JP2013152984A - Method for processing wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for processing a wafer which has a reflection film on a rear surface thereof and does not break along a modified layer when carrying out the wafer from a laser processing device and transporting it to a next step.SOLUTION: A method for processing a wafer 11 having a device region in which a device is formed and an outer peripheral region surrounding the device region on a surface thereof comprises: a masking step of forming a mask 27 of a prescribed width on a rear surface corresponding to an outer peripheral region of the wafer 11 from the outermost periphery of the wafer 11; a modified layer forming step of holding a surface side of the wafer 11 by a chuck table 28, positioning a condensing point of a pulse laser beam 69 having a wavelength permeable from a rear surface side of the wafer 11 to the inside of the wafer 11, and forming a modified layer 29 serving as a division start point inside the wafer 11 along a division schedule line by irradiating the wafer with the pulse laser beam 69; and a transporting step of carrying out the wafer 11 and transporting it to a next step after performing the modified layer forming step.

Description

  The present invention relates to a wafer processing method in which a wafer such as an optical device wafer is irradiated with a laser beam to form a modified layer inside the wafer, and then an external force is applied to the wafer to divide the wafer into individual devices.

  A street in which a semiconductor layer (epitaxial layer) such as gallium nitride (GaN) is formed on a crystal growth substrate such as a sapphire substrate or SiC substrate, and a plurality of optical devices such as LEDs are formed in a lattice shape on the semiconductor layer ( Since the optical device wafer formed by dividing by the dividing line) has a relatively high Mohs hardness and is difficult to divide by a cutting blade, it is divided into individual optical devices by laser beam irradiation. Devices are used in various electric devices such as mobile phones, lighting devices, liquid crystal televisions, and personal computers.

  As methods for dividing an optical device wafer into individual optical devices using a laser beam, first and second processing methods described below are known. In the first processing method, a semiconductor layer is formed by positioning a condensing point of a laser beam having a wavelength transparent to the substrate (for example, 1064 nm) inside the substrate corresponding to the division line. This is a method of forming an altered layer inside the substrate by irradiating along the planned dividing line from the back side, and then applying an external force to divide the optical device wafer into individual optical devices (for example, Japanese Patent No. 3408805) reference).

  In the second processing method, a laser beam having a wavelength (for example, 355 nm) having an absorptivity with respect to the substrate is irradiated from the surface side to a region corresponding to the planned split line, and a split starting groove serving as a split starting point is formed by ablation processing. In this method, an external force is applied and the optical device wafer is divided into individual optical devices (see, for example, JP-A-10-305420). In any processing method, the optical device wafer can be surely divided into individual optical devices.

  In general, a reflective film is formed on the back surface of an optical device such as an LED (Light Emitting Diode) in order to improve the light extraction efficiency. This reflective film is formed on the back surface of the wafer by sputtering, CVD (Chemical Vapor Deposition), etc. in the state of the optical device wafer.

  As described above, when a reflective film made of gold, aluminum, or the like is formed on the back surface of the optical device wafer, there is a problem that the laser beam cannot be irradiated from the back surface of the optical device wafer.

  In order to solve this problem, sapphire is used to form a modified layer that forms the base point of division along the planned division line by irradiating a laser beam from the back side of the wafer before forming a reflective film on the back side of the wafer. A method of dividing a wafer is disclosed in Japanese Patent Application Laid-Open No. 2011-243875.

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

  However, the optical device wafer on which the modified layer is formed is unloaded from the laser processing apparatus and is transported to the reflection film forming apparatus that forms the reflection film on the back surface, or when the optical device wafer is unloaded from the laser processing apparatus. There is a problem that may break.

  The present invention has been made in view of the above points, and the object of the present invention is that the back surface does not break along the modified layer when transported to the next process from the laser processing apparatus. It is another object of the present invention to provide a method for processing a wafer having a reflective film.

  According to the present invention, there is provided a wafer processing method having a device region in which a device is formed in each region divided by a plurality of division lines and an outer peripheral region surrounding the device region, the outer peripheral region of the wafer A masking process for applying a mask having a predetermined width from the outermost periphery of the wafer to the back surface corresponding to the wafer surface, and after performing the masking process, the wafer front surface side is held by a chuck table and the wafer back surface side corresponds to the scheduled division line. A condensing point of a pulse laser beam having a wavelength that is transparent to the wafer is positioned inside the wafer and irradiated with the pulse laser beam, and a modified layer serving as a starting point for dividing along the planned dividing line is placed inside the wafer. A reformed layer forming step to be formed, and after carrying out the reformed layer forming step, the wafer is unloaded from the chuck table to the next step. A conveying step of conveying the wafer, the wafer processing method characterized by comprising the is provided.

  Preferably, the wafer is composed of an optical device wafer in which a semiconductor layer is laminated on the surface of a sapphire substrate, and a plurality of optical devices are defined on the semiconductor layer by lines to be divided. The wafer is transported to the back surface processing step in which the reflective film is laminated on the substrate.

  Preferably, the wafer processing method further includes a dividing step of dividing the wafer into individual devices by applying an external force to the division line of the wafer after performing the modified layer forming step.

  According to the wafer processing method of the present invention, before the reflective film is laminated on the back surface of the wafer, the condensing point of the pulse laser beam having a wavelength transmissive to the wafer corresponds to the planned dividing line from the back surface side of the wafer. When a modified layer is formed inside the wafer by being positioned and irradiated, a mask having a predetermined width is applied to the outermost periphery of the back surface of the wafer corresponding to the outer peripheral region, so that the modified layer is formed in the outer peripheral region. It is never formed.

  Therefore, the outer peripheral region of the wafer serves as a reinforcing portion, and when the wafer is unloaded from the chuck table and transported to the next process, the wafer does not break along the modified layer, and the wafer has a reflective film on the back surface. However, the modified layer can be formed along the division line.

It is a perspective view of a laser processing apparatus. It is a block diagram of a laser beam generation unit. It is a perspective view of an optical device wafer. 4A is an exploded perspective view showing a state where a protective tape is attached to the surface of the optical device wafer, and FIG. 4B is a rear perspective view of the optical device wafer having the protective tape attached to the surface. . It is a back surface side perspective view of the optical device wafer by which the mask of predetermined width was given to the back surface of the optical device wafer from the outermost periphery by the masking process. It is a perspective view which shows a modified layer formation process. It is a perspective view explaining a conveyance process. It is a back surface side perspective view of the optical device wafer by which the reflective film was formed in the back surface by the back surface process. It is a perspective view of the optical device wafer supported by the annular frame via the adhesive tape. It is a longitudinal cross-sectional view which shows a division | segmentation process.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a schematic configuration diagram of a laser processing apparatus 2 suitable for performing a modified layer forming step in the wafer processing method of the present invention.

  The laser processing apparatus 2 includes a first slide block 6 mounted on a stationary base 4 so as to be movable in the X-axis direction. The first slide block 6 is moved along the pair of guide rails 14 in the machining feed direction, that is, the X-axis direction, by the machining feed means 12 including the ball screw 8 and the pulse motor 10.

  A second slide block 16 is mounted on the first slide block 6 so as to be movable in the Y-axis direction. That is, the second slide block 16 is moved in the indexing direction, that is, the Y-axis direction along the pair of guide rails 24 by the indexing feeding means 22 constituted by the ball screw 18 and the pulse motor 20.

  A chuck table 28 is mounted on the second slide block 16 via a cylindrical support member 26, and the chuck table 28 can be moved in the X-axis direction and the Y-axis direction by the processing feed means 12 and the index feed means 22. . The chuck table 28 is provided with a clamp 30 that clamps an annular frame that supports the wafer sucked and held by the chuck table 28.

  A column 32 is erected on the stationary base 4, and a casing 35 for accommodating the laser beam generating unit 37 shown in FIG. 2 is attached to the column 32. Reference numeral 34 denotes a laser beam irradiation unit, which includes the laser beam generation unit 37 shown in FIG. 2 and a condenser (laser head) 36 attached to the tip of the casing 35.

  As shown in FIG. 2, the laser beam generation unit 37 includes a laser oscillator 62 that oscillates a YAG laser or a YVO4 laser, a repetition frequency setting unit 64, a pulse width adjustment unit 66, and a power adjustment unit 68. .

  The pulse laser beam adjusted to a predetermined power by the power adjusting means 68 of the laser beam generating unit 37 is reflected by the mirror 70 of the condenser 36 attached to the tip of the casing 35 and further collected by the condenser objective lens 72. The light is applied to the optical device wafer 11 held on the chuck table 28.

  At the tip of the casing 35, an image pickup means 38 for detecting a processing region to be laser processed in alignment with the condenser 36 in the X-axis direction is disposed. The imaging means 38 includes an imaging element such as a normal CCD that images the processing region of the optical device wafer 11 with visible light.

  The imaging means 38 further outputs an infrared irradiation means for irradiating the optical device wafer 11 with infrared rays, an optical system for capturing the infrared rays irradiated by the infrared irradiation means, and an electrical signal corresponding to the infrared rays captured by the optical system. Infrared imaging means including an infrared imaging device such as an infrared CCD is included, and the captured image signal is transmitted to a controller (control means) 40.

  The controller 40 includes a central processing unit (CPU) 42 that performs arithmetic processing according to a control program, a read-only memory (ROM) 44 that stores a control program, and a random read / write that stores arithmetic results. An access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52 are provided.

  Reference numeral 56 denotes a processing feed amount detection means comprising a linear scale 54 disposed along the guide rail 14 and a read head (not shown) disposed on the first slide block 6. Is input to the input interface 50 of the controller 40.

  Reference numeral 60 denotes index feed amount detection means comprising a linear scale 58 disposed along the guide rail 24 and a read head (not shown) disposed on the second slide block 16. The detection signal is input to the input interface 50 of the controller 40.

  An image signal picked up by the image pickup means 38 is also input to the input interface 50 of the controller 40. On the other hand, a control signal is output from the output interface 52 of the controller 40 to the pulse motor 10, the pulse motor 20, the laser beam generation unit 37, and the like.

  Referring to FIG. 3, there is shown a front side perspective view of an optical device wafer 11 to be processed by the processing method of the present invention. The optical device wafer 11 is configured by laminating an epitaxial layer (semiconductor layer) 15 such as gallium nitride (GaN) on a sapphire substrate 13. The optical device wafer 11 has a front surface 11a on which an epitaxial layer 15 is stacked and a back surface 11b on which the sapphire substrate 13 is exposed. The back surface 11b is processed into a mirror surface.

  The sapphire substrate 13 has a thickness of 120 μm, for example, and the epitaxial layer 15 has a thickness of 5 μm, for example. A plurality of optical devices 19 such as LEDs are formed on the epitaxial layer 15 by being partitioned by division lines (streets) formed in a lattice pattern.

  The optical device wafer 11 has a device region 21 in which a plurality of optical devices 19 are formed and an outer peripheral region 23 surrounding the device region 21 on its surface. In this specification, the outer peripheral area 23 is an area 0.2 to 2 mm inside from the outermost periphery of the optical device wafer 11, and may include a part of the outer periphery of the device area 21.

  In the wafer processing method of the present invention, in order to protect the optical device 19 formed on the surface, a protective tape 25 is attached to the surface 11a of the optical device wafer 11 as shown in FIG.

  Next, as shown in FIG. 5, a masking process is performed in which a mask 27 having a predetermined width W <b> 1 is applied from the outermost periphery to the back surface 11 b corresponding to the outer peripheral region 23 of the optical device wafer 11. This mask 27 is formed of, for example, a photoresist. Or you may form with magic ink. The predetermined width W1 is 0.2 to 2 mm, more preferably 1 to 2 mm.

  After performing the masking step, a modified layer forming step for forming a modified layer inside the optical device wafer 11 is performed. In this modified layer forming step, the protective tape 25 attached to the surface of the optical device wafer 11 is sucked and held by the chuck table 28 of the laser processing apparatus 2 to expose the back surface 11 b of the optical device wafer 11.

  Then, the optical device wafer 11 is imaged from the back surface 11b side by the infrared imaging element of the imaging means 38, and alignment for detecting a region corresponding to the planned division line 17 is performed. For this alignment, a well-known pattern matching technique is used.

  In this modified layer forming step, as shown in FIG. 6, a condensing point of a laser beam 69 having a wavelength that is transmissive to the sapphire substrate 13 is collected from the back surface 11b side of the optical device wafer 11 which is mirror-finished. The optical device 36 is positioned inside the sapphire substrate 13 corresponding to the planned division line 17 and irradiates the laser beam 69 along the planned division line 17 to form a modified layer 29 serving as a division starting point inside the sapphire substrate 13. .

  The pulse laser beam is also irradiated to the outermost peripheral portion of the optical device wafer 11 to which the mask 27 is applied. However, since the mask 27 at least partially blocks the transmission of the laser beam 69, The modified layer 29 is not formed on the outer periphery.

  In this modified layer forming step, the modified layer 29 is formed along the division line 17 that extends in the first direction while the chuck table 28 is processed and fed in the direction of the arrow X1. The modified layer 29 is formed inside the sapphire substrate 13 along all the planned division lines 17 extending in the first direction of the optical device wafer 11 while sequentially indexing and feeding.

  Next, the chuck table 28 is rotated 90 degrees to form a similar modified layer 29 serving as a division starting point along all the division lines 17 extending in the second direction orthogonal to the first direction. FIG. 7 shows a rear perspective view of the optical device wafer 11 in a state in which the modified layer 29 serving as the division start point is formed along all the planned division lines 17.

  The processing conditions of the modified layer forming step are set as follows, for example.

Light source: LD excitation Q switch Nd: YAG
Wavelength: 1064nm
Average output: 0.4W
Repetition frequency: 100 kHz
Condensing spot diameter: 1 μm
Pulse width: 100ps
Processing feed rate: 100-200 mm / sec Sapphire substrate: Thickness 120 μm
Focus point position: 60 μm from the back
Modified layer width: 30 μm

  After carrying out the modified layer forming step, as shown in FIG. 7, the chucking process of releasing the chuck table 28, unloading the optical device wafer 11 from the chuck table 28, and transporting the optical device wafer 11 to the next step is performed. carry out.

  Since the modified layer 29 is not formed on the outermost peripheral portion of the optical device wafer 11 to which the mask 27 is applied, the outermost peripheral portion becomes a kind of reinforcing portion, and the transporting step of transporting the optical device wafer 11 to the next step. The optical device wafer 11 is prevented from breaking along the modified layer 29 inside.

  In the wafer processing method of this embodiment, the next process of transporting the optical device wafer 11 in the transport process is a back surface processing process (reflective film forming process) of forming a reflective film on the back surface 11b of the optical device wafer 11.

  Referring to FIG. 8, there is shown a back side perspective view of the optical device wafer 11 having a modified layer 29 inside and a reflective film 31 formed on the back surface 11b. The reflective film 31 is also formed on the mask 27. The reflective film 31 is made of gold, aluminum, or the like, and is formed by a well-known sputtering method, CVD method, or the like.

  After performing the back surface processing step, a dividing step of dividing the optical device wafer 11 on which the modified layer 29 is formed into individual chips 33 having the optical device 19 is performed. As a pre-process of this dividing process, as shown in FIG. 9, the optical device wafer 11 is attached to an adhesive tape T having an outer peripheral part attached to an annular frame F.

  Next, as shown in FIG. 10, the annular frame F is placed on the placement surface of the cylinder 80, and the annular frame F is clamped by the clamp 82. A bar-shaped dividing jig 84 is disposed in the cylinder 80.

  The dividing jig 84 has an upper stage holding surface 86a and a lower stage holding surface 86b, and a vacuum suction path 88 that opens to the lower stage holding surface 86b is formed. The detailed structure of the dividing jig 84 is disclosed in Japanese Patent No. 4361506.

  In order to perform the dividing step by the dividing jig 84, the upper holding surface 86a and the lower holding surface 86b of the dividing jig 84 are moved downward while the vacuum suction path 88 of the dividing jig 84 is vacuum-sucked as indicated by an arrow 90. The dividing jig 84 is moved in the direction of arrow A by contacting the adhesive tape T from the side. That is, the dividing jig 84 is moved in a direction orthogonal to the planned dividing line 17 to be divided.

  As a result, when the modified layer 29 moves directly above the inner edge of the upper holding surface 86a of the dividing jig 84, bending stress is concentrated on the portion of the planned dividing line 17 having the modified layer 29. The optical device wafer 11 is cleaved along the division line 17 by the bending stress.

  When division along all the planned division lines 17 extending in the first direction is completed, the dividing jig 84 is rotated 90 degrees or the cylinder 80 is rotated 90 degrees to extend in the first direction. The division line 17 extending in the second direction orthogonal to the division line 17 is similarly divided. As a result, the optical device wafer 11 is divided into individual chips 33.

  Although the modified layer 29 is not formed inside the sapphire substrate 13 corresponding to the mask 27, this portion is very narrow, so that the dividing line 84 having the modified layer 29 is extended by the dividing jig 84. The line can be easily cleaved.

DESCRIPTION OF SYMBOLS 11 Optical device wafer 13 Sapphire substrate 17 Scheduled division line 19 Optical device 21 Device area 23 Outer peripheral area 25 Protective tape 27 Mask 28 Chuck table 29 Modified layer 31 Reflective film 33 Chip 34 Light beam irradiation unit 35 Light beam generation unit 36 Condensing 84 Dividing jig

Claims (4)

A wafer processing method having a device region in which a device is formed in each region partitioned by a plurality of division lines and an outer peripheral region surrounding the device region on the surface,
A masking step of applying a mask having a predetermined width from the outermost periphery of the wafer to the back surface corresponding to the outer peripheral region of the wafer;
After performing the masking step, the front side of the wafer is held by the chuck table, and a pulsed laser beam having a wavelength that is transparent to the wafer from the back side of the wafer to the inside of the wafer corresponding to the planned division line is collected. A modified layer forming step of irradiating the pulsed laser beam with a point positioned, and forming a modified layer serving as a division starting point inside the wafer along the division planned line;
After carrying out the modified layer forming step, a carrying step for carrying out the wafer from the chuck table and carrying the wafer to the next step;
A wafer processing method characterized by comprising: The wafer is composed of an optical device wafer in which a semiconductor layer is laminated on the surface of a sapphire substrate, and a plurality of optical devices are defined on the semiconductor layer by dividing lines.
The wafer processing method according to claim 1, wherein in the transporting step, the wafer is transported to a back surface processing step in which a reflective film is laminated on the back surface of the wafer.   3. The wafer processing method according to claim 2, further comprising a back surface processing step of laminating a reflective film on the back surface of the wafer.   The wafer according to any one of claims 1 to 3, further comprising a dividing step of dividing the wafer into individual devices by applying an external force to the scheduled dividing line of the wafer after performing the modified layer forming step. Processing method.

Images