JPH07100672A - Working method for ceramics by laser beam - Google Patents

Abstract

PURPOSE:To reduce the sticking of debris, and keep a working surface smooth by selecting a laser energy density in a range where the laser energy density on the surface to be worked of a composite sintered body is an abrasion threshold value or more and the coarsening of grains after the melting and the solidification on the working surface, is few. CONSTITUTION:For instance, the energy density of a KvF laser beam 10 irradiating on the AlTiC plate 1, is selected to approximately 1J/cm<2>. This energy density is a little higher than a threshold value to the extent that the threshold value can be secured even in the case of a fluctuation. The smoothness of a worked bottom surface with subjected to an abrasion work, is satisfactorily kept by an energy density with a low value like this. Also, since a melted layer on the worked surface of the AlTiC plate, is thin and a cooling speed is fast, the coarsening of grains, is few by resolidification. Also, since the mass of splashed matters, is small, the generation and the attachment of debris in a working area, is few. Further, since the energy density is low, an increase in temperature of the AlTiC plate, is suppressed, thermal strain is lower, and the development of a cracking, is remarkably reduced.

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 of a composite sintered body of aluminum oxide and titanium carbide known as Altic.

[0002]

2. Description of the Related Art Excimer laser light has a high photon energy capable of breaking a chemical bond, and a photochemical reaction called ablation can remove an object to be processed with little thermal influence.

By irradiating an excimer laser beam having an adjusted energy density, various materials such as plastics, metals and ceramics can be ablated. Depending on the object to be processed, scattered objects called debris adhere to the periphery of the processing area due to the ablation process. In addition, unevenness may occur on the bottom surface of the processing region. If debris or unevenness on the bottom surface occurs, the desired processing accuracy may not be obtained.

In the magnetic storage device, the magnetic head is moved 0.2 μm from the surface of the magnetic disk disk by the aerodynamic action.
A magnetic head slider with a fine groove is used in order to levitate with a minute gap of about m. Altic (Al ₂ O ₃ —TiC composite sintered body) is used for the magnetic head slider.

Conventionally, AlTiC for a magnetic head has been processed by ion milling. Ion milling for spot machining has a slow machining speed, so YAG is advantageous for high-speed machining in recent surface machining.
Laser processing and excimer laser processing are drawing attention.

The excimer laser processing of ceramics has a slower processing speed than the excimer laser processing of polymer materials such as polymers. The excimer laser processing of ceramics is usually performed with an energy density of 10 J / cm ² or more.
Ceramics mainly composed of Al ₂ O ₃ or Si ₃ N ₄ have good workability by excimer laser, and the bottom surface after processing is smooth. However, the workability of Altic is poor, and the bottom surface after processing becomes rough. Along with the attachment of debris around the processing area, the unevenness of the processing bottom surface deteriorates the processing quality.

[0007]

As described above,
In the excimer laser ablation process of Altic, the generation of debris and the roughening of the processed bottom surface deteriorate the processing quality.

The object of the present invention is to reduce the deposition of debris,
It is an object of the present invention to provide Altic excimer laser processing capable of maintaining a processed surface smooth (roughness of the processed surface is 20% or less of the processed depth).

[0009]

The laser processing method of the present invention is a laser processing method for processing a composite sintered body of aluminum oxide and titanium carbide by an excimer laser,
The laser energy density on the processed surface of the composite sintered body is selected to be in a range above the ablation threshold value, where crystal grain growth due to melting and solidification on the processed surface is small. This range is preferably equal to or more than the processing threshold value and within twice the processing threshold value.

[0010]

[Function] In Altic excimer laser processing, the reason why the processed bottom surface becomes rough is that the object to be processed is partially melted by the irradiation of the excimer laser and re-solidified to coarsen the crystal grains, resulting in unevenness of the processed bottom surface. It is expected to become fierce.

By selecting the energy density of the excimer laser for processing to be equal to or higher than the threshold value for ablation and to reduce the coarsening of crystal grains due to melting and solidification on the processing surface,
It is possible to maintain the smoothness of the processed bottom surface. Also, by selecting the energy density of the excimer laser in this way, the attachment of debris is reduced.

[0012]

EXAMPLE FIG. 1 schematically shows the structure of an excimer laser processing machine. The excimer laser oscillator 10 of KrF or the like pulse-oscillates the excimer laser light under the control of the control device 11. The excimer laser light emitted from the excimer laser oscillator 10 passes through the mirrors M1 and M2 and the mask pattern M.
Irradiated on P. The mask pattern MP is formed by patterning a light-shielding material such as chromium on a transparent substrate such as quartz, a metal plate having openings formed therein, or the like.

The excimer laser light that has passed through the mask pattern MP is further incident on the imaging lens L via the mirror M3, and is imaged on the Altic plate 1 placed on the XYZ-stage 3. The XYZ-stage 3 is installed in the atmosphere.

By controlling the energy density and the number of pulses of the excimer laser light, the Altic plate 1 is ablated into a desired shape according to the shape of the mask pattern MP.

In order to continuously control the energy density without changing the beam pattern, a variable attenuator utilizing a difference in angular dependence of reflectance with respect to the optical axis was used.

In the processing of general ceramics,
The reduction ratio of the imaging lens L is, for example, about 1/5 to 1/10 (energy density is 1 / 25-1 / 100),
The ceramic surface is processed by increasing the energy density of laser light. In this embodiment, the energy density of the excimer laser light to be irradiated is extremely reduced as compared with the conventional technique.

FIG. 2 shows the energy density dependence of the working depth in the excimer laser processing of AlTiC. The horizontal axis represents the energy density, and the vertical axis represents the processing depth of the irradiated portion. The excimer laser light is 248n of KrF.
A pulsed light of 1,000 pulses was irradiated using m laser light. Altic is Al ₂ O ₃ : TiC≈7
A composite sintered product of 5:25 was used.

As is clear from FIG. 2, in the region where the energy density of the excimer laser light is very low, laser processing is not performed and the processing depth remains zero. When the energy density exceeds a certain value, excimer laser processing starts,
The working depth increases almost linearly with the energy density.
As a threshold value for starting processing, a value under atmospheric pressure is somewhat higher than a value under vacuum. The threshold value when performed in air is about 0.7 J / cm ² .

When the energy density increases, the working depth under vacuum linearly increases, whereas the working depth under atmospheric pressure is slightly low and tends to be gradually saturated. In a region having a high energy density, it is considered that the incident laser light is absorbed and the loss is increased in the light emission portion (plume) corresponding to the scattering due to the processing.

In this embodiment, the energy density of the KrF laser beam with which the AlTiC plate is irradiated is selected to be about 1 J / cm ² . This energy density is slightly higher than the threshold value so that the threshold value can be secured even if fluctuation occurs.

By selecting the energy density to such a low value, the smoothness of the machined bottom surface after ablation processing was kept good. Since the energy density is low, the melted layer is thin on the processed surface of AlTiC, and the cooling rate is high, so that it is considered that re-solidification does not cause coarsening of crystal grains.

Further, the generation and adhesion of debris in the periphery of the processed area was small. The cause of this is awaiting further clarification, but it is thought that the small mass of the scattered matter is effective because the dissolved layer is thin.

Further, in the AlTiC after processing, the occurrence of cracks is extremely small. It is considered that this phenomenon is caused by thermal strain at the time of melting and re-solidifying due to the temperature rise of the processed surface of AlTiC when the laser beam of high energy density is irradiated. It is considered that by lowering the energy density, the temperature rise of AlTiC was suppressed and the thermal strain was lowered.

That is, in the processing of Altic excimer laser light, by limiting the energy density of the excimer laser light to be irradiated to the threshold value or more and within twice the threshold value, the smoothness of the processing bottom surface is compensated and at the same time debris is generated. Oppressed.

Although the present invention has been described based on the embodiments, the present invention is not limited to the embodiments. For example, an excimer laser other than KrF can be used as the excimer laser. Altics are not limited to magnetic heads, and can be processed into Altics of various compositions according to the application, and can also be applied to other ceramics that are difficult to process. Laser processing may be performed under atmospheric pressure or under vacuum. It will be apparent to those skilled in the art that various other modifications, improvements, and combinations can be made.

[0026]

As described above, according to the present invention,
The quality of processing of AlTiC by the excimer laser light can be improved.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of an excimer laser processing machine according to an embodiment of the present invention.

FIG. 2 is a graph showing energy density dependence of processing depth in excimer laser processing.

[Explanation of symbols]

 1 Altic Plate 3 XYZ-Stage 10 Excimer Laser 11 Controller M Mirror L Lens MP Mask Pattern

Claims (1)

[Claims] 1. A laser processing method for processing a composite sintered body of aluminum oxide and titanium carbide with an excimer laser, wherein the laser energy density on the processed surface of the composite sintered body is equal to or higher than an ablation threshold and is melted and solidified on the processed surface. A laser processing method characterized by selecting a range in which coarsening of particles afterward is small.