JP2014225562A - Optical device wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device wafer processing method which can successfully divide an optical device wafer composed of a single crystal substrate along a division scheduled line into individual devices after formation of a reflection film on a rear face even when a thickness of the optical device wafer is thick.SOLUTION: An optical device wafer processing method comprises: a numerical aperture setting process of setting a numerical aperture (NA) of a condenser lens within a range of 0.05-0.2 obtained by division of the numerical aperture of a condenser lens 422a for condensing pulse laser beams LB by a refraction index (N) of a single crystal substrate 2; a light condensing point positioning process of positioning a light condensing point of laser beams from a rear face side of a substrate to a position near a surface side; a shield tunnel formation process of forming a shield tunnel 24 along a division scheduled line by growing fine pores 241 and amorphous materials 242 for shielding the fine pores on the side where the laser beams are irradiated and incident from the condensing point positioned near the surface side; a reflection film formation process of forming a reflection film on the rear face of the substrate; and a division process of dividing the substrate into individual optical devices by applying an external force.

Description

  The present invention relates to an optical device wafer in which a light emitting layer is formed on the surface of a single crystal substrate such as sapphire and an optical device is formed in a plurality of regions partitioned by a plurality of grid-like division lines. The present invention relates to a method of processing an optical device wafer that is divided into individual optical devices.

  In the optical device manufacturing process, a light emitting diode is formed in a plurality of regions partitioned by a plurality of streets formed by laminating a light emitting layer made of a gallium nitride compound semiconductor on the surface of a sapphire substrate having a substantially disc shape, An optical device such as a laser diode is formed to constitute an optical device wafer. Then, the optical device wafer is cut along the streets to divide the region where the optical device is formed to manufacture individual optical devices.

  The above-mentioned cutting along the street of the optical device wafer is usually performed by a cutting device called a dicer. The cutting apparatus includes a chuck table for holding a workpiece, a cutting means for cutting the workpiece held on the chuck table, and a cutting feed means for relatively moving the chuck table and the cutting means. It has. The cutting means includes a rotary spindle, a cutting blade mounted on the spindle, and a drive mechanism that rotationally drives the rotary spindle. The cutting blade is composed of a disk-shaped base and an annular cutting edge mounted on the outer periphery of the side surface of the base. The cutting edge is fixed to the base by electroforming, for example, diamond abrasive grains having a particle size of about 3 μm. It is formed to a thickness of about 20 μm.

  However, since the sapphire substrate constituting the optical device wafer has a high Mohs hardness, cutting with the cutting blade is not always easy. Furthermore, since the cutting blade has a thickness of about 20 μm, the street that partitions the device needs to have a width of about 50 μm. For this reason, the area ratio which a street occupies becomes high, and there exists a problem that productivity is bad.

  In order to solve the above-mentioned problems, as a method of dividing the optical device wafer along the street, laser processing that becomes the starting point of breakage by irradiating the wafer with a pulsed laser beam having a wavelength that absorbs the wafer. There has been proposed a method of cleaving by forming a groove and applying an external force along the street where the laser-processed groove that is the starting point of the fracture is formed (see, for example, Patent Document 1).

  However, when laser processing grooves are formed by irradiating a laser beam along the street formed on the surface of the sapphire substrate constituting the optical device wafer, the outer periphery of the optical device such as a light emitting diode is ablated, and a melt called debris is formed. Since it adheres, there exists a problem that a brightness | luminance falls and the quality of an optical device falls. In order to solve such a problem, there is a problem that productivity is poor because a step of removing debris by etching is required before the optical device wafer is divided into individual optical devices.

  In order to solve such problems, a laser beam having a wavelength that is transparent to the sapphire substrate is placed on the street from the back side of the sapphire substrate where the light emitting layer (epi layer) is not formed. A processing method for dividing the sapphire substrate along the street where the modified layer is formed by irradiating along the street and forming the modified layer along the street inside the sapphire substrate is disclosed in Patent Document 2 below. Yes.

In recent years, as an optical device wafer with a light emitting layer formed on the surface of a sapphire substrate, a reflective film (DBR film) is formed on the back surface of the sapphire substrate to reflect light emitted from the light emitting layer and improve the light extraction efficiency. A technique for laminating layers has been proposed.
However, an optical device wafer in which a reflective film (DBR film), particularly a reflective film made of a metal film such as gold or aluminum, is laminated on the back surface of the sapphire substrate, the reflective film interferes with the laser beam and irradiates the laser beam from the back surface side of the sapphire substrate. There is a problem that you can not.

  In order to eliminate such problems, a pulsed laser beam having a wavelength that is transparent to sapphire is focused on and irradiated from the back side of the sapphire wafer, and divided into the sapphire wafer. After forming the modified layer along the planned line, a reflective film is formed on the back surface of the sapphire wafer, and then, by applying an external force to the sapphire wafer, the modified layer is divided along the planned divided line. A method for dividing a sapphire wafer is disclosed in Patent Document 3 below.

JP-A-10-305420 Japanese Patent No. 3408805 JP 2011-243875 A

Thus, in order to form a modified layer inside a single crystal substrate like a sapphire wafer, it is necessary to set the peak power density of the laser beam high, and the condensing with a numerical aperture (NA) of 0.8 or more. In addition to the use of lenses, it is necessary to reduce the thickness of the single crystal substrate to 150 μm or less as a thickness that can be divided along the division line on which the modified layer is formed.
However, when a modified layer is formed inside a single crystal substrate having a thickness as thin as 150 μm or less, there is a problem in that the single crystal substrate is warped to hinder the formation of a reflective film.
On the other hand, when the thickness of the single crystal substrate is set to 150 μm or more, for example, 300 μm, and the modified layer is formed inside, no warping occurs, but the modified layer having a sufficient thickness with respect to the thickness of the single crystal substrate is formed. Therefore, there is a problem that the single crystal substrate cannot be reliably divided along the division line on which the modified layer is formed.

  The present invention has been made in view of the above-mentioned facts, and the main technical problem is that the optical device wafer is formed after the reflective film is formed on the back surface of the single crystal substrate even if the thickness of the optical device wafer made of the single crystal substrate is thick. An object of the present invention is to provide a method of processing an optical device wafer that can be surely divided into individual devices along a division line.

In order to solve the above-mentioned main technical problem, according to the present invention, an optical device in which a light emitting layer is formed on the surface of a single crystal substrate and an optical device is formed in a plurality of regions partitioned by a plurality of grid-like division lines. An optical device wafer processing method for dividing a wafer into individual optical devices along a planned dividing line,
The numerical aperture (NA) of the condensing lens is in the range of 0.05 to 0.2 when the numerical aperture (NA) of the condensing lens that collects the pulsed laser beam is divided by the refractive index (N) of the single crystal substrate. A numerical aperture setting step to be set;
A condensing point positioning step for positioning the condensing point of the pulse laser beam in the vicinity of the surface side of the single crystal substrate from the back side of the single crystal substrate constituting the optical device wafer;
Amorphous that shields the pores and the pores on the side where the pulsed laser beam is incident from the focused point positioned near the surface side of the single crystal substrate by irradiating the pulsed laser beam after performing the focusing point positioning step Forming a shield tunnel adjacent to each other along the planned dividing line by growing the quality,
A reflective film forming step of forming a reflective film on the back surface of the single crystal substrate constituting the optical device wafer in which the shield tunnel forming step is performed;
A wafer dividing step of applying an external force to the optical device wafer on which the reflective film forming step has been performed to break the optical device wafer along a planned division line on which a shield tunnel is formed and dividing the optical device wafer into individual optical devices. Including,
An optical device wafer processing method is provided.

In the numerical aperture setting step, when the single crystal substrate is a sapphire (Al ₂ O ₃ ) substrate, the numerical aperture (NA) of the condenser lens is set to 0.1 to 0.35, and the single crystal substrate is carbonized. In the case of a silicon (SiC) substrate, the numerical aperture (NA) of the condenser lens is set to 0.15 to 0.55.
In addition, before performing the reflective film forming step, a back surface grinding step of grinding the back surface of the single crystal substrate constituting the optical device wafer subjected to the shield tunnel forming step to form the optical device wafer to a predetermined thickness. carry out.

  In the processing method of the optical device wafer according to the present invention, the value obtained by dividing the numerical aperture (NA) of the condensing lens for condensing the pulse laser beam by the refractive index (N) of the single crystal substrate is 0.05 to 0.2. The numerical aperture (NA) of the condensing lens is set in the range, and the condensing point positioned near the surface side of the single crystal substrate constituting the optical device wafer by irradiating the pulse laser beam and the side on which the pulse laser beam is incident Since a pore and an amorphous material that shields the pore are grown and a shield tunnel is formed adjacent to the line to be divided, the optical device wafer having a thickness of, for example, 300 μm can be Since a shield tunnel can be formed from the condensing point located in the vicinity to the surface side where the pulse laser beam is incident, the pulse laser beam can be used even if the optical device wafer is thick. Since irradiation may be one, the productivity is very good. In this way, even if the thickness of the optical device wafer is large, the shield tunnel can be formed from the front surface side to the back surface that is the incident surface, so that the optical device wafer does not warp.

1 is a perspective view of an optical device wafer divided into individual optical devices by an optical device wafer processing method according to the present invention and a cross-sectional view showing an enlarged main part thereof. The perspective view which shows the state which affixed the protective tape on the surface of the optical device wafer shown in FIG. The principal part perspective view of the laser processing apparatus for enforcing the shield tunnel formation process in the processing method of the optical device wafer by this invention. Explanatory drawing of the shield tunnel formation process in the processing method of the optical device wafer by this invention. The figure which shows the relationship between the numerical aperture (NA) of a condensing lens, the refractive index (N) of an optical device wafer, and the value (S = NA / N) which remove | divided the numerical aperture (NA) by the refractive index (N). The graph which shows the relationship between the energy of a pulse laser beam in the state in which the shield tunnel was formed in the sapphire substrate, the silicon carbide (SiC) substrate, and the gallium nitride (GaN) substrate, and the length of the shield tunnel. The principal part perspective view of the grinding device for implementing the back surface grinding process in the processing method of the optical device wafer by this invention. Explanatory drawing which shows the back surface grinding process in the processing method of the optical device wafer by this invention. Explanatory drawing of the reflective film lamination process in the processing method of the optical device wafer by this invention. The perspective view of the optical device wafer in which the reflective film lamination process shown in FIG. 8 was implemented. Explanatory drawing which shows the wafer support process and masking tape peeling process in the processing method of the optical device wafer by this invention. The perspective view of the tape expansion apparatus for implementing the wafer division | segmentation process in the processing method of the optical device wafer by this invention. Explanatory drawing which shows the wafer division | segmentation process in the processing method of the optical device wafer by this invention.

  Hereinafter, a method for processing an optical device wafer according to the present invention will be described in more detail with reference to the accompanying drawings.

  1A and 1B are perspective views of an optical device wafer divided into individual optical devices by the optical device wafer processing method according to the present invention. In an optical device wafer 2 shown in FIG. 1, a light emitting layer (epi layer) 21 made of a nitride semiconductor is laminated on a surface 20a of a sapphire substrate 20 which is a single crystal substrate having a thickness of 300 μm. The light emitting layer (epi layer) 21 is partitioned by a plurality of division lines 22 formed in a lattice shape, and optical devices 23 such as light emitting diodes and laser diodes are formed in the partitioned plurality of regions.

  In order to protect the optical device 23, the protective tape 3 is attached to the surface 21a of the light emitting layer (epi layer) 21 constituting the optical device wafer 2 described above (protective tape attaching step). . Therefore, the back surface 20b of the sapphire substrate 20 is exposed in the optical device wafer 2 to which the protective tape 3 is attached.

  FIG. 3 shows a laser processing apparatus that performs laser processing along a division line 22 of the optical device wafer 2 on which the above-described protective tape attaching step has been performed. A laser processing apparatus 4 shown in FIG. 3 includes a chuck table 41 that holds a workpiece, laser beam irradiation means 42 that irradiates a workpiece held on the chuck table 41 with a laser beam, and a chuck table 41 that holds the workpiece. An image pickup means 43 for picking up an image of the processed workpiece is provided. The chuck table 41 is configured to suck and hold the workpiece. The chuck table 41 is moved in a processing feed direction indicated by an arrow X in FIG. 3 by a processing feed means (not shown) and is also shown in FIG. 3 by an index feed means (not shown). It can be moved in the index feed direction indicated by the arrow Y.

  The laser beam application means 42 includes a cylindrical casing 421 arranged substantially horizontally. In the casing 421, pulse laser beam oscillation means including a pulse laser beam oscillator and repetition frequency setting means (not shown) are arranged. A condenser 422 equipped with a condenser lens 422a for condensing the pulse laser beam oscillated from the pulse laser beam oscillation means is attached to the tip of the casing 421. The condenser lens 422a of the condenser 422 has a numerical aperture (NA) set as follows. That is, the numerical aperture (NA) of the condenser lens 422a is set to a value obtained by dividing the numerical aperture (NA) by the refractive index (N) of the single crystal substrate in the range of 0.05 to 0.2 (numerical aperture). Setting process). The laser beam irradiation unit 42 includes a condensing point position adjusting unit (not shown) for adjusting the condensing point position of the pulsed laser beam collected by the condensing lens 422a of the condenser 422.

  The imaging means 43 attached to the tip of the casing 421 constituting the laser beam irradiation means 42 is an infrared illumination means for irradiating a workpiece with infrared rays in addition to a normal imaging device (CCD) for imaging with visible light. And an optical system that captures infrared rays irradiated by the infrared illumination means, and an image sensor (infrared CCD) that outputs an electrical signal corresponding to the infrared rays captured by the optical system. It sends to the control means which is not illustrated.

  In order to perform laser processing along the scheduled division line 22 of the optical device wafer 2 on which the above-described protective tape attaching process has been performed using the above-described laser processing apparatus 4, first, the laser processing shown in FIG. 3 described above is performed. The protective tape 3 attached to the optical device wafer 2 is placed on the chuck table 41 of the apparatus 4. Then, the optical device wafer 2 is held on the chuck table 41 via the protective tape 3 by operating a suction means (not shown) (wafer holding step). Therefore, in the optical device wafer 2 held on the chuck table 41, the back surface 20b of the sapphire substrate 20 which is a single crystal substrate is on the upper side. In this way, the chuck table 41 that sucks and holds the optical device wafer 2 is positioned directly below the imaging unit 43 by a processing feed unit (not shown).

  When the chuck table 41 is positioned immediately below the image pickup means 43, an alignment operation for detecting a processing region to be laser processed of the optical device wafer 2 is executed by the image pickup means 43 and a control means (not shown). That is, the image pickup means 43 and the control means (not shown) are a division line 22 formed in a predetermined direction of the optical device wafer 2 and a condenser of the laser beam irradiation means 42 that irradiates a laser beam along the division line 22. Image processing such as pattern matching for alignment with 422 is executed, and alignment of the laser beam irradiation position is performed (alignment process). In addition, the alignment of the laser beam irradiation position is similarly performed on the division line 22 formed on the optical device wafer 2 in the direction orthogonal to the predetermined direction. At this time, although the surface 21a of the light emitting layer (epi layer) 21 on which the division line 22 of the optical device wafer 2 is formed is positioned on the lower side, the imaging means 43 is connected to the infrared illumination means and the infrared rays as described above. Since the image pickup means is composed of an optical system that captures light and an image pickup device (infrared CCD) that outputs an electric signal corresponding to infrared rays, the line to be divided is watermarked from the back surface 20b of the sapphire substrate 20 that is a single crystal substrate. 22 can be imaged.

  When the alignment step described above is performed, the chuck table 41 is moved to the laser beam irradiation region where the condenser 422 of the laser beam irradiation means 42 for irradiating the laser beam as shown in FIG. It is positioned directly below the condenser 422. At this time, as shown in FIG. 4A, the optical device wafer 2 is positioned such that one end of the planned dividing line 22 (the left end in FIG. 4A) is located directly below the condenser 422. Then, the condensing point position adjusting means (not shown) is operated to move the concentrator 422 in the optical axis direction, and the pulse laser beam LB is emitted from the back surface 20b side of the sapphire substrate 20 which is a single crystal substrate constituting the optical device wafer 2. The condensing point P is positioned in the vicinity of the surface 20a side (the light emitting layer (epi layer) 21 side) of the sapphire substrate 20 (condensing point positioning step).

  When the focusing point positioning step is performed as described above, the sapphire substrate which is a single crystal substrate constituting the optical device wafer 2 by operating the laser beam irradiation means 42 and irradiating the pulse laser beam LB from the collector 422. A shield that forms a shield tunnel by forming a pore and an amorphous material that shields the pore on the side (the back surface 20b side of the sapphire substrate 20) on which the pulse laser beam is incident from the condensing point P positioned at 20 Implement the tunnel formation process. That is, the chuck table 41 is irradiated with the pulse laser beam LB having a wavelength having transparency to the sapphire substrate as the single crystal substrate constituting the optical device wafer 2 from the condenser 422, and the arrow X1 in FIG. It is moved at a predetermined feed speed in the direction indicated by (shield tunnel forming step). Then, as shown in FIG. 4B, when the other end of the planned dividing line 22 (the right end in FIG. 4A) reaches the irradiation position of the condenser 422 of the laser beam irradiation means 42, irradiation with a pulse laser beam is performed. And the movement of the chuck table 41 is stopped.

  By performing the above-described shield tunnel forming step, the condensing point P of the pulsed laser beam LB is formed inside the sapphire substrate 20 which is a single crystal substrate constituting the optical device wafer 2 as shown in FIG. The pores 241 and the amorphous 242 formed around the pores 241 grow from the front surface 20a side of the single crystal substrate 20 where the substrate is positioned to the back surface 20b of the single crystal substrate 20 which is the incident surface, and are divided. Amorphous shield tunnels 24 are formed along the predetermined line 22 at a predetermined interval (in the illustrated embodiment, an interval of 10 μm (processing feed rate: 500 mm / second) / (repetition frequency: 50 kHz)). As shown in FIGS. 4D and 4E, the shield tunnel 24 includes a pore 241 having a diameter of about φ1 μm formed at the center and an amorphous material having a diameter of φ10 μm formed around the pore 241. In the illustrated embodiment, adjacent amorphous 242s are connected to each other. The amorphous shield tunnel 24 formed in the above-described shield tunnel forming step is a single crystal substrate that is an incident surface from the surface 20a side of the sapphire substrate 20 that is a single crystal substrate constituting the optical device wafer 2. Since it can be grown and formed over the back surface 20b of the sapphire substrate 20, the pulse laser beam only needs to be irradiated once even if the wafer is thick, so that the productivity is extremely good. Thus, even if the thickness of the optical device wafer 2 is as thick as 300 μm, for example, the shield tunnel 24 can be formed from the front surface (lower surface) side to the rear surface 20b from the front surface 20a side of the sapphire substrate 20 which is the incident surface. The optical device wafer 2 is not warped. Further, since the debris does not scatter in the shield tunnel forming process, the problem of degrading the quality of the device is also solved.

  As described above, when the shield tunnel forming process is performed along the predetermined division line 22, the chuck table 41 is indexed and moved in the direction indicated by the arrow Y by the interval of the division line 22 formed on the optical device wafer 2. (Indexing step), the shield tunnel forming step is performed. If the shield tunnel forming process is performed along all the division lines 22 formed in the predetermined direction in this way, the chuck table 41 is rotated 90 degrees to form the division division formed in the predetermined direction. The shield tunnel forming step is performed along the planned dividing line 22 extending in a direction orthogonal to the line 22.

In order to form a good shield tunnel 24 in the above-described shield tunnel formation process, as described above, the numerical aperture (NA) of the condenser lens 422a is set to the refractive index (N) of the single crystal substrate. It is important that the value divided by (S = NA / N) is set in the range of 0.05 to 0.2.
Here, the relationship between the numerical aperture (NA), the refractive index (N), and the value obtained by dividing the numerical aperture (NA) by the refractive index (N) (S = NA / N) will be described with reference to FIG. . In FIG. 5, the pulse laser beam LB incident on the condenser lens 422a is condensed at an angle (θ) with respect to the optical axis. At this time, sin θ is the numerical aperture (NA) of the condenser lens 422a (NA = sin θ). When the pulsed laser beam LB condensed by the condensing lens 422a is applied to the optical device wafer 2 composed of a single crystal substrate, the single crystal substrate constituting the optical device wafer 2 has a higher density than air, so the pulse laser beam LB is angled. The light is refracted from (θ) to an angle (α) and is condensed at a condensing point P. At this time, the angle (α) with respect to the optical axis varies depending on the refractive index (N) of the single crystal substrate constituting the optical device wafer 2. Since the refractive index (N) is (N = sin θ / sin α), the value (S = NA / N) obtained by dividing the numerical aperture (NA) by the refractive index (N) of the single crystal substrate is sin α. Therefore, it is important to set sin α in the range of 0.05 to 0.2 (0.05 ≦ sin α ≦ 0.2).
The reason why the value (S = NA / N) obtained by dividing the numerical aperture (NA) of the condenser lens 422a by the refractive index (N) of the single crystal substrate is set in the range of 0.05 to 0.2 will be described below. To do.

[Experiment 1]
A shield tunnel was formed on a sapphire (Al ₂ O ₃ ) substrate (refractive index: 1.7) having a thickness of 300 μm under the following processing conditions, and the quality of the shield tunnel was judged.

Processing condition wavelength: 1030 nm pulse laser Repetition frequency: 50 kHz
Pulse width: 10 ps
Average output: 3W
Condensing spot diameter: φ10μm
Processing feed rate: 500 mm / sec

Condenser lens numerical aperture (NA) Shield tunnel good / bad S = NA / N
0.05 None
0.1 Somewhat good 0.058
0.15 Good 0.088
0.2 Good 0.117
0.25 Good 0.147
0.3 Good 0.176
0.35 Slightly good 0.205
0.4 Defect
0.45 Defect: Void is generated 0.5 Defect: Void is formed 0.55 Defect: Void is formed 0.6 Defect: Void is formed

As described above, in the sapphire (Al ₂ O ₃ ) substrate (refractive index: 1.7), the numerical aperture (NA) of the condenser lens 422a that condenses the pulse laser beam is set to the refractive index (N) of the single crystal substrate. By setting the divided value (S = NA / N) within a range of 0.05 to 0.2, a shield tunnel is formed. Therefore, in the sapphire (Al ₂ O ₃ ) substrate (refractive index: 1.7), the numerical aperture (NA) of the condenser lens 422a for condensing the pulsed laser beam should be set to 0.1 to 0.35. is important.

[Experiment 2]
A shield tunnel was formed on a silicon carbide (SiC) substrate (refractive index: 2.63) having a thickness of 300 μm under the following processing conditions, and the quality of the shield tunnel was determined.

Processing condition wavelength: 1030 nm pulse laser Repetition frequency: 50 kHz
Pulse width: 10 ps
Average output: 3W
Condensing spot diameter: φ10μm
Processing feed rate: 500 mm / sec

Condenser lens numerical aperture (NA) Shield tunnel good / bad S = NA / N
0.05 None
0.1 None
0.15 Somewhat good 0.057
0.2 Good 0.076
0.25 Good 0.095
0.3 Good 0.114
0.35 Good 0.133
0.4 Good 0.153
0.45 Good 0.171
0.5 Good 0.19
0.55 Slightly good 0.209
0.6 Defect: A void is formed

As described above, in the silicon carbide (SiC) substrate (refractive index: 2.63), the numerical aperture (NA) of the condenser lens 422a that condenses the pulse laser beam is divided by the refractive index (N) of the single crystal substrate. By setting the value (S = NA / N) in the range of 0.05 to 0.2, a shield tunnel is formed. Therefore, in the silicon carbide (SiC) substrate, it is important to set the numerical aperture (NA) of the condenser lens 422a that condenses the pulse laser beam to 0.15 to 0.55.

[Experiment 3]
A shield tunnel was formed on a gallium nitride (GaN) substrate (refractive index: 2.3) having a thickness of 300 μm under the following processing conditions, and the quality of the shield tunnel was determined.

Processing condition wavelength: 1030 nm pulse laser Repetition frequency: 50 kHz
Pulse width: 10 ps
Average output: 3W
Condensing spot diameter: φ10μm
Processing feed rate: 500 mm / sec

Condenser lens numerical aperture (NA) Shield tunnel good / bad S = NA / N
0.05 None
0.1 Slightly good 0.043
0.15 Good 0.065
0.2 Good 0.086
0.25 Good 0.108
0.3 Good 0.130
0.35 Good 0.152
0.4 Good 0.173
0.45 Good 0.195
0.5 Slightly good 0.217
0.55 Defect: A void is formed 0.6 Defect: A void is formed

As described above, in the gallium nitride (GaN) substrate (refractive index: 2.3), the numerical aperture (NA) of the condensing lens 422a that collects the pulsed laser beam is divided by the refractive index (N) of the single crystal substrate. By setting the value (S = NA / N) in the range of 0.05 to 0.2, a shield tunnel is formed. Therefore, in the gallium nitride (GaN) substrate, it is important to set the numerical aperture (NA) of the condenser lens 422a for condensing the pulse laser beam to 0.1 to 0.5.

  From Experiment 1, Experiment 2, and Experiment 3 described above, the numerical aperture (NA) of the condenser lens 422a that condenses the pulsed laser beam is a value obtained by dividing the numerical aperture (NA) by the refractive index (N) of the single crystal substrate ( It was confirmed that a shield tunnel was formed by setting S = NA / N) in the range of 0.05 to 0.2.

FIG. 6 shows the energy of a pulsed laser beam in a state where a shield tunnel is formed on a sapphire (Al ₂ O ₃ ) substrate, a silicon carbide (SiC) substrate, or a gallium nitride (GaN) substrate obtained by the inventors' experiments. The relationship between (μJ / 1 pulse) and the length of the shield tunnel (μm) is shown. From the graph shown in FIG. 6, for example, in order to form a shield tunnel from the lower surface to the upper surface on a sapphire (Al ₂ O ₃ ) substrate having a thickness of 300 μm, the energy of the pulse laser beam is 85 μJ / 1 pulse or more. Accordingly, when the repetition frequency of the pulse laser beam is 50 kHz, the average output of the pulse laser beam may be set to 4.5 W in order to form a shield tunnel having a length of 300 μm on the sapphire (Al ₂ O ₃ ) substrate.

  If the shield tunnel forming process is performed as described above, the back surface 20b of the sapphire substrate 20 that is a single crystal substrate constituting the optical device wafer 2 on which the shield tunnel forming process has been performed is ground as necessary. A back grinding process for forming the device wafer 2 to a predetermined thickness is performed. This back grinding process is performed using a grinding apparatus 5 shown in FIG. A grinding apparatus 5 shown in FIG. 7 includes a chuck table 51 that holds a workpiece, and a grinding unit 52 that grinds the workpiece held on the chuck table 51. The chuck table 51 is configured to suck and hold a workpiece on the upper surface, which is a holding surface, and is rotated in a direction indicated by an arrow 51a in FIG. 7 by a rotation driving mechanism (not shown). The grinding means 52 includes a spindle housing 521, a rotating spindle 522 that is rotatably supported by the spindle housing 521 and rotated by a rotation driving mechanism (not shown), a mounter 523 mounted on the lower end of the rotating spindle 522, and the mounter And a grinding wheel 524 attached to the lower surface of 523. The grinding wheel 524 includes an annular base 525 and a grinding wheel 526 that is annularly attached to the lower surface of the base 525, and the base 525 is attached to the lower surface of the mounter 523 with fastening bolts 527. ing.

  In order to perform the back surface grinding process using the grinding apparatus 5 described above, the protective tape for the optical device wafer 2 in which the shield tunnel forming process is performed on the upper surface (holding surface) of the chuck table 51 as shown in FIG. Place 3 side. Then, the optical device wafer 2 is sucked and held on the chuck table 51 via the protective tape 3 by operating a suction means (not shown) (wafer holding step). Accordingly, in the optical device wafer 2 held on the chuck table 51, the back surface 20b of the sapphire substrate 20 which is a single crystal substrate is on the upper side. When the optical device wafer 2 is sucked and held on the chuck table 51 via the protective tape 3 in this way, the grinding means 52 is ground while rotating the chuck table 51 in the direction indicated by the arrow 51a in FIG. The wheel 524 is rotated in the direction indicated by an arrow 524a in FIG. 7 at, for example, 6000 rpm, and the grinding wheel 526 is rotated as shown in FIG. 7, and the back surface of the sapphire substrate which is a single crystal substrate constituting the optical device wafer 2 which is a processing surface. 2b, the grinding wheel 524 is ground and fed by a predetermined amount downward (in a direction perpendicular to the holding surface of the chuck table 51) at a grinding feed rate of 1 μm / second, for example, as indicated by an arrow 524b in FIGS. . As a result, the back surface 20b of the sapphire substrate 20 which is a single crystal substrate constituting the optical device wafer 2 is ground to form the optical device wafer 2 with a predetermined thickness (for example, 200 μm).

  Next, a reflecting film forming step is performed in which a reflecting film is formed on the back surface 20b of the sapphire substrate 20 that is a single crystal substrate constituting the optical device wafer 2 on which the shield tunnel forming step (and the back surface grinding step) has been performed. This reflective film forming step is performed using a sputtering apparatus 6 shown in FIG. A sputtering apparatus 6 shown in FIG. 9 includes a housing 62 that forms a sputtering chamber 61, an electrostatic adsorption holding table 63 that is disposed in the sputtering chamber 61 of the housing 62 and serves as an anode that holds a workpiece, A cathode 65 to which a target 64 made of a metal (for example, gold, aluminum) or an oxide (for example, SiO 2, TiO 2, ZnO) disposed and opposed to the holding table 63 is attached; and an excitation means 66 for exciting the target 64 And a high frequency power source 67 for applying a high frequency voltage to the cathode 65. The housing 62 is provided with a decompression port 621 that communicates with the decompression means (not shown) in the sputtering chamber 61 and an introduction port 622 that communicates with the sputtering gas supply means (not shown) within the sputtering chamber 61.

In order to carry out the above-described reflective film forming step using the sputtering apparatus 6 configured as described above, the optical device wafer 2 in which the above-described shield tunnel forming step (and back surface grinding step) is carried out on the holding table 63. The surface of the protective tape 3 attached to the surface is placed and electrostatically held. Therefore, the back surface 20b of the sapphire substrate 20 which is a single crystal substrate constituting the optical device wafer 2 electrostatically held on the holding table 63 is on the upper side. Next, the excitation means 66 is operated to excite the target 64 and a high frequency voltage of 40 kHz, for example, is applied to the cathode 65 from a high frequency power supply 67. Then, the decompression means (not shown) is operated to decompress the inside of the sputtering chamber 61 to about 10 ⁻² Pa to 10 ⁻⁴ Pa, and the sputtering gas supply means (not shown) is operated to introduce argon gas into the sputtering chamber 61. To generate plasma. Accordingly, the argon gas in the plasma collides with a target 64 made of a metal such as gold or aluminum or an oxide such as SiO2, TiO2, or ZnO attached to the cathode 65, and the metal particles or oxide particles scattered by the collision are as follows. A metal layer or an oxide layer is deposited on the back surface 20 b of the sapphire substrate 20 constituting the optical device wafer 2. As a result, a reflective film 210 made of a metal film or an oxide film is formed on the back surface 20b of the sapphire substrate 20 constituting the optical device wafer 2 as shown in FIG. The reflective film 210 made of this metal film or oxide film is set to a thickness of 0.5 to 2 μm.

  If the reflective film formation process mentioned above is implemented, the wafer support process which sticks the back surface 20b of the sapphire substrate 20 which comprises the optical device wafer 2 in which the reflective film 210 was formed to the adhesive tape with which the cyclic | annular flame | frame was mounted | worn. carry out. That is, as shown in FIG. 11, the reflective film formed on the back surface 20b of the sapphire substrate 20 constituting the optical device wafer 2 on the surface of the adhesive tape T having the outer periphery mounted so as to cover the opening of the annular frame F. Adhere 210 side. Then, the protective tape 3 attached to the surface of the optical device wafer 2 is peeled off (protective tape peeling step).

  Next, an external force is applied to the optical device wafer 2 on which the reflective film forming step has been performed, so that the optical device wafer 2 is broken along the planned division line 22 where the shield tunnel 23 is formed, and divided into individual optical devices 21. The wafer dividing process is performed. This dividing step is performed using a wafer dividing apparatus 7 shown in FIG. The wafer dividing apparatus 7 shown in FIG. 12 includes a frame holding means 71 for holding the annular frame F and a tape extending means for expanding the adhesive tape T attached to the annular frame F held by the frame holding means 71. 72. The frame holding means 71 includes an annular frame holding member 711 and a plurality of clamps 712 as fixing means provided on the outer periphery of the frame holding member 711. An upper surface of the frame holding member 711 forms a placement surface 711a on which the annular frame F is placed, and the annular frame F is placed on the placement surface 711a. The annular frame F placed on the placement surface 711 a is fixed to the frame holding member 711 by the clamp 712. The frame holding means 71 configured as described above is supported by the tape expanding means 72 so as to be able to advance and retreat in the vertical direction.

  The tape expansion means 72 includes a cylindrical expansion drum 721 as a pressing member disposed inside the annular frame holding member 711. The expansion drum 721 has an inner diameter and an outer diameter that are smaller than the inner diameter of the annular frame F and larger than the outer diameter of the optical device wafer 2 attached to the adhesive tape T attached to the annular frame F. The expansion drum 721 includes a support flange 722 at the lower end. The tape expansion means 72 in the illustrated embodiment includes support means 73 that can advance and retract the annular frame holding member 711 in the vertical direction. The support means 73 includes a plurality of air cylinders 731 disposed on the support flange 722, and the piston rod 732 is connected to the lower surface of the annular frame holding member 711. As described above, the support means 73 including the plurality of air cylinders 731 has a predetermined amount from the reference position where the mounting surface 711 a is substantially flush with the upper end of the expansion drum 721 and the upper end of the expansion drum 721. Move up and down between the lower extended positions. Therefore, the support means 73 composed of a plurality of air cylinders 731 functions as expansion movement means for relatively moving the expansion drum 721 and the frame holding member 711 in the vertical direction.

  A dividing process performed using the wafer dividing apparatus 7 configured as described above will be described with reference to FIG. That is, as shown in FIG. 13A, an annular frame F to which the adhesive tape T attached to the reflective film 210 side formed on the back surface 20b of the sapphire substrate 20 constituting the optical device wafer 2 is attached. Are mounted on a mounting surface 711 a of a frame holding member 711 constituting the frame holding means 71 and fixed to the frame holding member 711 by a clamp 712. At this time, the frame holding member 711 is positioned at the reference position shown in FIG. Next, a plurality of air cylinders 731 as the support means 73 constituting the tape expansion means 72 are operated to lower the annular frame holding member 711 to the expansion position shown in FIG. Accordingly, the annular frame F fixed on the mounting surface 711a of the frame holding member 711 is also lowered, so that the adhesive tape T attached to the annular frame F is light-transmitted as shown in FIG. An annular region between the device wafer 2 and the inner periphery of the annular frame F is pressed against the upper end edge of a cylindrical expansion drum 721 as a pressing member to be expanded. As a result, since a tensile force acts radially on the optical device wafer 2 attached to the adhesive tape T, the optical device wafer 2 is divided into lines that are reduced in strength due to the formation of the shield tunnel 24. It is broken along 22 and divided into individual optical devices 23. At this time, since the reflective film 210 formed on the back surface 20b of the sapphire substrate 20 constituting the optical device wafer 2 is as thin as 1 μm or less, it is broken along the planned dividing line 22.

  When the dividing step is performed as described above, the pickup mechanism 8 is operated and the optical device 21 positioned at a predetermined position by the pickup collet 81 is picked up (pickup step) as shown in FIG. Not transported to tray or die bonding process.

2: Optical device wafer 21: Optical device 22: Planned division line 23: Shield tunnel 210: Reflective film 3: Protection tape 4: Laser processing device 41: Chuck table of laser processing device 42: Laser beam irradiation means 422: Condenser 5 : Grinding device 51: Chuck table of grinding device 52: Grinding means 524: Grinding wheel 526: Grinding wheel 6: Sputtering device 61: Sputtering chamber 63: Holding table 64: Target 7: Wafer dividing device 71: Frame holding means 72: Tape Expansion means 721: Expansion drum F: Annular frame T: Adhesive tape

Claims (3)

An optical device wafer in which a light emitting layer is formed on the surface of a single crystal substrate and an optical device is formed in a plurality of regions partitioned by a plurality of grid-like division lines is divided into individual optical devices along the division lines. An optical device wafer processing method comprising:
The numerical aperture (NA) of the condensing lens is in the range of 0.05 to 0.2 when the numerical aperture (NA) of the condensing lens that collects the pulsed laser beam is divided by the refractive index (N) of the single crystal substrate. A numerical aperture setting step to be set;
A condensing point positioning step for positioning the condensing point of the pulse laser beam in the vicinity of the surface side of the single crystal substrate from the back side of the single crystal substrate constituting the optical device wafer;
Amorphous that shields the pores and the pores on the side where the pulsed laser beam is incident from the focused point positioned near the surface side of the single crystal substrate by irradiating the pulsed laser beam after performing the focusing point positioning step Forming a shield tunnel adjacent to each other along the planned dividing line by growing the quality,
A reflective film forming step of forming a reflective film on the back surface of the single crystal substrate constituting the optical device wafer in which the shield tunnel forming step is performed;
A wafer dividing step of applying an external force to the optical device wafer on which the reflective film forming step has been performed to break the optical device wafer along a planned division line on which a shield tunnel is formed and dividing the optical device wafer into individual optical devices. Including,
An optical device wafer processing method characterized by the above. In the numerical aperture setting step, when the single crystal substrate is a sapphire (Al ₂ O ₃ ) substrate, the numerical aperture (NA) of the condenser lens is set to 0.1 to 0.35, and the single crystal substrate is carbonized. In the case of a silicon (SiC) substrate, the numerical aperture (NA) of the condenser lens is set to 0.15 to 0.55, and in the case where the single crystal substrate is a gallium nitride (GaN) substrate, the numerical aperture of the condenser lens. The method for processing an optical device wafer according to claim 1, wherein (NA) is set to 0.1 to 0.5.   Before performing the reflective film forming step, a back surface grinding step is performed in which the back surface of the single crystal substrate constituting the optical device wafer on which the shield tunnel forming step has been performed is ground to form the optical device wafer to a predetermined thickness. A method for processing an optical device wafer according to claim 1 or 2.

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