Laser processing equipment

Abstract

[Problem] To solve the problem that when processing workpieces to form grooves of desired depth by irradiating them with pulsed laser light, operators have to calculate the number of laser spots to be positioned in the width direction and the number of pulsed laser beams to be irradiated each time workpieces of different thicknesses are processed, which is extremely troublesome. [Solution] The controller of the laser processing apparatus includes a processing trajectory memory unit, a thickness memory unit, a limit processing depth memory unit, a pass count memory unit, a spot overlap rate memory unit, and a selection unit. It further includes: a processing width calculation unit that calculates the processing width by multiplying the thickness (memoryed in the thickness memory unit) by the spot diameter; and a pass count calculation unit that calculates the number of passes of pulsed laser light to irradiate the cross-section of the processing width by multiplying the thickness (memoryed in the thickness memory unit) by the pass count memory unit, and by multiplying the number of spots obtained from the spot diameter, spot overlap rate, and processing width. The controller is configured to irradiate the non-product area selected by the selection unit with pulsed laser light at the number of passes calculated by the pass count calculation unit, relative to the processing width, based on the X and Y coordinates memorized in the processing trajectory memory unit.

Description

Technical Field

[0001] This invention relates to a laser processing apparatus for performing desired processing on a workpiece held in a work jig. Prior Technology

[0002] A wafer containing multiple devices such as ICs and LSIs, which are divided by multiple intersecting predetermined dividing lines on the front side, can be diced into individual device chips by a dicing device or a laser processing device. The diced device chips can be used in electrical machines such as mobile phones and personal computers.

[0003] The laser processing apparatus generally consists of a work chuck, an imaging unit, a laser beam irradiation unit, and a processing feed mechanism, and can process wafers with high precision. The aforementioned work chuck holds the wafer, the aforementioned imaging unit images the wafer held on the work chuck and detects the area to be processed, the aforementioned laser beam irradiates the wafer held on the work chuck with pulsed laser beams, and the aforementioned processing feed mechanism feeds the work chuck and the laser beam irradiation unit relative to each other (see, for example, Patent Document 1). Previous technical documents Patent documents

[0004] Patent Document 1: Japanese Patent Application Publication No. 2015-085347 Summary of the Invention

[0005] The problem the invention aims to solve

[0006] When using the laser processing apparatus described in the aforementioned Patent Document 1 and irradiating a pulsed laser beam with a wavelength that is absorbent to the wafer to form a trench of the desired depth, even if, for example, the focus point of the pulsed laser beam is positioned at a predetermined dividing line to set the number of irradiations to be performed and the pulsed laser beam is irradiated repeatedly, the following problem still exists: the desired processing cannot be performed due to the limitation of the processing depth relative to the size of the laser spot.

[0007] Therefore, the applicant of this invention considered the limit of the processing depth relative to the spot diameter of the pulsed laser beam and the thickness of the wafer to be divided, and reviewed the following approach: calculating the number of spots positioned in the width direction of the predetermined dividing line and the number of pulsed laser beams to be irradiated, inputting the processing information required by the laser processing apparatus, and forming a groove of the desired depth.

[0008] However, it is clear that whenever processing wafers of varying thicknesses, operators must perform the aforementioned calculations, which is extremely tedious. Furthermore, the following problem arises: wafer damage can occur if calculation errors prevent proper laser processing. This problem is not limited to processing the predetermined dividing lines of wafers with multiple intersecting dividing lines on the front side; it can also occur when cutting plate-like materials into desired shapes.

[0009] Accordingly, the present invention aims to provide a laser processing apparatus that can solve the problem that, when processing workpieces of varying thicknesses, operators must calculate the number of laser spots to be positioned in the width direction and the number of pulse laser beams to be applied to form a groove of desired depth by irradiating the workpiece with pulsed laser light, which is extremely tedious. The means to solve the problem

[0010] According to the present invention, a laser processing apparatus is provided, comprising: a work chuck having a holding surface defined in the X-axis and Y-axis directions for holding a workpiece; a laser beam irradiation unit for irradiating pulsed laser beams onto the workpiece held in the work chuck; and a controller. The laser beam irradiation unit includes: a laser oscillator that emits pulsed laser beams; and a concentrator that focuses the pulsed laser beams emitted by the laser oscillator onto the workpiece held on the work chuck. The controller includes: a machining trajectory memory unit that stores the X and Y coordinates of the machining trajectory of the workpiece held on the worktable; a thickness memory unit that stores the thickness of the workpiece; a limit machining depth memory unit that stores the limit values ​​of the laser beam spot diameter and machining depth; a pass count memory unit that stores the number of laser beam passes required to reach the limit value of the machining depth; an overlap rate memory unit that stores the overlap rate of the laser beam spot; a selection unit that selects the workpiece area and the non-workpiece area; and a machining width calculation unit that divides the thickness stored in the thickness memory unit by the thickness stored in the other unit. The processing width is calculated by multiplying the limit value of the ultimate processing depth memory unit by the spot diameter; and the pass count calculation unit calculates the number of passes of pulsed laser light to irradiate the profile of the processing width by multiplying the thickness already memorized in the thickness memory unit by the limit value already memorized in the ultimate processing depth memory unit, and multiplying by the number of passes already memorized in the pass count memory unit, and by multiplying by the spot diameter of the pulsed laser light, the overlap rate of the spot already memorized in the overlap rate memory unit, and the number of spots calculated by the processing width calculation unit. The controller is configured to irradiate a non-workpiece area selected by the selection unit based on the X and Y coordinates of the processing trajectory memory unit, with a pulsed laser beam relative to the processing width calculated by the processing width calculation unit and the number of passes calculated by the pass count calculation unit, thereby performing the desired processing on the workpiece held on the work chuck.

[0011] Preferably, the aforementioned laser processing apparatus further comprises: an X-axis feed mechanism for machining the worktable and the laser beam irradiation unit relative to each other in the X-axis direction; and a Y-axis feed mechanism for machining the worktable and the laser beam irradiation unit relative to each other in the Y-axis direction. The controller can control the laser oscillator and the X-axis feed mechanism and the Y-axis feed mechanism to perform the machining. The laser beam irradiation unit further includes an X-axis optical scanner that guides the pulsed laser beam in the X-axis direction and a Y-axis optical scanner that guides the pulsed laser beam in the Y-axis direction. The condenser includes an fθ lens. Invention Effects

[0012] According to the laser processing apparatus of the present invention, since the controller considers the limit value of the processing depth relative to the spot diameter of the pulsed laser beam and the thickness of the workpiece to be segmented, it calculates the number of spots positioned in the width direction of the desired processing trajectory and the number of pulsed laser beam passes to be irradiated, and this is reflected in the laser processing performed under the control of the controller. Therefore, it is not necessary for the operator to calculate the aforementioned parameters one by one and input them into the laser processing apparatus to form a groove of the desired depth. This also solves the problem of having to perform the aforementioned tedious calculations every time workpieces of different thicknesses are processed, which is extremely troublesome. Furthermore, it also solves the problem of damage to the workpiece due to calculation errors. Simple Explanation of the Diagram

[0013] Figure 1 is an overall perspective view of the laser processing apparatus according to an embodiment of the present invention. Figure 2 is a block diagram showing the optical system of the laser beam irradiation unit of the laser processing apparatus shown in Figure 1. Figure 3 is a block diagram showing an optical system of another embodiment of the laser beam irradiation unit of the laser processing apparatus shown in Figure 1. Figure 4 is a perspective view of a wafer that can be processed using the laser processing apparatus shown in Figure 1. Figure 5 is a block diagram showing details of the controller installed in the laser processing apparatus shown in Figure 1. Figure 6(a) is a schematic cross-sectional view of the processing groove formed by the laser processing apparatus shown in Figure 1, and (b) is a schematic cross-sectional view of the dividing groove formed by the processing groove shown in (a). Figure 7 is a magnified plan view of a portion of the wafer shown in Figure 4. Figure 8 is a perspective view showing the laser processing implementation of this embodiment. Implementation

[0014] Forms used to implement inventions

[0015] Hereinafter, a laser processing apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0016] Figure 1 shows an overall perspective view of the laser processing apparatus 1 according to this embodiment. The laser processing apparatus 1 is mounted on a base 2 and includes a holding unit 3, a laser beam irradiation unit 6, and a controller 100. The holding unit includes a work chuck 35 for holding the wafer 10 shown in the figure, and the laser beam irradiation unit 6 irradiates pulsed laser beams onto the wafer 10 held in the work chuck 35.

[0017] Furthermore, the laser processing apparatus 1 includes: a moving mechanism 4, comprising an X-axis feed mechanism 41 for moving the worktable 35 in the X-axis direction and a Y-axis feed mechanism 42 for moving the worktable 35 in the Y-axis direction; a frame 5, comprising a vertical wall 5a erected on the base 2 on the side of the moving mechanism 4 and a horizontal wall 5b extending horizontally from the upper end of the vertical wall 5a; and an imaging unit 7 for performing calibration by imaging the wafer 10 held on the worktable 35. An input unit 8 and a display unit (not shown) are connected to the controller 100. Alternatively, the display unit can be configured using a touch-sensitive input panel, and the display unit can be used as the input unit 8.

[0018] As shown in Figure 1, the holding unit 3 includes a rectangular X-axis movable plate 31 movably mounted on the base 2 in the X-axis direction, a rectangular Y-axis movable plate 32 movably mounted on the X-axis movable plate 31 in the Y-axis direction, a cylindrical support column 33 fixed to the upper surface of the Y-axis movable plate 32, and a rectangular cover plate 34 fixed to the upper end of the support column 33. A working clamp 35 is provided on the cover plate 34, and the working clamp 35 extends upward through an elongated hole formed in the cover plate 34. The working clamp 35 is rotatable by a rotation drive mechanism (not shown) housed within the support column 33. A holding surface 36 defined in the X-axis and Y-axis directions is formed on the upper surface of the working clamp 35, and the holding surface 36 is made of a porous material with air permeability. The holding surface 36 is connected to an attraction component (not shown) via a flow path through the support column 33, and four clamps 37 are arranged at equal intervals around the holding surface 36 for use when holding the wafer 10 (described later) in the work chuck 35. The wafer 10 can be attracted and held in the holding surface 36 of the work chuck 35 by actuating the attraction component.

[0019] The X-axis feed mechanism 41 converts the rotational motion of the motor 43 into linear motion via the ball screw 44 and transmits it to the X-axis movable plate 31, causing the X-axis movable plate 31 to move along a pair of guide rails 2a, 2a arranged on the base 2 along the X-axis direction. The Y-axis feed mechanism 42 converts the rotational motion of the motor 45 into linear motion via the ball screw 46 and transmits it to the Y-axis movable plate 32, causing the Y-axis movable plate 32 to move along a pair of guide rails 31a, 31a arranged on the X-axis movable plate 31 along the Y-axis direction.

[0020] The optical system constituting the laser beam irradiation unit 6 and the imaging unit 7 are housed inside the horizontal wall portion 5b of the frame 5. A condenser 61 is disposed on the lower surface of the front end of the horizontal wall portion 5b. The condenser 61 constitutes part of the laser beam irradiation unit 6 and irradiates pulsed laser beams LB toward the wafer 10. The imaging unit 7 is an imaging component that captures images of the wafer 10 held on the worktable 35 to detect the position or orientation of the wafer 10, the position of the irradiated pulsed laser beam, etc., and is disposed adjacent to the condenser 61 in the X-axis direction indicated by arrow X in the figure.

[0021] Figure 2 shows a block diagram of an example of the optical system of the laser beam irradiation unit 6 described above. The laser beam irradiation unit 6 of this embodiment includes: a laser oscillator 62 that oscillates to generate pulsed laser beams LB; an attenuator 63 that adjusts the output of the pulsed laser beams LB generated by the laser oscillator 62; a reflector 64 that redirects the optical path of the pulsed laser beams LB toward the worktable 35; and a concentrator 61, including a condenser lens 61a, which focuses the pulsed laser beams LB onto the wafer 10 held on the holding surface 36 of the worktable 35. When the workpiece, i.e., the wafer 10, is irradiated with pulsed laser beams LB by the laser beam irradiation unit 6, the X-axis feed mechanism 41 and the Y-axis feed mechanism 42 are controlled by the controller 100, thereby irradiating the pulsed laser beams LB onto the desired X and Y coordinate positions of the wafer 10 held on the worktable 35.

[0022] Furthermore, the laser beam irradiation unit of the present invention is not limited to the laser beam irradiation unit 6 shown in FIG2 above, and may also be provided in other forms, such as the laser beam irradiation unit 6' constructed with the optical system shown in FIG3. The laser beam irradiation unit 6' provides the same laser oscillator 62 and attenuator 63 as described above, and provides: an X-axis optical scanner 65 that guides the pulsed laser beam LB toward the wafer 10 held on the holding surface 36 of the work chuck 35 in the X-axis direction; a Y-axis optical scanner 66 that guides the pulsed laser beam LB toward the wafer 10 held on the work chuck 35 in the Y-axis direction; and a condenser 61', including an fθ lens 61a'. The X-axis optical scanner 65 and Y-axis optical scanner 66 are constructed using, for example, a galvanometer scanner. When the pulsed laser beam LB is irradiated onto the workpiece, i.e., the wafer 10, the controller 100 controls the X-axis optical scanner 65 and Y-axis optical scanner 66, thereby ensuring that the pulsed laser beam LB is irradiated at the desired position on the wafer 10 held on the work chuck 35. Furthermore, the X-axis optical scanner 65 and Y-axis optical scanner 66 are not limited to the aforementioned galvanometer scanner; they can also be constructed using an acousto-optic element (AOE), a diffraction optical element (DOE), a multifaceted mirror, etc.

[0023] Next, the following description will focus on the configuration of the workpiece, i.e., the wafer 10, and the controller 100 of the laser processing apparatus 1 in this embodiment. Furthermore, the embodiment described below is provided in which the laser processing apparatus 1 is equipped with the laser beam irradiation unit 6 shown in FIG2.

[0024] The workpiece that can be processed by the laser processing apparatus 1 of this embodiment can be, for example, a silicon (Si) wafer 10 as shown in FIG4. The wafer 10 is a wafer on the front side 10a having a plurality of devices 12 divided by a plurality of intersecting predetermined dividing lines, and is positioned in the opening Fa of an annular frame F having an opening Fa that can accommodate the wafer 10, and is held by the annular frame F by adhesive tape T to form a whole.

[0025] The controller 100 is composed of a computer and includes a central processing unit (CPU) for performing calculations according to the control program, a read-only memory (ROM) for storing the control program, a read-write random access memory (RAM) for temporarily storing calculation results, an input interface, and an output interface. The controller 100 can be connected to a shooting unit 7, an input unit 8, a laser oscillator 62, an X-axis feed mechanism 41, a Y-axis feed mechanism 42, etc.

[0026] The laser processing apparatus 1 of this embodiment has a general structure as described above. The functions and roles of the laser processing apparatus 1 will be specifically explained below.

[0027] In this embodiment, the laser processing apparatus 1 performs laser processing on the wafer 10 by means of a controller 100.

[0028] Referring to Figures 5 and 6, the various functional units 101 to 108 that can be implemented by the control program stored in the controller 100 and various memory units will be described. The controller 100 includes: a thickness memory unit 101 that stores the thickness H of the workpiece, i.e., the wafer 10; a limit processing depth memory unit 102 that stores the spot diameter S of the pulsed laser beam LB and the limit value R of the processing depth; a pass count memory unit 103 that stores the pass count P of the pulsed laser beam LB that reaches the limit value R of the processing depth; and an overlap rate memory unit 104 that stores the overlap rate W of the spot during laser processing.

[0029] In addition, it includes: a processing width calculation unit 105, which calculates the processing width V by multiplying the value of the thickness H stored in the thickness memory unit 101 by the limit value R stored in the limit processing depth memory unit 102 by the spot diameter S; and a pass count calculation unit 106, which calculates the pass count Pt of the pulsed laser beam LB that should irradiate the cross section of the processing width V by multiplying the value of the thickness H stored in the thickness memory unit 101 by the limit value R stored in the limit processing depth memory unit 102 by the pass count P stored in the pass count memory unit 103, and by multiplying the overlap rate W of the spot stored in the overlap rate memory unit 104 and the number of spots St obtained from the processing width V calculated by the processing width calculation unit 105. Furthermore, the controller 100 includes: a machining trajectory memory unit 107 that stores coordinate information I of the X and Y coordinates of the machining trajectory of the wafer 10 held on the worktable 35; and a selection unit 108 that selects the product area A and the non-product area B, and controls the laser oscillator 62, the X-axis feed mechanism 41 and the Y-axis feed mechanism 42 by means of the machining execution unit 109 that performs laser processing, based on the information summarized from the machining width calculation unit 105, the number of passes calculation unit 106, the machining trajectory memory unit 107 and the selection unit 108, to achieve the desired laser processing.

[0030] The functional units of the controller 100 described above will be explained in more detail. The thickness H of the wafer 10, which is stored in the thickness memory unit 101, can be obtained and stored by, for example, by an operator operating the input unit 8 to input or read the barcode information formed on the wafer 10. In this embodiment, the thickness H of the wafer 10 can be, for example, 300 μm, and the thickness H = 300 μm of the wafer 10 can be stored in the thickness memory unit 101.

[0031] The limit processing depth memory unit 102 is a memory unit that stores the limit value R of the processing depth based on the spot diameter S of the pulsed laser beam LB irradiated by the laser beam irradiation unit 6. To illustrate this, referring to Figure 6(a), for example, if the spot diameter S of the pulsed laser beam LB irradiated by the laser beam irradiation unit 6 in this embodiment is 10 μm, and the pulsed laser beam LB is repeatedly irradiated along a desired position, the depth of the processing groove 20 formed at the predetermined position will gradually increase. However, it does not increase indefinitely proportional to the number of times the pulsed laser beam LB is irradiated along the desired processing position (number of passes P), but rather there is a limit value R of the processing depth that cannot be further increased. In the limit processing depth memory unit 102 of this embodiment, the limit value R of the processing depth is determined by conducting experiments in advance, based on the spot diameter S=10μm set in the laser processing conditions of this embodiment (described later), and the measured value (100μm in this embodiment) is memorized as the limit value R.

[0032] The pass count memory unit 103 is a memory unit that stores the number of passes P that reach the limit value R of the processing depth measured in the limit processing depth memory unit 102. In this embodiment, the pass count P = 8 passes is stored as the measured value. Also, as shown in FIG6(b), the overlap rate memory unit 104 is a component that stores the overlap rate of the light spots in the X-axis direction and Y-axis direction when the pulsed laser light LB is irradiated and the dividing groove 18 is formed by a plurality of processing grooves 20. In this embodiment, the overlap rate is set to 50% in either the X-axis direction or the Y-axis direction.

[0033] The processing width calculation unit 105 is configured to calculate the processing width V required to form the dividing trench 18 to completely divide the wafer 10. Specifically, it can be calculated by dividing the thickness H (300 μm) stored in the thickness memory unit 101 by the limit value R (100 μm) stored in the limit processing depth memory unit 102, and then multiplying the value by the spot diameter S (10 μm). Processing width V = (H / R)·S = (300 / 100)·10 = 30 [μm] Therefore, the processing width V = 30 μm can be calculated and memorized.

[0034] The pass count calculation unit 106 is configured to calculate the pass count Pt of the pulsed laser beam LB that should irradiate the cross section of the aforementioned processing width V. This pass count Pt is the number of pulsed laser beams LB required to form the slitting groove 18 that completely divides the wafer 10 along the predetermined slitting line 14 of the wafer 10. The pass count Pt is calculated by dividing the thickness H (300 μm) stored in the thickness memory unit 101 by the limit value R (100 μm) stored in the limit processing depth memory unit 102, multiplying it by the pass count P (8 times) stored in the pass count memory unit 103, and multiplying it by the number of spots St obtained from the overlap rate W (50%) of the spots stored in the overlap rate memory unit 104 and the processing width V (30 μm) calculated by the processing width calculation unit 105.

[0035] Here, the number of pulsed laser beams LB irradiating the processing width V, represented by the number of pulsed laser beams LB irradiating the width direction in a way that overlaps with the initial beam, is x. This x is expressed as "St = 1 + x", and x is determined by the following relationship: (spot diameter S)·{1+(100%-overlap rate W)·x}=processing width V, The solution obtained by solving for x in 10·{1+(1-0.5)·x}=30 is (x=4). Therefore, the number of light spots St irradiated relative to the processing width V=30μm is “5” (see also Figure 6(b)).

[0036] Then, the number of pulsed laser beams LB that should irradiate the section of the processing width V is calculated as follows. Pt=(H / R)·P·St=(300 / 100)·8·5=120

[0037] As can be understood by referring to Figure 6(b), the number of pulsed laser beams LB that should irradiate the cross section of the processing width V in this embodiment, Pt, represents the sum of the following numbers (Pt=120): First, on the processing width V (30μm) to be processed in wafer 10, at each of the five spot positions that are positioned with 50% overlap in the processing width direction, pulsed laser beams LB reaching the limit value of processing depth (100μm) are irradiated a number of times P (8 times), and the first groove 22 with a width of 30μm and a depth of 100μm is formed a number of times (40 times). After forming the first groove 22, the focusing point of the pulsed laser beam LB is positioned at the bottom of the first groove 22, and the same laser processing as described above is performed, forming the second groove 24 with a width of 30 μm and a depth of 200 μm 40 times; and After forming the first trench 22 and the second trench 24, the focus point of the pulsed laser beam LB is positioned at the bottom of the second trench 24, and the same laser processing as described above is performed to form the third trench 26, which has a width of 30 μm and a depth of 300 μm, i.e., completely divides the wafer 10, 40 times. By forming the first trench 22, the second trench 24, and the third trench 26 as described above, the dividing trench 18 that completely divides the wafer 10 can be formed.

[0038] As described above, the controller 100 has a machining trajectory memory unit 107. The machining trajectory memory unit 107 stores the coordinate information I of the X and Y coordinates of the machining trajectory to be formed on the wafer 10 held on the work chuck 35. In this embodiment, the stored coordinate information I is specifically the coordinate information I of the X and Y coordinates of the center line 16 along the predetermined dividing line 14 of the wafer 10, which is shown in the enlarged view of FIG7. This coordinate information represents the machining trajectory. The machining trajectory memory unit 107 has pre-registered and stored the coordinate information I of the X and Y coordinates of the center line 16 in advance through the input unit 8.

[0039] Furthermore, as described above, the controller 100 includes a selection unit 108 for selecting the product area A and the non-product area B. In this embodiment, the product area A refers to the aforementioned device 12, or the area containing the device 12 and its outer edge where laser processing is not permitted, and the non-product area B refers to the area where laser processing is permitted. That is, referring to FIG7, in the wafer 10, the area where the device 12 is located is selected as the product area A, and the area where the slitting predetermined line 14 is formed is selected as the non-product area B, and this is stored in the selection unit 108. The slitting groove 18 formed by the aforementioned laser processing is formed in the area of ​​the non-product area B (slitting predetermined line 14), and is configured as a processing predetermined area 18' represented by a dashed line along the central line 16 represented by a dotted chain line. Based on the information stored in the selection unit 108, the situation where laser processing accidentally processes the product area A can be prevented. Furthermore, the selection unit 108 can actually be configured to select only either the product area A or the non-product area B, and can also be configured to use an area other than the product area as another area (product area A or non-product area B) to perform this embodiment. Also, in this embodiment, the width of the predetermined dividing line 14 selected as the non-product area B is 70 μm as shown in the figure. If the processing width V calculated by the processing width calculation unit 105 exceeds 70 μm, even if the dividing groove 18 is formed along the center line 16 of the predetermined dividing line 14, it is still impossible to perform proper laser processing within the non-product area B (predetermined dividing line 14), so it will be determined that processing is not possible. In this case, the laser processing conditions described below will be adjusted.

[0040] As described above, once the controller 100 obtains the processing width V, the number of pulse laser beams LB to be irradiated on the cross section of the processing width V, and the coordinate information I of the X and Y coordinates of the processing trajectory to be formed, and selects the product area A and the non-product area B, the laser processing of the wafer 10 can be performed according to the processing execution unit 109 of the controller 100.

[0041] Furthermore, the laser processing conditions in this embodiment are set as follows, for example. Wavelength: 355nm Repetition frequency: 50kHz Average output: 2W Pulse energy: 40μJ Pulse width: 10ps Spot diameter: 10μm

[0042] The wafer 10, which has been transferred to the laser processing apparatus 1 as described in Figure 1, is placed on the holding surface 36 of the work chuck 35 of the holding unit 3 with its front side 10a facing upwards and is attracted thereto. The annular frame F is held and fixed by the clamp 37. The wafer 10, which is held on the work chuck 35, is photographed using the imaging unit 7 provided in the laser processing apparatus 1. The X and Y coordinates of the processing trajectory to be processed, which is stored in the processing trajectory memory unit 107, are calibrated. The position of the predetermined dicing line 14 on the front side 10a of the wafer 10 is detected. The wafer 10 is rotated by the rotary drive mechanism so that the predetermined dicing line 14 is aligned with the X-axis direction.

[0043] Based on the information detected by the above calibration, as shown in FIG8, the concentrator 61 of the laser beam irradiation unit 6 is positioned at a predetermined processing start position in the processing predetermined area 18' (also refer to FIG7) where the segmentation groove 18 is formed in the segmentation predetermined line 14 in the first direction. The focusing point of the pulsed laser beam LB is positioned on the front side 10a, and the above-mentioned X-axis feed mechanism 41 and Y-axis feed mechanism 42 are activated to process the wafer 10 in the X-axis direction. The above-mentioned ablation process is performed along the processing predetermined area 18' on the segmentation predetermined line 14 extending in the first direction of the wafer 10. The wafer 10 is processed in the Y-axis direction according to the overlap ratio W (50% in this embodiment). The laser processing based on the above-mentioned laser processing conditions is performed within the processing width V of the processing predetermined area 18' according to the number of light spots St (5 in this embodiment). Furthermore, by actuating the laser beam irradiation unit 6, the X-axis feed mechanism 41, and the Y-axis feed mechanism 42, the laser processing is repeatedly performed in such a way that the laser beam is irradiated a number of times P (8 times in this embodiment) corresponding to one laser spot, thereby forming a groove with a width of 30 μm and a depth of 100 μm (the first groove 22 in FIG. 6(b)) along the predetermined dividing line 14. Moreover, the order in which the pulsed laser beams LB are irradiated to reach the limit value R of the processing depth, corresponding to each of the 5 laser spots in this embodiment, can be arbitrarily determined.

[0044] Next, while lowering the position of the focusing point along the Z-axis direction (indicated by arrow Z in Figure 8) to position the light spot at the bottom of the groove, the same laser processing as described above is performed along the aforementioned groove to form the second groove 24 and the third groove 26. In this way, by irradiating with a pulsed laser beam LB of a total number of passes Pt=120, a sizing groove 18 with a depth of 300 μm is formed along the predetermined processing area 18' of the predetermined sizing line 14. After forming the sizing groove 18 along the predetermined sizing line 14 extending in the first direction, the wafer 10 can be indexed to the spacing between adjacent sizing lines 14 in the Y-axis direction to position the unprocessed sizing line 14 directly below the focusing unit 61. Then, as described above, the pulsed laser beam LB is positioned at the processing predetermined area 18' of the dicing predetermined line 14 on the wafer 10 and irradiated to form a dicing groove 18. Similarly, the wafer 10 is fed along the X-axis and indexed along the Y-axis, forming the dicing groove 18 along all the dicing predetermined lines 14 extending in the first direction. Next, the wafer 10 is rotated 90 degrees so that the unprocessed dicing predetermined lines 14, which are orthogonal to the dicing predetermined lines 14 extending in the first direction with the dicing groove 18 already formed, are aligned with the X-axis. Then, for the remaining dicing predetermined lines 14, the pulsed laser beam LB is positioned and irradiated in the same manner as described above, forming the dicing groove 18 along all the dicing predetermined lines 14 formed on the front side 10a of the wafer 10.

[0045] According to the above implementation, since the controller 100 considers the limit value R of the processing depth relative to the spot diameter S of the pulsed laser beam LB and the thickness H of the wafer 10 to be divided, it calculates the number St of laser spots positioned in the width direction of the predetermined dividing line 14 and the number of passes Pt of the pulsed laser beam LB to be irradiated. This is reflected in the laser processing performed by the controller 100. Therefore, it is not necessary for the operator to calculate the aforementioned parameters one by one and input them into the laser processing device 1 to form the dividing groove 18 of the desired depth. This also solves the problem that the operator has to perform the aforementioned complicated calculations whenever processing other wafers of different thicknesses, which is extremely troublesome. Furthermore, it also solves the problem of wafer damage due to calculation errors.

[0046] In the above-described embodiment, an example is described where a laser processing apparatus 1 is used to process a wafer 10 having multiple devices 12 divided by multiple intersecting predetermined dividing lines 14 on its front side 10a to form a trench of desired depth. However, the present invention is not limited to this. For example, a circular silicon substrate can be processed as the workpiece. In the case of obtaining a product of a desired shape, such as a quadrangular silicon substrate, from the circular silicon substrate by means of the X and Y coordinates of the processing trajectory to be formed, which is stored in the processing trajectory memory unit 107, the desired quadrangular region can be selected as the product region A in the selection unit 108, and the region surrounding the product region A can be selected as the non-product region B. The laser processing described above is then performed on the non-product region B along the outer edge of the product region A to form the dividing trench 18, thereby obtaining the desired quadrangular silicon substrate as the product.

[0047] 1: Laser processing equipment 2:Abutment 2a, 31a: Guide rails 3: Holding unit 31: Movable plate in the X-axis direction 32: Movable plate in the Y-axis direction 33: Pillar 34: Cover plate 35: Worktable 36: Keep the surface 4: Mobile mechanism 41: X-axis feed mechanism 42: Y-axis feed mechanism 43, 45: Motor 44, 46: Ball screw 5: Frame 5a: Vertical wall portion 5b: Horizontal wall portion 6,6': Laser beam irradiation unit 61,61': Concentrator 61a: Condensing lens 61a':fθ lens 62: Laser Oscillator 63: Attenuator 64: Reflector 65: X-axis optical scanner 66: Y-axis optical scanner 7: Filming Unit 8: Input Unit 10: Wafer 10a: Front 12: Devices 14: Pre-defined dividing line 16: Central Line 18: Dividing Ditch 18': Processing Pre-determined Area 20: Processing trench 22: First Ditch 24: Second Ditch 26: Third Ditch 100: Controller 101: Thickness Memory Section 102: Extreme processing depth memory unit 103: Number of times memory department 104: Overlap Rate Memory Unit 105: Machining Width Calculation Section 106: Number of passes calculation department 107: Processing Trajectory Memory Department 108: Selection Department 109: Processing Execution Department A: Product Area B: Non-product area F: Ring-shaped frame Fa: Opening H: Thickness of the workpiece LB: Pulsed Laser Beam P: The number of pulsed laser beams LB used to reach the limit value of the processing depth R. Pt: The number of pulsed laser beams LB that should irradiate the section with a processing width V. R: Limit value of machining depth S: Spot diameter St: Number of light spots T: Adhesive tape V: Processing width W: Overlap rate of light spots I: Coordinate information of X and Y coordinates of the machining trajectory LB: Pulsed Laser Beam X, Y, Z: Direction (arrow)

Claims

1. A laser processing apparatus comprising: a worktable having a holding surface defined in the X-axis and Y-axis directions for holding a workpiece; a laser beam irradiation unit for irradiating pulsed laser beams onto the workpiece held on the worktable; and a controller, the laser beam irradiation unit comprising: a laser oscillator for emitting pulsed laser beams; and a concentrator for focusing the pulsed laser beams emitted by the laser oscillator onto the workpiece held on the worktable, the controller comprising: a processing trajectory memory unit for storing the X and Y coordinates of a processing trajectory to be formed on the workpiece held on the worktable; a thickness memory unit for storing the thickness of the workpiece; a limit processing depth memory unit for storing the limit values ​​of the spot diameter and processing depth of the pulsed laser beams; a pass count memory unit for storing the number of passes of the pulsed laser beams required to reach the limit value of the processing depth; an overlap rate memory unit for storing the overlap rate of the laser spots; and a selection unit for selecting a workpiece area and a non-workpiece area. The processing width calculation unit calculates the processing width by multiplying the value (after dividing the thickness stored in the thickness memory unit by the limit value stored in the limit processing depth memory unit) by the spot diameter. The pass count calculation unit calculates the number of passes of pulsed laser light to irradiate the cross-section of the processing width by multiplying the value (after dividing the thickness stored in the thickness memory unit by the limit value stored in the limit processing depth memory unit) by the pass count stored in the pass count memory unit, and by multiplying this by the spot diameter of the pulsed laser beam, the overlap rate of the spot stored in the overlap rate memory unit, and the number of spots obtained from the processing width calculated by the processing width calculation unit. The controller is configured to irradiate a non-workpiece area selected by the selection unit based on the X and Y coordinates of the processing trajectory memory unit with a pulsed laser beam relative to the processing width calculated by the processing width calculation unit and the number of passes calculated by the pass count calculation unit, thereby performing the desired processing on the workpiece held on the work chuck.

2. The laser processing apparatus of claim 1 further comprises: an X-axis feed mechanism for processing and feeding the worktable and the laser beam irradiation unit relative to each other in the X-axis direction; and a Y-axis feed mechanism for processing and feeding the worktable and the laser beam irradiation unit relative to each other in the Y-axis direction, wherein the controller controls the laser oscillator and controls the X-axis feed mechanism and the Y-axis feed mechanism to perform the processing.

3. The laser processing apparatus of claim 1, wherein the laser beam irradiation unit further includes an X-axis optical scanner for guiding the pulsed laser beam in the X-axis direction and a Y-axis optical scanner for guiding the pulsed laser beam in the Y-axis direction, the condenser includes an fθ lens, the controller controls the laser oscillator, and controls the X-axis optical scanner and the Y-axis optical scanner to perform the processing.

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