JP3082013B2 - Laser processing method and apparatus - 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 using ultraviolet laser light such as an excimer laser.

An excimer laser beam has a high photon energy capable of breaking a chemical bond, and can selectively remove an object to be processed by reducing a thermal effect by a photochemical reaction called ablation. Laser processing by such an ablation method has attracted attention.

[0003]

2. Description of the Related Art Various materials such as plastics, metals, and ceramics can be ablated by irradiating an excimer laser beam whose energy density is adjusted.

[0004] In the ablation process, scattered matter called debris adheres to a surface around a processing portion from a processing object irradiated with laser. In laser ablation of a polymer material such as polyimide, a method of blowing a gas such as O ₂ or He has been attempted as a measure against debris adhering in the form of soot.

[0005] It is considered that oxygen spraying is effective for C or the like which becomes a gas state by oxidation. Also,
There is also a proposal to convert to a gas state by combining with H. Also,
He having a small molecular weight is considered to be effective as a blowing gas because He having a small reaction due to collision with flying objects.

On the other hand, a technique has been proposed in which after generating debris, an excimer laser beam is irradiated at a lower energy density than during laser processing to remove the generated debris. This method is also effective when debris is easily removed.

In a magnetic storage device, a magnetic head is moved from the surface of a magnetic disk by 0.1 mm by an aerodynamic action.
A magnetic head slider with a fine groove is used in order to levitate in a minute gap of about μm. An altic material (a composite sintered body of Al ₂ O ₃ / TiC) is used for the magnetic head slider.

Conventionally, altic materials for magnetic heads are processed by ion milling, but the processing speed is slow.
Recently, attention has been focused on YAG laser processing and ablation processing using excimer laser, which are advantageous for high-speed processing.

However, when the Altic is processed by ablation processing using an excimer laser, debris adheres to the periphery of the processing area, causing a serious hindrance to the stable flying of the magnetic head. In this case, even if a gas such as oxygen was blown during laser ablation, the effect was small.

[0010]

As described above,
Laser ablation processing is an effective processing method,
The problem of debris has not been completely solved.

An object of the present invention is to provide a laser processing technique capable of reducing the problem of debris.

[0012]

According to the laser processing method of the present invention, there is provided a step of arranging an object to be processed in a container having a light transmitting window and capable of evacuating, and evacuating the container to a vacuum state.
A step of irradiating an ultraviolet laser beam having a first energy density onto a processing object from a light transmission window to perform laser processing by ablation; and a step of applying the first energy density to a scattered substance attached around a processing area of the processing object. irradiating ultraviolet laser beam at a lower second energy density, see containing and removing the debris, irradiating ultraviolet laser beam of the first energy density
The atmosphere in the container at the time of
The extent to which debris adheres to
Larger than the area where debris scatters when
It is characterized in that the degree of vacuum is such that

[0013]

By performing laser ablation under reduced pressure evacuated to a vacuum state, the generation of debris cannot be avoided, but debris is generated thinly over a wide range. By irradiating such a mild debris with an ultraviolet laser beam having a reduced energy density, it is possible to remove flying objects and effectively solve the debris.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Gas blowing, which has been used in the past, is a measure to reduce or prevent debris itself.

In the laser processing of Altic, even if debris once generated is to be removed, the debris firmly adheres to the object to be processed, and the removal is not easy.
Therefore, according to the related art, in order to solve such a problem of debris, the generation itself of debris will be reduced or prevented. However, good results could not be obtained with gas blowing.

The present inventor has sought a measure to change the idea and convert the generated debris into something that can be easily removed.
As factors for changing the debris generation conditions, factors such as the energy density, repetition frequency, and wavelength of the excimer laser beam to be irradiated, as well as factors such as atmosphere and substrate temperature can be considered.

The inventor paid attention to the pressure of the atmosphere among these factors. FIG. 1 shows a laser ablation process according to an embodiment of the present invention. FIG. 1A is a cross-sectional view schematically showing a configuration of a laser ablation apparatus.
(B) is a plan view showing a laser ablation processing area,
FIG. 1C is a plan view showing a cleaning shot area.

In FIG. 1A, a vacuum chamber 6 has an airtight structure and is connected to a vacuum pump 5 capable of evacuating. The vacuum pump 5 is constituted by, for example, an oil rotary pump or a turbo molecular pump.

When an oil rotary pump is used, the degree of vacuum in the vacuum chamber 6 can be evacuated to about 3 × 10 ⁻³ Torr. When a turbo molecular pump is used, the vacuum chamber 6 can be evacuated.
The inside can be evacuated to about 2 × 10 ⁻⁶ Torr.

The vacuum chamber 6 has a quartz window 1 in a part thereof, and a laser beam 8 can be introduced through the quartz window 1. The laser beam 8 is, for example, an ultraviolet laser beam having a wavelength of about 248 nm emitted from a KrF excimer laser.

In the vacuum chamber 6, a processing stage 3 on which a workpiece 2 as a processing sample is mounted is arranged, and a sample moving device 4 is connected to the processing stage 3. When the operator operates the sample moving device 4, the position of the processing stage 3 can be adjusted. The laser beam 8 is formed into a desired pattern by transmitting through a mask before entering the quartz window 1.

The work 2 is set on the processing stage 3 in the vacuum chamber 6 and its position is adjusted.
To exhaust the inside of the vacuum chamber 6. After evacuating the vacuum chamber 6 to a predetermined degree of vacuum, a laser beam 8 is selectively irradiated onto a desired area of the work 2 through the quartz window 1. The surface of the work 2 irradiated with the laser light 8 is subjected to laser processing by ablation.

FIG. 1B shows an example of an ablation processing area. The processing area 11 is a part of the surface of the work 2 and has a rectangular pattern in the illustrated case. The ablation processing area 11 is processed under desired conditions to form a rectangular recess. At this time, debris also adheres around the processing area 11. After the ablation processing, as shown in FIG. 1C, a cleaning shot is irradiated on a cleaning area 12 wider than the ablation processing area 11.
The cleaning shot is a process of irradiating a cleaning region 12 wider than the processing region 11 with an ultraviolet laser beam having a lower energy density than during processing. The cleaning shot removes debris to such an extent that the debris is not substantially affected.

In the test, the work 2 was 50 m
An altic plate of mx 2.75 mm x 0.67 mm was used. At the time of ablation processing, a rectangular area of 1.2 mm × 0.76 mm was irradiated with 1000 shots of excimer laser light at an energy density (fluence) of 4.2 J / cm ² to perform ablation processing. Due to the ablation process in a vacuum atmosphere, debris flies over a wider range than in the ablation process in the atmosphere, and the thickness of the debris becomes thinner.

As shown in FIG. 1 (C), the energy density is reduced to the cleaning area 12 wider than the ablation processing area 11 including the area where debris to be removed is present (for example, fluence of about 1.5 J / cm ^2). Extent) Cleaning was performed by irradiating an excimer laser beam. For example, the irradiation area was enlarged to 1.7 mm × 1.3 mm, and 10 cleaning shots were irradiated.

FIG. 2 shows the result of such ablation processing in comparison with the ablation processing at normal pressure. FIG. 2A shows a state of a work surface after ablation processing performed in a vacuum atmosphere. Debris 14 adheres in a thin film around the ablation region 11,
Interference fringes due to debris 14 are observed.

FIG. 2B shows the state of the sample surface after ablation processing performed in the atmosphere. Around the ablation processing area 11, dark debris 15 adhered at a high concentration. In this case, almost no interference fringes were observed.

FIG. 2C shows a result obtained by irradiating the material obtained in FIG. 2A with an excimer laser beam having a reduced energy density to a cleaning region 12 wider than the ablation region 11 in the air.

The energy density of the excimer laser light was reduced to about 1.5 J / cm ^{2 of} fluence, and the irradiation area was expanded to about 1.7 mm × 1.3 mm. Such excimer laser light was irradiated for 10 shots.

As a result, debris almost disappeared in the cleaning region 12 irradiated with the excimer laser light with reduced energy density, and the debris 14a remained only in the outer region where the excimer laser light was not irradiated.

FIG. 2 (D) shows the result of performing the same cleaning irradiation as in FIG. 2 (C) on the sample of FIG. 2 (B) which has been ablated at normal pressure. The debris 15 formed around the ablation region 11 was reduced as shown by 15a in the figure, but could not be completely removed.

Considering only the inside of the cleaning region 12, the cleaning in FIG. 2C performed in a vacuum atmosphere almost completely solves the problem of debris, but the cleaning in FIG. 2D performed under normal pressure. The results do not solve the problem of debris.

From the results of various experiments performed simultaneously, the frequency of laser irradiation during ablation was 200H.
50 Hz is more preferable than z, and the processing edge is sharper in the case of laser light irradiation having a low repetition frequency with less thermal influence.

Comparing the processing speed of the ablation processing in vacuum with the processing speed of the ablation processing under normal pressure, it is about 0.035 μm / shot in vacuum, while it is 0.028 μm / shot in air. / Shot, and the processing speed was higher in vacuum. The degree of vacuum in the test for obtaining this data was about 4.5 × 10
^-3 Torr.

The degree of vacuum was changed stepwise from the atmospheric pressure of 760 Torr to 3.5 × 10 ⁻³ Torr, but the obtained result changed according to the degree of vacuum. Considering the mean free path of particles flying in a gas, it is expected that the mean free path is inversely proportional to pressure. It is considered that the lower the pressure, the longer the mean free path, and the scattered matter generated by laser ablation can scatter far away without being affected by the atmospheric gas.

The extent to which debris extends is determined from the shock wave theory as follows: R = (P ₀ / E ₀ ) ^1/3 (where, R: debris scattering radius, P ₀ : atmosphere pressure, E
₀ : kinetic energy of debris), and the phenomenon that debris spreads over a wide range under an exhaust atmosphere can be understood. Therefore, if laser ablation is performed in an evacuated atmosphere, debris will be thinly distributed over a wide range.

The phenomenon in which debris formed thinly over a wide area can be efficiently removed by low-energy-density cleaning irradiation will be understood from the above discussion.

Although the atmospheric pressure during the ablation process varies depending on the material, it has been found that the atmospheric pressure is preferably set to about 10 Torr or less in the case of the Altic ceramics. It is necessary to perform the processing in a reduced pressure atmosphere during the ablation processing, but the atmosphere does not necessarily need to be under normal pressure during the cleaning irradiation. Perform ablation processing in a reduced pressure atmosphere,
Although it is preferable to perform cleaning irradiation in a reduced pressure atmosphere as it is, either condition may be adopted from the viewpoint of working efficiency.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example,
It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0040]

As described above, according to the present invention,
The effect of debris in laser processing can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining laser ablation according to an embodiment of the present invention. FIG. 1A is a cross-sectional view schematically showing a configuration of a laser ablation apparatus.
(B), (C) is a top view for explaining laser ablation processing.

FIG. 2 is a plan view showing laser ablation according to an embodiment of the present invention as compared with laser ablation according to the related art.

[Explanation of symbols]

 Reference Signs List 1 quartz window 2 work 3 processing stage 4 sample moving device 5 vacuum pump 6 vacuum chamber 8 laser beam 11 processing area 12 cleaning area 14, 15 debris

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C04B 41/80 C04B 41/80 A (56) References JP-A-4-158998 (JP, A) JP-A-3-248794 ( JP, A) JP-A-3-268889 (JP, A) JP-A-53-44996 (JP, A) JP-A-2-290687 (JP, A) JP-A-2-289478 (JP, A) JP JP-A-2-182389 (JP, A) JP-A-1-3211088 (JP, A) JP-A-3-62831 (JP, A)

Claims (3)

(57) [Claims] Disposing a 1. A workpiece in a vacuum evacuable vessel, the ultraviolet laser beam of the first energy density, performs laser processing by ablation irradiation <br/> shines in the object A step and irradiating the debris attached to the processing object with an ultraviolet laser beam at a second energy density lower than the first energy density,
Laser processing method odor comprising the step of removing the debris
Te, when irradiating the ultraviolet laser beam of the first energy density
The atmosphere in the container adheres to the workpiece.
The area where debris scatters is ablated in the atmosphere.
It will be wider than the debris scattered if you work
A laser processing method characterized in that the degree of vacuum is such. 2. The laser processing method according to claim 1, wherein the object to be processed is an Altic material , and the ultraviolet laser light is excimer laser light. 3. The method according to claim 1, wherein the degree of vacuum is 10 Torr or less.
The laser processing method according to claim 2.