TW201836748A - Laser machining device and laser machining method - Google Patents

Abstract

A laser machining device, provided with: a measurement light source; a condensing lens; a displacement detector for detecting the displacement of a laser beam incidence surface on the basis of reflected light of measurement light reflected by the laser beam incidence surface; and an imaging state adjustment unit for moving the imaging state of the measurement light and/or the reflected light of the measurement light. The displacement detector has: a branching unit for branching the reflected light of the measurement light into a plurality of branched reflected lights; a plurality of astigmatism imparting units for imparting astigmatism amounts of different sizes to each of the plurality of branched reflected lights; a plurality of beam shape detectors for detecting the respective beam shapes of each of the branched reflected lights to which astigmatism has been imparted; and a signal acquisition unit for selecting, from the light paths of the plurality of branched reflected lights, a light path corresponding to the imaging state to be adjusted by the imaging state adjustment unit, and acquiring a signal relating to displacement on the basis of the result of detection by the beam shape detector on the light path of the selected branched reflected light.

Description

Laser processing device and laser processing method

One aspect of the present invention relates to a laser processing device and a laser processing method.

Conventionally, there has been known a laser processing device that focuses a laser beam for processing on a processing object to form a modified region in the processing object (see, for example, Patent Document 1). The laser processing device as described above includes a measurement light source that emits the measurement light, a lens for condensing the processing laser light and the measurement light on the processing object, and a lens according to the processing object. The reflected light of the measurement light reflected by the laser light incident surface is a displacement detecting unit that detects a displacement of the laser light incident surface (hereinafter, also referred to simply as "displacement"). The displacement detection unit adds astigmatism to the reflected light of the measurement light, detects the beam shape of the reflected light to which astigmatism is added, and obtains a signal related to the displacement based on the detection result. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2015-186825

(Problems to be solved by the invention)

In the laser processing apparatus as described above, the variation of the signal (inclination of the signal) with respect to the displacement may be too gentle. At this time, for example, if the incident surface of the laser light is a grinding surface, the light used for measurement is scattered by the grinding mark (also referred to as a saw mark). Therefore, even if the same displacement occurs, the signal is different. The error of the detected displacement is more obvious. As a result, it may be difficult to detect the displacement of the laser light incident surface with high accuracy.

An object of one aspect of the present invention is to provide a laser processing device and a laser processing method that can accurately detect a displacement of a laser light incident surface. (Means for solving problems)

A laser processing apparatus according to an aspect of the present invention is a laser processing apparatus that focuses a processing laser beam on a processing object and forms a modified region on the processing object. The laser processing apparatus includes a measurement light source, It is used for measuring light; a lens for condensing is used for condensing laser light for processing and measuring light on the object to be processed; and a displacement detecting unit for measuring is reflected based on the laser light incident surface of the object to be processed. The reflected light of the light detects the displacement of the incident surface of the laser light; and the imaging state adjustment unit moves the imaging state of at least one of the measurement light and the reflected light of the measurement light, and the displacement detection unit has: divergence The multiple astigmatism adding unit is provided on each of the optical paths of the complex divergent reflected light, and each of the complex divergent reflected light is attached with images of different sizes from each other. Diffuse amount; a complex beam shape detection unit, which is provided in each of the optical paths of the plural branched reflected light, and detects the beam shape of each of the plural branched reflected light to which astigmatism is added; and signal acquisition , Which is selected from the optical paths of the plurality of branched reflected light, one corresponding to the imaging state adjusted by the imaging state adjustment section, and obtained according to the detection result of the beam shape detection section in the selected optical path of the branched reflected light. Signal about displacement.

The present inventors have conducted intensive studies and found that the tilt of the obtained signal is related to the imaging state of at least one of the measurement light and the reflected light of the measurement light. In addition, for the reason that the tilt of the signal is too gentle, it is found that the imaging state arises from the mismatch of the astigmatism amount added by the reflected light. Therefore, in the laser processing apparatus according to an aspect of the present invention, the reflected light of the measurement light is divided into a plurality of branched reflected light, and a difference in the amount of astigmatism of a different magnitude is added to the optical path of each of the branched reflected light. The beam shape of the reflected light. Next, from among the optical paths of the plurality of branched reflected light, one of the imaging states corresponding to the movement of the imaging state adjustment section is selected, and a signal based on the beam shape of the branched reflected light of the selected optical path is obtained. Thereby, the amount of astigmatism added by the divergent reflected light about the obtained signal can be formed to correspond to the imaging state. It is possible to suppress the tilt of the obtained signal from becoming too gentle. Therefore, the displacement of the incident surface of the laser light can be detected with high accuracy.

In the laser processing device according to one aspect of the present invention, the imaging state adjustment unit may adjust the offset by moving the imaging state, and the signal acquisition unit selects the imaging path corresponding to the plurality of divergent reflected light paths. The state adjustment unit performs one of the offsets. Here, the offset refers to a dimension indicating the relative displacement of the laser incident surface of the processing object when the signal of the displacement from the laser incident surface of the processing object becomes a reference value (typically zero). For example, an offset of 0 μm means that when parallel light having the same wavelength as the measurement light is incident on the condenser lens, it becomes a configuration that minimizes the laser incident surface of the object to be processed. The signal becomes the geometric configuration state of the reference value. In addition, for example, the offset is -180 μm, which refers to the geometrical configuration in which the signal becomes a reference value when the laser incident surface of the object to be processed approaches 180 μm from the above-mentioned configuration when the offset is 0 μm. status. When the value of the offset is small (the negative amplitude is large), the offset or offset is called deep, and when the value of the offset is large (the negative amplitude is small), the offset or offset is called shallow.

It is found that the tilt of the obtained signal is, in particular, related to the offset tool, and the perception is too gentle due to the mismatch between the offset amount and the astigmatism amount. Therefore, in the laser processing apparatus according to an aspect of the present invention, one corresponding to the offset is selected from among the optical paths of the plural branched reflected light. Thereby, the astigmatism amount added by the divergent reflected light about the obtained signal can be formed as a corresponding offset amount. This prevents the acquired signal from tilting too gently.

In the laser processing apparatus according to an aspect of the present invention, the branching unit may branch the reflected light of the measurement light into at least a first branched reflected light and a second branched reflected light. The astigmatism adding unit includes: An astigmatism adding section is provided on the optical path of the first branched reflected light, and a first astigmatism amount is added to the first branched reflected light; and a second astigmatism addition section is provided on the second branched reflected light. In the optical path, a second astigmatism amount greater than the first astigmatism amount is added to the second branched reflected light. The signal acquisition unit: if the offset adjusted by the imaging state adjustment unit is in the first range, select the first branch If the offset of the optical path of the reflected light is in the second range which is deeper than the first range, the optical path of the second branched reflected light is selected.

More specifically, it is found that if the same signal astigmatism is added to the tilt of the obtained signal, the deeper the shift, the more gradual the perception. Therefore, in the laser processing apparatus according to an aspect of the present invention, if the offset is in the first range, the optical path of the first branched reflected light is selected, and if the offset adjusted by the imaging state adjustment section is located in When the 1 range is a deeper second range, the optical path of the second branched reflected light is selected. As a result, the astigmatism added to the divergent reflected light of the obtained signal can be increased (if it is shallow, it is reduced). This prevents the acquired signal from tilting too gently.

The laser processing apparatus according to an aspect of the present invention may further include: an offset setting unit configured to set an offset adjusted by the imaging state adjustment unit; and an imaging state control unit configured to be at the offset The method of the offset amount set by the amount setting section controls the imaging state adjustment section. With this configuration, it is possible to automatically adjust the imaging state as a set offset.

The laser processing apparatus according to an aspect of the present invention may further include a driving mechanism that operates at least one of a processing object and a focusing lens along the optical axis direction of the focusing lens; and The drive mechanism control unit operates the drive mechanism such that the signal obtained by the signal acquisition unit maintains the target value. With this configuration, the focusing lens can be relatively moved along the optical axis direction so as to follow the laser light incident surface.

The laser processing apparatus according to an aspect of the present invention may further include an optical axis adjustment mechanism configured to align the optical axis of the measurement light with the optical axis of the laser light for processing. With this configuration, the optical axis of the measurement light can be aligned with the optical axis of the laser light for processing with high accuracy.

In the laser processing apparatus according to an aspect of the present invention, the light source system for measurement can emit any one of a plurality of light having different wavelengths, and the light having a plurality of wavelengths has a reflectance to a processing object The light having the highest wavelength is used as the measurement light. In this case, it is possible to easily detect the reflected light that reflects the measurement light on the laser light incident surface.

A laser processing method according to one aspect of the present invention is a laser processing method in which a processing laser is focused on a processing object to form a modified region on the processing object. The laser processing method includes: a laser processing step; While focusing the processing laser light on the processing object with a focusing lens, the measurement light is focusing on the processing object with the focusing lens, and the laser light incident surface of the processing object is reflected. The reflected light of the measurement light is branched into at least the first branched reflected light and the second branched reflected light, and the beam shape of the first branched reflected light with a first astigmatism amount added to the optical path of the first branched reflected light is detected, and Detect the beam shape of the second divergent reflected light with a second astigmatism amount that is greater than the first astigmatism amount on the optical path of the second divergent reflected light, and obtain the laser beam incident surface based on the detection result of the beam shape. The displacement signal moves at least one of the processing object and the light-condensing lens along the optical axis direction of the light-converging lens so that the obtained signal maintains the target value. The laser processing step includes: Step 1, which Set the offset; in the second step, if the offset set in the first step is the first range, the optical path of the first branched reflected light is selected. If the offset set in the first step is If the first range is a deeper second range, the optical path of the second divergent reflected light is selected. In the third step, the measurement light and the measurement light are set so as to have the offset amount set in the first step. The imaging state of at least one of the reflected light is moved. In the fourth step, at least one of the object to be processed and the lens for focusing is moved so as to become the offset amount set in the first step. ; The fifth step is to obtain the target value after the third step and the fourth step; and the sixth step is to condensate the laser light for processing with the condenser lens while processing the object after the fifth step Object, while detecting the beam shape in the optical path of the branched reflected light selected in the second step, obtaining a signal based on the detection result of the beam shape, and maintaining the target value with the obtained signal, the light is collected along the light path. The optical axis of the lens allows the object to be processed and the light to be focused. At least either one is operated.

In this laser processing method, if the offset is deep, the amount of astigmatism added to the divergent reflected light of the obtained signal can be increased (if it is shallower, it is reduced). With the above knowledge, it is possible to suppress the tilt of the obtained signal from becoming too gentle. Therefore, the displacement of the incident surface of the laser light can be detected with high accuracy. (Effect of the invention)

According to one aspect of the present invention, a laser processing device and a laser processing method capable of detecting a displacement of a laser light incident surface with high accuracy can be provided.

Hereinafter, embodiments will be described in detail with reference to the drawings. It should be noted that the same or corresponding parts are denoted by the same symbols in each figure, and repeated descriptions are omitted.

In the laser processing apparatus and laser processing method according to the embodiment, a modified region is formed in the processing object by concentrating laser light on the processing object along a predetermined cutting line. Therefore, first, the formation of the modified region will be described with reference to FIGS. 1 to 6.

As shown in FIG. 1, the laser processing device 100 is provided with a laser light source 101 that oscillates laser light L, which is laser light for processing, as a laser light source for processing, and an optical system that guides laser light L. 103; and a condenser lens 105 for condensing the laser light L. The laser processing apparatus 100 includes a support table 107 for supporting the processing object 1 irradiated with the laser light L condensed by the focusing lens 105, a stage 111 for moving the support table 107, and control. The laser light source 101 is a laser light source control unit 102 that adjusts the output (pulse energy, light intensity) or pulse width of the laser light L, and a stage control unit 115 that controls the movement of the stage 111.

In the laser processing apparatus 100, the laser light L emitted from the laser light source 101 is guided by the optical system 103, and is focused by the focusing lens 105 on the processing object placed on the support table 107. 1 inside. The stage 111 is moved with this, and the processing object 1 is relatively moved along the planned cutting line 5 with respect to the laser light L. Thereby, a modified region along the planned cutting line 5 is formed in the processing object 1. Here, the stage 111 is moved in order to relatively move the laser light L, but the condenser lens 105 may be moved, or both of them may be moved.

For the object 1 to be processed, a plate-shaped member (for example, a substrate, a wafer, or the like) including a semiconductor substrate formed of a semiconductor material or a piezoelectric substrate formed of a piezoelectric material is used. As shown in FIG. 2, the processing object 1 is provided with a planned cutting line 5 for cutting the processing object 1. The planned cutting line 5 is an imaginary line extending linearly. If a modified region is formed inside the processing object 1, as shown in FIG. 3, the laser light L is cut along the cutting state in a state where the focusing point (condensing position) P is aligned inside the processing object 1. The predetermined breaking line 5 (that is, in the direction of arrow A in FIG. 2) is relatively moved. Thereby, as shown in FIG. 4, FIG. 5, and FIG. 6, the modified region 7 is formed on the object 1 along the planned cutting line 5, and the modified region 7 formed along the planned cutting line 5 is cut. Broken starting area 8.

The condensing point P refers to a portion where the laser light L is condensed. The planned cutting line 5 is not limited to a straight line, may be a curved line, may be a three-dimensional shape of these combinations, or may be designated by coordinates. The planned cutting line 5 is not limited to an imaginary line, and may be a line actually drawn on the surface 3 of the processing object 1. The modified region 7 may be formed continuously or intermittently. The modified region 7 may be in a row shape or a dot shape. In short, the modified region 7 may be formed at least inside the processing object 1. In addition, a crack may be formed from the modified region 7 as a starting point, and the crack and the modified region 7 may be exposed on the outer surface (surface 3, back surface, or outer peripheral surface) of the object 1 to be processed. The laser light incident surface when the modified region 7 is formed may be the back surface of the processing object 1 instead of being limited to the surface 3 of the processing object 1.

Incidentally, if the modified region 7 is formed inside the processing object 1, the laser light L is transmitted through the processing object 1 and is particularly absorbed near the light-condensing point P located inside the processing object 1. Thereby, a modified region 7 is formed in the object 1. At this time, since the energy density of the laser light L is low on the surface 3 of the processing object 1, the surface 3 of the processing object 1 does not melt. On the other hand, if a modified region 7 is formed on the surface 3 or the back surface of the object 1, the laser light L is absorbed particularly near the light-condensing point P located on the surface 3 or the back surface, and is melted and removed by the surface 3 or the back surface. A cutout such as a hole or a groove is formed.

The modified region 7 refers to a region where the density, refractive index, mechanical strength, or other physical characteristics are different from those of the surroundings. The modified region 7 includes, for example, a melt-treated region (meaning at least one of a region that is solidified after being melted, a region in a molten state, and a region that is re-solidified by melting), and a crack region. , Insulation damage area, refractive index change area, etc., there are also such mixed areas. In addition, the modified region 7 includes a region in which the density of the modified region 7 is changed from the density of the non-modified region in the material of the processing object 1 or a region in which lattice defects are formed. If the material of the processing object 1 is single crystal silicon, the modified region 7 may also be referred to as a high dislocation density region.

The melt-processed region, the refractive index change region, the density of the modified region 7 and the density of the non-modified region are changed compared to the density of the non-modified region, and the region where the lattice defect is formed is also inside or modified region of these regions. 7 Cracks (cracks, micro-cracks) are contained in the interface with the non-modified region. The internal cracking system may cover the entire area of the modified region 7 or may be formed only in one part or plural parts. The object 1 to be processed includes a substrate made of a crystalline material having a crystalline structure. For example, the processing target 1 includes a substrate formed of at least any one of gallium nitride (GaN), silicon (Si), silicon carbide (SiC), LiTaO ₃ , and sapphire (Al ₂ O ₃ ). In other words, the processing object 1 includes, for example, a gallium nitride substrate, a silicon substrate, a SiC substrate, a LiTaO ₃ substrate, or a sapphire substrate. The crystalline material may be any of anisotropic crystals and isotropic crystals. The processing object 1 may include a substrate made of an amorphous material having an amorphous structure (amorphous structure), and may include, for example, a glass substrate.

In the embodiment, a plurality of modified spots (processing marks) are formed along the planned cutting line 5, whereby the modified region 7 can be formed. At this time, a plurality of modified spots are gathered to form a modified region 7. Regarding the modification point, the required cutting accuracy, the required flatness of the cutting surface, the thickness, type, and crystal orientation of the object 1 can be considered, and the size or the length of the cracks can be appropriately controlled. . In addition, in the embodiment, a modified point may be formed as the modified region 7 along the planned cutting line 5.

Next, a laser processing apparatus and a laser processing method according to the embodiment will be described. The following is an example in which the back surface 21 of the object 1 is set as a laser light incident surface. The thickness direction of the object 1 will be described as the Z direction.

As shown in FIG. 7, the laser processing apparatus 300 includes a laser light source 202, a reflective spatial light modulator 203, a 4f optical system 241, and a condensing optical system 204 in a housing 231. The laser processing apparatus 300 focuses the laser light L on the processing object 1 and forms a modified region 7 on the processing object 1 along the planned cutting line 5.

The laser light source 202 emits laser light L. The laser light source 202 emits laser light having a pulse width of 1 μs or less, that is, pulsed laser light, as the laser light L. The laser light source 202 includes an ultra-short pulse laser light source as a laser oscillator. For a laser oscillator, it can be composed of, for example, a solid laser, a fiber laser, or an external modulation element. The laser light source 202 includes an output adjustment unit that adjusts the output of the laser light L. The output adjustment unit can be composed of a λ / 2 wavelength plate unit, a polarizing plate unit, and the like. The laser light source 202 includes a beam expander that is parallelized while adjusting the diameter of the laser light L.

The wavelength of the laser light L emitted from the laser light source 202 includes any wavelength band of 500 to 550 nm, 1000 to 1150 nm, or 1300 to 1400 nm. The wavelength of the laser light L here is 1064 nm. The laser light source 202 shown above is fixed to the top plate 236 of the frame 231 with screws or the like so as to emit the laser light L in a horizontal direction.

The reflective spatial light modulator 203 is a modulator that modulates the laser light L emitted from the laser light source 202. The reflective spatial light modulator 203 is, for example, a spatial light modulator (SLM: Spatial Light Modulator) of a reflective liquid crystal (LCOS: Liquid Crystal on Silicon). The reflection-type spatial light modulator 203 modulates the laser light L incident from the horizontal direction and reflects it obliquely upward from the horizontal direction.

As shown in FIG. 8, the reflective spatial light modulator 203 is formed by sequentially stacking a reflective film 215 such as a silicon substrate 213, a driving circuit layer 914, a plurality of pixel electrodes 214, a dielectric multilayer film reflector, an alignment film 999a, and a liquid crystal. The layer 216, the alignment film 999b, the transparent conductive film 217, and a transparent substrate 218 such as a glass substrate are configured. The transparent substrate 218 has a surface 218a along a predetermined plane. The surface 218a of the transparent substrate 218 is a surface constituting the reflective spatial light modulator 203. The transparent substrate 218 is made of a light-transmitting material such as glass. The transparent substrate 218 transmits the laser light L of a predetermined wavelength incident on the surface 218 a of the reflective spatial light modulator 203 to the inside of the reflective spatial light modulator 203. The transparent conductive film 217 is formed on the back surface of the transparent substrate 218. The transparent conductive film 217 is made of a conductive material (for example, ITO) that transmits the laser light L.

The plurality of pixel electrodes 214 are arranged on the silicon substrate 213 in a matrix shape along the transparent conductive film 217. The plurality of pixel electrodes 214 are formed of a metal material such as aluminum. The surface 214a of the plurality of pixel electrodes 214 is flat and smoothly processed. The plurality of pixel electrodes 214 are driven by an active matrix circuit provided in the driving circuit layer 914.

The active matrix circuit is provided between the plurality of pixel electrodes 214 and the silicon substrate 213. The active matrix circuit controls the voltage applied to each pixel electrode 214 in accordance with the light image to be output by the reflective spatial light modulator 203. For example, the active matrix circuit includes a first driver circuit that controls the applied voltage of each pixel column arranged in one direction along the surface 218a, and controls that it is arranged orthogonal to the one direction and arranged in the other direction along the surface 218a. A second driver circuit for applying a voltage to each pixel column. The active matrix circuit described above is configured such that a predetermined voltage is applied to the pixel electrode 214 of a pixel designated by both driver circuits by the control unit 250 (see FIG. 7).

The alignment films 999a and 999b are arranged on both end surfaces of the liquid crystal layer 216, so that the liquid crystal molecular groups are aligned in a certain direction. The alignment films 999a and 999b are formed of a polymer material such as polyimide. A contact surface with the liquid crystal layer 216 in the alignment films 999a and 999b is subjected to a rubbing treatment or the like.

The liquid crystal layer 216 is disposed between the plurality of pixel electrodes 214 and the transparent conductive film 217. The liquid crystal layer 216 modulates the laser light L according to an electric field formed by each of the pixel electrodes 214 and the transparent conductive film 217. That is, if an active matrix circuit of the driving circuit layer 914 is used, an electric field is formed between the transparent conductive film 217 and each pixel electrode 214 when a voltage is applied to each pixel electrode 214, and the alignment direction of the liquid crystal molecules 216a is formed in The magnitude of the electric field of the liquid crystal layer 216 changes. Next, when the laser light L passes through the transparent substrate 218 and the transparent conductive film 217 and enters the liquid crystal layer 216, the laser light L is modulated by the liquid crystal molecules 216a through the liquid crystal layer 216, and is reflected on the reflection film 215. Thereafter, the liquid crystal layer 216 is modulated again to emit light.

At this time, the voltage applied to each pixel electrode 214 is controlled by the control unit 250 (see FIG. 7), and according to this voltage, the refraction of the portion of the liquid crystal layer 216 sandwiched between the transparent conductive film 217 and each pixel electrode 214 is controlled. The rate is changed (the refractive index of the liquid crystal layer 216 corresponding to the position of each pixel is changed). With this change in refractive index, the phase of the laser light L can be changed for each pixel of the liquid crystal layer 216 according to the applied voltage. That is, the phase adjustment corresponding to the full-image pattern can be given to each pixel by the liquid crystal layer 216. The laser light L incident to the modulation pattern and transmitted has its wavefront adjusted, and a phase of a component in a direction orthogonal to the traveling direction among the respective rays constituting the laser light L is shifted. Therefore, by appropriately setting the modulation pattern displayed by the reflective spatial light modulator 203, the laser light L can be modulated (for example, the intensity, amplitude, phase, and polarization of the laser light L can be modulated).

Returning to FIG. 7, the 4f optical system 241 is an adjustment optical system that adjusts the wavefront shape of the laser light L modulated by the reflective spatial light modulator 203. The 4f optical system 241 includes a first lens 241a and a second lens 241b. The first lens 241a and the second lens 241b are the distance of the optical path between the reflective spatial light modulator 203 and the first lens 241a, and become the first focal distance f1 of the first lens 241a. The focusing optical system 204 and the second lens The distance between the optical paths between 241b becomes the second focal distance f2 of the second lens 241b, and the distance between the optical paths between the first lens 241a and the second lens 241b becomes the sum of the first focal distance f1 and the second focal distance f2 (also That is, f1 + f2) is arranged on the optical path between the reflective spatial light modulator 203 and the condenser optical system 204 so that the first lens 241a and the second lens 241b become a telecentric optical system on both sides. With the 4f optical system 241, it is possible to suppress a situation in which the laser light L modulated by the reflection-type spatial light modulator 203 changes the wavefront shape and increases aberration due to space propagation.

The condensing optical system 204 condenses the laser light L emitted by the laser light source 202 and modulated by the reflective spatial light modulator 203 and the measurement light LB1 emitted by the AF unit 212 described later. Light on the processing object 1. The condensing optical system 204 is provided on the bottom plate 233 of the housing 231 through a driving unit 232 including a piezoelectric element and the like. The condensing optical system 204 is a lens for condensing, and includes a plurality of lenses.

In the laser processing apparatus 300 configured as described above, after the laser light L emitted from the laser light source 202 travels horizontally in the housing 231, it is reflected downward by the mirror 205a, and The attenuator 207 adjusts the light intensity. Thereafter, the laser light L is reflected in the horizontal direction by the reflecting mirror 205b, and the intensity distribution of the laser light L is uniformized by the beam homogenizer 260, and is incident on the reflective spatial light modulator 203.

The laser light L incident on the reflective spatial light modulator 203 is modulated in accordance with the modulation pattern displayed by passing through the liquid crystal layer 216. After that, the laser light L is reflected upward by the reflector 206a, the polarization direction is changed by the λ / 2 wavelength plate 228, and it is reflected in the horizontal direction by the reflector 206b and is incident on the 4f optical system 241.

The laser light L incident on the 4f optical system 241 is adjusted to have a wavefront shape such that parallel light is incident on the condensing optical system 204. Specifically, the laser light L passes through the first lens 241a and is converged, is reflected downward by the reflector 219, is diverged through the light collecting point O, and passes through the second lens 241b to be parallel light again. convergence. Next, the laser light L sequentially passes through the dichroic mirrors 210 and 238 and is incident on the condensing optical system 204, and the condensing optical system 204 is condensed on the processing placed on the stage 111. Inside the object 1.

In addition, the laser processing apparatus 300 includes a surface observation unit 211 in the housing 231 for observing the laser light incident surface of the processing object 1, and a distance between the condensing optical system 204 and the processing object 1. An AF (AutoFocus) unit 212 that performs fine adjustment.

The surface observation unit 211 includes a light source 211a for observation that emits visible light VL1, and a detector 211b that detects reflected light VL2 of visible light VL1 reflected on the laser light incident surface of the processing object 1. In the surface observation unit 211, the visible light VL1 emitted from the observation light source 211a is reflected / transmitted by the reflecting mirror 208, the half mirror 209, and the dichroic mirrors 210 and 238, and is focused toward the processing object 1 in the condenser optical system 204. Spotlight. The reflected light VL2 reflected on the laser light incident surface of the processing object 1 is condensed by the condensing optical system 204 and transmitted / reflected by the dichroic beam splitters 238 and 210, and then transmitted through the half mirror 209 and then by the detector 211b By light.

The AF unit 212 emits the measurement light LB1 and detects the reflected light LB2 of the measurement light LB1 reflected on the incident surface of the laser light, thereby obtaining displacement data of the incident surface of the laser light along the planned cutting line 5 This is the error signal (signal about displacement). The AF unit 212 outputs the acquired error signal to the control unit 250 when the modified region 7 is formed. The control unit 250 drives the drive unit 232 based on the error signal, and causes the condensing optical system 204 to move back and forth in the direction of the optical axis so as to fluctuate along the incident surface of the laser light. The configuration and operation of the AF unit 212 will be described in detail later.

The laser processing apparatus 300 is provided with the control part 250 which controls the operation | movement of each part of this laser processing apparatus 300. The control unit 250 is composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like.

The control unit 250 controls the operation of the laser light source 202, and the laser light source 202 emits the laser light L. The control unit 250 controls the operation of the laser light source 202, and adjusts the output of the laser light L emitted from the laser light source 202, the pulse width, and the like. When the modified section 7 is formed, the control unit 250 sets the light-condensing point P of the laser light L at a predetermined distance from the front surface 3 or the back surface 21 of the object 1, and the light-condensing point P of the laser light L is cut along The relative movement of the predetermined line 5 controls at least one of the positions of the housing 231, the stage 111, and the driving of the driving unit 232. The control unit 250 has the functions of the laser light source control unit 102 and the stage control unit 115.

When the modified region 7 is formed, the control unit 250 applies a predetermined voltage to each pixel electrode 214 in the reflective spatial light modulator 203 to display a predetermined modulation pattern on the liquid crystal layer 216. As a result, the control unit 250 tunes the laser light L to the desired spatial light modulator 203. The modulation pattern displayed by the liquid crystal layer 216 is based on, for example, the position where the modified region 7 is to be formed, the wavelength of the laser light L to be irradiated, the material of the processing object 1, and the refraction of the focusing optical system 204 or the processing object 1. The rate and the like are derived in advance and stored in the control unit 250. The modulation pattern includes: an individual difference correction pattern for correcting individual differences (for example, deformation generated in the liquid crystal layer 216) generated by the laser processing device 300, a spherical aberration correction pattern for correcting spherical aberration, and the like .

Next, the configuration of the AF unit 212 will be specifically described.

As shown in FIG. 9, the AF unit 212 includes a measurement light source 30, a displacement detection unit 50, and an imaging state adjustment unit 70. The measurement light source 30 emits measurement light LB1. The measurement light source 30 is capable of emitting any of a plurality of light having different wavelengths. The light source 30 for measurement includes a plurality of SLD (Super Luminescent Diode) light sources 31 and 32. In the light source 30 for measurement, the control unit 250 selects one of the plurality of SLD light sources 31 and 32 to emit light of a wavelength having a high reflectance to the processing object 1. The light source for measurement 30 is one of the selected SLD light sources 31 and 32 and emits light having a wavelength of high reflectance to the object 1 as the light for measurement LB1. The SLD light source 31 emits light having a wavelength of, for example, 650 nm. The SLD light source 32 emits light having a wavelength of, for example, 830 nm.

The measurement light source 30 is not limited to the SLD light sources 31 and 32, and may include, for example, an LED (Light Emitting Diode) light source or an LD (Laser Diode) laser light source. It is only necessary that the wavelength of the measurement light LB1 has a reflectance greater than zero on the back surface 21 which is the incident surface of the laser light. The light source 30 for measurement may not be capable of emitting light with a plurality of wavelengths, for example, only one of the SLD light sources 31 and 32 is provided, and only light of one wavelength may be emitted.

The light source 30 for measurement transmits WDM (Wavelength Division Multiplexing) 33 and a single-mode optical fiber 34 for synthesizing laser light at a plurality of wavelengths, and transmits the emitted measurement light LB1 to the adjustment optical system. 60. However, if the measurement light source 30 emits only the measurement light LB1 of one wavelength, the WDM 33 is not required. Instead of the optical fiber 34, a spatial light transmission element may be used. The adjustment optical system 60 has a plurality of types of lenses, and is adjusted so that the measurement light LB1 becomes an appropriate beam diameter.

The displacement detection unit 50 detects the displacement of the back surface 21 based on the reflected light LB2 of the measurement light LB1 reflected on the laser light incident surface of the processing object 1, that is, the back surface 21. The displacement detection section 50 includes a first branching section 51, a second branching section (branching section) 52, first and second astigmatism adding sections (astigmatism adding section) 53, 54, and first and second beam shapes. The detection sections (beam shape detection sections) 55 and 56 and the error signal generation section 57.

The first branching section 51 is a beam splitter that splits the measurement light LB1 and the reflected light LB2. The first branching section 51 divides the optical path of the measurement light LB1 and the reflected light LB2 into an optical path of the measurement light LB1 and an optical path of the reflected light LB2. The first branching portion 51 transmits the measurement light LB1 and reflects the reflected light LB2. The first branching section 51 is provided between the imaging state adjustment section 70 and the adjustment optical system 60 in the optical paths of the measurement light LB1 and the reflected light LB2.

The second branching portion 52 is a beam splitter that splits the reflected light LB2 at the first branching portion 51 and splits into a first branched reflected light LS1 and a second branched reflected light LS2. The second branching section 52 divides the optical path OP of the reflected light LB2 into an optical path of the first branched reflected light LS1, that is, the first branched optical path OP1, and an optical path of the second branched reflected light LS2, that is, the second branched optical path OP2. The second branched portion 52 transmits the second branched reflected light LS2 and reflects the first branched reflected light LS1. The second branching portion 52 is provided on the optical path OP of the reflected light LB2 downstream of the first branching portion 51.

The first astigmatism adding section 53 is provided downstream of the second branching section 52 on the first branching optical path OP1. The first astigmatism adding section 53 adds a first astigmatism amount smaller than the amount of astigmatism added by the second astigmatism adding section 54 to the first branched reflected light LS1. The amount of astigmatism is a scale representing the magnitude of astigmatism, and is defined as follows. When a parallel beam having the same wavelength as the measurement light LB1 is incident on the astigmatism adding section, there is a short axis of the beam width projected on a plane perpendicular to the optical axis of the beam emitted from the astigmatism adding section. The minimum point is the direction of the short axis of the astigmatism adding part on the surface perpendicular to the optical axis. When the focal distance in the characteristic axis direction of the relative astigmatism adding portion is set to fL1 and the focal distance in the direction perpendicular to the characteristic axis is set to fL2, fL2 / fL1 is set to the amount of astigmatism. The first astigmatism adding portion 53 is configured by a combination of a convex lens 53a and a cylindrical lens 53b. For example, the focal distance of the convex lens 53a is 40 mm, and the focal distance of the cylindrical lens 53b is 100 mm.

The second astigmatism adding section 54 is provided downstream of the second branching section 52 through the reflecting mirror 58 in the second branching optical path OP2. The second astigmatism adding unit 54 adds an astigmatism amount different from the first astigmatism amount to the second branched reflected light LS2. The second astigmatism adding unit 54 adds a second astigmatism amount to the second branched reflected light LS2 that is larger than the first astigmatism amount. The second astigmatism adding section 54 is configured by a combination of a convex lens 54 a and a cylindrical lens 54 b. For example, the focal distance of the convex lens 53a is 75 mm, and the focal distance of the cylindrical lens 53b is 75 mm.

The first beam shape detection unit 55 is provided on the first branched optical path OP1. The first beam shape detection unit 55 transmits the filter 59a to receive the first branched reflection light LS1 to which the first astigmatism amount is added, and detects the beam shape of the first branched reflection light LS1. The second beam shape detection unit 56 is provided on the second branched optical path OP2. The second beam shape detection unit 56 transmits the filter 59b to receive the second branched reflection light LS2 to which the second astigmatism amount is added, and detects the beam shape of the second branched reflection light LS2.

The filter 59a attenuates light having a wavelength of the laser light L in the first branched reflected light LS1. The filter 59 a prevents light having a wavelength of the laser light L from entering the first beam shape detection unit 55. The filter 59b attenuates light having a wavelength of the laser light L in the second branched reflected light LS2. The filter 59 b prevents light having a wavelength of the laser light L from entering the second beam shape detection unit 56.

A four-quadrant sensor can be used as the first beam shape detection section 55 and the second beam shape detection section 56. The first beam shape detection unit 55 and the second beam shape detection unit 56 output the detection results to the error signal generation unit 57. Specifically, each of the first beam shape detection unit 55 and the second beam shape detection unit 56 receives light by dividing the beam shape formed on the light receiving surface thereof, and outputs the light (voltage value) corresponding to each light amount. ) Is output to the error signal generating section 57. Among them, the first beam shape detection unit 55 is not particularly limited as long as it can detect the beam shape, and may be, for example, a two-dimensional PD (Photo Diode) array.

The error signal generation unit 57 receives the outputs from the first beam shape detection unit 55 and the second beam shape detection unit 56 to generate an error signal. Specifically, the error signal generation unit 57 is based on the first and second beam shape detection units 55 and 56 provided in one of the first and second branched optical paths OP1 and OP2 selected by the control unit 250. The detection result of any one generates an error signal. The error signal generation unit 57 generates an error signal using the detection result of the first beam shape detection unit 55 when the first branched optical path OP1 is selected by the control unit 250. The error signal generation unit 57 generates an error signal using the detection result of the second beam shape detection unit 56 when the second branched optical path OP2 is selected by the control unit 250. The error signal generation unit 57 outputs the generated error signal to the control unit 250.

Here, the error signal and its obtaining principle will be specifically described below.

The AF unit 212 measures the displacement (relative displacement) of the laser light incident surface of the processing object 1, that is, the back surface 21, using the Through the Lens method, that is, the measurement using the focusing optical system 204 that condenses the laser light L. Measurement was performed with light LB1. The AF unit 212 measures the displacement of the back surface 21 using astigmatism. The AF unit 212 uses an optical system whose distance varies depending on the relative displacement of the condensing optical system 204 and the back surface 21, and the position of the image point of the reflected light LB2 of the measurement light LB1 when passing through the optical system moves. .

In the AF unit 212, the beam shape of the reflected light LB2 is changed by the beam shape detection sections 55, 56 of a 4-quadrant sensor or the like according to the displacement of the back surface 21 in the processing object 1 from a reference position described later. Specifically, the reflected light LB2 reflected on the back surface 21 has a beam widening angle that varies according to the displacement of the back surface 21, and is formed so that the beam widening angle is formed on the beam shape detection sections 55 and 56. For different beam shapes. For example, as shown in FIG. 10, the beam shape H of the reflected light LB2 is formed by a vertically long ellipse (see FIG. 10 (a)), a perfect circle (see FIG. 10 (b)), and a horizontally long ellipse (see FIG. 10 (c)). Change between. In the AF unit 212, the change in beam shape as shown above is divided into light receiving surfaces _{S A, S B, S C} , S D to detect the beam shape detecting unit 55,56. Next, in the AF unit 212, an error signal is generated by the calculation of the following formula (1) based on the detection result of the beam shape. Error signal = [(I _A + I _C )-(I _B + I _D )] / [(I _A + I _B + I _C + I _D )] ... (1) Among them, I _A : According to the light receiving surface S _A Signal value output by the amount of light in the light, I _B : Signal value output by the amount of light in the light receiving surface S _B , I _C : Signal value output by the amount of light in the light receiving surface S _C , I _D : According to the value of the light receiving surface S The signal value output by the amount of light in _D.

FIG. 11 is a graph showing an example of an error signal. In the graph shown in FIG. 11, the horizontal axis represents the displacement of the laser light incident surface from the position where the error signal becomes zero, and the vertical axis represents the magnitude of the error signal. The smaller the displacement (the leftward in the figure), the closer the laser light incident surface is to the direction of the condensing optical system 204. The larger the displacement (the farther to the right in the figure), the farther the laser light incident surface is located away from the condenser optical system 204.

As shown in FIG. 11, the error signal changes into an S-shaped curve on the graph. The displacement when the error signal becomes zero is the displacement when the beam shape becomes a perfect circle on the beam shape detection sections 55 and 56. The range usable in the error signal is a monotonically decreasing range around the zero periphery (hereinafter, this range is referred to as a "length measurement area"). The length-measuring region in this embodiment is a variation in displacement of the back surface 21 at the laser processing start position due to warpage of the object 1 to be processed, and it is at least ± 10 μm in consideration of practicality. The length measurement area of this embodiment is ± 20 μm or more.

Returning to FIG. 9, the imaging state adjustment unit 70 moves the imaging state of the measurement light LB1 and the reflected light LB2. The imaging state adjustment section 70 is provided between the first branching section 51 and the dichroic beam splitter 238 in the optical paths of the measurement light LB1 and the reflected light LB2. The imaging state adjustment unit 70 includes a concave lens 71 and a convex lens 72. The imaging state adjustment unit 70 changes the distance between the concave lens 71 and the convex lens 72 according to an instruction from the control unit 250, and moves the imaging state. Thereby, the imaging state adjustment unit 70 adjusts the shift amount. The movement system of the imaging state includes a case where a set of all imaging position relationships on the optical path is mapped to a set of other imaging position relationships (that is, a movement of the imaging position).

The reference position refers to the depth position of the laser light incident surface set at the time of reference position positioning (step S5) described later. Specifically, the reference position is the position of the back surface 21 when the back surface 21 is imaged by the surface observation unit 211 and the contrast of the projected grating is maximized.

When the imaging state adjustment unit 70 is a silicon substrate having a maximum thickness of 775 μm, the imaging state adjustment unit 70 moves the imaging state of the measurement light LB1 and the reflected light LB2 so that the shift amount is in the range of 0 μm to -180 μm. variable.

When the processing object 1 is a silicon substrate having a thickness of 775 μm and the modified region 7 is formed at a position shallower from the back surface 21 in the processing object 1, the convergence power of the imaging state adjustment unit 70 is weakened, and the offset is formed as With a value of 0 μm or close to 0 μm, the distance between the condensing optical system 204 and the back surface 21 is formed as a long distance. In contrast, when the processing object 1 is a silicon substrate having a thickness of 775 μm and the modified region 7 is formed at a position deeper from the back surface 21 in the processing object 1, the convergence power of the imaging state adjustment unit 70 becomes stronger and shifts. The amount system is formed to a value of -180 μm or close to -180 μm, and the distance system between the condensing optical system 204 and the surface 3 is formed to be a short distance.

The control unit 250 sets an offset according to a command from a higher-level system such as a higher-level controller. The control unit 250 controls the imaging state adjustment unit 70 so as to become a set offset amount. Specifically, the control unit 250 stores a data table about the position of the concave lens 71 set for each shift amount in advance. The control unit 250 refers to the data table to find the position of the concave lens 71 that is the set offset, and outputs a command to move the concave lens 71 to the determined position of the concave lens 71 to the imaging state adjustment unit 70.

The control unit 250 selects one of the first branched optical path OP1 and the second branched optical path OP2 corresponding to the imaging state moved by the imaging state adjustment unit 70. Specifically, the control unit 250 selects one of the first branched optical path OP1 and the second branched optical path OP2 corresponding to the offset amount adjusted by the imaging state adjustment unit 70. More specifically, the control unit 250 selects the first branched optical path OP1 that is the optical path of the first branched reflected light LS1 when the set offset is in the first range. When the set offset is in the second range, the optical path of the second branched reflected light LS2, that is, the second branched optical path OP2 is selected. The second range is a deeper range than the first range. The first range is a range of 0 μm or less and greater than -40 μm. The second range is a range of -40 μm or less and −180 μm or more. The control unit 250 outputs an instruction regarding the selection results of the first branched optical path OP1 and the second branched optical path OP2 to the error signal generating unit 57. The control unit 250 operates the drive unit 232 so that the error signal generated by the error signal generation unit 57 maintains the target value (here, zero).

The AF unit 212 further includes a first steering mirror 81 and a second steering mirror 82. The first and second steering mirrors 81 and 82 are arranged between the imaging state adjustment unit 70 and the dichroic beam splitter 238 in the optical paths of the measurement light LB1 and the reflected light LB2. The first and second steering mirrors 81 and 82 align (align) the optical axis of the measurement light LB1 on the optical axis of the laser light L. The first and second steering mirrors 81 and 82 constitute an optical axis adjustment mechanism.

Next, a laser processing method performed in the laser processing apparatus 300 will be described.

The laser processing method according to the present embodiment is used as a manufacturing method of a wafer in which a plurality of wafers are manufactured by laser processing the processing object 1. The object 1 to be processed has a plate shape. The object 1 to be processed is, for example, a sapphire substrate, a SiC substrate, a glass substrate (reinforced glass substrate), a silicon substrate, a semiconductor substrate, or a transparent insulating substrate. The object to be processed 1 is a silicon substrate. A functional element layer is formed in the processing object 1 on the surface 3 side which is the side opposite to the laser light incident surface side, that is, the back surface 21 side. The functional element layer system includes a plurality of functional elements arranged in a matrix (for example, a light receiving element such as a photodiode, a light emitting element such as a laser diode, or a circuit element formed as a circuit). The back surface 21 side of the processing object 1 is ground so that the processing object 1 is thinned to a desired thickness. A plurality of planned cutting lines 5 are set in the processing object 1 so as to extend between adjacent functional elements. The plurality of planned cutting lines 5 extend in a grid pattern.

In the laser processing method of this embodiment, first, the processing object 1 is placed on the support table 107 of the stage 111 so that the back surface 21 becomes a laser light incident surface. The laser light source 202 emits the laser light L, and the laser light L is condensed inside the processing object 1 by the focusing optical system 204. At the same time, the control unit 250 controls the movement of the stage 111, etc., so that the laser light L is relatively moved (scanned) toward the processing advance direction along the planned cutting line 5, and the object is processed along the planned cutting line 5. A modified region 7 is formed inside 1. After that, the expansion tape adhered to the front surface 3 or the back surface 21 of the processing object 1 is expanded to cut the processing object 1, and the processing object 1 is cut into a plurality of wafers.

Here, the back surface 21 of the processing object 1 is warped or undulated due to the influence of stress and the like caused by the formation of the functional element layer on the surface 3. Therefore, in order to condense the laser light L and form the modified region 7 to a desired depth, it is necessary to perform control to maintain the relative displacement of the condenser optical system 204 and the back surface 21 to the intended displacement.

Therefore, in the laser processing method of this embodiment, the laser light L is focused on the processing target 1 while the measurement light LB1 is focused on the processing target 1. The reflected light LB2 of the measurement light LB1 reflected on the back surface 21 is branched into first and second branched reflected lights LS1 and LS2, and the first branched reflected light LS1 with a first astigmatism amount added to the first branched optical path OP1 is detected The beam shape detects the beam shape of the second branched reflected light LS2 with a second astigmatism amount added to the second branched optical path OP2. An error signal is obtained based on the detection result of the beam shape, and the focusing optical system 204 is caused to operate in the Z direction by the drive unit 232 so that the error signal maintains a target value. Specifically, perform the following steps.

That is, as shown in FIG. 12, according to a command from a higher-level system, the offset is set by the control unit 250 (step S1). In accordance with an instruction from a higher-level system, the control unit 250 selects one of the SLD light sources 31 and 32 of the measurement light source 30 to emit light having a wavelength having a high reflectance to the processing object 1 (step S2). .

The control unit 250 selects the branched optical paths OP1 and OP2 that generate error signals based on the set offset (step S3). In step S3, if the set offset amount is in the first range (-40 μm <offset amount ≦ 0 μm), the optical path of the first branched reflected light LS1, that is, the first branched optical path, is selected to be added to the first astigmatism amount. OP1. If the set offset is in the second range (-180 μm ≦ offset ≦ -40 μm), a second astigmatism amount greater than the first astigmatism amount is selected to be added to the optical path of the second branched reflected light LS2, that is, the first 2 branch optical path OP2.

The control unit 250 controls the imaging state adjustment unit 70 so as to have a set offset, and moves the imaging states of the measurement light LB1 and the reflected light LB2 (step S4). In step S4, referring to the data table, the position of the concave lens 71 corresponding to the set offset is derived, and the concave lens 71 is moved to that position.

The reference position positioning in which the object 1 is located at the reference position is performed (step S5). In step S5, the back surface 21 which is the laser light incident surface is imaged by the surface observation unit 211, and the stage is controlled by the control unit 250 such that the back surface 21 is located at a depth position where the contrast of the projected grating is maximized. 111 moves in the Z direction. If the wavelength of the light projected by the grating is equal to the wavelength of the measurement light LB1, when the offset is 0 μm, the magnitude of the error signal at this stage becomes zero. On the other hand, if the wavelength of the light projected by the grating is different from the wavelength of the measurement light LB1, when the offset is 0 μm, the magnitude of the error signal at this stage is corresponding to the projection of the grating on the condenser optical system 204 Value of the chromatic aberration between the light and the measurement light LB1. The reference position is related to the offset as shown above. After that, the control unit 250 moves the stage 111 so as to be a set offset to bring the processing object 1 closer to the condensing optical system 204 (step S6).

The target value of the error signal is acquired and stored in the control unit 250 (step S7). In step S7, one of the SLD light sources 31 and 32 of the measurement light source 30 selected in step S2 above emits the measurement light LB1. The measurement light LB1 is adjusted by the adjustment optical system 60 to adjust the beam diameter, passes through the first branching section 51, and after the imaging state is adjusted by the imaging state adjustment section 70, the first and second manipulation mirrors 81, 82, and the two-way beam splitting The mirror 238 sequentially reflects, and is condensed by the condensing optical system 204 on the processing object 1 and is reflected on the back surface 21.

The reflected light LB2 reflected on the back surface 21 passes through the condensing optical system 204, and is sequentially reflected by the dichroic beam splitter 238, the second and first manipulation mirrors 82 and 81, and the imaging state is adjusted by the imaging state adjusting section 70. After the first branching portion 51 reflects, the second branching portion 52 is branched into the first and second branched reflected lights LS1 and LS2. The first divergent reflected light LS1 is in the first divergent optical path OP1. After the first astigmatism amount is added by the first astigmatism adding unit 53, it passes through the filter 59a and is received by the first beam shape detecting unit 55. The second divergent reflected light LS2 is in the second divergent optical path OP2. After the second astigmatism amount is added by the second astigmatism adding section 54, it passes through the filter 59b and is received by the second beam shape detecting section 56. When the error signal generation unit 57 selects the first branched optical path OP1 by the control unit 250 in the above step S3, the beam corresponding to the beam detected by the first beam shape detection unit 55 is generated according to the above formula (1). Shape error signal. On the other hand, when the second branched optical path OP2 is selected by the control unit 250 in the above step S3, a beam shape corresponding to the beam shape detected by the second beam shape detection unit 56 is generated according to the above formula (1). Error signal. The generated error signal is stored in the control unit 205 as a target value.

Next, laser processing is started (step S8). In step S8, while scanning the laser light L along the planned cutting line 5, an error signal is obtained in the same manner as in step S7 described above, and the obtained error signal is used to maintain the target value and the light is focused by the drive unit 232 The optical system 204 operates in the Z direction. Thereby, along with the scanning of the laser light L, the relative displacement of the condensing optical system 204 and the back surface 21 is maintained at a certain feedback control, and the condensing optical system 204 follows the displacement of the back surface 21. After that, it is determined whether laser processing has been completed along the planned cutting line 5 (step S9). If it is No in step S9, the above-mentioned steps S1 to S9 are repeatedly performed along the planned cutting line 5 in which laser processing is not completed. On the other hand, if it is Yes in step S9, the laser processing is ended.

FIG. 13 is a graph showing an error signal generated based on only the beam shape detected by the first beam shape detection unit 55. In the figure, the error signals are shown when the offset is changed from 0 μm to -180 μm, and every 10 μm to 20 μm is changed. As shown in FIG. 13, the inclination of the error signal has a correlation with an offset amount (that is, an imaging state in which the imaging state adjustment section 70 is moved). In addition, it can be seen that the more the offset becomes deeper in the processing object 1, the more the tilt of the error signal becomes more gentle. The tilt of the error signal refers to the change of the error signal to the obtained displacement. The tilt of the error signal refers to the proportion of change in the error signal with respect to displacement. The tilt of the error signal corresponds to the proportional constant if the error signal decreases monotonically in proportion. The tilt of the error signal corresponds to the amount of change when the error signal changes with the change in displacement.

Here, for the reason that the tilt of the error signal is too gentle, a mismatch between the amount of astigmatism and the amount of shift added to the reflected light LB2 of the measurement light LB1 is found. Therefore, in the laser processing apparatus 300, one of the first and second branched optical paths OP1 and OP2 is selected in accordance with the offset, and based on the detection of the selected one of the first and second branched optical paths OP1 and OP2. The shape of the beam produces an error signal. As a result, the amount of astigmatism added to one of the first and second divergent reflected lights LS1 and LS2 used for generating the error signal can be formed to correspond to the amount of shift. As a result, the inclination of the error signal can be suppressed from being too gentle. Therefore, the displacement of the laser light incident surface, that is, the back surface 21 can be detected with high accuracy.

In particular, since the back surface 21 is ground until the object to be processed 1 is thinned to a desired thickness, a state where a grinding mark is formed on the back surface 21 (a state in which many grooves having a very shallow depth are formed) is formed. At this time, the measurement light LB1 is scattered on the back surface 21 and the error signal may be uneven even if it is the same displacement. Therefore, if the tilt of the error signal is too gentle, problems in practicality may occur. Therefore, if a grinding mark is formed on the back surface 21 as described above, the above-mentioned effect of suppressing the tilt of the error signal from being too gentle is significant.

In the laser processing apparatus 300, if the offset is in the first range, the first branched optical path OP1 is selected, and if the offset is in the second range that is deeper than the first range, the second branched optical path OP2 is selected. At this time, if the shift is shallow, the first divergent reflected light LS1 with a smaller astigmatism amount can be used for the generation of the error signal. If the shift is deep, the second divergence with a larger astigmatism amount can be used. The reflected light LS2 is used in the generation of the error signal. The tilt of the error signal can be suppressed from being too gentle, and the displacement of the back surface 21 can be detected with high accuracy.

FIG. 14 is a graph showing error signals generated in the laser processing apparatus 300. The figure shows various error signals when the offset is changed from 0 μm to -180 μm every 10 μm to every 20 μm. In the name of each item (series) in the figure, if it is an error signal based on the beam shape of the first branched optical path OP1, label "OP1", and if it is an error signal based on the beam shape of the second branched optical path OP2, then Mark "OP2". As shown in FIG. 14, it can be seen that the laser processing apparatus 300 can suppress the tilt of the error signal from being too gentle. For example, in the laser processing apparatus 300, the error signal has a tilt of more than a certain value within a practical range due to a measurement error due to a grinding mark. For example, the error signal may have an absolute value of a tilt of 0.025 / μm or more in the displacement where the error signal becomes zero. For example, the error signal may have an absolute value of a tilt of 0.0275 / μm or more in a displacement where the error signal becomes zero.

Among them, if the offset is -40 μm, it can be seen that it is an error signal based on the beam shape of the first branched optical path OP1 or an error signal based on the beam shape of the second branched optical path OP2, and the tilt thereof also becomes more than a certain value. Therefore, in this embodiment, the first range is set to a range of 0 μm or less and greater than -40 μm, and the second range is set to a range of -40 μm or less and −180 μm or more. However, the first range may also be set to 0 μm. In the following range of -40 μm or more, the second range is set to a range of less than -40 μm and −180 μm or more.

FIG. 15 is a graph showing an error signal generated based on only the beam shape detected by the second beam shape detection unit 56. The figure shows each error signal when the offset is changed from 0 μm to -180 μm every 10 μm to every 20 μm. From the results shown in FIG. 15, it can be seen that the offset becomes shallower in the processing object 1, the tilt of the error signal becomes more sharp, and the length measurement area becomes insufficient. On the other hand, in the laser processing apparatus 300, it is possible to suppress the inclination of the error signal from being too sharp, and to sufficiently secure the length measurement area (see FIG. 14).

In the laser processing apparatus 300, the offset amount is set by the control unit 250, and the imaging state adjustment unit 70 is controlled so as to be the set offset amount. With this configuration, it is possible to automatically adjust the imaging states of the measurement light LB1 and the reflected light LB2 as a set offset.

The laser processing apparatus 300 is provided with a drive unit 232 that causes the condensing optical system 204 to operate in the Z direction, and the drive unit 232 is operated by the control unit 205 so that an error signal maintains a target value. With this configuration, the focusing optical system 204 can be moved in the Z direction so as to follow the back surface 21.

The laser processing apparatus 300 includes first and second steering mirrors 81 and 82 that align the optical axis of the measurement light LB1 with the optical axis of the laser light L. With this configuration, the optical axis of the measurement light LB1 can be accurately aligned with the optical axis of the laser light L.

In the laser processing apparatus 300, among the light beams of a plurality of wavelengths emitted from the measurement light source 30, light having a wavelength having a high reflectance to the processing object 1 is used as the measurement light LB1. Thereby, the measurement light LB1 can be easily reflected on the back surface 21.

Incidentally, it is also considered to reduce the tilt of the error signal by shortening the physical distance between the imaging state adjustment section 70 and the condenser optical system 204 or by inserting a 4f lens system therebetween. The change. However, it is difficult to shorten the physical distance due to the limitation of the device configuration, and the insertion of a 4f lens system may increase the size of the device, which may make it difficult to achieve. In particular, if the first and second steering mirrors 81 and 82 are arranged, it is difficult to shorten the physical distance. In this regard, in the laser processing apparatus 300, there are few restrictions on the configuration of the apparatus, and further, the size of the apparatus can be suppressed. The laser processing apparatus 300 may include first and second steering mirrors 81 and 82.

FIG. 16 is a configuration diagram showing a part of an AF unit 212B according to a modification. As shown in FIG. 16, each of the first and second beam shape detection sections 55 and 56 of the AF unit 212B may move along the first and second branched optical paths OP1 and OP2 according to the movement of the concave lens 71 of the imaging state adjustment section 70. Each move. Specifically, the concave portion 71 can also be moved by the control unit 250 in such a manner that the offset lens becomes deeper and deeper, so that the first and second beam shape detection units 55 and 56 are separated from the first and second astigmatism adding units 53, and 54 moves closer to each other (in other words, the first and second beam shape detection units 55 and 56 may be brought closer to the first and second astigmatism adding units 53 and 54 as the offset deepens.

FIG. 17 is a graph for explaining an effect obtained by the AF unit 212B of FIG. 16. FIG. 17 shows an error signal generated based on the beam shape detected by the first beam shape detection unit 55. FIG. 17 (a) is an error signal when the first beam shape detection unit 55 is fixed. FIG. 17 (b) is an error signal generated by the AF unit 212B, that is, an error signal when the first beam shape detection unit 55 is movable. As shown in FIG. 17 (a) and FIG. 17 (b), in the AF unit 212B of the modified example, for any offset amount, the S-shaped curve of the error signal can be formed to be obtained on the horizontal axis with zero as the center. Even shape. This system contributes to the improvement of responsiveness such as PID control.

In the AF unit 212B, instead of the movement of the first and second beam shape detection sections 55 and 56 or in addition, the convex lenses 53a and 54a of the first and second astigmatism adding sections 53 and 54 and At least one of the cylindrical lenses 53b and 54b is similarly moved. The same effect was achieved at this time.

Although the embodiments have been described above, the present invention is not limited to those described above, and may be applied to modifications or others without changing the gist described in each claim.

In the above embodiment, the optical path OP of the reflected light LB2 is split into two optical paths (the first and second branched optical paths OP1 and OP2) by the second branching section 52, but may be branched into three or more optical paths. For each of the optical paths having three or more optical paths, a complex astigmatism adding unit for adding astigmatic amounts of mutually different sizes, and a complex beam shape detection for detecting each beam shape of the complex branched reflected light to which astigmatism is added are provided. Department. At this time, the optical path may also be selected from the plural optical paths such that astigmatism with a deeper and larger offset is added to the divergent reflected light, and the beam shape of the divergent reflected light of the selected optical path is detected. As a result, an error signal is generated.

In the above embodiment, the imaging state adjustment unit 70 is arranged between the first branching portion 51 and the dichroic beam splitter 238 in the optical path of the measurement light LB1 and the reflected light LB2. Not limited. The arrangement of the above embodiment may be replaced, or in addition, the optical path of the measurement light LB1 is more upstream than the first branching portion 51, and the optical path OP of the reflected light LB2 is at the first branching portion 51 and the second At least one of the diverging sections 52 is provided with an imaging state adjustment section 70.

In the above embodiment, the imaging state adjustment unit 70 is configured by the concave lens 71 and the convex lens 72, but the imaging state adjustment unit 70 is not particularly limited, and may be, for example, a variable focus distance lens. The optical system of the above embodiment includes the dichroic beam splitter 238 that transmits the laser light L and reflects the measurement light LB1 and the reflected light LB2. However, the optical system may include the laser light L and the measurement light LB1 and The configuration of the dichroic mirror through which the reflected light LB2 passes is replaced. Similarly, the optical system of the above-mentioned embodiment may have a configuration in which the measurement light LB1 is reflected by the first branching portion 51 and the reflected light LB2 is transmitted. Similarly, the optical system of the above embodiment may have a configuration in which the first branched reflected light LS1 is transmitted through the second branched portion 52 and the second branched reflected light LS2 is reflected.

In the above-mentioned embodiment, between step S6 and step S7, the bias offset values of the first and second beam shape detection units 55 and 56 are obtained (the first and the first in the state where the beam shape is not detected). 2 beam shape detection units 55, 56). In the above embodiment, the offset is set to the optical arrangement with the error signal being zero, but it is not limited to the optical arrangement where the error signal is zero, and the offset can also be set to the optical arrangement where the error signal is the reference value.

In the above embodiment, the offset is set in accordance with a command from a higher-level system, but the offset can also be set by the operator's operation, and the offset can be set in advance according to the position of the modified region 7 formed. Shift amount. In the embodiment described above, the imaging state adjustment unit 70 is controlled by the control unit 250 so as to be a set offset amount. However, the imaging state adjustment unit 70 may be controlled by an operator's operation.

The above-mentioned embodiment is provided with the reflective spatial light modulator 203 as a spatial light modulator, but the spatial light modulator is not limited to a reflective one, and may be provided with a transmissive spatial light modulator. In the embodiment described above, the back surface 21 of the object 1 is set as the laser light incident surface, but the surface 3 of the object 1 may be set as the laser light incident surface. In the above, the control unit 250 and the error signal generation unit 57 constitute a signal acquisition unit. The control section 250 constitutes an offset setting section, an imaging state control section, and a drive mechanism control section.

1‧‧‧ processing object

3‧‧‧ surface

5‧‧‧ cut off the planned line

7‧‧‧ Improved area

8‧‧‧ cut off the starting area

21‧‧‧ back

30‧‧‧light source for measurement

31, 32‧‧‧SLD light source

33‧‧‧WDM

34‧‧‧optical fiber

50‧‧‧Displacement detection section

51‧‧‧First Division

52‧‧‧Second Division (Division)

53‧‧‧The first astigmatism addition unit (astigmatism addition unit)

53a, 54a‧‧‧ convex lens

53b, 54b‧‧‧ cylindrical lens

54‧‧‧ 2nd astigmatism addition section (astigmatism addition section)

55‧‧‧ 1st beam shape detection unit (beam shape detection unit)

56‧‧‧ 2nd beam shape detection unit (beam shape detection unit)

57‧‧‧Error signal generation section (signal acquisition section)

58‧‧‧Mirror

59a, 59b‧‧‧ filters

60‧‧‧Adjust the optics

70‧‧‧ Imaging state adjustment section

71‧‧‧ concave lens

72‧‧‧ convex lens

81‧‧‧The first operating mirror (optical axis adjustment mechanism)

82‧‧‧Second steering mirror (optical axis adjustment mechanism)

100, 300‧‧‧laser processing equipment

101‧‧‧laser light source

102‧‧‧Laser light source control unit

103‧‧‧ Department of Optics

105‧‧‧ condenser lens

107‧‧‧Support Desk

111‧‧‧ carrier

115‧‧‧ Carrier Control Department

202‧‧‧laser light source

203‧‧‧Reflective Space Light Modulator

204‧‧‧ Condensing optics (condensing lens)

205a, 205b‧‧‧Mirror

206a, 206b‧‧‧Mirror

207‧‧‧ Attenuator

208‧‧‧Reflector

209‧‧‧half mirror

210, 238‧‧‧ two-way beamsplitters

211‧‧‧Surface observation unit

211a‧‧‧ Observation light source

211b‧‧‧ Detector

212, 212B‧‧‧AF units

213‧‧‧Si substrate

214‧‧‧pixel electrode

214a‧‧‧ surface

215‧‧‧Reflective film

216‧‧‧LCD layer

216a‧‧‧Liquid crystal molecules

217‧‧‧Transparent conductive film

218‧‧‧Transparent substrate

218a‧‧‧ surface

219‧‧‧Reflector

228‧‧‧λ / 2 wave plate

231‧‧‧Frame

232‧‧‧Drive unit (drive mechanism)

233‧‧‧ floor

236‧‧‧Top plate

241‧‧‧4f Optics

241a‧‧‧1st lens

241b‧‧‧ 2nd lens

250‧‧‧control section (signal acquisition section, offset setting section, imaging state control section, drive mechanism control section)

260‧‧‧ Beam Homogenizer

914‧‧‧Drive circuit layer

999a, 999b‧‧‧Alignment film

H‧‧‧ Beam shape

L‧‧‧laser light (laser light for processing)

LB1‧‧‧Measurement light

LB2‧‧‧Reflected light

LS1‧‧‧The first branched reflected light (branched reflected light)

LS2‧‧‧Second branched reflected light (branched reflected light)

OP‧‧‧Light Path

OP1‧‧‧1st branched light path (light path of 1st branched reflected light)

OP2‧‧‧ 2nd branched optical path

P‧‧‧condensing point (condensing position)

S _A , S _B , S _C , S _D ‧‧‧ light receiving surface

VL1‧‧‧visible light

VL2‧‧‧Reflected light

FIG. 1 is a schematic configuration diagram of a laser processing apparatus used for forming a modified region. FIG. 2 is a plan view of a processing object that is a target of formation of a modified region. FIG. 3 is a cross-sectional view taken along the line III-III of the object to be processed in FIG. 2. FIG. 4 is a plan view of a processing object after laser processing. FIG. 5 is a cross-sectional view taken along the line V-V of the object to be processed in FIG. 4. FIG. 6 is a cross-sectional view taken along the line VI-VI of the object to be processed in FIG. 4. FIG. 7 is a schematic configuration diagram of a laser processing apparatus according to an embodiment. FIG. 8 is a partial cross-sectional view of a reflective spatial light modulator of the laser processing apparatus of FIG. 7. FIG. 9 is a schematic configuration diagram of an autofocus control system including an AF unit of the laser processing apparatus of FIG. 7. FIG. 10 (a) is a diagram illustrating a case where the beam shape of the reflected light is a vertically long ellipse. FIG. 10 (b) is a diagram illustrating a case where the beam shape of the reflected light is a perfect circle. (c) is a figure explaining the case where the beam shape of reflected light is a horizontally long ellipse. Figure 11 is a graph showing an example of the error signal. FIG. 12 is an example of a flowchart showing a laser processing method performed by the laser processing apparatus of FIG. 7. FIG. 13 is a graph showing an error signal generated based on only the beam shape detected by the first beam shape detection unit. FIG. 14 is a graph showing error signals generated in the laser processing apparatus of FIG. 7. FIG. 15 is a graph showing an error signal generated based on only the beam shape detected by the second beam shape detection unit. FIG. 16 is a schematic configuration diagram of an AF unit according to a modification. FIG. 17 (a) is a graph for explaining the effect obtained by the AF unit of FIG. 16, and the error signal when the first beam shape detection unit is fixed. FIG. 17 (b) is a graph for explaining the effect obtained by the AF unit of FIG. 16, and the error signal when the first beam shape detecting section is movable.

Claims (8)

A laser processing device is a laser processing device for concentrating laser processing light on a processing object to form a modified region in the processing object. The laser processing device includes: a light source for measurement, which is used for emission measurement A light-condensing lens for condensing the laser light for processing and the light for measurement on the object to be processed; a displacement detecting unit based on the light reflected on the incident surface of the laser light for the object to be processed The reflected light of the measurement light detects the displacement of the incident surface of the laser light; and the imaging state adjustment section moves the imaging state of at least one of the measurement light and the reflected light of the measurement light, and the displacement The detection section includes: (i) a branching section that divides the reflected light of the measurement light into a plurality of branched reflected light; (ii) a complex astigmatism adding section that is provided on each of the optical paths of the plurality of branched reflected light and for the plurality of branched reflected light Each with an astigmatism amount different from each other; a complex beam shape detecting section, which is It is provided in each of the optical paths of the plurality of branched reflected light, and detects a beam shape of each of the plurality of the branched reflected light to which astigmatism is added; and a signal acquisition unit, which is selected from the optical paths of the plurality of the branched reflected light, and corresponds to the aforementioned. One of the imaging states adjusted by the imaging state adjustment unit obtains a signal regarding the displacement based on a detection result of the beam shape detection unit in the optical path of the branched reflected light selected. For example, the laser processing device in the first scope of the patent application, wherein the imaging state adjustment unit adjusts the offset by moving the imaging state, and the signal acquisition unit selects from among the optical paths of the plurality of branched reflected light. Corresponds to one of the shift amounts adjusted by the imaging state adjustment section. For example, the laser processing device in the second scope of the patent application, wherein the branching section divides at least the reflected light of the measurement light into a first branched reflected light and a second branched reflected light, and the astigmatic addition section has: The first astigmatism adding section is provided on the optical path of the first branched reflected light, and adds the first astigmatism amount to the first divided reflected light; and the second astigmatism adding section is provided on the aforementioned The optical path of the second branched reflected light is added to the second branched reflected light with a second astigmatism amount greater than the first astigmatism amount. The signal acquisition unit: If the offset is adjusted by the imaging state adjustment unit. The amount is in the first range, and the optical path of the first branched reflected light is selected. If the offset adjusted by the imaging state adjustment section is in a second range that is deeper than the first range, the second branched reflection is selected. Light path of light. For example, the laser processing device according to the second or third aspect of the patent application scope includes: (1) an offset setting unit that is set at the aforementioned offset adjusted by the aforementioned imaging state adjustment unit; and an imaging state control unit It controls the imaging state adjustment unit so as to become the offset amount set by the offset amount setting unit. For example, the laser processing device according to any one of claims 1 to 4 includes: a drive mechanism for moving the object to be processed and the object along the optical axis direction of the light-condensing lens. At least one of the condenser lenses operates; and a drive mechanism control unit that operates the drive mechanism such that the signal obtained by the signal acquisition unit maintains a target value. For example, the laser processing device according to any one of claims 1 to 5 of the scope of patent application, further comprising: an optical axis adjustment mechanism that aligns the optical axis of the measurement light with the laser light for processing. Optical axis. For example, the laser processing device according to any one of claims 1 to 5, wherein the light source for measurement can emit any one of a plurality of light having different wavelengths from each other and emit light among a plurality of wavelengths. Light having a wavelength with the highest reflectance to the object to be processed is used as the measurement light. A laser processing method is a laser processing method for concentrating laser processing light on a processing object to form a modified region in the processing object. The laser processing method includes: (1) a laser processing step, The processing laser light is focused on the processing object by a focusing lens, while the measurement light is focused on the processing object by the focusing lens, and the laser light incident surface of the processing object is reflected. The reflected light of the measurement light is branched into at least a first branched reflected light and a second branched reflected light, and the emission of the first branched reflected light with a first astigmatism amount added to the optical path of the first branched reflected light is detected. A beam shape, and a beam shape of the second divergent reflected light having a second astigmatism amount greater than the first astigmatism amount added to the optical path of the second divergent reflected light, and based on a detection result of the beam shape, Obtaining a signal about the displacement of the incident surface of the laser light, and maintaining the target value of the obtained signal, along the optical axis direction of the focusing lens, the processing object and the At least one of the optical lenses is operated. The above laser processing step includes: the first step, which sets an offset; the second step, where the above-mentioned offset set in the first step is In the first range, the optical path of the first branched reflected light is selected. If the offset amount set in the first step is a second range deeper than the first range, the optical path of the second branched reflected light is selected. The third step is to move the imaging state of at least one of the measurement light and the reflected light of the measurement light so as to become the offset amount set in the first step; The fourth step The step is to operate at least one of the object to be processed and the light-condensing lens so as to become the offset amount set in the first step; The fifth step is the third step. After the step and the fourth step, the target value is obtained; and in the sixth step, after the fifth step, the processing laser light is condensed by a condenser lens The processing object detects the beam shape on the optical path of the branched reflected light selected in the second step, obtains the signal based on the detection result of the beam shape, and maintains the target with the obtained signal. In the form of a value, at least one of the object to be processed and the light-condensing lens is operated along the optical axis direction of the light-condensing lens.