylic, or rubber-based adhesive. The adhesive layer may also be made of an ultraviolet-curable resin.

[0037] With the workpiece 28 positioned inside the opening of the frame 32, the central part of the sheet 34 is attached to one side of the workpiece 28, and the outer periphery of the sheet 34 is attached to one side of the frame 32. As a result, the workpiece 28 is supported by the frame 32 via the sheet 34.

[0038] As shown in Figure 1, the upper surface 26a of the chuck table 26 is a flat surface aligned with the horizontal plane (XY plane) and constitutes a holding surface for holding the workpiece 28. The upper surface (holding surface) 26a is connected to a suction source (not shown), such as an ejector, via a flow path (not shown), a valve (not shown), etc., formed inside the chuck table 26.

[0039] Furthermore, a rotational drive source (not shown), such as a motor, is connected to the lower part of the chuck table 26 to rotate the chuck table 26 around a rotation axis aligned vertically (Z direction). As a result, the chuck table 26 rotates around an axis aligned vertically (Z direction) relative to the X-axis moving table 22.

[0040] When the rotational drive source 14 of the Y-axis movement unit 6 operates, the chuck table 26 moves along the Y-direction together with the Y-axis movement table 12 and the X-axis movement unit 16. When the rotational drive source 24 of the X-axis movement unit 16 operates, the chuck table 26 moves along the X-direction together with the X-axis movement table 22.

[0041] These moving mechanisms (Y-axis moving unit 6 and X-axis moving unit 16) cause the chuck table 26 and the laser irradiation unit 40 to move relative to each other along the Y-axis and X-axis. Here, the mechanism for moving the chuck table 26 relative to the laser irradiation unit 40 has been described, but the laser processing apparatus 2 may also be equipped with a mechanism for moving the laser irradiation unit 40, either in addition to or instead of the mechanism for moving the chuck table 26.

[0042] A support structure 36 is provided on the base 4 at a position on the rear side when viewed from the moving mechanism (Y-axis moving unit 6, X-axis moving unit 16) and the chuck table 26, so as to protrude upward from the upper surface 4a. The support structure 36 is a wall-like structure provided above the upper surface 4a of the base 4, and the surface (front) of the support structure 36 is a surface that aligns with the XZ plane. A rod-shaped support member 38 that protrudes forward is attached to the surface of the support structure 36.

[0043] A laser processing head 42, which is a component of the laser irradiation unit 40, is attached to the support member 38. The laser irradiation unit 40 is a mechanism for generating a laser beam and irradiating it onto a workpiece 28 held on a holding table (chuck table) 26. The laser processing head 42 is the component of the laser irradiation unit 40 that focuses the laser beam and irradiates it onto the workpiece 28.

[0044] The support member 38 extends upward from the support structure 36 to the chuck table 26, and the laser processing head 42 is mounted on the tip of the support member 38.

[0045] An imaging unit (not shown) may be provided at the tip of the support member 38. The imaging unit is equipped with an image sensor such as a CCD (Charged-Coupled Devices) sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) sensor and captures images of the workpiece 28 held on the chuck table 26. Based on the image acquired by the imaging unit, for example, alignment of the workpiece 28 and the laser processing head 42 is performed. For example, a visible light camera or an infrared camera can be used as the imaging unit, but there are no restrictions on the type or mechanism of the imaging unit.

[0046] The support member 38 may be connected to the support structure 36 via a Z-axis movement unit (not shown) that moves the support member 38 up and down along the Z-axis direction. For example, a ball screw type movement mechanism may be installed on the front side of the support structure 36 as the Z-axis movement unit. In this case, the Z-axis movement unit moves (raises and lowers) the support member 38 along the Z-axis direction, thereby adjusting the height of the focal point of the laser beam emitted from the laser processing head 42 and focusing the imaging unit.

[0047] The Z-axis movement unit only needs to move the chuck table 26 and the laser processing head 42 or a part thereof relative to each other along the Z-direction. For example, the tip of the support member 38 may move the laser processing head 42 or a part thereof up and down. Alternatively, the Z-axis movement unit may move the chuck table 26 side up and down.

[0048] The laser processing apparatus 2 is equipped with a display unit 44 that displays various information related to the operation of the laser processing apparatus 2. For example, a touch panel display is used as the display unit 44. When the display unit 44 is a touch panel display, the display unit 44 displays, for example, information regarding the operating status of each part of the laser processing apparatus 2, as well as an operation screen for inputting information to the laser processing apparatus 2, and the operator can input information to the laser processing apparatus 2 by touching the operation screen. In other words, in this case, the display unit 44 also functions as an input unit for inputting various information to the laser processing apparatus 2.

[0049] The input unit may be a separate input device such as a mouse or keyboard, independent of the display unit 44.

[0050] Furthermore, the laser processing apparatus 2 is equipped with a notification unit 46 that notifies the operator of specific information. The notification unit 46 is, for example, an indicator light that lights up or flashes when any abnormality occurs in the laser processing apparatus 2 to notify the operator of the error.

[0051] However, there are no restrictions on the type or mechanism of the notification unit 46. For example, the notification unit 46 may be a speaker that notifies the operator of information by voice. Alternatively, the display unit 44 may also have the function of a notification unit.

[0052] Furthermore, the laser processing apparatus 2 is equipped with a controller 48 that controls the laser processing apparatus 2. The controller 48 is a device that monitors and controls each part of the laser processing apparatus 2 and is connected to each component of the laser processing apparatus 2 (movement mechanism (Y-axis movement unit 6, X-axis movement unit 16), holding table (chuck table) 26, laser irradiation unit 40, display unit 44, notification unit 46, etc.). The controller 48 inputs control signals to each component of the laser processing apparatus 2.

[0053] The controller 48 is configured, for example, by a computer. Specifically, the controller 48 comprises a processing unit that performs calculations and other processing necessary for the operation of the laser processing device 2, and a storage unit that stores various information (data, programs, etc.) used for the operation of the laser processing device 2. The processing unit includes a processor such as a CPU (Central Processing Unit). The storage unit includes memory such as ROM (Read Only Memory) and RAM (Random Access Memory).

[0054] Next, the details of the laser irradiation unit 40 will be described. Figure 3 is a schematic diagram showing an example of the configuration of the laser irradiation unit 40. The laser irradiation unit 40 includes a laser processing head 42, a laser oscillator 50, an output adjustment unit 52, and an optical system 54, and performs laser processing such as ablation on the workpiece 28 by irradiating the workpiece 28 with a laser beam L.

[0055] The laser oscillator 50 is, for example, a YAG laser, a YVO4 laser, a YLF laser, etc., and generates a laser beam L by pulse oscillation. The output adjustment unit 52 is, for example, an attenuator. The laser beam L emitted from the laser oscillator 50 is incident on the output adjustment unit 52, and the output is adjusted before being emitted.

[0056] The optical system 54 is a mechanism that controls the direction of travel, shape, and focusing position of the laser beam L, and is composed of multiple optical elements. The optical system 54 guides the laser beam L to the workpiece 28 held in the holding table (chuck table) 26.

[0057] Specifically, the optical system 54 in this embodiment includes mirrors 56, 58, a polygon mirror 60, a light condenser 66, and a spot adjuster 70.

[0058] Mirrors 56 and 58 are, for example, dielectric multilayer mirrors. The laser beam L emitted from the output adjustment unit 52 is reflected by the reflective surfaces of mirrors 56 and 58 and incident on the polygon mirror 60.

[0059] The polygon mirror 60 is formed in a polygonal prism shape, and each side forming the outer circumference of the polygon mirror 60 forms a plurality of flat reflective surfaces 62 that reflect the laser beam L. Each reflective surface 62 is adjacent to a pair of reflective surfaces 62 across the side of the polygonal prism shape of the polygon mirror 60. That is, each reflective surface 62 is connected to an adjacent pair of reflective surfaces 62 at its side.

[0060] A rotational drive source 64, such as a motor, is connected to the polygon mirror 60. The rotation axis of the polygon mirror 60 is set to align with the axial direction (thickness direction, Y direction) of the polygon mirror 60, which has a polygonal prism shape. Driven by the rotational drive source 64, the polygon mirror 60 rotates along the XZ plane around its rotation axis.

[0061] In Figure 3, the polygon mirror 60 is formed in an octagonal prism shape and has eight reflective surfaces 62. However, the shape of the polygon mirror 60 and the number of reflective surfaces 62 are not limited to these and can be appropriately selected depending on the content of the laser processing, etc.

[0062] When the polygon mirror 60 is rotating and the laser beam L is shone upon it, the laser beam L is incident on one of the reflective surfaces 62 (the surface to be illuminated) and is reflected there. The angle of the surface to be illuminated changes according to the timing of the laser beam L's incidence as the polygon mirror 60 rotates.

[0063] As a result, the direction of the laser beam L irradiated onto the polygon mirror 60 changes, and the irradiation position of the laser beam L is dispersed within a certain area along the XY plane. When the laser beam L is irradiated, the polygon mirror 60 rotates at high speed, and the irradiated surface is sequentially switched, so that the laser beam L irradiates the certain area.

[0064] The laser beam L reflected by the reflective surface 62 of the polygon mirror 60 passes through the concentrator 66 and is irradiated onto the workpiece 28. The concentrator 66 is equipped with a focusing lens 68, such as an fθ lens. The laser beam L reflected by the reflective surface 62 enters the concentrator 66 and is focused by the focusing lens 68 at a predetermined position (such as the surface 28a, back surface, or interior of the workpiece 28 held in the chuck table 26).

[0065] Furthermore, the optical system 54 of this embodiment includes a spot adjuster 70 in the optical path between the output adjustment unit 52 and the mirror 56. The spot adjuster 70 is, for example, a diffractive optical element (DOE) and has the function of splitting the incident laser beam L. This changes the shape of the spot of the laser beam L irradiated onto the workpiece 28.

[0066] The laser beam L is guided to the workpiece 28 by the various optical elements described above, which are components of the optical system 54. Note that the configuration of the optical system 54 described above is merely an example, and there are no restrictions on the type or number of optical elements included in the optical system 54.

[0067] For example, the optical system 54 may include a position adjustment unit that adjusts the direction of propagation of the laser beam L. The position adjustment unit may consist of, for example, an acousto-optic deflector (AOD), an electro-optic deflector (EOD), a galvanometer scanner, an optical MEMS, etc., and adjusts the irradiation position of the laser beam L in the Y direction, for example.

[0068] The optical system 54 may be equipped with a beam damper (not shown) at an appropriate position on the optical path of the laser beam L (for example, on the exit side of the position adjustment unit) to block the laser beam L. When stopping the irradiation of the workpiece 28 with the laser beam L, the direction of travel of the laser beam L is adjusted by the position adjustment unit so that it enters the beam damper. This safely stops the irradiation of the workpiece 28 with the laser beam L.

[0069] In addition, the optical system 54 may further include other mirrors, other lenses, polarizing beam splitters (PBS), LCOS-SLM (Liquid Crystal On Silicon - Spatial Light Modulator), and other optical elements.

[0070] Each component of the laser irradiation unit 40 (laser oscillator 50, output adjustment unit 52, rotation drive source 64 for the polygon mirror 60, etc.) is connected to the controller 48. The controller 48 inputs control signals to these components and controls the operation of each component.

[0071] The laser processing method for the workpiece 28 and the method for manufacturing the chip using the laser processing apparatus 2 described above will be explained below.

[0072] First, as a reference example, we will explain the movement of the irradiation position of the laser beam L on the workpiece 28 in conventional laser processing.

[0073] The pulsed laser beam L is irradiated onto the workpiece 28 in a spot-like manner with each pulse. Hereinafter, each spot of the laser beam L irradiated onto the workpiece 28 with each pulse will be referred to as the "irradiation spot".

[0074] Figure 4 is a schematic diagram illustrating an example of the movement of the irradiation spot along the street 30 of a workpiece 28 in conventional laser processing. In the figure, the planned irradiation positions of the laser beam L are indicated by the symbols P1 to P12 along the street 30 (shown as a dashed line in the figure) set on the workpiece 28. The numbers 1 to 12 of the symbols P1 to P12 assigned to each planned irradiation position are assigned sequentially along the direction of the street 30.

[0075] In conventional laser processing, for example, each time the laser beam L is pulsed, the laser beam L is irradiated onto adjacent irradiation target positions P1 to P12 in the order of irradiation target position P1, irradiation target position P2, irradiation target position P3, and so on.

[0076] Figure 4 shows the state where the laser beam L is irradiating the planned irradiation position P4 (the irradiation spot SP is overlapping the planned irradiation position P4). At this point, the laser beam L has already irradiated the planned irradiation positions P1 to P3, and processing marks M have been formed. The processing marks M formed at each of the planned irradiation positions P1 to P3 overlap in part, forming a single linear processing mark.

[0077] Subsequently, each time the laser beam L pulses, the position of the irradiation spot SP moves to the planned irradiation position P5, P6, P7, and so on, creating a new processing mark each time, and the processing mark M shown in the diagram extends. For the sake of explanation, 12 planned irradiation positions P1 to P12 are shown here, but in reality, the laser beam L irradiates many more planned irradiation positions along the street 30, creating more processing marks M.

[0078] When the laser beam L is irradiated along the street 30 in this manner, after the laser beam L is irradiated to one planned irradiation position, there will be a delay of one pulse oscillation period, after which the laser beam L will be irradiated to another adjacent planned irradiation position.

[0079] Here, depending on conditions such as the output of the laser beam L, the pulse oscillation period, the irradiation time per pulse oscillation, the irradiation area on the workpiece 28, and the material of the workpiece 28, the next irradiation may occur at an adjacent planned irradiation location while the heat generated by the previous irradiation is still present. If the next irradiation occurs before the heat generated by the irradiation of one planned irradiation location has sufficiently dissipated, the next irradiation will occur on the area where heat remains or its vicinity, potentially degrading the processing quality due to excessive heat.

[0080] Such problems can be avoided, for example, by making the pulse oscillation period sufficiently long. However, a long pulse oscillation period means that the number of laser beam irradiations per unit time is low, which can be a factor that hinders the improvement of production efficiency.

[0081] Therefore, the inventors of this application have developed a technique to avoid the above-mentioned problems while using a pulsed laser with a high repetition frequency (short period) by using a polygon mirror 60 and adjusting the irradiation order of the laser beam L to each planned irradiation position.

[0082] In this method, the position of each irradiation spot of the laser beam L in the X direction is adjusted by appropriately setting operating conditions such as the repetition frequency of the pulsed laser beam L, the rotation speed of the polygon mirror 60, and the feed rate of the workpiece 28 along the X direction. This adjustment of the irradiation spot position is achieved by changing the direction of travel of the laser beam L along the XZ plane using the polygon mirror 60.

[0083] Figure 5 is a schematic diagram showing an example of the relationship between the angle of the reflective surface 62 of the polygon mirror 60 and the direction of propagation of the laser beam L. In the figure, the polygon mirror 60 is rotating clockwise, and the laser beam L is incident on one of the reflective surfaces 62 (for convenience, let's call it the first surface 62a).

[0084] As the polygon mirror 60 rotates, the angle of the first surface 62a changes, which in turn changes the direction of the laser beam L reflected by the first surface 62a. Of the pulses of the laser beam L irradiated by pulse oscillation, the first pulse incident on the first surface 62a, after being reflected by the first surface 62a, travels in the direction indicated by the sign L1 in the figure (path L1). Subsequently, when the second pulse is incident, the angle of the first surface 62a has changed due to the rotation of the polygon mirror 60, so the second pulse, after being reflected, travels in a different direction from the first pulse (path L2).

[0085] Similarly, the third pulse proceeds along path L3, and the fourth pulse proceeds along path L4. After the incidence of the fourth pulse, the rotation of the polygon mirror 60 causes the reflective surface (irradiated surface) onto which the laser beam L is incident to move from the first surface 62a to the second surface 62b. The fifth pulse is reflected by the second surface 62b and proceeds along the same path L1 as the first pulse. The sixth to eighth pulses are each reflected by the second surface 62b and proceed along paths L2 to L4, respectively.

[0086] In this way, the direction of propagation of the laser beam L incident on each reflective surface 62 of the polygon mirror 60 is distributed to four paths L1 to L4 by the rotation of the polygon mirror 60.

[0087] The laser beams L, distributed to each path, are irradiated onto the workpiece 28 held in the chuck table 26 located below. During irradiation, the workpiece 28 is moved along the X-axis direction (processing feed direction) by the X-axis movement unit 16.

[0088] Figure 6 is a schematic diagram illustrating an example of the movement of the irradiation spot SP along the street 30 of the workpiece 28 in laser processing. Figure 6(A) shows the position of the irradiation spot due to reflection from the first surface 6a of the polygon mirror's reflective surface.

[0089] The workpiece 28 is moved to the left in the figure by the X-axis moving unit 16 (see Figure 1) and irradiated with a pulsed laser beam L. Reflected off the first surface 62a (see Figure 5), each pulse of the laser beam L is distributed to paths L1 to L4 and irradiates the planned irradiation positions P1, P4, P7, and P10, respectively, among the planned irradiation positions P1 to P12 shown in Figure 6(A). In other words, among the planned irradiation positions P1 to P12 shown in Figure 6(A), the irradiation spots SP due to reflection from the first surface 62a become the irradiation spots SP.

[0090] At this time, the laser beam L is irradiated in the following order: planned irradiation position P10, planned irradiation position P7, planned irradiation position P4, and planned irradiation position P1.

[0091] The following four irradiations are performed by reflection from the second surface 62b (see Figure 5). Figure 6(B) shows the position of the irradiation spot due to reflection from the second surface 62b of the polygon mirror 60's reflective surface 62.

[0092] Due to the reflection from the first surface 62a, the laser beam L is irradiated to irradiation positions P1, P4, P7, and P10 among the irradiation positions P1 to P12, and processing marks M are formed at these positions. Due to the reflection from the second surface 62b, the laser beam L is irradiated to other irradiation positions P2, P5, P8, and P11, which are adjacent to the irradiation positions P1, P4, P7, and P10 where processing marks M have already been formed.

[0093] On the second surface 62b, the laser beam L generated by four pulses is distributed to paths L1 to L4, similar to the first surface 62a. However, during irradiation, the workpiece 28 is moved by the X-axis movement unit 16. Therefore, the position of the irradiation spot SP due to reflection on the second surface 62b (see Figure 6(B)) is shifted from the position of the irradiation spot SP due to reflection on the first surface 62a (see Figure 6(A)).

[0094] At this time, the laser beam L is irradiated in the following order: planned irradiation position P11, planned irradiation position P8, planned irradiation position P5, and planned irradiation position P2.

[0095] Here, by appropriately setting conditions such as the repetition frequency of the pulse oscillation of the laser beam L, the rotation speed of the polygon mirror 60, the size of the polygon mirror 60 used, the number of reflective surfaces 62, the size of each reflective surface 62, the feed rate of the workpiece 28, the shape of the irradiation spot, and the size of the irradiation spot, the spots irradiated to adjacent irradiation locations will partially overlap. Alternatively, the spots will be adjacent to each other (i.e., their outer edges will touch). As a result, a linear machining mark will be formed along the street 30.

[0096] If laser processing as described above continues, it is possible that the laser beam L may irradiate a location that has already been irradiated once. For example, in the examples shown in Figures 5, 6(A), and 6(B), a portion of the irradiation spot due to reflection from the fourth surface, which is three surfaces away from the first surface 62a, will overlap with a portion of the processing mark M formed by the reflection from the first surface 62a.

[0097] When performing laser processing, it is advisable to adjust the output, wavelength, and focusing position in the Z direction of the laser beam L, assuming that the same position will be irradiated multiple times.

[0098] In this way, during laser processing, the irradiation position of the laser beam L on the workpiece 28 (the position of the irradiation spot SP) is moved by the polygon mirror 60, and the irradiation order of the laser beam L to each planned irradiation position is adjusted. As a result, the irradiation interval of the laser beam L between adjacent planned irradiation positions becomes longer than the pulse oscillation period. That is, the irradiation interval to adjacent planned irradiation positions becomes an integer multiple of 2 or more of the pulse oscillation period.

[0099] For example, in the case of processing as shown in Figures 6(A) and 6(B), the time interval between the irradiation of the laser beam L to the planned irradiation position P1 and the irradiation of the laser beam L to the adjacent planned irradiation position P2 is four times the pulse oscillation period.

[0100] In the example shown in Figure 4, when laser processing is performed, the time interval between the irradiation of the laser beam L to the planned irradiation position P1 and the irradiation of the laser beam L to the adjacent planned irradiation position P2 corresponds to one period of pulse oscillation. If this period is short, as mentioned above, the heat generated by the irradiation of the planned irradiation position P1 may not dissipate sufficiently before the laser beam L is irradiated to the next planned irradiation position P2, which may lead to a deterioration in processing quality.

[0101] On the other hand, in the machining shown in Figures 6(A) and 6(B), there is a time interval of four pulse oscillation cycles between irradiation at the planned irradiation position P1 and irradiation at the planned irradiation position P2. During this time, heat is dissipated, which helps to suppress deterioration of machining quality.

[0102] In this example, the case where the laser beam L is incident on one reflective surface 62 four times during one rotation of the polygon mirror 60 is illustrated. However, the number of times the laser beam L is incident on the reflective surface 62 varies depending on conditions such as the size of the polygon mirror 60, the number of reflective surfaces 62 on the polygon mirror 60, the rotation speed of the polygon mirror 60, and the repetition frequency of the pulse oscillation of the laser beam L.

[0103] Let's explain the settings for laser processing. First, let's assume the rotation speed of the polygon mirror 60 per minute is N [rpm]. If the rotation speed of the polygon mirror 60 per second is n [rps], then n = N / 60.

[0104] Let m be the number of reflective surfaces 62 included in the polygon mirror 60. When the workpiece 28 on the chuck table 26 remains stationary, and the polygon mirror 60 rotates and a laser beam L is incident on its reflective surfaces 62, let w [mm] be the length along the X direction of the area on the workpiece 28 that is irradiated by the laser beam L (referred to as the "scan width").

[0105] Let f [Hz] be the repetition frequency (referred to as the "laser frequency") of the pulsed laser beam L. Let v [mm / s] be the feed rate of the chuck table 26 along the X direction. The feed rate v can be either positive or negative, depending on the direction of rotation of the polygon mirror 60.

[0106] If a polygon mirror 60 equipped with m reflective surfaces 62 rotates n times per second, the number of times per second the reflective surfaces 62 switch (referred to as the "scan frequency") is n·m. For each rotation of the polygon mirror 60, the time required for the laser beam L to be irradiated (scanned) by one reflective surface 62 (referred to as the "scan period") is 1 / (n·m)[s].

[0107] If the amount the workpiece 28 moves during scanning by one reflective surface 62 (first surface 62a) (referred to as the "movement pitch") is p [mm], then p = v / (n·m) [mm].

[0108] If D[mm] is the distance laser processing traveled per second along the street 30, taking into account the feed rate v of the workpiece 28 by the X-axis movement unit 16, then D = n·m·w + v[mm]. If d[mm] is the average distance between the centers of adjacent irradiation spots within one scan on a single reflective surface, then d = D / f[mm].

[0109] By adjusting parameters such as the rotation speed N and n of the polygon mirror 60, the laser frequency f, the feed rate v, and the average distance d between irradiation spots, laser processing as shown in Figures 6(A) and 6(B) becomes possible.

[0110] Based on the above, we will now explain the demonstration experiment conducted by the inventors of this invention regarding the relationship between processing conditions and processing quality. In the laser processing apparatus used in this demonstration experiment, the number of reflective surfaces m in the polygon mirror was 18, the scan width w was 26.69 [mm], and the width of the processing mark formed on the workpiece by one pulse of laser beam irradiation was 193 [μm].

[0111] In this laser processing apparatus, five different other conditions were set as follows, and the processing quality under each condition was verified. In all conditions, the wavelength of the laser beam was set to 1,064 [nm], and the rotation speed N of the polygon mirror was set to 6,000 [rpm]. A wafer containing gallium arsenide as the material was used as the workpiece 28. Condition 1: f=150[Hz], laser beam output=48[W], v=587[mm] Condition 2: f=200[kHz], laser beam output=64[W], v=440[mm] Condition 3: f=250[kHz], laser beam output=80[W], v=400[mm] Condition 4: f=400[kHz], laser beam output=128[W], v=440[mm] Condition 5: f=600[kHz], laser beam output=192[W], v=440[mm]

[0112] Under condition 1, the average distance d between the centers of irradiation spots within a single scan using a single reflective surface is 324 [μm], which is greater than the width of the machining mark formed by one pulse in the machining feed direction (193 [μm]). Therefore, the machining mark from one pulse and the machining mark from the next pulse do not overlap.

[0113] Next, when another adjacent reflective surface is scanned, a new machining mark is formed on the workpiece 28 at a position moved by a movement pitch p = 326 [μm] from the machining mark formed in the previous scan. The machining mark formed in one scan with one reflective surface and the machining mark formed in the next scan with the next reflective surface partially overlap with each other. As this process is repeated, machining marks are formed along the machining feed direction.

[0114] The same applies to condition 2. In condition 2, the average distance d between the centers of the irradiation spots within a single scan is 242 [μm], which is also greater than the width of the machining mark formed by a single pulse in the machining feed direction (193 [μm]). Therefore, the machining mark from one pulse and the machining mark from the next pulse do not overlap.

[0115] Next, when a scan is performed using an adjacent reflective surface, a new machining mark is formed on the workpiece 28 at a position moved by a movement pitch p = 244 [μm] from the machining mark formed in the previous scan. The machining mark formed in one scan using one reflective surface and the machining mark formed in the next scan using the next reflective surface partially overlap with each other.

[0116] Under condition 3, the average distance d between the centers of the irradiation spots within a single scan is 193 [μm], which is equal to the width of the machining mark formed by one irradiation in the machining feed direction (193 [μm]). Therefore, the machining mark from one pulse and the machining mark from the next pulse do not overlap, but the edges of the two machining marks are in contact. In the next scan, a machining mark is similarly formed at a position moved by a movement pitch p = 222 [μm]. In this way, machining marks are formed along the machining feed direction.

[0117] Under condition 4, the average distance d between the centers of the irradiation spots within a single scan is 121 [μm]. Under condition 5, d is 81 [μm]. These values ​​are smaller than the width of the machining mark formed by a single irradiation in the machining feed direction (193 [μm]). Therefore, the machining mark from one pulse and the machining mark from the next pulse overlap in some respects.

[0118] The processing quality around the processing marks of workpieces processed by laser according to conditions 1 to 5 above was inspected by microscopic observation. As a result, no thermal processing defects were observed around the processing marks of workpieces processed according to conditions 1 and 2. In workpieces processed according to condition 3, thermal processing defects were observed in some areas around the processing marks, but the proportion of these areas was not large and was at an acceptable level. In workpieces processed according to conditions 4 and 5, thermal processing defects were observed in almost the entire area around the processing marks.

[0119] Based on the above, it can be said that in laser processing, it is preferable to adjust the processing conditions such that the distance between the center of the x-th irradiation spot and the center of the x+1-th irradiation spot is equal to or greater than the width of the processed mark in the processing feed direction.

[0120] Here, if the distance between the center of the x-th irradiation spot and the center of the x+1-th irradiation spot is the same as the width of the machining trace in the machining feed direction, an acceptable level of machining quality can be obtained, and since the machining trace will extend continuously with each pulse, the production efficiency per unit of time can also be improved.

[0121] Next, the inventors of the present invention conducted an experiment to verify the appropriate time interval for laser beam irradiation. In this experiment, a workpiece containing gallium arsenide as a material was irradiated twice with pulses of a laser beam L with a wavelength of 1,064 nm at an output of 80 W, with different time intervals between pulses.

[0122] The width of the processing marks formed by irradiation was 193 [μm], and such a laser beam L was irradiated onto the workpiece such that the distance between the centers of the processing marks in the width direction was 193 [μm] (i.e., the width of the processing marks and the distance between the centers of the processing marks were equal).

[0123] Three time intervals were set for the irradiated pulses: 100 [μs], 66 [μs], and 33 [μs]. These numbers represent the time interval between the peaks of the pulses.

[0124] After pulse irradiation, the surface of the irradiated workpiece was examined by microscopic observation. The results showed that workpieces irradiated with two pulses at 100 μs intervals exhibited some machining defects, but these were within acceptable limits. Workpieces irradiated with two pulses at 66 μs and 33 μs intervals, respectively, exhibited machining defects throughout the entire irradiated area.

[0125] Based on the above, it can be said that, at least when processing a workpiece containing gallium arsenide as a material with laser beam L under the above conditions, if pulses of laser beam L are irradiated to adjacent irradiation locations at time intervals of 100 [μs] or more, processing defects due to heat can be suppressed and suitable processing can be performed.

[0126] The procedure for laser processing and chip manufacturing using the above method will be explained again with reference to a flowchart. Figure 7 is a flowchart illustrating an example of the procedure for laser processing and chip manufacturing.

[0127] The procedure shown in Figure 7 includes a preliminary machining mark formation step S10, a measurement step S20, a setting step S30, a first machining step S40, and a second machining step S50.

[0128] In the preliminary machining mark formation step S10, preliminary machining marks (preliminary machining marks) are formed on the workpiece 28 by irradiation with a laser beam L. Here, in order to determine the shape of the machining marks formed by irradiation with a single pulse of the pulsed laser beam L, for example, one pulse is irradiated onto the workpiece 28 held on the chuck table 26. Alternatively, irradiation (one scan) is performed using one of the reflective surfaces 62 provided on the polygon mirror 60. The machining marks thus formed on the workpiece 28 are the preliminary machining marks.

[0129] The workpiece 28 used here may be the same workpiece 28 that will be processed in the later first processing step S40 and second processing step S50, or it may be a different workpiece made of the same material, for example.

[0130] Next, the measurement step S20 is performed. In this measurement step S20, the width of the preliminary machining marks formed on the workpiece 28 in the preliminary machining mark formation step S10 is measured in the machining feed direction. The width can be measured, for example, using an imaging unit (not shown) attached to the tip of the support member 38.

[0131] Here, "processing feed direction" refers to the direction in which the spots of the laser beam L irradiated onto the workpiece 28 in the subsequent first processing step S40 and second processing step S50 are aligned, and in the above embodiment, it is the direction along the X direction in Figure 1 and other drawings. Note that the processing feed direction may also be set to a direction along a curve. For example, if the workpiece is subjected to laser processing while rotating, the processing feed direction will be the direction along the circumference.

[0132] The polygon mirror 60 rotates in an orientation along a plane (XZ plane) that is generally parallel to the processing feed direction. Also, during laser processing (first processing step S40 and second processing step S50), the workpiece 28 held in the chuck table 26 and the polygon mirror 60 provided in the laser irradiation unit 40 move relative to each other along the processing feed direction.

[0133] The shape of the spot (irradiation spot) of the laser beam L irradiated onto the workpiece 28, and the shape of the processing mark formed on the workpiece 28 as a result, can be adjusted by the spot adjuster 70. The shape of the irradiation spot and the processing mark can be, for example, an ellipse with a major axis along the processing feed direction.

[0134] Next, in setting step S30, based on the width of the pre-machining marks measured in measurement step S20 in the machining feed direction, at least one of the following is set: a value relating to the repetition frequency of the laser beam L in the subsequent first machining step S40 and second machining step S50, a value relating to the rotation speed of the polygon mirror 60, or a value relating to the relative movement speed of the workpiece 28 and the polygon mirror 60 along the machining feed direction.

[0135] The value relating to the repetition frequency of the laser beam L refers to a value that, when set, allows adjustment of the repetition frequency of the laser beam L pulsed from the laser oscillator 50. Examples include the laser frequency f or the period (reciprocal of the frequency) mentioned above.

[0136] The values ​​related to the rotation speed of the polygon mirror 60 refer to values ​​that, when set, allow the rotation speed of the polygon mirror 60 to be adjusted. These include, for example, the number of rotations per unit time N,n mentioned above, or the number of scans per unit time (the number of times the reflective surface to which the laser beam L is incident switches).

[0137] The value relating to the relative movement speed between the workpiece 28 and the polygon mirror 60 along the machining feed direction refers to a value that adjusts the relative movement speed between the workpiece 28 and the polygon mirror 60 along the machining feed direction by setting that value, and is, for example, the feed rate v of the chuck table 26 by the X-axis movement unit 16.

[0138] These values ​​are input to the controller 48 by the operator, for example, through a display unit 44 which is a touch panel display. Alternatively, the controller 48 may automatically set each value based on the measured width of the pre-machining marks.

[0139] Next, the first processing step S40 and the second processing step S50 are performed. The workpiece 28, which is the object to be laser processed, is held in the chuck table 26, and the workpiece 28 is moved in the processing feed direction by the operation of the X-axis movement unit 16. At the same time, the laser beam L emitted from the laser oscillator 52 by pulse oscillation is incident on the reflective surface 62 of the rotating polygon mirror 60, and the laser beam L reflected by the reflective surface 62 is irradiated onto the workpiece 28.

[0140] The first processing step S40 and the second processing step S50 can be executed as a continuous process by rotating the polygon mirror 60. For example, the formation of processing marks by a series of reflections on one of the multiple reflective surfaces 62 provided on the polygon mirror 60 (the first surface 62a in Figure 5) (irradiation of the laser beam L to the planned irradiation positions P1, P4, P7, and P10 shown in Figure 6(A)) corresponds to the first processing step S40, and the formation of processing marks by a series of reflections on the adjacent next reflective surface 62 (the second surface 62b in Figure 5) (irradiation of the laser beam L to the planned irradiation positions P2, P5, P8, and P11 shown in Figure 6(B)) corresponds to the second processing step S50.

[0141] In the example described above, the workpiece 28 and the polygon mirror 60 move relative to each other along the machining feed direction while the first machining step S40 and the second machining step S50 are executed consecutively. However, theoretically, other machining procedures are also possible, such as performing the first machining step S40 with the workpiece 28 and the polygon mirror 60 stationary relative to each other, then having the workpiece 28 and the polygon mirror 60 move relative to each other along the machining feed direction and then come to a stationary position before performing the second machining step S50.

[0142] In other words, when the workpiece 28 and the polygon mirror 60 move relative to each other along the machining feed direction, this movement may occur during the first machining step S40, during the second machining step S50, between the first machining step S40 and the second machining step S50, at multiple timings among them, or throughout the entire process. The speed and timing of the movement can be set in the setting step S30.

[0143] Alternatively, the processes from the first processing step S40 to the second processing step S50 may be performed without relative movement between the workpiece 28 and the polygon mirror 60. In this case, for example, the irradiation position of the laser beam L may be controlled by adjusting the rotation speed and angle of the polygon mirror 60 so that the irradiation position of the laser beam L in the first processing step S40 is different from the irradiation position of the laser beam L in the second processing step S50.

[0144] In the first machining step S40, multiple machining marks are formed on the workpiece 28 along the machining feed direction. These multiple machining marks (referred to as the first machining marks) do not overlap with each other. Similarly, in the second machining step S50, multiple machining marks are also formed on the workpiece 28 along the machining feed direction, but these multiple machining marks (referred to as the second machining marks) also do not overlap with each other. That is, the distance along the machining feed direction between the centers of each machining mark belonging to the first machining marks is equal to or longer than the width of each machining mark along the machining feed direction. The same applies to each machining mark belonging to the second machining marks.

[0145] On the other hand, each processing mark belonging to the first processing mark and each processing mark belonging to the second processing mark do not have to overlap with each other, they may overlap, or they may be adjacent to each other.

[0146] If the distance between the center of each machining mark belonging to the first machining mark and the center of each machining mark belonging to the second machining mark is equal to the width of each machining mark in the machining feed direction, then the first machining marks and the second machining marks are adjacent.

[0147] If the distance between the center of each processing mark belonging to the first processing mark and the center of each processing mark belonging to the second processing mark is shorter than the width of each processing mark, then the first processing marks and the second processing marks will overlap with each other in at least part.

[0148] In these cases, new machining marks are added to already formed machining marks, causing the machining marks to extend along the machining feed direction.

[0149] If the distance between the center of each processing mark belonging to the first processing mark and the center of each processing mark belonging to the second processing mark is greater than the width of each processing mark, the first and second processing marks will be separated from each other. In this case, if the laser beam L is irradiated to fill the gaps between these processing marks by performing laser processing continuously, processing marks will be formed linearly along the processing feed direction.

[0150] One processing mark formed on the workpiece 28 and another processing mark may overlap or be adjacent to each other in at least part. In such cases, it is desirable that the irradiation of both with the laser beam L be performed with a time interval sufficient to allow heat to dissipate sufficiently. To this end, for example, if the workpiece 28 contains gallium arsenide as a material, it is preferable that the irradiation of the laser beam L that forms the other processing mark is not performed at an interval of less than 100 microseconds ([μs]) from the irradiation of the laser beam L that forms the first processing mark.

[0151] Referring to the examples shown in Figures 5 and 6(A) and 6(B), for example, it is preferable that the first pulse irradiation by the first surface 62a (irradiation of a pulse that passes through path L1 and irradiates the planned irradiation position P10) and the first pulse irradiation by the second surface 62b (irradiation of a pulse that passes through path L1 and irradiates the planned irradiation position P11) be performed with an interval of 100 [μs] or more.

[0152] The positional relationship between the processing marks formed in the first processing step S40 and the second processing step S50, as well as the time intervals between the irradiation of the laser beam L to each planned irradiation position, are pre-adjusted by setting the operating conditions in the setting step S30.

[0153] The processing method described above can be used, for example, in ablation processing to form grooves on a workpiece 28 by ablating the workpiece 28 with a laser beam L. Furthermore, by applying laser ablation to the entire workpiece 28 in the thickness direction, the workpiece 28 can be divided. The workpiece 28 is divided into multiple chips along the street 30 (see Figure 2), thereby manufacturing chips.

[0154] Regarding laser processing, the above description explained the case where the laser beam L is incident multiple times (four times) on one reflective surface 62 for each rotation of the polygon mirror 60 (i.e., the workpiece 28 is irradiated four times with the laser beam L for each scan). However, the manner in which the laser beam L is irradiated is not limited to this.

[0155] For example, the operating conditions, such as the repetition frequency of the laser beam L and the rotation speed of the polygon mirror 60, may be adjusted so that the laser beam L is incident on each reflective surface 62 only once for each rotation of the polygon mirror 60. Alternatively, there may be reflective surfaces 62 that are not incident on by the laser beam L during one rotation of the polygon mirror 60. Furthermore, the direction of propagation of the laser beam L after reflection from each reflective surface 62 may differ for each reflective surface 62.

[0156] Furthermore, even if the laser beam L is incident on a single reflective surface 62 multiple times for each rotation of the polygon mirror 60, the direction of propagation of the laser beam L after reflection from the reflective surface 62 may differ for each reflective surface 62.

[0157] Furthermore, if, for example, the adjacent reflective surfaces 62 of the polygon mirror 60 are defined as the first surface, second surface, third surface...nth surface in order along the rotation direction, then laser processing may be performed in such a manner that, for example, the processing marks formed on the surface of the workpiece 28 by the reflection of the laser beam L on the first surface do not overlap with the processing marks formed on the surface of the workpiece 28 by the reflection of the laser beam L on the second surface, while the processing marks formed on the surface of the workpiece 28 by the reflection of the laser beam L on the first surface and the processing marks formed on the surface of the workpiece 28 by the reflection of the laser beam L on the third surface and subsequent reflective surfaces 62 overlap with the processing marks on the first surface.

[0158] With respect to each processing step and the processing marks formed thereby, the definitions of "first processing step," "second processing step," "first processing mark," and "second processing mark" may vary depending on the nature of the processing.

[0159] For example, if the processing is performed such that the laser beam L is incident only once on each reflective surface 62 for each rotation of the polygon mirror 60, and the direction of travel of the laser beam L after reflection from the reflective surface 62 is different for each reflective surface 62, the processing by one rotation of the polygon mirror 60 may be defined as the first processing step, and the processing mark formed therefrom as the first processing mark. The processing by the next rotation of the polygon mirror 60 may be defined as the second processing step, and the processing mark formed therefrom as the second processing mark. The processing may be performed such that the first processing marks do not overlap with each other, and the second processing marks do not overlap with each other.

[0160] Alternatively, the processing using a plurality of adjacent reflective surfaces 62 (for example, processing using the first to third surfaces) may be defined as the first processing step, and the subsequent processing using a plurality of reflective surfaces 62 (for example, processing using the fourth to sixth surfaces) may be defined as the second processing step, and the processing may be carried out such that the first processing marks formed by the first processing step do not overlap with each other, and the second processing marks formed by the second processing step do not overlap with each other.

[0161] Furthermore, each of the above embodiments may be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of Symbols]

[0162] 2: Laser processing device, 4: Base, 4a: Top surface 6: Moving mechanism (Y-axis moving unit), 8: Y-axis guide rail, 10: Ball screw 12: Y-axis moving table, 14: Rotation drive source 16: Moving mechanism (X-axis moving unit), 18: X-axis guide rail, 20: Ball screw 22: X-axis moving table, 24: Rotation drive source 26: Holding table (chuck table), 26a: Holding surface (top surface) 28: Workpiece, 28a: Surface, 30: Street, 32: Frame, 34: Sheet 36: Support structure, 38: Support member 40: Laser irradiation unit, 42: Laser processing head 44: Display unit, 46: Notification unit, 48: Controller 50: Laser oscillator, 52: Output adjustment unit 54: Optics, 56: Mirror, 58: Mirror 60: Polygon mirror, 62: Reflecting surface, 62a: First surface, 2b: Second surface 64: Rotary drive source 66: Focuser, 68: Focusing lens, 70: Spot adjuster L: Laser beam, L1~L4: Path M: Processing marks, P1~P12: Planned irradiation locations, SP: Irradiation spot

Claims

1. A laser processing method in which a laser beam is irradiated onto a workpiece, A first processing step involves irradiating the workpiece with the laser beam by irradiating it with the reflective surface of a rotating polygon mirror, thereby forming a plurality of first processing marks on the workpiece that are aligned along the processing feed direction and do not overlap with each other. A second processing step is performed in which, after the first processing step, the laser beam is incident on the reflective surface of the rotating polygon mirror, and the laser beam reflected from the reflective surface is irradiated onto the workpiece to form a plurality of second processing marks on the workpiece that are aligned along the processing feed direction and do not overlap with each other. A laser processing method comprising the following features.

2. The laser processing method according to claim 1, wherein each of the plurality of second processing marks overlaps with at least a portion of any of the plurality of first processing marks.

3. The laser processing method according to claim 1 or 2, wherein, when one processing mark and another processing mark overlap or are adjacent in at least part, the irradiation of the laser beam that forms the other processing mark is not performed at an interval of less than 100 microseconds from the irradiation of the laser beam that forms the first processing mark.

4. The laser processing method according to claim 1 or claim 2, wherein the width of the plurality of first processing marks in the processing feed direction is equal to the distance between the centers of the plurality of first processing marks in the processing feed direction.

5. Prior to the first processing step, a preliminary processing mark formation step is performed, in which the workpiece is irradiated with the laser beam to form preliminary processing marks, A measurement step is performed after the preliminary machining mark formation step and before the first machining step to measure the width of the preliminary machining mark in the machining feed direction, The method further comprises a setting step, after the measurement step and before the first processing step, setting at least one of the following based on the width of the pre-processing mark in the processing feed direction: a value relating to the repetition frequency of the laser beam in the first and second processing steps, a value relating to the rotation speed of the polygon mirror, or a value relating to the relative movement speed of the workpiece and the polygon mirror along the processing feed direction. The laser processing method according to claim 1 or 2, wherein, if a value relating to the relative movement speed of the workpiece and the polygon mirror along the processing feed direction is set, the workpiece and the polygon mirror are moved relative to each other along the processing feed direction during the first processing step, during the second processing step, or at least between the first processing step and the second processing step.

6. A laser processing method according to claim 1 or claim 2, wherein grooves are formed on a workpiece by ablation of the workpiece with the laser beam.

7. The laser processing method according to claim 1 or claim 2, wherein the workpiece contains gallium arsenide.

8. A method for manufacturing chips, comprising dividing a workpiece into a plurality of chips using the laser processing method described in claim 1.

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