JP5318545B2 - Wafer processing method - Google Patents

Description

The present invention relates to a wafer processing how to process the wafer or the like using a sapphire substrate.

  An optical device wafer in which a plurality of regions are defined by dividing lines called streets formed in a lattice pattern on the surface of a sapphire substrate or the like, and an optical device such as a gallium nitride compound semiconductor is stacked on the partitioned regions. It is divided into optical devices such as individual light emitting diodes along the street, and is widely used in electronic equipment.

  Such cutting along the streets of the optical device wafer is usually performed by a cutting device that performs cutting by rotating a cutting blade at a high speed. However, since the sapphire substrate has a high Mohs hardness and is a difficult-to-cut material, there is a problem that it is necessary to slow the processing speed and productivity is poor.

  In recent years, as a method of dividing an optical device wafer along a street, a laser processing groove is formed by irradiating the wafer with a pulsed laser beam having a wavelength that absorbs the wafer. A method of dividing by applying an external force has been proposed (see, for example, Patent Document 1).

JP-A-10-305420

  Here, in order to enable high-quality division, it is considered that a laser processing groove having a depth of about 20% with respect to the wafer thickness is necessary. In order to increase productivity, a laser of a pulse laser beam is used. Although it is necessary to increase the output, there is a concern that damage to the light emitting device may increase at the same time.

  Therefore, as a practical measure, there is no choice but to improve the productivity because the laser output is suppressed and the wafer processing feed rate is set to a low speed of about 70 to 120 mm / s, for example.

The present invention was made in view of the above, while suppressing the laser output to be irradiated, the wafer processing how that can process the wafer faster without disturbing the resolution of high-quality wafers The purpose is to provide.

In order to solve the above-described problems and achieve the object, a wafer processing method according to the present invention includes a plurality of streets formed by a plurality of streets in which a nitride semiconductor layer is formed on a surface of a sapphire substrate and arranged in a lattice pattern. A laser processing groove is formed on a wafer having a light-emitting device formed in the region by irradiating the wafer with a pulsed laser beam having a wavelength that absorbs the wafer along the street to apply an external force to the wafer. A wafer processing method for forming a laser processing groove by irradiation with a preceding pulsed laser beam when sequentially irradiating a wafer with a pulse laser beam and continuously forming the laser processing groove by ablation processing. Followed by an interval that does not cancel out the thermal strain formed to grow from the bottom of the laser processed groove So as to irradiate the pulsed laser beam, with the laser output is 23W, and if the repetition frequency is 200kHz, the relative movement speed is not higher than 300 mm / s or more and 600 mm / s, the laser output Is 62 W and the repetition frequency is 90 kHz, the relative movement speed is 150 mm / s or more and 450 mm / s or less .

  The wafer processing method according to the present invention further includes a dividing step of dividing the wafer by applying an external force to the wafer after completion of the step of forming the laser processing groove by irradiation with a pulsed laser beam. Features.

  The wafer processing method according to the present invention is characterized in that, in the above invention, the dividing step is executed within 24 hours after the step of forming the laser processing groove by irradiation with a pulsed laser beam.

According to the wafer processing how according to the present invention, when continuously forming a laser processed grooves in the wafer by ablation processing by irradiating a pulsed laser beam, subsequent pulse laser beam with respect to the preceding pulse laser beam irradiation The thermal strain formed with the formation of the laser processing groove is not canceled by optimizing the interval to be processed, so that even if the laser processing groove formed is shallow, the thermal strain formed accompanying the laser processing groove Wafer splitting is possible due to the residual stress that decreases the bending strength of the wafer due to the residual stress, so that it is possible to reduce the laser power to irradiate the wafer without disturbing the splitting of high-quality wafers. There is an effect that it can be processed at high speed.

Hereinafter, with the wafer processing how is the best mode for carrying out the present invention will be described with reference to the drawings. In the present embodiment, for example, a wafer in which a light-emitting device is formed in a plurality of regions formed by a plurality of streets in which a nitride semiconductor layer is formed on the surface of a sapphire substrate and is arranged in a lattice pattern is applied to the wafer. An application example in the case of forming a laser processing groove for applying an external force to a wafer to divide the wafer by irradiating a pulsed laser beam having an absorptive wavelength along the street will be described. The present invention is not limited to the embodiment, and various modifications can be made without departing from the spirit of the present invention.

  FIG. 1 is an external perspective view showing a main part of a laser processing apparatus for carrying out a laser processing step in the wafer processing method of the present embodiment, and FIG. 2 is a schematic block diagram showing a configuration example of processing means. It is. The laser processing apparatus 20 according to the present embodiment includes a holding unit 21 that holds the wafer 1, a pulse laser beam irradiation unit 22 that irradiates the wafer 1 held on the holding unit 21 with a pulsed laser beam, and a holding unit 21. And an image pickup means 23 for picking up an image of the wafer 1 held on the wafer. The holding means 21 sucks and holds the wafer 1 and is rotatably connected to a motor (not shown) in the cylindrical portion 24.

  The holding means 21 is mounted on two stages of sliding blocks 25 and 26. The holding means 21 is provided so as to be movable in the X-axis direction, which is the machining feed direction, by a machining feed means 29 constituted by a ball screw 27, a nut (not shown), a pulse motor 28, etc. with respect to the sliding block 25. The processed wafer 1 is processed and fed relative to the pulse laser beam irradiated by the pulse laser beam irradiation means 22. Similarly, the holding means 21 is provided so as to be movable with respect to the sliding block 26 in the Y-axis direction which is an indexing feed direction by an indexing feed means 32 constituted by a ball screw 30, a nut (not shown), a pulse motor 31 and the like. Then, the mounted wafer 1 is indexed and sent relative to the pulse laser beam irradiated by the pulse laser beam irradiation means 22.

  Further, the pulse laser beam irradiation means 22 basically divides the wafer 1 by applying an external force to the wafer 1 in a subsequent division step by irradiating the wafer 1 with a pulsed laser beam having an absorptive wavelength. This is for carrying out a laser processing step for forming the laser processing groove.

  Such a pulsed laser beam irradiation means 22 includes a casing 35 arranged substantially horizontally, and is movable in the Z-axis direction by a Z-axis moving means (not shown) via the casing 35 with respect to the support block 36. Is provided. As shown in FIG. 2, the pulse laser beam irradiating means 22 includes a pulse laser beam oscillating means 37 and a transmission optical system 38 provided in the casing 35, and a pulse laser beam oscillating means 37 provided at the tip of the casing 35. A condenser 39 for irradiating the oscillated pulse laser beam onto the wafer 1 held by the holding means 21 is provided. The pulse laser beam oscillating means 37 comprises a pulse laser beam oscillator 37a composed of a YAG laser oscillator or a YVO4 laser oscillator, and a Q switch 37b attached thereto. The pulse laser beam oscillator 37a and the Q switch 37b are controlled by a control means to be described later, and output laser output (peak power: a value obtained by dividing the energy of one pulse by the pulse width; the same applies hereinafter) and a repetition frequency of the pulse laser beam. (The total number of pulses repeated per second; the same applies hereinafter). The transmission optical system 38 includes an appropriate optical element such as a beam splitter. The condenser 39 accommodates a condenser lens (not shown) having a known configuration such as a combined lens.

  The imaging means 23 mounted on the tip of the casing 35 images the upper surface of the wafer 1 held on the holding means 21 and the pulse laser beam emitted from the condenser 39 of the pulse laser beam irradiation means 22. This is for detecting a region to be processed. The image pickup means 23 is composed of an image pickup device (CCD) that picks up an image with visible light, and sends the picked-up image signal to a control means described later.

  Moreover, the laser processing apparatus 20 of this Embodiment is equipped with the control means 10, as shown in FIG. The control means 10 is constituted by a microcomputer, and although not particularly shown, a central processing unit (CPU) that performs arithmetic processing according to a control program, a ROM that stores a control program, etc., and a wafer 1 for irradiating a pulsed laser beam. Are provided with a readable / writable RAM or the like for storing setting information about the streets set based on the X and Y coordinate values such as the start point and end point of each street, calculation results, and the like. In addition, when the laser processing step is performed, the control unit 10 sequentially irradiates the wafer 1 with a pulsed laser beam based on a laser processing program to form laser processing grooves continuously, as will be described later. Pulse laser beam irradiation means 22, processing feed means 29, etc. so as to irradiate the subsequent pulse laser beam with an interval that does not cancel the thermal strain formed by the formation of the laser processing groove by irradiation of the preceding pulse laser beam Control the operation of each part.

  Next, the laser processing process of the wafer 1 using such a laser processing apparatus 20 will be described. FIG. 3 is an external perspective view showing the wafer. The wafer 1 is prepared in a state where it is attached to a protective tape 3 made of a synthetic resin sheet such as polyolefin mounted on an annular frame 2 with the surface 1a facing upward. The wafer 1 is a device in which a device is formed in a plurality of regions formed by a plurality of streets in which a functional layer is formed on the surface of a transparent substrate and arranged in a lattice pattern. Specifically, for example, in a plurality of rectangular regions defined by a plurality of first streets 4 and a plurality of second streets 5 formed by forming a nitride semiconductor layer on the surface of a sapphire substrate and arranged in a lattice pattern. A device 6 made of a light emitting diode (LED) is formed. The substrate of the wafer 1 may be quartz glass, lithium tantalate or the like in addition to the sapphire substrate.

  As shown in FIG. 3, the wafer 1 supported on the annular frame 2 via the protective tape 3 places the protective tape 3 side on the holding means 21 of the laser processing apparatus 20 shown in FIG. Then, by operating a suction means (not shown), the wafer 1 is sucked and held on the holding means 21 via the protective tape 3. The annular frame 2 is fixed by a clamp 21a.

  Then, the holding means 21 that sucks and holds the wafer 1 is positioned immediately below the imaging means 23 by the processing feeding means 29, and the alignment work for detecting the region of the wafer 1 to be laser processed by the imaging means 23 and the control means 10 and the first operation. The street detection operation for the second streets 4 and 5 is executed.

  Next, the control means 10 refers to the coordinate values of the machining feed start position and the machining feed end position obtained in the above-described street detection work, and the pulse laser is directed from one end to the other end of each street 4, 5. A laser processing step of forming a laser processing groove by sequentially irradiating a pulse laser beam by the beam irradiation means 22 is performed.

  That is, the holding means 21 is moved so that the processing feed start position, which is one end of the first street 4 to be processed, is positioned directly below the condenser 39 as shown in FIG. At this time, the irradiation point P of the pulse laser beam is matched with the vicinity of the surface 1 a (upper surface) of the wafer 1. Then, while the holding means 21, that is, the wafer 1 is processed and fed in the direction indicated by the arrow X 1 in FIG. When the processing feed end position which is the other end of the first street 4 reaches the irradiation position of the condenser 39 of the pulse laser beam irradiation means 22, the irradiation of the pulse laser beam is stopped and the holding means 21, that is, the wafer. Stop processing feed of No.1.

  After performing the laser processing step on the first street 4 to be processed formed on the wafer 1 as described above, the holding means 21 is moved in the direction indicated by the arrow Y in FIG. And the laser machining process is performed on the next street 4 to be machined.

  When the laser processing steps for all the first streets 4 extending in the predetermined direction of the wafer 1 are completed in this way, the holding means 21, and therefore the wafer 1 held by the holding means 21, is rotated by 90 degrees. By performing the above-described laser processing step in the same manner along the second street 5 formed in the direction orthogonal to the one street 4, all the first and second streets 4, 5 of the wafer 1 are obtained. A laser processing groove is formed along the line.

  As described above, the wafer 1 on which the laser processing step has been performed is transported to a dividing step by a dividing device (not shown) which is the next step. In the dividing step, an external force is applied along the laser processing grooves formed on the first and second streets 4 and 5 of the wafer 1. As a result, the laser-processed groove serves as a starting point of breakage, and the wafer 1 is reliably broken along the first and second streets 4 and 5.

  Here, when the laser processing groove is continuously formed by sequentially irradiating the wafer with the pulse laser beam, conventionally, the laser output of the pulse laser beam to be irradiated is suppressed and the processing feed rate is set to 70 to 120 mm, for example. The depth of the laser processing groove to be formed is increased by reducing the speed to about / s.

  On the other hand, in the present embodiment, while the wafer 1 (holding means 21) is processed and fed at a predetermined processing feed speed in the processing feed direction by the processing feed means 29, the pulse laser beam irradiation means 22 is applied to the wafer 1. When the laser processing grooves are continuously formed by sequentially irradiating the pulse laser beam with the laser beam, the laser output of the pulse laser beam to be irradiated is suppressed and the processing feed rate is increased to, for example, about 300 mm / s, so The wafer 1 can be divided with high quality while enabling laser processing. FIG. 5 is an explanatory diagram schematically and planarly showing a state in which a pulse laser beam having a predetermined laser output is successively and sequentially irradiated onto a street on which the wafer 1 is located. In FIG. 5, in the present embodiment, for example, by optimizing the interval T at which the preceding pulse laser beam B1 is irradiated with the subsequent pulse laser beam B2, the processing feed rate is appropriately adjusted while suppressing the laser output. The speed can be increased.

  This is because when a laser processing groove is formed by ablation processing by irradiating the wafer 1 with a pulsed laser beam, simultaneously, a thermal strain that grows from the bottom accompanying the laser processing groove is formed. This is based on the fact that the present inventors have found that the bending strength of the wafer is lowered by the residual stress of the thermal strain portion when the processing is performed and this thermal strain remains.

  FIG. 6 is a schematic diagram showing the state of the ablation process and the thermal strain formation process in time series by sequentially irradiating the wafer 1 with the pulsed laser beam B while being relatively moved. That is, when the pulse laser beam B is applied to the wafer 1, a laser processing groove 7 is formed in the wafer 1 by ablation processing by generating plasma P. Here, in order to continuously form the laser processing groove 7 along the street, the pulse laser beam B is sequentially irradiated so as to overlap, and the plasma P is also generated so as to overlap. In addition, the generated plasma P becomes gradually smaller as time passes. When the laser processing groove 7 is formed by such ablation processing, the sapphire substrate expands on the bottom side of the laser processing groove 7 with the heating by the plasma P, and then naturally cooled, thereby A thermal strain forming process is performed in which a thermal strain 8 that grows directly from the bottom is formed.

  Here, since the thermal strain 8 is generated by heating → natural cooling, the thermal strain 8 is hardly generated when the natural cooling is hindered. That is, the plasma P overlaps with the pulse laser beam B that is successively irradiated, but if it is too close, the rate of natural cooling after the generation of the plasma P is suppressed and the generation of the thermal strain 8 is hindered. It becomes. Therefore, in the present embodiment, attention is paid to such characteristics of the thermal strain 8, and the laser processing groove 7 is formed so as to grow from the bottom of the laser processing groove 7 by the formation of the laser processing groove 7 by irradiation with the preceding pulsed laser beam B1. The subsequent pulse laser beam B2 is irradiated with an interval T that does not cancel the thermal strain 8 that is applied.

  Hereinafter, the wafer processing method according to the present embodiment will be described with reference to the experimental results while comparing with the conventional method. First, an experimental result of measuring a change in bending strength due to a difference in processing feed rate will be described. Here, as shown in FIG. 7, the bending strength measurement method was performed such that the line of the laser processing groove 7 formed on the wafer 1 and the division position by the division blade 41 were in the same position vertically. Is. At this time, the pressing amount of the split blade 41 was 80 μm, the blade dropping speed was 2000 μm / s, and the width of the receiving blade 42 was 525 μm.

  First, in the first experiment, the wavelength of the pulse laser beam irradiated to the wafer 1 by the pulse laser beam irradiation means 22 is set to 355 nm, the laser output is set to 23 W (peak power), the repetition frequency is set to 200 kHz, and the irradiated spot diameter φ The wafer 1 made of a sapphire substrate having a chip size of 350 μm and a thickness of 100 μm using a protective tape 3 made of a PET base material is irradiated with a pulsed laser beam while changing the processing feed rate. As processing feed rates, in addition to the conventional 120 mm / s, 150 mm / s, and 200 mm / s, experiments were performed at the respective speeds of 300 mm / s, 400 mm / s, 500 mm / s, and 600 mm / s of the present embodiment. It is a thing. The experimental results are shown in FIG. The horizontal axis indicates the interval T between pulses that changes according to the machining feed rate (the same applies to FIGS. 9 and 10). The bending strength was measured within 30 minutes after laser processing. The broken line of the bending strength is obtained by connecting the average values at each speed.

  According to the experimental results shown in FIG. 8, it can be seen that, at low speeds of 120 mm / s and 150 mm / s of the conventional method, the bending strength is lowered as intended because the formed laser processing groove is deep. On the other hand, in the case of 200 mm / s of the conventional method, the depth of the laser-processed groove formed is about 20 μm, and the bending strength remains at 334.8 MPa. Therefore, in the case of the conventional method, when the laser output is 23 W (peak power), it can be said that in reality it is inevitably processed at a low speed of 150 mm / s or less.

  On the other hand, when the processing feed rate is increased to 300 mm / s or more as in the present embodiment, the bending strength is 200 mm / s even when the depth of the laser processing groove 7 to be formed is shallow. It turns out that it has fallen. In particular, when the processing feed rate is 300 mm / s (interval between pulses T = 1.5 μm), the bending strength decreases to 212.6 MPa, which is higher than the bending strength of 280.7 MPa when 120 mm / s. It turns out that it is low. In addition, it can be seen that even when the processing feed rate is increased to 600 mm / s, the bending strength is lower than that in the case of 200 mm / s, and it can be divided.

  In the second experiment, the laser output of the pulse laser beam irradiated to the wafer 1 by the pulse laser beam irradiation means 22 is 62 W (peak power), the repetition frequency is 90 kHz, and the same wafer 1 as in the first experiment. Is irradiated with a pulse laser beam at a different processing feed rate. As processing feed rates, in addition to the conventional 70 mm / s, 85 mm / s, and 110 mm / s, experiments were performed at the respective speeds of 150 mm / s, 180 mm / s, 270 mm / s, and 450 mm / s of the present embodiment. It is a thing. The experimental results are shown in FIG. The bending strength was measured within 30 minutes after laser processing. The broken line of the bending strength is obtained by connecting the average values at each speed.

  According to the experimental results shown in FIG. 9, it can be seen that, at low speeds such as 70 mm / s and 85 mm / s of the conventional method, the bending strength is lowered as intended because the formed laser processing groove is deep. On the other hand, in the case of 110 mm / s in the conventional method, the depth of the laser processed groove to be formed is about 17 μm, and the bending strength remains at about 380 MPa. Therefore, in the case of the conventional method, when the laser output is set to 62 W (peak power), it can be said that it is practically necessary to process at a low speed of 85 mm / s or less.

  On the other hand, when the machining feed rate is increased to 150 mm / s or more as in the present embodiment, the bending strength is 110 mm / s even when the depth of the formed laser machining groove 7 is shallow. It turns out that it has fallen. In particular, when the processing feed rate is 270 mm / s (interval between pulses T = 3.0 μm), the bending strength decreases to about 180 MPa, which is higher than the bending strength (about 300 MPa) at 85 mm / s. It turns out that it is low. In addition, it can be seen that even when the processing feed rate is increased to 450 mm / s, the bending strength is lower than that in the case of the conventional method, and it can be divided.

  According to the results of Experiments 1 and 2, when the laser output (peak power) is large, the interval T between the pulsed laser beams at which the bending strength is lowered becomes long. Therefore, it is estimated that the interval T between the pulsed laser beams with the lowest bending strength shows a linear characteristic as shown in FIG. 10 when the laser output (peak power) is changed.

  As described above, according to the system of the present embodiment, the machining feed rate is increased, and the laser machining groove 7 to be formed is easily cracked despite being shallow. This is accompanied by the laser processing groove 7 by ablation processing by deliberately increasing the processing feed rate so as to irradiate the subsequent pulse laser beam with an interval T that does not cancel the thermal strain 8 that has already been formed. It is presumed that the formed thermal strain 8 portion remains on the bottom side of the laser processed groove 7 as schematically shown by a broken line in FIG. 7 and the bending strength of the wafer 1 is lowered by the residual stress. On the contrary, conventionally, in order to form a laser processing groove having a target depth so as to reduce the bending strength, the processing feed rate is reduced as much as possible. Therefore, the amount of overlap between the pulse laser beams that are successively irradiated increases inevitably, and even if a thermal strain portion is formed by the irradiation of the preceding pulse laser beam, the subsequent pulse laser beam is also irradiated immediately. Since cooling is hindered, thermal distortion is unlikely to occur, or even if it occurs, it is not canceled out and remains. Therefore, the effect of lowering the bending strength due to thermal strain cannot be obtained, and it depends only on the depth of the laser processed groove.

  Thus, according to the present embodiment, when the laser processing groove 7 is continuously formed on the wafer 1 by ablation processing by irradiation with a pulse laser beam, the laser processing groove 7 by irradiation with the preceding pulse laser beam is formed. Since the subsequent pulse laser beam is irradiated with an interval T that does not cancel the thermal strain 8 that is formed along with the formation, even if the laser processing groove 7 formed by ablation is shallow, the laser processing groove 7 8 part of the thermal strain formed along with the residual stress remains, and the bending strength of the wafer 1 is lowered by the residual stress. Therefore, by dividing the wafer 1 with the laser processed groove 7 and the thermal strain 8 as starting points, high quality division is possible. In this way, according to the present embodiment, it is possible to process the wafer 1 at a higher speed without hindering the division of a high-quality wafer while suppressing the laser output to be irradiated. Further, since the depth of the laser processing groove 7 formed by ablation processing can be reduced, damage to the light emitting surface of the device 6 made up of light emitting diodes (LEDs) dividedly formed as a chip can be reduced, and cleavage is performed. The number of surfaces is increased, and the light emission luminance can be improved.

  Further, FIG. 11 shows a result of comparison of oblique cracks at the time of division when the processing feed rate in Experiment 1 is 200 mm / s in the past and 300 mm / s as in the present embodiment. Here, the oblique crack means the horizontal shift amount of the actual crack with respect to the split position by the split blade 41. The number of samples was 30 for each. As a result of comparison, the amount of oblique cracks (average) was 4.54 μm at 200 mm / s, whereas the amount of oblique cracks (average) was 300 mm / s in the present embodiment. It was improved to 2.31 μm, and oblique cracking of the chip could be suppressed. As described above, the thermal strain 8 portion remains at the time of division and the bending strength is reduced, and the thermal strain 8 portion is located immediately below the bottom of the laser processing groove 7 and serves as a trigger at the time of division, thereby increasing straightness. It seems to be because.

  Furthermore, when laser processing was performed with the processing feed rate in Experiment 1 set to 300 mm / s in the present embodiment, changes in the bending strength with time were examined, and the results shown in FIG. 12 were obtained. It is a thing. That is, the bending strength was 212.6 MPa (average value) as described above when measured within 30 minutes after laser processing, but increased to 305.8 MPa (average value) after 48 hours. However, it is harder to break. This is because the laser processing groove 7 formed by ablation is permanently deformed, whereas the residual stress of the thermal strain 8 generated by heating-cooling is released or relaxed over time. It is guessed. Therefore, in this embodiment, after the laser processing step is completed, the splitting step is performed within 24 hours, so that the bending strength reduction effect due to the thermal strain 8 is effectively used.

It is an external appearance perspective view which shows the principal part of the laser processing apparatus for implementing the laser processing process in the wafer processing method of embodiment of this invention. It is a schematic block diagram which shows the structural example of a process means. It is an appearance perspective view showing a wafer. It is a schematic side view which shows a laser processing process. It is explanatory drawing which shows a mode that the pulse laser beam of a predetermined laser output is irradiated sequentially with respect to the street with a wafer sequentially continuously. It is a schematic diagram which shows the state of an ablation process and a heat distortion formation process in time series order. It is explanatory drawing which shows the measuring method of bending strength. It is a graph which shows the relationship between pulse interval-bending strength, and processing depth as a 1st experimental result. It is a graph which shows the relationship between pulse interval-bending strength, and processing depth as a 2nd experimental result. It is a characteristic view which shows the relationship between the pulse interval and peak power that the bending strength becomes the minimum. It is explanatory drawing which shows the comparative example of the experimental result of process feed rate-slanting crack. It is explanatory drawing which shows the experimental result of the time passage characteristic of bending strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wafer 4, 5 Street 6 Device 7 Laser processing groove 8 Thermal strain 10 Control means 20 Laser processing apparatus 21 Holding means 22 Pulse laser beam irradiation means 29 Processing feed means B, B1, B2 Pulse laser beam T Interval

Claims (3)

A pulse having a wavelength that absorbs light from a wafer in which a light emitting device is formed in a plurality of regions formed by a plurality of streets arranged in a lattice form with a nitride semiconductor layer formed on the surface of a sapphire substrate. A wafer processing method for forming a laser processing groove for splitting by applying an external force to a wafer by irradiating a laser beam along the street,
When the laser processing groove is continuously formed by ablation processing by sequentially irradiating the wafer with a pulsed laser beam, the bottom of the laser processing groove is formed along with the formation of the laser processing groove by irradiation with the preceding pulsed laser beam. In order to irradiate the subsequent pulse laser beam with an interval that does not cancel the thermal strain formed to grow from ,
When the laser output is 23 W and the repetition frequency is 200 kHz, the relative movement speed is 300 mm / s or more and 600 mm / s or less,
When the laser output is 62 W and the repetition frequency is 90 kHz, the relative moving speed is 150 mm / s or more and 450 mm / s or less . 2. The wafer processing method according to claim 1 , further comprising a dividing step of dividing the wafer by applying an external force to the wafer after completion of the step of forming the laser processing groove by irradiating a pulsed laser beam. 3. 3. The wafer processing method according to claim 2 , wherein the dividing step is performed within 24 hours after the step of forming the laser processing groove by irradiating a pulse laser beam.

Images