Laser beam processing method and device therefor

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to laser processing, and more particularly to laser processing using an ultraviolet laser beam such as an excimer laser.

【0002】

The excimer laser light 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 is attracting attention.

【0003】

[Conventional technology]

By irradiating excimer laser light with adjusted energy density, various substances such as plastics, metals, and ceramics can be ablated.

【0004】

In the ablation process, scattered debris called debris adheres to the surface around the processed portion from the object to be processed that has been irradiated with the laser. In laser ablation of polymer materials such as polyimide, O is a countermeasure against soot-like debris.₂A method of spraying a gas such as He or He has been attempted.

【0005】

It is considered that oxygen spraying is effective for C and the like which are in a gas state due to oxidation. There is also a proposal to combine it with H to convert it to a gas state. In addition, He having a small molecular weight is considered to be effective as a blowing gas because it has a small reaction due to collision with scattered matter.

【0006】

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

【0007】

In a magnetic storage device, a magnetic head slider with fine grooves is used in order to levitate the magnetic head from the surface of a magnetic disk disk with a minute gap of about 0.1 μm by aerodynamic action. Altic material (Al) on this magnetic head slider₂O₃/ TiC composite sintered body) is used.

【0008】

Conventionally, altic materials for magnetic heads are processed by ion milling, but since the processing speed is slow, YAG laser processing and excimer laser ablation processing, which are advantageous for high-speed processing, have recently attracted attention.

【0009】

However, when the altic is processed by ablation processing with an excimer laser, debris adheres around the processed area, which seriously hinders the stable floating of the magnetic head. In this case, even if a gas such as oxygen was blown at the time of laser ablation, the effect was small.

【0010】

[Problems to be Solved by the Invention]

As described above, laser ablation processing is an effective processing method, but the problem of debris has not been completely solved.

【0011】

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

【0012】

[Means for solving problems]

The laser processing method of the present invention includes a step of arranging an object to be processed in a container having a light transmitting window and capable of vacuum exhaust, and an ultraviolet laser beam having a first energy density while exhausting the inside of the container to a vacuum state. Is laser-processed by ablation by irradiating the object to be processed with light from a light transmitting window, and the scattered matter adhering to the vicinity of the processed area of the object to be processed is ultraviolet with a second energy density lower than the first energy density. It includes a step of irradiating a laser beam and removing scattered matter.

【0013】

[Action]

Debris is unavoidable by performing laser ablation under reduced pressure exhausted to a vacuum state, but debris is thinly generated in a wide range. By irradiating such mild debris with an ultraviolet laser beam having a reduced energy density, it is possible to remove scattered debris and effectively resolve the debris.

【0014】

[Example]

Conventionally used gas spraying is a measure to reduce or prevent debris itself.

【0015】

In the laser machining of Altic, even if an attempt was made to remove the debris once generated, the debris adhered firmly to the object to be machined, and the removal was not easy. Therefore, according to the conventional technique, in order to solve such a debris problem, the occurrence of debris itself will be reduced or prevented. However, good results could not be obtained by spraying gas.

【0016】

The present inventor has sought measures to change the way of thinking and convert the generated debris into something that is easy to remove. Factors that change the debris generation conditions include factors such as the energy density, repetition frequency, and wavelength of the excimer laser beam to be irradiated, as well as the atmosphere and substrate temperature.

【0017】

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

【0018】

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

【0019】

When using an oil rotary pump, the degree of vacuum in the vacuum chamber 6 is about 3 × 10.^-3It is possible to exhaust up to Torr, and when using a turbo molecular pump, the degree of vacuum in the vacuum chamber 6 is about 2 × 10.^-6It can exhaust up to Torr.

【0020】

The vacuum chamber 6 has a quartz window 1 as a part thereof, and the 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.

【0021】

A processing stage 3 on which the work 2 which is a processing sample is placed is arranged in the vacuum chamber 6, and a sample moving device 4 is connected to the processing stage 3. The position of the machining stage 3 can be adjusted by the operator operating the sample moving device 4. Further, the laser beam 8 is formed into a desired pattern by passing through the mask before it enters the quartz window 1.

【0022】

The work 2 is installed on the processing stage 3 in the vacuum chamber 6, the position is adjusted, and then the inside of the vacuum chamber 6 is exhausted by the vacuum pump 5. After the vacuum chamber 6 is exhausted to a predetermined degree of vacuum, the laser beam 8 is selectively irradiated onto the desired region of the work 2 through the quartz window 1. The surface of the work 2 irradiated with the laser beam 8 undergoes laser processing by ablation.

【0023】

FIG. 1 (B) shows an example of the ablation processing region. The processing area 11 is a part of the surface of the work 2, and is a rectangular pattern in the figure. The ablation processing region 11 is processed under desired conditions to create a rectangular recess. At this time, debris also adheres to the periphery of the processing region 11. After the ablation process, as shown in FIG. 1 (C), a cleaning shot is irradiated in the cleaning area 12 wider than the ablation process area 11. The cleaning shot is a process of irradiating the cleaning area 12 wider than the processing area 11 with an ultraviolet laser beam having a lower energy density than that at the time of processing. This cleaning shot removes debris to the extent that it has virtually no effect.

【0024】

In the test, a 50 mm × 2.75 mm × 0.67 mm altic plate was used as the work 2. Energy density (fluence) 4.2J / cm during ablation processing²The excimer laser beam was irradiated to a rectangular area of 1.2 mm × 0.76 mm for 1000 shots, and ablation processing was performed. Due to the ablation process in the vacuum atmosphere, the debris flies over a wider range than the ablation process in the atmosphere, and the adhesion thickness becomes thinner.

【0025】

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

【0026】

The results of such ablation processing are shown in Fig. 2 in comparison with the ablation processing under normal pressure. FIG. 2 (A) shows the state of the work surface after the ablation process performed in a vacuum atmosphere. Debris 14 adheres in a thin film around the ablation processing region 11, and interference fringes due to the debris 14 are observed.

【0027】

Figure 2 (B) shows the state of the sample surface after ablation processing performed in the atmosphere. A high concentration of blackish debris 15 adhered to the periphery of the ablation processing region 11. In this case, almost no interference fringes were observed.

【0028】

FIG. 2C shows the result of irradiating the cleaning region 12, which is wider than the ablation processing region 11 in the atmosphere, with the excimer laser light having a reduced energy density.

【0029】

The energy density of excimer laser light is fluence 1.5 J / cm²The irradiation area was expanded to about 1.7 mm x 1.3 mm. 10 shots of such excimer laser light were irradiated.

【0030】

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

【0031】

FIG. 2 (D) shows the results of performing the same cleaning irradiation as in FIG. 2 (C) on the sample of FIG. 2 (B) that had been ablated under normal pressure. The debris 15 formed around the ablation-processed region 11 decreased as shown in 15a in the figure, but could not be completely removed.

【0032】

Considering only the inside of the cleaning area 12, the cleaning of FIG. 2 (C) performed in a vacuum atmosphere almost completely solved the problem of debris, but the result of FIG. 2 (D) performed under normal pressure is , The problem of debris has not been solved.

【0033】

From the results of various experiments conducted at the same time, the laser irradiation frequency during ablation processing was preferably 50 Hz rather than 200 Hz, and the processing edge was sharper in laser light irradiation with a low repetition frequency, which had less thermal effect.

【0034】

Comparing the processing speed of ablation processing in vacuum with the processing speed of ablation processing under normal pressure, it is about 0.035 μm / shot in vacuum, while it is 0.028 μm / shot in air. The processing speed was faster in vacuum. The degree of vacuum in the test obtained from this data is about 4.5 x 10^-3It was Torr.

【0035】

The degree of vacuum is 3.5 x 10 from 760 Torr, which is the atmospheric pressure.^-3 It was changed stepwise up to Torr, but the results obtained changed according to the degree of vacuum. Considering the mean free path of particles flying in the gas, it is predicted that the mean free path is inversely proportional to the pressure. It is considered that the lower the pressure, the longer the mean free path, and the scattered matter generated by the laser ablation can be scattered far away without being affected by the atmospheric gas.

【0036】

The extent to which debris extends can be determined from shock wave theory. R = (P₀/ E₀)^1/3(Here, R: Debris scattering radius, P₀: Atmospheric pressure, E₀: Debris kinetic energy), and the phenomenon that debris covers a wide range under the exhaust atmosphere can be understood. Therefore, if the laser ablation process is performed in the exhausted atmosphere, the debris will be thinly distributed over a wide range.

【0037】

The phenomenon that debris formed thinly over a wide area could be efficiently removed by low energy density cleaning irradiation will be understood by considering as described above.

【0038】

The atmospheric pressure during the ablation process differs depending on the material, but in the case of Altic ceramics, it was found that the atmospheric pressure is preferably about 10 Torr or less. In the ablation process, it is necessary to perform the process in a reduced pressure atmosphere, but in the cleaning irradiation, the atmosphere does not necessarily have to be under normal pressure. It is preferable that the ablation process is performed in a reduced pressure atmosphere and the cleaning irradiation is performed in the reduced pressure atmosphere as it is, but either condition may be adopted from the viewpoint of work efficiency.

【0039】

Although the present invention has been described above with reference to Examples, the present invention is not limited thereto. For example, it will be obvious to those skilled in the art that various changes, improvements, combinations, etc. are possible.

【0040】

[Effect of the invention]

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

[Simple explanation of drawings]

[Figure 1]

It is a figure for demonstrating the laser ablation by the Example of this invention. FIG. 1 (A) is a cross-sectional view schematically showing the configuration of a laser ablation apparatus, and FIGS. 1 (B) and 1 (C) are plan views for explaining laser ablation processing.

[Figure 2]

It is a top view which shows the laser ablation by the Example of this invention in comparison with the laser ablation by the prior art.

[Explanation of symbols]

1 Quartz window 2 work 3 Processing stage 4 Sample transfer device 5 vacuum pump 6 vacuum chamber 8 laser light 11 Machining area 12 Cleaning area 14, 15 debris