TWI745509B - Laser processing device and laser processing method - Google Patents

Abstract

The laser processing device is equipped with: a measurement light source; a condenser lens; a displacement detection unit that detects the displacement of the laser light incident surface based on the reflected light of the measurement light reflected on the laser light incident surface; and the measurement light And an imaging state adjustment unit that moves the imaging state of at least one of the reflected light of the measurement light. The displacement detecting unit has: a branching part that splits the reflected light of the measurement light into a plurality of branched reflected lights; a complex astigmatism adding part that adds different amounts of astigmatism to each of the multiple branched reflected lights; and detects additional images. The multiple beam shape detection section for the beam shape of each of the scattered plural branch reflected light; and the optical path of the multiple branch reflected light, select one corresponding to the imaging state adjusted by the imaging state adjustment section, and select one according to the selected The detection result of the beam shape detection unit in the optical path of the branched reflected light is a signal acquisition unit that acquires a signal about the displacement.

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 apparatus that forms a modified region on the object by condensing laser light for processing on the object (see, for example, Patent Document 1). The laser processing device shown above is equipped with: a light source for measurement that emits light for measurement; a lens for condensing the laser light for processing and the light for measurement on the object to be processed; and The reflected light of the measurement light reflected on the laser light incident surface is a displacement detecting unit that detects the displacement of the laser light incident surface (hereinafter also referred to as "displacement"). The displacement detection unit adds astigmatism to the reflected light of the measurement light, detects the beam shape of the reflected light with the astigmatism, and obtains a signal related to the displacement based on the detection result. [Prior Technical Documents] [Patent Documents]

[Patent Document 1] JP 2015-186825 A

(The problem to be solved by the invention)

In the laser processing device as described above, there are cases where the acquired signal for displacement (the tilt of the signal) is too gentle. At this time, for example, if the laser light incident surface is a grinding surface, the grinding mark (also called a saw mark) scatters the light for measurement, and the phenomenon that the signal is different even if the displacement is the same is generated. The error of the detected displacement is more obvious. As a result, it may be difficult to accurately detect the displacement of the laser light incident surface.

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 the displacement of the laser light incident surface. (Means to solve the problem)

A laser processing device of one aspect of the present invention is a laser processing device that forms a modified area on the processing object by condensing laser light for processing on the processing object, and is provided with: a light source for measurement, and It is used for outgoing measurement light; Condensing lens, which focuses the processing laser light and measurement light on the object to be processed; Displacement detection unit, which is used for measurement based on the laser light incident surface of the processing object being reflected The reflected light of the light detects the displacement of the incident surface of the laser light; and the imaging state adjustment section which moves the imaging state of at least one of the measurement light and the reflected light of the measurement light, and the displacement detection section has: The part, which divides the reflected light of the measurement light into a plurality of branched reflected light; the complex astigmatism adding part, which is set in the optical path of the plural branched reflected light, adds images of different sizes to each of the plural branched reflected lights. The amount of astigmatism; the complex beam shape detection unit, which is set in the optical path of the complex reflected light, detects the beam shape of the complex reflected light with astigmatism; and the signal acquisition unit, which is reflected by the complex branch Among the optical paths of the light, one corresponding to the imaging state adjusted by the imaging state adjusting unit is selected, and a signal regarding the displacement is obtained based on the detection result of the beam shape detecting unit in the selected optical path of the branched reflected light.

The inventors of the present invention continue to study carefully, and found that the tilt system of the acquired 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, in terms of the reason why the tilt of the signal is too gentle, it is found that it is caused by a mismatch between the imaging state and the amount of astigmatism added by the reflected light. Therefore, in the laser processing apparatus of one aspect of the present invention, the reflected light of the measurement light is divided into plural divided reflections, and the difference in the amount of astigmatism added to the optical path of each divided reflected light is detected. The beam shape of the reflected light. Next, among the optical paths of the plurality of branched reflected lights, one corresponding to the imaging state moved by the imaging state adjustment unit is selected, and a signal of the beam shape of the branched reflected light selected according to the selected optical path is obtained. In this way, the amount of astigmatism added to the reflected light of the obtained signal can be formed to correspond to the imaging state. It can suppress the tilt of the acquired signal from becoming too gentle. Therefore, the displacement of the incident surface of the laser light can be detected accurately.

In the laser processing device of one aspect of the present invention, the imaging state adjustment unit may also adjust the offset by moving the imaging state, and the signal acquisition unit is selected from among the light paths of a plurality of branched reflected light, which corresponds to the imaging One of the offsets adjusted by the state adjustment unit. Here, the offset refers to a scale indicating the relative displacement of the laser incident surface of the object to be processed when the signal indicating the displacement relative to the laser incident surface of the object becomes a reference value (typically zero). For example, an offset of 0μm means that when parallel light of the same wavelength as the measurement light is incident on the condenser lens, the arrangement is minimized on the laser incident surface of the object to be processed, relative to the displacement signal at this time The signal becomes the geometrical configuration state of the reference value. In addition, for example, the offset is -180μm, which refers to the above arrangement when the offset is 0μm. When the laser incident surface of the object is close to 180μm toward the condenser lens, the signal becomes the reference value. state. When the offset value is small (large negative amplitude), the offset or offset is called deep, and when the offset value is large (small negative amplitude), the offset or offset is called shallow.

It is found that the tilt of the acquired signal, specifically, is related to the offset tool, and is too gentle due to the mismatch between the offset and the astigmatism. Therefore, in the laser processing apparatus of one aspect of the present invention, the optical path corresponding to the offset is selected from among the multiple branched light paths. In this way, the amount of astigmatism added to the reflected light of the obtained signal can be formed to correspond to the amount of offset. It can suppress the tilt of the acquired signal from being too gentle.

In the laser processing apparatus of one aspect of the present invention, the branching part may branch the reflected light of the measurement light into at least the first branched reflected light and the second branched reflected light, and the astigmatism adding part may have: The astigmatism adding section is set in the optical path of the first branch reflected light, and the first amount of astigmatism is added to the first branch reflected light; and the second astigmatism adding section is set in the second branch reflected light Add a second astigmatism greater than the first astigmatism to the second branch reflected light. The signal acquisition section: If the offset adjusted by the imaging state adjustment section is in the first range, select the first branch If the optical path of the reflected light is adjusted by the imaging state adjustment unit in a second range that is deeper than the aforementioned first range, the optical path of the second branched reflected light is selected.

More specifically, it is found that if the same astigmatism is added to the tilt of the acquired signal, the deeper the deviation, the more gentle it is. Therefore, in the laser processing apparatus of one aspect of the present invention, if the shift amount is in the first range, the first branched reflected light optical path is selected, and if the shift amount adjusted by the imaging state adjustment section is lower than the first When the first range is the deeper second range, select the light path of the second branch reflected light. In this way, the amount of astigmatism added to the reflected light with respect to the obtained signal can be increased if the deviation is deep (or decreased if it is shallow). It can suppress the tilt of the acquired signal from being too gentle.

The laser processing apparatus of one aspect of the present invention may also include: an offset setting part, which sets the offset adjusted by the imaging state adjustment part; and an imaging state control part, which is set to be in the offset The imaging state adjustment unit is controlled by the offset amount set by the amount setting unit. With this configuration, it is possible to automatically adjust the imaging state with the set shift amount.

The laser processing apparatus according to one aspect of the present invention may also include a drive mechanism that moves at least one of the object to be processed and the condenser lens along the optical axis direction of the condenser lens; and The drive mechanism control unit operates the drive mechanism so that the signal obtained by the signal acquisition unit maintains a target value. With this configuration, it is possible to move the condensing lens relative to the direction of the optical axis so as to follow the incident surface of the laser light.

The laser processing apparatus of one aspect of the present invention may also include an optical axis adjustment mechanism that aligns the optical axis of the measurement light with the optical axis of the processing laser light. With this configuration, the optical axis of the measurement light can be aligned with the optical axis of the processing laser light accurately.

In the laser processing apparatus of one aspect of the present invention, the light source for measurement can also emit any one of plural lights having different wavelengths, and the emitted light of the plural wavelengths has reflectance to the object to be processed. The light with the highest wavelength is used as the measurement light. In this case, it is possible to easily detect the reflected light that will reflect the measurement light on the incident surface of the laser light.

One aspect of the laser processing method of the present invention is a laser processing method that forms a modified area on the processing object by condensing laser light for processing on the processing object, and includes: a laser processing step, which The laser light for processing is condensed on the object by the condensing lens, while the measurement light is condensed on the object by the condensing lens, and the laser light is reflected on the incident surface of the object. The reflected light of the measurement light is divided into at least the first branch reflected light and the second branch reflected light, and the beam shape of the first branch reflected light with the first astigmatism added to the optical path of the first branch reflected light is detected, and Detect the beam shape of the second branch reflected light with the second astigmatism added to the optical path of the second branch reflected light larger than the first astigmatism, and obtain information about the laser light incident surface based on the detection result of the beam shape The displacement signal moves at least one of the object to be processed and the condenser lens along the optical axis direction of the condenser lens in such a way that the acquired signal maintains the target value. The laser processing steps include: The first step is to set the offset; the second step is to select the first branch of the reflected light path if the offset set in the first step is the first range, if the first step is set If the offset is the second range that is deeper than the first range, the second branch of the reflected light path is selected; the third step is to set the offset in the first step, and the measurement light will be used. And the imaging state of at least one of the reflected light of the measurement light is moved; the fourth step is to make at least one of the object to be processed and the condensing lens so as to become the offset set in the first step Any one of the actions; the fifth step, which is after the third step and the fourth step, to obtain the target value; and the sixth step, which is after the fifth step, while converging the laser light for processing with the lens for condensing Focusing on the object to be processed, the beam shape is detected by the optical path of the branched reflected light selected in the second step, and the signal is obtained based on the detection result of the beam shape, and the obtained signal maintains the target value. At least one of the object to be processed and the condensing lens is moved along the optical axis direction of the condensing lens.

In this laser processing method, if the deviation is deeper, the amount of astigmatism added to the reflected light of the obtained signal can be increased (if it is shallower, the amount of astigmatism added) can be increased. Based on the above knowledge, the tilt of the acquired signal can be suppressed from becoming too gentle. Therefore, the displacement of the incident surface of the laser light can be detected accurately. (Effects of the invention)

With one aspect of the present invention, a laser processing device and a laser processing method that can accurately detect the displacement of the laser light incident surface can be provided.

Hereinafter, the embodiment will be described in detail with reference to the drawings. Among them, the same or equivalent parts are marked with the same symbols in each figure, and repeated descriptions are omitted.

In the laser processing apparatus and the laser processing method of the embodiment, laser light is condensed on the object to be processed to form a modified region in the object to be processed along the planned 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 apparatus 100 is provided with: a laser light source 101 as a laser light source for processing that pulses laser light L as a laser light for processing; and an optical system for guiding the laser light L 103; and a condensing lens 105 for condensing the laser light L. The laser processing apparatus 100 is provided with: a support table 107 for supporting the processing object 1 irradiated with the laser light L condensed by the condensing lens 105; a stage 111 for moving the support table 107; control The laser light source 101 is a laser light source control unit 102 that adjusts the output (pulse energy, light intensity), pulse width, pulse waveform, etc. 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 in the optical system 103, and is condensed on the object to be processed placed on the support 107 by the condensing lens 105 1's interior. The stage 111 is moved together with this, and the object 1 to be processed is moved relative to the laser light L along the planned cutting line 5. Thereby, the modified region along the planned cutting line 5 is formed in the object 1. Here, the stage 111 is moved in order to move the laser light L relatively, but the condenser lens 105 may be moved, or both may be moved.

For the object 1 to be processed, a plate-shaped member (for example, a substrate, a wafer, etc.) including a semiconductor substrate formed of a semiconductor material, a piezoelectric substrate formed of a piezoelectric material, or the like is used. As shown in FIG. 2, a planned cutting line 5 for cutting the object 1 is set in the object 1 system. The planned cutting line 5 is an imaginary line extending linearly. If a modified region is formed inside the object 1, as shown in FIG. 3, in a state where the condensing point (condensing position) P is aligned with the inside of the object 1, the laser light L is made to follow the cut The predetermined breaking line 5 (that is, in the direction of arrow A in FIG. 2) relatively moves. Thereby, as shown in FIGS. 4, 5, and 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 becomes a cut Starting point area 8.

The condensing point P refers to the part where the laser light L is condensed. The planned cutting line 5 is not limited to a linear shape, and may be a curved shape, a three-dimensional shape of these combinations, or one designated by coordinates. The planned cutting line 5 is not limited to a virtual line, and may be a line actually drawn on the surface 3 of the object 1 to be processed. The modified region 7 may also be formed continuously or intermittently. The modified regions 7 may be in the form of rows or dots. In short, the modified regions 7 may be formed at least inside the object 1 to be processed. In addition, a crack may be formed starting from the modified region 7 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 forming the modified region 7 may be the back surface of the object 1 instead of being limited to the surface 3 of the object 1.

Incidentally, if the modified region 7 is formed inside the object 1, the laser light L passes through the object 1 and is especially absorbed near the condensing point P located inside the object 1. Thereby, a modified region 7 is formed in the object 1 to be processed. At this time, since the energy density of the laser light L on the surface 3 of the object 1 is low, the surface 3 of the object 1 does not melt. On the other hand, if the modified region 7 is formed on the front surface 3 or the back surface of the object 1, the laser light L is absorbed in the vicinity of the condensing point P located on the front surface 3 or the back surface, and the surface 3 or the back surface is melted and removed. Form removal parts such as holes or grooves.

The modified region 7 refers to a region in which the density, refractive index, mechanical strength, or other physical properties are different from the surroundings. The modified region 7 includes, for example, a molten processed region (meaning at least any one of a region that is once melted and then solidified, a region in a molten state, and a region in a state that is resolidified by melting), and a crack region , Insulation failure area, refractive index change area, etc., there are also areas where these are mixed. In addition, in the modified region 7, there are regions in which the density of the modified region 7 changes compared with the density of the non-modified region in the material of the object 1, or regions in which lattice defects are formed. If the material of the object 1 is single crystal silicon, the modified region 7 can also be said to be a high dislocation density region.

The melt-processed area, the refractive index change area, the area where the density of the modified area 7 is changed compared to the density of the non-modified area, and the area where the lattice defect is formed are also inside these areas or the modified area. 7 There are cracks (fractures, micro cracks) in the interface with the non-modified area. The crack system contained may cover the entire modified region 7 or may be formed only in a part or a plurality of parts. The object to be processed 1 includes a substrate made of a crystalline material having a crystalline structure. For example, the object 1 is 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 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. In addition, the object 1 may include a substrate made of an amorphous material having an amorphous structure (amorphous structure), or 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, it becomes the modified area 7 due to the accumulation of plural modified points. Regarding the modified point, considering the required cutting accuracy, the required flatness of the cut surface, the thickness, type, and crystal orientation of the object 1 to be processed, the size or the length of the cracks that occur can be appropriately controlled. . In addition, in the embodiment, modified spots may be formed as modified regions 7 along the planned cutting line 5.

Next, the laser processing apparatus and laser processing method of the embodiment will be described. The following is an example of a case where the back surface 21 of the object 1 is used as the 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 device 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 condenses laser light L on the object 1 to form a modified region 7 in the 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 less than 1 μs, that is, pulsed laser light as the laser light L. The laser light source 202 includes an ultrashort pulse laser light source as a laser oscillator. In the case of a laser oscillator, it can be composed of, for example, a solid laser, an optical 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. In terms of the output adjustment unit, it can be composed of a λ/2 wavelength plate unit and a polarizing plate unit. In addition, 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 by the laser light source 202 is included in 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 body 231 with screws or the like so as to emit the laser light L in the horizontal direction.

The reflective spatial light modulator 203 modulates the laser light L emitted by the laser light source 202. The reflective spatial light modulator 203 is, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator). The reflective spatial light modulator 203 modulates the laser light L incident from the horizontal direction and reflects it diagonally upward with respect to the horizontal direction.

As shown in FIG. 8, the reflective spatial light modulator 203 is formed by sequentially stacking a silicon substrate 213, a driving circuit layer 914, a plurality of pixel electrodes 214, a reflective film 215 such as a dielectric multilayer film mirror, 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 formed. The transparent substrate 218 has a surface 218a along a predetermined plane. The surface 218 a of the transparent substrate 218 constitutes the surface of 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 from 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 in a matrix on the silicon substrate 213 along the transparent conductive film 217. The plurality of pixel electrodes 214 are formed of metal materials 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 on the driving circuit layer 914.

The active matrix circuit is arranged 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 has: a first driver circuit that controls the voltage applied to each pixel column arranged in one direction along the surface 218a; and controls the arrangement to be orthogonal to the one direction and along the other direction of the surface 218a The second driver circuit for applying voltage to each pixel column. The active matrix circuit shown above is configured such that a predetermined voltage is applied to the pixel electrode 214 of the pixel designated by both driver circuits by the control unit 250 (refer to FIG. 7).

The alignment films 999a and 999b are arranged on both ends of the liquid crystal layer 216, so that the liquid crystal molecule groups are arranged in a certain direction. The alignment films 999a and 999b are formed of polymer materials such as polyimide. The contact surface with the liquid crystal layer 216 in the alignment films 999a and 999b is subjected to 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 the electric field formed by each pixel electrode 214 and the transparent conductive film 217. That is, if a voltage is applied to each pixel electrode 214 by the active matrix circuit of the driving circuit layer 914, an electric field is formed between the transparent conductive film 217 and each pixel electrode 214, and the arrangement direction of the liquid crystal molecules 216a is formed in accordance with The size of the electric field of the liquid crystal layer 216 changes. Then, 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 between passing through the liquid crystal layer 216, and is reflected on the reflective film 215 After that, the liquid crystal layer 216 is modulated again for emission.

At this time, the control unit 250 (see FIG. 7) controls the voltage applied to each pixel electrode 214, and according to the voltage, the refraction of the portion sandwiched between the transparent conductive film 217 and each pixel electrode 214 in the liquid crystal layer 216 is controlled. The rate will change (the refractive index of the liquid crystal layer 216 corresponding to the position of each pixel will change). 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 in accordance with the applied voltage. That is, for each pixel, the phase modulation corresponding to the holographic pattern can be given by the liquid crystal layer 216. The wavefront of the laser light L that is incident on the modulating pattern and transmitted therethrough is adjusted, and the phases of the components in the direction orthogonal to the traveling direction of the light rays constituting the laser light L are 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, polarization, etc. of the laser light L can be modulated).

Returning to FIG. 7, the 4f optical system 241 is an adjusting 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 has a first lens 241a and a second lens 241b. The first lens 241a and the second lens 241b are reflective spatial light modulator 203 and the optical path distance between the first lens 241a becomes the first focal length f1 of the first lens 241a, the condensing optical system 204 and the second lens The distance of the optical path between 241b becomes the second focal length f2 of the second lens 241b, and the distance of the optical path 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) are arranged on the optical path between the reflective spatial light modulator 203 and the condensing optical system 204 so that the first lens 241a and the second lens 241b become both-side telecentric optical systems. With the 4f optical system 241, it is possible to prevent the laser light L modulated by the reflective spatial light modulator 203 from changing the wavefront shape and increasing aberration due to spatial propagation.

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

In the laser processing apparatus 300 configured as described above, the laser light L emitted from the laser light source 202 travels in the horizontal direction in the frame 231, and is reflected downward by the reflector 205a. The attenuator 207 adjusts the light intensity. After that, the laser light L is reflected in the horizontal direction by the reflector 205 b, and the intensity distribution of the laser light L is uniformized by the beam homogenizer 260 and enters the reflective spatial light modulator 203.

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

The laser light L incident to the 4f optical system 241 is adjusted in wavefront shape such that parallel light enters 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, diverges through the condensing point O, and passes through the second lens 241b, and is again turned into parallel light. convergence. Next, the laser light L is sequentially transmitted through dichroic mirrors 210 and 238 and enters the condensing optical system 204, and is condensed by the condensing optical system 204 on the processing table 111. Within object 1.

In addition, the laser processing device 300 is provided in the housing 231 with: a surface observation unit 211 for observing the laser light incident surface of the object 1; and a distance between the condensing optical system 204 and the object 1 An AF (AutoFocus) unit 212 that performs fine adjustments.

The surface observation unit 211 includes an observation light source 211a that emits visible light VL1, and a detector 211b that receives reflected light VL2 of visible light VL1 reflected on the laser light incident surface of the object 1 and detects it. In the surface observation unit 211, the visible light VL1 emitted by 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 directed toward the object 1 by the condensing optical system 204 Spotlight. The reflected light VL2 reflected on the laser light incident surface of the object 1 is condensed by the condensing optical system 204 and transmitted/reflected by the dichroic mirrors 238 and 210, then passes through the half mirror 209 and is received by the detector 211b. By the light.

The AF unit 212 emits the measurement light LB1 and receives the reflected light LB2 of the measurement light LB1 reflected on the laser light incident surface for detection, thereby obtaining displacement data of the laser light incident surface along the planned cutting line 5 That is, the error signal (signal about displacement). The AF unit 212 outputs the obtained error signal to the control unit 250 when the modified area 7 is formed. The control unit 250 drives the driving unit 232 based on the error signal, and moves the condensing optical system 204 back and forth in the direction of the optical axis in a manner along the undulations of the laser light incident surface. The configuration and operation of the AF unit 212 will be described in detail later.

The laser processing device 300 is provided with a control unit 250 that controls the operation of each part of the laser processing device 300. The control unit 250 is composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory, random access memory), etc.

The control unit 250 controls the operation of the laser light source 202, and the laser light L is emitted from the laser light source 202. The control unit 250 controls the operation of the laser light source 202 and adjusts the output or pulse width of the laser light L emitted from the laser light source 202. When the modified region 7 is formed, the control unit 250 assumes that the condensing point P of the laser light L is located at a predetermined distance from the front surface 3 or the back surface 21 of the object 1, and the condensing point P of the laser light L is cut along the cut The relative movement of the predetermined line 5 controls at least one of the position of the housing 231, the position of 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 described above.

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. In this way, the control unit 250 adjusts the laser light L to a desired value by the reflective spatial light modulator 203. The modulation pattern displayed by the liquid crystal layer 216 is based on, for example, the position of the modified region 7 to be formed, the wavelength of the laser light L irradiated, the material of the object 1, and the refraction of the condensing optical system 204 or the object 1 The rate and the like are derived in advance, and are stored in the control unit 250. Modulation patterns include: individual difference correction patterns for correcting individual differences generated by the laser processing device 300 (for example, distortion generated in the liquid crystal layer 216), spherical aberration correction patterns for correcting spherical aberration, etc. .

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

As shown in FIG. 9, the AF unit 212 includes a light source 30 for measurement, 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 can emit any one of plural lights having mutually different wavelengths. The measurement light source 30 includes plural SLD (Super Luminescent Diode) light sources 31 and 32. In the measurement light source 30, the control unit 250 selects one of the plurality of SLD light sources 31 and 32 to emit light of a wavelength with a high reflectivity to the object 1 to be processed. The measurement light source 30 is one of the selected SLD light sources 31 and 32, and emits light of a wavelength with a high reflectance to the object 1 as the measurement light 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. For example, it may have an LED (Light Emitting Diode) light source or an LD (Laser Diode) light source. The wavelength of the measurement light LB1 may have a reflectance greater than zero on the back surface 21 that is the incident surface of the laser light. The measurement light source 30 may not be able to emit light of a plurality of wavelengths. For example, it has only one of the SLD light sources 31 and 32, and can emit light of only one wavelength.

The measurement light source 30 transmits WDM (Wavelength Division Multiplexing) 33 and a single-mode optical fiber 34 used for the synthesis of laser light of multiple wavelengths, and transmits the emitted measurement light LB1 to the adjustment optical system 60. However, if the measurement light source 30 emits only one wavelength of the measurement light LB1, WDM 33 is not required. It is also possible to replace the optical fiber 34 and use a spatial light transmission element. The adjustment optical system 60 has a plurality of types of lenses, and is adjusted so that the measurement light LB1 has 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 back surface 21 that is the laser light incident surface of the object 1. The displacement detection unit 50 has: a first branching part 51, a second branching part (branch part) 52, first and second astigmatism adding parts (astigmatism adding parts) 53, 54 and first and second beam shapes The detection units (beam shape detection units) 55 and 56 and the error signal generation unit 57.

The first branching part 51 is a spectroscope that branches the measurement light LB1 and the reflected light LB2. The first branching part 51 divides the optical path of the measurement light LB1 and the reflected light LB2 into the optical path of the measurement light LB1 and the optical path of the reflected light LB2. The first branch portion 51 transmits the measurement light LB1, and on the other hand, reflects the reflected light LB2. The first branching part 51 is provided between the imaging state adjustment part 70 and the adjustment optical system 60 in the optical path of the measurement light LB1 and the reflected light LB2.

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

The first astigmatism adding section 53 is provided downstream of the second branching section 52 in the first branching optical path OP1. The first astigmatism adding section 53 adds a first astigmatism amount smaller than the astigmatism amount added by the second astigmatism adding section 54 to the first branch reflected light LS1. The amount of astigmatism is a scale indicating the magnitude of the astigmatism, and here is defined as follows. When a parallel beam with the same wavelength as the measurement light LB1 is incident on the astigmatism adding section, there is a minor axis of the beam width projected on a plane perpendicular to the optical axis of the beam emitted by the astigmatism adding section The minimum point is, on a plane perpendicular to the optical axis, the direction of the minor axis is set as the characteristic axis of the astigmatism adding section. When the focal distance in the direction of the characteristic axis of the relative astigmatism adding section is fL1, and the focal distance in the direction perpendicular to the characteristic axis is fL2, fL2/fL1 is set as the amount of astigmatism. The first astigmatism adding section 53 is composed of 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 section 54 adds an astigmatism amount different from the first astigmatism amount to the second branch reflected light LS2. The second astigmatism adding section 54 adds a second astigmatism larger than the first astigmatism to the second branch reflected light LS2. The second astigmatism adding section 54 is composed of a combination of a convex lens 54a and a cylindrical lens 54b. 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 in the first branch optical path OP1. The first beam shape detection unit 55 receives the first branched reflected light LS1 to which the first astigmatism is added through the filter 59a, and detects the beam shape of the first branched reflected light LS1. The second beam shape detection unit 56 is provided on the second branch optical path OP2. The second beam shape detection unit 56 receives the second branched reflected light LS2 to which the second amount of astigmatism is added through the filter 59b, and detects the beam shape of the second branched reflected light LS2.

The filter 59a attenuates the light of the wavelength of the laser light L in the first branch reflected light LS1. The filter 59 a prevents light of the wavelength of the laser light L from entering the first beam shape detection unit 55. The filter 59b attenuates the light of the wavelength of the laser light L in the second branch reflected light LS2. The filter 59b prevents light of the 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 unit 55 and the second beam shape detection unit 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 divides the beam shape formed on its light-receiving surface to receive light, and the output value (voltage value) corresponding to each light quantity ) Output to the error signal generating unit 57. Among them, the first beam shape detection unit 55 is not particularly limited as long as the beam shape can be detected, and may be, for example, a 2-dimensional PD (Photo Diode) array.

The error signal generation unit 57 receives the output 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, 56 provided on one of the first and second branch optical paths OP1 and OP2 selected by the control unit 250 The detection result of either one generates an error signal. The error signal generation unit 57 uses the detection result of the first beam shape detection unit 55 to generate an error signal when the first branch optical path OP1 is selected by the control unit 250. The error signal generation unit 57 uses the detection result of the second beam shape detection unit 56 to generate an error signal when the second branch optical path OP2 is selected by the control unit 250. The error signal generating unit 57 outputs the generated error signal to the control unit 250.

Here, the error signal and its acquisition principle will be explained in detail below.

The AF unit 212 uses the Through the Lens method to measure the displacement (relative displacement) of the laser light incident surface of the object 1, that is, the rear surface 21, that is, the condensing optical system 204 that condenses the laser light L Use LB1 to measure. In addition, the AF unit 212 uses astigmatism to measure the displacement of the back surface 21. The distance of the AF unit 212 using the optical system changes according to 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 is shifted .

In the AF unit 212, the beam shape of the reflected light LB2 changes on the beam shape detection units 55, 56 such as a 4-quadrant sensor according to the displacement of the back surface 21 of the 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 to correspond to the beam widening angle, and is formed on the beam shape detection units 55, 56 For different beam shapes. For example, as shown in FIG. 10, the beam shape H of the reflected light LB2 is in a vertical ellipse (refer to FIG. 10(a)), a perfect circle (refer to FIG. 10(b)) and a horizontally long ellipse (refer to 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 The signal value output by the light quantity in the light _{receiving surface, I B} : the signal value output according to the light quantity in the light receiving surface S _{B , I C} : the signal value output according to the light quantity in the light receiving surface S _{C , I D} : according to the light receiving surface S The signal value output by the amount of light in _D.

Figure 11 is a graph showing an example of the 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 more to the left in the figure), the closer the laser light incident surface is to the direction of the condensing optical system 204. The greater the displacement (the farther to the right in the figure), the farther away from the condensing optical system 204 the laser light incident surface is.

As shown in Figure 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 detecting sections 55 and 56. The usable range in the error signal is a monotonically decreasing range around zero (hereinafter, this range is referred to as the "length measurement area"). The length measurement area of this embodiment is due to the uneven displacement of the back surface 21 at the start position of the laser processing caused by the warpage of the object 1 and 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 branch section 51 and the dichroic mirror 238 in the optical path of the measurement light LB1 and the reflected light LB2. The imaging state adjustment unit 70 has 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 to move the imaging state. Thereby, the imaging state adjustment unit 70 adjusts the offset amount. The movement system of the imaging state includes a situation in which the set of all imaging position relationships on the optical path is mapped to a set of other imaging position relationships (that is, the movement of the imaging position).

The reference position refers to the depth position of the laser light incident surface set during the 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 becomes the maximum.

The imaging state adjustment unit 70 moves the imaging state of the measurement light LB1 and the reflected light LB2 when the processing object 1 is a silicon substrate with a maximum thickness of 775 μm, so that the shift amount is in the range of 0 μm to -180 μm variable.

If the object 1 is a silicon substrate with a thickness of 775 μm and the modified region 7 is formed at a position shallower from the back surface 21 in the object 1, the convergence power of the imaging state adjustment unit 70 becomes weak, and the offset is formed as At a value of 0 μm or close to 0 μm, the distance between the condensing optical system 204 and the back surface 21 is a long distance. On the other hand, if the object 1 is a silicon substrate with a thickness of 775 μm and the modified region 7 is formed at a position deep from the back surface 21 in the object 1, the convergence power of the imaging state adjustment unit 70 becomes stronger and shifts The amount is formed to be -180 μm or a value close to -180 μm, and the distance between the condensing optical system 204 and the surface 3 is formed to be a short distance.

The control unit 250 sets the offset amount based on 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 achieve the set shift amount. Specifically, the control unit 250 stores in advance a data table regarding the position of the concave lens 71 set for each shift amount. The control unit 250 refers to the data table to obtain the position of the concave lens 71 that is the set shift amount, and outputs a command to move the concave lens 71 to the obtained position of the concave lens 71 to the imaging state adjustment unit 70.

The control unit 250 selects the one corresponding to the imaging state moved by the imaging state adjustment unit 70 among the first branch optical path OP1 and the second branch optical path OP2. Specifically, the control unit 250 selects the one corresponding to the offset adjusted by the imaging state adjustment unit 70 from among the first branched optical path OP1 and the second branched optical path OP2. 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. If 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 result of the first branch optical path OP1 and the second branch optical path OP2 to the error signal generation unit 57. The control unit 250 causes the driving unit 232 to operate such that the error signal generated by the error signal generation unit 57 maintains the target value (here, zero).

The AF unit 212 additionally 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 mirror 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, the laser processing method implemented in the laser processing device 300 will be described.

The laser processing method of this embodiment is used as a wafer manufacturing method for laser processing the object 1 to manufacture a plurality of wafers. The object to be processed 1 has a plate shape. The object to be processed 1 is, for example, a sapphire substrate, a SiC substrate, a glass substrate (tempered glass substrate), a silicon substrate, a semiconductor substrate, or a transparent insulating substrate. The object 1 to be processed here is a silicon substrate. A functional element layer is formed on the surface 3 side of the object 1 opposite to the laser light incident surface side, that is, the back surface 21 side. The functional element layer includes a plurality of functional elements arranged in a matrix (for example, light-receiving elements such as photodiodes, light-emitting elements such as laser diodes, or circuit elements formed as circuits). The back surface 21 side of the object 1 is ground so that the object 1 is thinned to a desired thickness. The object 1 is provided with a plurality of planned cutting lines 5 extending so as to pass between adjacent functional elements. The plurality of planned cutting lines 5 extend in a lattice shape.

In the laser processing method of this embodiment, first, the object 1 to be processed is placed on the support table 107 of the table 111 so that the back surface 21 becomes the laser light incident surface. The laser light L is emitted from the laser light source 202, and the laser light L is condensed inside the object 1 by the condensing 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) in the processing travel direction along the planned cutting line 5. The inside of 1 forms a modified region 7. After that, the expansion tape adhered to the front surface 3 or the back surface 21 of the object 1 is expanded to cut the object 1, and the object 1 is cut into a plurality of wafers.

Here, the back surface 21 of the object 1 is affected by stress or the like due to the formation of the functional element layer on the surface 3, and has warpage or undulation. Therefore, in order to condense the laser light L and stably form the modified region 7 to the intended depth, it is necessary to perform control to keep the relative displacement of the condensing optical system 204 and the back surface 21 at the intended displacement.

Therefore, in the laser processing method of the present embodiment, the laser light L is condensed on the object 1 while the measurement light LB1 is condensed on the object 1. The reflected light LB2 of the measurement light LB1 reflected on the back surface 21 is divided into the first and second branch reflected lights LS1 and LS2, and the first branch reflected light LS1 with the first astigmatism added to the first branch optical path OP1 is detected. The beam shape is detected, and the beam shape of the second branch reflected light LS2 with the second astigmatism added to the second branch optical path OP2 is detected. According to the detection result of the beam shape, an error signal is obtained, and the driving unit 232 causes the condensing optical system 204 to operate in the Z direction so that the error signal maintains the target value. Specifically, perform the following steps.

That is, as shown in FIG. 12, the offset amount is set by the control unit 250 in accordance with an instruction from the higher-level system (step S1). According to an instruction from the host 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 with a high reflectivity to the object 1 (step S2) .

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

The control section 250 controls the imaging state adjustment section 70 so as to be the set shift amount, and moves the imaging state 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 shift amount is derived, and the concave lens 71 is moved to the position.

The reference position positioning for positioning the object 1 at the reference position is performed (step S5). In step S5, the back surface 21, which is the incident surface of the laser light, is imaged by the surface observation unit 211, and the back surface 21 is positioned at the depth position where the contrast of the projected grating becomes the maximum. 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 corresponds to the grating projection of the light-converging optical system 204 The value of the magnitude of the chromatic aberration between the light and the measurement light LB1. The reference position and the offset are related as shown above. After that, the control unit 250 moves the stage 111 so as to become the set offset so that the object to be processed 1 approaches the condensing optical system 204 (step S6).

The target value of the error signal is obtained and stored in the control unit 250 (step S7). In step S7, the measurement light LB1 is emitted from one of the SLD light sources 31 and 32 of the measurement light source 30 selected in the above step S2. The measurement light LB1 system adjusts the beam diameter by adjusting the optical system 60, passes through the first branching part 51, and after the imaging state adjustment part 70 adjusts the imaging state, it passes through the first and second steering mirrors 81, 82 and the bidirectional beam splitter. The mirror 238 reflects sequentially, is condensed on the object 1 by the condensing optical system 204, 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 mirror 238, the second and first steering mirrors 82, 81, and the imaging state is adjusted by the imaging state adjustment section 70 After being reflected in the first branch part 51, the second branch part 52 is branched into first and second branch reflected lights LS1 and LS2. The first branched reflected light LS1 is in the first branched optical path OP1. After the first astigmatism is added by the first astigmatism adding section 53, the first beam shape detection section 55 passes through the filter 59a and is received. The second branched reflected light LS2 is in the second branched optical path OP2, and after the second astigmatism is added by the second astigmatism adding unit 54, it passes through the filter 59 b and is received by the second beam shape detection unit 56. When the error signal generation unit 57 selects the first branch optical path OP1 by the control unit 250 in the above step S3, it generates a beam corresponding to the beam detected by the first beam shape detection unit 55 according to the above formula (1) Error signal of shape. On the other hand, if the second branch optical path OP2 is selected by the control unit 250 in the above step S3, according to the above formula (1), a beam shape corresponding to the beam shape detected by the second beam shape detection unit 56 is generated. 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 acquired in the same manner as in the above step S7, and the drive unit 232 is used to converge the light so that the acquired error signal maintains the target value. The optical system 204 operates in the Z direction. In this way, together with the scanning of the laser light L, feedback control is performed in which the relative displacement of the condensing optical system 204 and the back surface 21 is maintained at a certain level, and the concentrating optical system 204 follows the displacement of the back surface 21. After that, it is determined whether or not all laser processing along the planned cutting line 5 has been completed (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 where the laser processing has not been 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 only based on the beam shape detected by the first beam shape detecting unit 55. The figure shows the error signals when the offset is changed from 0μm to -180μm from every 10μm to every 20μm. As shown in FIG. 13, the tilt system of the error signal has a correlation with the offset amount (that is, the imaging state in which the imaging state adjustment unit 70 moves). In addition, it can be seen that the more the offset becomes deeper in the processing object 1, the more gentle the inclination of the error signal becomes. Among them, the tilt of the error signal refers to the variation of the error signal to the obtained displacement. The tilt of the error signal refers to the ratio of the change in the error signal with respect to the displacement. The slope of the error signal corresponds to the constant of proportionality when the error signal is monotonically decreasing in proportion. The inclination of the error signal corresponds to the amount of change when the error signal changes with the change of displacement.

Here, in terms of the cause of the excessively gentle slope of the error signal, it is found that the amount of astigmatism added to the reflected light LB2 of the measurement light LB1 is mismatched with the offset amount. Therefore, in the laser processing apparatus 300, one of the first and second branch optical paths OP1 and OP2 is selected in accordance with the amount of offset, based on the detection in the selected one of the first and second branch optical paths OP1, OP2 The shape of the beam generates an error signal. Thereby, the amount of astigmatism added to one of the first and second branched reflected lights LS1 and LS2 used for generating the error signal can be formed to correspond to the offset amount. As a result, the tilt of the error signal can be suppressed from being too gentle. Therefore, it is possible to accurately detect the displacement of the laser light incident surface, that is, the back surface 21.

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

In the laser processing apparatus 300, if the offset is in the first range, the first branch optical path OP1 is selected, and if the offset is in the second range that is deeper than the first range, the second branch optical path OP2 is selected. At this time, if the offset is shallow, the first branch reflected light LS1 with a smaller amount of astigmatism can be used to generate the error signal, and if the offset is deep, the second branch with a larger amount of astigmatism can be added. 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 21 can be detected accurately.

FIG. 14 is a graph showing the error signal generated in the laser processing apparatus 300. The figure shows the error signals when the offset is changed from 0μm to -180μm every 10μm to every 20μm. In the name of each item (series) in the figure, if it is an error signal based on the beam shape of the first branch optical path OP1, mark "OP1", if it is an error signal based on the beam shape of the second branch optical path OP2, then Mark "OP2". As shown in FIG. 14, it can be seen that the laser processing device 300 can suppress the tilt of the error signal from being too gentle. For example, in the laser processing device 300, the error signal has a tilt of a certain level or more at which the measurement error caused by the grinding mark falls within the practical range. For example, the error signal may have an absolute value of the slope 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 the slope of 0.0275/μm or more in the 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 inclination has also become a certain amount or more. Therefore, in this embodiment, the first range is formed to be 0 μm or less and greater than -40 μm, and the second range is formed to be -40 μm or less and -180 μm or more. However, the first range may be formed to be 0 μm. In the following and in the range of -40 μm or more, the second range is formed to be a range of less than -40 μm and -180 μm or more.

FIG. 15 is a graph showing an error signal generated only based on the beam shape detected by the second beam shape detecting unit 56. The figure shows the error signals when the offset is changed from 0μm to -180μm every 10μm to every 20μm. From the results shown in FIG. 15, it can be seen that the shift becomes shallower in the object 1, the tilt of the error signal becomes too steep, and the length measurement area becomes insufficient. In contrast, in the laser processing apparatus 300, it is possible to prevent the error signal from tilting too sharply, and it is possible to sufficiently secure the length measurement area (refer to FIG. 14).

In the laser processing apparatus 300, the offset amount is set by the control section 250, and the imaging state adjustment section 70 is controlled so as to become the set offset amount. With this configuration, it is possible to automatically adjust the imaging state of the measurement light LB1 and the reflected light LB2 in accordance with the set shift amount.

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 the error signal maintains the target value. With this configuration, the condensing optical system 204 can be moved in the Z direction so as to follow the back surface 21.

The laser processing device 300 is provided with 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 aligned with the optical axis of the laser light L with high accuracy.

In the laser processing apparatus 300, the measurement light source 30 emits light having a high reflectance to the object 1 among light having a plurality of wavelengths 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 physical distance between the imaging state adjustment unit 70 and the condensing optical system 204, or to shorten the optical distance by inserting a 4f lens system therebetween, so as to suppress the tilt of the error signal. The change. However, it is difficult to shorten the physical distance due to the limitation of the device structure, and the insertion of the 4f lens system will cause the device to be enlarged, so it may be difficult to realize it. 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 structure of the apparatus, and in addition, the enlargement of the apparatus can be suppressed. In the laser processing apparatus 300, first and second steering mirrors 81 and 82 can be arranged.

FIG. 16 is a diagram showing the configuration of a part of the AF unit 212B of the modified example. As shown in FIG. 16, the first and second beam shape detection sections 55 and 56 of the AF unit 212B may each follow the movement of the concave lens 71 of the imaging state adjustment section 70 along the first and second branch optical paths OP1 and OP2. Each move. Specifically, the control unit 250 may also be used to move the concave lens 71 in such a way that the shift becomes 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, 54 is interlocked with the closer direction (in other words, the first and second beam shape detection units 55 and 56 may be moved closer to the first and second astigmatism adding units 53, 54 as the shift deepens).

FIG. 17 is a graph for explaining the effect obtained by the AF unit 212B of FIG. 16. In FIG. 17, the error signal generated based on the beam shape detected by the first beam shape detection unit 55 is displayed. Fig. 17(a) is an error signal when the first beam shape detection unit 55 is fixed. FIG. 17(b) shows the error signal generated by the AF unit 212B, that is, the 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, the S-shaped curve of the error signal can be formed as the center of zero on the horizontal axis. Uniform shape. This system contributes to the improvement of responsiveness such as PID control.

In the AF unit 212B, it is also possible to replace the movement of the first and second beam shape detection units 55, 56, or in addition to it, to make the convex lenses 53a, 54a of the first and second astigmatism adding units 53, 54 and At least one of the cylindrical lenses 53b and 54b moves similarly. The same effect is also achieved at this time.

The embodiments have been described above, but the present invention is not limited to the above-mentioned embodiments, and can be applied to modifications or others within the scope that does not change the gist described in each claim.

In the above embodiment, the optical path OP of the reflected light LB2 is branched into two optical paths (the first and second branched optical paths OP1 and OP2) by the second branching portion 52, but it may be branched to three or more optical paths. For each of the three optical paths or more, install: a complex astigmatism adding section with different magnitudes of astigmatism, and a complex beam shape detection to detect the beam shape of the complex branched reflected light with astigmatism added Department can be. At this time, it is also possible to select the optical path from the multiple optical paths in which the astigmatism with the deeper the deviation is added to the branched reflected light, and the detection of the beam shape of the branched reflected light of the selected optical path As a result, an error signal is generated.

In the above embodiment, in the optical path of the measurement light LB1 and the reflected light LB2, the imaging state adjustment section 70 is arranged between the first branch 51 and the dichroic mirror 238. However, the arrangement of the imaging state adjustment section 70 is different. Not limited. The arrangement of the above-mentioned embodiment may be replaced, or in addition, the optical path of the measurement light LB1 is more upstream than the first branch 51, and the optical path OP of the reflected light LB2 is between the first branch 51 and the second branch 51. At least any one of the branching parts 52 is provided with an imaging state adjustment part 70.

In the above embodiment, the imaging state adjustment section 70 is constituted by the concave lens 71 and the convex lens 72, but the imaging state adjustment section 70 is not particularly limited, and may be, for example, a variable focal length lens. The optical system of the above-mentioned embodiment is provided with a dichroic mirror 238 that transmits the laser light L and reflects the measurement light LB1 and the reflected light LB2. However, it may also be provided with a dichroic mirror 238 that reflects the laser light L and uses the measurement light LB1 and The structure of a dichroic mirror through which the reflected light LB2 passes is replaced. Similarly, the optical system of the above-mentioned embodiment may be configured to reflect the measurement light LB1 and transmit the reflected light LB2 in the first branch portion 51. Similarly, the optical system of the above-mentioned embodiment may be configured to transmit the first branch reflected light LS1 and reflect the second branch reflected light LS2 in the second branch portion 52.

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

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

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

1‧‧‧Processing object 3‧‧‧Surface 5‧‧‧Cutting plan line 7‧‧‧Modification area 8‧‧‧Cutting starting point area 21‧‧‧Back 30‧‧‧Measurement light source 31, 32 ‧‧‧SLD light source 33‧‧‧WDM34. Section (Astigmatism Adding Section) 53a, 54a‧‧‧Convex Lens 53b, 54b‧‧‧Cylinder Lens 54‧‧‧Second Astigmatism Adding Section (Astigmatism Adding Section) 55‧‧‧First Beam Shape Detection Section (Beam shape detection unit) 56‧‧‧Second beam shape detection unit (beam shape detection unit) 57‧‧‧Error signal generation unit (signal acquisition unit) 58‧‧‧Mirror 59a, 59b‧‧‧ Filter 60‧‧‧Adjusting optical system 70‧‧‧Imaging state adjustment part 71‧‧‧Concave lens 72‧‧‧Convex lens 81‧‧‧The first steering mirror (optical axis adjustment mechanism) 82‧‧‧The second steering reflection Mirror (Optical axis adjustment mechanism) 100, 300‧‧‧Laser processing device 101‧‧‧Laser light source 102‧‧‧Laser light source control unit 103‧‧‧Optical system 105‧‧‧Condensing lens 107‧‧ ‧Support 111‧‧‧Carrier 115‧‧‧Carrier control unit 202‧‧‧Laser light source 203‧‧‧Reflective spatial light modulator 204‧‧‧Condensing optical system (condensing lens) 205a ,205b‧‧‧Reflection mirror 206a, 206b‧‧‧Reflection mirror 207‧‧‧Attenuator 208‧‧‧Reflection mirror 209‧‧‧Half mirror 210,238‧‧‧Two-way beam splitter 211‧‧‧Surface observation unit 211a. 216a. Unit (driving mechanism) 233‧‧‧Bottom plate 236‧‧‧Top plate 241‧‧‧4f Optical system 241a‧‧‧First lens 241b‧‧‧Second lens 250‧‧‧Control unit (signal acquisition unit, offset Setting part, imaging state control part, driving mechanism control part) 260‧‧‧Beam homogenizer 914‧‧‧Drive circuit layers 999a, 999b‧‧‧Alignment film H‧‧‧Beam shape L‧‧‧Laser ( Laser light for processing) LB1‧‧‧Light for measurement LB2‧‧‧Reflected light LS1‧‧‧First branch reflected light (branch reflected light) LS2‧‧‧Second branch reflected light (branch reflected light) OP‧‧‧ Optical path OP1‧‧‧The first branch optical path (the optical path of the first branch reflected light) OP2‧‧‧The second branch optical path (the optical path of the second branch reflected light) P‧‧‧ Light spot (condensing position) S _A , S _B , S _C , S _D ‧‧‧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 an object to be processed 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.　　 Figure 4 is a plan view of the 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 VI-VI line 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 the 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 the 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 oblong 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 diagram illustrating a case where the beam shape of the reflected light is a horizontally oblong ellipse.　　 Figure 11 is a graph showing an example of the error signal.　　 FIG. 12 is an example of a flowchart of the laser processing method implemented by the laser processing device of FIG. 7.　　 FIG. 13 is a graph showing an error signal generated only based on the beam shape detected by the first beam shape detection unit.　　 Fig. 14 is a graph showing the error signal generated in the laser processing device of Fig. 7.　　 FIG. 15 is a graph showing an error signal generated only based on the beam shape detected by the second beam shape detection unit.　　 Figure 16 is a schematic configuration diagram of an AF unit in a modified example.　　 FIG. 17(a) is a graph for explaining the effect obtained by the AF unit of FIG. 16, and the first beam shape detection unit is an error signal when it 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 detection unit is movable.

1‧‧‧Processing object

3‧‧‧Surface

5‧‧‧Cut off the scheduled line

7‧‧‧Modified area

21‧‧‧Back

30‧‧‧Light source for measurement

31, 32‧‧‧SLD light source

33‧‧‧WDM

34‧‧‧Fiber

50‧‧‧Displacement Detection Department

51‧‧‧ Division 1

52‧‧‧Second Division (Division Division)

53‧‧‧First astigmatism addition part (Astigmatism addition part)

53a、54a‧‧‧Convex lens

53b、54b‧‧‧Cylinder lens

54‧‧‧Second astigmatism addition part (astigmatism addition part)

55‧‧‧The first beam shape detection unit (beam shape detection unit)

56‧‧‧Second beam shape detection unit (beam shape detection unit)

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

58‧‧‧Mirror

59a, 59b‧‧‧Filter

60‧‧‧Adjusting the optical system

70‧‧‧Imaging status adjustment part

71‧‧‧Concave lens

72‧‧‧Convex lens

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

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

107‧‧‧Support Desk

111‧‧‧ Stage

204‧‧‧Condensing optics (condensing lens)

238‧‧‧Two-way beam splitter

212‧‧‧AF unit

232‧‧‧Drive unit (drive mechanism)

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

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

LB1‧‧‧Measuring light

LB2‧‧‧Reflected light

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

LS2‧‧‧Second branch reflected light (branch reflected light)

OP‧‧‧Optical Path

OP1‧‧‧The first branch optical path (the first branch reflected light optical path)

OP2‧‧‧The second branch optical path (the second branch reflected light optical path)

Claims (8)

A laser processing device, which is a laser processing device that forms a modified area on the processing object by condensing laser light for processing on an object to be processed. Condenser lens, which condenses the processing laser light and the measurement light on the object to be processed; displacement detection unit, which is based on the laser light incident surface of the object to be processed The reflected light of the measurement light detects the displacement of the incident surface of the laser light; and an imaging state adjustment section that moves the image formation state of at least one of the measurement light and the reflected light of the measurement light, the displacement The detection unit has: a branching part, which branches the reflected light of the aforementioned measurement light into a plurality of branched reflected lights; a complex astigmatism adding part, which is provided in each of the optical paths of the plurality of branched reflected lights, for the plurality of branched reflected lights Each is added with mutually different amounts of astigmatism; a complex beam shape detection unit, which is provided in each of the optical paths of the plurality of branched reflected lights, detects the beam shape of each of the plurality of branched reflected lights with added astigmatism; And the signal acquisition unit, which is selected from among the light paths of the plurality of branched reflected light, corresponding to the aforementioned imaging state adjusted by the aforementioned imaging state adjustment unit In one of the states, a signal regarding the displacement is obtained based on the detection result of the beam shape detection unit in the selected optical path of the branched reflected light. For example, the laser processing device of the first item in the scope of patent application, wherein the imaging state adjustment section adjusts the offset by moving the imaging state, and the signal acquisition section selects from among the multiple light paths of the branched reflected light Corresponds to one of the aforementioned offsets adjusted by the aforementioned imaging state adjustment unit. For example, the laser processing device of the second item in the scope of patent application, wherein the branch part divides the reflected light of the measurement light into at least a first branch reflected light and a second branch reflected light, and the aforementioned astigmatism adding part has: The first astigmatism adding section is provided in the optical path of the first branched reflected light, and the first amount of astigmatism is added to the first branched reflected light; and the second astigmatism adding section is provided in the foregoing In the optical path of the second branch reflected light, a second astigmatism amount greater than the first astigmatism amount is added to the second branch reflected light. The amount of light is located 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 unit is in the second range that is deeper than the first range, the second branched light is selected. The light path of the shot light. For example, the laser processing device of item 2 or item 3 of the scope of patent application is provided with: an offset setting part which sets the offset amount adjusted by the imaging state adjustment part; and an imaging state control part , Which 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 of the first item of the scope of patent application, which is provided with: a drive mechanism that moves at least one of the object to be processed and the lens for condensing along the optical axis direction of the lens for condensing And the drive mechanism control unit, which operates the drive mechanism in such a way that the signal obtained by the signal acquisition unit maintains a target value. For example, the laser processing device of the first item of the scope of patent application includes an optical axis adjustment mechanism that aligns the optical axis of the measurement light with the optical axis of the processing laser light. For example, the laser processing device of the first item in the scope of patent application, wherein the light source for measurement can emit any one of a plurality of light having different wavelengths, and the emitted light of the plurality of wavelengths reflects the object to be processed. The light with the highest wavelength is used as the aforementioned measurement light. A laser processing method, which is a laser processing method that forms a modified area on the processing object by condensing laser light for processing on an object to be processed. The laser processing method includes: a laser processing step, which The laser light for processing is condensed on the object to be processed by a condensing lens, while the measurement light is condensed on the object to be processed by the lens for condensing, and is reflected on the laser light incident surface of the object to be processed The reflected light of the measurement light is divided into at least the first branch reflected light and the second branch reflected light, and the first branch reflected light with the first astigmatism added to the optical path of the first branch reflected light is detected. The beam shape of the second branched reflected light is detected in the optical path of the second branched reflected light with a second astigmatism greater than the first astigmatism. Based on the detection result of the beam shape, Acquire a signal regarding the displacement of the laser light incident surface, and make at least any of the object to be processed and the condensing lens along the optical axis direction of the condensing lens so that the obtained signal maintains the target value. One is to perform the operation, the aforementioned laser processing steps include: the first step, which is to set the offset; the second step, which is to select the aforementioned offset if the offset set in the first step is the first range The optical path of the first branched reflected light, if the offset set in the first step is a second range that is deeper than the first range, then the optical path of the second branched reflected light is selected; the third step is that Is to become the aforementioned bias set in the aforementioned first step The shift amount is to move the imaging state of at least one of the measurement light and the reflected light of the measurement light; the fourth step is to become the shift amount set in the first step In the method, at least one of the object to be processed and the condenser lens is operated; the fifth step is to obtain the target value after the third step and the fourth step; and the sixth step, which After the fifth step, the laser beam for processing is condensed on the object to be processed with a condensing lens, and the beam shape is detected by the optical path of the branched reflected light selected in the second step. According to the detection result of the beam shape, the signal is obtained, and the object to be processed and the condensing lens are set along the optical axis direction of the condensing lens so that the obtained signal maintains the target value. At least any one of the actions.

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