JP5143222B2 - Laser processing method - Google Patents

Description

The present invention relates to a laser processing how to form a large damage aspect ratio on the surface of the silicon carbide.

  Silicon carbide (silicon carbide; hereinafter abbreviated as “SiC”) is superior in voltage resistance and heat resistance compared to silicon (hereinafter abbreviated as “Si”). SiC is attracting attention as a material for semiconductor devices that support power electronics because it can reduce device power loss to about 1/10 compared to Si. However, since SiC is much harder than Si, it has been impossible to efficiently cut a SiC wafer with a diamond blade or the like that has been used conventionally.

  On the other hand, in recent years, a laser processing method has been proposed as a new technique for cutting glass wafers, semiconductor wafers, and the like. In the laser processing method, a laser beam is irradiated on the surface or the inside of the wafer, thereby forming damage that becomes a starting point of cutting on the surface or inside of the wafer. For example, Patent Document 1 discloses a method of forming a modified region by multiphoton absorption along a planned cutting line by irradiating a glass wafer or Si wafer with laser light. Thereafter, by applying mechanical stress to the wafer on which the modified region is formed, the wafer can be cut starting from the modified region.

  As in the laser processing method described in Patent Document 1, a laser processing method using multiphoton absorption generally irradiates linearly polarized laser light. When processing a hard material such as sapphire, it is common to irradiate a laser beam having a short pulse width such as a picosecond pulse laser beam or a femtosecond pulse laser beam.

JP 2005-313237 A

  As described above, since the SiC wafer is very hard compared to the Si wafer or the like, the diamond blade or the like conventionally used cannot be cut with high accuracy and efficiency.

  Therefore, the inventors tried to cut the SiC wafer by the laser processing method described above. That is, an attempt was made to form damage on the SiC wafer by irradiating the surface or inside of the SiC wafer with linearly polarized femtosecond pulsed laser light. However, with the conventional laser processing method, it has not been easy to perform high-quality processing at a high speed without disturbing the shape and with little debris (processing waste).

  The present invention has been made in view of the above points, and a laser processing method and a laser processing apparatus capable of forming damage with a large aspect ratio on the surface of SiC with high accuracy and high speed while suppressing the occurrence of debris. The purpose is to provide.

  The present inventor found that the above-mentioned problems can be solved by irradiating SiC with non-polarized laser light having a wavelength of 500 nm or more, contrary to the technical common sense in the field of laser processing, and further studies were made to complete the present invention. It was.

That is, the present invention relates to the following laser processing method.
[1] A laser processing method including a step of irradiating silicon carbide with non-polarized laser light having a wavelength of 500 nm or more to form damage on the surface of the silicon carbide.
[2] The laser processing according to [1], wherein the laser light is irradiated along a planned cutting line of the silicon carbide, and the damage is formed on a surface of the silicon carbide along the planned cutting line. Method.
[3] The laser processing method according to [1] or [2], wherein the laser beam is a pulsed laser beam having a pulse width of 100 nanoseconds or more.
[4] The laser processing method according to [1] or [2], wherein the laser beam is a continuous wave laser beam.
[5] The laser processing method according to any one of [1] to [4], wherein the wavelength of the laser beam is 10 μm or less.
[6] The laser processing method according to any one of [1] to [5], wherein the condensing point of the laser light is located within a range of 100 μm above the surface of the silicon carbide to 100 μm inside from the surface. .
[7] The laser processing method according to any one of [1] to [6], wherein the damage is formed by multiphoton absorption of the laser light.

The present invention also relates to the following laser processing apparatus.
[8] A laser processing apparatus that irradiates silicon carbide with laser light to form damage on the surface of the silicon carbide: a laser light source that emits laser light that is non-polarized and has a wavelength of 500 nm or more, and the non-polarized light And an optical system that irradiates silicon carbide with laser light having a wavelength of 500 nm or more.
[9] The laser processing apparatus according to [8], further including a drive unit that moves at least one of the optical system and the silicon carbide to relatively move the optical system and the silicon carbide.
[10] The laser processing apparatus according to [8] or [9], wherein the laser beam is a pulsed laser beam having a pulse width of 100 nanoseconds or more.
[11] The laser processing apparatus according to [8] or [9], wherein the laser beam is a continuous wave laser beam.
[12] The laser processing apparatus according to any one of [8] to [11], wherein the wavelength of the laser beam is 10 μm or less.

  According to the laser processing method and the laser processing apparatus of the present invention, damage with a large aspect ratio can be formed on the surface of SiC with high accuracy and high speed while suppressing the generation of debris. For example, if the laser processing method and laser processing apparatus of the present invention are used, a SiC wafer can be cut with high accuracy and at high speed.

It is a schematic diagram which shows an example of the cutting method of SiC using the laser processing method of this invention. FIG. 1A is a schematic diagram illustrating a state in which laser light is irradiated. FIG. 1B is a schematic diagram showing a state in which damage is formed in SiC. FIG. 1C is a schematic diagram showing a state in which SiC is cut. It is a schematic diagram which shows the structure of the laser processing apparatus which concerns on one embodiment of this invention. It is a schematic diagram for demonstrating shot pitch. It is a graph which shows the relationship between the polarization state of a pulse laser beam, and the depth of the formed damage. It is a photograph of the periphery of the processed part of the SiC wafer after irradiation with pulsed laser light. FIG. 5A is a photograph of a SiC wafer processed with a pulse laser beam with a pulse width of 30 nanoseconds, FIG. 5B is a photograph of a SiC wafer processed with a pulse laser beam with a pulse width of 100 nanoseconds, and FIG. It is a photograph of a SiC wafer processed with a pulse laser beam having a pulse width of 200 nanoseconds. It is a photograph of the periphery of the processed part of the SiC wafer after irradiation with continuous wave laser light. 6A is a photograph of the surface of the SiC wafer after laser processing, FIG. 6B is a photograph of a cross section of the SiC wafer after laser processing, and FIG. 6C is a portion surrounded by a broken line in the photograph of FIG. 6B. It is an enlarged photo. It is a graph which shows the relationship between the pulse width of a pulse laser beam, and the depth of the formed damage. It is the photograph of the periphery of the process part of a SiC wafer after performing laser processing using the laser I. 8A is a photograph of a cross section of a SiC wafer processed with an offset of 20 μm, FIG. 8B is a photograph of a cross section of the SiC wafer processed with an offset of 40 μm, and FIG. 8C is a cross section of the SiC wafer processed with an offset of 60 μm. FIG. 8D is a photograph of a cross section of a SiC wafer processed with an offset of 80 μm. It is the photograph around the process part of a SiC wafer after performing laser processing using the laser J. 9A is a photograph of a cross section of a SiC wafer processed at an offset of 0 μm, FIG. 9B is a photograph of a cross section of the SiC wafer processed at an offset of 20 μm, and FIG. 9C is a cross section of the SiC wafer processed at an offset of 40 μm. FIG. 9D is a photograph of a cross section of a SiC wafer processed with an offset of 60 μm, FIG. 9E is a photograph of a cross section of a SiC wafer processed with an offset of 80 μm, and FIG. 9F is a SiC processed with an offset of 100 μm. It is a photograph of the section of a wafer. It is the photograph around the process part of a SiC wafer after performing laser processing using the laser J. 10A is a photograph of the surface of a SiC wafer processed at an offset of 0 μm, FIG. 10B is a photograph of the surface of a SiC wafer processed at an offset of 20 μm, and FIG. 10C is a photograph of the surface of the SiC wafer processed at an offset of 40 μm. FIG. 10D is a photograph of the surface of the SiC wafer processed at an offset of 60 μm, FIG. 10E is a photograph of the surface of the SiC wafer processed at an offset of 80 μm, and FIG. 10F is an SiC processed at an offset of 100 μm. It is a photograph of the surface of a wafer. It is a graph which shows the relationship between the focal position (offset) of a pulse laser beam, and the depth of the formed damage. It is a graph which shows the relationship between the repetition frequency and shot pitch of a pulse laser beam, and the presence or absence of debris generation | occurrence | production. It is a photograph of the periphery of the processed part of the SiC wafer after irradiation with pulsed laser light. FIG. 13A is a photograph of the surface of the SiC wafer after laser processing under condition A (F: 100 kHz, S: 0.1 μm), and FIG. 13B shows a condition B (F: 100 kHz, S: 0.3 μm). FIG. 13C is a photograph of the surface of the SiC wafer after laser processing, and FIG. 13C is a photograph of the surface of the SiC wafer after laser processing under the condition C (F: 500 kHz, S: 0.1 μm). It is the photograph of the surface of the SiC wafer after carrying out laser processing on condition D (F: 500kHz, S: 0.4micrometer).

1. Laser Processing Method of the Present Invention The laser processing method of the present invention includes a step of irradiating a silicon carbide (SiC) to be processed with laser light to form damage (for example, a groove) on the surface of SiC. As will be described later, the laser processing method of the present invention is characterized in that the polarization state of the laser light applied to SiC is non-polarized and the wavelength of the laser light is 500 nm or more.

  FIG. 1 is a schematic diagram showing an example of cutting SiC using the laser processing method of the present invention. As shown in FIG. 1A, the relative position between the laser beam 100 and the SiC 110 is changed while irradiating the SiC 110 with the non-polarized laser beam 100. At this time, the condensing point of the laser beam 100 is located near the surface of the SiC 110 and moves along the planned cutting line 120 of the SiC 110. By scanning the non-polarized laser beam 100 in this way, a damage 130 having a large aspect ratio can be formed along the planned cutting line 120 as shown in FIG. 1B. As shown in FIG. 1C, the SiC 110 can be easily cleaved along the planned cutting line 120 by applying mechanical stress to the SiC 110 on which the damage 130 is formed.

  Hereinafter, the irradiation conditions of the laser beam in the laser processing method of the present invention will be described in detail.

[Polarization state]
One feature of the laser processing method of the present invention is that the polarization state of laser light applied to SiC is non-polarized. Here, “non-polarized laser light” means laser light in which the electric field vector of light is distributed substantially uniformly in all directions. It can be said that the non-polarized laser beam is an aggregate of linearly polarized laser beams having different polarization directions.

  In the laser processing method of the present invention, damage is formed using multiphoton absorption. The processing mechanism of the laser processing method of the present invention is not limited to this, but is presumed to be “processing by thermal effect”. That is, when non-polarized laser light having a wavelength of 500 nm or more is irradiated onto SiC, an interband transition of SiC electrons occurs due to multiphoton absorption (substantially two-photon absorption or three-photon absorption). Due to the heat released when the excited electrons relax, the temperature of the irradiated region rises locally. As a result, it is considered that SiC is decomposed, melted, or explode in volume at the irradiated site, and damage is formed.

  When damage with a large aspect ratio is to be formed using multiphoton absorption, it is necessary to allow laser light to enter from the surface of SiC to the deep inside. For this purpose, it is preferable to reduce the probability that multiphoton absorption occurs in SiC to some extent. In order to reduce the probability that multiphoton absorption occurs, it is conceivable to irradiate laser light having a wavelength with a small absorption cross-sectional area of multiphoton absorption. However, the absorption cross section of multiphoton absorption is only known to be an approximate value. Also, the wavelength dependence of the absorption cross section of multiphoton absorption is not well understood. Furthermore, it is not easy to arbitrarily adjust the wavelength of the laser beam. For the above reasons, it is not realistic to reduce the probability of multiphoton absorption by controlling the wavelength of laser light.

  Therefore, the present inventor examined whether the probability of multiphoton absorption occurring could be reduced by controlling parameters other than the wavelength. As a result, the present inventor has found that the probability of occurrence of multiphoton absorption inside SiC can be reduced by using non-polarized laser light. Here, “multiphoton absorption” means continuous simultaneous multiphoton absorption via a virtual level, which is substantially two-photon absorption or three-photon absorption.

For example, the probability W that two-photon absorption occurs can be expressed as the following formula (1) (reference: Koji Kushida, “Quantum Optics”, Asakura Modern Physics Course 8, Asakura Shoten, pp. 134). . Here, E ₁ and E ₂ are electric field (polarization) vectors of incident light.

  As can be seen from the above formula (1), the probability that two-photon absorption occurs depends greatly on the polarization direction of incident light. That is, the probability of two-photon absorption is maximized when the electric field vectors of the two photons of incident light are aligned. On the other hand, when the directions of the electric field vectors of two photons of incident light are orthogonal, the probability of occurrence of two-photon absorption is zero. Therefore, when the direction of the electric field vector of incident light is not aligned, that is, when unpolarized laser light is used, the probability that two-photon absorption will occur is reduced. As a result, the laser beam can penetrate deep into the SiC, and damage with a large aspect ratio can be formed.

  Actually, the depth of damage formed between the case of irradiation with non-polarized laser light and the case of irradiation with linearly polarized laser light were compared. As a result, it was possible to form deeper damage when irradiated with unpolarized laser light than when irradiated with linearly polarized laser light (see Example 1).

  As described above, in the laser processing method of the present invention, SiC is irradiated with non-polarized laser light in order to form damage with a large aspect ratio.

[wavelength]
One feature of the laser processing method of the present invention is that the wavelength of the laser light applied to SiC is 500 nm or more.

  As described above, in the laser processing method of the present invention, damage is formed by multiphoton absorption. Therefore, in order to realize the desired processing, it is necessary to avoid the occurrence of 1-photon 1 absorption. The band gap (Eg) of SiC is about 3 eV, which is 413 nm when converted into a wavelength. Therefore, in order to avoid the occurrence of one-photon one absorption, laser light having a wavelength exceeding 413 nm may be irradiated. In consideration of the absorption skirt, impurity level, and the like, it is preferable to irradiate a laser beam having a wavelength of 500 nm or more in order to surely avoid the occurrence of one-photon one absorption.

  By irradiating SiC with light having a wavelength of 500 nm or more, absorption due to electronic transition can be avoided. On the other hand, when SiC is irradiated with light having a wavelength of 10 μm or more, absorption due to vibrational transition occurs, which may prevent desired processing from being performed. Therefore, it is preferable that the wavelength of the laser beam irradiated to SiC is 10 μm or less.

[Oscillation method]
The laser beam applied to SiC may be a pulsed laser beam or a continuous wave (CW) laser beam. From the viewpoint of reducing the amount of debris (work scrap) generated and forming damage with a large aspect ratio, pulse laser light or continuous wave laser light (pulse width: infinite) with a pulse width of 100 nanoseconds or more is irradiated. It is preferable to do.

  By irradiating pulsed laser light or continuous wave laser light having a pulse width of 100 nanoseconds or more, the amount of debris generated during processing can be significantly reduced. On the other hand, when a pulse laser beam having a pulse width of less than 100 nanoseconds is irradiated, a large amount of debris may be generated (see Examples 2 and 3).

  In addition, the aspect ratio of damage formed can be increased by irradiation with pulsed laser light or continuous wave laser light having a pulse width of 100 nanoseconds or more. This is probably because the peak output decreases as the pulse width increases, and the probability of multiphoton absorption also decreases. On the other hand, when a pulse laser beam having a pulse width of less than 100 nanoseconds is irradiated, the aspect ratio of damage formed may be reduced (see Example 4).

  Here, the reasoning mechanism for the reason why the generation amount of debris is reduced by irradiating pulsed laser light or continuous wave laser light having a pulse width of 100 nanoseconds or more will be described. Table 1 shows the physical properties of SiC and Si.

  As shown in Table 1, the specific heat is almost the same between SiC and Si. Therefore, if the laser beam is irradiated under the same conditions, the temperature rises similarly in the vicinity of the condensing point, and thermal stress is similarly applied. On the other hand, since the fracture toughness value of SiC is significantly larger than the fracture toughness value of Si, the laser beam energy required for processing is larger in SiC than in Si. Therefore, in the case of processing SiC, the temperature rises in the vicinity of the condensing point at the time of processing, and the thermal stress becomes larger than when processing Si.

  However, the Young's modulus of SiC is significantly larger than the Young's modulus of Si. That is, SiC is less likely to be deflected by thermal stress due to expansion than Si. Therefore, SiC cannot release thermal stress by bending like Si. The melting point of SiC is 1000 ° C. higher than the melting point of Si. Therefore, SiC cannot release thermal stress by liquefying like Si. As a result, SiC cannot be released from thermal stress generated during laser processing, and is destroyed. For the above reasons, SiC is considered to be more easily crushed during laser processing than Si.

  Actually, when damage was formed on SiC by irradiating a pulse laser beam having a pulse width of 30 nanoseconds, a large amount of debris was observed around the formed damage (Example 2). reference). This is thought to be because, when processing with a pulse laser beam having a short pulse width of 30 nanoseconds, thermal expansion and stress generation accompanying the temperature rise occur rapidly, and SiC that cannot withstand the rapid stress is crushed. Moreover, since the cycle of heating and cooling was repeated for SiC, it is considered that SiC was easily crushed.

  The present inventor has examined means for suppressing the fracture of SiC due to the rapidly generated thermal stress. As a result, the present inventor considered that the crushing of SiC can be suppressed by increasing the pulse width of the pulse laser beam (decreasing the time between pulses).

  That is, by increasing the pulse width of the pulse laser beam, the rate of thermal stress generation can be reduced. As a result, it is thought that SiC crushing due to thermal stress is suppressed. Further, by shortening the interval between pulses of the pulse laser beam, it is possible to prevent SiC from being cooled between the pulses. As a result, it is thought that SiC crushing by heating and cooling cycles is suppressed.

  Actually, when damage was formed by irradiating a pulse laser beam having a pulse width of 100 nanoseconds, the amount of debris generated was significantly reduced. Further, when damage was formed by irradiating a pulse laser beam having a pulse width of 200 nanoseconds, almost no debris was observed (see Example 2). In addition, even when a continuous wave laser beam (pulse width: infinite) was irradiated to form damage, almost no debris was observed (see Example 3).

  As described above, from the viewpoint of reducing the amount of debris generated, it is preferable to irradiate SiC with pulsed laser light or continuous wave laser light having a pulse width of 100 nanoseconds or more.

[Others]
In the laser processing method of the present invention, the type of laser used as a laser light source is not particularly limited as long as it can emit laser light that is non-polarized and has a wavelength of 500 nm or more. Examples of such lasers include Ho lasers, Er lasers, various semiconductor lasers, and the like.

  The position of the condensing point of the laser light is preferably located in the vicinity of the surface of SiC. From the viewpoint of the processing efficiency and the width of damage, the position of the laser beam condensing point is preferably located within the range of 100 μm above the surface of SiC to 100 μm inside from the surface, and 20 μm above the surface of SiC. More preferably, it is located within the range of 80 μm from the inside.

If the laser light is pulsed laser light, it is preferable the light intensity density per pulse at the condensing position of the pulsed laser beam is in the range of 1~5000J / cm ^2. If the light intensity density per pulse is less than 1 J / cm ² , damage may not be sufficiently induced. On the other hand, when the light intensity density per pulse exceeds 5000 J / cm ^2, a large amount of debris may be generated, and the processing quality may be deteriorated. The repetition frequency of the pulse laser beam is not particularly limited, but is preferably in the range of 1 kHz to 10 MHz.

Further, from the viewpoint of reducing the amount of debris generated, it is preferable that the distance between the centers of the laser spots (shot pitch; see FIG. 3) is somewhat short. For example, when the pulse energy is 10 μJ, the amount of debris generated can be significantly reduced by adjusting the shot pitch so as to satisfy S <(2.5 × 10 ⁻⁴ ) F + 0.225. Here, “S” is the shot pitch (μm) of the pulse laser beam, and “F” is the repetition frequency (kHz) of the pulse laser beam. When the pulse energy changes, the coefficient of the mathematical formula changes. However, it is the same in that the amount of debris generated can be significantly reduced by appropriately shortening the shot pitch.

On the other hand, when the laser beam is a continuous wave laser beam, the light intensity density at the condensing position of the laser beam is preferably in the range of 1 × 10 ^{7 to} 5 × 10 ⁹ W / cm ² . When the light intensity density is less than 1 × 10 ⁷ W / cm ² , damage may not be sufficiently induced. On the other hand, when the light intensity density is more than 5 × 10 ⁹ W / cm ^2, a large amount of debris may be generated and the processing quality may be deteriorated.

  Means for carrying out the laser processing method of the present invention is not particularly limited. For example, the laser processing method of the present invention can be implemented using the laser processing apparatus of the present invention described below.

2. Laser Processing Apparatus of the Present Invention The laser processing apparatus of the present invention is an apparatus that forms damage on the surface of SiC by irradiating SiC to be processed with laser light. The laser processing apparatus of the present invention irradiates SiC with non-polarized laser light having a wavelength of 500 nm or more.

  The laser processing apparatus of the present invention includes at least a laser light source that emits laser light that irradiates SiC, and an optical system that irradiates SiC with laser light emitted from the laser light source. Hereinafter, each component will be described.

  The laser light source emits laser light that is not polarized and has a wavelength of 500 nm or more. As described above, the type of laser used as the laser light source is not particularly limited as long as it can emit non-polarized laser light having a wavelength of 500 nm or more. Examples of such lasers include Ho lasers, Er lasers, various semiconductor lasers, and the like.

  The optical system irradiates SiC with laser light emitted from the laser light source so that the focal point is located at a desired position near the surface of SiC. Usually, the optical system includes a telescope optical system that optimizes the beam diameter of the laser light, a condensing lens that condenses the laser light at a desired position, and the like. As described above, the laser processing apparatus of the present invention is characterized by irradiating SiC with non-polarized laser light. Therefore, unlike the conventional laser processing apparatus, it is not necessary to arrange a polarization adjuster such as a half-wave plate or a polarizing plate in the optical system.

  In many cases, the laser processing apparatus of the present invention includes a drive unit that relatively moves the optical system (laser light) and SiC. By relatively moving the optical system (laser light) and SiC, it is possible to irradiate the laser light along a planned cutting line of SiC. As a result, damage can be formed along the planned cutting line of SiC. The drive unit may move the stage on which the SiC is placed, may move the optical system, or may move both the stage and the optical system.

  In addition, as will be described in the embodiments described later, the laser processing apparatus of the present invention has a stage on which SiC to be processed is placed, an automatic aiming system for positioning a condensing point at a desired position, and the like. You may do it.

  As described above, the laser processing method and the laser processing apparatus of the present invention are characterized by irradiating non-polarized laser light to SiC to be processed. As described above, the conventional laser processing method and laser processing apparatus generally irradiate linearly polarized laser light. On the other hand, in the laser processing method and the laser processing apparatus of the present invention, contrary to the conventional technical common sense, non-polarized laser light is irradiated on the SiC to be processed instead of linearly polarized light. The fact that the non-polarized laser beam is suitable for processing of SiC is a finding first found by the present inventors.

  The laser processing method and the laser processing apparatus of the present invention irradiate laser light having a non-polarized wavelength and a wavelength of 500 nm or more to cause multiphoton absorption with a certain small probability, thereby causing damage on the surface of SiC with a high aspect ratio. It can be formed with high accuracy and high speed. Therefore, if the laser processing method and laser processing apparatus of this invention are utilized, a SiC wafer can be cut | disconnected with high precision and high speed.

  In addition, even if a non-polarized laser beam having a wavelength of 500 nm or more is irradiated to a substance other than SiC, a high aspect ratio damage cannot be formed with high accuracy and high speed as when SiC is irradiated.

As an example, a case where a typical difficult-to-work material such as quartz or sapphire is irradiated with non-polarized laser light having a wavelength of 500 nm or more will be described. In this case, since the band gap of these transparent dielectric materials is as large as 5 to 9 eV, 3-photon absorption or 4-photon absorption occurs only with light having a wavelength of 500 nm or more, and an interband transition of electrons can be induced only. In order to induce three-photon absorption or four-photon absorption with laser light having a long pulse width (nanosecond to microsecond), it is necessary to irradiate pulse laser light having a very large peak output (GW / cm ² or more). is there. However, when such intense light is condensed and irradiated, other nonlinear processes (dielectric breakdown) are always induced before three-photon absorption or four-photon absorption occurs, so that the shape of damage is greatly disturbed. Therefore, even if quartz or sapphire is irradiated with laser light that is not polarized and has a wavelength of 500 nm or more, only damage in a very disordered shape can be formed.

  In metal processing, a carbon dioxide laser (non-polarized light with a wavelength of 10 μm) may be irradiated. However, even with this method, high aspect ratio damage cannot be formed with high accuracy and high speed. In other words, since this method is a hot-melt process performed by directly exciting metal lattice vibrations, it is not possible to form damage with a high aspect ratio or to perform high-precision processing (with a spatial resolution of μm level). Can not.

3. Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited thereto.

  FIG. 2 is a schematic diagram showing a configuration of a laser processing apparatus (SiC wafer scribing apparatus) according to an embodiment of the present invention.

  As shown in FIG. 2, the laser processing apparatus 200 of the present invention includes a laser light source 210, a telescope optical system 220, a condenser lens 230, a stage 240, an AF camera 250, an XY stage controller 260, a Z controller 270, and a computer 280. Have

The laser light source 210 emits non-polarized laser light having a wavelength of 500 nm or more. The laser light source is, for example, a pulse laser beam having a wavelength of 500 nm to 10 μm, a pulse width of 100 nanoseconds or more, a repetition frequency of 1 kHz to 10 MHz, a light intensity density of 1 to 5000 J / cm ² per pulse, or a wavelength of 500 nm to 10 μm, a light intensity. A continuous wave laser beam having a density of 1 × 10 ^{7 to} 5 × 10 ⁹ W / cm ² is emitted.

  The telescope optical system 220 optimizes the beam diameter of the laser light emitted from the laser light source 210 in order to obtain a preferable processing shape.

  The condensing lens 230 condenses the laser light that has passed through the telescope optical system 220. For example, the condensing lens 230 is an objective lens for a microscope.

  The stage 240 has a mounting table on which a SiC (SiC wafer) 110 to be processed is mounted, and a drive mechanism that can move the mounting table. The drive mechanism can move the mounting table in the X-axis or Y-axis direction or rotate the X-axis or Y-axis as a center. SiC 110 on stage 240 is moved in the XY-axis direction along the planned cutting line by this drive mechanism.

  The AF camera 250 is a camera for acquiring a surface profile of a processed part of the SiC 110. The acquired profile is output to the computer 280.

  Based on an instruction from the computer 280, the XY stage controller 260 moves the stage 240 in the XY axis direction so that the condensing position of the laser light follows the planned cutting line of SiC 110.

  Based on an instruction from the computer 280, the Z controller 270 moves the condensing lens 230 in the Z-axis direction so that the condensing position of the laser light matches a desired position near the surface of the SiC 110.

  The computer 280 is connected to the laser light source 210, the AF camera 250, the XY stage controller 260, and the Z controller 270, and comprehensively controls these units. For example, the computer 280 controls the AF camera 250 and the XY stage controller 260 to acquire the surface profile of the SiC 110. In addition, the computer 280 controls the XY stage controller 260 and the Z controller 270 to scan the laser light along the planned cutting line of the SiC 110.

  Next, a procedure for cutting SiC 100 using laser processing apparatus 200 having the above configuration will be described.

  First, SiC 110 is placed on a stage 240 and a surface profile of SiC 110 is acquired by AF camera 250 and XY stage controller 260. Next, laser light is emitted from the laser light source 210 and irradiated near the surface of the SiC 110. At this time, the line to be cut is scanned with the laser beam by moving the stage 240 in the XY axis direction (horizontal direction) based on the surface profile acquired in advance. Thereby, damage with a large aspect ratio can be formed along the planned cutting line of SiC 110.

  Finally, mechanical stress is applied to the damaged SiC 110 to cleave the SiC 110 along the planned cutting line. Thereby, SiC (SiC wafer) 110 is divided into minute chips.

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

[Example 1]
Example 1 shows an experimental result in which the relationship between the polarization state of the pulse laser beam and the depth of damage in the case where damage is formed on the surface of the SiC wafer by irradiation with the pulse laser beam is shown.

  A SiC single crystal wafer was prepared as a processing object. A condensing point was set at a position of 20 μm inside from the surface of the wafer, and a non-polarized or linearly polarized pulsed laser beam was irradiated onto the wafer. At this time, the stage was moved in the XY axis direction (horizontal direction), and the wafer was irradiated with pulsed laser light along the planned cutting line of the wafer. The moving speed was adjusted so that the distance between the centers of the laser spots (shot pitch; see FIG. 3) was 0.05 to 0.5 μm. Table 2 shows the irradiation conditions of the pulse laser beam.

  As shown in Table 2, the irradiation conditions other than the polarization state are almost the same. In this experiment, since light with a wavelength of 1064 nm is irradiated, it is considered that damage is formed by three-photon absorption.

  FIG. 4 is a graph showing the relationship between the polarization state of pulsed laser light and the depth of damage formed. As described above, the “shot pitch” on the horizontal axis means the center-to-center distance between adjacent laser spots. From this graph, it can be seen that deeper damage can be formed when non-polarized pulse laser light is irradiated than when linearly polarized pulse laser light is irradiated. It can also be seen that the shorter the shot pitch, the greater the difference in damage depth.

  From the above results, it can be seen that when laser processing a SiC wafer, non-polarized laser light is preferable to linearly polarized laser light.

[Example 2]
Example 2 shows the experimental results of examining the relationship between the pulse width of the pulse laser beam and the amount of debris generated when the SiC wafer is damaged by irradiation with the pulse laser beam.

  The same SiC wafer as Example 1 was prepared as a processing target. The focal point was aligned with the surface of the wafer (0 μm from the surface), and pulsed laser light having a pulse width of 30 nanoseconds, 100 nanoseconds, or 200 nanoseconds was irradiated onto the wafer. At this time, the stage was moved in the XY axis direction (horizontal direction), and the wafer was irradiated with pulsed laser light along the planned cutting line of the wafer. Table 3 shows the irradiation conditions of the pulse laser beam.

  As shown in Table 3, the irradiation conditions other than the pulse width are exactly the same. In this experiment as well, since light with a wavelength of 1064 nm is irradiated, it is considered that damage is formed by three-photon absorption.

  FIG. 5 is a photograph of the periphery of the processed portion of the SiC wafer after laser processing. FIG. 5A is a photograph of a SiC wafer processed with laser C (pulse width 30 nanoseconds), FIG. 5B is a photograph of a SiC wafer processed with laser D (pulse width 100 nanoseconds), and FIG. It is a photograph of a SiC wafer processed with laser E (pulse width 200 nanoseconds). Both photographs are taken of the surface of a SiC wafer. The depth of damage formed was about 100 μm.

  As shown in FIG. 5A, when the pulse laser beam having a pulse width of 30 nanoseconds was irradiated, a large amount of debris was generated around the formed damage. On the other hand, as shown in FIGS. 5B and 5C, when the pulse laser beam having a pulse width of 100 nanoseconds or 200 nanoseconds was irradiated, almost no debris was observed around the formed damage. Further, when FIG. 5B and FIG. 5C are compared, there was less debris when the pulse laser beam having a pulse width of 200 nanoseconds was irradiated than when the pulse laser beam having a pulse width of 100 nanoseconds was irradiated.

  From the above results, when laser processing is performed by irradiating a SiC wafer with pulsed laser light, pulsed laser light having a pulse width of 100 nanoseconds or more is preferable to pulsed laser light having a pulse width of less than 100 nanoseconds. I understand that.

[Example 3]
Example 3 shows an experimental result in which damage is formed on a SiC wafer by irradiating continuous wave laser light.

  The same SiC wafer as Example 1 was prepared as a processing target. A converging point was set at a position of 20 μm from the surface of the wafer to irradiate the wafer with continuous wave laser light. At this time, the stage was moved in the XY-axis direction (horizontal direction), and the wafer was irradiated with continuous wave laser light along the planned cutting line of the wafer. Table 4 shows the irradiation conditions of the continuous wave laser beam. In this experiment as well, since light with a wavelength of 1064 nm is irradiated, it is considered that damage is formed by three-photon absorption.

  FIG. 6 is a photograph of the periphery of the processed portion of the SiC wafer after laser processing. 6A is a photograph of the surface of the SiC wafer after laser processing, FIG. 6B is a photograph of a cross section of the SiC wafer after laser processing, and FIG. 6C is a portion surrounded by a broken line in the photograph of FIG. 6B. It is an enlarged photo.

  As shown in FIG. 6A, even when the continuous wave laser beam was irradiated, almost no debris was observed around the formed damage. Further, as shown in FIGS. 6B and 6C, when the continuous wave laser beam was irradiated, the depth of the formed damage was 64 μm.

  From the above results, it can be understood that extremely deep damage can be formed by irradiating a SiC wafer with continuous wave laser light and laser processing.

[Example 4]
Example 4 shows the experimental results of examining the relationship between the pulse width of the pulse laser beam and the depth of damage formed when the SiC wafer is damaged by irradiation with the pulse laser beam.

  The same SiC wafer as Example 1 was prepared as a processing target. The focal point was set at a position of 20 μm from the surface of the wafer, and the wafer was irradiated with pulsed laser light having a pulse width of 30 nanoseconds or 200 nanoseconds. At this time, the stage was moved in the XY axis direction (horizontal direction), and the wafer was irradiated with pulsed laser light along the planned cutting line of the wafer. The moving speed was adjusted so that the shot pitch was 0.01 to 0.50 μm. Table 5 shows the irradiation conditions of the pulse laser beam.

  As shown in Table 5, the irradiation conditions other than the pulse width are almost the same. In this experiment as well, since light with a wavelength of 1064 nm is irradiated, it is considered that damage is formed by three-photon absorption.

  FIG. 7 is a graph showing the relationship between the pulse width of the pulse laser beam and the depth of damage formed. From this graph, it can be seen that deeper damage can be formed when the pulse laser beam having a pulse width of 200 nanoseconds is irradiated than when the pulse laser beam having a pulse width of 30 nanoseconds is irradiated.

  From the above results, it can be seen that when laser processing is performed by irradiating a SiC wafer with a pulsed laser beam, a longer pulse width is preferable not only from the amount of debris generated but also from the viewpoint of the depth of damage to be formed.

[Example 5]
Example 5 shows the experimental results of examining the relationship between the position of the focal point and the depth of damage formed when damage is formed on the SiC wafer by irradiation with pulsed laser light.

  In this embodiment, the distance between the surface of the SiC wafer to be processed and the focal point is called “offset”. When the condensing point is located inside the SiC wafer, the offset takes a positive value, and when the condensing point is located outside (above) the SiC wafer, the offset takes a negative value. Specifically, when the offset is 0 μm, the condensing point is located on the surface of the SiC wafer. When the offset is + x μm, the focal point is located inside x μm from the surface of the SiC wafer. On the other hand, when the offset is −x μm, the focal point is located outside (upward) x μm from the surface of the SiC wafer.

  The same SiC wafer as Example 1 was prepared as a processing target. The condensing point was set to a position from 20 μm above the wafer surface (offset−20 μm) to 100 μm inside (offset + 100 μm) from the wafer surface, and pulsed laser light was applied to the wafer. At this time, the stage was moved in the XY axis direction (horizontal direction), and the wafer was irradiated with pulsed laser light along the planned cutting line of the wafer. Table 6 shows the irradiation conditions of the pulse laser beam.

  As shown in Table 6, the irradiation conditions other than the focal position (offset) of the laser light are substantially the same. In this experiment as well, since light with a wavelength of 1064 nm is irradiated, it is considered that damage is formed by three-photon absorption.

  FIG. 8 is a photograph of the periphery of the processed portion of the SiC wafer after laser processing using laser I. 8A is a photograph of a cross section of a SiC wafer processed with an offset of 20 μm, FIG. 8B is a photograph of a cross section of the SiC wafer processed with an offset of 40 μm, and FIG. 8C is a cross section of the SiC wafer processed with an offset of 60 μm. FIG. 8D is a photograph of a cross section of a SiC wafer processed with an offset of 80 μm.

  9 and 10 are photographs of the periphery of the processed portion of the SiC wafer after laser processing using the laser J. FIG. 9A is a photograph of a cross section of a SiC wafer processed at an offset of 0 μm, FIG. 9B is a photograph of a cross section of the SiC wafer processed at an offset of 20 μm, and FIG. 9C is a cross section of the SiC wafer processed at an offset of 40 μm. FIG. 9D is a photograph of a cross section of a SiC wafer processed with an offset of 60 μm, FIG. 9E is a photograph of a cross section of a SiC wafer processed with an offset of 80 μm, and FIG. 9F is a SiC processed with an offset of 100 μm. It is a photograph of the section of a wafer.

  10A is a photograph of the surface of the SiC wafer processed with an offset of 0 μm, FIG. 10B is a photograph of the surface of the SiC wafer processed with an offset of 20 μm, and FIG. 10C is a photograph of the SiC wafer processed with an offset of 40 μm. FIG. 10D is a photograph of the surface of a SiC wafer processed at an offset of 60 μm, FIG. 10E is a photograph of the surface of a SiC wafer processed at an offset of 80 μm, and FIG. 10F is processed at an offset of 100 μm. It is the photograph of the surface of the manufactured SiC wafer. From these photographs, it can be seen that the amount of debris decreases as the offset increases (when the focal position is located inside the SiC).

  FIG. 11 is a graph showing the relationship between the focal position (offset) of pulse laser light and the depth of damage formed. From this graph, it can be seen that sufficiently deep damage can be formed by setting the offset within the range of −20 to +100 μm. It can also be seen that the change in the depth of damage is small (Δ6 μm or less) when the offset is in the range of −20 to +80 μm.

  From the above results, when laser processing is performed by irradiating a SiC wafer with pulsed laser light, it is sufficient if at least the focal position of the pulsed laser light is within a range of 20 μm above the surface of SiC to 100 μm inside from the surface. It can be seen that damage can be formed.

[Example 6]
Example 6 shows the experimental results of examining the relationship between the laser spot center distance (shot pitch) and the amount of debris generated when the SiC wafer is damaged by irradiation with pulsed laser light.

  The same SiC wafer as Example 1 was prepared as a processing target. The focal point was aligned with the surface of the wafer (0 μm from the surface), and the wafer was irradiated with pulsed laser light having a repetition frequency of 100 to 500 kHz. At this time, the stage was moved in the XY axis direction (horizontal direction), and the wafer was irradiated with pulsed laser light along the planned cutting line of the wafer. The moving speed was adjusted so that the shot pitch was 0.1 to 0.4 μm. Table 7 shows the irradiation conditions of the pulse laser beam.

  Under the above conditions, the boundary condition of whether or not debris was generated (many) was examined in detail by changing the repetition frequency and shot pitch of the pulse laser beam. As a result, when the repetition frequency was 100 kHz, it was observed that debris was generated when the shot pitch was 0.25 μm or more. Similarly, when the repetition frequency was 300 kHz, it was observed that debris was generated when the shot pitch was 0.3 μm or more. When the repetition frequency was 500 kHz, it was observed that debris was generated when the shot pitch was 0.35 μm or more.

FIG. 12 is a graph showing the relationship between the repetition frequency and shot pitch of pulsed laser light and the occurrence of debris, created based on the above results. The horizontal axis represents the repetition frequency F (kHz) of the pulse laser beam, and the vertical axis represents the shot pitch S (μm) of the pulse laser beam. As shown in this graph, when the pulse energy is 10 μJ, the boundary condition for the presence or absence of debris (multiple) is S = (2.5 × 10 ⁻⁴ ) F + 0.225. That is, debris was generated when S ≧ (2.5 × 10 ⁻⁴ ) F + 0.225, whereas almost no debris was generated when S <(2.5 × 10 ⁻⁴ ) F + 0.225.

  In order to confirm that the above conditional expression is correct, it was further examined whether or not machining waste was generated under the conditions indicated by A to D in FIG.

  FIG. 13 is a photograph of the periphery of the processed portion of the SiC wafer after laser processing. FIG. 13A is a photograph of the surface of the SiC wafer after laser processing under condition A (F: 100 kHz, S: 0.1 μm), and FIG. 13B shows a condition B (F: 100 kHz, S: 0.3 μm). FIG. 13C is a photograph of the surface of the SiC wafer after laser processing, and FIG. 13C is a photograph of the surface of the SiC wafer after laser processing under the condition C (F: 500 kHz, S: 0.1 μm). It is the photograph of the surface of the SiC wafer after carrying out laser processing on condition D (F: 500kHz, S: 0.4micrometer).

As shown in FIG. 13B and FIG. 13D, when processed with S ≧ (2.5 × 10 ⁻⁴ ) F + 0.225, debris was generated around the formed damage. On the other hand, as shown in FIGS. 13A and 13C, when processed at S <(2.5 × 10 ⁻⁴ ) F + 0.225, almost no debris was observed around the formed damage.

  From the above results, it can be seen that when laser processing is performed by irradiating a SiC wafer with pulsed laser light, the amount of debris generated can be reduced by shortening the shot pitch so as to satisfy a predetermined condition.

  The laser processing method and laser processing apparatus of the present invention can form high-accuracy and high-speed damage on SiC, which has been difficult to process, with a high aspect ratio. Therefore, the laser processing method and laser processing apparatus of the present invention are useful as a SiC scribing technique and a dicing technique.

DESCRIPTION OF SYMBOLS 100 Laser beam 110 Silicon carbide 120 Planned cutting line 130 Damage 200 Laser processing apparatus 210 Laser light source 220 Telescope optical system 230 Condensing lens 240 Stage 250 AF camera 260 XY stage controller 270 Z controller 280 Computer

Claims (4)

Unpolarized light a and the wavelength 500nm or more of the pulsed laser light in silicon carbide by irradiating along the line to cut the silicon carbide, saw including a step of forming a damage to the surface of the silicon carbide along the line to cut ,
The damage is formed by multiphoton absorption of the pulsed laser light.
Laser processing method. Pulse width of the pulsed laser beam is 1 00 is on nanosecond or more, the laser processing method according to claim 1. The laser processing method according to claim 1, wherein the pulsed laser beam has a wavelength of 10 μm or less. 2. The laser processing method according to claim 1, wherein a condensing point of the pulsed laser light is located within a range of 100 μm above the surface of the silicon carbide to 100 μm inside from the surface.