JP5378314B2 - Laser cutting method - Google Patents

Description

  The present invention relates to a laser cutting method using sapphire as an object to be processed.

  With the rapid development of advanced technology fields such as electronics and photonics in recent years, further miniaturization of various device elements that support these has been greatly desired. Conventionally, a mechanical cutting technique using a diamond blade or the like has been used as means for miniaturizing a semiconductor device. Although these are well-established technologies, they are approaching the essential limits such as a reduction in material yield due to “cutting” and processing resolution for miniaturization. On the other hand, there is a laser processing method as a fine processing technology which is rapidly progressing instead of such a mechanical processing technology.

  The laser processing method is a method of irradiating a processing object with a high-intensity laser pulse and cutting the processing object starting from damage (crack) generated by structural destruction or modification of the substance in a minute region at the focal position. It is. In this method, a plurality of damages caused by laser irradiation are formed along a planned cutting line, and then a mechanical stress is applied to cut the workpiece into a fine chip shape. Among the objects to be processed, those that are particularly important in practical use include thin plate-like devices made of a dielectric substrate (such as sapphire or glass) on which functional semiconductor layers (such as silicon or gallium arsenide) are stacked. .

  For example, Patent Document 1 discloses that a laser pulse having a wavelength transparent to a processing target (a wavelength that the processing target does not absorb) is condensed inside the processing target, and has a size of several tens at the focusing position. A method is disclosed in which damage (cracks) having a disordered shape of about several hundred μm is generated, and mechanical stress is applied to cut the substrate starting from the cracks.

  Further, Patent Document 2 discloses that a laser pulse is condensed and irradiated on the surface of an object to be processed through an optical system to form a V-shaped damage on the surface of the object to be processed. A method of processing is described.

JP 2003-19582 A JP 2006-114786 A

  In the processing method of Patent Document 1, processing is performed by inducing a modified region (a crack region, a melt processing region, or a region in which a refractive index is changed) by multiphoton absorption inside a workpiece. Formation of cracks is induced by optical breakdown (breakdown), and formation of the melt heat treatment region is induced by photothermal effects. Therefore, in the processing method of Patent Document 1, the damage size becomes relatively large (about several tens to several hundreds μm), and there is a certain limit in processing accuracy.

  On the other hand, in the processing method of Patent Document 2, although the processing object can be processed with high resolution (crack width: 10 μm), the depth of the crack to be formed is shallow (30 μm), so the processing object is cut ( In order to cleave, it was necessary to connect cracks, and the processing speed had a certain limit (10 mm / s).

  This invention is made | formed in view of this point, and it aims at providing the method of laser-cutting sapphire with high precision and high speed.

  The present inventor has found that a stress-strain region can be formed with high accuracy and high speed up to a deep portion in sapphire by propagating a laser pulse in the optical axis direction by utilizing the self-channeling effect, and further studies are added to the present invention. Was completed.

  That is, this invention relates to the laser cutting method shown below.

[1] Scanning a sapphire cutting line with the laser pulse beam while condensing and irradiating a sapphire with a laser pulse through a condensing lens, and forming a plurality of stress strain regions on the sapphire along the cutting planned line. And a step of applying mechanical stress to the sapphire in which the plurality of stress strain regions are formed, and cutting the sapphire along the planned cutting line, wherein the stress is In the step of forming a strain region, the laser pulse is condensed and irradiated in the vicinity of the surface of the sapphire, and the laser intensity of the laser pulse on the surface of the sapphire is within a range of 0.5 to 500 PW / cm ² , Stress with a shape extending in the optical axis direction, starting from the surface of the sapphire and going inward Zumi the region to form a self-channeling effects, laser cutting method.
[2] The laser pulse is linearly polarized light, and the polarization direction of the laser pulse is substantially perpendicular to the direction of the cutting line of the sapphire and substantially parallel to the surface of the sapphire. The laser cutting method as described.
[3] The laser cutting method according to [1] or [2], wherein the distance between the condenser lens and sapphire is a working distance of the condenser lens of ± 500 μm.

  According to the present invention, sapphire can be laser-cut with high accuracy and high speed. Further, according to the present invention, it is possible to cut the microdevice layer / wafer while avoiding damage to the microdevice layer on the wafer.

The figure which shows an example of the cutting method of the workpiece using the laser processing method of this invention The figure which shows the example which introduces a several laser beam to one condensing lens Illustration for explaining the self-channeling effect The figure which shows a mode that drilling is carried out to a workpiece using the laser processing method of this invention. Graph showing the relationship between the distance from the laser irradiation position and the electron density The block diagram which shows an example of a structure of the laser processing apparatus of this invention The flowchart which shows the process using the laser processing apparatus of this invention Photograph showing the results of Example 1 Photograph showing results of Example 2 Photograph showing the results of Example 3

1. Laser processing method of the present invention The laser processing method of the present invention includes a step of condensing and irradiating a laser pulse near the surface of a workpiece by a condensing lens, and processing a laser pulse having a predetermined pulse width with a predetermined intensity. Irradiating near the surface of the object. As will be described later, the laser pulse applied to the workpiece propagates in the direction of the optical axis along the transient optical waveguide formed by the self-channeling effect, and stress is applied to the workpiece. A strain region is formed.

  In this specification, “stress-strain region” means non-uniformity in a uniform workpiece due to phenomena such as modification, coulomb explosion, atomic structure rearrangement, thermal expansion, and melting caused by absorbing laser light. This means a region where a large area appears and as a result, stress is applied in the workpiece and becomes brittle. Here, “modification” includes amorphization, polycrystallization, breaking of chemical bonds, change of electronic valence or ionic valence due to ionization, and the like.

  FIG. 1 is a diagram illustrating an example of cutting a workpiece using the laser processing method of the present invention. As shown in FIG. 1A, stress is changed by changing the relative position of the laser pulse 100 and the workpiece 110 while repeating the step of condensing and irradiating the laser pulse 100 near the surface of the workpiece 110. A plurality of strain regions 130 can be formed along the planned cutting line 120. As shown in FIG. 1B, after forming a plurality of stress strain regions 130 on the workpiece 110, mechanical stress (for example, bending stress, shear stress, etc.) is applied to the workpiece 110. As shown in 1 (C), the workpiece 110 can be easily cut (cleaved) along the planned cutting line 120. A workpiece to be cut using the laser processing method of the present invention has a flat and sharp cut surface without any disturbance (see Examples).

In the laser processing method of the present invention, the light source of the laser pulse is not particularly limited. Ti: sapphire laser, chrome forsterite laser, Yb: YAG laser, Yb: KGW laser, Yb: KG (WO ₄ ) ₂ laser, various types A fiber laser, various disk lasers, various dye lasers, and the like can be used. The type of laser beam (classification relating to the light intensity distribution) is not particularly limited, but a Gaussian beam is preferable from the viewpoint of utilizing the self-channeling effect due to the action of the ponderamomotive force, as will be described later.

One feature of the present invention is that the laser intensity of the laser pulse is in the range of 0.5 to 500 PW (petawatt) / cm ² . Here, “laser intensity of the laser pulse” means the laser intensity at the focal point. As will be described later, by irradiating a laser beam with a laser intensity of 0.5 PW / cm ² or more to the workpiece, a ponderamomotive force can be applied to electrons in the workpiece, resulting in self-channeling. Laser pulse propagation and stress strain region formation using the effect can be realized. The reason why the upper limit of the laser intensity is set to 500 PW / cm ² is that it is the maximum value of the practical laser intensity of the laser at the present stage.

  Another feature of the present invention is that the pulse width of the laser pulse is in the range of 100 to 1000 femtoseconds. When the pulse width of the laser pulse is less than 100 femtoseconds, it is difficult to stably irradiate a high-power laser pulse as a practical problem. When the pulse width of the laser pulse exceeds 1000 femtoseconds, the processing accuracy is lowered. There is a risk that optical breakdown (breakdown) will occur.

  The polarization characteristic of the laser pulse is not particularly limited, but is preferably linearly polarized light from the viewpoint of utilizing the self-channeling effect due to the action of the ponderamotive force as will be described later. When the laser pulse is linearly polarized light, the polarization direction of the laser pulse is substantially perpendicular to the line to be cut and is substantially parallel to the surface of the workpiece (the direction of the arrow 102 in FIG. 1A). Preferably there is. When sapphire, which is a crystalline material, was processed using the laser processing method of the present invention, it was clearly recognized that sapphire tends to be cut (cleaved) in a direction perpendicular to the polarization direction of the laser pulse. Therefore, when sapphire is cut (cleaved) using the laser processing method of the present invention, the laser pulse is easily cut (cleaved) by setting the polarization direction of the laser pulse to a direction substantially perpendicular to the line to be cut. The direction and the direction of the planned cutting line can be matched, and cutting (cleaving) can be performed more efficiently.

  The laser pulse is usually linearly polarized light, but its polarization plane is rotated or canceled when it passes through the lens or is reflected by a mirror. Therefore, the polarization direction of the laser pulse is changed to a desired direction (for example, a direction substantially perpendicular to the line to be cut) by using a polarization adjuster such as a wave plate (1/2 wave plate, 1/4 wave plate) or a polarizing plate. ) Is preferably adjusted.

  The pulse energy of the laser pulse is not particularly limited, but is preferably in the range of 1 to 1000 μJ / pulse. Here, “pulse energy” means energy per one pulse of the laser pulse after passing through the condenser lens. The pulse energy of the laser pulse may be within a range in which electrons of the workpiece can be excited and a ponderamomotive force can be applied to the excited electrons. May be selected as appropriate.

  The wavelength of the laser pulse may be appropriately selected according to the band gap of the workpiece, but is preferably in the range of 500 to 1600 nm. For example, the energy h (c / λ) (h: Planck's constant, c: speed of light, λ: wavelength of laser light) of one photon of a laser pulse is “1h (c / λ) ≦ with respect to the band gap (Eg). Eg ≦ nh (c / λ) ”(n = about 8 to 9) may be satisfied. As can be seen from this equation, the stress strain region can be formed by either one-photon absorption or multi-photon absorption. Note that it is possible to form a stress-strain region even if it slightly deviates from this range.

  The repetition frequency of the laser pulse is not particularly limited, but is preferably in the range of 1 kHz to 1 MHz.

  For example, when the object to be processed is sapphire having a thickness of 50 to 200 μm, the pulse energy of the laser pulse is preferably in the range of 5 to 15 μJ / pulse, and the wavelength is preferably in the range of 500 to 1500 nm. When the thickness of the object to be processed increases, adjustments such as increasing the pulse energy of the laser pulse, increasing the repetition frequency, or decreasing the scanning speed may be performed as appropriate.

  Further, when the workpiece has a functional layer on the surface opposite to the laser pulse irradiation surface, the pulse energy of the laser pulse is preferably strong enough that the stress-strain region does not reach the functional layer. This is because when the stress-strain region reaches the functional layer, the function of the functional layer is hindered and the life of the device may be shortened.

The condensing lens is a convex lens for condensing the laser pulse near the surface of the workpiece. The numerical aperture of the condenser lens is preferably in the range of 0.4 to 0.95 from the viewpoint of setting the laser intensity of the laser pulse to 0.5 PW / cm ² or more.

The laser pulse condensed by the condenser lens is irradiated near the surface of the workpiece. Here, “irradiating near the surface of the object to be processed” means irradiating so that the focal point of the laser pulse is located within a range of ± 500 μm from the surface of the object to be processed. It is preferable that the distance (L) between the condenser lens and the object to be processed is within the range of the working distance (WD) ± 500 μm of the condenser lens, that is, the following expression is satisfied.
WD−500 μm ≦ L ≦ WD + 500 μm

  Here, the “working distance (WD)” means the shortest distance from the tip (surface) of the condenser lens (objective lens) to the object to be processed when focusing on the surface of the object to be processed. Therefore, the condensing point of the laser pulse may be outside or inside the workpiece, but is preferably inside the workpiece.

  The laser beam emitted from the light source may be divided into two or more laser beams. At this time, the energy intensity of the laser beam to be divided can be adjusted by using a half mirror or the like. When dividing the laser beam in this way, each laser beam may be irradiated to different workpieces through different condenser lenses. By doing in this way, a plurality of processing objects can be laser-processed simultaneously using one laser light source.

  A plurality of laser beams may be introduced into one condenser lens. At this time, each laser beam may be a laser beam emitted from a different laser light source, or may be a laser beam obtained by dividing a laser beam emitted from one laser light source. Each laser pulse may be introduced simultaneously into the condenser lens or may be introduced at different timings. The number of laser beams introduced into one condenser lens is not particularly limited, but is preferably in the range of 1 to 8.

  When a plurality of laser beams are introduced into one condenser lens, each laser beam is preferably introduced into the condenser lens so as to irradiate a different region of the workpiece. For example, the irradiation position of each laser beam can be made different by changing the incident angle of each laser beam to the condenser lens. For example, as shown in FIG. 2, the incident angles of the laser beams 100a and 100b to the condenser lens 150 can be changed by reflecting the laser beams 100a and 100b using different mirrors 140a and 140b, respectively. More specifically, the incident angles of the laser beams 100a and 100b on the condenser lens 150 can be controlled by adjusting the tilt angles of the mirrors 140a and 140b. The interval between the irradiation positions of the laser beams is preferably in the range of 1 to 50 μm as will be described later. In this way, the processing time can be further shortened by introducing a plurality of laser beams into one condenser lens.

  The workpiece is not particularly limited, but is preferably a crystalline member from the viewpoint of facilitating cutting when it is cut (cleaved) by applying mechanical stress after laser processing. Further, the band gap of the workpiece is preferably 0.9 eV or more. Examples of such a processing object include sapphire, silicon carbide, glass, and diamond.

  As described above, by repeating the step of condensing and irradiating the laser pulse near the surface of the workpiece, by changing the relative position of the laser pulse and the workpiece, multiple stress strain regions are formed along the planned cutting line. (See FIG. 1). For example, the workpiece may be moved at a speed of 10 to 2000 mm / second while repeating the step of irradiating the laser pulse, and the planned cutting line may be scanned with the laser beam. The number of scans is not particularly limited, but may be scanned once or may be repeatedly scanned two or more times.

  Further, it is preferable that the object to be processed is moved by about 1 to 50 μm between the start of oscillation of a laser pulse and the start of oscillation of the next laser pulse (referred to as “one cycle time”). By doing in this way, the space | interval (distance between each center) of the stress-strain area | region (or hole) formed in a workpiece becomes in the range of 1-50 micrometers, and it is a cutting plan when mechanical stress is applied It can be easily cut (cleaved) along the line. Note that adjacent stress-strain regions may be connected or separated. In the laser processing method of the present invention, since the stress strain region is formed up to the deep part of the workpiece, it can be easily cut along the planned cutting line even if the adjacent stress strain regions are separated.

2. Formation of Stress Strain Region Utilizing Self-Channeling Effect In the laser processing method of the present invention, the laser pulse irradiated to the processing object is generated in the processing object along a transient optical waveguide formed by the self-channeling effect. Is propagated in the optical axis direction to form a stress strain region in the workpiece. Hereinafter, with reference to FIG. 3, the mechanism by which the stress strain region is formed in the laser processing method of the present invention will be described.

  First, when a laser pulse 100 (one pulse) having a very high laser intensity is focused and irradiated on the vicinity of the surface of the workpiece 110, multiphotons are generated near the surface of the workpiece 110 by the first half portion 100-1 of the laser pulse. Absorption occurs and electrons are excited to enter a weakly bound state or an ionized state (see FIG. 3A). Note that when the laser intensity of the laser pulse 100 is higher, plasma is further generated (not shown).

  When a laser pulse 100 (the same pulse as in FIG. 3A) enters the workpiece 110, a ponderamotive force 210 (described later) by the laser pulse 100 acts on the excited electrons 200. By this ponderamomotive force, the excited electrons 200 are expelled around the irradiation region of the laser pulse 100 (see FIG. 3B). As a result, in the irradiation region of the laser pulse 100, the excited electrons 200 are expelled, so that the electron density is low. In the peripheral region of the irradiation region, the electron density is increased by the amount of the excited electrons 220 that have been expelled.

  As will be described later, since the electron density contributes to the refractive index, the region 230 having a high electron density formed near the periphery of the irradiated region has a small refractive index, and the region 240 having a low electron density in the irradiated region has a refractive index. growing. As described above, a refractive index distribution is generated in the irradiation region and its peripheral region, whereby a transient waveguide is formed, and the intermediate portion 100-2 and the latter half portion 100-3 of the laser pulse are formed in the waveguide. It progresses while being confined and forms a stress-strain region 130 (see FIG. 3C). Forming a waveguide by itself is called “self-channeling”.

  Thereafter, until the energy of the laser pulse 100 disappears, the progress to the deep part by the self-channeling effect and the formation of the stress strain region 130 continue (see FIG. 3D). The energy of the laser pulse is consumed not only by multiphoton absorption by the workpiece but also by scattering by the plasma. Finally, the stress-strain region 130 can be formed up to a deep portion in the workpiece 110 by simply irradiating the laser pulse 100 (see FIG. 3E).

Note that the hole 250 having a high aspect ratio can be formed in the workpiece 110 by repeatedly irradiating the same region with the laser pulse 100 (see FIG. 3F). Number for irradiating laser pulses 100 in the same region is not particularly limited, is preferably in the range of 1 to 10 ⁷ times.

  FIG. 4 is a diagram showing a state in which a hole with a high aspect ratio is formed in the workpiece, and shows each step in time series from left to right. In FIG. 4, when the first laser pulse 100a is irradiated, the stress strain region 130 is formed as described above. Next, when the same region is irradiated with the second laser pulse 100b, ablation 260 occurs in the outermost layer of the stress strain region 130, and the outermost layer portion of the stress strain region 130 is removed. Thereafter, similarly, by irradiating the same region with the laser pulses 100 c and d three times and four times, the hole 250 having a high aspect ratio can be formed in the region which is the stress strain region 130.

3. About the ponderamomotive force Here, the “ponderamomotive force” which is the essence of the mechanism of the laser processing method of the present invention will be briefly described.

  When light of frequency n is irradiated to free electrons or loosely-bound electrons, the electrons irradiated with the light are swayed by the alternating electric field of light and try to vibrate following the electric field E (t). In the case of completely free electrons, when light of frequency (frequency) n is irradiated, the electrons try to vibrate at frequency n. This process is a basic process of the interaction between electrons and light, and is a linear process.

However, when the intensity (number of photons) of incident light increases, various nonlinear processes are induced in addition to the linear processes as described above. In particular, when the laser intensity (I) of incident light is 0.5 PW or more per 1 cm ² (I ≧ 0.5 PW / cm ² ), a non-linear force called a ponderomotive force acts on the electrons. become.

The ponderamotive force is a force generated by an interaction between an electromagnetic field of incident light and electrons through Lorentz force. The force vector F _p of the ponderamomotive force can be written as the following equation (1).
Here, e is the electron elementary charge, m _e is the electron mass, omega frequency (frequency) of the incident light, E is the electric field vector of the incident light, ∇ is nabla operator.

  From equation (1), when an electron is subjected to a ponderamomotive force by a gradient electric field such as light, the ponderamomotive force is a force that attempts to expel the electron in a direction from a region where the electric field is strong toward a region where the electric field is weak. It can be seen that Therefore, when the laser pulse has a Gaussian beam type intensity distribution, as shown in FIG. 3B, the excited electrons are moved from the central portion of the laser beam optical axis to the peripheral portion by the ponderamomotive force. It is kicked out.

  As described above, in the laser processing method of the present invention, when a processing object is irradiated with a laser pulse, electrons existing in the irradiation region are excited by the first half of the laser pulse and enter a weakly bound state or an ionized state (see FIG. 3 (A)). Next, when the intermediate portion of the laser pulse enters the region, the intermediate portion of the laser pulse applies a ponderamomotive force to the excited electrons. Here, when the laser has a Gaussian beam type intensity distribution, the excited electrons are expelled from the central part of the beam optical axis to the peripheral part by the ponderamomotive force (see FIG. 3B), and the refractive index in the irradiation region. And a transient “waveguide” is formed (see FIG. 3C).

This action is formulated and described below. As a result of the movement of the electrons by the above ponderamomotive force, the refractive index distribution n (r) is as shown in Equation (2).
Here, the coordinate r is an axis perpendicular to the optical axis. n ₀ is the refractive index of the material, n ₂ is the nonlinear refractive index (due to Kerr effect), I (r) is the intensity distribution function (Gaussian function) of incident light, and ω _p (r) is in the material Of the plasma frequency.

Where ω _p (r) is
It is. N _e (r) is a function representing the electron density.

As a result, the following equation is established for N _e (r) when the electron density (N _b ) in the bulk is used.

FIG. 5 is a graph showing the relationship between the distance from the laser condensing point and the electron density at the laser condensing point obtained from the above equation (4). The horizontal axis (r) indicates the coordinates (distance) in the direction perpendicular to the optical axis, and 0 indicates the optical axis center. The vertical axis (N _e (r) / N _b ) represents the electron density when the electron density (N _b ) in the bulk is 1. Curve 1 shows the simulation result when the beam diameter is “1D” and the laser intensity is “7.8I”, and curve 2 is when the beam diameter is “2D” and the laser intensity is “4I”. The curve 3 shows the simulation result when the beam diameter is “2.8D” and the laser intensity is “1I” (“D” and “I” have no special meaning). As described above, the refractive index increases in the region where the electron density is low, and the refractive index decreases in the region where the electron density is high. Therefore, it can be seen from this graph that a “waveguide” having a large refractive index in the central portion of the beam optical axis and a small refractive index in the peripheral portion is temporarily formed.

4). Summary As described above, the laser processing method of the present invention has a self-channeling effect by condensing and irradiating a laser pulse (0.5 PW / cm ² or more) having a very high laser intensity near the surface of the workpiece. A laser pulse can be propagated along a transient optical waveguide formed in a workpiece, and a stress strain region having a high aspect ratio can be formed with high accuracy. Therefore, if the workpiece is cut using the laser processing method of the present invention, the workpiece can be cut with high accuracy and easily along the planned cutting line.

  Further, the laser processing method of the present invention can form a stress strain region having a high aspect ratio by single irradiation of a laser pulse, and adjacent stress strain regions do not need to be connected to each other. Can be processed in a short time. Therefore, if the workpiece is cut using the laser processing method of the present invention, the workpiece can be cut at high speed.

  Further, the laser processing method of the present invention can reduce the width of the processing line to about 2 μm. Therefore, if the workpiece is cut using the laser processing method of the present invention, the chip yield can be improved.

  In addition, the laser processing method of the present invention can form a stress strain region without drilling. Therefore, if the object to be processed is cut using the laser processing method of the present invention, the object to be processed can be cut while suppressing the amount of dust generation to a very small amount.

5. Laser Processing Apparatus of the Present Invention The laser processing method of the present invention is not limited to this, but can be carried out using the laser processing apparatus shown in FIG.

  In FIG. 6, a laser processing apparatus 300 includes a laser light source 310, a telescope optical system 320, a polarization adjustment optical system 330, a dichroic mirror 340, a condenser lens 150, a stage 350, an observation optical system 360, an automatic aiming system 370, and a half. It has a mirror 380, an XYZ stage controller 390, a computer 400, and a monitor 410.

The laser light source 310 generates a laser pulse. For example, the laser light source generates a laser pulse having a wavelength of 500 to 1600 nm, a pulse width of 100 to 1000 femtoseconds, a repetition frequency of 1 kHz to 1 MHz, and a pulse energy of 1 to 1000 μJ / pulse. The laser light source 310 is, for example, a Ti: sapphire laser, a chrome forsterite laser, a Yb: YAG laser, a Yb: KGW laser, a Yb: KG (WO ₄ ) ₂ laser, various fiber lasers, various disk lasers, various dye lasers, or the like. is there.

  The telescope optical system 320 is an optical system that optimizes the beam diameter of the laser pulse output from the laser light source 310 in order to obtain a preferable processing shape.

  The polarization adjustment optical system 330 adjusts the laser pulse that has passed through the telescope optical system 320 to linearly polarized light that is perpendicular to the line to be cut of the workpiece 110. For example, the polarization adjustment optical system 330 includes a polarization adjuster such as a half-wave plate or a polarizing plate.

  The dichroic mirror 340 is a mirror that reflects almost 100% of the pulse laser that has passed through the polarization adjusting optical system 330 and transmits almost 100% of the observation light from the observation optical system 360 and the measurement laser from the automatic aiming system 370. .

  The condensing lens 150 is an objective lens for a microscope having a numerical aperture of 0.4 to 0.95, and condenses the laser pulse reflected by the dichroic mirror 340. The condensing lens 150 is arranged so that the distance (L) between the condensing lens 150 and the surface of the workpiece 110 satisfies the range of the condensing lens working distance (WD) ± 500 μm.

  The stage 350 includes a mounting table on which the workpiece 110 is mounted, and a drive mechanism that can move the mounting table in the XYZ axis direction and rotate the XYZ axis as a center. The workpiece 110 on the stage 350 can be moved not only in the XY axis direction along the planned cutting line but also in the Z axis direction by this drive mechanism. By moving the workpiece 110 in the Z-axis direction, the focal point of the laser pulse can be set at a desired position near the surface of the workpiece 110.

  The observation optical system 360 is an optical system for observing a processing site of the processing object 110. For example, the observation optical system 360 includes an illumination optical system, an optical aperture, a CCD camera, and the like. Image data captured by the CCD camera is output to the computer 400 and displayed on the monitor 410.

  The automatic aiming system 370 includes a measurement light source that generates a measurement laser for measuring the position of the surface of the workpiece 110, a detector that detects reflected light of the measurement laser from the surface of the workpiece 110, and the like. Have The automatic aiming system 370 detects the surface position of the processing object 110 by detecting the reflected light of the measurement laser from the surface of the processing object 110 on the stage 350. The detection result is output to the XYZ stage controller 390.

  The half mirror 380 is a mirror that reflects almost 100% of the measurement laser from the automatic aiming system 370 and transmits almost 100% of the observation light from the observation optical system 360. The measurement laser from the automatic aiming system 370 passes through the half mirror 380, the dichroic mirror 340, and the condenser lens 150, reaches the surface of the workpiece 110, and is reflected. The reflected light passes through the condenser lens 150 and the dichroic mirror 340 again, is reflected by the half mirror 380, and reaches the automatic aiming system 370.

  The XYZ stage controller 390 has a feedback circuit, and based on the information on the surface position of the workpiece 110 obtained by the automatic aiming system 370, the irradiation of the laser pulse matches the planned cutting line (XY axis direction). The stage 350 is feedback-controlled.

  The computer 400 is connected to a laser light source 310, an observation optical system 360, and an XYZ stage controller 390, and comprehensively controls these components. For example, the computer 400 scans an arbitrary scheduled cutting line with a laser beam by driving the stage 350 through feedback control by the XYZ stage controller 390 according to a predetermined program.

  Next, a machining process using the laser machining apparatus 300 having the above configuration will be described with reference to a flowchart shown in FIG.

First, the optimum laser intensity of the laser light source 310 for the workpiece 110 is determined (S1000). As described above, it is preferable that the laser intensity on the surface of the workpiece 110 is determined so as to be in the range of 0.5 to 500 PW / cm ² . Next, the stage 350 is moved to determine the irradiation position of the laser pulse (S1100), and the cutting line is programmed to the computer 400 (S1200).

  Next, the workpiece 110 is placed on the stage 350 and positioned (S1300). At this time, the light sources for measurement and illumination are turned on. Next, the laser light source 310 is turned on, and a laser pulse is focused and irradiated on the planned cutting line of the workpiece 110 (S1400). As a result, a stress strain region is formed on the planned cutting line of the workpiece 110. At this time, by moving the stage 350 in the XY axis direction (horizontal direction) along the planned cutting line, a stress strain region can be formed along the planned cutting line.

  Finally, mechanical stress is applied to the workpiece 110 to cut (cleave) it along the planned cutting line of the workpiece 110 (S1500). As a result, the workpiece 110 is cut into small chips.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail with reference to an Example, this invention is not limited by these Examples.

  Example 1 shows an example in which a sapphire substrate is cut (cleaved) using the laser processing method of the present invention.

  In this example, a laser processing apparatus having the configuration shown in FIG. 6 was used. A laser light source (Yb: KGW) was irradiated with excitation light from a high-power semiconductor laser to oscillate a laser pulse (pulse width: about 300 femtoseconds, wavelength: 1030 nm, repetition frequency: 30 kHz). The numerical aperture of the condenser lens was 0.68.

A sapphire substrate (Al ₂ O ₃ ) having a thickness of about 100 μm was placed on the stage, and the substrate was irradiated with a laser pulse oscillated from a laser light source so as to be condensed near the surface of the substrate. At this time, the polarization direction of the laser pulse was linearly polarized in a direction perpendicular to the scanning direction (direction of the line to be cut) and parallel to the surface of the substrate. The pulse energy of the laser pulse after passing through the condenser lens was 14 μJ / pulse. The laser intensity was ˜5 PW / cm ² .

  The stage on which the substrate was placed was moved in the direction of the planned cutting line at a speed of 150 mm / second, so that a laser pulse was irradiated once every 5 μm along the planned cutting line. The number of scans of the planned cutting line was set to 1 (single scan).

  FIG. 8A is a photomicrograph of the substrate surface after laser irradiation. As shown in this figure, the width of the formed stress strain region (the width of the processing line) was about 5 μm, and could be processed with extremely high resolution. The stress strain regions were not connected to each other, and the distance between the centers of the adjacent stress strain regions was about 5 μm.

  When mechanical stress was applied to the laser-irradiated substrate, it was easily cut (cleaved). FIG. 8B is a photomicrograph showing the state of the cross section of the substrate after cutting. FIG. 8C is a photomicrograph further enlarging the cross section. As shown in FIG. 8B and FIG. 8C, the stress strain region extends to a depth (about 60 μm) that is about half the thickness of the substrate and does not reach the back surface of the substrate. It was. The cut surface was smooth and perpendicular to the substrate surface.

  Thus, by using the laser processing method of the present invention, a stress strain region having a high aspect ratio can be formed along the planned cutting line with high accuracy and at high speed, and as a result, the sapphire substrate can be formed along the planned cutting line. Can be cut with high accuracy and high speed.

  Example 2 shows an example in which the sapphire substrate is cut (cleaved) using the laser processing method of the present invention under laser irradiation conditions (repetition frequency, laser pulse energy, laser intensity, laser irradiation interval) different from those in Example 1. .

  In this example, a laser processing apparatus having the same configuration as that of Example 1 was used. A laser light source (Yb: KGW) was irradiated with excitation light from a high-power semiconductor laser to oscillate a laser pulse (pulse width: about 300 femtoseconds, wavelength: 1030 nm, repetition frequency: 10 kHz). The numerical aperture of the condenser lens was 0.68.

A sapphire substrate similar to that in Example 1 was placed on a stage, and the substrate was irradiated with a laser pulse oscillated from a laser light source so as to be condensed near the surface of the substrate. At this time, the polarization direction of the laser pulse was linearly polarized in a direction perpendicular to the scanning direction (direction of the line to be cut) and parallel to the surface of the substrate. The pulse energy of the irradiated laser pulse was 5 μJ / pulse. The laser intensity was ˜1.8 PW / cm ² .

  By moving the stage on which the substrate was placed at a speed of 100 mm / second along the direction of the planned cutting line, the substrate was irradiated with a laser pulse once every 10 μm along the planned cutting line. The number of scans of the planned cutting line was set to 1 (single scan).

  FIG. 9A is a photomicrograph of the substrate surface after laser irradiation. As shown in this figure, the width of the stress strain region (the width of the processing line) was about 2 μm, and it was possible to process with extremely high resolution. The stress strain regions were not connected to each other, and the distance between the centers of the adjacent stress strain regions was about 10 μm.

  When mechanical stress was applied to the laser-irradiated substrate, it could be easily cut. FIG. 9B is a photomicrograph showing the state of the cross section of the substrate after cutting. FIG. 9C is a photomicrograph further enlarging the cross section. As shown in FIG. 9B and FIG. 9C, the stress strain region extends to a depth of about half the thickness of the substrate (vertical scale bar in the figure: about 44 μm), It did not reach the back of the substrate. The cut surface was smooth and perpendicular to the substrate surface.

  Thus, by using the laser processing method of the present invention, a stress strain region having a high aspect ratio can be formed along the planned cutting line with high accuracy and at high speed, and as a result, the sapphire substrate can be formed along the planned cutting line. Can be cut with high accuracy and high speed.

  In the first and second embodiments, the example in which the stress strain region is formed by irradiating the laser pulse once per region is shown. Example 3 shows an example in which a laser pulse is irradiated a plurality of times (100 times) per region to make a hole.

  In this example, a laser processing apparatus having the same configuration as that of Example 1 was used. A laser light source (Yb: KGW) was irradiated with excitation light from a high-power semiconductor laser to oscillate a laser pulse (pulse width: about 300 femtoseconds, wavelength: 1030 nm, repetition frequency: 80 kHz). The numerical aperture of the condenser lens was 0.65.

A sapphire substrate similar to that in Example 1 was placed on a stage, and a laser pulse oscillated from a laser light source was irradiated 100 times on one region of the substrate so as to be condensed near the surface of the substrate. At this time, the polarization direction of the laser pulse was linearly polarized light in a direction parallel to the surface of the substrate. The pulse energy of the irradiated laser pulse was 10 μJ / pulse. The laser intensity was ~3.3PW / cm ^2.

  FIG. 10A is a photomicrograph of the substrate surface after laser irradiation. As shown in this figure, the size of the formed hole was about 12 μm and could be processed with extremely high resolution. FIG. 10B is a photomicrograph showing the cross section of the substrate after laser irradiation. As shown in FIG. 10B, the formed hole extended to a depth of about 20 μm and did not reach the back surface of the substrate.

  As described above, by using the laser processing method of the present invention, a hole with a high aspect ratio can be formed along the planned cutting line with high accuracy and at high speed, and as a result, the sapphire substrate can be formed along the planned cutting line. It can cut accurately and at high speed.

  The laser cutting method of the present invention not only can form a stress strain region with a high aspect ratio along the planned cutting line with high accuracy and high speed, but also has a small processing line width and an extremely small amount of dust generation. It is useful as a next-generation dicing technology.

100 Laser pulse (laser beam)
DESCRIPTION OF SYMBOLS 100-1 First half part of laser pulse 100-2 Middle part of laser pulse 100-3 Second half part of laser pulse 102 Polarization direction 110 Work object 120 Line to be cut 130 Stress strain region 140 Mirror 150 Condensing lens 200 Excited electron 210 Ponde Lamotive force 220 Excited excitation electrons 230 High electron density area 240 Low electron density area 250 Hole formed in workpiece 260 Ablation 300 Laser processing apparatus 310 Laser light source 320 Telescope optical system 330 Polarization adjustment optical system 340 Dichroic mirror 350 Stage 360 Observation optical system 370 Automatic aiming system 380 Half mirror 390 XYZ stage controller 400 Computer 410 Monitor

Claims (2)

A step of scanning the sapphire cutting line with the laser pulse beam while condensing and irradiating the sapphire with a laser pulse through a condensing lens, thereby forming a plurality of stress strain regions in the sapphire along the cutting line. When,
Applying a mechanical stress to the sapphire in which the plurality of stress strain regions are formed, and cutting the sapphire along the planned cutting line,
In the step of forming the stress-strain region, the laser pulse is focused and irradiated near the surface of the sapphire, and the laser intensity of the laser pulse on the surface of the sapphire is set within a range of 0.5 to 500 PW / cm ^2. The stress strain region of the shape extending in the optical axis direction toward the inside starting from the surface of the sapphire is formed by a self-channeling effect.
Laser cutting method.   The laser cutting method according to claim 1, wherein a distance between the condensing lens and sapphire is a working distance of the condensing lens within a range of ± 500 μm.