JP5385999B2 - Laser processing method - Google Patents

Description

The present invention relates to a laser processing how to form lesions on the surface of the silicon carbide substrate.

  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, a conventionally used diamond blade or the like cannot efficiently cut the SiC substrate.

  On the other hand, in recent years, a laser processing method has been proposed as a new technique for cutting glass substrates and semiconductor substrates. In the laser processing method, the laser beam is irradiated on the surface or the inside of the substrate, thereby forming damage that becomes the starting point of the division on the surface or the inside of the substrate. Thereafter, by applying mechanical stress to the damaged substrate, the substrate can be divided starting from the damage.

  In such a laser processing method, debris (processing waste) may be generated when the laser beam is irradiated. If debris adheres to the substrate, the reliability and yield of the product will decrease. For this reason, various methods for suppressing adhesion of debris have been proposed (see, for example, Patent Documents 1 to 3).

  For example, the invention described in Patent Document 1 prevents debris from adhering to the Si substrate by forming a protective film on the surface of the Si substrate before laser processing. In the present invention, it is necessary to remove the protective film after laser processing. In addition, the invention described in Patent Document 2 prevents debris from adhering to the substrate by sucking and removing the debris before adhering to the substrate. In the present invention, it is necessary to provide a dedicated nozzle for the laser processing apparatus. Further, the invention described in Patent Document 3 prevents the occurrence of debris by forming damage inside the substrate. In the present invention, in order to divide the substrate, it is necessary to scan the laser beam a plurality of times to develop cracks generated in the substrate.

JP 2010-5629 A Japanese Patent Laid-Open No. 2005-88068 JP 2011-2000926 A

  As described above, since the SiC substrate is very hard as compared with the Si substrate or the like, the diamond blade or the like conventionally used cannot be cut with high accuracy and efficiency. Therefore, the present inventors tried to divide the SiC substrate by a conventional general laser processing method. However, with the conventional laser processing method, a large amount of debris adheres to the SiC substrate, and high quality processing cannot be performed. Moreover, as a method of suppressing adhesion of debris, there are methods described in the above-mentioned Patent Documents 1 to 3, but each method requires a new process or equipment.

  The present invention has been made in view of the above points, and a laser processing method capable of forming damage on the surface of a SiC substrate with high accuracy and high speed while suppressing generation of debris only by irradiation with laser light. And it aims at providing a laser processing apparatus.

  The present inventor has found that the above problem can be solved by using a laser beam having a wavelength of 500 nm or more, contrary to technical common sense in the field of laser processing. More specifically, the present inventor has determined that the SiC substrate has a pulse laser beam having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more so that the distance between the centers of irradiation spots exceeds 0 μm and is less than 1.7 μm. The present inventors have found that the above-mentioned problems can be solved by irradiating the film, and have further studied to complete the present invention.

That is, the present invention relates to the following laser processing method.
[1] A laser processing method including a step of irradiating a silicon carbide substrate with a pulsed laser beam through a lens to form damage on a surface of the silicon carbide substrate, wherein the wavelength of the pulsed laser beam is 500 nm or more The pulse energy of the pulse laser beam is 70 μJ or less; the repetition frequency of the pulse laser beam is 80 kHz or more; and the distance between centers of the irradiation spots of the pulse laser beam on the surface of the silicon carbide substrate is 0 μm And a laser processing method of less than 1.7 μm.
[2] The pulse laser beam is irradiated along a planned division line of the silicon carbide substrate; the damage is formed on the surface of the silicon carbide substrate along the planned division line. Laser processing method.
[3] The laser processing method according to [1] or [2], wherein a pulse width of the pulsed laser light is 100 nanoseconds or more.
[4] The laser processing method according to any one of [1] to [3], wherein the pulsed laser beam has a wavelength of 10 μm or less.
[5] The laser processing method according to any one of [1] to [4], wherein the condensing point of the pulse laser beam is located in a range of 100 μm above the surface of the silicon carbide substrate to 100 μm from the surface to the inside. .
[6] When the focal depth of the lens is b (μm) and the damage depth is d (μm), 0.7 ≦ d / b ≦ 1.6, [1] to [5] ] The laser processing method in any one of.

The present invention also relates to the following laser processing apparatus.
[7] A laser light source that emits a pulse laser beam having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more, an optical system that irradiates the silicon carbide substrate with the pulse laser beam, the optical system, and the silicon carbide substrate A driving unit that relatively moves the optical system and the silicon carbide substrate by moving at least one of the following: a distance between centers of the irradiation spots of the pulsed laser light on the surface of the silicon carbide substrate is A laser processing apparatus that exceeds 0 μm and is less than 1.7 μm.
[8] The laser processing apparatus according to [7], wherein a pulse width of the pulsed laser light is 100 nanoseconds or more.
[9] The laser processing apparatus according to [7], wherein the pulse laser beam has a wavelength of 10 μm or less.

  According to the laser processing method and the laser processing apparatus of the present invention, it is possible to form damage on the surface of the SiC substrate with high accuracy and at 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, the SiC substrate can be divided with high accuracy and at high speed.

1A to 1D are schematic views showing an example of a step of dividing an SiC substrate using the laser processing method of the present invention. It is a schematic diagram for demonstrating shot pitch. It is a schematic diagram for demonstrating the initial condition of simulation. 4A to 4F are graphs showing simulation results. It is a schematic diagram which shows the structure of the laser processing apparatus which concerns on one embodiment of this invention. 6A to 6C are photographs showing examples of the periphery of the processed portion of the SiC substrate after laser processing. 7A to 7F are photographs of the periphery of the processed portion of the SiC substrate after irradiation with pulsed laser light. 8A and 8B are photographs of the periphery of the processed portion of the SiC substrate after irradiation with pulsed laser light. 9A to 9E are photographs of the periphery of the processed portion of the SiC substrate after irradiation with pulsed laser light. 10A to 10D are photographs of the periphery of the processed portion of the SiC substrate after irradiation with pulsed laser light. FIGS. 11A to 11G are photographs of fractured surfaces of a SiC substrate laser-processed using a lens having a depth of focus of 15 μm. 12A to 12G are photographs of a fractured surface of a SiC substrate laser-processed using a lens having a focal depth of 26 μm.

1. Laser processing method of the present invention The laser processing method of the present invention includes the step of irradiating a silicon carbide (SiC) substrate to be processed with pulsed laser light to form damage (for example, grooves) on the surface of the SiC substrate. As will be described later, the laser processing method of the present invention includes 1) irradiating a pulse laser beam having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more, and 2) the pulse laser beam on the surface of the SiC substrate. The distance between the centers of the irradiation spots (hereinafter referred to as “shot pitch”; see FIG. 2) is less than 1.7 μm.

  FIG. 1 is a schematic diagram showing an example of dividing a SiC substrate using the laser processing method of the present invention. As shown in FIG. 1A, the relative position between the pulse laser beam 100 and the SiC substrate 110 while irradiating the SiC substrate 110 with the pulse laser beam 100 having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more. change. At this time, the condensing point of the pulsed laser light 100 is located outside, on the surface, or inside the SiC substrate 110, and the planned dividing line 120 of the SiC substrate 110 is such that the shot pitch of the irradiation spot is less than 1.7 μm. Move along. By scanning the predetermined pulse laser beam 100 in this way, as shown in FIG. 1B, the damage 130 can be formed along the planned division line 120 (scribing process). Thereafter, as shown in FIG. 1C and FIG. 1D, the SiC substrate 110 is easily cleaved along the division line 120 by applying a bending force and a tensile force to the SiC substrate 110 on which the damage 130 is formed. (Break process and expanding process).

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

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

  In the laser processing method of the present invention, damage is formed by multiphoton absorption, absorption by impurities, absorption by lattice defects, or the like. 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 the SiC substrate with laser light having a wavelength of 500 nm or more, absorption due to electron transition can be avoided, and the amount of debris generated during processing can be significantly reduced (see Example 2). On the other hand, when a SiC substrate is irradiated with laser light having a wavelength of less than 500 nm, a large amount of debris may be generated. If a SiC substrate is irradiated with a laser beam having a wavelength of 10 μm or more, absorption due to vibration transition occurs, and there is a possibility that desired processing cannot be performed. Therefore, it is preferable that the wavelength of the laser beam irradiated to the SiC substrate is 10 μm or less.

[Pulse energy]
One feature of the laser processing method of the present invention is that the pulse energy of the pulse laser beam applied to the SiC substrate is 70 μJ or less. By setting the pulse energy to 70 μJ or less, the amount of debris generated during processing can be significantly reduced (see Example 3). On the other hand, when a pulse laser beam having a pulse energy exceeding 70 μJ is irradiated, a large amount of debris may be generated.

  Here, the inferred mechanism for the reason that the generation amount of debris is reduced by irradiating pulsed laser light having a pulse energy of 70 μJ or less 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 pulse laser beam is irradiated under the same conditions, the temperature rises similarly in the vicinity of the condensing point, and the 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 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. And if excessive energy is supplied to SiC, it will be thought that excessive stress will be added to a peripheral region and it will be crushed. Therefore, if SiC is processed with pulse laser light having a high pulse energy (over 70 μJ), SiC is easily crushed and a large amount of debris is generated.

  Therefore, from the viewpoint of reducing the amount of debris generated, it is preferable to irradiate the SiC substrate with pulsed laser light having a pulse energy of 70 μJ or less. For the same reason, the pulse width of the pulse laser beam is preferably 100 nanoseconds or more. By increasing the pulse width, the peak output of the pulse laser beam can be reduced, and as a result, SiC fracture can be suppressed.

[Spatial and temporal intervals of irradiation spots]
In the laser processing method of the present invention, the repetition frequency of the pulsed laser light applied to the SiC substrate is 80 kHz or more, the shot pitch of the pulsed laser light on the surface of the SiC substrate (see FIG. 2) exceeds 0 μm, and 1. One feature is that it is less than 7 μm. By adjusting the repetition frequency and the shot pitch to be within the above ranges, the amount of debris generated during processing can be significantly reduced (see Example 1 and Example 4). On the other hand, if the repetition frequency and shot pitch are out of the above ranges, a large amount of debris may be generated.

  As described above, when the SiC substrate is irradiated with pulsed laser light, the thermal stress accompanying the cooling cycle is repeatedly generated. At this time, SiC that cannot withstand the thermal stress generated suddenly is crushed and debris is generated. The present inventor examined a means for suppressing such SiC crushing. As a result, the time interval of pulse laser light irradiation and the shot pitch of the irradiation spot were shortened to suppress a rapid temperature change, thereby crushing SiC. We thought that we can suppress.

  As described above, by reducing the pulse energy 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. Moreover, it is possible to prevent SiC from being rapidly cooled between pulses by increasing the repetition frequency of the pulse laser beam and shortening the shot pitch of the irradiation spot. As a result, it is thought that SiC crushing by heating and cooling cycles is suppressed.

The inventor simulated the temperature change of the SiC substrate when irradiated with pulsed laser light based on the heat conduction equation. FIG. 3 is a schematic diagram (cross-sectional view of a SiC substrate) showing simulation conditions. As shown in FIG. 3, it is assumed that an SiC substrate having a thickness of 150 μm is irradiated with pulsed laser light, and each point on the optical axis reaches 2730 ° C. (melting point of SiC). As shown in the figure, it is assumed that air at 23 ° C. is convection around the SiC substrate. The thermal conductivity of the SiC substrate is assumed to be ^{100Wm -1 K} -1 or ^{350Wm -1 K} -1. With this state at time t = 0 (μ seconds), temperature changes were simulated at four points along the optical axis (T1, T2, T3, and T4).

4A to 4C are graphs showing simulation results of temperature changes at respective points when the thermal conductivity is 100 Wm ⁻¹ K ⁻¹ . FIG. 4A is a graph showing a temperature change during 0 to 1 microsecond after pulse laser light irradiation, and FIG. 4B is a graph showing a temperature change between 0 and 10 microsecond after pulse laser light irradiation. FIG. 4C is a graph showing a temperature change during 0 to 1 millisecond after irradiation with the pulse laser beam. 4D to 4F are graphs showing simulation results of temperature changes at respective points when the thermal conductivity is 350 Wm ⁻¹ K ⁻¹ . FIG. 4D is a graph showing a temperature change between 0 and 1 microsecond after pulse laser light irradiation, and FIG. 4E is a graph showing a temperature change between 0 and 10 microseconds after pulse laser light irradiation. FIG. 4F is a graph showing a temperature change during 0 to 1 millisecond after irradiation with the pulse laser beam. In each graph, “■” indicates the temperature of T1, “●” indicates the temperature of T2, “▲” indicates the temperature of T3, and “▼” indicates the temperature of T4 (each plot has almost the same position). ).

  As shown in the graphs of FIGS. 4A, 4B, 4D, and 4E, the temperature is maintained at each point along the optical axis up to 10 microseconds after irradiation with the pulse laser beam. This means that when the repetition frequency is 100 kHz, the temperature hardly decreases between pulses. On the other hand, as shown in the graphs of FIG. 4C and FIG. 4F, the temperature is reduced by about 5 ° C. at each point on the optical axis at the point of 1 millisecond after the pulse laser beam irradiation. This means that when the repetition frequency is 1 kHz, the temperature drops by about 5 ° C. between pulses.

  As described above, from the viewpoint of reducing the amount of generated debris, it is preferable to perform processing while maintaining a molten state rather than providing a cooling cycle. From the above simulation results, it is suggested that the amount of debris generated can be reduced by setting the repetition frequency of the pulsed laser light to around 100 kHz or more. According to an experiment by the present inventor, it has been found that the amount of debris generated can be significantly reduced by setting the repetition frequency of the pulse laser beam to 80 kHz or more (see Example 4). Therefore, the repetition frequency of the pulse laser beam is preferably 80 kHz or more. For the same reason, it is preferable that the shot pitch of the pulse laser beam is more than 0 μm and less than 1.7 μm.

[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 of pulsed laser light having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz 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 beam is not particularly limited, and may be any of the outside, the surface, or the inside of the SiC substrate. From the viewpoint of processing efficiency and the width of damage, the position of the condensing point of the laser light is preferably located within the range of 100 μm above the surface of the SiC substrate to 100 μm inside from the surface, and 20 μm above the surface of the SiC substrate. -More preferably, it is located within the range of 80 μm from the surface. Here, “the position of the laser beam condensing point” means the position of the condensing point (lens offset) when it is assumed that the refractive index of the SiC substrate is the same as that of air.

  When the SiC substrate is divided from the damage after the damage is formed on the SiC substrate by the laser processing method of the present invention, the height of the unevenness of the fractured surface may increase depending on the conditions. Thus, it is not preferable from the viewpoint of processing accuracy that the height of the unevenness of the fractured surface is increased. The present inventor has assumed that 0.7 ≦ d / b ≦ when the focal depth (Rayleigh length) of the condenser lens is b (μm) and the depth of damage formed on the SiC substrate is d (μm). It has been found that when the processing conditions are adjusted to satisfy 1.6, the smoothness of the fractured surface is improved (see Example 5). Therefore, when smoothness of the fractured surface is required, it is preferable to adjust various conditions so as to satisfy the above conditions. When “d / b” is less than 0.7, the damage is shallow, and it is not possible to divide appropriately, and the smoothness of the fractured surface may be reduced. On the other hand, when “d / b” exceeds 1.6, the reason is unclear, but the smoothness of the fractured section tends to decrease (see Example 5).

  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 irradiates a SiC substrate to be processed with pulsed laser light to form damage on the surface of the SiC substrate. The laser processing apparatus of the present invention irradiates a SiC substrate with a pulse laser beam having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more so that the shot pitch of the irradiation spot exceeds 0 μm and less than 1.7 μm. It is characterized by doing.

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

  The laser light source emits pulsed laser light having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more. As described above, the type of laser used as the laser light source is not particularly limited as long as pulsed laser light having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more can be emitted. Examples of such lasers include Ho lasers, Er lasers, various semiconductor lasers, and the like.

  The optical system irradiates the SiC substrate with laser light emitted from the laser light source so that the focal point is located at a desired position. 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.

  The drive unit relatively moves the optical system (laser beam) and the SiC substrate so that the pulsed laser beam is irradiated along the planned division line of the SiC substrate. Further, the drive unit relatively moves the optical system (laser light) and the SiC substrate so that the shot pitch of the pulsed laser light exceeds 0 μm and is less than 1.7 μm. The drive unit may move the stage on which the SiC substrate 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 includes a stage on which a SiC substrate to be processed is placed, an automatic aiming system for positioning a focusing point at a desired position, and the like. You may have.

  As described above, the laser processing method and the laser processing apparatus of the present invention use pulse laser light having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more, and the shot pitch of the irradiation spot exceeds 0 μm and less than 1.7 μm. By irradiating the SiC substrate so as to be, damage can be formed with high accuracy and high speed without causing almost any debris on the surface of the SiC substrate. Therefore, if the laser processing method and laser processing apparatus of the present invention are used, the SiC substrate can be divided with high accuracy and at high speed.

  In addition, even if a pulse laser beam having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more is irradiated to a substance other than SiC, the damage is caused with high accuracy without causing almost any debris as when irradiated to SiC. It cannot be formed at high speed.

As an example, a case where pulsed laser light having a wavelength of 500 nm or more is irradiated onto typical difficult-to-work materials such as quartz and sapphire 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 (insulation breakdown) are necessarily induced before three-photon absorption or four-photon absorption occurs, so that a large amount of debris is generated and the shape of the damage is generated. Will be greatly disturbed. Therefore, even if quartz or sapphire is irradiated with laser light having a wavelength of 500 nm or more, only a very disordered shape can be formed.

  In metal processing, a carbon dioxide laser (wavelength: 10 μm) may be irradiated. However, even with this method, damage cannot be formed with high accuracy and high speed. That is, since this method is a hot-melt process performed by directly exciting a metal lattice vibration, high-accuracy processing (spatial resolution of μm level) cannot be performed.

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

  As shown in FIG. 5, 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 pulsed laser light having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more. For example, the laser light source emits pulsed laser light having a wavelength of 500 nm to 10 μm, a pulse width of 100 nanoseconds or more, a repetition frequency of 80 kHz to 10 MHz, and a pulse energy of 1 to 70 μJ.

  The telescope optical system 220 optimizes the beam diameter of the pulsed 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.

  Stage 240 has a mounting table on which SiC substrate 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. The SiC substrate 110 on the stage 240 is moved in the XY-axis direction along the planned division line by this drive mechanism.

  AF camera 250 is a camera for acquiring a surface profile of a processed part of SiC substrate 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 beam is along the planned division line of the SiC substrate 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 substrate 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 substrate 110. In addition, computer 280 controls XY stage controller 260 and Z controller 270 to scan the laser beam along the planned division line of SiC substrate 110.

  Next, a procedure for dividing SiC substrate 110 using laser processing apparatus 200 having the above configuration will be described.

  First, the SiC substrate 110 with the dicing tape 140 attached to the back surface is placed on the stage 240 and the surface profile of the SiC substrate 110 is acquired by the AF camera 250 and the XY stage controller 260. Next, pulse laser light is emitted from the laser light source 210 and the SiC substrate 110 is irradiated with the laser light. At this time, by moving the stage 240 in the XY axis direction (horizontal direction) based on the surface profile acquired in advance, the division planned line is scanned with the pulse laser beam. Thereby, damage can be formed along the planned dividing line of SiC substrate 110.

  Next, mechanical stress is applied to SiC substrate 110 by a break device and an expand device (not shown), and SiC substrate 110 is divided starting from damage (see FIGS. 1C and 1D). By the above procedure, SiC substrate 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 the experimental results of examining the relationship between the shot pitch of pulsed laser light and the occurrence of debris when the surface of the SiC substrate is damaged by irradiation with pulsed laser light.

A SiC single crystal substrate (thickness 150 μm) was prepared as a processing object. The SiC substrate was irradiated with pulsed laser light (wavelength 1064 nm, pulse width 190 nanoseconds) to form damage on the surface of the SiC substrate. At this time, the stage was moved in the XY axis direction (horizontal direction), and damage was formed along the planned dividing line of the SiC substrate. The condensing point was adjusted to the surface of the SiC substrate. The irradiation spot diameter (1 / e ² width) on the substrate surface was 4.34 μm. The pulse energy of the pulsed laser beam is 14 μJ. In terms of energy density, it is 94.6 J / cm ² , and in terms of peak power density, it is 4.98 × 10 ⁸ W / cm ² . The moving speed of the stage was adjusted so that the shot pitch of the irradiation spot (see FIG. 2) was 0.1 to 1.7 μm. The repetition frequency of the pulse laser beam is 235 kHz, 333 kHz, or 500 kHz.

  After laser processing, the presence or absence of debris was examined. 6A to 6C are photographs showing an example of the periphery of the processed portion of the SiC substrate after laser processing (determination criteria for the presence or absence of debris). FIG. 6A is a photograph of the surface of the SiC substrate when no debris is generated, FIG. 6B is a photograph of the surface of the SiC substrate when the strip debris is generated, and FIG. 6C is a photograph of the strip debris and the scattered debris. It is a photograph of the surface of a SiC substrate when this occurs.

  FIG. 7 is a photograph of the periphery of the processed portion of the SiC substrate after actual laser processing. FIG. 7A is a photograph of the surface of the SiC substrate processed at a shot pitch of 0.1 μm, FIG. 7B is a photograph of the surface of the SiC substrate processed at a shot pitch of 0.5 μm, and FIG. 7D is a photograph of the surface of a SiC substrate processed at 8 μm, FIG. 7D is a photograph of the surface of a SiC substrate processed at a shot pitch of 1.2 μm, and FIG. 7E is a surface of the SiC substrate processed at a shot pitch of 1.5 μm. FIG. 7F is a photograph of the surface of the SiC substrate processed at a shot pitch of 1.7 μm.

  As shown in FIGS. 7A to 7E, when the pulse laser beam was irradiated so that the shot pitch was 0.1 to 1.5 μm, almost no debris was observed around the formed damage. On the other hand, as shown in FIG. 7F, when the pulse laser beam was irradiated so that the shot pitch was 1.7 μm, a large amount of debris was generated in the vicinity of the formed damage.

  Table 2 is a table showing the relationship between the shot pitch of the pulse laser beam and the occurrence of debris. As shown in Table 2, when irradiating a SiC substrate with a pulse laser beam having a wavelength of 500 nm or more, a pulse energy of 70 μJ or less, and a repetition frequency of 80 kHz or more to form damage on the surface of the SiC substrate, It can be seen that the occurrence of debris can be suppressed by setting the shot pitch to less than 1.7 μm.

[Example 2]
Example 2 shows the experimental results of examining the relationship between the wavelength of pulsed laser light and the occurrence of debris when the surface of the SiC substrate is damaged by irradiation with pulsed laser light.

A SiC single crystal substrate (thickness 150 μm) was prepared as a processing object. Damage was formed on the surface of the SiC substrate by irradiating the SiC substrate with pulsed laser light (wavelength 355 nm or 1064 nm, repetition frequency 100 kHz). At this time, the stage was moved in the XY axis direction (horizontal direction), and damage was formed along the planned dividing line of the SiC substrate. The condensing point was adjusted to the surface of the SiC substrate. The pulse width of the pulsed laser light is 25 nanoseconds (when the wavelength is 355 nm) or 190 nanoseconds (when the wavelength is 1064 nm). The irradiation spot diameter (1 / e ² width) on the substrate surface was 6.28 μm (when the wavelength was 355 nm) or 5.81 μm (when the wavelength was 1064 nm). The pulse energy of the pulse laser beam is 10 μJ. When converted to energy density, it is 32.3 J / cm ² (when the wavelength is 355 nm) or 37.7 J / cm ² (when wavelength is 1064 nm), and when converted to the peak power density, 1.70 × 10 ⁸ W / cm. ² (when the wavelength is 355 nm) or 1.98 × 10 ⁸ W / cm ² (when the wavelength is 1064 nm). The moving speed of the stage was adjusted so that the shot pitch of the irradiation spot was 0.1 μm.

  FIG. 8 is a photograph of the periphery of the processed portion of the SiC substrate after laser processing. FIG. 8A is a photograph of the surface of the SiC substrate irradiated with a pulsed laser beam having a wavelength of 1064 nm, and FIG. 8B is a photograph of the surface of the SiC substrate irradiated with a pulsed laser beam having a wavelength of 355 nm.

  As shown in FIG. 8A, when the pulse laser beam having a wavelength of 1064 nm was irradiated, almost no debris was observed around the formed damage. On the other hand, as shown in FIG. 8B, when pulse laser light having a wavelength of 355 nm was irradiated, strip debris and scattered debris were generated around the formed damage.

  From the above results, it can be seen that even if the pulse energy is 70 μJ or less, the repetition frequency is 80 kHz or more, and the shot pitch is less than 1.7 μm, debris is generated when the wavelength is less than 500 nm.

[Example 3]
Example 3 shows the experimental results of examining the relationship between the pulse energy of the pulse laser beam and the generation of debris when the surface of the SiC substrate is damaged by irradiation with the pulse laser beam.

A SiC single crystal substrate (thickness 350 μm) was prepared as a processing object. The SiC substrate was irradiated with pulsed laser light (wavelength 1064 nm, pulse width 190 nanoseconds) to form damage on the surface of the SiC substrate. At this time, the stage was moved in the XY axis direction (horizontal direction), and damage was formed along the planned dividing line of the SiC substrate. The condensing point was adjusted to the surface of the SiC substrate. The irradiation spot diameter (1 / e ² width) on the substrate surface was 4.34 μm. The pulse energy of the pulsed laser beam was changed from 14 to 80 μJ. In terms of energy density, it is 94.6 to 540 J / cm ² , and in terms of peak power density, it is 4.98 × 10 ^{8 to} 2.84 × 10 ⁹ W / cm ² . The repetition frequency was varied from 200 to 500 kHz. The moving speed of the stage was adjusted so that the shot pitch of the irradiation spot was 0.1 μm.

  FIG. 9 is a photograph of the periphery of the processed portion of the SiC substrate after laser processing. FIG. 9A is a photograph of the surface of a SiC substrate irradiated with pulse laser light having a pulse energy of 14 μJ (repetition frequency 500 kHz), and FIG. 9B is a photograph of the SiC substrate irradiated with pulse laser light having a pulse energy of 40 μJ (repetition frequency 300 kHz). FIG. 9C is a photograph of the surface, FIG. 9C is a photograph of the surface of the SiC substrate irradiated with pulse laser light having a pulse energy of 70 μJ (repetition frequency 300 kHz), and FIG. 9D is a pulse laser light having a pulse energy of 80 μJ (repetition frequency 200 kHz). It is the photograph of the surface of the SiC substrate which irradiated. FIG. 9E is a partially enlarged photograph of a broken line region in the photograph of FIG. 9D.

  Table 3 is a table showing the relationship between the pulse energy of the pulse laser beam and the occurrence of debris. As shown in Table 3, a pulse laser is used in the case where damage is formed on the surface of the SiC substrate by irradiating the SiC substrate with a pulse laser beam having a wavelength of 500 nm or more and a repetition frequency of 80 kHz or more with a shot pitch of less than 1.7 μm. It turns out that generation | occurrence | production of a debris can be suppressed by making the pulse energy of light into 70 microJ or less.

[Example 4]
Example 4 shows the experimental results of examining the relationship between the repetition frequency of pulse laser light and the occurrence of debris when damage is formed on the surface of the SiC substrate by irradiation with pulse laser light.

A SiC single crystal substrate (thickness 150 μm) was prepared as a processing object. The SiC substrate was irradiated with pulsed laser light (wavelength 1064 nm, pulse width 190 nanoseconds) to form damage on the surface of the SiC substrate. At this time, the stage was moved in the XY axis direction (horizontal direction), and damage was formed along the planned dividing line of the SiC substrate. The condensing point was adjusted to the surface of the SiC substrate. The irradiation spot diameter (1 / e ² width) on the substrate surface was 5.81 μm. The pulse energy of the pulsed laser beam is 14 μJ. When converted to energy density, it is 52.7 J / cm ² , and when converted to peak power density, it is 2.78 × 10 ⁸ W / cm ² . The repetition frequency was varied from 50 to 500 kHz. The moving speed of the stage was adjusted so that the shot pitch of the irradiation spot was 0.1 μm.

  FIG. 10 is a photograph of the periphery of the processed portion of the SiC substrate after laser processing. FIG. 10A is a photograph of the surface of the SiC substrate irradiated with pulsed laser light having a repetition frequency of 500 kHz, FIG. 10B is a photograph of the surface of the SiC substrate irradiated with pulsed laser light having a repetition frequency of 100 kHz, and FIG. FIG. 10D is a photograph of the surface of the SiC substrate irradiated with pulsed laser light having a repetition frequency of 50 kHz, and FIG. 10D is a photograph of the surface of the SiC substrate irradiated with pulsed laser light having a repetition frequency of 50 kHz.

  Table 4 is a table showing the relationship between the repetition frequency of the pulse laser beam and the occurrence of debris. As shown in Table 4, when the SiC substrate is irradiated with a pulse laser beam having a wavelength of 500 nm or more and a pulse energy of 70 μJ or less at a shot pitch of less than 1.7 μm to form damage on the surface of the SiC substrate, It can be seen that the occurrence of debris can be suppressed by setting the repetition frequency of the laser light to 80 kHz or more.

[Example 5]
Example 5 shows the experimental results of examining the relationship between the focal depth and damage depth of the lens and the smoothness of the fractured surface when the SiC substrate is divided by irradiation with pulsed laser light.

A SiC single crystal substrate (thickness 150 μm) was prepared as a processing object. The SiC substrate was irradiated with pulsed laser light (wavelength 1064 nm, repetition frequency 500 kHz, pulse width 190 nanoseconds) to form damage on the surface of the SiC substrate. At this time, the stage was moved in the XY axis direction (horizontal direction), and damage was formed along the planned dividing line of the SiC substrate. For focusing the pulsed laser light, a lens having a focal depth of 15 μm or a lens having a focal depth of 26 μm was used. The condensing point was adjusted to the surface of the SiC substrate. The irradiation spot diameter (1 / e ² width) on the substrate surface was 4.3 μm (when a lens with a focal depth of 15 μm was used) or 5.8 μm (when a lens with a focal depth of 26 μm was used). The pulse energy of the pulsed laser beam was changed from 6 to 20 μJ. The moving speed of the stage was adjusted so that the shot pitch of the irradiation spot was 0.05 to 0.30 μm.

  After forming damage on the surface of the SiC substrate, the SiC substrate was divided along the planned dividing line by performing a break process (see FIG. 1C) and an expanding process (see FIG. 1D). Then, about each SiC substrate, while measuring the depth of the damage formed by laser processing, the smoothness of the fractured surface was evaluated. The smoothness of the fractured surface was measured using a 3D measurement laser microscope (OLS4000; Olympus Corporation). When the height of the unevenness formed on the fractured surface was 5 μm or less, it was evaluated as “◯”, and when it was more than 5 μm, it was evaluated as “x”.

  FIG. 11 is a photograph of a fractured surface of a SiC substrate laser-processed using a lens having a focal depth of 15 μm. FIGS. 11A and 11B are photographs of a fractured surface of a SiC substrate processed with a pulse energy of 10 μJ and a shot pitch of 0.30 μm (d / b = 0.75). FIGS. 11C and 11D show a pulse energy of 10 μJ, FIG. 11E is a photograph of a section of a SiC substrate processed at a shot pitch of 0.05 μm (d / b = 0.95), and FIGS. 11E and 11F are SiC substrates processed at a pulse energy of 14 μJ and a shot pitch of 0.20 μm. FIG. 11G is a photograph of a fractured surface of a SiC substrate processed with a pulse energy of 18 μJ and a shot pitch of 0.10 μm (d / b = 1.09). 84).

  FIG. 12 is a photograph of a cut section of a SiC substrate laser-processed using a lens having a focal depth of 26 μm. 12A and 12B are photographs of a fractured surface of a SiC substrate processed with a pulse energy of 10 μJ and a shot pitch of 0.10 μm (d / b = 0.91), and FIGS. 12C and 12D show a pulse energy of 14 μJ, FIG. 12E is a photograph of a broken section of a SiC substrate processed with a shot pitch of 0.20 μm (d / b = 1.29), and FIGS. 12E and 12F are SiC substrates processed with a pulse energy of 18 μJ and a shot pitch of 0.10 μm. FIG. 12G is a photograph of a fractured surface of an SiC substrate processed with a pulse energy of 20 μJ and a shot pitch of 0.10 μm (d / b = 1.60). 90).

  Tables 5 and 6 are tables showing the relationship between the focal depth of the lens and the depth of damage formed, and the smoothness of the fractured surface. Table 5 shows the results when laser processing is performed using a lens having a focal depth of 15 μm, and Table 6 shows the results when laser processing is performed using a lens having a focal depth of 26 μm. As shown in Table 5 and Table 6, the smoothness of the fractured surface can be improved by setting the value of “damage depth d / lens focal depth b” to 0.7 or more and 1.6 or less. I understand that.

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

DESCRIPTION OF SYMBOLS 100 Pulse laser beam 110 Silicon carbide board | substrate 120 Scheduled division 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 (5)

A laser processing method comprising a step of irradiating a silicon carbide substrate with a pulsed laser beam through a lens to form damage on a surface of the silicon carbide substrate,
The wavelength of the pulse laser beam is 500 nm or more,
The pulse energy of the pulse laser beam is 70 μJ or less,
The repetition frequency of the pulse laser beam is 80 kHz or more,
Distance between centers of irradiation spots of the pulsed laser light on the surface of the silicon carbide substrate is greater than 0 .mu.m, and Ri der less than 1.7 [mu] m,
When the focal depth of the lens is b (μm) and the depth of damage is d (μm), 0.7 ≦ d / b ≦ 1.6.
Laser processing method. The pulse laser beam is irradiated along a division line of the silicon carbide substrate,
The damage is formed on the surface of the silicon carbide substrate along the division line.
The laser processing method according to claim 1.   The laser processing method according to claim 1, wherein a pulse width of the pulsed laser light is 100 nanoseconds or more.   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 substrate to 100 μm inside from the surface.