JP5739396B2 - Laser processing method and electronic device manufacturing method - Google Patents

Description

  The present invention relates to a laser processing method for forming damage by irradiating a workpiece with laser light, and a method for manufacturing an electronic device using the laser processing method.

  In the manufacture of electronic devices, it is essential to divide the electronic devices partitioned and formed in a lattice shape into individual electronic devices. In addition, it is required to perform drilling at a desired position on each electronic device or to perform other fine processing. Recently, it is becoming mainstream that a laser processing apparatus is used for these processes. Many laser processing apparatuses used in these processes have high output and ultrashort pulses and perform processing with high energy in order to improve throughput and cope with difficult-to-process materials. However, it is desirable to perform processing with low energy from the viewpoints of energy saving, shortening of the processing time, reduction of damage to the workpiece, reduction of scattered matter, apparatus price, and the like.

  Patent Document 1 discloses a technique that allows laser processing of an inorganic material with less energy by forming a coating made of a metal material or a plastic material on the inorganic material. In this technique, laser processing is performed only on a portion where a film is formed. Further, after the laser light irradiation, the film is removed for etching.

JP 2003-329821 A

  The laser processing method described in Patent Document 1 requires a step of removing the film after irradiating the laser beam, which causes a problem that the step becomes complicated and the manufacturing cost increases. In addition, since a coating must be formed on all the parts to be subjected to laser processing, there is a problem that the manufacturing cost increases.

  The present invention has been made in view of such a point, and an object of the present invention is to provide a method capable of performing laser processing with a low-energy laser beam more easily.

  The present invention relates to the following laser processing method.

[1] A step of preparing a workpiece in which a damage formation starting portion is arranged on a part of the surface; and after irradiating the damage formation starting portion with a laser beam, the laser beam is directly applied to the workpiece continuously. Irradiating and forming a damage to the workpiece starting from the damage formation starting portion, and the damage formation starting portion is made of a material having a processing threshold lower than that of the workpiece. A laser processing method in which the intensity of the laser beam exceeds a processing threshold value of the damage formation starting point and is lower than a processing threshold value of the workpiece.
[2] The laser processing method according to [1], wherein the damage formation starting portion is made of a metal, an alloy, a metal compound, or a metal oxide.
[3] The laser processing method according to [1] or [2], wherein the workpiece is made of a dielectric.
[4] The laser processing method according to any one of [1] to [3], wherein the damage is a groove formed on a surface of the workpiece.

  Moreover, this invention relates to the manufacturing method of the following electronic devices.

  [5] A method for manufacturing an electronic device using the laser processing method according to any one of [1] to [4].

  According to the laser processing method of the present invention, it is possible to perform laser processing with low energy laser light more easily.

1A to 1D are diagrams showing examples of arrangement of damage formation starting points. 2A to 2C are diagrams showing patterning examples of damage formation starting points. 3A and 3B are photographs of the processing peripheral portion after laser processing is performed on the SiC substrate. 4A and 4B are photographs of the processing peripheral portion after laser processing is performed on a SiC substrate on which a damage formation starting portion made of Al having a thickness of 100 nm is arranged. FIGS. 5A and 5B are photographs of the processing peripheral portion after laser processing is performed on the SiC substrate on which the 400 nm-thickness damage start point portion is disposed. FIGS. 6A and 6B are photographs of the processing peripheral portion after laser processing is performed on the SiC substrate on which the 400 nm-thickness damage starting point portion made of Mo is arranged. FIGS. 7A and 7B are photographs of peripheral portions after laser processing is performed on a SiC substrate on which a damage formation starting portion made of Al having a thickness of 100 nm is arranged. 8A and 8B are photographs of the processing peripheral portion after laser processing is performed on the SiC substrate on which the 400 nm-thickness damage start point portion is disposed. FIGS. 9A and 9B are photographs of processing peripheral portions after laser processing is performed on an SiC substrate on which a 400 nm-thickness damage starting point portion made of Mo is arranged. FIGS. 10A and 10B are photographs of processing peripheral portions after laser processing is performed on a sapphire substrate on which a 400 nm-thickness damage starting point portion is formed of Al.

  The laser processing method of the present invention includes (1) a first step of preparing a workpiece in which a damage formation starting portion is arranged on a part of its surface, and (2) a second step of irradiating the workpiece with laser light. Including. Hereinafter, each step will be described in detail.

(1) First Step In the first step, a workpiece is prepared in which a damage formation starting portion is arranged on a part of the surface.

  The kind of workpiece is not particularly limited. Examples of workpieces include dielectrics such as glass, silicon, silicon carbide (SiC), gallium nitride, silicon nitride, sapphire, alumina, gallium arsenide, quartz, and diamond. Further, the workpiece may be laminated on another material. For example, the workpiece may be a part of a laminated substrate such as an SOS substrate, an SOQ substrate, or an SOG substrate.

One feature of the laser processing method of the present invention is that a damage formation starting portion made of a material having a processing threshold lower than that of the workpiece is disposed on a part of the surface of the workpiece. The material type of the damage formation starting point is not particularly limited as long as the processing threshold is lower than the processing threshold of the workpiece. For example, the material of the damage formation starting portion is a material having an absorption coefficient higher than that of the workpiece on the irradiated laser beam. Examples of the material of the damage starting point portion include one or more metal elements selected from the group consisting of Al, Au, Ag, Pt, Pd, Ni, Cu, Fe, Cr, Ti, Ta, and Mo. One or more metals selected from the group consisting of pure metals, alloys or metal compounds, and SiO ₂ , Al ₂ O ₃ , CaO, Na ₂ O, B ₂ O ₃ , TiO ₂ , ZnO and Fe ₂ O ₃ Oxides and the like are included.

  The method for forming the damage formation starting point is not particularly limited. For example, when the damage formation starting portion is made of a pure metal or an alloy, the metal thin film may be attached to the surface of the workpiece, or the metal thin film may be formed by a thin film forming method such as sputtering or vacuum deposition. In addition, various methods such as plating, printing, and ink jet can be used. Further, a patterned metal thin film may be formed on the surface of the workpiece by a method such as photolithography (see FIG. 2). On the other hand, when the damage formation starting portion is made of a metal oxide, a composition containing a metal oxide powder may be applied to the damage formation starting portion and dried. Further, the damage formation starting point portion may be arranged directly on the workpiece, or may be arranged via an adhesive in order to improve adhesiveness.

  FIG. 1 is a diagram illustrating an arrangement example of damage formation starting points. FIG. 2 is a diagram illustrating a patterning example of a damage formation starting point portion. As shown in these drawings, the damage formation starting point portion 1 may be disposed on the surface of the workpiece 2 (surface irradiated with the laser beam 3) (see FIG. 1A), or the workpiece 2 You may arrange | position to a side surface (refer FIG. 1B and FIG. 1C), and may arrange | position to the back surface (surface which is not irradiated with the laser beam 3) of the to-be-processed object 2 (refer FIG. 1D). Further, when the damage formation starting portion 1 is arranged on the front surface or the back surface of the workpiece, the damage formation starting portion 1 may be arranged in a circle around the electronic device group partitioned and formed in a lattice shape (FIG. 2A). (See FIG. 2B), or in a polygonal shape around the electronic device group (see FIG. 2B). Moreover, although the thickness of a damage formation starting part is not specifically limited, For example, they are 20 nm-20 micrometers.

  The procedure for forming the damage formation starting portion on the workpiece is not particularly limited. For example, only a damage starting point may be formed in a single workpiece by an independent process, or in a workpiece having a plurality of structures on the surface or inside, such as a semiconductor device or a MEMS device, At the same time during the process of manufacturing the structure, the damage formation starting portion may be formed.

(2) Second Step In the second step, the workpiece prepared in the first step is irradiated with laser light to form damage on the workpiece. At this time, after irradiating the laser beam to the damage formation starting part arranged on a part of the surface, the part directly to the part where the damage formation starting part of the workpiece is not arranged (hereinafter referred to as “bearing part”) is directly applied. By irradiating the laser beam, damage is formed on the workpiece starting from the damage formation starting point. As described above, the laser processing method of the present invention is characterized in that the laser beam is continuously irradiated to the bare portion after the damage formation starting portion is irradiated with the laser beam.

  The irradiation start position of the laser beam is not particularly limited. For example, laser beam irradiation may be started from a damage formation starting point. Alternatively, after starting the laser beam irradiation at the bare part, the laser beam may be irradiated onto the damage formation starting point, and then the laser beam may be irradiated onto the bare part. In either case, damage can also be formed in the bare portion starting from the damage formation starting point.

  For example, when the work piece is a dielectric substrate, the condensing point of the laser beam is moved along the surface direction of the substrate from the damage formation starting portion arranged on a part of the front surface, back surface or side surface of the substrate. Thus, a groove can be formed in the substrate. Moreover, a hole can be formed in a board | substrate by moving the condensing point of a laser beam along the thickness direction of a board | substrate from the damage formation origin part arrange | positioned in the front surface or a part of back surface of a board | substrate.

  The laser beam may be either a pulsed laser beam or a continuous wave (CW) laser beam. In both cases of pulsed laser light and CW laser light, the irradiation energy of the laser light and the physical property values of the workpiece and the damage starting point are related to this phenomenon. In the case of a pulsed laser beam, the thermal energy generated for each pulse must be continuous on the workpiece, and the repetition frequency and pulse width of the pulsed laser beam, as well as the relative position between the laser irradiation position and the workpiece. The amount of change in position is a parameter.

  As the irradiation condition of the pulse laser beam, the higher the repetition frequency and the larger the pulse width, the more the thermal continuity is maintained, the closer to the CW laser beam processing mode, and the higher the processing continuity. However, the pulse laser beam has better controllability of heat energy supplied to the processing point.

  Here, the mechanism (the 1st theory and the 2nd theory) presumed about the reason why damage is continuously formed also in the bare part after the damage is formed starting from the damage formation starting part will be described. However, the mechanism by which damage is formed is not limited to these.

A) First explanation When damage is formed from the damage formation starting point, heat is transferred from the damaged part to the peripheral part. This heat lowers the value of the band gap of the work piece and lowers the processing threshold value, so that the processing of the bare portion is continued with low energy laser light. This phenomenon is presumed to require a state of continuous thermal energy on the workpiece during machining.

B) Second explanation When the damage formation starting point is irradiated with laser light and processing is started at the damage formation starting point, the vicinity of the processing point is in a high temperature state. When the workpiece is a material with good heat conduction, the heat diffuses quickly, and the temperature decreases rapidly as the distance from the processing point increases. When the temperature gradient becomes steep in this manner, heat stress occurs in the high temperature portion and the low temperature portion. Further, a shock wave due to machining is also generated near the machining point. Combining these factors, simultaneously with processing with laser light, a lattice defect is formed near the laser processing point, and laser light acts on this lattice defect, so that the bare portion can also be processed with low-energy laser light. Presumed to continue.

  The intensity of the laser beam is not particularly limited as long as it exceeds the processing threshold value of the damage formation starting portion, but it exceeds the processing threshold value of the damage formation starting portion and is less than the processing threshold value of the workpiece preferable. Here, the “processing threshold” refers to the maximum amount of laser light that can be irradiated to the object without forming damage. Specifically, the processing threshold value can be specified by the energy density or peak power density of laser light.

  The material has an inherent processing threshold for the irradiated laser light. For this reason, in order to perform laser processing, it is necessary to irradiate a laser beam having a laser beam intensity exceeding a processing threshold. That is, no damage is formed on the workpiece even when the laser beam having a laser beam intensity lower than the processing threshold of the workpiece is irradiated. However, according to the present invention, it is possible to form damage to the bare portion with a laser beam having a laser beam intensity that exceeds the processing threshold value of the damage starting point and is lower than the processing threshold value of the workpiece. Become.

  In order to perform desired processing on the workpiece, in order to determine the irradiation condition of the laser beam, it is necessary to measure the processing threshold values of the workpiece and the damage formation starting portion in advance. Here, the method for measuring the processing threshold is not particularly limited. For example, the laser is gradually increased from the low peak power density condition to the workpiece and the damage formation starting point, and the maximum peak power density at which no damage is formed on the workpiece is defined as the machining threshold. Can be measured.

  The means for measuring the machining threshold is not particularly limited, but a laser machining apparatus for measuring the machining threshold and each component thereof will be described below.

  The laser processing apparatus includes at least a laser light source that emits laser light to be irradiated on a workpiece, an optical system that irradiates the workpiece with laser light emitted from the laser light source, an optical system (laser light), and a target. A drive unit that relatively moves the workpiece.

  The type of the laser light source is not particularly limited, and for example, a Ho laser, an Er laser, various semiconductor lasers, or the like can be used. Further, the oscillating laser beam may be a pulse laser beam or a CW laser beam.

  The optical system irradiates the workpiece 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 light) and the workpiece so that the laser beam is irradiated to a desired processing position of the workpiece. The drive unit may move the stage on which the workpiece is placed, may move the optical system, or may move both the stage and the optical system.

  In addition, a laser processing apparatus for measuring a processing threshold value may include a stage on which a workpiece is placed, an automatic aiming system for positioning a condensing point at a desired position, and the like.

  The laser processing apparatus for carrying out the present invention may be, for example, an apparatus having the same configuration as the apparatus for measuring the processing threshold, and is not limited to this.

  The laser processing method of the present invention can form grooves on the surface of the workpiece. For example, when the workpiece is a wafer, the wafer can be divided into chips starting from a groove formed on the surface of the workpiece. In this case, the workpiece can be adhered to the dicing tape before or after laser irradiation, and the workpiece can be divided from the groove as a starting point using a braking device, an expanding device, or the like.

  As described above, according to the laser processing method of the present invention, the damage is formed on the bare portion starting from the damage formation starting portion, so that the process of removing the damage formation starting portion can be performed more easily with a low energy laser beam. Laser processing can be performed. The laser processing method of the present invention is suitable for manufacturing electronic devices, for example.

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

[Example 1]
A SiC single crystal substrate (thickness: 355 μm) was prepared as a workpiece. After a thin film made of Al or Mo was formed on the surface of the SiC single crystal substrate using vacuum deposition, patterning was performed using photolithography to form a damage formation starting portion. The thickness of the damage starting point is 100 nm or 400 nm (when the material is Al), or 400 nm (when the material is Mo).

First, a pulse laser beam (wavelength 1064 nm, pulse width 190 nanoseconds, repetition frequency 500 kHz) was irradiated to a SiC substrate on which no damage formation starting portion was formed, and the processing threshold value of the SiC substrate was measured. At this time, the stage was moved in the XY axis direction (horizontal direction) to form damage on the surface 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 moving speed of the stage was 50 mm / sec.

FIG. 3 is a photograph of the processing peripheral portion after laser processing is performed on the SiC substrate. The broken line indicates the machining start position, and machining was performed from the left side to the right side. FIG. 3A is a photograph of the surface of the SiC substrate irradiated with pulsed laser light having a peak power density of 6.11 × 10 ⁸ W / cm ² , and FIG. 3B is a peak power density of 6.27 × 10 ⁸ W / cm ² . It is a photograph of the surface of the SiC substrate irradiated with pulsed laser light.

As shown in FIG. 3A, when the pulsed laser light with a peak power density of 6.11 × 10 ⁸ W / cm ² was irradiated, damage could not be formed on the SiC substrate, but as shown in FIG. 3B, When the pulse laser beam having a peak power density of 6.27 × 10 ⁸ W / cm ² was irradiated, damage could be formed on the SiC substrate.

From the above results, the processing threshold value of the SiC substrate when irradiated with laser light under the above conditions exceeds the peak power density of 6.11 × 10 ⁸ W / cm ² and the peak power density of 6.27 × 10 6. ^It can be seen that it is less than ⁸ W / cm ² .

Similarly, a pulse laser beam (wavelength 1064 nm, pulse width 190 nanoseconds, repetition frequency 500 kHz) is irradiated to the damage formation starting portion of the SiC substrate on which the damage formation starting portion is formed, and then irradiated to the bare portion of the SiC substrate. Then, the processing threshold value at the starting point of damage formation was measured. At this time, the stage was moved in the XY axis direction (horizontal direction) to form damage on the surface 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 moving speed of the stage was 50 mm / sec.

FIG. 4 is a photograph of the processing peripheral portion after laser processing is performed on the SiC substrate on which the damage formation starting portion made of Al having a thickness of 100 nm is arranged. The broken line indicates the machining start position, and machining was performed from the left side to the right side. The white part on the left is the damage formation starting part, and the gray part on the right is the bare part of the SiC substrate where the damage formation starting part is not arranged. FIG. 4A is a photograph of the surface of the SiC substrate irradiated with pulsed laser light having a peak power density of 1.07 × 10 ⁸ W / cm ² , and FIG. 4B is a peak power density of 1.15 × 10 ⁸ W / cm ^2. It is the photograph of the surface of the SiC substrate which irradiated the pulse laser beam of.

As shown in FIG. 4A, when the pulse laser beam with a peak power density of 1.07 × 10 ⁸ W / cm ² was irradiated, damage could not be formed at the damage formation starting point. As shown in the figure, when pulse laser light having a peak power density of 1.15 × 10 ⁸ W / cm ² was irradiated, damage could be formed at the damage starting point.

From the above results, the processing threshold value of the damage formation starting portion formed on the SiC substrate when irradiated with laser light under the above conditions exceeds the peak power density of 1.07 × 10 ⁸ W / cm ² , It can be seen that the peak power density is less than 1.15 × 10 ⁸ W / cm ² .

Further, from FIG. 4B, a pulsed laser beam having a laser beam intensity (peak power density of 1.15 × 10 ⁸ W / cm ² ) that exceeds the processing threshold value of the damage formation starting portion and is lower than the processing threshold value of the SiC substrate. Thus, it can be seen that damage can be formed on the SiC substrate starting from the damage formation starting point. That is, since the processing threshold value of the SiC substrate exceeds the peak power density 6.11 × 10 ⁸ W / cm ² and is less than the peak power density 6.27 × 10 ⁸ W / cm ² , the surface of the SiC substrate It can be seen that by forming a damage formation starting portion in a part of the substrate, damage can be formed on the SiC substrate with a laser beam having a low energy of about 1/5.

FIG. 5 is a photograph of the processing peripheral portion after laser processing is performed on the SiC substrate on which the 400 nm-thickness damage formation starting portion made of Al is arranged. The broken line indicates the machining start position, and machining was performed from the left side to the right side. The white part on the left is the damage formation starting part, and the gray part on the right is the bare part of the SiC substrate where the damage formation starting part is not arranged. FIG. 5A is a photograph of the surface of the SiC substrate irradiated with pulsed laser light having a peak power density of 1.37 × 10 ⁸ W / cm ² , and FIG. 5B is a peak power density of 1.45 × 10 ⁸ W / cm ^2. It is the photograph of the surface of the SiC substrate which irradiated the pulse laser beam of.

As shown in FIG. 5A, when a pulse laser beam having a peak power density of 1.37 × 10 ⁸ W / cm ² was irradiated, damage could not be formed at the damage formation starting point. As shown, damage was able to be formed at the damage formation starting point when the pulse laser beam having a peak power density of 1.45 × 10 ⁸ W / cm ² was irradiated.

From the above results, the processing threshold of the damage formation starting portion disposed on the SiC substrate when the laser beam is irradiated under the above conditions exceeds the peak power density of 1.37 × 10 ⁸ W / cm ² , It can be seen that the peak power density is less than 1.45 × 10 ⁸ W / cm ² .

Further, from FIG. 5B, a pulsed laser beam having an intensity of laser light (peak power density of 1.45 × 10 ⁸ W / cm ² ) that exceeds the processing threshold of the damage formation starting portion and is lower than the processing threshold of the SiC substrate. Thus, it can be seen that damage can be formed on the SiC substrate starting from the damage formation starting point. That is, since the processing threshold value of the SiC substrate exceeds the peak power density 6.11 × 10 ⁸ W / cm ² and is less than the peak power density 6.27 × 10 ⁸ W / cm ² , the surface of the SiC substrate It can be seen that by forming a damage formation starting portion in a part of the substrate, damage can be formed on the SiC substrate with a laser beam having a low energy of about 1/4.

FIG. 6 is a photograph of a processing peripheral portion after laser processing is performed on a SiC substrate on which a 400 nm-thickness damage starting point portion made of Mo is arranged. The broken line indicates the machining start position, and machining was performed from the left side to the right side. The white part on the left is the damage formation starting part, and the gray part on the right is the bare part of the SiC substrate where the damage formation starting part is not arranged. 6A is a photograph of the surface of the SiC substrate irradiated with pulsed laser light having a peak power density of 0.63 × 10 ⁸ W / cm ² , and FIG. 6B is a peak power density of 0.71 × 10 ⁸ W / cm ^2. It is the photograph of the surface of the SiC substrate which irradiated the pulse laser beam of.

As shown in FIG. 6A, when pulse laser light with a peak power density of 0.63 × 10 ⁸ W / cm ² was irradiated, damage could not be formed at the damage formation starting point. As shown in the figure, when the pulse laser beam having a peak power density of 0.71 × 10 ⁸ W / cm ² was irradiated, damage could be formed at the damage starting point.

From the above results, the processing threshold of the damage formation starting portion disposed on the SiC substrate when the laser beam is irradiated under the above conditions exceeds the peak power density of 0.63 × 10 ⁸ W / cm ² , It can be seen that the peak power density is less than 0.71 × 10 ⁸ W / cm ² .

Further, from FIG. 6B, a pulsed laser beam having a laser beam intensity (peak power density of 0.71 × 10 ⁸ W / cm ² ) exceeding the processing threshold value of the damage formation starting portion and lower than the processing threshold value of the SiC substrate. Thus, it can be seen that damage can be formed on the SiC substrate starting from the damage formation starting point. That is, since the processing threshold value of the SiC substrate exceeds the peak power density 6.11 × 10 ⁸ W / cm ² and is less than the peak power density 6.27 × 10 ⁸ W / cm ² , the surface of the SiC substrate It can be seen that by forming a damage formation starting portion in a part of the substrate, damage can be formed on the SiC substrate with a laser beam having a low energy of about 1/9.

[Example 2]
A SiC single crystal substrate (thickness: 355 μm) was prepared as a workpiece. After a thin film made of Al or Mo was formed on the surface of the SiC single crystal substrate using vacuum deposition, patterning was performed using photolithography to form a damage formation starting portion. The thickness of the damage starting point is 100 nm or 400 nm (when the material is Al), or 400 nm (when the material is Mo).

First, a CW laser beam (wavelength: 1064 nm) was irradiated to a SiC substrate on which no damage formation starting portion was formed, and the processing threshold value of the SiC substrate was measured. At this time, the stage was moved in the XY axis direction (horizontal direction) to form damage on the surface 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 moving speed of the stage was 50 mm / sec.

Irradiation with CW laser light having a peak power density of 1.02 × 10 ⁸ W / cm ² failed to form damage on the surface of the SiC substrate. The peak power density is the maximum value that can be output in the implementation facility. That is, it can be seen that the processing threshold value of the SiC substrate when irradiated with laser light under the above conditions exceeds 1.02 × 10 ⁸ W / cm ² .

Similarly, a CW laser beam (wavelength 1064 nm) is irradiated to the damage formation start portion of the SiC substrate on which the damage formation start portion is formed, and then irradiated to the bare portion of the SiC substrate, thereby processing threshold of the damage formation start portion. Was measured. At this time, the stage was moved in the XY axis direction (horizontal direction) to form damage on the surface 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 moving speed of the stage was 50 mm / sec.

FIG. 7 is a photograph of a processing peripheral portion after performing laser processing on a SiC substrate on which a damage forming starting portion made of Al having a thickness of 100 nm is formed. The broken line indicates the machining start position, and machining was performed from the left side to the right side. The white part on the left side is the damage formation starting part, and the gray part on the right side is the bare part of the SiC substrate where the damage formation starting part is not formed. FIG. 7A is a photograph of the surface of the SiC substrate irradiated with CW laser light having a peak power density of 0.78 × 10 ⁸ W / cm ² , and FIG. 7B is a peak power density of 0.80 × 10 ⁸ W / cm ^2. It is the photograph of the surface of the SiC substrate which irradiated CW laser beam of.

As shown in FIG. 7A, when a CW laser beam having a peak power density of 0.78 × 10 ⁸ W / cm ² was irradiated, damage could not be formed at the damage starting point, but as shown in FIG. 7B. In addition, when CW laser light having a peak power density of 0.80 × 10 ⁸ W / cm ² was irradiated, damage could be formed at the damage starting point.

From the above results, the processing threshold of the damage formation starting portion disposed on the SiC substrate when the laser beam is irradiated under the above conditions exceeds the peak power density of 0.78 × 10 ⁸ W / cm ² , It can be seen that the peak power density is less than 0.80 × 10 ⁸ W / cm ² .

Further, from FIG. 7B, a CW laser beam having an intensity (peak power density of 0.80 × 10 ⁸ W / cm ² ) of laser light that exceeds the processing threshold value of the damage formation starting portion and is lower than the processing threshold value of the SiC substrate. Thus, it can be seen that damage can be formed on the SiC substrate starting from the damage formation starting point. That is, it can be seen that the damage can be formed on the SiC substrate with a laser beam of lower energy by disposing the damage starting point portion on a part of the surface of the SiC substrate. Further, in the case of CW laser light, since it is a continuous wave, the output required for processing increases (the peak power density conversion value is the same), so that it is possible to form damage at a low peak power density. An increase in output can be suppressed.

FIG. 8 is a photograph of the processing peripheral portion after performing laser processing on the SiC substrate on which the 400 nm-thickness damage starting point portion made of Al is formed. The broken line indicates the machining start position, and machining was performed from the left side to the right side. The white part on the left is the damage formation starting part, and the gray part on the right is the bare part of the SiC substrate where the damage formation starting part is not arranged. FIG. 8A is a photograph of the surface of the SiC substrate irradiated with CW laser light having a peak power density of 0.86 × 10 ⁸ W / cm ² , and FIG. 8B is a peak power density of 0.87 × 10 ⁸ W / cm ^2. It is the photograph of the surface of the SiC substrate which irradiated CW laser beam of.

As shown in FIG. 8A, when a CW laser beam having a peak power density of 0.86 × 10 ⁸ W / cm ² was irradiated, damage could not be formed at the damage starting point, but as shown in FIG. 8B. In addition, when the CW laser beam having a peak power density of 0.87 × 10 ⁸ W / cm ² was irradiated, damage could be formed at the damage formation starting part.

From the above results, the processing threshold value of the damage formation starting portion disposed on the SiC substrate when irradiated with laser light under the above conditions exceeds the peak power density of 0.86 × 10 ⁸ W / cm ² , It can be seen that the peak power density is less than 0.87 × 10 ⁸ W / cm ² .

Further, as shown in FIG. 8B, the intensity of the laser beam that exceeds the processing threshold value of the damage formation starting portion and is lower than the processing threshold value of the SiC substrate (peak power density 0.87 × 10 ⁸ W / cm ² ). It can be seen that with the CW laser light, damage can be formed on the SiC substrate starting from the damage starting point. That is, it can be seen that the damage can be formed with a lower energy laser beam by forming the damage formation starting point part on the surface of the SiC substrate. Further, in the case of CW laser light, since it is a continuous wave, the output required for processing increases (the peak power density conversion value is the same), so that it is possible to form damage at a low peak power density. An increase in output can be suppressed.

FIG. 9 is a photograph of the processing peripheral portion after laser processing is performed on the SiC substrate on which the 400 nm-thickness damage starting point portion made of Mo is formed. The broken line indicates the machining start position, and machining was performed from the left side to the right side. The white part on the left is the damage formation starting part, and the gray part on the right is the bare part of the SiC substrate where the damage formation starting part is not arranged. FIG. 9A is a photograph of the surface of the SiC substrate irradiated with CW laser light having a peak power density of 0.37 × 10 ⁸ W / cm ² , and FIG. 9B is a peak power density of 0.39 × 10 ⁸ W / cm ^2. It is the photograph of the surface of the SiC substrate which irradiated the pulse laser beam of.

As shown in FIG. 9A, when a CW laser beam having a peak power density of 0.37 × 10 ⁸ W / cm ² was irradiated, damage could not be formed in the SiC substrate, but as shown in FIG. 9B, When the CW laser beam having a peak power density of 0.39 × 10 ⁸ W / cm ² was irradiated, damage could be formed on the SiC substrate.

From the above results, the processing threshold value of the damage formation starting portion disposed on the SiC substrate when the laser beam is irradiated under the above conditions exceeds the peak power density of 0.37 × 10 ⁸ W / cm ² , It can be seen that the peak power density is less than 0.39 × 10 ⁸ W / cm ² .

Further, from FIG. 9B, a CW laser beam having a laser beam intensity (peak power density of 0.39 × 10 ⁸ W / cm ² ) that exceeds the processing threshold value of the damage formation starting portion and is lower than the processing threshold value of the SiC substrate. Thus, it can be seen that damage can be formed on the SiC substrate starting from the damage formation starting point. That is, it can be seen that the damage can be formed on the SiC substrate with a laser beam of lower energy by disposing the damage starting point portion on a part of the surface of the SiC substrate. Further, in the case of CW laser light, since it is a continuous wave, the output required for processing increases (the peak power density conversion value is the same), so that it is possible to form damage at a low peak power density. An increase in output can be suppressed.

[Example 3]
A sapphire single crystal substrate (thickness 120 μm) was prepared as a workpiece. After a thin film made of Al was formed on the surface of the sapphire single crystal substrate by vacuum deposition, patterning was performed using photolithography to form a damage formation starting portion. The thickness of the damage formation starting point is 400 nm.

First, the processing threshold value of the sapphire substrate was measured by irradiating the sapphire substrate not formed with the damage formation starting portion with CW laser light (wavelength 1064 nm). At this time, the stage was moved in the XY axis direction (horizontal direction) to form damage on the surface of the sapphire substrate. The condensing point was adjusted to the surface of the sapphire substrate. The irradiation spot diameter (1 / e ² width) on the substrate surface was 4.34 μm. The moving speed of the stage was 50 mm / sec.

Irradiation with CW laser light having a peak power density of 1.02 × 10 ⁸ W / cm ² failed to form damage on the sapphire substrate. The peak power density is the maximum value that can be output in the implementation facility. A sapphire substrate has very little absorption with respect to a laser beam having a wavelength of 1064 nm, and irradiation with a CW laser beam having a very high peak power density is required to form damage.

From the above results, it can be seen that the processing threshold of the sapphire substrate when irradiated with laser light under the above conditions exceeds at least the peak power density of 1.02 × 10 ⁸ W / cm ² .

Similarly, after irradiating the damage formation starting portion of the sapphire substrate on which the damage formation starting portion is disposed with CW laser light (wavelength 1064 nm), the bare threshold portion of the sapphire substrate is irradiated to process the threshold value of the damage formation starting portion. Was measured. At this time, the stage was moved in the XY axis direction (horizontal direction) to form damage on the surface of the sapphire substrate. The condensing point was adjusted to the surface of the sapphire substrate. The irradiation spot diameter (1 / e ² width) on the substrate surface was 4.34 μm. The moving speed of the stage was 400 mm / sec.

FIG. 10 is a photograph of the processing periphery after laser processing is performed on the sapphire substrate. The broken line indicates the machining start position, and machining was performed from the left side to the right side. The white part on the left is the damage formation starting part, and the gray part on the right is the bare part of the sapphire substrate where the damage formation starting part is not arranged. FIG. 10A is a photograph of the surface of the sapphire substrate irradiated with CW laser light having a peak power density of 0.27 × 10 ⁸ W / cm ² , and FIG. 10B is a peak power density of 0.29 × 10 ⁸ W / cm ^2. It is a photograph of the surface of the sapphire substrate irradiated with CW laser light.

As shown in FIG. 10A, when the CW laser light having a peak power density of 0.27 × 10 ⁸ W / cm ² was irradiated, damage could not be formed at the damage starting point, but as shown in FIG. 10B. In addition, when CW laser light having a peak power density of 0.29 × 10 ⁸ W / cm ² was irradiated, damage could be formed at the damage starting point.

From the above results, the processing threshold of the damage formation starting portion disposed on the sapphire substrate when irradiated with laser light under the above conditions exceeds the peak power density of 0.27 × 10 ⁸ W / cm ² , It can be seen that the peak power density is less than 0.29 × 10 ⁸ W / cm ² .

Further, from FIG. 10B, a CW laser beam having a laser beam intensity (peak power density of 0.29 × 10 ⁸ W / cm ² ) that exceeds the processing threshold value of the damage formation starting portion and is lower than the processing threshold value of the sapphire substrate. Thus, it can be seen that damage can be formed on the sapphire substrate starting from the damage formation starting point.

  Since the sapphire substrate is a transparent material, it cannot normally be processed with CW laser light. In general, as a method of forming damage on a sapphire substrate, there is a method of forming damage by multiphoton absorption using pulsed laser light. By placing a damage formation starting portion on a part of the surface of the sapphire substrate It can be seen that damage can be formed on the sapphire substrate with low energy laser light using CW laser light.

  According to the laser processing method of the present invention, damage can be easily formed on a workpiece with low-energy laser light. For example, the laser processing method of the present invention is useful as a method for cutting a workpiece such as dicing in manufacturing an electronic device.

1 Damage Formation Start Point 2 Workpiece 3 Laser Light

Claims (4)

Preparing a workpiece in which a damage formation starting portion is arranged on a part of the surface;
Irradiating the workpiece with laser light continuously after irradiating the damage formation starting portion with laser light, and forming damage on the workpiece with the damage formation starting portion as a starting point; and Have
The damage formation starting portion is made of a metal, an alloy, a metal compound, or a metal oxide having a lower processing threshold than the workpiece,
The intensity of the laser light exceeds a processing threshold value of the damage formation starting point and is lower than a processing threshold value of the workpiece.
Laser processing method.   The laser processing method according to claim 1, wherein the workpiece is made of a dielectric.   The laser processing method according to claim 1, wherein the damage is a groove formed on a surface of the workpiece. The manufacturing method of an electronic device using the laser processing method as described in any one of Claims 1-3 .