JP5583981B2 - Laser processing method - Google Patents

Description

  The present invention relates to a laser processing method for forming a deteriorated layer inside a wafer such as a semiconductor wafer or an optical device 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 devices. In addition, optical device wafers with gallium nitride compound semiconductors laminated on the surface of sapphire substrates are also divided into optical devices such as individual light emitting diodes and laser diodes by cutting along the streets, and are widely used in electrical equipment. ing.

  As a method of dividing a wafer such as the above-mentioned semiconductor wafer along the street, a pulsed laser beam having a wavelength that is transparent to the wafer is used, and the focused laser beam is irradiated to the inside of the region to be divided. Laser processing methods have been tried. The dividing method using this laser processing method is to irradiate a pulse laser beam having a wavelength of 1064 nm, for example, having a light converging point from one surface side of the wafer and having the light converging point inside, so that a street is formed inside the wafer. The deteriorated layer is continuously formed along the surface, and the workpiece is divided by applying an external force along the street whose strength is reduced by the formation of the deteriorated layer. (For example, refer to Patent Document 1.) When an altered layer is formed inside along the street formed on the wafer as described above, a laser beam condensing point is positioned at a predetermined depth from the upper surface of the wafer and irradiated. ing.

  However, since the wafer has undulation and the thickness varies, it is difficult to perform uniform laser processing. That is, when forming a deteriorated layer along the street inside the wafer, if there is variation in the thickness of the wafer, it will be uniform at a predetermined depth position from the irradiation surface that irradiates the laser beam due to the refractive index when irradiating the laser beam. However, a deteriorated layer cannot be formed.

  In order to solve the above problem, the upper surface height position of the wafer held on the chuck table is detected, and the condensing point position by the condenser that irradiates the laser beam based on the detected upper surface height position of the wafer is determined. A laser processing apparatus to be controlled is disclosed in Patent Document 2 below.

Japanese Patent No. 3408805 JP 2005-313182 A

  Thus, when a denatured layer is formed by irradiating a laser beam having a wavelength transmissive to the wafer at a predetermined depth from the back surface of the wafer to form a denatured layer, the denatured layer is formed on the surface of the substrate at a portion where the substrate is thin. The altered layer may reach the functional layer formed by stacking. When the altered layer formed on the substrate by irradiating the laser beam in this way reaches the functional layer or approaches very close to the functional layer, there is a problem that the functional layer is damaged by the influence of energy by irradiating the laser beam. Such a problem is that the wavelength having transparency to the sapphire substrate from the back side of the optical device wafer in which the optical device in which the n-type nitride semiconductor layer and the p-type nitride semiconductor layer are laminated on the surface of the sapphire substrate is formed. This occurs especially when a deteriorated layer is formed along the street inside the sapphire substrate by irradiating the laser beam.

  The present invention has been made in view of the above-mentioned facts, and its main technical problem is to form a deteriorated layer along the street without damaging the functional layer inside the wafer in which the functional layer is formed on the surface of the substrate. It is to provide a laser processing method that can be performed.

In order to solve the above-mentioned main technical problem, according to the present invention, a substrate in a wafer in which devices are formed in a plurality of regions partitioned by a plurality of streets in which functional layers are stacked on the surface of the substrate and are formed in a lattice shape. A laser processing method of irradiating a laser beam of a wavelength having transparency to the substrate from the back side of the substrate, and forming a deteriorated layer along the street inside the substrate,
A wafer holding step for holding the wafer on the chuck table holding the workpiece of the laser processing apparatus with the back side of the substrate facing up;
A detection light having a wavelength that is transparent to the wafer substrate held on the chuck table is irradiated along the street from the back side of the substrate along the street, and along the street based on the reflected light reflected on the back and front surfaces of the substrate. A height position measuring step for measuring a first height position (h1) from the upper surface of the chuck table to the back surface of the substrate and a second height position (h2) from the upper surface of the chuck table to the surface of the substrate;
A condensing point of the laser beam is positioned at an intermediate portion between the first height position (h1) and the second height position (h2) measured in the height position measuring step, and is irradiated along the street. seen containing a deteriorated layer forming step for forming a deteriorated layer which does not reach the functional layer along the streets in the substrate, the by,
The height position measuring step includes a light emitting source that emits light having a predetermined wavelength region, and a reflected light that guides the light from the light emitting source to the first path and reverses the first path to the second path. A first light branching unit that guides the light to the first path, a collimation lens that forms the light guided to the first path into parallel light, and a third path and a fourth path that convert the light formed by the collimation lens into parallel light. A second light splitting unit that divides the path, an objective lens that is disposed in the third path and guides the light guided to the third path to a wafer held by the chuck table, and the second light Parallel light arranged between the branching means and the objective lens is guided to the third path, and a focusing point is positioned on the objective lens to generate light from the objective lens as pseudo-parallel light. A condensing lens that is disposed on the fourth path and a parallel led to the fourth path Reflecting mirror for reflecting the reflected light back to the fourth path, and reflecting the fourth path, the second light branching means, the collimation lens and the first path reflected by the reflecting mirror. Then, the reflected light guided from the first light branching means to the second path, and reflected by the wafer held on the chuck table, the objective lens, the condenser lens, and the second light branching means. And a diffraction grating that diffracts the interference between the collimation lens and the first path and the reflected light guided from the first light branching means to the second path, and the reflection diffracted by the diffraction grating An image sensor that detects light intensity in a predetermined wavelength range of light, a spectral interference waveform is obtained based on a detection signal from the image sensor, and waveform analysis is performed based on the spectral interference waveform and a theoretical waveform function. The fourth An optical path length difference (d) between an optical path length to the reflecting mirror in the path and an optical path length to the wafer held on the chuck table in the third path is obtained, and based on the optical path length difference (d) A first optical path length difference (reflected by the back surface of the substrate) using a measuring means comprising a control means for determining the distance from the front surface of the chuck table to the back surface and front surface of the wafer held by the chuck table. The first height position (h1) from the top surface of the chuck table to the back surface of the substrate and the top surface of the substrate from the top surface of the chuck table based on d1) and the second optical path length difference (d2) reflected by the surface of the substrate Measuring the second height position (h2) up to
A laser processing method is provided.

In the altered layer forming step, based on the first height position (h1) and the second height position (h2), the condensing point of the laser beam is set to a position {h2 + (h1−h2) / 2}. Position and implement.
The deteriorated layer forming step is based on the first height position (h1) and the second height position (h2). It is carried out by positioning at the position of h2 + (h1−h2) / 2}, and the irradiation of the laser beam is stopped at the position where the thickness of the substrate is less than the set thickness.

In the laser processing method according to the present invention, detection light having a wavelength that is transparent to the wafer substrate held on the chuck table is irradiated along the street from the back surface side of the substrate, and reflected by the back surface and the front surface of the substrate. Based on the reflected light, the first height position (h1) from the upper surface of the chuck table to the back surface of the substrate and the second height position (h2) from the upper surface of the chuck table to the surface of the substrate are measured along the street. A position where the laser beam condensing point is located in the middle of the height position measuring step and the first height position (h1) and the second height position (h2) measured in the height position measuring step. and a deteriorated layer forming step for forming a deteriorated layer which does not reach the inside functional layer along the streets of the substrate by irradiating along the height position measurement step, a predetermined wavelength territory A light-emitting source that emits light having a first light branching means that guides light from the light-emitting source to a first path and guides reflected light that travels backward through the first path to a second path; A collimation lens for forming the light guided to the path into parallel light, a second light branching means for splitting the light formed into the parallel light by the collimation lens into a third path and a fourth path, An objective lens that guides the light guided to the third path to the wafer held on the chuck table, and the third path disposed between the second light branching means and the objective lens. A condensing lens that condenses the guided parallel light, positions a condensing point on the objective lens, and generates light from the objective lens as pseudo-parallel light, and is disposed in the fourth path and guided to the fourth path. A reflection mirror that reflects the reflected parallel light and reverses the reflected light to the fourth path; The fourth path, the second light branching means, the collimation lens, and the reflected light guided from the first light branching means to the second path after being reflected by the reflecting mirror, and the chuck table The reflected light reflected by the wafer held on the objective lens, the condensing lens, the second light branching means, the collimation lens, and the first path and led to the second path from the first light branching means A diffraction grating that diffracts the interference with the image sensor, an image sensor that detects light intensity in a predetermined wavelength range of the reflected light diffracted by the diffraction grating, and a spectral interference waveform based on a detection signal from the image sensor, Waveform analysis is performed based on the spectral interference waveform and the theoretical waveform function, and the optical path length to the reflecting mirror in the fourth path and the wafer held on the chuck table in the third path Control for obtaining an optical path length difference (d) with respect to the optical path length to c and obtaining distances from the surface of the chuck table to the back surface and the surface of the wafer substrate held on the chuck table based on the optical path length difference (d) And measuring means comprising: a first optical path length difference (d1) reflected on the back surface of the substrate and a second optical path length difference (d2) reflected on the surface of the substrate; Since the first height position (h1) from the upper surface to the back surface of the substrate and the second height position (h2) from the upper surface of the chuck table to the surface of the substrate are measured , the substrate has waviness and the thickness of the substrate is Even if there is a thin portion, the altered layer can be formed without damaging the functional layer formed by being laminated on the surface of the substrate.

The perspective view and principal part expanded sectional view of the optical device wafer as a wafer processed by the laser processing method by this invention. The perspective view of the laser processing apparatus for enforcing the laser processing method by this invention. FIG. 3 is a block configuration diagram of a position measurement device and a laser beam irradiation means constituting a position measurement / laser irradiation unit equipped in the laser processing apparatus shown in FIG. 2. Explanatory drawing which shows the spectral interference waveform calculated | required by the control means which comprises the position measuring device shown in FIG. Explanatory drawing of the optical path length difference which shows the optical path length difference to the back surface of the workpiece calculated | required by the control means which comprises the position measuring apparatus shown in FIG. 3, the optical path length to the surface of a workpiece, and the thickness of a workpiece . FIG. 3 is an explanatory diagram showing a relationship with a coordinate position in a state where the optical device wafer shown in FIG. 1 is held at a predetermined position of a chuck table of the laser processing apparatus shown in FIG. 2. Explanatory drawing of the height position detection process implemented by the measuring device of the workpiece hold | maintained at the chuck table with which the laser processing apparatus shown in FIG. 2 was equipped. Explanatory drawing which shows 1st Embodiment of the deteriorated layer formation process which forms a deteriorated layer in the optical device wafer shown in FIG. 1 with the laser processing apparatus shown in FIG. Explanatory drawing which shows 2nd Embodiment of the deteriorated layer formation process which forms a deteriorated layer in the optical device wafer shown in FIG. 1 with the laser processing apparatus shown in FIG.

  Hereinafter, a preferred embodiment of a laser processing method according to the present invention will be described in detail with reference to the accompanying drawings.

  1A and 1B show a perspective view of an optical device wafer processed by the laser processing method according to the present invention and a sectional view showing an enlarged main part. An optical device wafer 10 shown in FIGS. 1A and 1B includes an optical device layer (for example, an n-type nitride semiconductor layer and a p-type nitride semiconductor layer formed on a surface 11a of a sapphire substrate 11 having a thickness of 120 μm). (Epi layer) 12 (functional layer) is laminated with a thickness of 10 μm, for example. 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 optical device layer (epi layer) 12 is formed in a lattice shape. If the sapphire substrate 11 constituting the optical device wafer 10 has waviness, the thickness of the sapphire substrate 11 and the optical device layer (epi layer) 12 varies as shown in FIG. Hereinafter, a laser beam having a wavelength having transparency to the substrate 11 is irradiated from the back surface side of the substrate 11 of the optical device wafer 10 having variations in thickness of the sapphire substrate 11 and the optical device layer (epi layer) 12. A laser processing method for forming a deteriorated layer along the street 121 inside will be described.

  FIG. 2 is a perspective view of a laser processing apparatus for carrying out the laser processing method according to the present invention. A laser processing apparatus 1 shown in FIG. 2 includes a stationary base 2 and a chuck table mechanism that is disposed on the stationary base 2 so as to be movable in a machining feed direction (X-axis direction) indicated by an arrow X and holds a workpiece. 3, a laser beam irradiation unit support mechanism 4 disposed on the stationary base 2 so as to be movable in an indexing feed direction (Y axis direction) indicated by an arrow Y orthogonal to the X axis direction, and the laser beam irradiation unit support mechanism 4 And a position measurement / laser irradiation unit 5 disposed so as to be movable in a condensing point position adjustment direction (Z-axis direction) indicated by an arrow Z.

  The chuck table mechanism 3 includes a pair of guide rails 31 and 31 disposed in parallel along the X-axis direction on the stationary base 2, and is arranged on the guide rails 31 and 31 so as to be movable in the X-axis direction. A first sliding block 32 provided, a second sliding block 33 movably disposed on the first sliding block 32 in the Y-axis direction, and a cylindrical member on the second sliding block 33 And a chuck table 36 as a workpiece holding means. The chuck table 36 includes a suction chuck 361 formed of a porous material, and holds a workpiece on a holding surface which is the upper surface of the suction chuck 361 by suction means (not shown). The chuck table 36 configured as described above 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 that supports the workpiece via a protective tape.

  The first sliding block 32 has a pair of guided grooves 321 and 321 fitted to the pair of guide rails 31 and 31 on the lower surface thereof, and is parallel to the upper surface along the X-axis direction. A pair of formed guide rails 322 and 322 are provided. The first sliding block 32 configured in this manner moves in the X-axis direction along the pair of guide rails 31, 31 when the guided grooves 321, 321 are fitted into the pair of guide rails 31, 31. Configured to be possible. The chuck table mechanism 3 in the illustrated embodiment includes a processing feed means 37 for moving the first slide block 32 along the pair of guide rails 31, 31 in the X-axis direction. 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. Therefore, the first slide block 32 is moved in the X-axis direction along the guide rails 31 and 31 by driving the male screw rod 371 forward and backward by the pulse motor 372.

  The laser processing apparatus 1 in the illustrated embodiment includes processing feed amount detection means 374 for detecting the processing feed amount of the chuck table 36. The processing feed amount detection means 374 includes a linear scale 374a disposed along the guide rail 31, and a read head disposed along the linear scale 374a along with the first sliding block 32 disposed along the first sliding block 32. 374b. In the illustrated embodiment, the reading head 374b of the feed amount detecting means 374 sends a pulse signal of one pulse every 1 μm to the control means described later. Then, the control means to be described later detects the machining feed amount of the chuck table 36 by counting the input pulse signals. When the pulse motor 372 is used as the drive source of the machining feed means 37, the machining feed amount of the chuck table 36 is counted by counting the drive pulses of the control means to be described later that outputs a drive signal to the pulse motor 372. Can also be detected. When a servo motor is used as a drive source for the machining feed means 37, a pulse signal output from a rotary encoder that detects the rotation speed of the servo motor is sent to a control means described later, and the pulse signal input by the control means. By counting, the machining feed amount of the chuck table 36 can also be detected.

  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 Y-axis direction. The chuck table mechanism 3 in the illustrated embodiment has a first index 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 Y-axis direction. A 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, by driving the male screw rod 381 forward and backward by the pulse motor 382, the second slide block 33 is moved along the guide rails 322 and 322 in the Y-axis direction.

  The laser processing apparatus 1 in the illustrated embodiment includes index feed amount detection means 384 for detecting the index processing feed amount of the second sliding block 33. The index feed amount detecting means 384 includes a linear scale 384a disposed along the guide rail 322 and a read head disposed along the linear scale 384a along with the second sliding block 33 disposed along the second sliding block 33. 384b. In the illustrated embodiment, the reading head 384b of the feed amount detection means 384 sends a pulse signal of one pulse every 1 μm to the control means described later. Then, the control means described later detects the index feed amount of the chuck table 36 by counting the input pulse signals. When the pulse motor 382 is used as the drive source of the first indexing and feeding means 38, the drive table of the chuck table 36 is counted by counting the drive pulses of the control means to be described later that outputs a drive signal to the pulse motor 382. The index feed amount can also be detected. When a servo motor is used as a drive source for the machining feed means 37, a pulse signal output from a rotary encoder that detects the rotation speed of the servo motor is sent to a control means described later, and the pulse signal input by the control means. It is possible to detect the index feed amount of the chuck table 36 by counting.

  The laser beam irradiation unit support mechanism 4 includes a pair of guide rails 41 and 41 disposed in parallel along the Y-axis direction on the stationary base 2 and a direction indicated by an arrow Y on the guide rails 41 and 41. A movable support base 42 is provided so as to be movable. 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 Z-axis direction 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 along the pair of guide rails 41 and 41 in the Y-axis direction. 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 reversely by the pulse motor 432, the movable support base 42 is moved along the guide rails 41, 41 in the Y-axis direction.

  The position measurement and laser irradiation unit 5 in the illustrated embodiment includes a unit holder 51 and a cylindrical unit housing 52 attached to the unit holder 51, and the unit holder 51 is connected to the movable support base 42. The mounting portion 422 is movably disposed along a pair of guide rails 423 and 423. A unit housing 52 attached to the unit holder 51 has a position measuring means for detecting the height position of the optical device wafer 10 which is a workpiece held on the chuck table 36 and a workpiece held on the chuck table 36. Laser beam irradiation means for irradiating the workpiece with a laser beam is provided. The position measuring unit and the laser beam irradiation unit will be described with reference to FIG.

  The position measuring means 6 in the illustrated embodiment emits light having a predetermined wavelength region, guides the light from the light source 61 to the first path 6a, and reverses the first path 6a. The first light splitting means 62 that guides the reflected light to the second path 6b, the collimation lens 63 that forms the light guided to the first path 6a into parallel light, and the collimation lens 63 form the parallel light. And a second light branching means 64 for dividing the light into a third path 6c and a fourth path 6d.

  As the light emitting source 61, for example, an LED, an SLD, an LD, a halogen power source, an ASE power source, or a supercontinuum power source that emits light having a wavelength of 820 to 870 nm can be used. As the first optical branching unit 62, a polarization maintaining fiber coupler, a polarization maintaining fiber circulator, a single mode fiber coupler, a single mode fiber coupler circulator, or the like can be used. In the illustrated embodiment, the second optical branching unit 64 is constituted by a beam splitter 641 and a direction conversion mirror 642. The path from the light emitting source 61 to the first light branching means 62 and the first path 6a are constituted by optical fibers.

  The third path 6c includes an objective lens 65 that guides the light guided to the third path 6c to the optical device wafer 10 as a workpiece held by the chuck table 36, the objective lens 65, and the A condensing lens 66 is disposed between the second light branching means 64. This condensing lens 66 condenses the parallel light guided from the second light branching means 64 to the third path 6c, positions the condensing point in the objective lens 65, and quasi-parallels the light from the objective lens 65. Generate into light. As described above, the condenser lens 66 is disposed between the objective lens 65 and the second light branching means 64 to generate the light from the objective lens 65 as quasi-parallel light, which is held on the chuck table 36. When the reflected light reflected by the optical device wafer 10 travels backward through the objective lens 65, the condenser lens 66, the second light branching means 64, and the collimation lens 63, it is converged on the optical fiber constituting the first path 6a. Can do. The optical device wafer 10 is placed on the chuck table 36 at the optical device layer (epi layer) 12 side. Accordingly, in the optical device wafer 10 held on the chuck table 36, the back surface 11b of the sapphire substrate 11 is on the upper side (wafer holding step). The objective lens 65 is mounted on a lens case 651. The lens case 651 is held in the vertical direction in FIG. 3, that is, the chuck table 36 by a first focusing point position adjusting means 650 comprising a voice coil motor, a linear motor or the like. It can be moved in the condensing point position adjustment direction (Z-axis direction) perpendicular to the surface. The first focusing point position adjusting unit 650 is controlled by a control unit described later.

  The fourth path 6d is provided with a reflection mirror 67 that reflects the parallel light guided to the fourth path 6d and reverses the reflected light to the fourth path 6d. The reflection mirror 67 is attached to the lens case 651 of the objective lens 65 in the illustrated embodiment.

  In the second path 6b, a collimation lens 68, a diffraction grating 69, a condenser lens 70, and a line image sensor 71 are disposed. The collimation lens 68 is reflected by the reflecting mirror 67 and travels backward from the first light branching means 62 to the second path 6d, the second light branching means 64, the collimation lens 63, and the first path 6a. The reflected light guided to 6b and reflected by the optical device wafer 10 held on the chuck table 36 are reflected through the objective lens 65, the condensing lens 66, the second light branching means 64, the collimation lens 63, and the first path 6a. Reversely, the reflected light guided from the first light branching means 62 to the second path 6b is formed into parallel light. The diffraction grating 69 diffracts the interference of the both reflected lights formed in the parallel light by the collimation lens 68 and sends a diffraction signal corresponding to each wavelength to the line image sensor 71 via the condenser lens 70. The line image sensor 71 detects the light intensity at each wavelength of the reflected light diffracted by the diffraction grating 69 and sends a detection signal to the control means 80.

  The control means 80 obtains the spectral interference waveform from the detection signal from the image sensor 71, executes waveform analysis based on the spectral interference waveform and the theoretical waveform function, and the optical path length to the reflection mirror 67 in the fourth path 6d. And a first optical path length difference (d1) between the optical path length to the back surface 11b (upper surface) of the sapphire substrate 11 constituting the optical device wafer 10 held on the chuck table 36 in the third path 6c, and 4 to the reflection mirror in the path 6d and to the surface 11a of the sapphire substrate 11 constituting the optical device wafer 10 held by the chuck table 36 in the third path 6c (interface with the optical device layer 12). A second optical path length difference (d2) from the optical path length is obtained. That is, the control means 10 obtains a spectral interference waveform as shown in FIG. 4 based on the detection signal from the image sensor 71. In FIG. 4, the horizontal axis indicates the wavelength of the reflected light, and the vertical axis indicates the light intensity.

Hereinafter, an example of waveform analysis performed by the control unit 80 based on the spectral interference waveform and a theoretical waveform function will be described.
The optical path length from the beam splitter 641 of the second optical branching means 64 in the third path 6c to the upper surface (holding surface) of the chuck table 35 is (L0), and the second optical branch in the fourth path 6d. The optical path length from the beam splitter 641 of the means 64 to the reflection mirror 67 is (L1), and the difference between the optical path length (L1) and the optical path length (L0) is the optical path length difference (d = L1-L0). In the illustrated embodiment, the optical path length difference (d = L1−L0) is set to 500 μm, for example. Note that the optical path length from the beam splitter 641 of the second optical branching means 641 to the reflection mirror 67 in the fourth path 6d is (L1), and the beam of the second optical branching means 64 in the third path 6c. The optical path length from the splitter 641 to the back surface 11b (upper surface) of the sapphire substrate 11 constituting the optical device wafer 10 held on the chuck table 36 is (L2), and the second optical branching means 64 in the third path 6c. The optical path length from the beam splitter 641 to the surface 11a (interface with the optical device layer 12) of the sapphire substrate 11 constituting the optical device wafer 10 held on the chuck table 36 is defined as (L3), and the optical path length (L1) Is the first optical path length difference (d1 = L1-L2), and the difference between the optical path length (L1) and the optical path length (L3) is the second optical path length difference (d2 = L1). -L3) And

  Next, the control means 80 performs waveform analysis based on the spectral interference waveform and the theoretical waveform function. This waveform analysis can be executed based on, for example, Fourier transformation theory or wavelet transformation theory. In the embodiment described below, examples using the Fourier transformation formulas shown in the following formulas 1, 2, and 3 are used. explain.

In the above formula, λ is a wavelength, d is the first optical path length difference (d1 = L1−L2) and second optical path length difference (d2 = L1−L3), and W (λi) is a window function.
The above Equation 1 shows that the wave period is closest (highly correlated) in comparison between the theoretical waveform of cos and the spectral interference waveform (I (λ _n )), that is, the spectral interference waveform and the theoretical waveform function. An optical path length difference (d) having a high correlation coefficient is obtained. Further, the above formula 2 is obtained by comparing the theoretical waveform of sin and the spectral interference waveform (I (λ _n )) with the closest wave period (high correlation)), that is, the spectral interference waveform and the theoretical waveform. A correlation coefficient with the function obtains a first optical path length difference (d1 = L1-L2) and a second optical path length difference (d2 = L1-L3). Then, the above Equation 3 obtains the average value of the result of Equation 1 and the result of Equation 2.

  As shown in FIG. 5, the control means 80 performs calculations based on the above-described Equation 1, Equation 2, and Equation 3, so that the signal intensity becomes the first optical path length difference (d1 = L1-L2) and the second optical path as shown in FIG. Find the length difference (d2 = L1-L3). In FIG. 5, the horizontal axis represents the optical path length difference (d), and the vertical axis represents the signal intensity. In the example shown in FIG. 5, the signal intensity is high at the position where the optical path length difference (d) is 630 μm and the optical path length difference (d) is 510 μm. The signal intensity (A) at the position where the optical path length difference (d) is 630 μm is the position of the first optical path length difference (d1 = L1-L2), and the sapphire substrate 11 constituting the optical device wafer 10 from the upper surface of the chuck table 36. The first height position (h1) up to (upper surface) is shown. The signal intensity (B) at the position where the optical path length difference (d) is 510 μm is the position of the second optical path length difference (d2 = L1−L3), and the sapphire constituting the optical device wafer 10 from the upper surface of the chuck table 36. The second height position (h2) to the surface 11a of the substrate 11 (interface with the optical device layer 12) is shown. The control means 80 displays the analysis result shown in FIG.

  Returning to FIG. 3, the description is continued. The laser beam irradiation means 9 disposed in the unit housing 52 of the position measurement / laser irradiation unit 5 shown in FIG. 2 oscillates from the pulse laser beam oscillation means 91 and the pulse laser beam oscillation means 91. A dichroic mirror 92 for changing the direction of the pulsed laser beam directed toward the objective lens 65 is provided. The pulse laser beam oscillating means 91 includes a pulse laser beam oscillator 911 made of a YAG laser oscillator or a YVO4 laser oscillator and a repetition frequency setting means 912 attached thereto, and oscillates a pulse laser beam having a wavelength of 1064 nm, for example. The dichroic mirror 92 is disposed between the condenser lens 66 and the objective lens 65, and allows the light from the condenser lens 66 to pass through. However, the pulse laser beam oscillated from the pulse laser beam oscillation means 91 is passed to the objective lens 65. Change direction. Accordingly, the pulse laser beam (LB) oscillated from the pulse laser beam oscillating means 91 is changed in direction by 90 degrees by the dichroic mirror 92 and enters the objective lens 65, and is condensed by the objective lens 65 and held on the chuck table 36. The optical device wafer 10 as a workpiece is irradiated. Accordingly, the objective lens 65 has a function as a condensing lens constituting the laser beam irradiation means 7.

  Returning to FIG. 2 and continuing the description, the laser processing apparatus 1 in the illustrated embodiment is configured so that the unit holder 51 moves along an arrow Z along a pair of guide rails 423 and 423 provided on the mounting portion 422 of the movable support base 42. The second condensing point position adjusting means 53 for moving in the condensing point position adjusting direction (Z-axis direction) shown in FIG. 1, that is, the direction perpendicular to the upper surface (holding surface) of the chuck table 36 is provided. The second condensing point position adjusting means 53 is driven by a male screw rod (not shown) disposed between a pair of guide rails 423 and 423, a pulse motor 532 for rotating the male screw rod, and the like. The position measuring and laser irradiation unit 5 is moved along the guide rails 423 and 423 in the Z-axis direction by driving a male screw rod (not shown) forward and backward by a pulse motor 532. In the illustrated embodiment, the position measurement / laser irradiation unit 5 is moved upward by driving the pulse motor 532 forward, and the position measurement / laser irradiation unit 5 is moved downward by driving the pulse motor 532 in the reverse direction. It is supposed to move.

  An imaging means 95 is disposed at the front end of the unit housing 52 that constitutes the position measurement / laser irradiation unit 5. The imaging unit 95 includes an infrared illumination unit that irradiates a workpiece with infrared rays, an optical system that captures infrared rays emitted by the infrared illumination unit, in addition to a normal imaging device (CCD) that captures visible light. An image pickup device (infrared CCD) that outputs an electrical signal corresponding to the infrared light captured by the optical system is used, and the picked-up image signal is sent to the control means 80 described later.

  The laser processing apparatus 1 in the illustrated embodiment is configured as described above, and the operation thereof will be described below.

  Using the laser processing apparatus 1 described above, a laser beam having a wavelength having transparency to the substrate 11 is irradiated from the back side of the sapphire substrate 11 constituting the optical device wafer 10, and along the street 121 inside the sapphire substrate 11. An embodiment of laser processing for forming a deteriorated layer will be described. In addition, when forming a deteriorated layer inside the sapphire substrate 11 constituting the optical device wafer 10, if the sapphire substrate 11 has waviness and variations in thickness, a laser beam is given from the back surface 11 b (upper surface) of the sapphire substrate 11. When the condensing point is positioned and irradiated at the depth position, the energy of the laser beam is applied to the optical device layer (epilayer) 12 formed by being laminated on the surface 11a of the sapphire substrate 11 in the portion where the thickness of the sapphire substrate 11 is thin. There is a problem that the optical device layer (epi layer) 12 is damaged by the influence. Therefore, before laser processing, the position of the back surface 11b (upper surface) of the sapphire substrate 11 constituting the optical device wafer 10 held by the chuck table 36 by the position measuring means 6 and the sapphire substrate constituting the optical device wafer 10 are provided. 11, the position of the surface 11a (boundary surface with the optical device layer 12) is measured. That is, the optical device layer (epi layer) 12 side of the optical device wafer 10 is first placed on the chuck table 36 of the laser processing apparatus 1 shown in FIG. 2 and the optical device wafer 10 is sucked onto the chuck table 36. Hold. Accordingly, in the optical device wafer 10 held on the chuck table 36, the back surface 11b of the sapphire substrate 11 is on the upper side (wafer holding step). The chuck table 36 that sucks and holds the optical device wafer 10 is positioned immediately below the imaging unit 95 by the processing feeding unit 37.

  When the chuck table 36 is positioned immediately below the image pickup means 95, the image pickup means 95 and the control means 8 execute an alignment operation for detecting a processing region to be laser processed of the optical device wafer 10. That is, the imaging unit 95 and the control unit 80 are configured to measure the position of the street 121 formed in a predetermined direction of the optical device wafer 10 and the position measurement / laser irradiation unit 5 of the optical device wafer 10 along the street 121. Image processing such as pattern matching for performing alignment with the objective lens 65 of the apparatus 6 is executed, and alignment of detection positions is performed. Similarly, the alignment of the detection position is performed on the street 121 formed in the direction orthogonal to the predetermined direction formed in the optical device wafer 10. At this time, the surface 10a on which the street 121 of the optical device wafer 10 is formed is located on the lower side. However, since the sapphire substrate 11 is a transparent body, even if it is visible light, from the back surface 11b of the sapphire substrate 11. The street 121 can be imaged through the watermark.

  When alignment is performed as described above, the optical device wafer 10 on the chuck table 36 is positioned at the coordinate position shown in FIG. 6B shows a state in which the chuck table 36, that is, the optical device wafer 10, is rotated by 90 degrees from the state shown in FIG. 6A.

  It should be noted that the feed start position coordinate values (A1, A2, A3... Of each street 101 formed on the semiconductor wafer 10 in the state positioned at the coordinate positions shown in FIGS. An), feed end position coordinate value (B1, B2, B3 ... Bn), feed start position coordinate value (C1, C2, C3 ... Cn) and feed end position coordinate value (D1, D2, D3 ... For Dn), the data of the design value is stored in the memory of the control means 80.

As described above, when the street 121 formed on the optical device wafer 10 held on the chuck table 36 is detected and the detection position is aligned, the chuck table 36 is moved to move the position (a) of FIG. ), The uppermost street 121 is positioned immediately below the objective lens 65 of the position measuring means 6 constituting the position measuring / laser irradiation unit 5. Further, as shown in FIG. 7, the feed start position coordinate value (A1) (see FIG. 6A) that is one end (the left end in FIG. 7) of the street 121 is positioned immediately below the objective lens 65. Then, the position measuring means 6 is operated, and the chuck table 36 is moved in the direction indicated by the arrow X1 in FIG. 7 to move to the feed end position coordinate value (B1). As a result, the optical device wafer 10 is moved from the first optical path length difference (d1 = L1−L2) and the upper surface of the chuck table 36 along the uppermost street 121 in FIG. 6A of the optical device wafer 10. The optical device wafer 10 is moved from the first height position (h1) to the back surface 11b (upper surface) of the sapphire substrate 11 to be configured, the second optical path length difference (d2 = L1-L3) and the upper surface of the chuck table 36. The second height position (h2) to the surface 11a (boundary surface with the optical device layer 12) of the sapphire substrate 11 to be configured is measured by the position measuring means 6 as described above ( height position measuring step ). The optical device wafer 10 is configured from the first height position (h1) from the measured upper surface of the chuck table 36 to the back surface 11b (upper surface) of the sapphire substrate 11 constituting the optical device wafer 10 and the upper surface of the chuck table 36. The second height position (h2) to the surface 11a of the sapphire substrate 11 (the boundary surface with the optical device layer 12) is stored in the memory of the control means 80. In this way, the height position measurement process is performed along all the streets 121 formed in the optical device wafer 10, and the sapphire substrate 11 constituting the optical device wafer 10 is formed from the upper surface of the chuck table 36 in each street 121. Height position (h1) to the back surface 11b (upper surface) and height position (h2) from the upper surface of the chuck table 36 to the surface 11a (boundary surface with the optical device layer 12) of the sapphire substrate 11 constituting the optical device wafer 10 Is stored in the memory of the control means 80.

If the height position measurement step is performed along all the streets 121 formed on the optical device wafer 10 as described above, the altered layer that forms an altered layer along the street 121 inside the optical device wafer 10. A forming step is performed. A first embodiment of the deteriorated layer forming step will be described with reference to FIG.
In the first embodiment of the deteriorated layer forming step, first, the chuck table 36 is moved, and the uppermost street 121 in FIG. 6A is collected by the laser beam irradiation means 9 constituting the position measurement / laser irradiation unit 5. It is positioned directly below the objective lens 65 that functions as a lens. Further, as shown in FIG. 8A, the feed start position coordinate value (A1) (see FIG. 6A) which is one end of the street 121 (the left end in FIG. 8A) is used as the objective lens 65. Position directly below. And the condensing point P of the pulse laser beam irradiated from the objective lens 65 which comprises the laser beam irradiation means 9 is matched with the intermediate position (50% position) of the thickness of the sapphire substrate 11 which comprises the optical device wafer 10. FIG. That is, the control means 80 has a first height from the upper surface of the chuck table 36 detected in the height position measuring step and stored in the memory to the back surface 11b (upper surface) of the sapphire substrate 11 constituting the optical device wafer 10. Based on the position (h1) and the second height position (h2) from the upper surface of the chuck table 36 to the surface 11a (interface with the optical device layer 12) of the sapphire substrate 11 constituting the optical device wafer 10, the objective The first condensing point position adjusting means 650 is controlled so that the condensing point P of the pulse laser beam emitted from the lens 65 is at the position {h2 + (h1−h2) / 2}.

  Next, the laser beam irradiation means 9 is operated to move the chuck table 36 in the direction indicated by the arrow X1 at a predetermined processing feed speed while irradiating the objective lens 65 with the pulse laser beam. Then, as shown in FIG. 8B, when the irradiation position of the objective lens 65 reaches the other end of the street 101 (the right end in FIG. 8B), the irradiation of the pulse laser beam is stopped and the chuck table 36 is stopped. Stop moving. In this deteriorated layer forming step, the controller 80 extends from the upper surface of the chuck table 36 on the street 121 of the optical device wafer 10 stored in the memory to the back surface 11b (upper surface) of the sapphire substrate 11 constituting the optical device wafer 10. The first height position (h1) and the second height position (h2) from the upper surface of the chuck table 36 to the surface 11a of the sapphire substrate 11 constituting the optical device wafer 10 (boundary surface with the optical device layer 12). Based on this, the first condensing point position adjusting means 650 is controlled to move the position measurement / laser irradiation unit 5 in the Z-axis direction (condensing point position adjusting direction), thereby forming the objective lens 65 constituting the laser beam irradiation means 9. As shown in FIG. 8B, the focusing point P of the pulse laser beam irradiated from the objective lens 65 is set to the position {h2 + (h1−h2) / 2}. Move it down. As a result, in the sapphire substrate 11 constituting the optical device wafer 10, the altered layer 110 is formed at the middle position (50% position) of the thickness as shown in FIG.

Note that the processing conditions in the deteriorated layer forming step are set as follows, for example.
Laser: YVO4 pulse laser Wavelength: 1064nm
Average output: 1.2W
Repetition frequency: 80 kHz
Pulse width: 120 ns
Condensing spot diameter: φ2μm
Processing feed rate: 100 mm / sec

  When the deteriorated layer forming step is performed under the above processing conditions, the deteriorated layer 110 having a thickness of about 50 μm is formed along the street 121 at an intermediate position of the sapphire substrate 11. Therefore, even if the sapphire substrate 11 has waviness and the sapphire substrate 11 has a thin portion, the altered layer 110 that does not reach the optical device layer (epilayer) 12 formed by being laminated on the surface 11a of the sapphire substrate 11 is formed. Since it is formed, the problem that the optical device layer (epilayer) 12 is damaged by the action of the laser beam is solved.

  As described above, when the deteriorated layer forming step is executed along all the streets 121 extending in the predetermined direction of the optical device wafer 10, the chuck table 36 is rotated by 90 degrees to move in the predetermined direction. The altered layer forming step is executed along each street 121 extending in a direction perpendicular to the vertical direction. In this way, if the altered layer forming step is performed along all the streets 121 formed on the optical device wafer 10, the chuck table 36 holding the optical device wafer 10 is first set to the optical device wafer 10. 10 is returned to the position where the optical device wafer 10 is sucked and held, and the suction holding of the optical device wafer 10 is released here. Then, the optical device wafer 10 is transported to the dividing step by a transport means (not shown).

Next, a second embodiment of the deteriorated layer forming step will be described with reference to FIG.
Also in the second embodiment, as shown in FIG. 9A, the feed start position coordinate value (A1) which is one end of the street 121 (the left end in FIG. 9A) (see FIG. 6A). ) Is positioned directly below the objective lens 65. Then, the control means 80 has a first height position from the upper surface of the chuck table 36 on the street 121 of the optical device wafer 10 stored in the memory to the back surface 11b (upper surface) of the sapphire substrate 11 constituting the optical device wafer 10. (h1) and the second height position (h2) from the upper surface of the chuck table 36 to the surface 11a (interface with the optical device layer 12) of the sapphire substrate 11 constituting the optical device wafer 10, based on the sapphire substrate. 11 (t = h1−h2) is equal to or greater than a set thickness (for example, 90 μm in the illustrated embodiment), the condensing point P of the pulsed laser beam emitted from the objective lens 65 causes the optical device wafer 10 to The intermediate position (50% position) of the thickness of the sapphire substrate 11 to be formed, that is, detected in the height position measuring step and stored in the memory. The first height position (h1) from the upper surface of the chuck table 36 to the rear surface 11b (upper surface) of the sapphire substrate 11 constituting the optical device wafer 10 and the sapphire substrate 11 constituting the optical device wafer 10 from the upper surface of the chuck table 36. Based on the second height position (h2) up to the surface 11a (boundary surface with the optical device layer 12), the condensing point P of the pulsed laser beam emitted from the objective lens 65 is {h2 + (h1−h2) / 2} to control the first focusing point position adjusting means 650.

  Next, the laser beam irradiation means 9 is operated to move the chuck table 36 in the direction indicated by the arrow X1 at a predetermined processing feed speed while irradiating the objective lens 65 with the pulse laser beam. 9A, when the thickness (t = h1−h2) of the sapphire substrate 11 is less than a set thickness (for example, 90 μm in the illustrated embodiment), a laser beam is irradiated. If the altered layer formed on the substrate reaches the optical device layer 12 or approaches very close (for example, less than 20 μm), the optical device layer 12 may be damaged. Stop. Then, the chuck table 36 is further moved in the direction indicated by the arrow X1, and in FIG. 9A, the portion D passes just below the objective lens 65, and the thickness (t = h1-h2) of the sapphire substrate 11 is the first. Is equal to or greater than the set thickness (for example, 90 μm in the case of the illustrated embodiment), the control means 80 again sets the condensing point P of the pulse laser beam irradiated from the objective lens 65 to {h2 + (h1−h2) / 2. The first condensing point position adjusting unit 650 is controlled so as to be in the position of}, and the laser beam irradiation unit 9 is operated to irradiate a pulse laser beam from the objective lens 65. 9B, when the irradiation position of the objective lens 65 reaches the other end of the street 121 (the right end in FIG. 9B), the irradiation of the pulse laser beam is stopped and the chuck table 36 is stopped. Stop moving. As a result, the sapphire substrate 11 constituting the optical device wafer 10 has undulations in the sapphire substrate 11 as shown in FIG. 9B, and the thickness of the sapphire substrate 11 is set to a set thickness (for example, the illustrated embodiment). In this case, the altered layer 110 is formed at an intermediate position (50% position) of the thickness of the sapphire substrate 11, and the thickness of the sapphire substrate 11 is set to a set thickness (for example, 90 μm in the case of the illustrated embodiment). The deteriorated layer is not formed in the portion below. Thus, since the irradiation of the pulsed laser beam is stopped at the portion where the thickness of the sapphire substrate 11 is thin, damage to the optical device layer (epi layer) 12 can be prevented in advance.

2: stationary base 3: chuck table mechanism 36: chuck table 37: processing feed means 374: processing feed amount detection means 38: first index feed means 4: laser beam irradiation unit support mechanism 42: movable support base 43: first 2 index feeding means 5: height measurement / laser irradiation unit 53: focusing point position adjusting means 6: position measuring device 61: light source 62: first light branching means 63: collimation lens 64: second light branching Means 65: Objective lens 65
66: Condensing lens 67: Reflection mirror 68: Collimation lens 69: Diffraction grating 70: Condensing lens 71: Line image sensor 80: Control unit 9: Laser beam irradiation unit 91: Pulse laser beam oscillation unit 92: Dichroic mirror 10: Optical device Wafer

Claims (3)

Transparency to the substrate from the back side of the substrate inside the substrate in the wafer where the device is formed in multiple areas partitioned by multiple streets formed in a lattice shape with functional layers laminated on the surface of the substrate A laser processing method of irradiating a laser beam having a wavelength having a wavelength, and forming an altered layer along the street inside the substrate,
A wafer holding step for holding the wafer on the chuck table holding the workpiece of the laser processing apparatus with the back side of the substrate facing up;
A detection light having a wavelength that is transparent to the wafer substrate held on the chuck table is irradiated along the street from the back side of the substrate along the street, and along the street based on the reflected light reflected on the back and front surfaces of the substrate. A height position measuring step for measuring a first height position (h1) from the upper surface of the chuck table to the back surface of the substrate and a second height position (h2) from the upper surface of the chuck table to the surface of the substrate;
A condensing point of the laser beam is positioned at an intermediate portion between the first height position (h1) and the second height position (h2) measured in the height position measuring step, and is irradiated along the street. seen containing a deteriorated layer forming step for forming a deteriorated layer which does not reach the functional layer along the streets in the substrate, the by,
The height position measuring step includes a light emitting source that emits light having a predetermined wavelength region, and a reflected light that guides the light from the light emitting source to the first path and reverses the first path to the second path. A first light branching unit that guides the light to the first path, a collimation lens that forms the light guided to the first path into parallel light, and a third path and a fourth path that convert the light formed by the collimation lens into parallel light. A second light splitting unit that divides the path, an objective lens that is disposed in the third path and guides the light guided to the third path to a wafer held by the chuck table, and the second light Parallel light arranged between the branching means and the objective lens is guided to the third path, and a focusing point is positioned on the objective lens to generate light from the objective lens as pseudo-parallel light. A condensing lens that is disposed on the fourth path and a parallel led to the fourth path Reflecting mirror for reflecting the reflected light back to the fourth path, and reflecting the fourth path, the second light branching means, the collimation lens and the first path reflected by the reflecting mirror. Then, the reflected light guided from the first light branching means to the second path, and reflected by the wafer held on the chuck table, the objective lens, the condenser lens, and the second light branching means. And a diffraction grating that diffracts the interference between the collimation lens and the first path and the reflected light guided from the first light branching means to the second path, and the reflection diffracted by the diffraction grating An image sensor that detects light intensity in a predetermined wavelength range of light, a spectral interference waveform is obtained based on a detection signal from the image sensor, and waveform analysis is performed based on the spectral interference waveform and a theoretical waveform function. The fourth An optical path length difference (d) between an optical path length to the reflecting mirror in the path and an optical path length to the wafer held on the chuck table in the third path is obtained, and based on the optical path length difference (d) A first optical path length difference (reflected by the back surface of the substrate) using a measuring means comprising a control means for determining the distance from the front surface of the chuck table to the back surface and front surface of the wafer held by the chuck table. The first height position (h1) from the top surface of the chuck table to the back surface of the substrate and the top surface of the substrate from the top surface of the chuck table based on d1) and the second optical path length difference (d2) reflected by the surface of the substrate Measuring the second height position (h2) up to
The laser processing method characterized by the above-mentioned. In the altered layer forming step, the focal point of the laser beam is set to {h2 + (h1−h2) / 2} based on the first height position (h1) and the second height position (h2). The laser processing method according to claim 1 , wherein the laser processing method is performed while being positioned. In the altered layer forming step, the condensing point of the laser beam is determined at a location where the thickness of the substrate is equal to or larger than a set value based on the first height position (h1) and the second height position (h2). 3. The laser processing method according to claim 2 , wherein the laser processing is performed at a position of {h2 + (h1-h2) / 2}, and the irradiation of the laser beam is stopped at a position where the thickness of the substrate is less than a set value thickness.

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