JP2013258365A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer processing method capable of excellently grinding capable of successfully grinding an optical device wafer by forming a grinding promotion layer allowing a grinding wheel to easily bite into a rear surface side of the optical device wafer by laser processing even if the rear surface of the optical device wafer is a mirror surface.SOLUTION: A wafer processing method for dividing an optical device wafer (W) into individual device chips along a division schedule line (402) formed on a surface turns a rear surface (406) of the optical device wafer (W) into a concavo-convex shape by forming a grinding promotion layer (404) by irradiating the rear surface (406) of the optical device wafer (W) with a laser beam, brings a grinding wheel (221) into contact with the rear surface (406) of the optical device wafer (W) in which the grinding promotion layer (404) is formed, and processes the optical device wafer (W) into a prescribed thickness.

Description

  The present invention relates to a method for processing a wafer, and more particularly to a method for processing an optical device wafer such as a sapphire wafer.

  Known optical device wafers include a sapphire substrate or silicon carbide substrate having a gallium nitride compound semiconductor layer laminated on the surface thereof. On the surface of the optical device wafer, a grid-like division planned line is formed, and an optical device is formed in each region partitioned by the division planned line. An optical device wafer is divided into individual device chips along a division line, and is widely used in electrical equipment.

  As a method for dividing the optical device wafer, there has been proposed a dividing method in which a linear modified layer is formed by laser processing, and the modified layer having reduced strength is used as a starting point (for example, see Patent Document 1). . In the dividing method described in Patent Document 1, after the optical device wafer is thinned to a predetermined thickness by backside grinding, a laser beam is irradiated with the focusing point inside the wafer, and a modified layer along the planned dividing line is formed. It is formed. Subsequently, when an external force is applied to the modified layer of the optical device wafer, a crack occurs in the thickness direction starting from the modified layer, and the optical device wafer is divided into individual device chips.

Japanese Patent No. 3762409

  By the way, the sapphire substrate and silicon carbide substrate which are optical device wafers have high hardness, and the back surface is formed in a mirror surface. When grinding a wafer having a mirror back surface, the optical device wafer splitting method described in Patent Document 1 has a problem that the grinding wheel of the grinding wheel does not bite into the back surface of the wafer and the back surface is easily burnt. It was.

  This invention is made | formed in view of this point, and it aims at providing the processing method of the wafer which can grind favorably even if the back surface of an optical device wafer is a mirror surface.

  The wafer processing method of the present invention is a wafer processing method in which the back surface of an optical device wafer in which a plurality of optical devices are formed by laminating an optical semiconductor layer on the surface of a sapphire substrate is ground and thinned to a predetermined thickness. Then, after carrying out the sticking step of sticking an adhesive sheet to the surface of the optical device wafer and the sticking step, the adhesive sheet side is held by a holding means, and the back surface of the optical device wafer is irradiated with a laser beam. A grinding promoting layer forming step for forming a grinding promoting layer in the vicinity of the back surface, and a grinding step for bringing a grinding wheel into contact with the back surface of the optical device wafer on which the grinding promoting layer is formed and thinning to a predetermined thickness. Composed.

  According to this configuration, the back surface of the optical device wafer is irradiated with the laser beam, and the grinding promoting layer is formed in the vicinity of the back surface, whereby the back surface is formed in an uneven shape (rough surface). This grinding acceleration layer makes it easy for the grinding wheel of the grinding wheel to bite into the back surface of the optical device wafer in the grinding process, and it is possible to satisfactorily grind even if the optical device wafer has a high hardness and a mirror surface.

  In the grinding acceleration layer forming step of the wafer processing method of the present invention, the grinding acceleration layer is formed at a position corresponding to a division planned line that partitions the plurality of optical devices on the back surface.

  In the grinding acceleration layer forming step of the wafer processing method of the present invention, a laser beam having energy that does not affect the optical semiconductor layer on the surface side is irradiated.

  In the wafer processing method of the present invention, the back surface of the optical device wafer is obtained by holding the pressure-sensitive adhesive sheet side by a holding unit along a planned division line that partitions the plurality of optical devices before the grinding promoting layer forming step. A laser beam having a wavelength that is transmissive to the optical device wafer is irradiated along the planned division line, and a modified layer serving as a division starting point having a predetermined thickness is formed from the surface along the planned division line. In the grinding step, the optical device wafer is ground from the back surface of the optical device wafer by a grinding means and thinned to a finished thickness, and the optical device wafer is started from the modified layer by a grinding operation. Divide along the division line.

  In the wafer processing method of the present invention, after performing the grinding step, a laser beam is irradiated from the ground back side to form a groove serving as a division starting point along a division planned line that partitions the plurality of optical devices. And a dividing step of dividing the optical device wafer along the planned dividing line from the groove by applying an external force after the groove forming step.

  According to the present invention, it is possible to perform good grinding even when the back surface of the optical device wafer is a mirror surface by forming a grinding acceleration layer that facilitates the grinding wheel to bite into the back surface side of the optical device wafer by laser processing. it can.

It is a perspective view which shows an example of the laser processing apparatus which concerns on 1st Embodiment. It is a perspective view which shows an example of the grinding device which concerns on 1st Embodiment. It is explanatory drawing of the flow of the processing method of the wafer which concerns on 1st Embodiment. It is a modification of the grinding | polishing acceleration | stimulation layer formation process which concerns on 1st Embodiment. It is explanatory drawing of the flow of the processing method of the wafer which concerns on 2nd Embodiment. It is a modification of the grinding promotion layer formation process which concerns on 2nd Embodiment.

  A wafer processing method using stealth dicing according to the first embodiment will be described below with reference to the accompanying drawings. The wafer processing method according to the first embodiment is performed through a sticking process, a modified layer forming process using a laser processing apparatus, a grinding promoting layer forming process, and a grinding process using a grinding apparatus. In the attaching step, an adhesive sheet is attached to the surface of the optical device wafer on which the optical semiconductor layer is formed. In the modified layer forming step, a modified layer is continuously formed along the planned division line inside the optical device wafer.

  In the grinding promotion layer forming step, a grinding promotion layer is formed in the vicinity of the back surface of the optical device wafer along the planned division line. In this grinding layer forming step, cracks and the like are generated in the vicinity of the back surface by laser processing, so that the back surface of the optical device wafer is formed in an uneven shape (rough surface). In the grinding process, the optical device wafer is thinned so that the modified layer is divided into individual device chips using the division starting point. In this grinding step, the grinding wheel bites into the concavo-convex back surface of the optical device wafer, so that even if it is an optical device wafer having a high hardness and a back surface, the surface is satisfactorily ground. Hereinafter, the details of the processing method according to the present embodiment will be described.

  With reference to FIG. 1, a laser processing apparatus for forming a modified layer inside an optical device wafer and forming a grinding acceleration layer in the vicinity of the back surface of the optical device wafer will be described. FIG. 1 is a perspective view of the laser processing apparatus according to the present embodiment. Note that the laser processing apparatus according to the present embodiment is not limited to the configuration shown in FIG. The laser processing apparatus may have any configuration as long as the modified layer and the grinding acceleration layer can be formed on the optical device wafer.

  As shown in FIG. 1, a laser processing apparatus 100 processes an optical device wafer W by relatively moving a laser processing unit 102 that irradiates a laser beam and a chuck table (holding means) 103 that holds the optical device wafer W. It is configured as follows. The optical device wafer W is formed in a substantially disk shape, and an optical semiconductor layer 401 (see FIG. 3) is laminated on the surface of the sapphire substrate. The optical device wafer W is divided into a plurality of regions by division lines 402 (see FIG. 3) arranged in a lattice pattern, and an optical device is formed in each of the divided regions.

The optical device wafer W is attached to an adhesive sheet 412 stretched on the ring frame 411 with the upper surface on which the optical semiconductor layer 401 is formed facing downward. The adhesive sheet 412 is attached to the optical device wafer W by, for example, a known mounter device not shown. The optical device wafer W is not limited to a sapphire wafer in which an optical semiconductor layer 401 is laminated on a sapphire (Al ₂ O ₃ ) substrate, but is applied to an inorganic material substrate such as a gallium arsenide (GaAs) substrate or a silicon carbide (SiC) substrate. A semiconductor layer 401 may be stacked.

  The laser processing apparatus 100 has a rectangular parallelepiped base 101. On the upper surface of the base 101, there is provided a chuck table moving mechanism 104 that feeds the chuck table 103 in the X-axis direction and indexes it in the Y-axis direction. A standing wall 111 is erected on the rear side of the chuck table moving mechanism 104. An arm portion 112 projects from the front surface of the standing wall portion 111, and a laser processing unit 102 is supported on the arm portion 112 so as to face the chuck table 103.

  The chuck table moving mechanism 104 includes a pair of guide rails 115 arranged on the upper surface of the base 101 and parallel to the X-axis direction, and a motor-driven X-axis table 116 slidably installed on the pair of guide rails 115. Have. The chuck table moving mechanism 104 includes a pair of guide rails 117 arranged on the top surface of the X-axis table 116 and parallel to the Y-axis direction, and a motor-driven Y-axis table 118 slidably installed on the pair of guide rails 117. And have.

  A chuck table 103 is provided on the Y-axis table 118. Note that nut portions (not shown) are formed on the back surfaces of the X-axis table 116 and the Y-axis table 118, and ball screws 121 and 122 are screwed to these nut portions. The drive motors 123 and 124 connected to one end portions of the ball screws 121 and 122 are rotationally driven, whereby the chuck table 103 is moved along the guide rails 115 and 117 in the X-axis direction and the Y-axis direction.

  The chuck table 103 is formed in a disc shape, and is rotatably provided on the upper surface of the Y-axis table 118 via the θ table 125. On the upper surface of the chuck table 103, an adsorption surface is formed of a porous ceramic material. Around the chuck table 103, four clamp portions 126 are provided via a pair of support arms. The four clamp portions 126 are driven by the air actuator, whereby the ring frame 411 around the optical device wafer W is clamped and fixed from four directions.

  The laser processing unit 102 has a processing head 127 provided at the tip of the arm portion 112. An optical system of the laser processing unit 102 is provided in the arm portion 112 and the processing head 127. The processing head 127 condenses a laser beam oscillated from an oscillator (not shown) by a condensing lens, and laser-processes the optical device wafer W held on the chuck table 103. In this case, the laser beam has a wavelength that is transmissive to the optical device wafer W, and is adjusted so as to be condensed inside the optical device wafer W in the optical system.

  By this laser beam irradiation, a modified layer 403 (see FIG. 3B) serving as a division starting point is formed inside the optical device wafer W. The modified layer 403 is a region where the internal density, refractive index, mechanical strength, and other physical characteristics of the optical device wafer W are different from the surroundings due to the irradiation of the laser beam, and the strength is lower than the surroundings. . The modified layer 403 is, for example, a melt treatment region, a crack region, a dielectric breakdown region, or a refractive index change region, and may be a region in which these are mixed.

  Further, a grinding acceleration layer 404 (see FIG. 3C) that improves the biting of the grinding wheel against the back surface is formed near the back surface of the optical device wafer W by the irradiation of the laser beam. The grinding promoting layer 404 in the present embodiment is formed by modifying the vicinity of the back surface of the optical device wafer W by irradiation with a laser beam, similarly to the modifying layer 403. By modifying the vicinity of the back surface of the optical device wafer W, a crack or the like is generated on the back surface of the optical device wafer W, and the back surface of the optical device wafer W is formed in an uneven shape.

  In the laser processing apparatus 100 configured as described above, the exit of the processing head 127 is aligned with the planned division line 402 of the optical device wafer W. The alignment of the processing head 127 is performed by imaging the pattern surface formed on the front surface from the back surface side through the optical device wafer W by an infrared camera (not shown). Then, the chuck table 103 is moved in a state where a laser beam is irradiated from the processing head 127 to the inside of the optical device wafer W, so that the modified layer 403 along the planned division line 402 is formed. Thereafter, the chuck table 103 is moved in a state where a laser beam is irradiated from the processing head 127 to the vicinity of the back surface of the optical device wafer W, whereby the grinding promoting layer 404 along the division line 402 is formed.

  A grinding apparatus for grinding an optical device wafer will be described with reference to FIG. FIG. 2 is a perspective view of the grinding apparatus according to the present embodiment. Note that the grinding apparatus according to the present embodiment is not limited to the configuration shown in FIG. The grinding apparatus may have any configuration as long as the optical device wafer can be divided from the modified layer as a starting point by grinding the optical device wafer.

  As shown in FIG. 2, the grinding apparatus 200 is configured to grind the optical device wafer W by relatively rotating the chuck table 203 on which the optical device wafer W is held and the grinding wheel 221 of the grinding unit 202. ing. The grinding apparatus 200 has a base 201 having a substantially rectangular parallelepiped shape. A turntable 205 on which a pair of chuck tables 203 (only one is shown) is provided on the upper surface of the base 201. A standing wall portion 211 that supports the grinding unit 202 is erected on the rear side of the turntable 205.

  The turntable 205 is formed in the shape of a large-diameter disk, and a pair of chuck tables 203 are arranged on the upper surface at point-symmetrical positions around the rotation axis. Further, the turntable 205 is intermittently rotated at an interval of 180 degrees in the arrow D1 direction by a rotation driving mechanism (not shown). For this reason, the pair of chuck tables 203 are moved between a repositioning position where the optical device wafer W is carried in and out and a grinding position facing the grinding unit 202.

  The chuck table 203 is formed in a small-diameter disk shape, and is rotatably provided on the upper surface of the turntable 205. On the upper surface of the chuck table 203, an adsorption surface is formed of a porous ceramic material. An annular magnet 212 is provided around the chuck table 203. Since the ring frame 411 around the optical device wafer W is made of a magnetic material, it is attracted and fixed by the annular magnet 212.

  A height gauge 213 is provided on the upper surface of the base 201 in the vicinity of the grinding position of the turntable 205. The height gauge 213 has one contact 214 that contacts the upper surface of the optical device wafer W and measures the thickness. In the height gauge 213, the surface position of the chuck table 203 is measured in advance by the contact 214, and the thickness of the optical device wafer W is measured based on the surface position. A measurement value obtained by the height gauge 213 is input to a control unit (not shown) via a transmission path.

  The standing wall portion 211 is provided with a grinding unit moving mechanism 204 that moves the grinding unit 202 up and down. The grinding unit moving mechanism 204 includes a pair of guide rails 215 arranged in front of the standing wall 211 and parallel to the Z-axis direction, and a motor-driven Z-axis table 216 slidably installed on the pair of guide rails 215. Have. A grinding unit 202 is supported on the front surface of the Z-axis table 216. On the back surface of the Z-axis table 216, a nut portion protruding rearward through the opening 217 of the standing wall portion 211 is provided.

  A ball screw provided on the back surface of the standing wall 211 is screwed into the nut portion of the Z-axis table 216. Then, the drive motor 218 connected to one end of the ball screw is driven to rotate, whereby the grinding unit 202 is moved along the guide rail 215 in the Z-axis direction.

  The grinding unit 202 is provided with a mount 223 at the lower end of a cylindrical spindle 222. The mount 223 is mounted with a grinding wheel 221 to which a plurality of grinding wheels 224 are fixed. The grinding wheel 224 is made of, for example, a diamond wheel in which diamond abrasive grains are hardened with a binder such as a metal bond or a resin bond. The grinding wheel 224 is rotated around the Z axis at a high speed as the spindle 222 is driven. And the optical device wafer W is ground from the back surface side by making the grinding wheel 221 and the optical device wafer W rotationally contact in a parallel state.

  At this time, a grinding promoting layer 404 is formed in the vicinity of the back surface of the optical device wafer W (see FIG. 3D), and the back surface of the optical device wafer W is uneven due to cracks or the like. For this reason, the grinding wheel 224 easily bites into the back surface of the optical device wafer W, and even if the optical device wafer W has a high hardness and a mirror surface on the back surface like a sapphire wafer, it can be ground well.

  Further, in the grinding apparatus 200 configured in this way, the thickness of the optical device wafer W is measured in real time by the height gauge 213. The feed amount of the grinding unit 202 is controlled so that the measurement result of the height gauge 213 approaches the final finished thickness of the optical device wafer W that is the target thickness. Then, after grinding to the vicinity of the finished thickness, a grinding load is applied from the grinding wheel 221 to the modified layer 403 formed inside the optical device wafer W, and the optical device wafer starts from the modified layer 403. W is divided into individual device chips C along the division line 402 (see FIG. 3E).

  With reference to FIG. 3, the flow of the wafer processing method according to the first embodiment will be described. Note that the steps shown in FIGS. 3A to 3E are merely examples, and the present invention is not limited to this configuration.

  First, the sticking process shown in FIG. 3A is performed. In the attaching step, the adhesive sheet 412 is attached to the surface 405 on which the optical semiconductor layer 401 of the optical device wafer W is formed. In addition, the sticking process may be performed manually by an operator or may be performed by a not-shown sticking device.

  Next, the modified layer forming step shown in FIG. 3B is performed. In the modified layer forming step, the adhesive sheet 412 side of the optical device wafer W is held by the chuck table 103. Further, the exit of the processing head 127 is positioned on the division planned line 402 of the optical device wafer W, and the condensing point of the laser beam is adjusted inside the optical device wafer W. Then, the chuck table 103 holding the optical device wafer W is moved in the X-axis direction and the Y-axis direction while adjusting the condensing point of the laser beam, and thus along the planned division line 402 inside the optical device wafer W. The modified layer 403 having a predetermined thickness is formed.

  In this case, first, the condensing point is adjusted in the vicinity of the surface 405 of the optical device wafer W, and laser processing is performed so that the lower end portion of the modified layer 403 is formed along all the division lines 402. The modified layer 403 having a predetermined thickness is formed inside the optical device wafer W by performing laser processing each time the height of the condensing point is moved up. This laser processing is repeated until the modified layer 403 exceeds the final finished thickness L (height L from the surface 405) of the optical device wafer W. In this way, a division starting point along the division line 402 is formed inside the optical device wafer W.

  Next, the grinding promotion layer forming step shown in FIG. 3C is performed. The grinding promoting layer forming step is continuously performed without changing the processing conditions of the laser processing from the grinding promoting layer forming step. In the grinding promoting layer forming step, the condensing point of the laser beam is adjusted near the back surface 406 of the optical device wafer W. Then, similarly to the modified layer forming step, the vicinity of the back surface 406 of the optical device wafer W is modified and the grinding promoting layer 404 is formed by irradiating a laser beam along the division line 402. When the vicinity of the back surface 406 of the optical device wafer W is modified, a crack or the like is generated, and the back surface 406 is formed in an uneven shape.

  Next, the grinding process shown in FIG. 3D is performed. In the grinding process, the adhesive sheet 412 side of the optical device wafer W is held by the chuck table 203. The grinding wheel 224 is moved closer to the chuck table 203 while rotating, and the grinding wheel 224 is pressed against the back surface 406 of the optical device wafer W to perform grinding. In this case, since the back surface 406 of the optical device wafer W is formed in a concavo-convex shape, the grinding wheel 224 can easily bite against the back surface 406 of the optical device wafer W. Therefore, grinding can be performed without strongly pressing the grinding wheel 224 against the optical device wafer W, and surface burn can also be prevented.

  During grinding, the thickness of the optical device wafer W is measured in real time by the height gauge 213 (see FIG. 2). As shown in FIG. 3E, when the optical device wafer W approaches the finished thickness L by grinding, a grinding load from the grinding wheel 221 is applied to each modified layer 403. The optical device wafer W is cracked along the scheduled division line 402 starting from the modified layer 403, and the optical device wafer W is divided into individual device chips C. Then, when the optical device wafer W is ground to the finished thickness L, the grinding process is stopped. In this way, the optical device wafer W is divided into individual device chips C while being thinned to a desired finish thickness L.

  As described above, according to the wafer processing method according to the first embodiment, the grinding promoting layer 404 is formed by laser processing in the vicinity of the back surface 406 of the optical device wafer W, so that the back surface 406 has an uneven shape ( (Rough surface). The grinding promoting layer 404 makes it easy for the grinding wheel 224 to bite into the back surface 406 of the optical device wafer W, so that the grinding can be satisfactorily ground even when the optical device wafer W has a high hardness and a mirror surface. In addition, since the grinding promoting layer forming step can be performed following the modified layer forming step in the same laser processing apparatus 100, productivity can be improved. Furthermore, the back surface 406 of the optical device wafer W can be easily formed in a concavo-convex shape in a short time compared with the case of using a cutting blade.

  By the way, in the stealth dicing process of the first embodiment, a laser beam is irradiated with a wavelength having transparency to the optical device wafer W. For this reason, when the laser beam deviates from the planned dividing line 402, the optical semiconductor layer 401 on the surface side of the optical device wafer W may be damaged. Therefore, in the grinding acceleration layer forming process of the first embodiment described above, the laser beam is irradiated along the division line 402. Thereby, even if it irradiates with a laser beam on the same process conditions as a modified layer formation process, the optical semiconductor layer 401 is not damaged.

  As shown in FIG. 4, it is possible to form the grinding promoting layer 404 over the entire back surface 406 of the optical device wafer W by suppressing the energy of the laser beam. In this case, the output of the laser beam in the grinding promoting layer forming step is made lower than the output of the laser beam in the modified layer forming step. With this configuration, the entire back surface 406 of the optical device wafer W is formed in an irregular shape, and the biting of the grinding wheel 224 against the back surface 406 of the optical device wafer W can be further improved. The details of the stealth dicing processing conditions according to the first embodiment shown in FIG. 3 and the modification shown in FIG. 4 will be described later.

  Next, a wafer processing method by ablation processing according to the second embodiment will be described. The laser processing apparatus according to the second embodiment is different from the laser processing apparatus according to the first embodiment that performs stealth dicing processing in that ablation processing is performed. That is, the laser processing apparatus according to the second embodiment irradiates the optical device wafer with a laser beam having an absorptive wavelength, and focuses the light on the processing surface (back surface) of the optical device wafer in the optical system. It has been adjusted. Thereby, ablation is caused on the processed surface of the optical device wafer, and the optical device wafer is partially etched.

  Here, ablation means that when the irradiation intensity of the laser beam exceeds a predetermined processing threshold, it is converted into electronic, thermal, photochemical and mechanical energy on the fixed surface, and as a result, neutral atoms, molecules, positive and negative A phenomenon in which ions, radicals, clusters, electrons, and light are explosively emitted and the fixed surface is edged. In addition, the laser processing apparatus and the grinding apparatus according to the second embodiment have substantially the same configuration as the laser processing apparatus and the grinding apparatus according to the first embodiment. For this reason, in 2nd Embodiment, description is abbreviate | omitted about description of the main apparatus structure.

  The wafer processing method according to the second embodiment is performed through an attaching process, a grinding promoting layer forming process using a laser processing apparatus, a grinding process using a grinding apparatus, a groove forming process using a laser processing apparatus, and a dividing process using an expansion apparatus. Is done. In the attaching step, an adhesive sheet is attached to the surface of the optical device wafer on which the optical semiconductor layer is formed. In the grinding layer promoting step, a grinding promoting layer is formed in the vicinity of the back surface of the optical device wafer along the line to be divided. In this grinding promoting layer forming step, a recess is formed in the vicinity of the back surface by ablation, and the back surface of the optical device wafer is formed in an uneven shape (rough surface).

  In the grinding process, the optical device wafer is ground to a predetermined thickness. In this grinding step, the grinding wheel bites into the concavo-convex back surface of the optical device wafer, so that even if it is an optical device wafer having a high hardness and a back surface, the surface is satisfactorily ground. In the groove forming step, a division groove (groove) along the division line is formed on the back surface of the optical device wafer by ablation. In the dividing step, an external force is applied to the optical device wafer, and the wafer is divided into individual device chips starting from the modified layer. Hereinafter, the details of the processing method according to the present embodiment will be described.

  With reference to FIG. 5, the flow of the wafer processing method according to the second embodiment will be described. Note that the steps shown in FIGS. 5A to 5E are merely examples, and the present invention is not limited to this configuration. In FIG. 5, portions having the same names as those in the first embodiment will be described using the same reference numerals. Moreover, although it was set as the structure which uses the expansion device which divides | segments an optical device wafer by expansion | extension of an adhesive sheet, it is also possible to use the braking apparatus which divides | segments an optical device wafer with a press blade. In the dividing step, any apparatus may be used as long as it is an apparatus that applies an external force to the optical device wafer and divides the wafer.

  First, the sticking process shown in FIG. 5A is performed. In the attaching step, the adhesive sheet 412 is attached to the surface 405 on which the optical semiconductor layer 401 of the optical device wafer W is formed. In addition, the sticking process may be performed manually by an operator or may be performed by a not-shown sticking device.

  Next, the grinding promotion layer forming step shown in FIG. 5B is performed. In the grinding promotion layer forming step, the adhesive sheet 412 side of the optical device wafer W is held by the chuck table 103. In addition, the exit of the processing head 127 is positioned on the planned division line 402 of the optical device wafer W, and the condensing point of the laser beam is adjusted near the back surface 406 of the optical device wafer W. At this time, the laser beam is set to a wavelength having an absorptivity with respect to the optical device wafer W.

  Then, the chuck table 103 holding the optical device wafer W is moved in the X-axis direction and the Y-axis direction, so that the vicinity of the back surface 406 of the optical device wafer W is etched to form the grinding promoting layer 408. When the vicinity of the back surface 406 of the optical device wafer W is etched, the back surface 406 is formed in a concavo-convex shape due to the etching recess. That is, the grinding promoting layer 408 in the second embodiment is a recess formed by etching the back surface 406 of the optical device wafer W by ablation.

  Next, the grinding step shown in FIG. 5C is performed. In the grinding process, the adhesive sheet 412 side of the optical device wafer W is held by the chuck table 203. The grinding wheel 224 is moved closer to the chuck table 203 while rotating, and the grinding wheel 224 is pressed against the back surface 406 of the optical device wafer W to perform grinding. In this case, since the back surface 406 of the optical device wafer W is formed in a concavo-convex shape, the grinding wheel 224 can easily bite against the back surface 406 of the optical device wafer W. Therefore, grinding can be performed without strongly pressing the grinding wheel 224 against the optical device wafer W, and surface burn can be prevented. During the grinding process, the thickness of the optical device wafer W is measured in real time by the height gauge 213 (see FIG. 2), and the optical device wafer W is ground until the finished thickness L is reached.

  Next, the groove forming step shown in FIG. 5D is performed. In the groove forming step, the adhesive sheet 412 side of the optical device wafer W is held by the chuck table 103. In addition, the exit of the processing head 127 is positioned at the division line 402 of the optical device wafer W, and the condensing point of the laser beam is adjusted to the back surface 406 of the optical device wafer W. Then, the chuck table 103 holding the optical device wafer W while irradiating the laser beam is moved in the X-axis direction and the Y-axis direction, so that the division grooves 409 along the division line 402 are formed. The dividing groove 409 is formed to a predetermined depth that becomes the dividing starting point of the optical device wafer W.

  Next, the dividing step shown in FIG. 5E is performed. The expansion device 300 used in the dividing step is configured to expand the adhesive sheet 412 by moving the annular table 301 on which the ring frame 411 is supported relative to the expansion drum 302 up and down. In the dividing step, the ring frame 411 is held by the clamp unit 305 on the annular table 301 with the adhesive sheet 412 side of the optical device wafer W facing downward. At this time, the expansion drum 302 is positioned between the optical device wafer W and the ring frame 411, and the adhesive sheet 412 is brought into contact with the upper end portion of the expansion drum 302.

  Then, when the annular table 301 holding the ring frame 411 is lowered, the expansion drum 302 is raised relative to the annular table 301. By the relative rise of the expansion drum 302, the adhesive sheet 412 pushed up at the upper end of the expansion drum 302 is expanded in the radial direction. When the adhesive sheet 412 is expanded, an external force is applied to the dividing groove 409 of the optical device wafer W. The optical device wafer W is divided into individual device chips C using a dividing groove 409 formed along the planned dividing line 402 as a starting point.

  As described above, according to the wafer processing method according to the second embodiment, similarly to the first embodiment, even when the optical device wafer W has a high hardness and a back surface having a mirror surface, it is ground well. be able to. Further, the grinding promoting layer forming step and the groove forming step can be performed in the same laser processing apparatus 100, and the productivity can be improved. Furthermore, the back surface of the optical device wafer W can be easily formed in a concavo-convex shape in a short time compared with the case of using a cutting blade.

  By the way, in the ablation processing of the second embodiment, the optical device wafer W is irradiated with a Labor ray at a wavelength having absorptivity. For this reason, even if the laser beam is irradiated to a position off the planned division line 402, the optical semiconductor layer 401 on the surface side of the optical device wafer W is not greatly affected. For this reason, as shown in FIG. 6, it is also possible to form a grinding promoting layer 408 over the entire back surface 406 of the optical device wafer W. With this configuration, the entire back surface 406 of the optical device wafer W is formed in an irregular shape, and the biting of the grinding wheel 224 against the back surface 406 of the optical device wafer W can be further improved. The details of the ablation processing conditions according to the second embodiment and the modification shown in FIG. 6 will be described later.

(Example)
Here, the wafer processing method according to the first and second embodiments described above and the laser processing in the modified example of each embodiment were performed under the processing conditions as shown in Table 1. Here, as an optical device wafer, a 6-inch diameter and 1 mm-thick sapphire substrate having an epi layer (optical semiconductor layer) stacked thereon is used, and is thinned to 100 μm by grinding.

  In the wafer processing method according to the first embodiment, the modified layer and the grinding accelerating layer were formed along the planned division line using the processing conditions at the time of division of the stealth dicing processing shown in Table 1. In the modified example of the wafer processing method according to the first embodiment, the modified layer is formed along the planned dividing line using the processing conditions at the time of the stealth dicing processing shown in Table 1, and the stealth shown in Table 1 is used. A division promoting layer was formed over the entire back surface of the optical device wafer by using the processing conditions when forming irregularities in the dicing process. The processing conditions at the time of forming the irregularities in the stealth dicing process can suppress the output of the laser beam and increase the feed rate as compared with the processing conditions at the time of division. The modified layer was formed inside the optical device wafer, and the division promoting layer was formed at a position of 30 μm from the back surface of the optical device wafer.

  In the wafer processing method according to the second embodiment, the grinding promoting layer and the division groove were formed along the division line by using the processing conditions at the time of division of the ablation processing shown in Table 1. In a modification of the wafer processing method according to the second embodiment, a division promoting layer is formed over the entire back surface of the optical device wafer using the processing conditions for forming the irregularities of the ablation processing shown in Table 1. Using the processing conditions at the time of the ablation division, a division groove was formed along the division planned line. The processing conditions at the time of forming irregularities in the ablation processing are higher than the processing conditions at the time of division.

  In any of the wafer processing methods according to the first and second embodiments and the modifications of each embodiment, the sapphire substrate can be satisfactorily ground in the grinding process and can be appropriately divided into individual device chips. did it.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  For example, in each of the above-described embodiments, the modified layer 403 is continuously formed along the planned dividing line 402, but the present invention is not limited to this configuration. If the optical device wafer W can be divided along the division line 402, the modified layer 403 may be intermittently formed along the division line 402. Similarly, the grinding promoting layers 404 and 408 may be formed continuously or intermittently.

  In this embodiment, the modified layer forming step and the division promoting layer forming step are performed by a laser processing apparatus and the grinding step is performed by a grinding apparatus. However, some or all of the steps are performed by one apparatus. May be.

  As described above, the present invention has an effect that the optical device wafer can be satisfactorily ground even if the back surface of the optical device wafer is a mirror surface, and is particularly useful for a method for dividing an optical device wafer such as a sapphire wafer. is there.

DESCRIPTION OF SYMBOLS 100 Laser processing apparatus 102 Laser processing unit 103 Chuck table (holding means)
200 grinding apparatus 202 grinding unit (grinding means)
221 Grinding wheel 222 Spindle 224 Grinding wheel 300 Expansion device 401 Optical semiconductor layer 402 Line to be divided 403 Modified layer 404, 408 Grinding acceleration layer 405 Front surface 406 Back surface 409 Divided groove (groove)
412 Adhesive sheet W Optical device wafer C Device chip

Claims (5)

A method of processing a wafer by grinding a back surface of an optical device wafer in which a plurality of optical devices are formed by laminating an optical semiconductor layer on a surface of a sapphire substrate, and thinning the wafer to a predetermined thickness,
An attaching step of attaching an adhesive sheet to the surface of the optical device wafer;
After carrying out the sticking step, holding the adhesive sheet side with a holding means, irradiating the back surface of the optical device wafer with a laser beam to form a grinding promotion layer in the vicinity of the back surface,
A grinding step in which a grinding wheel is brought into contact with the back surface of the optical device wafer on which the grinding acceleration layer is formed and thinned to a predetermined thickness; and
A wafer processing method comprising:   2. The wafer processing method according to claim 1, wherein, in the grinding acceleration layer forming step, the grinding acceleration layer is formed at a position corresponding to a division planned line that partitions the plurality of optical devices on the back surface. .   2. The wafer processing method according to claim 1, wherein, in the grinding promoting layer forming step, a laser beam having an energy that does not affect the optical semiconductor layer on the surface side is irradiated. Before the grinding promotion layer forming step, the adhesive sheet side is held by a holding unit along a planned division line that divides the plurality of optical devices, and the optical device wafer is made transparent from the back surface of the optical device wafer. Performing a modified layer forming step of irradiating a laser beam having a wavelength having along the planned division line to form a modified layer serving as a division starting point of a predetermined thickness from the surface along the planned division line,
In the grinding process, the optical device wafer is ground from the back surface of the optical device wafer by a grinding means to be thinned to a finished thickness, and the optical device wafer is divided along the scheduled division line from the modified layer as a starting point by a grinding operation. The wafer processing method according to claim 1, wherein: After performing the grinding step, a groove forming step of forming a groove serving as a division starting point along a division planned line that divides the plurality of optical devices by irradiating a laser beam from the ground back side;
After the groove forming step, a dividing step of applying an external force to divide the optical device wafer along the planned dividing line from the groove as a starting point;
The wafer processing method according to claim 1, comprising:

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