JP4478184B2 - Laser cleaving method and laser processing apparatus - Google Patents

Description

  The present invention relates to a laser cutting method and a laser processing apparatus.

  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. While these can be said to be well-established technologies, they are approaching the essential limits such as the reduction of material yield due to “cutting” and the processing resolution of miniaturization. On the other hand, instead of these mechanical processing techniques, a laser processing method is given as a fine processing technique that is rapidly progressing.

  This is a method of irradiating a processing object with a high-intensity laser pulse and cutting the processing object starting from damage (cracks) caused by structural destruction or modification of the substance in a minute region at the focal position. . In this method, after damages caused by laser irradiation are arranged along a planned cutting line, mechanical stress is applied to a material to be processed, and the material is cut into a fine chip shape. This is called “dicing”.

  As a processing object, what is particularly important in practical use is a thin plate-like device made of a dielectric substrate (for example, sapphire or glass) coated with a functional semiconductor layer (for example, silicon or gallium arsenide).

  For example, in Patent Document 1, a laser pulse having a transparent wavelength (for example, 1064 nm) (that is, not absorbing) is applied to a processing object such as glass in the processing object using an objective lens. Condensation occurs, and at this condensing position, damage (cracks) having a disordered shape with a size of several tens to several hundreds of μm is generated, and the substrate is cut by applying stress using the arranged cracks as a starting point. A method is disclosed.

In Patent Document 2, a laser pulse is condensed and irradiated on the surface of a workpiece by way of an optical system, V-shaped damage is formed on the surface of the workpiece, and the workpiece is processed with high resolution. 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 (crack region, melt processing region, or refractive index formation) region by multiphoton absorption inside a processing target. Crack formation is induced by optical breakdown (breakdown), and melt heat treatment region formation is induced by a photothermal effect. Therefore, the size of the damage becomes relatively large (several tens of μm to several hundreds of μm), and there is a certain limit in processing accuracy.

  In the processing method of Patent Document 2, although the processing object can be processed with high resolution (crack width: 10 μm), the crack depth is shallow (30 μm). For this reason, in order to process (cleave) the workpiece, it is necessary to form cracks connected to each other, and the processing speed is limited (10 mm / s).

  The present invention generates an ablation plasma on the surface of the workpiece, generates a stress strain region inside the workpiece, and uses a shock wave generated from the plasma to grow a crack in the stress strain region. It is an object of the present invention to provide a method for laser processing a workpiece in a short time and with high resolution.

[1] A laser cleaving method comprising: generating a laser pulse; and irradiating the laser pulse near the surface of the object to be processed through a condenser lens, the pulse of the laser pulse The width is 100 to 1000 femtoseconds, the numerical aperture of the condenser lens is 0.1 to 0.5, and the pulse energy of the laser pulse that has passed through the condenser lens is 1-1000 μJ / pulse. Laser cleaving method.
[2] A step of generating a laser pulse having a pulse width of 100 to 1000 femtoseconds, and irradiating the laser pulse in the vicinity of the surface of the object to be processed through a condenser lens and ablation plasma on the object to be processed Generating a crack by the ablation plasma energy, forming a stress strain around the crack, and a region where the stress strain is generated by a shock wave generated from the ablation plasma Extending the crack to a laser cleaving method.

  With the laser cleaving method and laser processing apparatus of the present invention, it is possible to laser process a workpiece with a high resolution in a short time.

1. About the laser cleaving method of the present invention The laser cleaving method of the present invention includes 1) a step of generating a laser pulse, and 2) a step of irradiating the laser pulse in the vicinity of the surface of the object to be processed through a condenser lens.

In step 1), a laser pulse is generated. The means for generating the laser pulse is not particularly limited. For example, Ti: sapphire laser, chrome forsterite laser, Yb: YAG laser, Yb: KGW laser, Yb: KG (WO ₄ ) ₂ laser, various fiber lasers, various disks There are lasers and various dye lasers. The type of the generated laser pulse is not particularly limited, but a preferable type of laser pulse is a Gaussian beam. Further, the generated laser pulse may be divided into two or more laser pulses. The laser pulse may be divided so as to be distributed to an appropriate energy intensity by, for example, a half mirror.

  In the present invention, the pulse width of the laser pulse is in the femtosecond region. By setting the pulse width of the laser pulse to the femtosecond region, ablation plasma described later can be efficiently generated on the surface of the workpiece. In addition, by setting the pulse width of the laser pulse in the femtosecond region, the life of the plasma can be shortened and the effect of shielding the subsequent laser pulse by the plasma can be avoided.

  If the pulse width of the laser pulse is 1000 femtoseconds or more, the processing threshold may increase, which is not preferable. Further, when the pulse width of the laser pulse is 100 femtoseconds or less, it becomes difficult to supply a high-power laser pulse in a practically stable manner. Therefore, the preferable pulse width of the laser pulse is 100 to 1000 femtoseconds.

  The pulse energy of the laser pulse is preferably 1 to 1000 μJ / pulse, the wavelength of the laser pulse is preferably 500 to 1600 nm, and the repetition frequency of the laser pulse is preferably 1 kHz to 1 MHz. Here, the pulse energy means energy per one pulse of a laser pulse after passing through a condenser lens described later. The pulse energy of the laser pulse is not particularly limited as long as it generates an ablation plasma on the surface of the workpiece, but is preferably selected as appropriate depending on the material and thickness of the workpiece. The wavelength of the laser pulse is preferably selected as appropriate according to the band gap energy of the material of the workpiece to be described later. For example, the energy h (c / l) (h: Planck constant, c: speed of light, l: wavelength of laser light) of one photon of a laser pulse is 1 h (c / l) with respect to the band gap energy (Eg). ≦ Eg ≦ nh (c / l), n may be in the range of about 8-9. That is, in the present invention, the stress strain region described later can be formed by either one-photon absorption or multi-photon absorption. Further, the machining can be performed even if it slightly deviates from this range.

  For example, when the workpiece is sapphire having a thickness of 50 to 200 μm, the pulse energy of the laser pulse is preferably 5 to 15 μJ / pulse, and the wavelength is preferably 500 to 1500 nm. When the thickness of the workpiece is increased, the laser pulse energy of the laser pulse may be increased, the repetition frequency may be increased, or the scanning speed may be decreased.

  Further, when the workpiece has a functional layer in the lower layer, the pulse energy of the laser pulse is preferably strong enough that a stress strain region described later 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 laser pulse may be polarized light such as linearly polarized light, circularly polarized light, or elliptically polarized light.

  In step 2), the laser pulse generated in step 1) is irradiated to the vicinity of the surface of the object to be processed through the condenser lens.

  The condensing lens is a convex lens for condensing the laser pulse. The numerical aperture of the condenser lens is preferably 0.1 to 0.5. That is, in the present invention, using a condensing lens having a small numerical aperture, the laser pulse is loosely focused and the stress strain region formed inside the workpiece is lengthened in the laser pulse irradiation direction (hereinafter referred to as “irradiation direction”). It is characterized by that. The “stress-strain region” means that the workpiece absorbs laser light and is modified (for example, amorphization or chemical bond breakage, change in electron valence / ion valence due to ionization), Coulomb explosion, atomic structure A region in which the density expands or contracts in the workpiece due to rearrangement and thermal expansion, and becomes brittle due to stress. The reason and mechanism for lengthening the stress strain region in the irradiation direction by loosely focusing the laser pulse will be described later.

  The laser pulse condensed by the condenser lens is irradiated near the surface of the workpiece. Here, “irradiate near the surface of the object to be processed” means to irradiate the condensing point of the laser pulse so as to be within a range of ± 200 μm from the surface of the object to be processed. That is, the distance (L) between the condenser lens and the object to be processed is arranged so as to satisfy the range of the working distance (WD) ± 200 μm of the condenser lens. That is, in the present invention, the following expression is satisfied.

      WD−200 μm ≦ L ≦ WD + 200 μm

Here, the working distance (WD) means the distance from the tip (surface) of the condensing (objective) lens to the object to be processed when the object surface is focused.
Therefore, the condensing point of the laser pulse may be arranged above the surface of the workpiece, or may be arranged inside the surface of the workpiece. Preferably, the condensing point of the laser pulse is arranged inside the surface of the workpiece.

The pulse fluence on the surface of the laser pulse workpiece is appropriately selected according to the material and thickness of the workpiece. As the thickness of the workpiece increases, it is preferable to increase the pulse fluence. Pulse fluence of the laser pulses is preferably in the range of 1~5000J / cm ^2. For example, when the object to be processed is sapphire with a thickness of 90 μm, the pulse fluence of the laser pulse is preferably 100 to 2000 J / cm ² .

  When the laser pulse is divided into two or more laser pulses in step 1), each laser pulse may pass through a different condenser lens and be irradiated near the surface of a different workpiece. . Thereby, two or more objects to be processed can be simultaneously processed with one laser light source.

  Two or more laser beams may be introduced into one condenser lens. The two or more laser beams may be laser pulses generated from different laser light sources, or may be laser pulses obtained by dividing laser pulses generated from one laser light source. The pulse energy and laser wavelength of each of the two or more laser beams may be such that ablation plasma is generated on the surface of the workpiece as described above. Two or more laser pulses may be simultaneously introduced into one condenser lens or may be introduced in time series.

  The two or more laser beams are preferably introduced into one condenser lens so as to irradiate different positions on the cutting line on the surface of the workpiece. Specifically, by changing the incident angles of two or more laser beams to the condensing lens, the irradiation position of the laser beam on the surface of the workpiece can be shifted. The incident angles of two or more laser beams to the condenser lens can be changed by reflecting the laser beams using a mirror, for example (see FIG. 2). More specifically, the incident angle of the laser beam to the condenser lens can be controlled by adjusting the tilt angle of the mirror. The interval between the irradiation positions of two or more laser beams is preferably 1 to 50 μm.

  By introducing two or more laser beams into one condenser lens, the processing time can be further shortened.

  The object to be processed is preferably a crystalline member. When the object to be processed is a crystalline member, the cleaving process described later becomes easy. The band gap energy of the workpiece is preferably 0.9 eV or more. Examples of the material of such a workpiece include sapphire, silicon carbide, glass, diamond and the like.

  When the laser pulse is applied to the vicinity of the surface of the workpiece, a crack extending in the laser irradiation direction from the surface of the workpiece is formed. Here, the “crack” means a crack formed on the surface of the workpiece or inside.

  Hereinafter, the mechanism by which a crack extends will be described with reference to the drawings. 1A to 1E show a flow in which cracks are formed in a workpiece after the laser pulse is irradiated near the surface of the workpiece in the present invention.

  FIG. 1A shows a state in which the laser pulse 20 is irradiated near the surface of the workpiece 10 through the condenser lens 109. In FIG. 1A, the focal point 21 of the laser pulse 20 is located on the surface of the workpiece 10.

In FIG. 1B, an ablation plasma 30 and a damaged region 34 (not shown) are simultaneously generated near the surface of the workpiece by the irradiation of the laser pulse 20, and the inside of the workpiece is almost at the same timing. A state in which the stress strain region 31 is formed in the irradiation direction of the laser pulse 20 is shown. However, it is preferable that the stress strain region does not reach the functional layer 11. Ablation plasma is a high-temperature ionized gas state created by local atomic dissociation (chemical bond breakage) or high-density ionization due to absorption of a focused femtosecond laser near the surface of a workpiece. Further, the damaged region formed by ablation plasma is a region serving as a starting point for growth of cracks described later. The size of the damaged region 34 depends on the material and thickness of the workpiece, but can be reduced to 1 μm or less.
Further, the ablation plasma generates a shock wave which will be described later. In the stress-strain region, cracks are easily extended by mechanical stimulation, that is, shock wave propagation.

  In the present invention, since a lens having a small numerical aperture is used as a condenser lens, the laser pulse is loosely focused. The loosely focused laser pulse has a focal depth extending in the irradiation direction. Therefore, when the workpiece is irradiated with the loosely focused laser pulse, the stress strain region formed inside the workpiece is elongated in the irradiation direction. That is, the present invention is characterized in that the stress strain region is formed long in the irradiation direction by using a lens having a small numerical aperture. On the other hand, it should be noted that the pulse energy of the laser pulse is appropriately selected so that the stress strain region does not reach the functional layer of the workpiece.

  FIG. 1C shows a state in which the shock wave 32 generated from the ablation plasma propagates inside the workpiece. As described above, in the stress-strain region, when a mechanical stimulus is applied, the crack expands. Therefore, in the stress-strain region 31 where the shock wave 32 that is a mechanical stimulus propagates, the crack 33 extends.

  FIG. 1D shows a situation in which cracks extend in the stress strain region due to the propagation of shock waves. Since the present invention is characterized in that the stress strain region is formed long in the irradiation direction, the crack 33 formed in the stress strain region 31 also extends in the irradiation direction. As a result, a sharp crack 33 extending in the irradiation direction is formed inside the workpiece. The extension of the crack 33 continues until the shock wave reaches the deepest portion of the stress strain region 31 or the shock wave disappears.

  FIG. 1E shows a state in which the shock wave 32 propagates to the deepest portion of the stress strain region 31 and the crack 33 is formed to the deepest portion of the stress strain region. The present invention is characterized in that the above phenomenon occurs by single-shot irradiation of laser pulses (only one pulse).

  By repeating the process including Step 1) and Step 2) (hereinafter simply referred to as “process”), two or more cracks can be formed on the breaking line by transferring the workpiece along the breaking line. (See FIG. 3). In this invention, it is preferable that the speed which moves a process target object along a scanning line is 10-2000 mm / s. In addition, it is preferable that the workpiece is transferred by 1 to 50 μm during a period (one cycle time) from the start of oscillation of one laser pulse to the start of oscillation of the next laser pulse. In addition, when two or more laser beams are introduced into one condenser lens, it is preferable that the object to be processed is transferred so that the intervals between the irradiation regions are equal. In the present invention, the cracks may be connected or separated. In the present invention, since the crack is formed long in the irradiation direction, the workpiece can be cleaved even if the cracks are separated from each other.

  The laser cleaving method of the present invention may further include a step of cleaving the processing object by applying a mechanical force from the outside to the processing object in which a plurality of cracks are formed on the cutting line (see FIG. 3). ). The cleaved workpiece has a flat and sharp split section without any disturbance.

  In this way, by irradiating the surface of the workpiece with a femtosecond laser having a high pulse energy (1-1000 μJ / pulse), ablation plasma can be generated on the surface of the workpiece. Further, by loosely focusing such a laser pulse, a stress strain region that is long in the irradiation direction can be formed inside the workpiece. That is, the present invention can form a crack extending in the irradiation direction by combining the ablation plasma and a stress strain region long in the irradiation direction. Thereby, a workpiece can be cleaved more easily.

  Further, in the present invention, cracks extending in the irradiation direction can be formed by single irradiation of a laser pulse, and since it is not necessary that the cracks are connected to each other, it is possible to process an object to be processed in a short time. . For example, the scanning speed in the present invention is 10 to 2000 mm / s, which is significantly faster than the scanning speed described in Patent Document 2 (10 mm / s).

  Furthermore, in the present invention, since it is not necessary for the cracks to be connected to each other, the workpiece can be cleaved with less laser irradiation. For this reason, generation | occurrence | production of the fragment of a processing target accompanying continuous crack formation can be suppressed.

2. About Laser Processing Apparatus of the Present Invention The laser cleaving method of the present invention can be implemented using the laser processing apparatus shown in FIG.

  A laser processing apparatus 100 in FIG. 4 includes a laser light source 101, a telescope optical system 103, a polarizing plate 105, a dichroic mirror 107, an objective lens 109, a protective window plate 111, a stage 113, a measurement light source 115, a beam shaper 117, A half mirror 119, a photodetector 121, a controller 123, an illumination light source 125, a CCD camera 127, a computer 129, and a monitor 131 are included.

  The laser light source 101 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.

Lasers that can be used for the laser light source 101 include Ti: sapphire laser, chrome forsterite laser, Yb: YAG laser, Yb: KGW laser, Yb: KG (WO ₄ ) ₂ laser, various fiber lasers, various disk lasers, There are various dye lasers.

  The telescope optical system 103 optimizes the beam diameter of the laser pulse output from the laser light source 101 in order to obtain a preferable processing shape.

  In order to obtain a preferable processing shape, the polarizing plate 105 adjusts the laser pulse that has passed through the telescope optical system 103 to linearly polarized light that is parallel / perpendicular to the processing line, circularly polarized light, or elliptically polarized light.

  The dichroic mirror 107 is a mirror that reflects almost 100% of the pulse laser that has passed through the polarizing plate 105 and transmits almost 100% of the measurement laser light from the measurement light source 115.

  The condensing lens 109 is an objective lens for a microscope, and condenses the laser pulse reflected by the dichroic mirror 107. In the present invention, as described above, the condensing lens 109 having a numerical aperture of 0.1 to 0.4 is used. The distance (L) between the condensing lens and the surface is arranged so as to satisfy the range of the working distance (WD) ± 200 μm of the condensing lens.

  The protective window plate 111 is provided to protect the condensing lens 109 from minute debris scattered from the surface due to processing when the surface of the workpiece 10 is processed.

  The stage 113 has a mounting table (not shown), and the workpiece 10 to be irradiated with the laser pulse condensed by the objective lens 109 is mounted on the mounting table. The stage 113 has a drive mechanism (not shown) that can move the mounting table in the XYZ axis directions and rotate around the XYZ axes. By this drive mechanism, the workpiece 10 on the stage 113 is driven along the breaking line (XY axis direction). The drive mechanism can also move the stage 113 in the Z-axis direction. The movement width of the stage 113 in the Z-axis direction is preferably about 400 μm. By moving the workpiece 10 in the Z-axis direction by the drive mechanism of the stage 113, the laser palace condensing point can be arranged near the surface of the workpiece 10.

  The measurement light source 115 generates laser light for measuring the position of the surface of the workpiece 10 on the stage 113.

  The beam shaper 117 adjusts the beam shape of the laser light output from the measurement light source 115 in order to optimize the measurement laser light.

  The half mirror 119 is a mirror that reflects / transmits the measurement laser beam translucently. The measurement laser light that has passed through the beam shaper 117 passes through the half mirror 119, the dichroic mirror 107, and the objective lens 109, reaches the surface of the workpiece 10, and is reflected. This reflected light passes through the objective lens 109 and the dichroic mirror 107 again, and a part of the reflected light is reflected by the half mirror 119 and reaches the photodetector 121.

  The photodetector 121 detects the reflected light from the surface of the processing object 10 to detect the surface position of the processing object 10. The detection result is output to the controller 123.

  The controller 123 has a feedback circuit, and based on the information on the surface position of the workpiece 10 obtained by the photodetector 121, the stage 113 is set so that the irradiation of the laser pulse matches the breaking line (XY axis direction). Feedback control.

  The illumination light source 125 is disposed below the stage 113 and generates illumination light for observing the processing portion of the processing target 10 on the stage 113.

  The CCD camera 127 takes in the illumination light emitted from the illumination light source 125 and transmitted through the processing object 10, images the processing site of the processing object 10, and outputs the imaging data to the computer 129.

  The computer 129 is connected to the laser light source 101, the measurement light source 115, the controller 123, and the CCD camera 127, and comprehensively controls these units. For example, the computer 129 scans an arbitrary breaking line with a laser pulse by driving the stage 113 through feedback control by the controller 123 according to a predetermined program.

  Next, processing steps using the laser processing apparatus 100 having the above-described configuration will be described using the flowchart shown in FIG.

  First, in step S1000, the optimum laser intensity of the laser light source 101 for the workpiece 10 is determined.

  In step S1100, the irradiation position of the laser pulse is determined by moving the stage 113.

  In step S1200, the computer 129 is programmed with a breaking line.

  In step S1300, the workpiece 10 is placed on the stage 113 and placed. At this time, the measurement light source 115 and the illumination light source 125 are turned on.

  In step S1400, the laser light source 101 is turned on to irradiate the cutting line of the workpiece 10 with a laser pulse. Then, the stage 113 is moved in the XY axis direction (horizontal direction) along the breaking line, and a crack is formed from the surface of the workpiece 10 along the breaking line.

  In step S1500, cleaving is performed using cracks arrayed along the cleaving line from the surface of the workpiece 10 to the inside through step S1400. That is, if a mechanical stress is applied to the workpiece 10, desired precision cutting is achieved. Thereby, the workpiece 10 is cleaved into small chips.

  Hereinafter, the present invention will be described using examples. However, the examples described below are not intended to limit the scope of the present invention.

Example 1
In Example 1, the sapphire substrate was cleaved using the cleaving method of the present invention. A sapphire (Al ₂ O ₃ ) substrate having a thickness of 90 μm was prepared as a processing object.

  A laser processing apparatus shown in FIG. 4 was prepared. The laser light source 101 was set to Yb: KGW, and excitation light from a high-power semiconductor laser was irradiated to oscillate a laser pulse (wavelength 1030 nm) of about 100 femtoseconds with a repetition frequency of 30 kHz. The output of the laser light source was 0.2W. The numerical aperture of the condensing lens 109 was set to 0.5.

The sapphire substrate was placed on the stage 113. The laser pulse from the laser light source 101 was condensed near the surface of the sapphire substrate through the condensing lens 109 and irradiated onto the sapphire substrate. The pulse energy of the irradiated laser pulse was 6 μJ / pulse, and the pulse fluence was ˜0.5 kJ / cm ² .

  While irradiating the sapphire substrate with the laser pulse, the stage on which the sapphire substrate was placed was moved at a speed of 150 mm / s along the breaking line. Thereby, a laser pulse was irradiated to the substrate every 5 μm along the breaking line. Each breaking line was scanned only once (single scan).

  FIG. 6A is a photomicrograph of the surface of the sapphire substrate obtained in Example 1 after laser irradiation. As shown in FIG. 6A, the width of the damaged region, that is, the width of the processing line was 3 μm, and the processing could be performed with extremely high resolution. The damaged areas are not connected to each other, and the distance between the centers of the adjacent damaged areas is about 5 μm.

  The sapphire substrate irradiated with laser in Example 1 was cleaved by applying mechanical stress. FIG. 6B is a photomicrograph showing a cross section obtained by the cleaving. FIG. 6C is a photomicrograph in which the cross section is further enlarged. As shown in FIGS. 6B and 6C, the cracks extended to a depth (about 45 μm) that was about half the thickness of the sapphire substrate (90 μm). Therefore, the cleaving was easy. Moreover, the split section was a flat surface, and a split section perpendicular to the surface of the workpiece could be obtained. Furthermore, in this example, damage to the back surface of the substrate was not confirmed.

  In FIG. 6C, cracks having different shapes were confirmed in the X region and the Y region. The crack in the X region has a length of about 12 μm. On the other hand, the crack in the Y region has a length about three times the length of the crack in the X region. In addition, the cracks in the X region have a constant length, whereas the lengths of the cracks in the Y region vary.

  The X region is considered to be a damaged region formed by ablation plasma and shock waves. On the other hand, the Y region is considered to be a mark in which a crack grows in the crushing process after laser irradiation in the stress strain region extended by laser processing (laser irradiation).

(Example 2)
In Example 2, the laser irradiation conditions (repetition frequency, laser output, laser pulse energy, laser pulse fluence, laser irradiation interval) of Example 1 were changed, and the sapphire substrate was cleaved using the cleaving method of the present invention. . First, the same sapphire substrate (thickness 90 μm, band gap energy: 8 eV) as in Example 1 was prepared.

  A laser processing apparatus shown in FIG. 4 was prepared. The laser light source 101 was set to Yb: KGW, and excitation light from a high-power semiconductor laser was irradiated to oscillate a laser pulse (wavelength 1030 nm) of about 100 femtoseconds with a repetition frequency of 60 kHz. The output of the laser light source was 0.75W. The numerical aperture of the condensing lens 109 was set to 0.5.

The sapphire substrate was placed on the stage 113. The laser pulse from the laser light source 101 was condensed near the surface of the sapphire substrate through the condensing lens 109 and irradiated onto the sapphire substrate. The pulse energy of the irradiated laser pulse was 12 μJ / pulse, and the pulse fluence was ˜1.0 kJ / cm ² .

  While irradiating the sapphire substrate with the laser pulse, the stage on which the sapphire substrate was placed was moved at a speed of 150 mm / s along the breaking line. Thereby, the laser pulse was irradiated to the substrate every 2.5 μm along the breaking line. Each breaking line was scanned only once (single scan).

  FIG. 7A is a photomicrograph of the surface of the sapphire substrate obtained in Example 2 after laser irradiation. As shown in FIG. 7A, the width of the damaged area, that is, the width of the processing line was 5 μm, and could be processed with extremely high resolution. In Example 2, damaged areas and cracks were connected.

  The sapphire substrate irradiated with laser in Example 2 was cleaved by applying mechanical stress. Cleavage was easy. FIG. 7B is a photomicrograph showing a cross section obtained by the cleaving. FIG. 7C is a photomicrograph in which the cross section is further enlarged. As shown in FIGS. 7B and 7C, the crack extended to a depth (about 18 μm) of about 20% of the thickness of the sapphire substrate. Moreover, the split section was a flat surface, and a split section perpendicular to the surface of the workpiece could be obtained. Further, in this example, damage to the wafer surface was not confirmed.

(Example 3)
In Example 3, a silicon carbide (6H—SiC) substrate was cleaved using the cleaving method of the present invention. A silicon carbide (6H—SiC) substrate having a thickness of 375 μm was prepared as a processing object.

  A laser processing apparatus shown in FIG. 4 was prepared. The laser light source 101 was set to Yb: KGW, and the laser beam (wavelength 1030 nm) of about 100 femtoseconds was oscillated with a repetition frequency of 100 kHz by irradiating excitation light from a high-power semiconductor laser. The output of the laser light source was 3W. The numerical aperture of the condensing lens 109 was set to 0.5.

The silicon carbide substrate was placed on the stage 113. Then, the laser pulse from the laser light source 101 was condensed and irradiated to the inside of 15 μm from the surface of the silicon carbide substrate through the condenser lens 109. The pulse energy of the irradiated laser pulse was 30 μJ / pulse, and the pulse fluence was ˜2.5 kJ / cm ² .

  While irradiating the silicon carbide substrate with the laser pulse, the stage on which the silicon carbide substrate was placed was moved along the breaking line at a speed of 300 mm / s. Thereby, a damaged region (spot) was formed on the substrate every 3 μm along the breaking line. Each breaking line was scanned only once (single scan).

  FIG. 8A is a photomicrograph of the surface of the silicon carbide substrate obtained in Example 3 after laser irradiation. FIG. 8B is a photomicrograph in which the surface is further enlarged. As shown in FIGS. 8A and 8B, the width of the damaged region, that is, the width of the processing line was about 20 μm, and could be processed with high resolution. In Example 3, damaged areas and cracks were connected.

  The silicon carbide substrate irradiated with laser in Example 3 was cleaved by applying mechanical stress. Cleavage was easy. FIG. 9A is a photomicrograph showing a cross section obtained by the cleaving. FIG. 9B is a photomicrograph in which the cross section is further enlarged. As shown in FIGS. 9A and 9B, the cracks extended to a depth (about 20 μm) of about 5% of the thickness of the silicon carbide substrate. Moreover, the split section was a flat surface, and a split section perpendicular to the surface of the workpiece could be obtained.

  FIG. 10A is a photomicrograph showing the cut surface of the surface of the silicon carbide substrate obtained by cleaving. FIG. 10B is a photomicrograph showing a cut surface on the back surface of the silicon carbide substrate obtained by cleaving. As shown in FIGS. 10A and 10B, in the present example, the cut surface of the workpiece was extremely sharp.

Example 4
In Example 4, the object to be processed was changed to a silicon carbide (4H-SiC; band gap energy: 3.26 eV) substrate, and the focusing position of the laser was changed from the silicon carbide substrate to 30 μm inside. The silicon carbide (4H—SiC) substrate was cleaved by the same method as in FIG.

  FIG. 11A is a photomicrograph of the surface of the silicon carbide substrate obtained in Example 4 after laser irradiation. FIG. 11 (B) is a micrograph showing the surface further enlarged. As shown in FIGS. 11A and 11B, the width of the damaged region, that is, the width of the processing line was about 30 μm, and could be processed with high resolution. In Example 4, damaged areas and cracks were connected.

  The silicon carbide substrate irradiated with laser in Example 4 was cleaved by applying mechanical stress. Cleavage was easy. FIG. 12A is a photomicrograph showing a cross section obtained by the cleaving. FIG. 12B is a photomicrograph in which the cross section is further enlarged. As shown in FIGS. 12A and 12B, the crack extended to a depth (about 12 μm) of about 3% of the thickness of the silicon carbide substrate. Moreover, the split section was a flat surface, and a split section perpendicular to the surface of the workpiece could be obtained.

  FIG. 13A is a photomicrograph showing the cut surface of the surface of the silicon carbide substrate obtained by cleaving. FIG. 13B is a photomicrograph showing a cut surface on the back surface of the silicon carbide substrate obtained by cleaving. As shown in FIGS. 13A and 13B, in the present example, the cut surface of the workpiece was extremely sharp.

  The laser cleaving method according to the present invention includes, for example, forming a crack extending in the laser irradiation direction inside a transparent dielectric material substrate such as sapphire, which is a typical semiconductor device substrate, and a lower layer portion of the substrate It is useful as a laser cleaving method that can process the substrate material in a short time, with high accuracy and spatial resolution, while avoiding damage to a functional layer such as a semiconductor located in the substrate.

The figure which shows the phenomenon which occurs in this invention The figure showing the state where two or more laser pulses were introduced into one condenser lens The figure showing the state where a plurality of cracks were formed along the breaking line The block diagram which shows the structure of the laser processing apparatus of this invention The flowchart which shows the process using the laser processing apparatus of this invention Micrograph of surface and cross section of sapphire substrate of Example 1 Micrographs of the surface and cross section of the sapphire substrate of Example 2 Micrograph of the surface of the silicon carbide substrate of Example 3 Micrograph of the cross section of the silicon carbide substrate of Example 3 Micrograph of cut surface of silicon carbide substrate of Example 3 Micrograph of the surface of the silicon carbide substrate of Example 4 Micrograph of a cross section of the silicon carbide substrate of Example 4 Micrograph of cut surface of silicon carbide substrate of Example 4

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Processing object 11 Functional layer 20, 20 'Laser pulse 21 Laser condensing point 30 Ablation plasma 31 Stress-strain area | region 32 Shock wave 33 Crack 34 Damaged area | region 100 Laser processing apparatus 101 Laser light source 103 Telescope optical system 105 Polarizing plate 107, 107 'Dichroic mirror 109 Objective lens 111 Protection window plate 113 Stage 115 Measurement light source 117 Beam shaper 119 Half mirror 121 Photo detector 123 Controller 125 Light source for illumination 127 CCD camera 129 Computer 131 Monitor

Claims (13)

Generating a laser pulse;
Wherein the laser pulse, is passed through a condenser lens, a laser processing method and a step of irradiating the vicinity of the surface of the workpiece,
The processing object is sapphire or silicon carbide,
The pulse width of the laser pulse is 100 to 1000 femtoseconds,
The numerical aperture of the condenser lens is 0.1 to 0.5,
The pulse energy of the laser pulse that has passed through the condenser lens is 1-1000 μJ / pulse,
The pulse fluence on the surface of the workpiece of the laser pulse is 500-2500 J / cm ² ,
Ablation plasma is generated near the surface of the workpiece to form a damaged region on the surface of the workpiece, and a stress strain region extending in the laser pulse irradiation direction is formed inside the workpiece. do it,
The damaged region Ru is extended to cracks in the irradiation direction of the laser pulse inside the stress-strain region as a starting point,
Laser processing method. The processing object is placed on a stage,
The stage is moved at 10 to 2000 mm / s while repeating a process including the step of generating the laser pulse according to claim 1 and the step of irradiating the workpiece with the laser pulse that has passed through the condenser lens. Scanning the cutting line of the workpiece with the repeatedly generated laser pulses,
The laser processing method according to claim 1. The laser processing method according to claim 2, wherein the irradiation position of the laser pulse is controlled by moving the stage. The laser processing method according to claim 3, wherein the workpiece is transferred by 1 to 50 μm in one cycle time of the repeated process. In the workpiece, two or more damaged areas are formed along the breaking line,
The damaged areas are spaced apart from each other;
The laser processing method according to claim 3. In the workpiece, two or more damaged areas are formed along the breaking line,
The damaged areas are connected to each other;
The laser processing method according to claim 3. The laser processing method according to claim 3, wherein the breaking line is scanned once or twice or more. 2. The laser processing method according to claim 1, wherein a distance between the condenser lens and the object to be processed is within a range of a working distance of the condenser lens of ± 200 μm. The laser processing method according to claim 1, wherein a wavelength of the laser pulse is 1030 to 1600 nm. The laser processing method according to claim 1, wherein a repetition frequency of the laser pulse is 1 kHz to 1 MHz. The laser processing method according to claim 1, wherein the polarization direction of the laser pulse that has passed through the condenser lens is linearly polarized light, circularly polarized light, or elliptically polarized light. Generating two or more laser beams;
Passing all of the laser beams through one condenser lens;
Irradiating the vicinity of the surface of the workpiece with the laser beam that has passed through the condenser lens, and a laser processing method comprising:
The processing object is sapphire or silicon carbide,
The pulse width of the laser beam light is 100 to 1000 femtoseconds,
The numerical aperture of the condenser lens is 0.1 to 0.5,
The pulse energy of each laser beam passing through the condenser lens is 1-1000 μJ / pulse,
The pulse fluence on the surface of the workpiece of the laser pulse is 500-2500 J / cm ² ,
Ablation plasma is generated near the surface of the workpiece to form a damaged region on the surface of the workpiece, and a stress strain region extending in the laser pulse irradiation direction is formed inside the workpiece. do it,
The damaged region Ru is extended to cracks in the irradiation direction of the laser pulse inside the stress-strain region as a starting point,
Laser processing method. Splitting the laser beam into two or more;
Passing each of the laser beams through a separate condenser lens;
The laser beam having passed through each of the condenser lens, and a step of irradiating the vicinity of the surface of another workpiece respectively, a laser processing method having,
The processing object is sapphire or silicon carbide,
The pulse width of the laser beam light is 100 to 1000 femtoseconds,
The numerical aperture of the condenser lens is 0.1 to 0.5,
The pulse energy of the laser beam light that has passed through each of the condenser lenses is 1-1000 μJ / pulse,
The pulse fluence on the surface of the workpiece of the laser pulse is 500-2500 J / cm ² ,
Ablation plasma is generated near the surface of the workpiece to form a damaged region on the surface of the workpiece, and a stress strain region extending in the laser pulse irradiation direction is formed inside the workpiece. do it,
The damaged region Ru is extended to cracks in the irradiation direction of the laser pulse inside the stress-strain region as a starting point,
Laser processing method.