JP4453112B2 - Laser processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing method using a laser processing apparatus including a beam shaping unit that shapes and introduces a laser beam into a pair of fly-eye lenses, and more specifically, for example, an ink ejection nozzle hole of an ink jet printer, etc. The present invention relates to a laser processing method capable of minimizing interference of a laser beam passing through a pair of fly-eye lenses when performing a plurality of holes.
[0002]
[Prior art]
A conventional general laser processing apparatus for processing the above-described nozzle holes for ink ejection includes a laser beam oscillator 1, a beam shaping unit 5 for shaping the laser beam A, and a laser beam A as shown in FIG. A beam expander 7 for enlarging and a pair of fly eye lenses 8 and 8 as a beam flattening optical system (homogenizer) are provided. The beam is dispersed and condensed by the condenser lens 9 to make the beam intensity uniform and control the light output. Further, the mask 11 disposed on the downstream side of the condenser lens 9 is provided with a laser processing shape to the workpiece B, that is, a hole pattern (not shown) in which a plurality of nozzle holes are arranged in a line. The long and rectangular laser beam A condensed by the lens 9 is condensed at a predetermined position (hole pattern position) of the mask 11.
[0003]
The laser beam A transmitted through the mask 11 in this manner is applied onto the workpiece B made of a polymer such as polyimide at a predetermined magnification (for example, 1/4 times or 1/5 times) by an imaging lens 12 as projection optical means. A plurality of nozzle holes (not shown) that are imaged and correspond to the hole pattern of the mask 11 are formed on the workpiece B. Here, with the XY table 5 on which the workpiece B is placed, the workpiece B is moved by a predetermined dimension in the X direction or the Y direction, the laser beam A is output again by the laser beam oscillator 1 and irradiated. By doing so, the nozzle hole group is formed with a certain pitch. Reference numerals 2, 3, and 4 in the figure denote total reflection mirrors.
[0004]
[Problems to be solved by the invention]
However, the above-described conventional laser processing apparatus has room for improvement in the following points. That is, as shown in FIG. 6, for example, when a plurality of nozzle holes C for ink ejection are laser processed in a nozzle plate (workpiece) B of an ink jet printer, each nozzle hole C is formed from the ink entering side. Although it is formed in a truncated cone shape whose diameter is gradually reduced toward the exit side, the phenomenon that the exit side shape Co of the nozzle hole C is distorted and does not become a perfect circle occurs. This phenomenon occurs regularly in the plurality of nozzle holes C on the workpiece B. In other words, when the plurality of nozzle holes C are simultaneously laser processed on the workpiece B through the hole pattern of the mask 11 (FIG. 1), the emission side shape Co is periodically distorted depending on the positions of the nozzle holes C. Or distorted. This is considered that the laser beam A interferes with the pair of fly-eye lenses 8 and 8 and the position of the interference periodically changes, so that the interference of the laser beam A causes distortion during processing. That is, since there is a distance corresponding to the thickness of the workpiece B (100 μm in this example) between the front and back of the workpiece B, the laser beam A at the position on the incident side of the laser beam with respect to the workpiece B However, since the condensing characteristics change on the exit side outside the depth of focus, the influence due to the light interference increases, and the exit side shape Co is distorted.
[0005]
The present invention has been made in view of the above points, and provides a laser processing method that enables high-precision laser processing with almost no distortion while minimizing laser beam interference between the pair of fly-eye lenses. It is something to be offered.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a laser processing method according to the present invention is configured to shape a pair of fly beams by shaping a laser beam having a substantially rectangular cross section output from a laser oscillator by a beam shaping unit including a cylindrical concave lens and a cylindrical convex lens. A laser processing method using a laser processing apparatus that irradiates a workpiece through a mask having a pattern corresponding to a plurality of holes that are introduced into an eye lens and processed at the same time, wherein the cylindrical lenses are rotated by rotating the beam shaping unit. wherein the central axis of the cylinder forming the cylindrical surface, by Rukoto tilted around the optical axis with respect to the longitudinal direction of the substantially rectangular cross-section of a laser beam outputted from said laser oscillator, as compared with the case where not inclined The step of setting the angle to suppress the interference of the laser beam between the pair of fly-eye lenses Characterized by a step of processing the plurality of holes by using a laser beam the interference is suppressed.
[0007]
According to the laser processing method of claim 1 having the above-described configuration, the direction of the center axis of the cylinder that forms the cylindrical surfaces of the two cylindrical lenses by rotating the beam shaping unit is substantially the same as that of the laser beam output from the laser oscillator. By tilting around the optical axis with respect to the longitudinal direction of the rectangle, the interference of light that occurs when the laser beam passes through a pair of fly-eye lenses is reduced compared to the case of not tilting, and a plurality of holes to be processed simultaneously The machining accuracy can be improved.
[0008]
Preferably, the laser beam is an excimer laser beam. The excimer laser has a substantially rectangular cross section of the laser beam emitted from the laser oscillator, and can be suitably implemented in the configuration of claim 1.
[0009]
Preferably, the beam shaping unit is an optical system that changes the cross section of the laser beam from a substantially rectangular shape to a substantially diamond shape. A laser beam with a substantially rectangular cross-section emitted from the laser oscillator is shaped into a roughly diamond shape at the beam shaping section, and then dispersed into a number of elongated beams when passing through a pair of fly-eye lenses, resulting in uniform beam intensity Is effectively achieved.
[0010]
[0011]
[0012]
According to a fourth aspect of the present invention, the beam shaping unit is preferably provided with a rotating means for rotating the beam shaping unit around the optical axis. According to this, by rotating the beam shaping unit in accordance with the magnitude of interference, it is possible to perform efficient laser processing by selecting a range with less energy loss and less interference.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a laser processing apparatus according to the present invention will be described below with reference to the drawings.
[0014]
FIG. 1 is an overall schematic view showing a laser processing apparatus to which the present invention is applied, and FIG. 2 is an enlarged perspective view showing a beam shaping unit in the processing apparatus of FIG. 3 is a schematic front view of the beam shaping unit of FIG. 2 as viewed from the downstream side, and FIG. 4 is an inclination angle θ of the beam shaping unit of FIG. 2 and the energy density of the laser beam on the emission side on the workpiece. FIG. 5 is a diagram (graph) showing the relationship with the position of the workpiece (outgoing side), and FIG. 5 shows the shape of the nozzle hole processed on the outgoing side on the workpiece for each inclination angle θ of the beam shaping section in FIG. FIG. 6 is a perspective view in which a nozzle hole is machined by applying a laser beam to the workpiece from below in the figure.
[0015]
As shown in FIG. 1, in the laser processing apparatus 20 of the present embodiment, an excimer laser beam (KrF laser beam) A having a wavelength of, for example, 248 nm output (emitted) from the laser oscillator 1 is inclined at 45 °. Then, the light is refracted in a right angle direction through the total reflection mirrors 2, 3, and 4, and reaches the processing table 5 that supports the workpiece B. Between the laser oscillator 1 and the first mirror 2, a beam shaping unit 6 for shaping the rectangular cross-sectional shape of the laser beam A into a predetermined shape is disposed.
[0016]
The laser beam A is refracted in the direction perpendicular to the first mirror 2 and goes straight upward in the figure. A beam expander (Beam Expander) 7 for expanding the laser beam A is disposed between the first mirror 2 and the second mirror 3, and this beam expander 7 is composed of a pair of convex lenses in this example. ing. A pair of fly-eye lenses (Fly-eye-Lenz) 8 and 8 as homogenizers are arranged on the downstream side of the second mirror 3 so as to face each other. The laser beam A refracted in the right angle direction by the second mirror 3 and traveling straight to the right in the figure in the horizontal direction is dispersed by the fly-eye lenses 8 and 8 into a number of elongated beams, and the condensing optical means. By condensing a large number of elongated beams by the condenser lens 9 as described above, the beam intensity can be made uniform and the output can be controlled.
[0017]
A mask 11 is disposed on the downstream side of the condenser lens 9, and the condensed laser beam A is condensed at a predetermined position (hole pattern position) of the mask 11.
[0018]
The mask 11 is provided with a shape for laser processing on the workpiece B, that is, a hole pattern corresponding to a plurality of nozzle holes, and the mask 11 is held by a mask holder (not shown). The laser beam A that has passed through the hole pattern of the mask 11 is refracted in the right-angle direction by the third mirror 4 and goes straight downward in the figure. On the downstream side of the third mirror 4, the workpiece B is placed on a processing table 5 that is movable in the horizontal direction. The processing table 5 can also be raised and lowered in the vertical direction so that the laser beam is focused on the workpiece B. Further, an imaging lens (also referred to as a projection lens) 12 is disposed between the third mirror 4 and the processing table 13. In this imaging lens 12, the laser beam A (image thereof) that has passed through the hole pattern of the mask 11 is reduced to a predetermined magnification (in this example, 1/5 times), and is imaged on the workpiece B. Laser processing is performed corresponding to the 11 hole patterns. In this example, a polyimide sheet (thickness: 100 μm), which is a polymer material, is used for the workpiece B, and a plurality of nozzle holes (diameter: 30 μm) are simultaneously formed in a row by the laser beam A.
[0019]
After a group of nozzle holes is formed at one location, the processing table 5 is moved horizontally so that the next processing area on the workpiece B faces directly below the imaging lens 12 and the laser beam A is output. Thus, a large number of nozzle holes can be formed sequentially.
[0020]
As shown in FIG. 2, in the beam shaping unit 6, a cylindrical concave lens 21 and a cylindrical convex lens 22 are arranged in the optical axis direction from the incident side. In a conventional general laser processing apparatus, the cylindrical lenses 21 and 22 each have a central axis direction of a cylinder forming the cylindrical surface in the longitudinal direction in a rectangle (8 mm × 24 mm in this example) having a cross-sectional shape of the laser beam. And put it in parallel. As will be described later, in the present embodiment, the central axis direction of the cylinder forming the cylindrical surface is used with a slight inclination.
[0021]
In the present embodiment, the cylindrical lenses 21 and 22 are configured to be rotatable around the optical axis A ′ of the laser beam A by the rotating means 23. That is, the beam shaping unit 6 is attached to a large-diameter gear 24 so as to be integrally rotatable, and the large-diameter gear 24 is engaged with a small-diameter drive gear 25 that is rotated by a motor 26. The motor 26 uses a stepping motor that rotates in the forward and reverse directions, but may be a manual rotating means as long as the apparatus can stop and hold the beam shaping unit 6 at an arbitrary position. In this example, members 24 to 26 constitute the rotating means 23.
[0022]
In FIG. 2, when the central axis direction of the cylinders forming the cylindrical surfaces of the cylindrical lenses 21 and 22 is placed parallel to the longitudinal direction of the rectangular cross section of the laser beam as in the conventional case, the laser oscillator 1 (FIG. 1) The emitted laser beam A is enlarged in the short direction of the rectangular cross section by the cylindrical concave lens 21, and the enlarged optical path is made parallel by the cylindrical convex lens 22, and the laser beam A is shaped into a square. Then, the light enters the pair of fly-eye lenses 8 and 8. In this case, depending on the position on the workpiece B among the plurality of nozzle holes processed simultaneously, the emission side shape Co of the nozzle hole C is distorted and formed as shown in FIG. This is because, due to the interference of the laser beams at the pair of fly-eye lenses 8 and 8, the energy density varies greatly periodically as shown in FIG. .
[0023]
Since there is a distance corresponding to the thickness of the workpiece B (100 μm in this example) between the front and back of the workpiece B, the focal point of the laser beam A on the laser beam incident side surface with respect to the workpiece B The incident side shape Ci of the nozzle hole C is circular without being distorted, and is less affected by interference within the depth. However, on the back surface of the workpiece B that is outside the range of the focal depth of the laser beam A, the influence of the interference by the pair of fly-eye lenses 8 and 8 appears as described above, and the emission side shape Co of the nozzle hole C is distorted. .
[0024]
On the other hand, according to the laser processing apparatus 20 of this example, the beam shaping unit 6 is rotated, and the axial direction of the cylindrical surface is inclined with respect to the longitudinal direction of the rectangular cross section of the laser beam. The emitted laser beam A has a diamond shape as shown by a two-dot chain line in FIG. When the inclination angle θ of the beam shaping unit 6 is 5 °, for example, the influence of laser beam interference on the pair of fly-eye lenses 8 and 8 is reduced, and as shown in FIG. On the laser beam emission side, the energy density change due to the difference in position becomes small, and the distortion of the emission side shape Co of the nozzle hole C is reduced as shown in FIG. Furthermore, when the inclination angle θ is 10 °, the energy density hardly changes as shown in FIG. 4C, and the emission side shape Co of the nozzle hole C is substantially true as shown in FIG. 5C. In addition to a circle, a plurality of nozzle holes are formed substantially uniformly.
[0025]
In the case of this example, when the tilt angle θ is around 10 °, the interference of the laser beam A is reduced to the minimum, and the emission side shape Co of the nozzle hole C at each position is substantially true as shown in FIG. Although it is a circle, the interference of the laser beam A is also reduced when the tilt angle θ exceeds 10 °. However, when the laser beam A is incident on the fly-eye lens 8, the cross-sectional shape is deformed into a substantially rhombus as described above, and a portion that is deleted when incident on the fly-eye lens 8 is generated, resulting in energy loss. May be. In the experiment of this example, a favorable result could be obtained when the inclination angle θ was around 10 °. Note that the inclination angle θ may be determined by the degree of interference of the laser beam A in the fly-eye lens and the energy efficiency.
[0026]
The embodiment of the laser processing apparatus 20 of the present invention, in particular, the embodiment of the beam shaping unit 6 has been described above, but the present invention can be implemented as follows.
[0027]
(1) The beam shaping unit 6 includes a combination of a concave lens and a convex lens, as well as other arbitrary number of lenses.
[0028]
(2) The beam shaping unit 6 is not arbitrarily rotatable and may be fixed at a desired angle.
[0029]
(3) A contact mask system in which the imaging lens 12 is omitted and the mask 11 is directly fixed on the workpiece B can be similarly implemented.
[0030]
(4) In addition to processing nozzle holes of ink jet printers, for example, the workpiece B can be changed to other materials such as ceramics, or can be applied to groove processing.
[0031]
【The invention's effect】
As is apparent from the above description, the laser processing method according to the present invention has the following excellent effects.
[0032]
(1) In the present invention of claim 1, by suppressing the interference of the laser beam in the fly-eye lens by the addition of a simple construction to a minimum, almost no distortion in a plurality of holes, high throughout plurality of holes to be processed at the same time Precision laser processing is possible. For example, when processing a plurality of nozzle holes for ink ejection, the emission side shape can be processed close to a perfect circle, and the plurality of nozzle holes can be processed substantially uniformly.
[0033]
(2) Since the invention according to claim 2 is an excimer laser, the cross-sectional shape of the laser beam emitted from the laser oscillator is substantially rectangular, and can be suitably implemented in the configuration of claim 1 above.
[0034]
(3) In the invention according to claim 3, since the beam shaping section is an optical system that changes the cross section of the laser beam from a substantially rectangular shape to a substantially rhombus shape, the laser beam having a substantially rectangular cross section emitted from the laser oscillator is After being shaped into a roughly rhombus by the shaping unit, when passing through a pair of fly-eye lenses, it is dispersed into a large number of elongated beams, and the beam intensity is effectively uniformed.
[0035]
[0036]
(4) In the invention described in claim 4, by rotating the beam shaping unit around the optical axis, it is possible to perform efficient laser processing by selecting a range with less energy loss and less interference. .
[Brief description of the drawings]
FIG. 1 is an overall schematic diagram showing a laser processing apparatus including a beam shaping unit to which the present invention is applied.
FIG. 2 is an enlarged perspective view showing an embodiment of the present invention of a beam shaping unit in the processing apparatus of FIG. 1;
FIG. 3 is a schematic front view of the beam shaping unit of FIG. 2 as viewed from the downstream side.
4 is a diagram (graph) showing the relationship between the inclination angle θ of the beam shaping section in FIG. 2, the energy density of the laser beam on the output side on the workpiece and the position of the workpiece (outgoing side). is there.
5 is a diagram showing the relationship between the inclination angle θ of the beam shaping unit in FIG. 2 and the shape of a nozzle hole machined on the exit side on the workpiece.
FIG. 6 is a perspective view of a workpiece in which a nozzle hole is machined by applying a laser beam to the workpiece from below in the drawing.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser oscillator 2,3,4 Total reflection mirror 5 Processing table 6 Laser shaping part 7 Beam expander 8 Fly eye lens (homogenizer)
DESCRIPTION OF SYMBOLS 9 Condenser lens 11 Mask 12 Imaging lens 20 Laser processing apparatus 21 Cylindrical concave lens 22 Cylindrical convex lens 23 Rotating means 24 Large diameter gear 25 Small diameter gear 26 Motor A Laser beam B Workpiece C Nozzle hole

Claims (4)

A laser beam having a substantially rectangular cross section output from the laser oscillator is shaped by a beam shaping unit including a cylindrical concave lens and a cylindrical convex lens and introduced into a pair of fly-eye lenses, and a pattern corresponding to a plurality of holes to be processed simultaneously is formed. A laser processing method using a laser processing apparatus for irradiating a workpiece through a mask having a mask,
The central axis direction of the cylinder forming the cylindrical surfaces of the cylindrical lenses by rotating the beam shaping unit is tilted around the optical axis with respect to the longitudinal direction of the substantially rectangular cross section of the laser beam output from the laser oscillator. a step of the angle to suppress the interference of the laser beam in the pair of fly-eye lens as compared with the case where the Rukoto is, not inclined,
And a step of processing the plurality of holes using a laser beam in which the interference is suppressed.   The laser processing method according to claim 1, wherein the laser beam is an excimer laser beam.   The laser processing method according to claim 2, wherein the beam shaping unit is an optical system that changes a cross section of the laser beam from a substantially rectangular shape to a substantially diamond shape.   The laser processing method according to claim 1, wherein the beam shaping unit is provided with rotating means for rotating the beam shaping unit around an optical axis.

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