JP2014116361A - Laser processing method and laser processing device for wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing method and a laser processing device for wafer that can form a suitable altered layer even on a wafer having an oxide film formed on its reverse surface.SOLUTION: There is provided a processing method of forming an altered layer in a substrate W having a device formed by irradiating a wafer which has an oxide film formed on a reverse surface of the substrate W with a laser light beam from the reverse surface side of the substrate W along a street. The method includes: a transmissivity calculation process of calculating transmissivity to the laser light beam transmitted into the substrate W by irradiating the substrate W with the laser light beam from the reverse surface side, and detecting energy of reflected light reflected by the oxide film formed on the reverse surface of the substrate W; an output calculation process of calculating an output of the irradiating laser light beam by dividing energy of the laser light beam to irradiate the inside of the substrate by the transmissivity; and an altered layer formation process of irradiating the substrate with the laser light beam having the output calculated by the output calculation process through the oxide film with its focusing point positioned in the substrate, and thereby forming the altered layer in the substrate along the street.

Description

  The present invention relates to a wafer laser processing method and a laser processing apparatus for irradiating a wafer such as a semiconductor wafer with a laser beam having transparency and forming a modified layer inside the wafer.

  In the semiconductor device manufacturing process, a plurality of regions are partitioned by dividing lines called streets arranged in a lattice pattern on the surface of a substantially wafer-shaped semiconductor wafer, and devices such as ICs, LSIs, etc. are partitioned in the partitioned regions. Form. Then, the semiconductor wafer is cut along the streets to divide the region in which the device is formed to manufacture individual semiconductor chips. In addition, an optical device wafer in which an optical device such as an LED is formed on the surface of a sapphire substrate is divided into individual optical devices by cutting along the street, and is widely used in electrical equipment.

  As a method of dividing a plate-like workpiece such as a semiconductor wafer, a pulsed laser beam having transparency to the workpiece is used, and a focused laser beam is irradiated inside the region to be divided and irradiated with the pulsed laser beam. Laser processing methods have also been attempted. The dividing method using this laser processing method is to irradiate a pulse laser beam having a wavelength that is transmissive to the workpiece by aligning the condensing point from one side of the workpiece to the inside. This is a technique for dividing a workpiece by continuously forming a modified layer along the street and applying an external force along the street whose strength is reduced by forming the modified layer. (For example, refer to Patent Document 1.)

  When forming a modified layer along the street inside the workpiece, if the laser beam is irradiated from the surface side of the wafer on which the device is formed, the device is damaged or the laser beam is blocked by the device. Since the modified layer cannot be reliably formed along the street in the interior of the wafer, the laser beam is irradiated from the back side of the wafer. (For example, see Patent Document 2.)

Japanese Patent No. 3408805 JP 2005-222986 A

In recent years, in a wafer having devices such as IC and LSI formed on the front surface, an oxide film such as SiO ₂ may be formed naturally or actively on the back surface in anticipation of a gettering effect. In such a wafer, when a laser beam having a wavelength that is transparent to the wafer is irradiated from the back side, a part of the light is reflected by the oxide film, and an appropriate deteriorated layer cannot be formed inside the wafer. There is.
Also in an optical device wafer in which an optical device such as an LED is formed on the surface of a sapphire substrate, an oxide film called DBR composed of SiO _{2 and} TiO ₂ is formed on the back surface of the sapphire substrate in order to improve luminance. In some cases, the same problem occurs when such an optical device wafer is irradiated with a laser beam having a wavelength having transparency to the wafer from the back side.

  The present invention has been made in view of the above-mentioned facts, and the main technical problem thereof is that a wafer having an oxide film formed on the back surface is irradiated with a laser beam having a wavelength that is transmissive to the wafer from the back surface side. Another object of the present invention is to provide a wafer laser processing method and a laser processing apparatus capable of forming an appropriate deteriorated layer inside a wafer.

In order to solve the main technical problem, according to the present invention, a wafer in which an oxide film is formed on the back surface of a substrate in which devices are formed in a plurality of regions partitioned by streets formed in a lattice pattern on the surface. In addition, the wafer laser processing method of irradiating a laser beam of a wavelength having transparency to the substrate along the street from the back side of the substrate, and forming a modified layer along the street inside the substrate,
The transmittance of the laser beam that is transmitted through the substrate by detecting the energy of the reflected light reflected from the oxide film formed on the back surface of the substrate by irradiating the substrate with a laser beam having a wavelength that is transparent to the substrate. A transmittance calculating step for calculating
An output calculation step of calculating the output of the laser beam to be irradiated by dividing the energy of the laser beam to be irradiated inside the substrate by the transmittance;
A modified layer that irradiates a laser beam having an output calculated in the output calculation step from the back side of the substrate through the oxide film with a focusing point positioned inside the substrate and forms a modified layer along the street inside the substrate. Including a forming step,
A wafer laser processing method is provided.

  After performing the modified layer forming step, an external force is applied to the wafer in which the modified layer is formed along the street inside the substrate, and the wafer is applied to each device along the street where the modified layer is formed. A dividing step of dividing is performed.

Further, according to the present invention, there is provided a workpiece holding means for holding the workpiece, a laser beam oscillation means for oscillating a laser beam, and an output adjusting means for adjusting the output of the laser beam oscillated by the laser beam oscillation means. Laser beam irradiating means for irradiating the workpiece held by the workpiece holding means with the laser beam whose output is adjusted by the adjusting means, and the workpiece holding means and the laser beam irradiating means are relatively processed and fed. In a laser processing apparatus comprising a processing feed means,
Reflected light receiving means for receiving reflected light of a laser beam applied to the workpiece held by the workpiece holding means;
The energy of the reflected light received by the reflected light receiving means is detected to determine the transmittance of the laser beam transmitted through the substrate, and the energy of the laser beam to be condensed inside the workpiece is divided by the transmittance. A control means for calculating the output of the laser beam to be irradiated and controlling the output adjusting means so as to irradiate the laser beam of the calculated output,
A laser processing apparatus is provided.

  In the wafer laser processing method according to the present invention, a laser beam having a wavelength transparent to the substrate is irradiated from the back side of the substrate, and the energy of the reflected light reflected by the oxide film formed on the back side of the substrate is detected. A transmittance calculating step for calculating the transmittance of the laser beam transmitted to the inside of the substrate, and an output calculating step for calculating the output of the laser beam to be irradiated by dividing the energy of the laser beam to be irradiated inside the substrate by the transmittance Then, the laser beam of the output calculated in the output calculation process is irradiated from the back surface side of the substrate through the oxide film with the focusing point positioned inside the substrate, and the modified layer is formed along the street inside the substrate. The layer formation process is included, so even if a part of the laser beam is reflected by the oxide film, the laser beam with the appropriate energy is irradiated inside the substrate. Can, it is possible to form an appropriate modified layer along the streets in the substrate.

  The laser processing apparatus according to the present invention includes a reflected light receiving unit that receives reflected light of a laser beam irradiated on a workpiece held by the workpiece holding unit, and a reflected light received by the reflected light receiving unit. Calculates the output of the laser beam to be irradiated by detecting the energy and calculating the transmittance of the laser beam that passes through the substrate, and dividing the energy of the laser beam to be focused inside the workpiece by the transmittance. Control means for controlling the output adjusting means of the laser beam irradiating means so as to irradiate the output laser beam, even if an oxide film is formed on the back surface of the substrate constituting the wafer as the workpiece In consideration of reflection of the laser beam by the oxide film, an appropriate modified layer can be formed inside the substrate.

The perspective view of the laser processing apparatus comprised according to this invention. The block block diagram of the laser beam irradiation means with which the laser processing apparatus shown in FIG. The block block diagram of the control means with which the laser processing apparatus shown in FIG. 1 is equipped. The perspective view and principal part expanded sectional view of the optical device wafer as a to-be-processed object processed by the laser processing method of the wafer by this invention. The perspective view which shows the state which affixed the optical device wafer shown in FIG. 4 on the dicing tape with which the cyclic | annular flame | frame was mounted | worn. Explanatory drawing of the transmittance | permeability calculation process in the laser processing method of the wafer by this invention. 6 is a control map showing the relationship between the voltage signal (V) corresponding to the energy of the received reflected light output from the photoelectric converter of the reflected light receiving means and the average output (W). Explanatory drawing of the modified layer formation process in the laser processing method of the wafer by this invention.

Preferred embodiments of a wafer laser processing method and a laser processing apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a perspective view of a laser processing apparatus constructed according to the present invention. A laser processing apparatus 1 shown in FIG. 1 includes a stationary base 2, a chuck table mechanism 3 that is disposed on the stationary base 2 so as to be movable in a machining feed direction indicated by an arrow X, and holds a workpiece. A laser beam irradiation unit support mechanism 4 disposed on the table 2 so as to be movable in an indexing direction indicated by an arrow Y perpendicular to the direction indicated by the arrow X, and a focal position adjustment direction indicated by an arrow Z on the laser beam irradiation unit support mechanism 4 And a laser beam irradiation unit 5 disposed so as to be movable.

  The chuck table mechanism 3 includes a pair of guide rails 31, 31 arranged in parallel along the direction indicated by the arrow X on the stationary base 2, and the direction indicated by the arrow X on the guide rails 31, 31. A first sliding block 32 movably disposed, a second sliding block 33 movably disposed on the first sliding block 32 in a direction indicated by an arrow Y, and the second sliding block A support table 35 supported by a cylindrical member 34 on a block 33 and a chuck table 36 as a workpiece holding means are provided. The chuck table 36 is made of a porous material and has a workpiece holding surface 361. A wafer as a workpiece is held on the chuck table 36 by suction means (not shown). Further, the chuck table 36 is rotated by a pulse motor (not shown) disposed in the cylindrical member 34. The chuck table 36 is provided with a clamp 362 for fixing an annular frame described later.

  The first sliding block 32 is provided with a pair of guided grooves 321 and 321 fitted to the pair of guide rails 31 and 31 on the lower surface thereof, and along the direction indicated by the arrow Y on the upper surface thereof. A pair of guide rails 322 and 322 formed in parallel are provided. The first sliding block 32 configured as described above has the guided grooves 321 and 321 fitted into the pair of guide rails 31 and 31, thereby the direction indicated by the arrow X along the pair of guide rails 31 and 31. It is configured to be movable. The chuck table mechanism 3 in the illustrated embodiment includes a processing feed means 37 for moving the first sliding block 32 in the direction indicated by the arrow X along the pair of guide rails 31, 31. The processing feed means 37 includes a male screw rod 371 disposed in parallel between the pair of guide rails 31 and 31, and a drive source such as a pulse motor 372 for rotationally driving the male screw rod 371. One end of the male screw rod 371 is rotatably supported by a bearing block 373 fixed to the stationary base 2, and the other end is connected to the output shaft of the pulse motor 372 by transmission. The male screw rod 371 is screwed into a penetrating female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the first sliding block 32. Accordingly, when the male screw rod 371 is driven to rotate forward and backward by the pulse motor 372, the first sliding block 32 is moved along the guide rails 31 and 31 in the machining feed direction indicated by the arrow X.

  The second sliding block 33 is provided with a pair of guided grooves 331 and 331 which are fitted to a pair of guide rails 322 and 322 provided on the upper surface of the first sliding block 32 on the lower surface thereof. By fitting the guided grooves 331 and 331 to the pair of guide rails 322 and 322, the guided grooves 331 and 331 are configured to be movable in the direction indicated by the arrow Y. The chuck table mechanism 3 in the illustrated embodiment is a first for moving the second slide block 33 along the pair of guide rails 322 and 322 provided in the first slide block 32 in the direction indicated by the arrow Y. The indexing and feeding means 38 is provided. The first index feed means 38 includes a male screw rod 381 disposed in parallel between the pair of guide rails 322 and 322, and a drive source such as a pulse motor 382 for rotationally driving the male screw rod 381. It is out. One end of the male screw rod 381 is rotatably supported by a bearing block 383 fixed to the upper surface of the first sliding block 32, and the other end is connected to the output shaft of the pulse motor 382. The male screw rod 381 is screwed into a penetrating female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the second sliding block 33. Therefore, when the male screw rod 381 is driven to rotate forward and reversely by the pulse motor 382, the second slide block 33 is moved along the guide rails 322 and 322 in the index feed direction indicated by the arrow Y.

  The laser beam irradiation unit support mechanism 4 includes a pair of guide rails 41, 41 arranged in parallel along the direction indicated by the arrow Y on the stationary base 2, and the arrow Y on the guide rails 41, 41. A movable support base 42 is provided so as to be movable in the direction. The movable support base 42 includes a movement support portion 421 that is movably disposed on the guide rails 41, 41, and a mounting portion 422 that is attached to the movement support portion 421. The mounting portion 422 is provided with a pair of guide rails 423 and 423 extending in the direction indicated by the arrow Z on one side surface in parallel. The laser beam irradiation unit support mechanism 4 in the illustrated embodiment includes a second index feed means 43 for moving the movable support base 42 in the direction indicated by the arrow Y along the pair of guide rails 41, 41. Yes. The second index feed means 43 includes a male screw rod 431 disposed in parallel between the pair of guide rails 41, 41, and a drive source such as a pulse motor 432 for rotationally driving the male screw rod 431. It is out. One end of the male screw rod 431 is rotatably supported by a bearing block (not shown) fixed to the stationary base 2, and the other end is connected to the output shaft of the pulse motor 432. The male screw rod 431 is screwed into a female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the moving support portion 421 constituting the movable support base 42. For this reason, when the male screw rod 431 is driven to rotate forward and backward by the pulse motor 432, the movable support base 42 is moved along the guide rails 41, 41 in the index feed direction indicated by the arrow Y.

  The laser beam irradiation unit 5 in the illustrated embodiment includes a unit holder 51 and laser beam irradiation means 6 attached to the unit holder 51. The unit holder 51 is provided with a pair of guided grooves 511 and 511 that are slidably fitted to a pair of guide rails 423 and 423 provided in the mounting portion 422. By being fitted to the guide rails 423 and 423, the guide rails 423 and 423 are supported so as to be movable in the direction indicated by the arrow Z.

  The laser beam irradiation unit 5 in the illustrated embodiment includes a condensing point position adjusting means 53 for moving the unit holder 51 along the pair of guide rails 423 and 423 in the direction indicated by the arrow Z. The condensing point position adjusting means 53 includes a male screw rod (not shown) disposed between the pair of guide rails 423 and 423, and a drive source such as a pulse motor 532 for rotationally driving the male screw rod. Thus, the unit holder 51 and the laser beam irradiation means 6 are moved along the pair of guide rails 423 and 423 in the direction indicated by the arrow Z by driving the male screw rod (not shown) in the forward or reverse direction by the pulse motor 532. In the illustrated embodiment, the laser beam irradiation means 6 is moved upward by driving the pulse motor 532 forward, and the laser beam irradiation means 6 is moved downward by driving the pulse motor 532 in the reverse direction. ing.

The laser beam irradiation means 6 in the illustrated embodiment includes a cylindrical casing 61 that is fixed to the unit holder 51 and extends substantially horizontally. The laser beam irradiation means 6 will be described with reference to FIG.
The laser beam irradiation means 6 shown in FIG. 2 includes a pulse laser beam oscillation means 62 disposed in a casing 61, an output adjustment means 63 for adjusting the output of the pulse laser beam oscillated by the pulse laser beam oscillation means 62, and the output adjustment. And a condenser 64 for condensing the pulse laser beam whose output is adjusted by means 63 and irradiating the workpiece W held on the chuck table 36. The pulse laser beam oscillation means 62 is composed of a pulse laser beam oscillator 621 composed of a YAG laser oscillator or a YVO4 laser oscillator, and a repetition frequency setting means 622 for setting the repetition frequency of the pulse laser beam oscillated by the pulse laser beam oscillator 621. The pulse laser beam oscillator 621, the repetition frequency setting unit 622, and the output adjustment unit 63 of the pulse laser beam oscillation unit 62 are controlled by a control unit described later.

  A condenser 64 constituting the laser beam irradiation means 6 is a half-wave plate 71, which is oscillated from the pulse laser beam oscillation means 62 and whose output is adjusted by the output adjustment means 63 and constitutes a reflected light receiving means 7 described later, a beam splitter. A condensing lens 641 for condensing the pulse laser beam guided through the 72 and the quarter-wave plate 73 and irradiating the workpiece W held on the chuck table 36 is provided.

  The reflected light receiving means 7 includes a half-wave plate 71 for adjusting the polarization plane of the linearly polarized pulse laser beam oscillated from the pulse laser beam oscillating means 62 and the output adjusted by the output adjusting means 63 to S-polarized light, and S-polarized light. A beam splitter 72 that reflects the P-polarized light and allows the P-polarized light to pass therethrough; a quarter-wave plate 73 that is disposed between the beam splitter 72 and the condenser lens 641 and converts linearly polarized light into circularly polarized light; A light receiving element 74 for receiving the reflected light applied to the workpiece W held on the chuck table 36, and a photoelectric converter 75 for outputting a voltage signal corresponding to the light energy received by the light receiving element 74; ing. The operation of the reflected light receiving means 7 configured as described above will be described. The linearly polarized pulse laser beam oscillated from the pulse laser beam oscillating means 62 and the output adjusted by the output adjusting means 63 is converted into a polarization plane by the ½ wavelength plate 71. Is adjusted to S-polarized light and guided to the beam splitter 72. The pulse laser beam whose polarization plane guided to the beam splitter 72 is adjusted to S-polarized light is reflected by the beam splitter 72 and guided to the ¼ wavelength plate 73, and the ¼ wavelength plate 73 converts the linearly polarized light into circularly polarized light. After the conversion, the workpiece W collected by the condenser lens 641 and held on the chuck table 36 is irradiated. In this way, even if the pulse laser beam applied to the workpiece W held on the chuck table 36 is a laser beam having a wavelength that is transmissive to the workpiece W, the pulse laser beam is uniform on the upper surface of the workpiece W. The reflected light that is reflected by the light is guided to the quarter-wave plate 73 through the condenser lens 641, and the S-polarized light whose rotational direction is reversed by the quarter-wave plate 73 is converted into the P-polarized light. The splitter 72 is reached. The P-polarized reflected light guided to the beam splitter 72 passes through the beam splitter 72, is received by the light receiving element 74, and is converted into a voltage signal corresponding to the light energy by the photoelectric converter 75. Then, the photoelectric converter 75 sends a voltage signal corresponding to the light energy of the reflected light received by the light receiving element 74 to the control means described later.

  Returning to FIG. 1, the description is continued. At the front end portion of the casing 61 constituting the laser beam irradiation means 6, an imaging means 8 for detecting a processing region to be laser processed by the laser beam irradiation means 6 is disposed. . In the illustrated embodiment, the imaging unit 8 includes, in addition to a normal imaging device (CCD) that captures an image with visible light, an infrared illumination unit that irradiates a workpiece with infrared rays, and an infrared ray that is irradiated by the infrared illumination units. And an imaging device (infrared CCD) that outputs an electrical signal corresponding to the infrared rays captured by the optical system, and sends the captured image signal to a control means (not shown).

  The laser processing apparatus 1 in the illustrated embodiment includes a control means 9 shown in FIG. The control means 9 is constituted by a computer, and a central processing unit (CPU) 91 that performs arithmetic processing according to a control program, a read-only memory (ROM) 92 that stores control programs and the like, and a readable and writable memory that stores arithmetic results and the like. A random access memory (RAM) 93, an input interface 94 and an output interface 95 are provided. Detection signals from the photoelectric converter 75 of the reflected light receiving means 7, the imaging means 8, the input means 90, and the like are input to the input interface 94 of the control means 9. From the output interface 95 of the control means 9, the pulse motor 372, pulse motor 382, pulse motor 432, pulse motor 532, pulse laser beam oscillator 621 of the pulse laser beam oscillation means 62, repetition frequency setting means 622, output adjustment means 63 To output a control signal.

The laser processing apparatus 1 in the illustrated embodiment is configured as described above, and the operation thereof will be described below.
4A and 4B show a perspective view of an optical device wafer as a wafer as a workpiece and a cross-sectional view showing an enlarged main part. In the optical device wafer 10 shown in FIGS. 4A and 4B, for example, a light emitting layer (epilayer) 12 made of a nitride semiconductor is laminated with a thickness of 5 μm on a surface 11a of a sapphire substrate 11 having a thickness of 100 μm. Yes. An optical device 122 such as a light emitting diode or a laser diode is formed in a plurality of regions partitioned by a plurality of streets 121 in which the light emitting layer (epi layer) 12 is formed in a lattice shape. On the back surface 11b of the sapphire substrate 11 constituting the optical device wafer 10 thus formed, an oxide film 13 called DBR made of SiO ₂ or TiO ₂ is formed in order to improve the luminance of the optical device. ing. Hereinafter, a processing method for forming a modified layer along the street 121 inside the sapphire substrate 11 constituting the optical device wafer 10 will be described.

  First, a wafer support step is performed in which the surface 12a of the light emitting layer (epi layer) 12 laminated on the surface 11a of the sapphire substrate 11 constituting the optical device wafer 10 is adhered to the surface of a dicing tape mounted on an annular frame. To do. That is, as shown in FIG. 5, the surface 12a of the light emitting layer (epi layer) 12 constituting the optical device wafer 10 on the surface of the dicing tape T having the outer peripheral portion mounted so as to cover the inner opening of the annular frame F. Affix. Accordingly, in the optical device wafer 10 attached to the surface of the dicing tape T, the oxide film 13 formed on the back surface 11b of the sapphire substrate 11 is on the upper side.

  When the wafer support process described above is performed, the dicing tape T side of the optical device wafer 10 is placed on the chuck table 36 of the laser processing apparatus 1 shown in FIG. Then, by operating a suction means (not shown), the optical device wafer 10 is sucked and held on the chuck table 36 via the dicing tape T (wafer holding step). Accordingly, in the optical device wafer 10 held on the chuck table 36, the oxide film 13 formed on the back surface 11b of the sapphire substrate 11 is on the upper side. The annular frame F on which the dicing tape T is mounted is fixed by a clamp 362 disposed on the chuck table 36.

  As described above, the chuck table 36 that sucks and holds the optical device wafer 10 is positioned directly below the imaging unit 8 by the processing feeding unit 37. When the chuck table 36 is positioned immediately below the image pickup means 8, the image pickup means 8 and a control means (not shown) execute an alignment operation for detecting a processing region to be laser processed on the optical device wafer 10. That is, the imaging unit 8 and the control unit 9 align the street 121 formed in a predetermined direction of the optical device wafer 10 with the condenser 64 of the laser beam irradiation unit 6 that irradiates the laser beam along the street 121. Image processing such as pattern matching is performed to perform alignment of the laser beam irradiation position. The alignment of the laser beam irradiation position is similarly performed on the street 121 formed in the optical device wafer 10 and extending in a direction orthogonal to the predetermined direction. At this time, the surface 12a of the light emitting layer (epi layer) 12 on which the streets 121 of the optical device wafer 10 are formed is located on the lower side, but the imaging means 8 captures infrared rays and infrared rays as described above. Since the image pickup means is composed of an optical system and an image pickup device (infrared CCD) that outputs an electric signal corresponding to infrared rays, the street 121 is seen through from the side of the oxide film 13 formed on the back surface 11b of the sapphire substrate 11. Can be imaged.

  If the street 121 formed on the optical device wafer 10 held on the chuck table 36 is detected as described above and alignment of the laser beam irradiation position is performed, the sapphire substrate constituting the optical device wafer 10 11 is irradiated with a laser beam having a wavelength (for example, 1064 nm) having transparency to the sapphire substrate 11, and the energy of the reflected light reflected by the oxide film 13 formed on the back surface 11b of the sapphire substrate 11 is detected. Then, a transmittance calculating step for calculating the transmittance of the laser beam transmitted through the sapphire substrate 11 is performed. In order to carry out this transmittance calculation step, the outer periphery surrounding the device region in which the optical device 122 of the optical device wafer 10 held on the chuck table 36 is formed by operating the processing feeding means 37 as shown in FIG. The surplus area (area where the optical device is not formed) is positioned directly below the condenser 64 of the laser beam irradiation means 6. Then, by adjusting the focal point P of the pulsed laser beam irradiated from the condenser 64 to a position below, for example, 25 μm from the upper surface of the oxide film 13 formed on the back surface 11 b of the sapphire substrate 11 constituting the optical device wafer 10. A condensing point is positioned inside the sapphire substrate 11. Next, a pulse having energy (for example, average output: 0.3 W) of a laser beam to be irradiated inside the sapphire substrate 11 in order to operate the laser beam irradiation means 6 to form a modified layer inside the sapphire substrate 11. Irradiate laser beam LB. In this way, the pulsed laser beam LB irradiated from the oxide film 13 side formed on the back surface 11 b of the sapphire substrate 11 is irradiated to the condensing point P, but a part thereof is reflected by the upper surface of the oxide film 13. The reflected light LB0 reflected from the upper surface of the oxide film 13 is received by the light receiving element 74 through the condenser lens 641, the quarter wavelength plate 73, and the beam splitter 72 as described above, and converted into light energy by the photoelectric converter 75. It is converted into a corresponding voltage signal. Then, the photoelectric converter 75 sends a voltage signal corresponding to the light energy of the reflected light received by the light receiving element 74 to the control means 9.

  Here, the relationship between the voltage signal (V) corresponding to the energy of the reflected light LB0 received by the photoelectric converter 75 and the average output (W) will be described with reference to the control map shown in FIG. In FIG. 7, the horizontal axis represents a voltage signal (V) corresponding to the energy of the reflected light LB0 received by the light receiving element 74 output from the photoelectric converter 75, and the vertical axis represents the pulse laser beam corresponding to the voltage signal (V). Average output (W) is shown. The control map set in this way is stored in a random access memory (RAM). Therefore, when the voltage signal (V) corresponding to the energy of the reflected light LB0 received by the light receiving element 74 output from the photoelectric converter 75 is 1.0 V, for example, the control means 9 uses the control map shown in FIG. The average output (W) of the reflected light LB0 received by the light receiving element 74 is determined to be 0.03 W, and the transmittance of the pulse laser beam is obtained. That is, since the average output of the pulse laser beam irradiated to the optical device wafer 10 is 0.3 W, the average output of the pulse laser beam transmitted to the optical device wafer 10 is 0.3 W−0.03 W = 0.27 W, which is transmitted. The rate is 0.27W / 0.3W = 0.9.

  If the transmittance of the pulse laser beam irradiated to the optical device wafer 10 is calculated by performing the above-described transmittance calculation step, the control means 9 uses the transmittance of the energy of the laser beam to be irradiated inside the sapphire substrate 11. An output calculation step of calculating the output of the laser beam to be irradiated by division is performed. That is, if the average output of the energy of the laser beam to be irradiated into the sapphire substrate 11 is 0.3 W, the output of the laser beam to be irradiated is 0.3 W ÷ 0.9 = 0.334 W. The output of the laser beam to be irradiated (0.334 W in this embodiment) calculated in this way is temporarily stored in a random access memory (RAM) 93 of the control means 9.

If the output calculation process is performed as described above, the laser beam of the output calculated in the output calculation process is irradiated from the back surface side of the substrate through the oxide film with the focusing point positioned inside the substrate, and the street inside the substrate is irradiated. A modified layer forming step of forming a modified layer along the line is performed.
In order to carry out the modified layer forming step, as shown in FIG. 8A, the chuck table 36 is moved to the laser beam irradiation area where the condenser 64 of the laser beam irradiation means 6 for irradiating the laser beam is located, and a predetermined street is formed. One end of 121 (the left end in FIG. 8A) is positioned directly below the condenser 64 of the laser beam irradiation means 6. Next, the condensing point P of the pulsed laser beam irradiated from the condenser 64 is adjusted to a position below, for example, 25 μm from the upper surface of the oxide film 13 formed on the back surface 11 b of the sapphire substrate 11 constituting the optical device wafer 10. The focusing point is positioned inside the sapphire substrate 11. Then, while irradiating the sapphire substrate 11 constituting the optical device wafer 10 from the condenser 64 with a pulsed laser beam having a wavelength having transparency, the chuck table 36 is set in a direction indicated by an arrow X1 in FIG. Move at the feed rate of. Then, as shown in FIG. 8B, when the irradiation position of the condenser 64 of the laser beam irradiation means 6 reaches the position of the other end of the street 121, the irradiation of the pulse laser beam is stopped and the chuck table 36 is moved. Stop. In this way, when the condensing point P of the pulsed laser beam having a wavelength that is transparent to the sapphire substrate 11 constituting the optical device wafer 10 is positioned from the concentrator 64 and irradiated inside the sapphire substrate 11, the control means 9 controls the output adjusting means 63 so that the output of the pulse laser oscillated from the pulse laser beam oscillating means 62 becomes 0.334 W calculated by the output calculating step. The pulse laser beam whose output is adjusted to 0.334 W in this way is irradiated from the condenser 64 with the condensing point P positioned inside the sapphire substrate 11, but a part is formed on the back surface 11 b of the sapphire substrate 11. Since the reflectivity is 0.9 and the transmittance is 0.9, the output of the pulse laser beam irradiated to the condensing point P is set as the average output of the energy of the laser beam to be irradiated inside the sapphire substrate 11. Is 0.3W. As a result, an appropriate modified layer 110 is formed along the street 121 inside the optical device wafer 10 (modified layer forming step).

The processing conditions in the modified layer forming step are set as follows, for example.
Wavelength: 1064 nm pulse laser Repeat frequency: 100 kHz
Average output: 0.3 W (should be irradiated inside the sapphire substrate 11
(Average output of laser beam energy)
Condensing spot diameter: φ1μm
Processing feed rate: 400 mm / sec

  When the modified layer forming step is performed along the predetermined street 121 as described above, the chuck table 36 is indexed and moved in the direction indicated by the arrow Y by the interval of the streets 121 formed on the optical device wafer 10 (indexing step). ), Performing the modified layer forming step. When the modified layer forming process is performed along all the streets 121 formed in the predetermined direction in this way, the chuck table 36 is rotated 90 degrees to form the streets 121 formed in the predetermined direction. On the other hand, the modified layer forming step is performed along the street 121 extending in a direction perpendicular to the vertical direction. The semiconductor wafer 10 in which the modified layer forming process is performed along all the streets 121 is transferred to a wafer dividing process in which the modified layer forming process is broken along the streets 121 in which the modified layer 110 is formed.

Although the present invention has been described based on the illustrated embodiment, the present invention is not limited to the embodiment, and various modifications are possible within the scope of the gist of the present invention. For example, in the above-described embodiment, a light emitting layer (epi layer) 12 made of a nitride semiconductor is stacked on the surface 11a of the sapphire substrate 11, and a DBR made of SiO ₂ or TiO ₂ on the back surface 11b of the sapphire substrate 11 Although an example in which the present invention is applied to an optical device wafer 10 on which a called oxide film 13 is formed has been shown, the present invention is such that an IC, LSI, or other device is formed on the surface of the substrate, and an oxide film such as SiO ₂ is formed on the back surface of the substrate. The same effect can be obtained even if it is applied to a semiconductor wafer on which is formed.
In the above-described embodiment, an example in which the transmittance calculation step, the output calculation step, and the modified layer formation step are performed separately is shown. However, the modified layer formation is performed while the transmittance calculation step and the output calculation step are performed. You may implement a process simultaneously.

2: stationary base 3: chuck table mechanism 36: chuck table 37: processing feed means 38: first index feed means 4: laser beam irradiation unit support mechanism 42: movable support base 43: second index feed means 5: Laser beam irradiation unit 53: Condensing point position adjusting unit 6: Laser beam irradiating unit 62: Pulse laser beam oscillating unit 63: Output adjusting unit 64: Condenser 641: Condensing lens 7: Reflected light receiving unit 71: 1/2 wavelength plate 72: Beam splitter 73: 1/4 wavelength plate 74: Light receiving element 75: Photoelectric converter 8: Imaging means 9: Control means 10: Optical device wafer

Claims (3)

A laser beam having a wavelength transparent to the substrate is applied to the wafer on which the oxide film is formed on the back surface of the substrate on which the device is formed in a plurality of regions partitioned by streets formed in a lattice pattern on the surface. A wafer laser processing method of irradiating along a street from the side and forming a modified layer along the street inside the substrate,
The transmittance of the laser beam that is transmitted through the substrate by detecting the energy of the reflected light reflected from the oxide film formed on the back surface of the substrate by irradiating the substrate with a laser beam having a wavelength that is transparent to the substrate. A transmittance calculating step for calculating
An output calculation step of calculating the output of the laser beam to be irradiated by dividing the energy of the laser beam to be irradiated inside the substrate by the transmittance;
A modified layer that irradiates a laser beam having an output calculated in the output calculation step from the back side of the substrate through the oxide film with a focusing point positioned inside the substrate and forms a modified layer along the street inside the substrate. Including a forming step,
A wafer laser processing method characterized by the above.   After performing the modified layer forming step, an external force is applied to the wafer in which the modified layer is formed along the street inside the substrate, and the wafer is applied to each device along the street where the modified layer is formed. The wafer laser processing method according to claim 1, wherein a dividing step of dividing is performed. A workpiece holding means for holding a workpiece, a laser beam oscillating means for oscillating a laser beam, and an output adjusting means for adjusting the output of the laser beam oscillated by the laser beam oscillating means. A laser beam irradiating unit for irradiating the workpiece held by the workpiece holding unit with a laser beam; and a process feeding unit for relatively processing and feeding the workpiece holding unit and the laser beam irradiating unit. In laser processing equipment,
Reflected light receiving means for receiving reflected light of a laser beam applied to the workpiece held by the workpiece holding means;
The energy of the reflected light received by the reflected light receiving means is detected to determine the transmittance of the laser beam transmitted through the substrate, and the energy of the laser beam to be condensed inside the workpiece is divided by the transmittance. A control means for calculating the output of the laser beam to be irradiated and controlling the output adjusting means so as to irradiate the laser beam of the calculated output,
Laser processing equipment characterized by that.

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