JP3052226B2 - Laser processing method and processing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to laser processing, and more particularly to laser processing in which debris is generated by irradiation with laser light.

[0002]

2. Description of the Related Art A laser beam can realize a high energy density, and the workpiece can be processed by irradiating the laser beam with a high energy density onto the workpiece.

[0003] As a processing laser, CO ₂ laser, Y
An AG laser, an Ar laser, an excimer laser and the like are known. Among these, the former three oscillation wavelengths exist in the infrared region or the visible region, and it can be said that the influence of these laser beams on the object to be processed is mainly a heating effect.

[0004] Excimer lasers have an oscillation wavelength in the ultraviolet region, and the effect on the object to be processed is dominated by photochemical effects rather than thermal effects. For example, by irradiating an organic polymer compound with an excimer laser, a chemical bond can be cut and scattered, and the irradiated region can be etched (deleted). It has been confirmed that organic polymer materials such as polyimide, metals, and ceramics such as alumina can be processed.

Generally, when a material is processed by an excimer laser, a by-product called debris is generated. Debris is simply like sawdust in wood processing, and if the object to be processed is a polymer such as polyimide, soot-like adhesion of carbon around the processing hole is recognized. The object to be processed is Altic (Al ₂ O ₃ / TiC)
In the case of ceramics (composite sintered body), accumulation of minute crushed material can be confirmed around the processing hole.

In order to remove such debris, a removal step is usually added after the processing step. This additional step is, for example, a wet cleaning step or a dry plasma processing step, both of which are performed after the processing.

A gas assist method is known as a method of removing processing by-products simultaneously with the laser gas processing step.
In the gas assist method, laser processing is performed by irradiating a laser beam while blowing a reactive or inert gas (for example, H ₂ , O ₂ , Ne, He, etc.).

However, an assist gas other than O ₂ or He has little effect on an organic polymer compound such as polyimide. Also, no remarkable effect is observed for ceramics such as Altic even if any assist gas is used.

[0009]

In laser processing in which the surface of an object to be processed is scraped, debris is often generated around the processing area as a processing by-product. In order to prevent the generation of such debris, a debris removal step is provided after the processing, or when the object to be processed is a predetermined material, gas assist is performed simultaneously with laser processing.

When the object to be processed is ceramic or the like,
A method for suppressing the generation of debris simultaneously with laser processing has not been known. An object of the present invention is to provide a laser processing technique capable of suppressing generation of debris and obtaining a good processed surface simultaneously with the end of laser processing.

[0011]

According to the laser processing method of the present invention, a laser beam having an ultraviolet wavelength is divided into a first beam and a second beam, and the first beam is divided into a first beam and a second beam .
Irradiating the organic material with a fluence to process the irradiated surface; and irradiating the second beam with a second fluence lower than the first fluence on the irradiated surface of the second beam.
Irradiation area on the irradiation surface of the first beam
Organic material at the same time as the first beam so that
Irradiating the fee, the organic material by irradiation of the first beam
Removing the debris adhering to the substrate , wherein the first fluence is absorbed by an organic material.
The minimum energy density at which the
The second fluence is ablation of organic materials
The energy density is smaller than the minimum energy density.
According to the present invention, there is also provided a step of dividing a laser beam having a wavelength in the ultraviolet region into a first beam and a second beam, and irradiating the first beam to the ceramic material with a first fluence, and Processing the second beam and the first beam.
A second fluence lower than the fluence of the second
The irradiation area on the irradiation surface of the beam is irradiated with the first beam.
The first area is set to include the irradiation value range on the launch surface .
Beam and simultaneously irradiating the ceramic material, a first Bee
Debris attached to the ceramic material by
In a laser processing method comprising the step of removing said first
1 Fluence ablation on ceramic material
Is not less than the lowest energy density at which the second full
-Ence causes ablation of ceramic material
It is characterized by being smaller than the minimum energy density.

[0012]

When a second laser beam having a low fluence is applied to the periphery of the processing area separately from the first laser beam for processing the processing object, formation of debris can be suppressed. Since both laser beams can be irradiated at the same time, a good surface of the object to be processed can be obtained at the same time when the processing is completed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present applicant has previously proposed a technique for removing debris by irradiating a cleaning laser beam with a reduced energy density (fluence), followed by laser processing by excimer laser beam irradiation (Japanese Patent Application Hei 4-139311).

Referring to FIG. 2, this reference example will be described first. FIG. 2A shows a processing optical system using an excimer laser. Laser beam 11 emitted from excimer laser 1
Is guided to the mask 4 by an optical system including the total reflection mirrors 2a and 2b and irradiates the mask 4.

The mask 4 has a pattern formed by punching a plate of, for example, Mo, CuNi, etc., and transmits only a laser beam having a desired shape. In this case, a laser beam having a desired shape with a uniform energy density (fluence) is generated by using only the central portion of the laser beam.

The holding means 9 and the workpiece 6 placed thereon are accommodated in a vacuum vessel 17.
The vacuum vessel 17 is provided with a window 18 for transmitting an excimer laser beam.

The image forming lens 5 for the mask 4 is for forming an image of the mask 4 on the object 6 to be processed.
A pattern having a predetermined magnification (reduction ratio) is formed on the processing target 6. The workpiece 6 is held on holding means 9 such as a table, and its position can be adjusted.

By changing the positions of the imaging lens 5 and the processing object 6 on the optical axis, the magnification of the image of the mask 4 formed on the processing object 6 can be changed. When an object is irradiated with an excimer laser beam at a certain energy density (fluence), a dry etching phenomenon called ablation occurs on the surface of the object,
The object to be processed is gradually reduced. The minimum energy density that enables processing is called a threshold.

As shown in FIG. 2B, when processing a rectangular pattern, for example, a processing beam irradiation area 15 is irradiated with a laser beam having a fluence sufficiently higher than a threshold value. A wider cleaning beam irradiation area 16 including the irradiation area 15 is irradiated with a cleaning beam having a fluence reduced below a threshold value. The cleaning beam does not have the ability to process the processing target 6, but has the ability to remove debris generated when processing is performed by the processing beam.

Although not disclosed in the previous proposal, the case of processing AlTiC (Al ₂ O ₃ / TiC composite sintered body) will be described below. Approximately 2 × 1
An excimer laser beam with a fluence of 4.2 J / cm ² is irradiated, for example, for 1000 shots in a vacuum atmosphere of 0 ⁻³ Torr. Ablation occurs on the surface of the processing target irradiated with such a high fluence excimer laser beam, and laser beam processing is performed.

When ablation is caused in a vacuum atmosphere, debris occurs in a wide area and thinly. Since it is a vacuum atmosphere, it is considered that almost no chemical reaction with air components such as oxidation and nitridation occurs.

Thereafter, the fluence is increased to 1.5 J / cm ²
Then, the irradiation area was enlarged to about 2.5 times and an excimer laser beam of 10 shots was irradiated. Note that an excimer laser beam having a fluence of 1.5 J / cm ² is less than or equal to a threshold value for an altic, and the altic itself cannot be processed. However, it has been confirmed that debris can be completely removed by excimer laser beam irradiation below such a threshold. The cleaning shot is not limited to the vacuum atmosphere, but may be performed in the air.

The distance between the mask 4 and the imaging lens 5 is represented by a, the distance between the imaging lens 5 and the object 6 is represented by b,
Assuming that the focal length of the imaging lens 5 is f, the lens formula of 1 / a + 1 / b = 1 / f is established.

When the distance a between the mask 4 and the imaging lens 5 is reduced, b becomes a large value and the reduction ratio becomes low in order to satisfy the formula of this lens. That is, the laser beam is applied to a large area of the processing target 6, and the energy density is reduced. By such adjustment, the irradiation area at the time of performing the cleaning shot can be widened, and the energy density can be set to an appropriate value equal to or less than the threshold.

As described above, it is possible to remove debris by performing a cleaning shot subsequent to the laser beam processing, but an operation subsequent to the laser processing is required, which complicates the entire processing process.

An embodiment of the present invention which solves such a problem will be described below. FIG. 1 shows a processing optical system using an excimer laser according to an embodiment of the present invention. Oscillation wavelength 248
A laser beam 11 emitted from an excimer laser 1 such as a KrF excimer laser of nm is guided to a beam splitter 7 through an optical system such as a total reflection mirror 2. The beam splitter 7 is formed of, for example, a partial reflection mirror, reflects a predetermined ratio of incident light, and transmits a predetermined ratio.
Such a beam splitter can be generally formed by a dielectric multilayer film, a partial metal mirror, or the like.

Thus, the incident laser beam 1
From 1, a partially reflected beam 12 and a partially transmitted beam 13 are formed. For example, the beam splitter 7 is formed by a partially reflecting mirror having a reflectivity of about 90%, and the partially transmitted beam 1 having an energy density of about 1/10 of the partially reflected beam 12 is obtained.
Form 3

The partially reflected beam 12 is guided to the mask 4, and the laser beam transmitted through the mask 4 is imaged on the object 6 by the imaging lens 5. As described above, the laser processing similar to that described in the reference example can be performed using the partially reflected beam 12.

The workpiece 6 is placed on a holding means 9 such as a table, and is housed in a vacuum vessel 17 together with the holding means 9. The vacuum vessel 17 is provided with a window 18 and can transmit an excimer laser beam.

The partially transmitted beam 13 split by the beam splitter follows an optical path different from that of the processing beam by an optical system such as a total reflection mirror 8 and is irradiated on the processing object 6 through a window 18. A cleaning shot can be irradiated by the partial transmission beam 13 simultaneously with laser processing.

In the configuration shown, the partially transmitted beam 1
No mask and no imaging lens are arranged on the optical path of No. 3. This is because the irradiation area of the partially transmitted beam 13 only needs to be irradiated to a sufficiently wide area including the irradiation area of the partially reflected beam 12 that has passed through the mask 4.

Of course, a convergence effect may be imparted to the partially transmitted beam 13 by making the total reflection mirror 8 a concave mirror having a radius of curvature of, for example, about 10 m. Further, a mask having the same shape as the mask 4 may be transmitted. However, the irradiation area on the processing target is set to include the processing area and the surrounding area where debris can adhere. Further, a shutter for blocking the beam may be provided.

As a test, a polyimide film was laser-processed. Processing threshold of polyimide film is about 50
It is said to be mJ / cm ² . We set the fluence of the processing beam to 100 mJ / cm ² and the fluence of the cleaning beam to about 1/10 of that. By simultaneously irradiating the processing beam and the cleaning beam onto the processing target, laser processing substantially free of debris could be performed.

The laser beam is divided, and one of the laser beams is used as a processing beam and the other is used as a cleaning beam so that cleaning can be performed simultaneously with laser processing. Can take.

The position of the beam splitter on the optical axis is not limited to the case shown in the figure, and may be provided after the mask. The optical axis of the cleaning beam does not need to be different from the optical axis of the processing beam, and may be coincident.
If necessary, the cleaning beam may be focused by a lens or the like.

Although the case of performing laser processing using an excimer laser has been described, the present invention can be applied to laser processing using another laser such as a YAG laser. Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0037]

As described above, according to the present invention,
Debris generated by laser processing can be removed simultaneously with laser processing. For this reason, laser processing is simplified as a whole.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining excimer laser processing according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a reference example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 excimer laser 2 total reflection mirror 4 mask 5 imaging lens 6 object to be processed 7 beam splitter 8 total reflection mirror 9 holding means 11 laser beam 12 partially reflected beam 13 partially transmitted beam 15 processing beam irradiation area 16 cleaning beam irradiation area 17 vacuum Container 18 window

Claims (8)

(57) [Claims] 1. A laser beam having a wavelength in the ultraviolet region,
Splitting the first beam into a second beam, irradiating the first beam to the organic material with a first fluence, and processing the irradiated surface; 2 fluence, the irradiation area of the second beam on the irradiation surface
The area includes the irradiation area on the irradiation surface of the first beam.
And irradiate the organic material simultaneously with the first beam, and adhere to the organic material by the irradiation of the first beam.
Removing said debris , wherein said first fluence is ablated by an organic material.
And the second fluence is ablation of the organic material.
Is smaller than the lowest energy density at which
Laser processing method. 2. A laser beam having a wavelength in the ultraviolet region,
Splitting the beam into a second beam and a second beam; irradiating the first beam to the ceramic material with a first fluence to process an irradiated surface; 2 fluence, the irradiation area of the second beam on the irradiation surface
The area includes the irradiation area on the irradiation surface of the first beam.
So To be, at the same time as the first beam is irradiated to the ceramic material <br/>, the ceramic by the irradiation of the first beam
Removing the debris attached to the material , wherein the first fluence is abraded on the ceramic material.
The second fluence is greater than the lowest energy density at which the abrasion occurs.
Is smaller than the lowest energy density at which
Laser processing method. 3. The method according to claim 1, wherein the organic material is polyimide.
And the first fluence is about 100 mJ / cm ²
Degree, the second fluence is about 10 mJ / cm ²
A laser processing method characterized by the above-mentioned. 4. The method according to claim 2, wherein the ceramic material is aluminum.
Ticks and the first fluence is 4.2 J / cm ²
Degree, the second fluence is about 1.5 J / cm ²
A laser processing method. 5. A holding means for holding an organic material , a beam splitter for splitting a laser beam having an ultraviolet wavelength into a first beam and a second beam, and holding the first beam at a first fluence. A first optical system for guiding the second beam on the irradiation surface of the second beam at a second fluence lower than the first fluence.
The area includes the irradiation area on the irradiation surface of the first beam.
A second optical system for guiding the first fluence onto an organic material.
And the second fluence is ablation of the organic material.
Is smaller than the lowest energy density at which
Laser processing equipment. 6. A holding means for holding a ceramic material , a beam splitter for splitting a laser beam having an ultraviolet wavelength into a first beam and a second beam, and holding the first beam at a first fluence. A first optical system for guiding the second beam on the irradiation surface of the second beam at a second fluence lower than the first fluence.
The area includes the irradiation area on the irradiation surface of the first beam.
A second optical system for guiding the first fluence onto the holding means so that the first fluence is abraded on the ceramic material.
The second fluence is greater than the lowest energy density at which the abrasion occurs.
Is smaller than the lowest energy density at which
Laser processing equipment. 7. The method according to claim 5, wherein the organic material is polyimide.
And the first fluence is about 100 mJ / cm ²
Degree, the second fluence is about 10 mJ / cm ²
A laser processing apparatus characterized by the above-mentioned. " 8. The method according to claim 6, wherein the ceramic material is aluminum.
Ticks and the first fluence is 4.2 J / cm
^{About 2} and the second fluence is about 1.5 J / cm ²
A laser processing apparatus, comprising: