Laser processing equipment

Abstract

The present invention provides a laser processing device that achieves excellent productivity without increasing the laser beam spot diameter. The laser beam irradiation unit of the laser processing device includes: a laser oscillator that oscillates laser light; a Y-axis scanner that scans the laser beam emitted from the laser oscillator at high speed along the Y-axis; an X-axis scanner that feeds the laser beam emitted from the laser oscillator along the X-axis for processing; and a condenser. The Y-axis scanner is selected from an acousto-optic deflector, a resonant scanner, and a polygonal scanner, while the X-axis scanner is selected from a galvano scanner or a resonant scanner.

Description

Technical Field

[0001] The present invention relates to a laser processing device having a laser beam irradiation unit for irradiating a workpiece with laser beam to form a damaged layer. Background Art

[0002] In a chip, a light-emitting layer is stacked on the upper surface of an epitaxial substrate such as a sapphire substrate or a SiC substrate. The light-emitting layer includes an epitaxial layer composed of a buffer layer, an n-type semiconductor layer, and a p-type semiconductor layer through epitaxial growth, and a plurality of electrodes arranged on the n-type semiconductor layer and the p-type semiconductor layer. A plurality of LEDs are formed which are divided by a plurality of predetermined dividing lines intersecting the light-emitting layer. The predetermined dividing lines of the chip are divided together with the epitaxial substrate by laser light, etc., to manufacture individual LED chips (for example, refer to Patent Document 1).

[0003] In addition, in order to increase the brightness of the LED and improve the cooling effect, the applicant has proposed the following technology: a transfer substrate such as a molybdenum substrate, a copper substrate, or a silicon substrate is bonded to the light-emitting layer via a bonding material (indium, palladium, etc.) to form a stacked wafer, and then, a laser beam is irradiated from the epitaxial substrate side to the buffer layer to destroy the buffer layer to form a destruction layer, and the light-emitting layer is transferred to the transfer substrate side (see patent document 2).

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 10-305420

[0005] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-21225

[0006] Furthermore, in recent years, the diameter of wafers used to produce LEDs has gradually increased to 200mm and 300mm, leading to a decrease in the production capacity required to process the wafers and produce individual LEDs. To improve this production capacity, one approach is to increase the spot diameter, for example, to several millimeters when irradiating the buffer layer with laser light from the epitaxial substrate side. However, increasing the spot diameter increases the energy of the pulsed laser light in proportion to the spot area, reducing the heat dissipation rate. This results in heat accumulation at the laser light irradiation point on the wafer side, potentially damaging LEDs near the laser light irradiation point. Summary of the Invention

[0007] Therefore, an object of the present invention is to provide a laser processing apparatus having excellent productivity without increasing the spot diameter of the laser beam.

[0008] According to the present invention, a laser processing device is provided, which comprises: a chuck table that holds a workpiece and has a holding surface defined by an X-axis and a Y-axis; and a laser beam irradiation unit that irradiates a laser beam toward the workpiece held by the chuck table to form a damaged layer, the laser beam irradiation unit comprising: a laser oscillator that oscillates laser light; a Y-axis scanner that scans the laser beam emitted from the laser oscillator at high speed in the Y-axis direction; an X-axis scanner that feeds the laser beam emitted from the laser oscillator in the X-axis direction for processing; and a condenser. The spot diameter D of the laser light irradiated onto the workpiece is set to 5μm~60μm, the overlap rate K of the laser light spot is set to 0.70~0.99, the scanning speed Vy in the Y-axis direction is set to 1m / s~300m / s, the energy E of the laser light per pulse is set to 0.07μJ~50μJ, the repetition frequency H of the laser light is set to H=Vy / {D·(1-K)}MHz, when the scanning width of the Y-axis scanner is set to Lmm, the scanning speed Vx in the X-axis direction is set to Vx=D·(1-K)·Vy / L mm / s, and the average output P of the laser light is set to P=E·Vy / {D·(1-K)}W.

[0009] Preferably, the Y-axis scanner is selected from an acousto-optic deflector, a resonant scanner, and a multi-faceted scanner, and the X-axis scanner is selected from a galvano scanner, a resonant scanner, and an X-axis feed mechanism that moves the holding unit in the X-axis direction. Preferably, the workpiece is a double-layer substrate having a light-emitting layer laminated on the upper surface of a sapphire substrate with a buffer layer interposed therebetween, and a transfer substrate disposed opposite the light-emitting layer. The laser beam transmits through the sapphire substrate to destroy the buffer layer. Preferably, when the light-emitting layer is laminated on the sapphire substrate, the wavelength of the laser beam is between 143 nm and 266 nm.

[0010] According to the present invention, the average output of the laser beam used to form the destruction layer is kept low. This prevents heat buildup and damage to the LEDs when forming the destruction layer on the buffer layer of a two-layer substrate. Furthermore, while the time required to form the destruction layer on the two-layer substrate is short and the beam spot diameter used during the destruction layer formation is small, production capacity is not compromised, and the light-emitting layer can be efficiently transferred to the transfer substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a perspective view of a laser processing device according to an embodiment of the present invention.

[0012] Figure 2 It shows the structure arranged in Figure 1FIG. 1 is a schematic block diagram of an optical system of a laser beam irradiation unit in the laser processing apparatus shown.

[0013] Figure 3 (a) is an exploded perspective view of a double-layer substrate constituting the workpiece. Figure 3 (b) is Figure 3 A partially enlarged cross-sectional view of the double-layer substrate shown in (a).

[0014] Figure 4 (a) is a perspective view showing a method of laser processing a double-layer substrate. Figure 4 (b) is the implementation Figure 4 (a) is a partially enlarged cross-sectional view of a wafer during laser processing, Figure 4 (c) is a plan view showing the method of performing laser processing.

[0015] Figure 5 This is a perspective view showing a method of peeling a sapphire substrate from a double-layer substrate.

[0016] Description of labels

[0017] 1: Laser processing device; 2: Base; 4: Frame; 6: Alignment unit; 8: Laser beam irradiation unit; 81: Condenser; 81a: fθ lens; 82: Laser oscillator; 83: Attenuator; 84: Y-axis scanner; 85: X-axis scanner; 9: Display unit; 10: Wafer; 10a: Buffer layer; 11: Light-emitting layer; 12: Sapphire substrate; 12a: Notch; 12b: Back surface; 13: Predetermined dividing line; 14: Light-emitting device (LED); 16: Transfer substrate; 18: Bonding metal layer; 20: Holding unit; 21: X-axis movable plate; 22: Guide rail; 23: Y-axis movable plate; 24: Holding workbench; 24a: Holding surface; 30: Moving mechanism; 32: X-axis feed mechanism; 34: Y-axis feed mechanism; 100: Destruction layer; LB: Laser beam. DETAILED DESCRIPTION

[0018] Hereinafter, a laser processing apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0019] Figure 1 The figure shows an overall perspective view of a laser processing apparatus 1 according to the present embodiment. The laser processing apparatus 1 includes a holding unit 20 for holding a workpiece, a moving mechanism 30 for moving the holding unit 20, an alignment unit 6, a laser beam irradiation unit 8 for irradiating a laser beam toward the workpiece held by the holding unit 20, and a display unit 9.

[0020] The holding unit 20 includes a rectangular X-axis movable plate 21, which is mounted on the base 2 so as to be movable in the X-axis direction indicated by arrow X in the figure; a rectangular Y-axis movable plate 23, which is mounted on the X-axis movable plate 21 so as to be movable in the Y-axis direction indicated by arrow Y in the figure, and is arranged on a pair of guide rails 22 arranged along the Y-axis on the X-axis movable plate 21; and a holding table 24, which is mounted on the upper surface of the Y-axis movable plate 23. The holding table 24 is configured to be rotatable by a rotation drive unit (not shown). The holding surface 24a constituting the upper surface of the holding table 24 is formed of a flat surface, which is defined by the X-axis and the Y-axis perpendicular to the X-axis.

[0021] The moving mechanism 30 includes an X-axis feed mechanism 32, which is mounted on the base 2 and feeds the holding unit 20 in the X-axis direction for machining; and a Y-axis feed mechanism 34, which indexes and feeds the Y-axis movable plate 23 in the Y-axis direction. The X-axis feed mechanism 32 converts the rotational motion of the pulse motor 35 into linear motion via a ball screw 36 and transmits it to the X-axis movable plate 21, causing the X-axis movable plate 21 to advance and retract in the X-axis direction along the guide rails 2a, 2a on the base 2. The Y-axis feed mechanism 34 converts the rotational motion of the pulse motor 37 into linear motion via a ball screw 38 and transmits it to the Y-axis movable plate 23, causing the Y-axis movable plate 23 to advance and retract in the Y-axis direction along the guide rails 22, 22 on the X-axis movable plate 21. Although not shown in the figure, position detection units are provided on the X-axis feed mechanism 32, the Y-axis feed mechanism 34, and the holding table 24 to accurately detect the X-axis position, the Y-axis position, and the rotational position of the holding table 24 and transmit the information to a control unit (not shown) provided in the laser processing apparatus 1. Then, based on an instruction signal from the control unit based on this position information, the X-axis feed mechanism 31, the Y-axis feed mechanism 32, and the rotation drive unit of the holding table 24 (not shown) are driven, thereby enabling the holding table 24 to be positioned at a desired position.

[0022] like Figure 1 As shown, a frame 4 is erected on the side of the moving mechanism 30. The frame 4 includes a vertical wall 4a mounted on the base 2 and a horizontal wall 4b extending horizontally from the upper end of the vertical wall 4a. The optical system of the laser beam irradiation unit 8 is housed within the horizontal wall 4b of the frame 4. The optical system includes a condenser 81 and an alignment unit 6 disposed on the lower surface of the front end of the horizontal wall 4b. The laser beam is irradiated from the condenser 81. The alignment unit 6 includes an illuminator for irradiating visible light and an image sensor (CCD) for capturing images of the workpiece using visible light. The image captured by the alignment unit 6 is transmitted to the control unit and displayed on the display unit 9.

[0023] Reference Figure 2 The structure of the optical system of the laser beam irradiation unit 8 will be briefly described. Figure 2 As shown, the laser beam irradiation unit 8 includes: a laser oscillator 82, which emits a pulsed laser beam LB; an attenuator 83, which adjusts the output of the laser beam LB emitted from the laser oscillator 82; a Y-axis scanner 84, which scans (scans) the laser beam LB emitted from the attenuator 83 at high speed along the Y-axis direction of the holding surface 24a of the specified holding workbench 24; an X-axis scanner 85, which processes and feeds the laser beam LB along the X-axis direction of the holding surface 24a of the specified holding workbench 24; and a condenser 81, which guides the laser beam LB that has passed through the optical system vertically to a specified position on the holding workbench 24 and condenses it for irradiation.

[0024] In addition, the Y-axis scanner 84 can be selected from known deflectors, such as an acousto-optic deflector (AOD), a resonant scanner, a multi-faceted scanner, etc. The X-axis scanner 85 can be any unit that has the function of processing and feeding the laser light LB emitted from the laser oscillator 82 along the X-axis direction of the holding surface 24a of the holding table 24, and can be selected from a current scanner and a resonant scanner. As described later, the speed at which the Y-axis scanner 84 scans on the holding surface 24a of the holding table 24 is set so as to scan at a speed higher than the speed at which the X-axis scanner 85 scans on the holding surface 24a. In addition, the X-axis scanner of the present invention is not limited to being arranged on Figure 2 In the optical system shown, an X-axis direction feeding mechanism 32 for feeding the holding table 24 of the holding unit 20 in the X-axis direction during processing can also be used as the X-axis scanner of the present invention.

[0025] The condenser 81 can be, for example, an fθ lens 81a as shown in the figure. The condenser 81 condenses the laser beam LB guided to the fθ lens 81a and irradiates the laser beam perpendicularly to the holding surface 24a of the holding table 24. However, the condenser 81 is not limited to the fθ lens 81a described above. For example, a parabolic mirror (parabolic reflector) may be used to condense the laser beam LB irradiated at a position different from the focal point of the parabola constituting the parabolic mirror and irradiate the laser beam perpendicularly to the holding table 24. The laser processing device 1 used in this embodiment generally has the above-described structure. The functions and effects of the laser processing device 1 of this embodiment will be described below.

[0026] Reference Figure 3 A workpiece processed by the laser processing apparatus 1 of this embodiment will be described. Figure 3(a) is a perspective view showing the workpiece in an exploded manner. Figure 3 (b) is a partially enlarged cross-sectional view of the workpiece. As shown in the figure, the workpiece is a double-layer substrate W consisting of a wafer 10 and a transfer substrate 16 arranged on a light-emitting layer 11 formed on the front surface of the wafer 10. The wafer 10 uses a sapphire substrate 12 as an epitaxial substrate, and a light-emitting layer 11 is stacked on the upper surface of the sapphire substrate 12. The light-emitting layer 11 is formed by dividing a plurality of light-emitting devices 14 (LEDs) composed of an epitaxial layer and a plurality of electrodes (not shown) by a plurality of intersecting predetermined dividing lines 13. The epitaxial layer is composed of an n-type semiconductor layer and a p-type semiconductor layer (neither of which are shown) formed on the sapphire substrate 12 by epitaxial growth through a buffer layer 10a, and the plurality of electrodes are arranged on the n-type semiconductor layer and the p-type semiconductor layer. The light-emitting layer 11 is formed of, for example, gallium nitride (GaN), but the present invention is not limited thereto, and can be selected from well-known semiconductors such as gallium phosphide (GaP) and indium arsenide (InAs). The buffer layer 10a is formed of the same type of raw material as the light-emitting layer 11. The wafer 10 has a notch 12a formed therein to indicate the crystal orientation of the sapphire substrate 12. The transfer substrate 16 is formed of, for example, molybdenum, copper, silicon, etc., and is disposed facing the light emitting layer 11 via a bonding metal layer 18 selected from, for example, gold, platinum, chromium, indium, palladium, etc. (see FIG. Figure 3 (b)).

[0027] The double-layer substrate W as described above is prepared in advance and transported to the laser processing device 1. Figure 4 As shown in (a), the back side 12b of the sapphire substrate 12 constituting the chip 10 is directed upward, and the transfer substrate 16 is directed downward and placed on the holding surface 24a of the holding table 24, and fixed using an appropriate adhesive, wax, etc.

[0028] Next, the holding workbench 24 is moved along the X-axis direction and positioned directly below the alignment unit 6, and a picture is taken from the back side 12b of the sapphire substrate 12 constituting the chip 10, and the position information of the outer edge, notch 12a, etc. of the double-layer substrate W is detected and stored in the control unit.

[0029] Next, based on the position information of the double-layer substrate W detected above, the double-layer substrate W is moved to the position directly below the condenser 81 of the laser light irradiation unit 8, and the double-layer substrate W is positioned at a predetermined position, such as Figure 4 As shown in (b), the depth of the focusing position P of the irradiated laser light LB is positioned at the buffer layer 10 a formed between the sapphire substrate 12 and the light emitting layer 11 .

[0030] As described above, when the focusing position P of the laser beam LB is positioned on the buffer layer 10a of the two-layer substrate W, the laser beam LB is irradiated on the two-layer substrate W to perform laser processing. The method of irradiating the laser beam LB will be described in more detail below.

[0031] In the laser processing performed by the laser processing apparatus 1 of this embodiment, as shown in FIG. Figure 4 As shown in (c), the scanning width (L) of the Y-axis scanner 84 in the Y-axis direction is set to an appropriate value (10 mm in this embodiment), and the X-axis scanner 85 and the Y-axis scanner 84 are operated to position the above-mentioned focusing position P of the laser beam LB at the left end position A1 of the column shown in (1). Then, while the double-layer substrate W is stopped, the laser oscillator 82 is operated to irradiate the laser beam LB and scan the scanning width (L) in the Y-axis direction. Then, the X-axis scanner 85 is operated to process and feed the laser beam LB in the X-axis direction at a size (spot diameter (D)·(1-K)) that achieves the overlap rate (K) described later. Then, the Y-axis scanner 84 is operated again to scan the laser beam LB in the Y-axis direction at the scanning width (L) as described above, and then the laser beam LB is again processed and fed in the X-axis direction at a size (spot diameter (D)·(1-K)) that achieves the overlap rate (K) described later. The action of the X-axis scanner 85 at this time is an intermittent action that repeats the stop and the action. By repeating such a scan, Figure 4 As shown in (c), the laser beam LB is irradiated in the entire X-axis direction of the first column (1), and a destructive layer 100 is formed in the buffer layer 10a (refer to Figure 4 (b)). In the first column (1) of the double-layer substrate W, as described above, if the destructible layer 100 is formed, the Y-axis scanner 84 and the X-axis scanner 85 are operated to position the focusing position P of the laser beam LB at the left end position A2 of the column (2). Then, as in the above-mentioned column (1), the destructible layer 100 is formed in the entire area of ​​the column (2). Similarly, for columns (3) and (4), the above-mentioned laser processing is also performed with the left end positions A3 and A4 as the processing start positions, and then the laser processing is performed in the entire area in the Y-axis direction, so that the destructible layer 100 is formed on the buffer layer 10a of the entire area of ​​the double-layer substrate W.

[0032] As described above, if the destruction layer 100 is formed, Figure 5 As shown, the sapphire substrate 12 is peeled off from the double-layer substrate W. Thus, the light-emitting layer 11 is transferred from the sapphire substrate 12 to the transfer substrate 16. The sapphire substrate 12 peeled off from the double-layer substrate W is polished and cleaned and then reused.

[0033] It is important that the laser processing according to the present embodiment described above is performed so as to satisfy the following conditions.

[0034] Spot diameter (D): 5μm~60μm

[0035] Spot overlap rate (K): 0.70~0.99 (70%~90%)

[0036] Y-axis scanning speed (Vy): 1m / s to 300m / s

[0037] Energy per pulse (E): 0.07μJ~50μJ

[0038] In this embodiment, specifically, the laser processing conditions are set as follows.

[0039] Spot diameter (D): 10 μm

[0040] Spot overlap rate (K): 0.90 (90%)

[0041] Y-axis scanning speed (Vy): 50m / s

[0042] Energy per pulse (E): 1 μJ

[0043] Y-axis scanning width (L): 10mm

[0044] In this embodiment, as described above, since the sapphire substrate 12 is selected as the epitaxial substrate constituting the wafer 10, the wavelength of the laser light LB oscillated by the laser oscillator 82 is set to a wavelength (143 nm to 266 nm) that is transmitted through the sapphire substrate 12. However, the present invention is not limited to this, and other well-known substrates (e.g., SiC substrates) may be selected as the epitaxial substrate. In this case, laser light having a wavelength that is transmitted through the selected material is irradiated.

[0045] The laser processing device 1 of this embodiment is set to the above-mentioned processing conditions, and the repetition frequency (H) of the laser beam, the scanning speed (Vx) in the X-axis direction, and the average output (P) of the laser beam LB are set to satisfy the following conditional expressions.

[0046] H=Vy / {D·(1-K)}MHz

[0047] Vx=D·(1-K)·Vy / L mm / sec

[0048] P=E·Vy / {D·(1-K)}W

[0049] That is, in this embodiment,

[0050] Repetition frequency (H) = 50 / {10·(1-0.90)} = 50 MHz

[0051] X-axis scanning speed (Vx) = 10·(1-0.90)·50 / 10 = 5 mm / sec

[0052] Average output (P) = 1.50 / {10.(1-0.90)} = 50W

[0053] As described above, the time required to process a wafer having a diameter of 200 mm is calculated as follows.

[0054] Processing time (T) = (200 / 5)·(200 / 10)·(3.14 / 4)

[0055] =628 seconds (=10 minutes and 28 seconds)

[0056] As described above, according to this embodiment, the average output (P) is kept relatively low, and even when forming the destructible layer 100 over the entire area of ​​the two-layer substrate W, heat accumulation that could damage the LEDs can be avoided. Furthermore, even though the time required to form the destructible layer 100 over the entire area of ​​the two-layer substrate W is short and the spot diameter (D) is set small, productivity is not compromised, and the light-emitting layer 11 can be efficiently transferred from the sapphire substrate 12 to the transfer substrate 16.

Claims

1. A laser processing device comprising: a chuck table that holds a workpiece and has a holding surface defined by an X-axis and a Y-axis; and A laser beam irradiation unit irradiates a workpiece held by the chuck table with a laser beam to form a damaged layer. The laser beam irradiation unit comprises: a laser oscillator that oscillates laser light; A Y-axis scanner that scans the laser beam emitted from the laser oscillator at high speed along the Y-axis direction; An X-axis scanner that feeds the laser beam emitted from the laser oscillator in the X-axis direction; and Concentrator, The spot diameter D of the laser beam irradiated on the workpiece is set to 5 μm to 60 μm, the overlap rate K of the laser beam spot is set to 0.70 to 0.99, the scanning speed Vy in the Y-axis direction is set to 1 m / s to 300 m / s, the energy E of the laser beam per pulse is set to 0.07 μJ to 50 μJ, and the scanning width L of the Y-axis scanner is set to a constant value. The repetition frequency H of the laser beam is set to H=Vy / {D·(1-K)}MHz, When the scanning width of the Y-axis scanner is L mm, the scanning speed Vx in the X-axis direction is set to Vx=D·(1-K)·Vy / L mm / second. The average output P of the laser beam is set to P=E·Vy / {D·(1-K)}W, In this laser processing device, it is configured to implement the following laser processing: based on the scanning width L scanned by the Y-axis scanner along the Y-axis direction, a plurality of columns to be processed having a certain width along the X-axis direction are set corresponding to the scanning width L, the laser oscillator is operated and the X-axis scanner and the Y-axis scanner are operated to position the focal position of the laser light at a specified position of the column to be processed and irradiate, then, scanning is performed along the Y-axis direction according to the scanning width L, then, the X-axis scanner is operated to perform processing and feeding along the X-axis direction according to a size that achieves the overlap rate K, then, the Y-axis scanner is operated again to scan the laser light along the Y-axis direction according to the scanning width L, then, processing and feeding along the X-axis direction according to a size that achieves the overlap rate K, and by repeating the above scanning, a destruction layer is formed corresponding to the column to be processed.

2. The laser processing device according to claim 1, wherein: The Y-axis scanner is selected from the group consisting of an acousto-optic deflector, a resonant scanner, and a multi-faceted scanner, and the X-axis scanner is selected from the group consisting of a current scanner, a resonant scanner, and an X-axis direction feed mechanism that moves the chuck worktable in the X-axis direction.

3. The laser processing device according to claim 1, wherein The workpiece is a double-layer substrate in which a light-emitting layer is stacked on the upper surface of a sapphire substrate with a buffer layer interposed therebetween and a transfer substrate is disposed facing the light-emitting layer. The laser beam passes through the sapphire substrate to destroy the buffer layer.

4. The laser processing device according to claim 3, wherein: The wavelength of the laser light is 143 nm to 266 nm.

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