JP2016030288A - Laser processing method and manufacturing method of sheet glass blank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of efficiently processing an object to be processed of high hardness composed of a single crystal sapphire, etc.SOLUTION: In a laser processing method for processing an object 1 to be processed which transmits a laser beam 2 used for laser processing with the laser beam 2, the laser beam 2 applied toward the object 1 to be processed is converged to a lower surface 6 of the object 1 to be processed in an optical axial direction Z, thereby, material of the object 1 to be processed is vaporized by generating multiphoton absorption on a focal position Fp of the laser beam 2, at the same time, the focal position Fp is moved toward the upper surface 5 from the lower surface 6 of the object 1 to be processed in the optical axial direction Z of the laser beam 2 and, thereby, a penetration part 7 is formed on the object 1 to be processed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laser processing method for processing a workpiece using laser light, and a method for manufacturing plate glass blanks.

  Generally, chemically tempered glass is used as a cover glass for portable electronic devices such as smartphones. However, in recent years, single crystal sapphire glass (hereinafter, simply referred to as “sapphire glass”) has been adopted as a cover glass for smartphones and the like. This is because sapphire glass has excellent heat resistance, corrosion resistance, and light transmittance required for the cover glass, and has higher wear resistance than chemically tempered glass. However, since sapphire glass has hardness next to diamond, there is a difficulty that processing is very difficult.

  Conventionally, single crystal sapphire has been widely used for device growth substrates of GaN (gallium nitride) based LED (Light Emitting Diode) and SOS (Silicon on Sapphire) semiconductor device growth substrates. These substrates are manufactured by the following method.

A process of cutting a substrate (hereinafter referred to as a Wafer “wafer”) from a grown crystal (hereinafter referred to as “Boule”) will be described.
First, the upper and lower ends of the boule, which is inferior in quality as a single crystal, such as a collection of defects at the early stage of growth or impurity analysis, are removed. This is called cropping.
Next, a cylindrical shape (hereinafter referred to as “Ingot”) having a predetermined diameter and length is cut out from the boule. A cup-shaped cylindrical drill (hereinafter referred to as “core drill”) with a diamond tip joined to the circumferential tip is rotated at a high speed and cut out. This process is called coring. The hollowing direction and angle are set so that the cylindrical end face is the main surface orientation of the wafer.

Subsequently, part or a plurality of belt-like regions on the outer periphery of the ingot are surface-ground parallel to the ingot axis. This is called an orientation flat showing a unique crystal axis perpendicular to the normal line of the ingot end face, and is necessary for selecting a cutting direction at the time of cutting.
Next, a plurality of wafers are obtained from one ingot by slicing the ingot using a multi-wire saw. With respect to a multi-wire saw, since the relative position of the wire and the material constantly changes, there is an essential problem that the cutting direction and the angle of the wire vary slightly. For this reason, in actual machining, a phenomenon called tracking in which the wire travels while slightly tilting from the cut surface can be seen. In order to reduce such a phenomenon, attempts have been made to mechanically swing the workpiece (Patent Document 1) or to cancel the compressive stress by applying an ultrasonic pulse to the workpiece. Further, as a higher-speed cutting process, a wire discharge in which a metal wire is used as an electrode and discharge is performed between the workpiece while feeding the wire has been studied (Patent Document 2).

JP 2011-240449 A JP 2014-8592 A

  However, in the conventional method described above, the slicing process using a multi-wire saw takes a long time.

  Specifically, in order to slice an ingot using a multi-wire saw, it is desirable to increase the wire diameter and feed the wire with high tension and high speed. However, if the wire diameter is large, a loss of material called kerfloss occurs. growing. Usually, a wire having a core diameter of 180 μm and a wire diameter of 250 μm in which a fine particle layer of diamond is fixed to 70 μm is used. In this case, the cutting speed is 10 hours for 4 inches and 15 hours for 6 inches for single crystal sapphire, and 20 hours for 4 inches and 40 hours for 6 inches for silicon carbide. Furthermore, since the diamond fixing layer is dropped by cutting, it is necessary to change the wire for each cutting in order to maintain high cutting accuracy. Even when cutting accuracy is not so high, it is necessary to replace the wire every 3 to 5 times. For this reason, the loss of the process time accompanying wire exchange and the expense of a wire are needed separately.

  A main object of the present invention is to provide a technique capable of efficiently processing a high-hardness workpiece made of single crystal sapphire or the like.

The first aspect of the present invention is:
A laser processing method for processing a workpiece that transmits laser light used for laser processing with the laser light,
The laser beam irradiated toward the workpiece is converged on one main surface of the workpiece in the optical axis direction of the laser beam, thereby causing multiphoton absorption at the focal position of the laser beam. In the laser processing method, the material of the workpiece is evaporated, and the focal position is moved from one main surface of the workpiece to the other main surface in the optical axis direction of the laser beam. is there.

The second aspect of the present invention is:
In the laser processing method according to the first aspect, the focal position of the laser light is moved from one main surface of the workpiece to the other main surface while scanning the laser light. is there.

The third aspect of the present invention is:
The second aspect of the present invention is characterized in that one main surface of the workpiece is a main surface located on an emission side of the laser beam when the laser beam is irradiated toward the workpiece. It is a laser processing method as described in above.

The fourth aspect of the present invention is:
The workpiece has a cylindrical shape,
Rotating the workpiece about the central axis of the workpiece, irradiating the rotating workpiece with the laser beam from a direction orthogonal to the central axis of the workpiece; and The focus position is moved from one main surface of the workpiece to the other main surface in the optical axis direction of the laser beam. Any one of the first to third aspects, It is a laser processing method as described in above.

According to a fifth aspect of the present invention,
Irradiating the workpiece with the laser light through a correction lens that has an effect opposite to the optical effect when the laser beam is incident on the outer peripheral surface, which is the main surface of the workpiece. It is the laser processing method as described in a 4th aspect.

The sixth aspect of the present invention is:
The workpiece is made of single crystal sapphire or silicon carbide. The laser processing method according to any one of the first to fifth aspects.

The seventh aspect of the present invention is
It is a manufacturing method of plate glass blanks for cover glass that covers the display surface of an electronic device,
A first step of excising the upper and lower ends of a boule made of single crystal sapphire;
A second step of cutting an ingot from the boule;
A third step of slicing the ingot to obtain the plate glass blanks,
In the second step, the ingot is cut out by laser processing,
In the laser processing, by converging the laser beam irradiated toward the boule to the main surface of the upper end or the lower end of the boule, multiphoton absorption is caused at the focal position of the laser beam, and the boule material is changed. A method for producing a sheet glass blank, characterized by evaporating and moving the focal position in the height direction of the boule while scanning the laser beam.

The eighth aspect of the present invention is
It is a manufacturing method of plate glass blanks for cover glass that covers the display surface of an electronic device,
A first step of excising the upper and lower ends of a boule made of single crystal sapphire;
A second step of cutting an ingot from the boule;
A third step of slicing the ingot to obtain the plate glass blanks,
In the third step, the ingot is sliced by laser processing,
In the laser processing, the ingot is rotated about the central axis of the ingot, and laser light irradiated from a direction orthogonal to the central axis of the ingot is applied to the main surface of the ingot with respect to the rotating ingot. Converging causes multiphoton absorption at the focal position of the laser beam to evaporate the material of the ingot, and the focal position from the main surface of the ingot toward the central axis in the optical axis direction of the laser beam It is a manufacturing method of the plate glass blanks characterized by moving.

  According to the present invention, a high-hardness workpiece made of single crystal sapphire or the like can be processed efficiently.

It is the schematic explaining an example of the laser processing method which concerns on embodiment of this invention. It is a figure which shows the change of the state of a workpiece at the time of moving the focus position of a laser beam in time series. It is a figure which shows the specific example in the case of cut | disconnecting a rectangular parallelepiped workpiece using the laser processing method which concerns on embodiment of this invention. It is a figure explaining the procedure in the case of cut | disconnecting a rectangular parallelepiped workpiece using the laser processing method which concerns on embodiment of this invention. It is a figure which shows the specific example in the case of cut | disconnecting a cylindrical workpiece using the laser processing method which concerns on embodiment of this invention. It is a figure explaining the procedure in the case of cut | disconnecting a cylindrical workpiece using the laser processing method which concerns on embodiment of this invention. It is a flowchart which shows the procedure of the manufacturing method of the plate glass blanks which concern on embodiment of this invention. It is a figure explaining the content of the cropping process. It is a figure explaining the content of the cutting-out process. It is a figure explaining the content of the slice process. It is the schematic which shows the structural example of the laser processing apparatus used by laser processing. It is a figure explaining the laser processing method applied to a slicing process. It is a figure which shows the other example of the cut shape of an ingot.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Laser processing method)
First, a laser processing method according to an embodiment of the present invention will be described.
FIG. 1 is a schematic diagram for explaining an example of a laser processing method according to an embodiment of the present invention.
In FIG. 1, it is assumed that the workpiece 1 to be laser processed is a rectangular parallelepiped, and the workpiece 1 is processed by irradiation with laser light 2. The workpiece 1 has a property of transmitting laser light 2 used for laser processing. Here, as an example, it is assumed that the workpiece 1 is made of single crystal sapphire. During laser processing, the laser beam 2 is irradiated to the workpiece 1 through the condenser lens 3. For this reason, the beam diameter of the laser beam 2 irradiated toward the workpiece 1 is gradually narrowed down by the optical effect of the condenser lens 3. Here, the position where the beam diameter of the laser beam 2 is minimized is defined as the focal position Fp of the laser beam 2. The beam diameter of the laser beam 2 at the focal position Fp is called a spot diameter.

  The upper surface 5 and the lower surface 6 of the workpiece 1 are respectively arranged at right angles to the optical axis J1 of the laser beam 2. In this specification, the “optical axis of the laser beam” means the optical axis J1 of the laser beam 2 from the condenser lens 3 to the workpiece 1 and passing through the workpiece 1. . For this reason, in the traveling direction of the laser beam 2, for example, even if the laser beam 2 is reflected by a mirror or the like upstream of the condenser lens 3, the optical axis J1 of the laser beam 2 is uniquely determined. .

  When the laser beam 2 is irradiated from the condenser lens 3 toward the workpiece 1, the laser beam 2 is incident perpendicularly on the upper surface 5 of the workpiece 1 and is emitted perpendicularly from the lower surface 6 of the workpiece 1. . For this reason, the upper surface 5 of the workpiece 1 is positioned on the incident side of the laser beam 2, and the lower surface 6 of the workpiece 1 is positioned on the emission side of the laser beam 2. Further, the upper surface 5 and the lower surface 6 of the workpiece 1 are the main surfaces of the workpiece 1 existing on the optical axis J1 of the laser beam 2, respectively.

  In actual laser processing, first, the lower surface 6 of the workpiece 1 is irradiated with the laser beam 2 irradiated toward the workpiece 1 in the optical axis direction Z (hereinafter also referred to as “Z direction”) of the laser beam 2. To converge. Thereby, the focal position Fp of the laser beam 2 is aligned with the lower surface 6 of the workpiece 1. At the focal position Fp of the laser beam 2, the photon density becomes very high due to the convergence of the laser beam 2. When the power density of the laser beam 2 exceeds a certain threshold value, multiphoton absorption (including two-photon absorption) in which the material constituting the workpiece 1 absorbs a large number of photons simultaneously occurs.

In the laser processing method of the present invention, a short-wavelength pulse laser capable of causing laser ablation (hereinafter simply referred to as “ablation”) to the workpiece 1 when the workpiece 1 is irradiated with the laser beam 2. Is used. Specifically, a nanosecond laser, a picosecond laser, a femtosecond laser, or the like can be used. As a condition of the laser beam necessary for the substance (single crystal sapphire in this embodiment) constituting the workpiece 1 to cause multiphoton absorption at the focal position Fp of the laser beam 2, for example, the wavelength of the laser beam = 1064 nm, repetition frequency = 500 kHz, power = 50 W, pulse width = 10 ps, pulse energy = 0.1 mJ, peak power = 10 MW, power density when focused to 30 μm in spot diameter = 1.4 TW (terawatt) / cm ² can be mentioned.

  As described above, when the focal position Fp of the laser beam 2 is aligned with the lower surface 6 of the workpiece 1 and multiphoton absorption is caused there, a part of the material of the workpiece 1 is evaporated by ablation. For this reason, a local dent is formed in the lower surface 6 of the workpiece 1. The size of the recess varies depending on the spot diameter of the laser beam 2. In the case where the material of the workpiece 1 is evaporated by ablation, a compressed gas may be blown onto the workpiece as necessary in order to efficiently remove the evaporated material. When the workpiece 1 is a material that is easily oxidized, an inert gas (for example, nitrogen gas) may be sprayed.

  When multi-photon absorption is caused at the focal position Fp of the laser beam 2 to evaporate the material of the workpiece 1, the focal position Fp of the laser beam 2 is subsequently changed from the lower surface 6 to the upper surface 5 of the workpiece 1. Move vertically toward. Specifically, the focal position Fp of the laser beam 2 is moved by raising the entire laser optical system including the condenser lens 3 or lowering the workpiece 1 in the optical axis direction Z of the laser beam 2. . As a result, the inside of the workpiece 1 is scraped off along with the movement of the focal position Fp of the laser beam 2 as shown in time series in FIGS. Then, when the focal position Fp of the laser beam 2 reaches the upper surface 5 of the workpiece 1, the penetrating portion 7 (see FIG. 1) is formed in the workpiece 1.

  If the above laser processing method is used, not only the through portion 7 and the like are formed in the workpiece 1 but also the workpiece 1 can be cut. Hereinafter, two specific examples will be described.

(First specific example: When the workpiece is a rectangular parallelepiped)
In the case where the workpiece 1 is a rectangular parallelepiped as shown in FIG. 3, the workpiece 1 is machined in a direction X (left and right direction in the drawing) orthogonal to the optical axis J1 of the laser beam 2 indicated by the downward arrow in the drawing. While the object 1 is reciprocated, the focal position Fp (see FIG. 2) of the laser beam 2 is moved from the lower surface 6 to the upper surface 5 of the workpiece as described above. If it does so, the to-be-processed object 1 will be scraped off in the following procedures.

  First, as shown in FIG. 4A, the focal position Fp of the laser beam 2 is aligned with the left end of the lower surface 6 of the workpiece 1 in the X direction. At this time, even if a part of the laser beam 2 is reflected by the side surface of the workpiece 1, the condition of the laser beam is set so that ablation occurs at the focal position Fp. Next, by moving the workpiece 1 in one direction in the X direction, the focal position Fp of the laser beam 2 is moved to the right end of the workpiece 1 as shown in FIG. If it does so, the lower surface 6 of the to-be-processed object 1 will be scraped off linearly by the movement of the focus position Fp.

Next, as shown in FIG. 4C, the focal position Fp of the laser beam 2 is moved upward by a predetermined amount. The predetermined amount may be about 30 μm when the laser spot diameter is set to 30 μm. Next, by moving the workpiece 1 to the other side in the X direction, the focal position Fp of the laser beam 2 is moved to the left end of the workpiece 1 as shown in FIG. Then, the lower surface 6 of the workpiece 1 is cut deeper than before.
Thereafter, the workpiece 1 is gradually and deeply scraped by repeating the same operation.

  Therefore, the scanning range of the laser beam 2 in the X direction is set to be equal to or greater than the full width W (see FIG. 3) of the workpiece 1, and the focal position Fp of the laser beam 2 is scanned while scanning the laser beam 2 in the X direction under this setting condition. Is moved to the upper surface 5 of the workpiece 1 so that the workpiece 1 can be cut at a position indicated by hatching in FIG.

(Second specific example: When the workpiece is cylindrical)
When the workpiece 1a has a cylindrical shape as shown in FIG. 5, the workpiece 1a is processed in a direction in which the central axis J2 of the workpiece 1a is orthogonal to the optical axis J1 of the laser beam 2 indicated by the downward arrow in the figure. Arrange the object 1a. And when irradiating the workpiece 1a with the laser beam 2, the laser beam 2 is irradiated from the direction orthogonal to the central axis J2 of the workpiece 1a. In this case, the outer peripheral surface of the workpiece 1a existing on the optical axis J1 of the laser beam 2 is a surface corresponding to the main surface of the workpiece 1a.

  In the laser processing, first, as shown in FIG. 6A, the focal position Fp of the laser light 2 is aligned with the lower outer peripheral surface of the workpiece 1a located on the laser light 2 emission side. Further, the workpiece 1a is rotated around the central axis J2 of the workpiece 1a. Thereby, the outer peripheral surface of the to-be-processed object 1a is scraped off in the shape of a thin groove over 1 round. The groove width that is scraped off at this time varies depending on the spot diameter of the laser beam 2. Next, as shown by the arrow in FIG. 6B, the focal position Fp of the laser beam 2 is changed from the lower outer peripheral surface (one main surface) to the workpiece 1a to the upper outer peripheral surface (the other main surface). Move towards. Then, the outer peripheral surface of the workpiece 1a is gradually scraped away toward the central axis J2 as the focal position Fp moves. Thereafter, as indicated by the arrow in FIG. 6C, when the focal position Fp of the laser beam 2 is moved to the central axis J2 of the workpiece 1, the workpiece 1a is completely at the hatching position shown in FIG. Scraped off. Therefore, by moving the focal position Fp of the laser beam 2 to the central axis J2 of the workpiece 1a, the workpiece 1a can be cut at the position indicated by hatching in FIG.

  In the first specific example, the workpiece 1 is reciprocated in the X direction. However, the present invention is not limited to this, and the laser optical system may be reciprocated in the X direction.

  In each of the above specific examples, the laser beam 2 is irradiated from the vertical direction (above) to the workpieces 1 and 1a. However, the present invention is not limited to this, and the laser beam 2 may be irradiated from the horizontal direction. Good.

  Moreover, the material of the to-be-processed objects 1 and 1a should just transmit the laser beam 2 used for laser processing other than single crystal sapphire, for example, may be silicon carbide.

  When the focal position Fp is moved in the optical axis direction Z of the laser light 2, the focal position FP of the laser light 2 is first set on the upper surface 5 of the workpiece 1, contrary to the first specific example described above. In addition, the focal position Fp may be moved from there toward the lower surface 6 of the workpiece 1. However, in carrying out the present invention, it is preferable to move the focal position Fp of the laser beam 2 from the lower surface 6 to the upper surface 5 of the workpiece 1. The reason is as follows.

  First, when the focal position Fp of the laser beam 2 is aligned with the upper surface 5 of the workpiece 1, a local recess is formed on the upper surface 5 of the workpiece 1 by ablation accompanying multiphoton absorption. Further, when the focal position Fp of the laser beam 2 is moved from there toward the lower surface 6 of the workpiece 1, the inside of the workpiece 1 is gradually scraped deeply. In this case, the recessed portion of the workpiece 1 exists on the upstream side in the traveling direction of the laser beam 2, and the focal position Fp of the laser beam 2 exists on the downstream side thereof. For this reason, there exists a possibility that presence of a dent part may have an optical influence on the method of convergence of the laser beam 2. FIG.

  On the other hand, when the focal position Fp of the laser beam 2 is moved from the lower surface 6 to the upper surface 5 of the workpiece 1, the concave portion is located upstream (upward) from the focal position Fp of the laser beam 2. Never exist. For this reason, there is no possibility that the presence of the recessed portion optically affects the way the laser beam 2 converges. Moreover, since the workpiece 1 is scraped away from the lower surface 6 toward the upper surface 5, the processed portion is opened downward. For this reason, the material of the workpiece 1 evaporated by ablation can be removed smoothly using the action of gravity. This also applies to the second specific example described above.

(Manufacturing method of plate glass blanks)
Then, the manufacturing method of the plate glass blanks which concern on embodiment of this invention is demonstrated.
In an embodiment of the present invention, as an example, a plate glass for producing a plate glass blank for a cover glass for covering a display surface of a portable electronic device typified by a smartphone, among display surfaces of various electronic devices. A method for manufacturing blanks will be described.

  The manufacturing method of the plate glass blank which concerns on this Embodiment uses the sapphire glass which consists of single-crystal sapphire for the glass material of the plate glass blanks used as the cover glass or the original plate of the touch panel using this. The plate glass blanks are manufactured in such a size that at least one cover glass can be arranged in a plane. Further, the cover glass is finally finished by polishing the front surface and the back surface. For this reason, when cutting out a plate glass blank from the ingot mentioned later, a plate glass blank is cut out thickly also by the thickness dimension of the cover glass finally obtained.

  The manufacturing method of plate glass blanks has a cropping step S1, a polishing step S2, a cutting step S3, and a slicing step S4 as shown in FIG.

(Cropping step S1)
First, a boule 10 made of single crystal sapphire is produced by crystal growth as shown in FIG. 8A, and then the upper end and lower end of the boule 10 are cut off as shown in FIG. 8B. The boule 10 of single crystal sapphire obtained by crystal growth has a columnar shape with unevenness as a whole including the outer periphery. Therefore, in the cropping step S1, the upper end and the lower end of the boule 10 are cut into a plane (flat) using a processing machine including a steel outer peripheral blade or an inner peripheral blade with diamond fine particles fixed to the tip. Thereby, flat upper end surface 11 and lower end surface 12 are formed at the upper end and lower end of boule 19, respectively. The upper end surface 11 and the lower end surface 12 of the boule 10 after excision are parallel to each other.

(Polishing step S2)
Next, at least the upper end surface 11 of the boule 10 is polished. This polishing process suppresses the reflection of the laser beam at the upper end surface of the workpiece when the workpiece is irradiated with the laser beam in the subsequent process, and allows more laser light to enter the workpiece. This is done for transmission (incident).

(Cutting step S3)
Next, as shown in FIG. 9, a cylindrical ingot 14 is cut out from the boule 10. Thereby, the ingot 14 with a constant outer diameter D is obtained. In the cutting step S3, the ingot 14 is cut out from the boule 10 by laser processing using laser light. A configuration of a laser processing apparatus to be used and a specific laser processing method will be described later.

(Slicing step S4)
Next, as shown in FIG. 10, the ingot 14 is sliced to cut out disk-shaped plate glass blanks 15. In the slicing step S4, the plate glass blanks 15 are cut out from the ingot 10 by laser processing using laser light. A configuration of a laser processing apparatus to be used and a specific laser processing method will be described later.
The plate glass blanks 15 are obtained by the above process.

(Configuration of laser processing equipment)
FIG. 11 is a schematic diagram illustrating a configuration example of a laser processing apparatus used in laser processing.
The illustrated laser processing apparatus 20 includes a laser oscillator 21, a propagation optical system 22, a galvano scanner 23, a condenser lens 24, a work holding mechanism 25, and a relative position variable mechanism 26. Among these, the laser oscillator 21, the propagation optical system 22, the galvano scanner 23, and the condenser lens 24 constitute a single laser optical system 27.

The laser oscillator 21 emits laser light (laser beam) having a predetermined wavelength used for laser processing. The laser oscillator 21 can be configured using, for example, a fixed laser such as a YAG laser.
The propagation optical system 22 propagates the laser light emitted from the laser oscillator 21. The propagation optical system 22 is disposed between the laser oscillator 21 and the galvano scanner 23.
The galvano scanner 23 reflects the laser beam propagated by the propagation optical system 22 by a plurality of mirrors and scans the laser beam according to a predetermined condition by appropriately changing the angle of each mirror. . The scanning drive shaft of the galvano scanner 23 has a two-axis configuration or a three-axis configuration.
The condensing lens 24 condenses the laser light scanned by the galvano scanner 23.

The workpiece holding mechanism 25 holds the boule 10 serving as a workpiece.
The relative position variable mechanism 26 changes the relative position between the boule 10 held by the work holding mechanism 25 and the laser optical system 27 in the Z direction (vertical direction).

(Laser processing in the cutting process)
Then, the laser processing method applied to cutting-out process S3 is demonstrated. In the cutting-out step S3, the laser processing apparatus 20 having the above configuration is used.

  First, the boule 10 serving as a workpiece is held by the workpiece holding mechanism 25. At this time, the boule 10 is held by the work holding mechanism 25 so that the central axis J3 of the boule 10 is parallel to the optical axis of the laser beam 28 irradiated through the condenser lens 24. Thereby, in the workpiece holding mechanism 25, the boule 10 is held in a vertical posture with the upper end surface 11 of the boule 10 facing the condenser lens 24. Further, the upper end surface 11 of the boule 10 is disposed upward, and the lower end surface 12 of the boule 10 is disposed downward.

  Next, laser light having a predetermined wavelength is emitted from the laser oscillator 21. This laser light reaches the condenser lens 24 via the propagation optical system 22 and the galvano scanner 23, and is further irradiated to the boule 10 through the condenser lens 24. At this time, as an initial setting condition of the laser processing apparatus 20, the laser light 28 condensed by the condenser lens 24 is converged below the lower end surface 12 of the boule 10 on the optical axis of the laser light 20. The relative position between the boule 10 and the laser optical system 27 is set by the relative position variable mechanism 26. Under this initial setting condition, the focal position of the laser beam exists at a position deviating from the boule 10.

  Next, under the above initial setting conditions, the galvano scanner 23 scans the laser light 28 in a circle as indicated by the two-dot chain line arrow in the figure. The diameter of the circle when scanning with the laser light is set according to the outer diameter D (see FIG. 9) of the ingot 14 cut out from the boule 10. Then, while the galvano scanner 23 scans the laser beam 28 in a circle, the relative position variable mechanism 26 moves the boule 10 away from the condenser lens 24, that is, downward. Thereby, the laser beam 28 condensed by the condenser lens 24 is converged on the lower end surface 12 of the boule 10 during the movement of the boule 10. Then, the focal position (not shown) of the laser light 28 is aligned with the lower end surface 12 of the boule 10. At the focal position of the laser beam 28, the photon density becomes very high due to the convergence of the laser beam 28. When the power density of the laser light exceeds a certain threshold, multiphoton absorption (including two-photon absorption) occurs.

  As described above, when multiphoton absorption occurs at the lower end surface 12 of the boule 10 which is the focal position of the laser beam, the material (atoms, molecules, etc.) of the boule 10 is evaporated by ablation. For this reason, when the galvano scanner 23 scans the laser light 28 in a circular shape, the lower end surface 12 of the boule 10 is cut into a circular shape (ring shape) by ablation. Further, when the focal position of the laser beam 28 is gradually moved from the lower end surface 12 to the upper end surface 11 of the boule 10 while the galvano scanner 23 scans the laser beam 28 in a circle, the laser beam is moved. As the focal position moves, the boule 10 is deeply cut away. Then, when the focal position of the laser light 28 reaches the upper end surface 11 of the boule 10, the ingot 14 (see FIG. 9) is separated from the boule 10. For this reason, the cylindrical ingot 14 can be cut out from the boule 10. At this time, the boule 10 after taking out the ingot 14 is in a state in which the inside is hollowed out into a cylindrical shape.

  In the above embodiment, the galvano scanner 23 is used to scan the laser beam 28 in a circular shape, but the present invention is not limited to this. For example, although not shown, a rotary optical mechanism may be provided in the laser optical system, and the laser light may be scanned in a circle by driving the rotary head mechanism. Alternatively, a rotation mechanism may be provided in the workpiece holding mechanism that holds the boule, and the laser beam may be scanned in a circular shape by rotating the boule by driving the rotation mechanism.

(Laser processing in slicing process)
Next, the laser processing method applied to slice process S4 is demonstrated using FIG. FIG. 12A is a view of an ingot during laser processing as seen from the central axis direction of the ingot, and FIG. 12B is a view taken along arrow E in FIG.
In the illustrated laser processing method, a laser processing apparatus different from the laser processing apparatus 20 configured as described above is used. Specifically, since it is not necessary to scan the laser beam during the laser processing in the slicing step S4, the configuration of the laser optical system may not include a galvano scanner. That is, the laser optical system only needs to include a laser oscillator, a propagation optical system, and a condenser lens. The laser optical system desirably includes a correction lens 32 in addition to the condenser lens 31. The reason will be described later.

  On the other hand, the work holding mechanism (not shown) holds a cylindrical ingot 14 that is a workpiece, and in this case, the ingot 14 is held horizontally. Further, the relative position variable mechanism (not shown) is referred to as a rotation mechanism that rotates the ingot 14 in the θ direction (or the opposite direction) and a moving mechanism that moves the ingot 14 in the Z direction (hereinafter referred to as “vertical movement mechanism”). ) And a moving mechanism for moving the ingot 14 in the Y direction (hereinafter referred to as “horizontal moving mechanism”). Among these, the rotation mechanism rotates the ingot 14 around the central axis J4 of the ingot 14. Further, the vertical movement mechanism moves the ingot 14 in a direction (Z direction) parallel to the optical axis of the laser beam 33 irradiated from the condenser lens 31 toward the ingot 14, and the horizontal movement mechanism is the ingot. The ingot 14 is moved in a direction (Y direction) parallel to the center axis J4.

  The correction lens 32 is a lens that achieves an effect opposite to the optical effect when the laser beam 33 is incident on the outer peripheral surface of the ingot 14. When viewed from the central axis direction of the ingot 14, the outer peripheral surface of the ingot 14 becomes a convex surface with respect to the laser beam 33. For this reason, when the laser beam 33 is irradiated (incident) on the outer peripheral surface of the ingot 14, a part of the laser beam 33 is affected by the convex surface. Therefore, in the present embodiment, in order to weaken (cancel) the optical effect of the convex surface (outer peripheral surface) of the ingot 14, a correction lens 32 having a concave surface whose concavo-convex relationship is opposite to that of the convex surface is added. It is desirable that the convex surface of the ingot 14 and the concave surface of the correction lens 32 have the same curvature when viewed from the central axis direction of the ingot 14. By adding the correction lens 32, the influence of the outer peripheral surface (convex surface) of the workpiece 1 can be reduced.

  When the ingot 14 is actually sliced by laser processing, the ingot 14 is held by the work holding mechanism. At this time, the ingot 14 is supported horizontally so that the central axis J4 of the ingot 14 is orthogonal to the optical axis of the laser beam 33 irradiated through the condenser lens 32. In this state, the central axis J4 of the ingot 14 is positioned on the optical axis J1 of the laser beam 33.

  Next, laser light having a predetermined wavelength is emitted from a laser oscillator (not shown). This laser light is applied to the ingot 14 through a condensing lens 31 and a correction lens 32 from a propagation optical system (not shown). At this time, as an initial setting condition of the laser processing apparatus, the ingot 14 and the laser are arranged so that the laser light 33 collected by the condenser lens 31 converges slightly below the outer peripheral surface on the lower side of the ingot 14 in the Z direction. A relative position with respect to the optical system is set by a vertical movement mechanism. In the Y direction, a position shifted to the other end face side of the ingot 14 by an amount corresponding to the thickness dimension of the plate glass blanks with respect to one end face of the ingot 14 is set as a slice position. The position of the optical axis J1 of the laser beam 33 is adjusted. Under this initial setting condition, the focal position (not shown) of the laser beam 33 exists at a position off the ingot 14.

  Next, the ingot 14 is rotated in the θ direction under the initial setting condition, and the focal position Fp of the laser light 33 is moved relatively upward with respect to the rotating ingot 14. The focal position Fp is moved by lowering the ingot 14 by a vertical movement mechanism. Thereby, as shown in FIG. 12, the laser beam 33 condensed by the condenser lens 31 is converged on the lower outer peripheral surface of the ingot 14. Then, the focal position Fp of the laser beam 33 is aligned with the lower outer peripheral surface of the ingot 14. As a result, multiphoton absorption occurs on the outer peripheral surface of the lower side of the ingot 14 at the focal position Fp of the laser beam 33, and the material of the ingot 14 is evaporated by ablation. Further, the outer surface of the ingot 14 is scraped off into a thin groove over the entire circumference by the rotation of the ingot 14. Further, when the focal position Fp of the laser beam 33 is moved relatively upward from that state, the outer peripheral surface of the ingot 14 is gradually scraped away toward the central axis J4 accordingly.

  Thereafter, when the focal position Fp of the laser beam reaches the height of the central axis J4 of the ingot 14 by the descending of the ingot 14, a part of the ingot 14 (part that becomes a plate glass blank) is cut off at the slice position. Therefore, one sheet glass blank 15 (see FIG. 10) can be cut out from the ingot 14. Note that the laser processing method applied to the slicing step S4 is basically the same as the method described with reference to FIGS.

  When one sheet glass blank 15 is cut out from the ingot 14 in this way, in order to cut out the second sheet glass blank 15, the ingot 14 is moved by the horizontal movement mechanism in an amount corresponding to the thickness dimension of the sheet glass blank in the Y direction. Then, the relative position between the ingot 14 and the laser optical system is returned to the initial setting condition, and the same operation as described above is performed. Thereby, the plate glass blanks 15 can be cut out from the ingot 14 again. Thereafter, a plurality of plate glass blanks 15 are obtained from one ingot 14 by repeating the same operation as described above.

Here, when slicing the ingot 14 to obtain the plate glass blank 15, the difference in processing time between using the conventional method and using the method of the present invention will be described.
First, in the conventional method using a multi-wire saw, since the processing speed is 0.08 to 0.27 mm / min as described above, if the outer diameter of the ingot is 4 inches, 10 slices per slice processing. It takes about 15 hours for 6 inches. On the other hand, according to the method according to the embodiment of the present invention, although depending on the power of the laser used, for example, when a laser with a power of 100 W is used, a processing speed of 200 mm / second or more can be obtained. For this reason, when the outer diameter of the ingot is 4 inches, one slicing process is 2 hours or less, and even 6 inches is 3 hours or less. Therefore, the processing time of the slicing process can be greatly shortened. Further, in the conventional method, the wire needs to be replaced, but in the method according to the embodiment of the present invention, it is not necessary. For this reason, it becomes possible to reduce significantly the manufacturing cost of plate glass blanks and cover glass using the same.

  In the slicing step S4 using the laser processing, the laser light irradiated on the ingot 14 enters the inside of the ingot 14 through the narrow groove portion formed on the outer peripheral surface of the ingot 14. However, the groove width of the narrow groove portion (for example, 30 μm or less) is sufficiently smaller than the beam diameter (for example, 3000 μm or more) of the laser light incident on the upper outer peripheral surface of the ingot 14. The influence of the narrow groove portion existing on the outer peripheral surface of the ingot 14 on the laser processing becomes relatively small.

  Further, in the cutting step S3 using the laser processing, the cylindrical ingot 14 is cut out from the boule 10 by scanning the laser beam 28 in a circle with the galvano scanner 23. However, the present invention is not limited to this. By scanning the laser light 28 into an arbitrary shape by the galvano scanner 23, a columnar ingot having the scanning shape as a cross-sectional shape can be cut out. As a specific example, when the galvano scanner 23 scans the laser light 28 into a rectangle (including a square), a rectangular column shape (a shape close to a rectangular parallelepiped as shown in FIG. 13) from the boule 10 has an angle R. Ingot 14a can be cut out. Further, in that case, by scanning the laser beam 2 in a round shape with a rectangular corner, a prismatic ingot 14a with a rounded corner can be cut out as shown in the figure. Further, by slicing the prismatic ingot 14a using the above laser processing method, rectangular plate glass blanks having four rounded corners can be obtained.

DESCRIPTION OF SYMBOLS 1, 1a ... Workpiece 2 ... Laser beam 3 ... Condensing lens 5 ... Upper surface 6 ... Lower surface 10 ... Boule 11 ... Upper end surface 12 ... Lower end surface 14 ... Ingot 15 ... Sheet glass blanks

Claims (8)

A laser processing method for processing a workpiece that transmits laser light used for laser processing with the laser light,
The laser beam irradiated toward the workpiece is converged on one main surface of the workpiece in the optical axis direction of the laser beam, thereby causing multiphoton absorption at the focal position of the laser beam. A laser processing method characterized by evaporating a material of a workpiece and moving the focal position from one main surface of the workpiece toward the other main surface in the optical axis direction of the laser beam. The laser processing method according to claim 1, wherein the focal position of the laser beam is moved from one main surface of the workpiece toward the other main surface while scanning the laser beam. The one main surface of the workpiece is a main surface positioned on the laser beam emission side when the laser beam is irradiated toward the workpiece. Laser processing method. The workpiece has a cylindrical shape,
Rotating the workpiece about the central axis of the workpiece, irradiating the rotating workpiece with the laser beam from a direction orthogonal to the central axis of the workpiece; and The focal position is moved from one main surface of the workpiece to the other main surface in the optical axis direction of the laser beam. Laser processing method. The laser beam is irradiated to the workpiece through a correction lens that has an effect opposite to an optical effect when the laser beam is incident on an outer peripheral surface that is a main surface of the workpiece. Item 5. The laser processing method according to Item 4. The laser processing method according to claim 1, wherein the workpiece is made of single crystal sapphire or silicon carbide. It is a manufacturing method of plate glass blanks for cover glass that covers the display surface of an electronic device,
A first step of excising the upper and lower ends of a boule made of single crystal sapphire;
A second step of cutting an ingot from the boule;
A third step of slicing the ingot to obtain the plate glass blanks,
In the second step, the ingot is cut out by laser processing,
In the laser processing, by converging the laser beam irradiated toward the boule to the main surface of the upper end or the lower end of the boule, multiphoton absorption is caused at the focal position of the laser beam, and the boule material is changed. A method for producing a plate glass blank, characterized by evaporating and moving the focal position in the height direction of the boule while scanning the laser beam. It is a manufacturing method of plate glass blanks for cover glass that covers the display surface of an electronic device,
A first step of excising the upper and lower ends of a boule made of single crystal sapphire;
A second step of cutting an ingot from the boule;
A third step of slicing the ingot to obtain the plate glass blanks,
In the third step, the ingot is sliced by laser processing,
In the laser processing, the ingot is rotated about the central axis of the ingot, and laser light irradiated from a direction orthogonal to the central axis of the ingot is applied to the main surface of the ingot with respect to the rotating ingot. Converging causes multiphoton absorption at the focal position of the laser beam to evaporate the material of the ingot, and the focal position from the main surface of the ingot toward the central axis in the optical axis direction of the laser beam The manufacturing method of the sheet glass blanks characterized by moving.

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