JP2009045637A - Laser beam machining apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining apparatus capable of performing fine machining at high speed. <P>SOLUTION: The laser beam machining apparatus 1 is equipped with: an ultra-short pulse laser beam oscillator 2 for emitting a laser beam 3 of the ultra-short pulse with an energy per pulse of ≤100 nJ at a cyclic frequency of ≥10 MHz; a condensing lens (a condensing element) 7 for receiving the laser beam 3 emitted from the ultra-short pulse laser beam oscillator 2 without via any amplifier or any attenuator and condensing the laser beam to a workpiece 8; a beam isolator (a return laser beam preventive means) 5 for preventing the laser beam 3 returning to the ultra-short pulse laser beam oscillator 2 by the reflection out of the laser beam 3 emitted from the ultra-short pulse laser beam oscillator 2; and a stage driving section (a moving means) 10 for moving the workpiece 8 with respect to the condensing lens 7 in the direction orthogonal to the optical axis of the incident laser beam 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser processing apparatus.

  In recent years, ultra-short pulse laser processing has attracted attention as a process that does not substantially affect the workpiece. Ultra-short pulse laser processing is to process a substance by enlarging energy per pulse instead of having a short pulse width, and is called ablation processing (for example, Patent Document 1).

  As a general conventional laser processing apparatus for performing this ablation processing, there is one in which energy per pulse is increased by an amplifier using laser light oscillated from a femtosecond laser oscillator (for example, Patent Document 2).

In this laser processing apparatus, a laser beam having a pulse width of 25 fs (femtosecond) emitted from a femtosecond laser oscillator and an energy per pulse of 5 nJ is applied to a pulse width of 40 fs by a pulse stretcher, an amplifier, and a pulse compressor. The repetition frequency is 10 Hz, the energy per pulse is increased to 40 mJ, and the spot diameter and the fluence are adjusted by passing through a filter and a lens. The spot diameter is about 200 μm, the fluence is 0.2 J / cm. No. ² laser beam is obtained, and this laser beam is irradiated onto a workpiece such as stainless steel (SUS) for fine processing.
JP 2005-533658 A JP 2003-211400 A

  An object of the present invention is to provide a laser processing apparatus capable of performing fine processing at high speed.

  One embodiment of the present invention provides the following laser processing apparatus to achieve the above object.

[1] Irradiation means for irradiating a workpiece with ultrashort pulse laser light having an energy per pulse of 100 nJ or less and a repetition frequency of 10 MHz or more; and an optical axis of the laser light emitted from the irradiation means A laser processing apparatus comprising: a moving unit that relatively moves the workpiece in a vertical direction.

[2] The irradiation means includes a laser oscillator that emits an ultrashort pulse laser beam having an energy per pulse of 100 nJ or less and a repetition frequency of 10 MHz or more, and an amplifier that emits the laser beam emitted from the laser oscillator. The laser processing apparatus according to [1], further including: a light collecting element that collects light so as to irradiate the workpiece with a predetermined fluence without passing through an attenuator.

[3] The laser processing apparatus according to [2], further comprising return laser beam prevention means for preventing laser light returning to the laser oscillator due to reflection among the laser beams emitted from the laser oscillator.

[4] The apparatus further includes a container that stores a liquid and a holding member that holds the workpiece in the liquid in the container, and the moving unit includes the container and the holding member, or the holding member. The laser processing apparatus according to any one of [1] to [3], wherein the laser processing apparatus is moved in a direction intersecting an optical axis of the laser light.

[5] The container has a transmission part that transmits the laser light on the laser light incident side, and the reflection part is formed with an antireflection film that prevents reflection of the laser light to the laser oscillator. The laser processing apparatus according to [4].

  According to the laser processing apparatus of the first aspect, fine processing can be performed at high speed.

  According to the laser processing apparatus of the second aspect, the configuration can be simplified.

  According to the laser processing apparatus of the third aspect, it is possible to stabilize the oscillation of the laser beam.

  According to the laser processing apparatus according to the fourth aspect, compared with the case of processing in the air, the flying powder such as scrap generated by the processing is less likely to adhere to the workpiece.

  According to the laser processing apparatus of the fifth aspect, the transmission efficiency of the laser incident light can be further improved (the laser beam passage loss is further suppressed) as compared with the configuration not including the antireflection film.

[First Embodiment]
FIG. 1 is a diagram showing a schematic configuration of a laser processing apparatus according to the first embodiment of the present invention. In the figure, X, Y, and Z indicate an X-axis direction, a Y-axis direction, and a Z-axis direction (optical axis direction) orthogonal to each other.

  This laser processing apparatus 1 has an ultrashort pulse laser oscillator 2 that emits an ultrashort pulse laser beam 3 that is generally used in communication, and a mirror 4 and an optical isolator (return) on the optical path of the laser beam 3. A laser beam preventing means) 5, a shutter 6, a condenser lens (light collecting element) 7, and a holding member 9 to which the workpiece 8 is attached are arranged, and a stage driving unit (moving means) 10 that moves the holding member 9. And a controller 11 that controls the shutter 6 and the stage drive unit 10. The ultrashort pulse laser oscillator 2, the mirror 4, the optical isolator 5, the shutter 6, and the condenser lens 7 constitute an irradiation unit that irradiates the workpiece 8 with the ultrashort pulse laser beam 3.

  In the optical system of the laser processing apparatus 1, the laser light 3 emitted from the ultrashort pulse laser oscillator 2 is condensed without using an amplifier that increases the intensity of the laser light 3 or an attenuator that reduces the intensity of the laser light 3. The lens 7 is reached.

  The ultrashort pulse laser oscillator 2 oscillates a low energy ultrashort pulse laser beam 3 having an energy per pulse of 100 nJ or less at a high repetition frequency of 10 MHz or more. It should be noted that other values such as 50 nJ or less and 20 nJ or less can be adopted as energy per pulse and other values such as 20 MHz or more and 50 MHz or more can be used as the repetition frequency without departing from the spirit of the present invention. Here, “ultra-short pulse” refers to a pulse having a pulse width of 10 ps or less. As the ultrashort pulse laser oscillator 2 that emits such an ultrashort pulse, in this embodiment, a femtosecond laser oscillator that emits linearly polarized laser light 3 (for example, s-polarized light) having a pulse width on the order of femtoseconds is used. .

The position of the condensing lens 7 in the optical axis direction (Z-axis direction) is adjusted by a moving mechanism (not shown) so that the laser light 3 is condensed on the surface 8a of the workpiece 8 or in the vicinity thereof. In addition, the condenser lens 7 has a magnification and a focal length that are selected so that the fluence has an optimum value, and the spot diameter becomes, for example, about 1 to 10 μm. The fluence is an energy density (J / cm ² ) obtained by dividing the energy per pulse of the laser light by the irradiation area. The minimum energy density (processing threshold value) at which the workpiece 8 can be processed and the maximum energy density at which there is almost no thermal effect vary depending on the material of the workpiece 8. In addition to the condensing lens 7, a concave mirror or the like may be used as the condensing element by changing the direction of the workpiece 8.

  The workpiece 8 can be a semiconductor substrate made of silicon, GaAs, or the like, or a metal such as stainless steel (SUS).

  The holding member 9 has an opening 9a large enough for the laser beam 3 to pass through, and is formed of a resin such as polymethyl methacrylate (PMMA), a metal such as aluminum, SUS, and the like by the stage driving unit 10. It can move in the axial direction, the Y-axis direction, and the Z-axis direction. In addition, when the through hole is not formed in the workpiece 8 by the laser beam 3, the opening 9a may not be provided.

  The stage driving unit 10 includes a mechanism for moving the holding member 9 in the X-axis direction, the Y-axis direction, and the Z-axis direction orthogonal to each other, and the X-axis direction and the Y-axis direction are faster than the Z-axis direction (for example, , 600 mm / s) can be used. The stage driving unit 10 is not limited to the X-axis direction and the Y-axis direction perpendicular to the optical axis, but is a holding member in a direction substantially perpendicular to the optical axis (for example, a direction of 80 ° to 100 ° with respect to the optical axis). 9 may be moved. Further, the stage drive unit 10 may include a mechanism that rotates the holding member 9 around an axis that is eccentric from the Z axis, and a mechanism that tilts the holding member 9 with respect to the Z axis direction.

  FIG. 2A is a diagram illustrating a configuration example of an optical isolator. This optical isolator 5 includes a first polarizer 50 formed by a polarized beam splitter (hereinafter referred to as “PBS”) having a polarization plane 50a in a vertical direction, a Ferroday rotator 51, a λ / 2 plate 52, and a polarization plane 53a. Includes a second polarizer 53 in the horizontal direction. The s-polarized laser light 3 emitted from the ultrashort pulse laser oscillator 2 passes through the first polarizer 50 as s-polarized light, is polarized by 45 ° by the Faraday rotator 51, and further 45 by the λ / 2 plate 52. The light is polarized to become p-polarized light, passes through the second polarizer 53 as p-polarized light, and travels toward the workpiece 8 side. In the return light from the workpiece 8 side, only the p-polarized return light passes through the second polarizer 53, is polarized by 45 ° by the λ / 2 plate 52, and is polarized by −45 ° by the Faraday rotator 51. Since it becomes p-polarized light, it does not pass through the first polarizer 50 but is reflected in another direction and theoretically does not return to the ultrashort pulse laser oscillator 2.

  FIG. 2B is a diagram illustrating another configuration example of the optical isolator. The optical isolator 5 includes a first polarizer 54 made of PBS whose polarization plane 54a is vertical, a Ferroday rotator 55, and a second polarizer 56 whose polarization plane 56a is inclined by 45 °. The s-polarized laser beam 3 emitted from the ultrashort pulse laser oscillator 2 passes through the first polarizer 54 as s-polarized light, is polarized by 45 ° by the Faraday rotator 55, and is polarized by the second polarizer 56. The surface passes while being inclined by 45 ° and heads toward the workpiece 8 side. As for the return light from the workpiece 8 side, only the return light whose polarization plane is inclined by 45 ° passes through the second polarizer 56 and is −45 ° polarized by the Faraday rotator 55 to become p-polarized light. It does not pass through one polarizer 54 but is reflected in another direction and does not return to the ultrashort pulse laser oscillator 2. The return laser beam preventing means is not limited to that shown in FIGS. 2A and 2B.

(Operation of laser processing equipment)
Next, the operation of the laser processing apparatus 1 will be described.

  The s-polarized laser light 3 emitted from the ultrashort pulse laser oscillator 2 is reflected by the mirror 4, passes through the optical isolator 5, passes through the shutter 6 controlled to be opened by the controller 11, and then enters the condenser lens 7. Thus, the light is condensed on the surface 8a of the workpiece 8, and the workpiece 8 is irradiated with the laser beam 3. On the other hand, the stage drive unit 10 is controlled by the controller 11 to move the workpiece 8 at, for example, 10 mm / s in the X-axis direction. Thereby, for example, a groove having a width of 2 to 6 μm and a depth of 1 to 6 μm is formed on the workpiece 8 along the X-axis direction.

  When the workpiece 8 is irradiated with the laser beam 3, the return laser beam reflected by the workpiece 8, the condenser lens 7, and the like is directed to the ultrashort pulse laser oscillator 2. Since the light is reflected off the optical path by the isolator 5, the return laser light does not return to the ultrashort pulse laser oscillator 2 and the oscillation mode of the ultrashort pulse laser oscillator 2 is not changed.

[Second Embodiment]
FIG. 3A is a diagram showing a schematic configuration of a laser processing apparatus according to the second embodiment of the present invention, and FIG. 3B is a partial sectional view of the container. In FIG. 3A, X, Y, and Z indicate an X-axis direction, a Y-axis direction, and a Z-axis direction (optical axis direction) that are orthogonal to each other.

  In the present embodiment, the workpiece 8 is laser processed in water. That is, as shown in FIG. 3A, the laser processing apparatus 1 of the present embodiment has an ultrashort pulse laser oscillator 2, a mirror 4, an optical isolator (preventing return laser light) as in the first embodiment. Means) 5, shutter 6, condensing lens (condensing element) 7, stage driving unit (moving unit) 10, and controller 11, and disposed on stage driving unit 10 and water (fluid) such as distilled water. 12 is provided with a container 13 in which 12 is accommodated, and a holding member 19 that holds the workpiece 8 in the water 12 in the container 13. In this optical system, as in the first embodiment, the laser beam 3 emitted from the ultrashort pulse laser oscillator 2 is an amplifier that increases the intensity of the laser beam 3 or an attenuator that reduces the intensity of the laser beam 3. The condenser lens 7 is reached without going through.

  The holding member 19 has an opening 19 a that is large enough for the laser beam 3 to pass through. The holding member 19 is formed of a resin such as PMMA, a metal such as aluminum or SUS, and is fixed to the container 13. Note that when the through hole is not formed in the workpiece 8 by the laser beam 3, the opening 19a may not be provided.

  As shown in FIG. 3B, the container 13 is formed of a resin such as PMMA having an opening 13a on the side on which the laser beam 3 is incident, a metal such as aluminum, SUS, or the like, and glass having translucency in the opening 13a. A translucent window (transmission portion) 14 made of resin or the like is provided. An AR (Anti Reflection) coat 14 a as an antireflection film that suppresses reflection of the laser light 3 is formed on the side of the translucent window 14 on which the laser light 3 is incident. In addition, without providing the opening 13a and the translucent window 14, the entire container 13 may be formed of translucent glass, resin, or the like.

The AR coat 14a suppresses reflection by light interference and is formed, for example, by alternately stacking thin films (for example, TiO ₂ and SiO ₂ ) having different refractive indexes. Further, it is preferable that the AR coat 14a has a small reflectance of, for example, 0.2% or less in the wavelength region (wavelength 800 nm) of the laser light 3.

  In the above-described embodiment, the stage driving unit 10 moves the container 13, but the holding member may be moved with respect to the container.

  Next, Example 1 of the present invention will be described. Example 1 corresponds to the second embodiment.

  As an ultrashort pulse laser oscillator 2, a titanium sapphire laser oscillator manufactured by Spectra Physics Co., Ltd. that oscillates a laser beam 3 having a pulse width of 100 fs (femtosecond), an output power of 1.3 W, a repetition frequency of 80 MHz, a wavelength of 800 nm, and 16 nJ / pulse. Was used.

FIG. 4 is a diagram showing the relationship between the fluence and the beam diameter when the workpiece 8 is a silicon (Si) substrate. The processing threshold when the material of the workpiece 8 is Si is 0.34 J / cm ² as shown in FIG. 4, and the beam diameter at that time is 2 μm. The focal length and magnification of the optical lens 7 are selected, and the position in the Z-axis direction is determined. In Example 1, a focal length f = 10 and a magnification of 20 times were used, and grooving was performed while moving the workpiece 8 in the X direction at 10 mm / s.

(Comparative Example 1)
In Comparative Example 1, an ultrashort pulse laser oscillator and a regenerative amplifier are used as a light source, and a laser beam having a pulse width of 100 fs, an output power of 0.8 W, a repetition frequency of 1 kHz, and a wavelength of 800 nm is passed through a mask attenuator with a mask diameter of 1 mm. The laser beam was adjusted to 1 mW, 0.1 μJ / pulse laser light was emitted, and the workpiece was moved at 10 μm / s.

(Comparative Example 2)
In Comparative Example 2, the same femtosecond laser oscillator as that of Example 1 was used as a light source, and the workpiece was irradiated with laser light without using a condenser lens. However, since the fluence was smaller than the machining threshold, the workpiece was processed. The grooves could not be machined.

Table 1 shows the comparison results of Example 1, Comparative Example 1, and Comparative Example 2.

  From Table 1, by the said structure of Example 1, compared with the comparative example 1, the fine groove | channel was able to be processed at a quick processing speed.

[Other embodiments]
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  For example, in each of the above embodiments, the case of processing the groove has been described. However, when a slit or a hole penetrating the substrate is processed, it can be applied to processing such as chamfering. When machining the hole, the workpiece may be moved in the optical axis direction. When machining such as chamfering, the workpiece may be tilted with respect to the optical axis and moved in the X-axis direction or the Y-axis direction.

  In each of the above embodiments, an optical system in which the laser beam 3 emitted from the ultrashort pulse laser oscillator 2 reaches the condenser lens 7 without passing through an amplifier or an attenuator is used. If the workpiece 8 can be irradiated with an ultrashort pulse of energy at a desired repetition frequency, an amplifier or an attenuator may be provided. For example, the mirror 4, the condensing lens 7, or the translucent window 14 may have a function of reducing the intensity of the laser light.

FIG. 1 is a diagram showing a schematic configuration of a laser processing apparatus according to the first embodiment of the present invention. FIG. 2A is a diagram illustrating a configuration example of an optical isolator. FIG. 2B is a diagram illustrating another configuration example of the optical isolator. FIG. 3A is a diagram showing a schematic configuration of a laser processing apparatus according to the second embodiment of the present invention, and FIG. 3B is a partial sectional view of the container. FIG. 4 is a diagram showing the relationship between the fluence and the beam diameter when the workpiece is a silicon (Si) substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser processing apparatus 3 Laser beam 2 Ultrashort pulse laser oscillator 4 Mirror 5 Optical isolator 6 Shutter 7 Condensing lens 8 Work piece 8a Surface 9 Holding member 9a Opening 10 Stage drive part 11 Controller 12 Water 13 Container 13a Opening 14 Light transmission Window 14a AR coat 19 holding member 19a opening 50 first polarizer 50a polarizing surface 51 Feraday rotator 52 λ / 2 plate 53 second polarizer 53a polarizing surface 54 first polarizer 54a polarizing surface 55 Feraday rotator 56 Second polarizer 56a Polarization plane

Claims (5)

An irradiation means for irradiating the workpiece with an ultrashort pulse laser beam having an energy per pulse of 100 nJ or less and a repetition frequency of 10 MHz or more;
A laser processing apparatus comprising: a moving unit that relatively moves the workpiece in a direction substantially perpendicular to an optical axis of the laser beam irradiated from the irradiation unit. The irradiation means includes a laser oscillator that emits the laser light of an ultrashort pulse having an energy per pulse of 100 nJ or less and a repetition frequency of 10 MHz or more;
2. A condensing element that receives the laser light emitted from the laser oscillator without passing through an amplifier and an attenuator and condenses the light so as to irradiate the workpiece with a predetermined fluence. The laser processing apparatus as described.   The laser processing apparatus according to claim 2, further comprising return laser light preventing means for preventing laser light returning to the laser oscillator by reflection out of the laser light emitted from the laser oscillator. And a container that contains the liquid;
A holding member for holding the workpiece in the liquid in the container,
4. The laser processing apparatus according to claim 1, wherein the moving unit moves the container and the holding member, or the holding member in a direction intersecting an optical axis of the laser beam. The container has a transmission part that transmits the laser light on the incident side of the laser light,
The laser processing apparatus according to claim 4, wherein the transmissive portion is formed with an antireflection film that prevents the laser light from being reflected to the laser oscillator.

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