JP4730591B2 - Laser processing apparatus and laser processing method - Google Patents

Description

  The present invention relates to a laser processing apparatus and a laser processing method.

As a laser processing apparatus, cutting and drilling of a metal plate using a CO ₂ laser and precision processing of a metal thin plate using a YAG laser are widely known. In particular, the YAG laser is suitable for various types of precision processing because it is small in size, has good maintainability, and can easily obtain a focused spot having a diameter of several tens of μm. Furthermore, since the second harmonic (wavelength of 532 nm) can be obtained with a YAG laser, it can be applied to fine thin film processing utilizing the ablation effect. Laser ablation is a phenomenon in which when a polymer material is irradiated with a short wavelength / short pulse laser such as an excimer laser or a YAG harmonic, the material is instantly decomposed, vaporized and scattered, and the material is locally removed. is there. In fact, Q-switched YAG lasers have begun to be used for defect correction of semiconductor manufacturing masks, patterning of detection portions of thin film sensors, electrode patterning of liquid crystal panels, and the like. The reason why the Q switch is used is that high-quality machining without thermal damage to the workpiece can be realized by using a beam having a short pulse width and a high peak power.

In general, the patterning of the electrodes of the liquid crystal panel is performed by cutting the conductive film at a predetermined interval while moving the substrate on which the light-transmitting conductive film is deposited with respect to the laser beam. The processing quality at this time, that is, the electrical characteristics of the conductive film is determined by the characteristics (mainly peak power) of the Q-switched YAG laser. The characteristics of the laser depend on the Q switch frequency. That is, when the Q switch frequency is lowered, the pulse width is narrowed and the peak power is increased. Conversely, when the Q switch frequency is increased, the pulse width is increased and the peak power is decreased.

  From the viewpoint of processing quality, it is desirable to increase the peak intensity of the beam by lowering the Q switch frequency. If it carries out like this, a process site | part can be removed instantaneously via an ablation effect, and a thermal damage will not be carried out to the process part vicinity or a film | membrane board | substrate.

  However, these processing methods have a problem in productivity. This is because lowering the Q switch frequency leads to a delay in the feed rate of the stage, and as a result, the machining speed is significantly reduced.

  On the other hand, from the viewpoint of processing speed, it is desirable to move the stage quickly by increasing the Q switch frequency. However, when the Q switch frequency is increased, the peak power is reduced and the pulse width is increased. For this reason, when the electrodes of the liquid crystal panel are patterned, the glass which is the electrode substrate is thermally damaged, and minute cracks and dents are generated. This crack or dent becomes a factor that impairs the display quality of the liquid crystal panel. In addition, alkali metal ions contained in minute amounts in the glass are eluted from the cracks and dents into the liquid crystal, which causes a display defect of the liquid crystal panel.

In order to solve this problem, the laser processing apparatus disclosed in Patent Document 1 branches a beam from a laser oscillator into a plurality of beams by a diffractive optical element having a phase modulation action, and simultaneously processes a plurality of parts on the surface of the workpiece. By doing so, the processing ability is greatly improved. That is, assuming that the number of beam branches is N, it is possible to achieve a processing capability that is N times that of processing with a single beam. In Patent Document 1, a concavo-convex binary phase grating having a substantially rectangular cross-sectional shape is used as a diffractive optical element.
Japanese Patent No. 3293136

  However, when a laser beam is split using a binary phase grating, energy leakage into high-order diffracted light increases. When high-order diffracted light unnecessary for processing is irradiated on the workpiece, the surface of the workpiece may be damaged. For this reason, conventionally, a light shielding mask for shielding unnecessary beams has been provided. However, the removal material generated during processing accumulates on the edge of the light shielding mask, obstructs the optical path of the processing beam and disturbs the intensity distribution of the beam, or the accumulated removal material falls onto the surface of the workpiece and covers the surface. In some cases, the workpiece was contaminated. In order to avoid such an adverse effect, it is necessary to replace the light-shielding mask in the middle of processing. However, since this operation involves adjustment of the laser optical system, much time and cost are required. Further, stopping the operation of the apparatus for adjusting the laser optical system leads to a decrease in processing capability.

  An object of the present invention is to obtain a laser processing apparatus and a laser processing method having high processing capability and excellent processing quality.

The laser processing apparatus of the present invention includes a laser oscillator and a diffractive optical element that divides a beam emitted from the laser oscillator into a plurality of beams and irradiates the workpiece, and the diffractive optical element includes the workpiece. The surface has a concavo-convex shape designed to suppress the generation of high-order diffracted light that is not necessary for processing, and the cross-sectional shape of the concavo-convex shape is a continuous smooth shape everywhere expressed by superposition of trigonometric functions It is .
When a diffractive optical element having a continuous cross-sectional shape is used everywhere, there is little energy leakage to higher-order diffracted light, so that it is possible to avoid the harmful effects caused by a beam unnecessary for processing. Thereby, the laser processing apparatus with high processing capability and excellent processing quality can be obtained.
Moreover, you may make it provide the condensing lens which each condenses the several beam branched by the said diffractive optical element, and irradiates a workpiece.

Further, when the maximum diffraction order of a plurality of diffracted beams used for processing among the diffracted beams generated from the diffractive optical element is N, the spatial frequency ν of the concavo-convex shape of the diffractive optical element is
A diffractive optical element that suppresses the generation of high-order diffracted light is designed by satisfying ν ≦ 2NΔ / λf (Δ is the beam branching pitch, λ is the beam wavelength, and f is the distance from the diffractive optical element to the workpiece). Obtainable.

The laser processing method of the present invention includes a step of emitting a beam from a laser oscillator, and a diffractive optical element having a concavo-convex shape that is a continuous smooth shape everywhere expressed by superposition of trigonometric functions on the surface. And a step of branching the beam into a plurality of beams while suppressing generation of high-order diffracted light unnecessary for processing the workpiece.
When a diffractive optical element having a continuous cross-sectional shape is used everywhere, there is little energy leakage to higher-order diffracted light, so that it is possible to avoid the harmful effects caused by a beam unnecessary for processing. Thereby, the laser processing apparatus with high processing capability and excellent processing quality can be obtained.
Moreover, you may make it have the process of condensing each multiple beam with a condensing lens, and irradiating the said to-be-processed object.

Further, when the maximum diffraction order of a plurality of diffracted beams used for processing among the diffracted beams generated from the diffractive optical element is N, the spatial frequency ν of the concavo-convex shape of the diffractive optical element is
A diffractive optical element that suppresses the generation of high-order diffracted light is designed by satisfying ν ≦ 2NΔ / λf (Δ is the beam branching pitch, λ is the beam wavelength, and f is the distance from the diffractive optical element to the workpiece). Obtainable.

Embodiments of the present invention will be described below with reference to the drawings.
The configuration of the laser processing apparatus of the present invention is shown in FIG. The laser oscillator 1101 is a Q-switched YAG laser and emits a linearly polarized TEM ₀₀ mode. The Q switch frequency of the laser oscillator 1101 is controlled by the Q switch driver 1102.
The expander collimator 1104 expands the beam 1103 emitted from the laser oscillator 1101, and the optical path bending mirror 1105 folds the optical path of the beam 1103. After the polarization of the beam is changed to elliptical polarization by the wave plate 1106, the beam is incident on the phase grating 1107. The phase grating 1107 has a function of branching one incident beam into a plurality of diffraction beams. A plurality of beams emitted from the phase grating 1107 are irradiated onto the workpiece held on the precision stage 1110 via the condenser lens 1108. Here, a plurality of condensing spots 1111 are formed at equal intervals on the surface of a translucent conductive film (ITO film) substrate 1109, and the precision stage 1110 is moved to cut the ITO film in a straight line or a curved line. .

  FIG. 2 is a diagram schematically showing cutting processing by the laser processing apparatus of the present invention. As shown in the drawing, a plurality of beams (here, 13 beams) branched by the phase grating 1107 are collected by the condenser lens 1108, and are shown on the translucent conductive film substrate 1109 in the inset A in the figure. 13 condensing spots as shown are formed. By moving the precision stage 1110 in the direction of the arrow in the figure, 13 places can be cut simultaneously.

  The phase grating 1107 is a one-dimensional surface uneven phase grating. There are three main design items of the phase grating 1107: the length of one period, the overall size, and the phase distribution within one period. The length of one cycle is determined by the machining shape. That is, here, it is determined from the interval between the open grooves formed on the ITO film. The overall size is determined by the incident beam diameter. The phase distribution within one period is determined by the required number of beam branches and the required uniformity of beam intensity.

From the diffraction theory, the period p of the phase grating is given by the following equation.
p = mλf / Δ (1)
Where m = 1 (when the number of beam branches is an odd number), m = 2 (when the number of beam branches is an even number), λ is the beam wavelength (532 nm), f is the focal length of the condenser lens 1110, and Δ is the beam This is the branch pitch (interval of the groove). For example, assuming that the number of branches is an even number and f = 100 mm and Δ = 200 μm, p = 532 μm.

The total size D of the phase grating needs to satisfy the following condition from the theory of wave optics.
D> d = 2f · tan [sin ⁻¹ (2λ / πw)] (2)
Here, d is the incident beam diameter (l / e ² ), and w is the required focused spot diameter (l / e ² ). For example, when f = 100 mm and w = 10 μm, D> d = 4 mm.

  For the calculation of the phase distribution of the phase grating, for example, a simulated annealing method (Science 220, 671-680 (1983), hereinafter abbreviated as SA method) can be used. The construction of the rules necessary for the operation of the SA method requires experience, and the optical performance of the phase grating is determined by the failure of the rules.

In order to design a phase grating using the SA method, it is necessary to define operational rules for at least the evaluation function definition and weight setting, temperature scheduling, and equilibrium state determination. The evaluation function is an amount corresponding to the difference between the estimated value regarding the performance of the phase grating and the target value, and the solution when the function value is the smallest is the optimal solution. The optical performance required for the phase grating 1107 used in this embodiment is determined based on the output of the laser oscillator, the processing threshold, and the required processing uniformity, and is as follows, for example.
(1) The light utilization efficiency is 80% or more.
(2) The beam intensity uniformity after branching is 0.90 or more.
Here, the light utilization efficiency means a ratio of light energy that can be supplied to a beam having a required diffraction order. Further, the beam intensity uniformity means a ratio between the minimum and maximum intensity of a plurality of branched diffraction beams.

  In actual calculation, the conditions of (1) and (2) are taken into the evaluation function, and the photomask drawing apparatus used for producing the phase grating from the solutions satisfying the conditions of (1) and (2) The pattern transfer capability of each of the exposure / development apparatus and the etching apparatus is determined.

  FIG. 3 is a diagram schematically showing the phase distribution (for one period) of the phase grating 1107 designed by the above method, and shows the cross-sectional shape of the phase grating 1107. As shown in the figure, the cross-sectional shape of the phase grating 1107 has a smooth shape and is continuous everywhere.

The cross-sectional shape of the phase grating 1107 is expressed by superposing trigonometric functions. When the maximum diffraction order by the phase grating 1107 is N, the spatial frequency ν of the phase grating 1107 generally satisfies the following conditions.
ν ≦ 2NΔ / λf (3)
Where Δ is the beam branch pitch, λ is the beam wavelength, and f is the distance from the diffractive optical element to the workpiece.

  FIG. 4 is a bird's-eye view of a one-dimensional surface concavo-convex binary phase grating designed by the above method according to a comparative example. The cross-sectional shape of the phase grating of the comparative example is almost rectangular and is classified as a so-called binary phase grating.

FIGS. 5A and 5B are diagrams showing the intensity distribution of the diffracted light reproduced by the phase grating 1107. FIG. FIGS. 6A and 6B are diagrams showing the intensity distribution of diffracted light reproduced by the phase grating of the above comparative example.
As can be seen from the figure, in the binary phase grating of the comparative example, peaks of high-order diffracted light appear outside the 13 beams necessary for processing. On the other hand, in the phase grating 1107, the peak of high-order diffracted light does not appear outside the 13 beams necessary for processing. Comparing both optical performances, the binary phase grating of the comparative example has a light utilization efficiency of 78% and a branching uniformity of 0.95, and the phase grating 1107 has a light utilization efficiency of 97% and a branching uniformity of 0.99. In addition, the binary phase grating has low light utilization efficiency. That is, only 3% of energy leaks to the high-order diffracted light in the phase grating 1107, whereas 22% of energy leaks to the high-order diffracted light in the binary phase grating. For this reason, the S / N ratio representing the intensity ratio between the branched light used for processing and the unnecessary high-order diffracted light is at most about 5 in the binary phase grating, but is improved to nearly 40 in the phase grating 1107.

  When the above binary phase grating is used, high-order diffracted light may damage the workpiece. FIG. 7 is a diagram for explaining damage caused to a workpiece by high-order diffracted light. As shown in the figure, an unnecessary cutting groove due to high-order diffracted light may be generated outside the required cutting groove.

In order to avoid this, when a binary phase grating is used, as shown in FIG. 8A, a light shielding mask is provided on the surface of the workpiece, and the higher-order diffracted light irradiates the workpiece. Need to prevent. However, since the interval between each diffracted light is about 100 to 200 μm, a light-shielding mask must be disposed very close to the processing region in order to block high-order diffracted light.
For this reason, as the processing progresses, the removed material generated by the processing accumulates on the edge 8001 of the light shielding mask, and as shown in FIG. 8B, the deposit blocks the optical path of the processing diffracted light and disturbs the intensity distribution. Can happen. In addition, deposits may fall on the workpiece and contaminate the workpiece.

  On the other hand, when the phase grating 1107 having a smooth cross-sectional shape is used, the energy leaked to the high-order diffracted light is small and there is no need to consider the damage due to the high-order diffracted light, so there is no need to provide a light shielding mask. In addition, since the light utilization efficiency is improved, the number of beam branches can be increased, and the processing throughput can be increased.

The laser processing apparatus of the present invention can be used, for example, for forming ink cavities in the manufacture of inkjet heads, and for cutting and separating antistatic conductive films in the manufacture of liquid crystal panels.
In these processing applications, it may be difficult to provide a light-shielding mask due to restrictions on the configuration of the apparatus, but damage due to higher-order diffracted light can be suppressed by using the above laser processing apparatus. High-quality ink cavities and liquid crystal panels can be obtained with high processing capability.

It is a figure which shows the structure of the laser processing apparatus of this invention. It is the figure which showed typically the cutting process by the laser processing apparatus of this invention. It is the figure which showed typically the phase distribution of the phase grating of this invention. It is a bird's-eye view of the binary phase grating of a comparative example. (A), (b) is the figure which showed intensity distribution of the diffracted light reproduced | regenerated with the phase grating which has a continuous cross-sectional shape. (A), (b) is the figure which showed intensity distribution of the diffracted light reproduced | regenerated by said comparative example. It is a figure explaining the damage given to a workpiece by high order diffracted light. (A), (b) is a figure explaining the method of providing a light-shielding mask and processing.

Explanation of symbols

  1101 Laser oscillator, 1102 Q switch driver, 1103 beam, 1104 expander collimator, 1105 optical path bending mirror, 1106 wave plate, 1107 phase grating (diffractive optical element), 1108 condenser lens, 1109 translucent conductive film substrate (processed) ) 1110 Precision stage, 1111 Condensing spot

Claims (6)

A laser oscillator;
A diffractive optical element that divides a beam emitted from the laser oscillator into a plurality of beams and irradiates a workpiece,
The diffractive optical element has a concavo-convex shape designed so as to suppress generation of high-order diffracted light unnecessary for processing the workpiece, and the cross-sectional shape of the concavo-convex shape is expressed by superposition of trigonometric functions. Laser processing equipment that has a continuous and smooth shape everywhere .   The laser processing apparatus according to claim 1, further comprising a condensing lens that condenses each of the plurality of beams branched by the diffractive optical element and irradiates the workpiece. When the maximum diffraction order of a plurality of diffracted beams used for processing among the diffracted beams generated from the diffractive optical element is N, the spatial frequency ν of the concavo-convex shape of the diffractive optical element is:
ν ≦ 2NΔ / λf (Δ is the beam branching pitch, λ is the beam wavelength, and f is the distance from the diffractive optical element to the workpiece)
The laser processing apparatus according to claim 1 or 2, wherein Emitting a beam from a laser oscillator;
While suppressing the generation of high-order diffracted light, which is unnecessary for processing the workpiece, by using a diffractive optical element that has a concavo-convex shape that is a continuous and smooth shape everywhere expressed by superposition of trigonometric functions. A laser processing method comprising a step of branching the beam into a plurality of beams.   The laser processing method according to claim 4, further comprising a step of condensing each of the plurality of beams with a condensing lens and irradiating the workpiece. When the maximum diffraction order of a plurality of diffracted beams used for processing among the diffracted beams generated from the diffractive optical element is N, the spatial frequency ν of the concavo-convex shape of the diffractive optical element is:
ν ≦ 2NΔ / λf (Δ is the beam branching pitch, λ is the beam wavelength, and f is the distance from the diffractive optical element to the workpiece)
The laser processing method according to claim 4 or 5, which satisfies the following conditions.

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