JP2003245791A - Laser beam machining device and laser beam machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining method which can prevent scattered objects generated when abrasion machining is conducted by laser beam irradiation from adhering to the surface of a workpiece. <P>SOLUTION: The laser beam machining device has a laser beam source and an optical system which optically projects the laser beam emitted from the laser beam source on the surface 50f to be machined of the workpiece 50 in a specific pattern, machines the surface 50f to be machined by abrasion, and has a liquid supply mechanism 30 to supply liquid 90 which transmits the laser beam on the surface 50f which is irradiated with the laser beam LB and to move the liquid 90 in a prescribed direction on the surface 50f. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing method and a laser processing apparatus utilizing ablation by laser light.

[0002]

2. Description of the Related Art Excited dimer laser
Has a high photon energy capable of breaking a chemical bond, and a photochemical reaction called abrasion can remove an object to be processed while suppressing thermal influence. Laser processing by such ablation is drawing attention. By irradiating the excimer laser beam whose energy density is adjusted, plastic, metal,
Various materials such as ceramics can be ablated.

In the ablation process, scattered objects called debris adhere to the periphery of the processing area from the object to be processed which has been irradiated with the laser. When debris occurs,
The desired processing accuracy may not be obtained. Known methods for reducing this debris include a method for suppressing the generation of debris itself, a method for reducing the accumulation of debris, and a method for removing the debris after the debris is accumulated. It is known that in order to reduce the amount of debris generated, it is effective to blow an assist gas at the same time as irradiating the object to be processed with laser light. As a method of suppressing the generation of debris itself, a method of decomposing with a predetermined atmosphere gas or preventing reattachment is known. Further, it is known that the amount of adhesion due to deposition can be greatly reduced by processing under a reduced pressure of a vacuum degree of about 10 ^-2 [Torr]. As a method of removing the debris after depositing the debris, a method of irradiating an excimer laser beam with an energy density lower than that at the time of laser processing and removing the generated debris is known. This method is effective when the debris is easy to remove.

[0004]

By the way, in the above-mentioned method, the debris may not be removed sufficiently. Another technique for preventing the debris generated during laser processing from adhering to the surface to be processed is disclosed in, for example, JP-A-9-141480. In the technology disclosed in this publication, a liquid such as water is brought into contact with the surface of an object to be ablated, and a laser beam is applied to the surface of the object to be ablated through the liquid to generate debris as a liquid. The debris is suspended inside and washed off with the liquid after the processing is finished to prevent the debris from adhering to the surface of the object to be processed. However, in the above method, there is a possibility that debris floating in the liquid in contact with the surface of the object to be processed will reattach to the surface of the object to be processed, and the debris will not be completely attached to the surface of the object to be processed. Cannot be prevented.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to prevent processing scattered matter generated during ablation processing by laser light irradiation from adhering to the surface of a processing object. It is to provide a laser processing method and a laser processing apparatus capable of performing the above.

[0006]

A laser processing apparatus according to the present invention comprises a laser light source and an optical system for optically projecting laser light emitted from the laser light source on a surface to be processed of a processing object in a predetermined pattern. Having a laser processing apparatus for ablating the surface to be processed, supplying a liquid that transmits the laser light to the surface to be processed irradiated with laser light,
It has an adhesion prevention mechanism that moves the liquid on the surface to be processed and prevents the processing scattering generated by ablation processing from adhering to the surface to be processed.

A laser processing method of the present invention optically projects a laser beam on a surface to be processed of a processing object in a predetermined pattern,
In the laser processing method, the surface to be processed is subjected to ablation, and a liquid that transmits laser light is irradiated onto the surface to be processed while moving the liquid on the surface to be processed.

In the present invention, the liquid is supplied to the surface to be processed of the object to be processed, and the liquid is irradiated on the surface to be processed while moving the liquid in a predetermined direction on the surface to be processed. The laser light passes through this liquid and processes the surface to be processed. When the surface to be processed is ablated by laser light, processing scatter is generated. At this time, since the liquid is moving on the surface to be processed, the processing scattered matter is carried together with the liquid. When the liquid containing the processing scattered material completely passes through the surface to be processed, the processing scattered material does not adhere to the surface to be processed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a diagram showing an example of a schematic configuration of a laser processing apparatus to which the present invention is applied. Laser processing apparatus 20 shown in FIG.
Has a laser light source 1, a plurality of mirrors 2, 3, and 4, a beam shaper 5, a mask 6, a reduction projection lens 7, and a stage 8.

The laser light source 1 outputs a laser beam LB. Laser beam L output from this laser light source 1
By B, the surface 50f to be processed of the processing object 50 is ablated. As the laser light source 1, for example, an excimer laser is used. There are a plurality of types of excimer lasers having different laser media. As a laser medium,
From the longest wavelength, XeF (351 nm), XeCl
(308 nm), KrF (248 nm), ArF (19
3 nm) and F ₂ (157 nm) are present. The excimer laser is greatly different from the YAG laser (1.06 μm) and the CO ₂ laser (10.6 μm) that perform processing using thermal energy in that the oscillation wavelength is in the ultraviolet range. The excimer laser essentially oscillates only in pulses, has a pulse width of about 20 ns and the laser beam is rectangular in shape. Further, the excimer laser performs a process called ablation, which is less susceptible to the thermal effect of photochemically dissociating the direct bond, so that the edge of the surface to be processed is extremely sharp. On the other hand, in the YAG laser and the CO ₂ laser, the processed portion is melted and then evaporated, so that the peripheral portion is rounded by the influence of heat and the end face is not clean. Further, the excimer laser has an initial beam cross section of about 10 × 10 mm, and a relatively large area is collectively formed by increasing the area and the area of this laser beam by a beam shaper described later. Can be processed. Therefore, the excimer laser is suitable for simultaneously processing a large area.

The beam shaper 5 expands and shapes the laser beam LB from the laser light source 1 reflected by the mirrors 2 and 3 and outputs it to the mirror 4.

The mask 6 has a predetermined pattern for passing the laser beam LB which is shaped by the beam shaper 5 and reflected by the mirror 4. As the mask 6, for example, a mask made of a metal material, a mask made of a transparent glass material or a transparent resin, a mask made of a dielectric material, or the like is used.

The reduction projection lens 7 reduces the laser beam LB that has passed through the pattern of the mask 6 at a predetermined magnification and projects it onto the surface 50f of the object 50 to be processed on the stage 8.

The stage 8 receives the laser beam LB projected from the reduction projection lens 7 on the surface 5 to be processed of the object 50 to be processed.
The reduction projection lens 7 is arranged so as to focus on 0f. The stage 8 can be moved and positioned along a plane perpendicular to the optical axis of the laser beam LB so that the laser beam LB can scan the surface 50f of the workpiece 50.

In the laser processing apparatus 20 having the above-mentioned configuration, by using an excimer laser as the laser light source 1, the surface 50f of the object 50 to be processed is irradiated with the laser beam LB having a predetermined pattern, and the surface 50f to be processed is ablated. To be done. By the ablation process, debris, which is a scattered material of the material forming the processed face 50f, which has been directly photochemically dissociated, is generated on the processed face 50f. If the debris adheres to the surface to be processed 50f, it may affect the processing accuracy and the like, and it is necessary to prevent the adhesion. less than,
The structure of the adhesion prevention mechanism for preventing the adhesion of debris will be described.

FIG. 2 is a sectional view showing the structure of an adhesion preventing mechanism according to an embodiment of the present invention. The adhesion prevention mechanism 60 according to the present embodiment supplies a liquid that passes through the laser beam LB to the surface to be processed 50f during the irradiation of the surface to be processed 50f of the processing object 50 with the laser beam LB, and the liquid concerned. Are moved in a predetermined direction on the surface to be processed 50f to wash away debris generated by the ablation process.

As shown in FIG. 2, the adhesion preventing mechanism 30 is
It has a holding mechanism 60 and a liquid supply source 70. The holding mechanism 60 is installed on the stage 8 and holds the workpiece 50. The holding mechanism 60 includes a processing container 61,
And a cover member 62.

The processing container 61 is installed on the stage 8 described above. The processing container 61 is open at the upper end side and the processing target object 50 is installed at the bottom.

The cover member 62 is installed on the inner circumference of the processing container 61 on the opening side, and is fixed to the processing container 61 by a fixing member 63 fixed to the opening end of the processing container 61. The laser beam LB is applied to the processing member 6 on the fixing member 63.
An opening 63a is formed for guiding the inside.
The cover member 62 is formed of a material that transmits the laser beam LB incident from the opening side of the processing container 61.
Specifically, for example, the laser light source has a wavelength of 248 nm.
When the KrF excimer laser is used, the one formed of synthetic quartz glass or calcium fluoride having a high transmittance with respect to the KrF excimer laser is used. Further, the cover member 62 is arranged at a predetermined height, for example, about 1 mm from the surface 50f to be processed of the processing target object 50 installed on the bottom of the processing container 61. That is, a predetermined gap Gp is formed between the processed surface 50f of the processing object 50 and the cover member 62. This gap Gp
Liquid 90 passes through.

By installing the cover member 62 on the inner circumference of the processing container 61, a closed space Sp is formed between the cover member 62 and the processing container 61. The liquid 90 is supplied to the closed space Sp, and the closed space Sp is filled with the liquid.

The processing container 61 is provided with a supply port 64 for supplying the liquid 90 and a discharge port 65 for discharging the liquid 90 supplied to the closed space Sp of the processing container 61 to the outside. A supply pipe 66 is connected to the supply port 64, and the supply pipe 66 is connected via a valve 67 to the liquid supply source 7.
It is connected to 0. The valve 67 opens and closes the conduit of the supply pipe 66 and adjusts the flow rate of the liquid 90 supplied from the liquid supply source 70. A discharge pipe 68 is connected to the discharge port 65, and a valve 69 is connected to the discharge pipe 68. The valve 69 opens and closes the conduit of the discharge pipe 68 and adjusts the flow rate of the liquid 90 discharged from the processing container 61.

The liquid supply source 70 adjusts the liquid 90 to a predetermined pressure and flow rate and supplies it to the processing container 61. The liquid 90 supplied by the liquid supply source 70 is a liquid that transmits the laser beam LB, and for example, water is used. Further, when the object 50 to be processed cannot be immersed in water, another liquid that transmits the laser beam LB is used.

FIG. 3 is a sectional view of the processing container 61 taken along a horizontal plane, showing the arrangement of the supply port 64 and the discharge port 65. As shown in FIG. 3, the processing container 61 has a rectangular outer shape, and the supply port 64 and the discharge port 65 are arranged near one diagonal of the processing container 61, respectively. The supply port 64 and the discharge port 65 are arranged in the vicinity of the diagonal line of the processing container 61, as shown in FIG. 3, so that the liquid 90 supplied from the supply port 64 passes through the entire processing container 61 substantially evenly. This is for directing it to the discharge port 65. That is, this is to prevent stagnation of the liquid 90 as much as possible at the corners of the rectangular processing container 61.

Next, a laser processing method by the laser processing apparatus having the adhesion preventing mechanism 30 having the above structure will be described. First, the workpiece 50 is installed on the bottom of the processing container 61 with the cover member 62 removed, and then the cover member 62 is fixed to the processing container 61 by the fixing member 63. As a result, the holding mechanism 60 is assembled.

Next, the processing container 61 of the holding mechanism 60 in the above state is set on the stage 8. The holding mechanism 6
The workpiece 50 to be set to 0 and the holding mechanism 60 to the stage 8 can be automated by a robot automation device.

Next, the liquid 90 is supplied from the liquid supply source 70 to the processing container 61 installed on the stage 8. At this time, the valve 69 connected to the discharge pipe 68 is opened. As a result, the liquid 90 is supplied to the closed space Sp formed by the processing container 61 and the cover member 62, and the closed space Sp is filled with the liquid 90. At this time, the processing object 50 is in a state of being immersed in the liquid 90, and the cover member 62 and the processed surface 50f of the processing object 50 are processed.
The liquid 90 is also filled in the gap Gp between and.

Further, since the valve 69 is opened, the liquid 90 supplied to the closed space Sp is discharged to the outside, and the liquid 90 supplied to the closed space Sp is supplied as shown in FIG. It moves from the mouth 64 toward the outlet 65. That is, the supply of the liquid 90 to the closed space Sp and the closed space Sp
By simultaneously discharging the liquid 90 from the liquid 9
0 moves in the closed space Sp. Therefore, the cover member 6
The liquid 90 existing in the gap Gp between the workpiece surface 50f of the workpiece 50 and the workpiece 2 also moves. As a result, the processing target 5
The liquid 90 having a constant thickness flows on the 0-processed surface 50f.

Next, as described above, the stage 8 is moved and positioned at a desired position while the liquid 90 is flowing on the surface 50f to be processed of the object 50 to be processed. From this state, the surface 50f to be processed is irradiated with the laser beam LB through the reduction projection lens 7. Thereby, the processed surface 50
f is ablated.

When the surface 50f to be processed is ablated, debris is generated as described above. Since the debris scatter toward the open space on the processed surface 50f, the debris is caught in the liquid 90 flowing on the processed surface 50f. At this time, since the liquid 90 is moving from the supply port 64 of the processing container 61 toward the discharge port 65, the debris caught in the liquid 90 is conveyed by the liquid 90 toward the discharge port 65. Finally, the debris is discharged from the discharge port 65.

After the processing of the desired portion of the surface to be processed 50f is completed, the stage 7 is moved and positioned again, and the ablation processing of the next processing portion is repeated in the same manner as described above. This completes the processing of the surface to be processed 50f. During processing of the surface to be processed 50f, the liquid 90 is continuously supplied.
Is supplied to the processing container 61, and debris generated during each processing is discharged to the outside of the processing container 61 by the liquid 90.

As described above, according to the present embodiment, the scattered material generated when the laser beam LB is applied to the surface 50f to be processed of the object 50 to be ablated is generated by the liquid 90 flowing on the surface 50f to be processed. Since it is captured and discharged to the outside of the processing container 61, it is extremely unlikely that the processing scattered matter once captured by the liquid 90 will adhere to the surface to be processed 50f again. As a result, it is possible to reliably prevent the processing scattered matter from adhering to the surface to be processed 50f. Further, according to the present embodiment, by appropriately selecting the supply position of the liquid 90 to the processing container 61 and the discharge position of the liquid 90 from the processing container 61, the inside of the processing container 61 can be formed without complicating the apparatus. Generation of stagnation of the liquid 90 can be prevented. As a result, it is possible to prevent the processing scattered matter captured by the liquid 90 from being discharged from the processing container 61 and staying in the processing container 61.

Further, according to the present embodiment, the processing container 61
The cover member 62 is fixed with respect to, and a constant gap Gp is provided between the cover member 62 and the processed surface 50f of the workpiece 50.
By forming the above, the height of the liquid surface of the liquid 90 flowing on the processed surface 50f is always constant, and the intensity of the laser beam LB irradiated to the processed surface 50f through the liquid 90 can be stabilized. As a result, the processing accuracy is stabilized.

Second Embodiment FIG. 4 is a sectional view showing the structure of an adhesion preventing mechanism according to another embodiment of the present invention. In FIG. 4, the same reference numerals are used for the same components as those of the adhesion prevention mechanism according to the first embodiment described above. The laser processing apparatus described in the above-described first embodiment is the processing target 5
Although the laser processing is performed in a state that 0 is immersed in the liquid, the laser processing in the liquid may not be performed depending on the type of the processing object 50, the material forming the surface to be processed, and the like. is there.

On the other hand, in order to prevent the debris generated by ablation from adhering to the surface to be processed, the object 50 to be processed is subjected to laser processing under a reduced pressure of, for example, a vacuum degree of 10 ^-2 [Torr]. This is also an effective method for reducing the amount of debris attached.

If laser processing is performed while the object 50 to be processed is immersed in a liquid and laser processing is performed under reduced pressure, if separate devices are prepared, the operating rate of the devices will decrease and the equipment cost will decrease. There are disadvantages such as being bulky. For this reason, in the present embodiment, the laser processing is performed in a state where the processing target 50 is immersed in the liquid, and the processing target 50 under reduced pressure is used.
A configuration capable of performing both laser processing will be described.

The adhesion preventing mechanism 120 shown in FIG. 4 includes a chamber 121, a liquid supply source 70 connected to the chamber 121 via a valve 67, and a valve 19 connected to the chamber 121.
2 and the vacuum pump 190 connected via the chamber 1
21 and a holding mechanism 160 installed inside.

The chamber 121 is installed on the stage 8. A transmission plate 122 that transmits the laser beam LB is provided on the ceiling of the chamber 121. Also,
The chamber 121 has an opening 121h on its side surface for loading and unloading a workpiece or the like. This opening 1
21h is opened / closed by the opening / closing door 123,
Is closed by a seal member 124.

The liquid supply source 70 is connected to the lower part of the chamber 121 by a supply pipe 66. Liquid supply source 70
The liquid 90 can be supplied into the chamber 121 through the valve 67, as in the first embodiment described above.

The vacuum pump 190 is connected to the chamber 121 via a valve 192. This vacuum pump 1
The inside of the chamber 121 sealed by 90 is made to have a reduced pressure atmosphere of, for example, about 10 ^-2 [Torr].

A discharge pipe 68 is connected to the lower portion of the chamber 121 opposite to the side to which the liquid supply source 70 is connected. The discharge pipe 68 can discharge the liquid 90 from the chamber 121 to the outside through the valve 69 as in the first embodiment described above.

A gas supply pipe 195 is connected to the chamber 121, and the gas supply pipe 195 has a valve 196.
It is opened and closed by. The gas supply pipe 195 is used to supply an atmosphere gas such as nitrogen or helium or a reaction gas such as hydrogen chloride or nitrogen trifluoride into the chamber 121.
The atmosphere gas and the reaction gas are supplied into the chamber 121 when the chamber 121 is used for etching or the like.

The holding mechanism 160 is installed at the bottom of the chamber 121 and has the same structure as the holding mechanism 60 according to the first embodiment described above. This holding mechanism 16
Reference numeral 0 has a processing container 161, a cover member 162, and a fixing member 163. One side 16 of processing container 161
An inlet 164 through which the liquid 90 flows into the processing container 161 is formed at 1a, and an outlet 165 through which the liquid 90 flows out from inside the processing container 161 is formed at the other side surface 161b facing the one side surface 161a. There is.

In the adhesion preventing mechanism 120 having the above structure,
When laser processing is performed with the workpiece 50 immersed in the liquid 90, the liquid 90 is supplied from the liquid supply source 70 into the chamber 121, and the valve 69 of the discharge pipe 68 is opened. Liquid 90 supplied into chamber 121
From the inflow port 164 of the processing container 161 to the processing container 161.
As the liquid level of the liquid 90 flowing into the chamber 121 and supplied to the chamber 121 rises, the closed space Sp formed between the cover member 162 and the processing container 161 is filled with the liquid 90. At this time, in order to keep the liquid 90 filled in the closed space Sp, the liquid supply source is set so that the height of the liquid surface of the liquid 90 outside the processing container 161 is higher than the height of the cover member 162. The amount of liquid 90 supplied from 70 is adjusted, and the opening degree of the valve 69 is adjusted.

The liquid 90 flowing from the inflow port 164 of the processing container 161 passes through the processing container 161 and flows out of the outflow port 16 of the processing container 161.
It flows out from 5. Therefore, the liquid 90 moves in the gap Gp between the surface to be processed 50f of the processing object 50 and the cover member 162.

In this state, similarly to the above-described first embodiment, while performing the movement positioning of the stage 8,
The surface 50f to be processed is irradiated with the laser beam LB to perform ablation processing.

The debris generated by the ablation process is carried by the liquid 90 on the surface 50f to be processed,
It is discharged to the outside of the processing container 161 through the outlet 165, and further discharged to the outside of the chamber 121 from the discharge pipe 68.

After the above processing is completed, the supply of the liquid 90 from the liquid supply source 70 to the chamber 121 is stopped, and all the liquid 90 in the chamber 121 is discharged from the discharge pipe 68. Then, the entire holding mechanism 160 is provided with the opening 12
It is carried out through 1h.

When the laser processing is performed on the object 50 to be processed under a reduced pressure atmosphere, the inside of the chamber 121 in which the liquid 90 is completely discharged is depressurized by the vacuum pump 190. While the chamber 121 is depressurized, the laser beam LB is applied to the surface 50 to be processed while the stage 8 is moved and positioned.
Irradiate f and perform ablation.

As described above, according to this embodiment, both laser processing in a liquid and laser processing in a reduced pressure atmosphere can be performed by the same apparatus, so that the operating rate of the apparatus can be improved. .

The present invention is not limited to the above embodiments. In the above-described embodiment, the processing container 60 is provided with the supply port 64.
And liquid 90 in the processing container 60 by forming the discharge port 65.
Is configured to move, but the supply port 64 and the discharge port 6
It is also possible to form a large number of 5 in the positions facing each other and to make the movement of the liquid 90 in the processing container 60 more uniform.

[0051]

According to the present invention, it is possible to prevent the debris from adhering to the surface to be processed by reducing the thermal influence during the ablation processing by laser light. As a result, precise laser processing can be realized, and it is possible to provide an excellent effect that debris can be prevented from adhering, the application of laser processing is expanded, and a fine pattern can be formed with high accuracy and low accuracy. It can be formed at a cost.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a schematic configuration of a laser processing apparatus to which the present invention is applied.

FIG. 2 is a cross-sectional view showing the structure of the liquid supply mechanism according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view of the processing container 61 taken along a horizontal plane.

FIG. 4 is a sectional view showing a structure of a liquid supply mechanism according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Laser light source, 2, 3, 4 ... Mirror, 5 ... Beam shaper, 6 ... Mask, 7 ... Reduction projection lens, 8 ... Stage,
30, 120 ... Liquid supply mechanism, 61 ... Processing container, 62 ...
Cover member, 50 ... Object to be processed, 50f ... Work surface, 7
0 ... Liquid supply source, 90 ... Liquid, 121 ... Chamber, 19
0 ... vacuum pump.

Continued front page    (72) Inventor Kiyomi Kiyomi             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation (72) Inventor Kazuhiko Yoshida             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation (72) Inventor Hidetoshi Murase             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F-term (reference) 4E068 CG05 CH08 CJ07 CJ09

Claims (8)

[Claims] 1. A laser having a laser light source and an optical system for optically projecting laser light emitted from the laser light source onto a surface to be processed of a processing object in a predetermined pattern, and performing ablation processing on the surface to be processed. A processing apparatus, which supplies a liquid that transmits the laser light to the surface to be processed that is irradiated with laser light, moves the liquid in a predetermined direction on the surface to be processed, and processing scattering generated by ablation processing A laser processing apparatus having an adhesion prevention mechanism for preventing an object from adhering to the surface to be processed. 2. The adhesion preventing mechanism has an entrance portion through which laser light can enter, a processing container that accommodates the processing target therein, a processing container that is fixed to the processing container, and has a predetermined distance from the surface to be processed. A cover member that is arranged at a height and transmits the laser beam, a liquid supply unit that supplies the liquid into a closed space formed between the cover member and the processing container, and a liquid supply unit that is supplied into the closed space. The laser processing apparatus according to claim 1, further comprising a liquid discharging unit configured to discharge the liquid. 3. The laser processing apparatus according to claim 2, further comprising a movement positioning unit that holds the processing container and changes the irradiation position of the laser beam on the surface to be processed. 4. The laser processing apparatus according to claim 1, wherein the laser light source is an excimer laser. 5. The laser processing apparatus according to claim 1, wherein the adhesion preventing mechanism further includes a depressurizing means for ablating the surface to be processed in a depressurized atmosphere without using the liquid. 6. A laser processing method for optically projecting a laser beam on a surface to be processed of a processing object in a predetermined pattern, and processing the surface to be processed by ablation. A laser processing method of irradiating the surface to be processed with laser light while moving the surface in a predetermined direction. 7. The laser processing method according to claim 6, wherein the processing surface is irradiated with laser light while the processing target is immersed in the moving liquid. 8. A cover member made of a material that transmits laser light is disposed at a predetermined height from the surface to be processed, and the height of the liquid surface of the moving liquid is kept constant while keeping the height of the liquid surface constant. The laser processing method according to claim 6, wherein irradiation with laser light is performed.