KR20180013680A - Method and apparatus for laser processing substrate of brittle material - Google Patents

Abstract

Disclosed is a method for laser processing for a brittle material substrate, irradiating a laser from a surface of a brittle material substrate. Therefore, more heat injuries can be inhibited, and processing time can be shorter than ever before when processing a plurality of points of the other surface in the thickness direction. Moreover, processing in a limited pitch can be possible. When a plurality of holes are formed in the thickness direction from the other surface of the brittle material substrate by irradiating the laser beam from the surface of the brittle material substrate, the apparatus allows the laser beam to repeatedly switch the focus thereof from the other surface of the brittle material substrate in the thickness direction as far as the predetermined distance in order to focus on a new height position whenever irradiation of the laser beam at one height position of one object for processing is completed. Therefore, a plurality of holes can be gradually formed.

Description

METHOD AND APPARATUS FOR LASER PROCESSING SUBSTRATE OF BRITTLE MATERIAL BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of processing a brittle material substrate using a laser, and more particularly to processing in a thickness direction at a plurality of locations.

For example, in the case of performing machining in the thickness direction (depth direction), such as a drilling process for forming a through hole or a non-through hole in a brittle material substrate typified by a glass substrate, a sapphire substrate or an alumina substrate, A method of using a laser is widely practiced.

In this type of drilling with a laser, a laser is radially concentrically irradiated to form a through hole or non-through hole having a diameter larger than the beam spot diameter of the laser (beam diameter at the focus position, condensed diameter) (For example, refer to Patent Document 1).

Japanese Patent Application Laid-Open No. 2013-146780

When a through hole or a non-through hole is formed in a thickness direction by laser with a plurality of portions of a brittle material substrate, conventionally, each through hole or non-through hole is sequentially formed. However, in the case of such a method, since the laser is continuously irradiated to the same region continuously until the formation of the hole is completed, there is a problem that thermal damage (occurrence of chipping and chipping) is likely to occur in the vicinity of the region .

In addition, when the depth of the hole to be formed is large, it is necessary to move the brittle material substrate in the thickness direction every time the individual hole is formed, so that it takes time to process.

In the case where holes are formed at a plurality of locations on the back surface side by irradiating a laser beam from the front surface side of the brittle material substrate, if the pitch of the areas to be formed holes is small, subsequent to the formation of holes in one area, There is a case where the laser interferes with the hole already formed in the adjacent area when the hole is to be formed, so that a defect that the shape of the relevant hole collapses may occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a brittle material substrate which is capable of reducing the machining time while suppressing thermal damage And a laser processing method of a brittle material substrate capable of processing at a narrow pitch.

According to a first aspect of the present invention, there is provided a laser processing method of a brittle material substrate for forming a plurality of holes in a thickness direction from a back surface of a brittle material substrate by irradiating a laser beam from a surface side of the brittle material substrate, And the laser beam is irradiated to the laser beam at all of the positions to be processed at the one height position, The focus of the laser beam is moved by a predetermined distance in the thickness direction from the back surface of the brittle material substrate every time the irradiation of the beam is finished, do.

According to a second aspect of the present invention, there is provided a laser machining method for a brittle material substrate according to claim 1, characterized in that the laser beam is scanned so that the plurality of holes are round holes, .

The invention of claim 3 is a laser machining method of a brittle material substrate according to claim 1 or 2, characterized in that it is a picosecond UV laser or a picosecond green laser of the laser beam.

According to a fourth aspect of the present invention, there is provided a laser machining apparatus for processing a back side of a brittle material substrate by irradiating a laser beam from a surface side of the brittle material substrate, the stage comprising: a stage on which the brittle material substrate is supported and fixed; And a head for irradiating the brittle material substrate mounted on the stage with the laser beam emitted from the light source. When the irradiation of the laser beam at one height position at one processing target position ends The stage is moved relative to the head every time the irradiation of the laser beam is finished at all of the machining target positions at the one height position, The focal point of the laser beam is moved a predetermined distance in the thickness direction from the back surface of the brittle material substrate By repeated turning on to the focus to a new height position characterized in that gradually formed a plurality of holes.

According to a fifth aspect of the present invention, there is provided a laser machining apparatus as set forth in the fourth aspect, wherein the plurality of holes are round holes, and the head scans the laser beam so that the focal point forms a locus of concentric circles at the target portion do.

The invention of claim 6 is the laser machining apparatus according to claim 4 or claim 5, characterized in that the laser beam is a picosecond UV laser or a picosecond green laser.

According to the invention of Claims 1 to 6, the perforation of the back surface of the brittle material substrate in the thickness direction at a plurality of places is carried out by a gradual processing method in which a plurality of holes are formed little by little in parallel, The machining time can be shortened as compared with the case where sequential machining is performed to sequentially form individual holes. Further, it is possible to form a plurality of holes having a narrow pitch and a large depth which can not be performed in sequential processing.

Fig. 1 is a diagram schematically showing a configuration of a laser machining apparatus 100. Fig.
Fig. 2 is a view for explaining the scanning form of the laser beam LB in the drilling process.
3 is a diagram for explaining the sequence of sequential machining.
Fig. 4 is a diagram for explaining the order of gradual processing.
Fig. 5 is a view for explaining a difference in machining at a narrow pitch in progressive machining and gradual machining.
Fig. 6 is a picked-up image of a glass substrate on which a plurality of round holes are formed by gradual machining and sequential machining from above the round holes.

<Outline of Laser Processing Apparatus>

Fig. 1 is a diagram schematically showing a configuration of a laser machining apparatus 100 used for processing a brittle material substrate W in an embodiment of the present invention. The laser processing apparatus 100 roughly irradiates the brittle material substrate W with the laser beam LB emitted from the light source 1 by irradiating the brittle material substrate W fixedly mounted on the stage 2, So as to execute machining.

Examples of the brittle material substrate W to be processed include a glass substrate, a sapphire substrate, and an alumina substrate.

The laser processing apparatus 100 includes a head 3 which is a direct irradiation source of a laser beam LB to a brittle material substrate W and a head 3 which is a light source 1 And a laser beam LB emitted from the light source 1 is reflected at a predetermined angle so as to be incident on the head 3 And a control section 10 for controlling the operation of each part of the laser processing apparatus 100. The laser processing apparatus 100 includes a mirror 5 for determining the optical path of the laser beam LB, In FIG. 1, two mirrors 5 are provided, but this is only an example, and the number and position of the mirrors 5 are not limited to those shown in FIG.

The laser beam LB may be appropriately selected depending on the material of the brittle material substrate W to be processed. For example, a picosecond UV laser or a picosecond green laser is suitable. As the light source 1, a laser beam LB used for processing may be employed. The operation of generating the laser beam LB in the light source 1 and the ON / OFF operation of the shutter 4 are controlled by the control unit 10. [

The stage 2 is a portion where the brittle material substrate W is horizontally mounted and fixed at the time of processing. The fixing of the brittle material substrate W to the stage 2 is fixed by sandwiching the end portion of the brittle material substrate W by a predetermined clamping means. The stage 2 is configured such that the air gap portion 2a is provided below the brittle material substrate in such a fixed state. The reason for this is to drop the processing debris generated in the brittle material substrate W to the void portion 2a when the processing is performed in the form described later. In addition, the processing residue is suitably removed by a removal means not shown.

The stage 2 is configured to be movable in the vertical direction by the driving mechanism 2m. By controlling the drive mechanism 2m by the control unit 10, the laser machining apparatus 100 can move the brittle material substrate W up and down in its thickness direction during processing. The driving mechanism 2m may be provided so that the stage 2 can be moved in the horizontal uniaxial direction or the biaxial direction and at least the supporting point of the brittle material substrate W among the stages 2 can be rotated It may be installed as much as possible. As a result, the machining position can be adjusted or changed appropriately.

The head 3 has a galvanometer mirror 3a and an f? Lens 3b. The galvanometer mirror 3a is controlled in its posture by the control unit 10 so that the incident laser beam LB can be emitted within a predetermined range in an arbitrary direction. The f? Lens 3b is horizontally disposed above the stage 2 and is arranged so that the laser beam LB emitted from the galvanometer mirror 3a can enter the galvanometer mirror 3a, The laser beam LB is irradiated vertically above the brittle material substrate W horizontally mounted and fixed to the stage 2 by passing through the f? Lens 3b. Thereby, the laser processing apparatus 100 is caused to perform laser beam irradiation on the brittle material substrate W mounted and fixed on the stage 2 by continuously changing the attitude of the galvanometer mirror 3a under the control of the control unit 10 LB can be successively different from each other. As a result, the brittle material substrate W can be scanned from above by the laser beam LB.

The irradiation range of the laser beam LB with respect to the brittle material substrate W supported and fixed on the stage 2 is predetermined in accordance with the size and attitude change range of the galvanometer mirror 3a. It is necessary to move the stage 2 by the drive mechanism 2m to perform the machining on the new irradiable range.

Instead of installing the drive mechanism 2m on the stage 2, a drive mechanism (not shown) may be provided on the head 3 to move the head 3 relative to the stage 2. [

The control unit 10 is implemented by, for example, a general-purpose computer. A control program not shown is executed in the control unit 10 to perform various operations in the laser machining apparatus 100 such as the emission of the laser beam LB from the light source 1 or the movement of the stage 2, And the attitude change of the mirror 3a is realized.

<Overview of drilling>

Next, a description will be given of an example in which machining is performed at one place for the drilling process according to the present embodiment, which is performed using the laser machining apparatus 100 described above with respect to the brittle material substrate W. FIG. In the present embodiment, the drilling process is performed on the back side of the brittle material substrate W by the laser beam LB incident on the brittle material substrate W (from the front side). Further, in the case of performing the boring process in this form, the brittle material substrate W to be the object is made of a material transparent to the laser beam LB to be used. Fig. 2 is a view for explaining a scanning form of the laser beam LB in such drilling.

2, z = z0 is the position of the back surface (lower surface) of the brittle material substrate W and the irradiation position of the laser beam LB is changed from z = z0 to z = Z1 so that a substantially cylindrical non-through hole (round hole) having a predetermined depth D in diameter in the thickness direction is formed from the surface of the brittle material substrate W. [ Here, the diameter D is a value larger than the diameter (beam spot diameter) d1 of the focal spot (beam spot F) of the laser beam LB. Hereinafter, the diameter D is set to a value at the surface of the brittle material substrate W, that is, at z = z0.

First, the height position of the stage 2 supporting and fixing the brittle material substrate W is adjusted so that the focal point F coincides with the back surface (z = z0) of the brittle material substrate W, And the output of the beam LB (hereinafter referred to as the laser output) is set to a predetermined value. Thereafter, by controlling the attitude of the galvanometer mirror 3a, the center C of the focus F is coaxial with the diameter D at z = z0, and a plurality of concentric circles of different diameters The beam LB is scanned. In other words, a plurality of rounds of scanning are performed with different diameters. In the following description, the locus of the center C of the focus F is simply referred to as the locus of the laser beam LB.

In the case shown in Fig. 2, the laser beam LB is scanned with the laser output E0 such that four concentric traces TR1, TR2, TR3 and TR4 are sequentially drawn counterclockwise from the outside. By such scanning, the vicinity of the surface of the brittle material substrate W is processed to form a concave portion. In FIG. 2, four trajectories TR1, TR2, TR3, and TR4 are described independently. However, at the time of actual machining, when one round of scanning by the laser beam LB is almost completed, LB may be maintained while maintaining the output state of the next main scan.

When the scanning by the laser beam LB at z = z0 in the above-described mode is completed, the stage 2 is moved down by the predetermined pitch? Z, i.e., the focus F of the laser beam LB, Is shifted in the depth direction of the brittle material substrate W by the distance DELTA z from z = z0, and then the concentric scanning as described above is performed. In addition, the depth of the concave portion formed first and the pitch [Delta] z may not always coincide with each other. Thereafter, until the focal point F of the laser beam LB reaches the position z = z1 and the movement of the stage 2 and the concentric circular shape by the laser beam LB are performed until the concentric scanning at this position is performed Is repeated. In other words, at each height position, a plurality of main scanning is performed in a concentric shape. The values of DELTA z and z1 are determined according to the material of the brittle material substrate W and the depth of the round hole to be formed. Usually, the position where z = z1 is determined to be shallower than the position where the bottom of the round hole is viewed from the back of the brittle material substrate W.

Thus, every time the concentric scanning of the laser beam LB at the different depth positions is repeated, the formation of the concave portion in the thickness direction of the brittle material substrate W proceeds, and finally, a round hole of a desired depth is formed do.

The diameter D of the round hole to be formed and the diameter d1 of the beam spot L2 are set so that the maximum diameter (the diameter of the locus TR1) d2 and the number of scan loci (i.e., the number of scans) ) And the attitude change range of the galvanometer mirror 3a may be determined experimentally or empirically in advance. For example, in the case where the diameter of the round hole to be formed is 50 mu m and the beam spot diameter d1 is 15 mu m, a desired round hole can be formed by performing 5 times of concentric circular scanning with d2 = 30 mu m .

In Fig. 2, a plurality of concentric circles of main scanning are sequentially performed from the outside, but they may be sequentially arranged from the inside. Or the scanning order may be changed every time the depth position of the focus F changes. Further, the laser output may be different depending on the depth position of the focus F.

In the case shown in Fig. 2, the height position of the focus F is changed by DELTA z so that the portion where the main scanning is performed is also decreased by the distance DELTA z in the thickness direction, but instead the height position of the focus F is continuously (Spiral scanning) in which a plurality of times of main scanning in a manner corresponding to the main scanning in a plurality of concentric circles described above are continuously performed while the focus F is shifted by a distance DELTA z in the thickness direction.

In the above description, the case of forming the non-through hole is described as an example, but the same method can be adopted even in the case of forming the through hole. That is, when the total movement distance of the focus F of the laser beam LB from the surface of the brittle material substrate W is made sufficiently large, the through hole can be formed. In this case as well, the specific processing conditions may be determined in accordance with the thickness of the brittle material substrate W and the irradiation conditions of the laser beam LB, as in the case of forming the non-through holes.

In the above explanation, the circular holes are formed by scanning the laser beam LB in the main scanning direction. However, when the diameter D of the circular holes to be formed is small, the main scanning is not essential.

&Lt; Processing of a plurality of holes &

Next, processing for forming a plurality of holes in the thickness direction from the surface of one brittle material substrate W to be carried out by using the laser machining apparatus 100 will be described. The machining of such a plurality of holes can be realized simply by a method of sequentially forming individual holes (hereinafter referred to as a sequential machining), but in the present embodiment, the machining is called gradual machining. Gradually, by using the above-described technique, while changing the portion to be processed each time the irradiation of the laser beam LB at one height position in one machining target position is completed, So that it is formed in small increments.

3 is a diagram for explaining the sequence of sequential machining. Now, a case will be considered in which a plurality of round holes (non-through holes) having a depth h in the thickness direction of the brittle material substrate W are formed with pitch p. It should be noted that irradiation of the laser beam LB at one height position is performed by the main scanning described above. Fig. 3 (a) shows four neighboring regions a, b, c, and d among the to-be-formed regions H0 of individual round holes. In Fig. 3, only the planned formation regions H0 adjacent to each other in the direction of the oblique view are shown, but in the actual processing, the planned formation region H0 may be determined two-dimensionally.

In the sequential processing, first, the focal point F of the laser beam LB is adjusted to the height (z = z0) of the back surface of the brittle material substrate W, and as shown in Fig. 3, The drilling process is performed by repeating the main scan of concentric circles and the shift of the height position of the focus F of the laser beam LB in the form shown. 3 (c), when a round hole Ha is formed in the region a, the laser beam LB is focused on the laser beam LB in the same manner as in the case of the concentric circular main scanning in the region b The round holes Hb are formed in the region b repeatedly as shown in Fig. 3 (d). After the formation of the round hole Hb is completed, processing is then performed on all of the to-be-formed regions H0 in the order of region c → region d. Finally, as shown in FIG. 3 (e) A desired plurality of round holes H (Ha, Hb, Hc and Hd) are formed in the to-be-formed region H0 (regions a, b, c and d).

On the other hand, Fig. 4 is a diagram for explaining the gradual processing procedure adopted in the present embodiment. Now, it is assumed that a plurality of round holes (non-through holes) having a depth h in the thickness direction of the brittle material substrate W are formed with pitch p as in the case of the sequential machining shown in Fig. 4 (a) also shows four neighboring regions a, b, c, and d among the to-be-formed regions H0 of individual round holes. Of course, also in the case of processing gradually, the to-be-formed region H0 may be determined two-dimensionally.

First, as shown in Fig. 4 (b), the focal point F of the laser beam LB is adjusted to the height (z = z0) of the back surface of the brittle material substrate W, (LB). As a result, as shown in Fig. 4 (c), a concave portion is formed in the region a. Subsequently, unlike sequential machining, gradual machining is performed in the region b while keeping the height position of the focus F at z = z0. As a result, as shown in Fig. 4 (d), a recess is formed in the region b following the region a. Subsequently, main scanning is performed on the area c.

Thus, the main scanning is performed for all the to-be-formed regions H0 (regions a, b, c, and d in Fig. 4) as shown in Fig. 4 (e) while maintaining the height position of the focus F at z = d), a recess is formed in each region, the height position of the focal point F is shifted by the distance DELTA z, and the main scanning is executed again for the region a. As a result, as shown in Fig. 4 (f), the formation of the recess in the region a proceeds. When the main scanning is completed, main scanning is performed on all the to-be-formed regions H0 in the order of region b? Region c? Region d without changing the height position of the focus F, As shown in Fig. Similarly, the shift of the distance DELTA z at the height position of the focus F and the main scanning in the order of the region a, the region b, the region c, and the region d are performed at a predetermined position along the depth h of the predetermined round hole z = z1). Finally, a desired plurality of round holes H (Ha, Hb, Hc and Hd) are formed in the respective to-be-formed regions H0 (regions a, b, c and d) .

If the sequential processing and the gradual machining are compared, the laser is continuously irradiated to the region until the formation of the hole in the one to-be-formed region is completed, so that the temperature in the vicinity of the region is raised So that thermal damage (cracking, occurrence of chipping) is likely to occur. On the other hand, in the case of gradual processing, the processing time per processing time in each of the formation scheduled regions is short, and the planned formation regions to be processed are changed in turn, so that the temperature rise in each of the planned formation regions is unlikely to occur. Therefore, thermal damage (generation of cracks and chipping) is hard to occur.

In the case of the sequential machining, the stage 2 is moved up and down every time the machining is performed in each of the processing target areas so that the focal point F of the laser beam LB is shifted from the z = z0 side of the brittle material substrate W to z = z1, while in the case of gradual processing, the movement of the focus F from z = z0 to z = z1 is only intermittent from the start of machining to the end of machining. This means that the machining time is shorter than the sequential machining. In addition, the effect of shortening the time is remarkable as the number of holes to be drilled is larger.

<Processing at Narrow Pitch>

The gradual processing described above is suitable for forming a plurality of holes at a narrow pitch on the back side of the brittle material substrate W. [ Fig. 5 is a view for explaining a difference in machining at a narrow pitch between progressive machining and gradual machining.

Now, as shown in Fig. 5 (a), when the pitch p is smaller than that shown in Figs. 3 (a) and 4 (a) A case of forming a plurality of larger non-through holes is considered.

In the case where such a formation is to be carried out by sequential processing, for example, formation of a hole Ha in one to-be-formed region H0 (region a) followed by formation of a to-be-formed region H0 (region b) The laser beam LB to be scanned in the area b in the region b is partly reflected by the portion p as shown in Fig. 5 (b), depending on the size of the pitch p and the depth h, And may interfere with the hole Ha in the region (I). When such interference occurs, defects such as collapsing the shape of the hole H formed first occur.

On the other hand, in the case of gradual processing, as shown in Fig. 5 (c), even if the laser beam LB is scanned in the area B where the concave part is to be formed in the area b after the formation of the concave part in the area a, The laser beam LB does not interfere with the concave portion formed in the region A since the difference in height between the focus F of the laser beam LB and the bottom portion of the concave portion formed in the region A is small. This is true even if the processing progresses further in the case shown in Fig. 5 (c). Therefore, the formation of a plurality of holes having a small pitch p and a large depth h, which can not be realized by the sequential machining as shown in Fig. 5 (d), can be realized finally.

As described above, according to the present embodiment, the perforation in the thickness direction at a plurality of places on the back surface of the brittle material substrate W is carried out by a gradual processing method in which a plurality of holes are formed little by little in parallel, Thermal damage on the substrate can be suppressed and the machining time can be shortened as compared with the case where sequential machining for forming individual holes sequentially is performed. Further, it is possible to form a plurality of holes having a deep depth at a narrow pitch that can not be obtained by sequential processing.

<Modifications>

In the above-described embodiment, the description is given on the premise that the hole is formed under a certain machining condition. However, the machining condition may be changed at the time the machining proceeds to the depth in the middle.

In the above-described embodiment, it is assumed that the parallel processing and the sequential processing are used alternatively. However, the parallel processing and the sequential processing may be combined. For example, parallel processing may be performed up to a certain depth, and then sequential processing may be performed on each concave portion. With this configuration, machining at a narrow pitch can be realized.

In the above-described embodiment, a description has been given of a mode in which the formation of a plurality of holes is sequentially performed by taking round hole processing as an example. However, the application of the sequential machining to the formation of a plurality of holes is not limited to a circular hole, The present invention is also applicable to a case where machining is performed in a direction For example, it can be applied to the formation of square holes and grooves. In the case of the former case, scanning of the laser beam LB at one height position may be performed by performing the main scanning so that rectangular trajectories of different sizes are coaxially formed, and a plurality of loci parallel to each other at a predetermined pitch . In the latter case, a plurality of loci parallel to each other at a predetermined pitch may be formed.

[Example]

The machining of a plurality of round holes having the same shape was gradually carried out by both the machining and the sequential machining.

Specifically, a soda glass substrate having a thickness of 1.1 mm was prepared as a brittle material substrate W, and 25 round holes having a diameter D of 100 占 퐉 were formed in a 5 占 5 square lattice shape to have a pitch p of 115 占 퐉 . That is, a plurality of round holes were formed under a condition of a narrow pitch that the gap between the round hole and the round hole was at least 15 μm. As the laser beam LB, a picosecond green laser was used. The specifications of the picosecond green laser are as follows.

Wavelength: 532 nm;

Repetition frequency: 20kHz;

Output: Initial value 0.08W → Final value 0.1W;

Scanning speed: 100 nm / s;

Pulse energy: 4 占 →? 5 占;;

Pulse fluence: 5J / cm2? 6.3J / cm2;

Pulse period: 5 占 퐉;

Pulse width: 50ps.

The beam spot diameter d1 of the laser beam LB is 10 m, the maximum diameter d2 of the scan locus of the laser beam LB is 96 m, and the number of scans at one height position is 7 , And? Z was 5 占 퐉, and the moving distance (z1-z0) of the focus F in the thickness direction was 850 占 퐉.

Fig. 6 is a picked-up image of a glass substrate on which a plurality of round holes are formed by respective machining methods from above the round holes. 6 (a) is an image in the case of gradual processing, and FIG. 5 (b) is an image in the case of progressive processing.

When the two images are compared with each other, it is confirmed that all round holes are formed in a nearly round shape in the image in the gradual processing as shown in Fig. 6 (a) The image is distorted or warped in many round holes including a circular hole indicated by an arrow, for example.

The above results indicate that the machining side is more suitable for a plurality of drilling operations at a narrower pitch than the sequential machining.

1 light source
2 stage
2m drive mechanism
3 head
3a Galvano Mirror
3b lens
4 Shutter
5 mirror
10 control unit
100 laser processing equipment
C Center of focus
D Diameter of round hole
F Focus
H0 (a, b, c, d) (round hole)
H (Ha, Hb, Hc, Hd) Round hole
LB laser beam
W brittle material substrate
d1 Beam spot diameter
h (depth of round hole)
p (pitch of round hole)

Claims (6)

A laser processing method of a brittle material substrate for forming a plurality of holes in a thickness direction from a back surface of a brittle material substrate by irradiating a laser beam from a surface side of the brittle material substrate,
Wherein the machining target position is switched at the one height position every time the irradiation of the laser beam at one height position in one machining target position is completed, The focal point of the laser beam is moved from the back surface of the brittle material substrate by a predetermined distance in the thickness direction every time the irradiation of the laser beam is finished, Of the brittle material substrate. The method according to claim 1,
Wherein the plurality of holes are round holes,
And the laser beam is scanned so that the focal point forms a locus of concentric circles in the portion to be processed. 3. The method according to claim 1 or 2,
Wherein the laser beam is a picosecond UV laser or a picosecond green laser. A laser processing apparatus for processing a back side of a brittle material substrate by irradiating a laser beam from a front side of the brittle material substrate,
A stage on which the brittle material substrate is supported and fixed,
A light source for emitting the laser beam;
And a head for irradiating the laser beam emitted from the light source to a brittle material substrate mounted on the stage,
Each time the irradiation of the laser beam at one height position in one machining target position ends, the head switches over the machining target portion at the one height position, and all the machining target portions at the one height position The focal point of the laser beam is shifted a predetermined distance in the thickness direction from the back surface of the brittle material substrate so that the focal point is set at a new height position by moving the stage relative to the head every time the irradiation of the laser beam in the brittle material substrate is completed And a plurality of holes are gradually formed by repeating the above-described steps. 5. The method of claim 4,
Wherein the plurality of holes are round holes,
Wherein the head scans the laser beam so that the focal point draws a concentric trajectory on the portion to be processed. The method according to claim 4 or 5,
Wherein the laser beam is a picosecond UV laser or a picosecond green laser.

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