JP2009186660A - Laser processing apparatus, laser processing method, and electronic device - Google Patents

Abstract

Provided are a laser processing apparatus that can be easily maintained and can control coherence, a laser processing method using the same, and an electronic device using the laser processing method.
A seed light source that emits seed light in an infrared wavelength band, a first fiber amplifier that is supplied with the seed light and emits a first laser light, and is supplied with the seed light. A second fiber amplifier that emits laser light; a first wavelength converter that converts the wavelength of the first laser light into a wavelength range of ultraviolet light to visible light; and the second laser light that is ultraviolet light to visible. A first wavelength conversion unit that converts the wavelength into a wavelength range of light; and an optical irradiation unit that combines the wavelength-converted first and second laser beams to form a combined beam. This laser beam and the second laser beam are synthesized in a state in which at least one of a center wavelength, an optical path length, a phase, and an emission timing is different.
[Selection] Figure 1

Description

  The present invention relates to a laser processing apparatus, a laser processing method, and an electronic device.

  For laser annealing of amorphous silicon formed on a glass substrate or semiconductor on a semiconductor substrate, excimer lasers with low coherence, high pulse energy, and easy to obtain a uniform line beam are widely used. It is done. In this case, if the material is silicon, ultraviolet light having a large absorption coefficient, for example, a wavelength near 308 nm is used.

  Since the excimer laser is an active gas laser using halogen gas, maintenance in gas exchange and chamber exchange is not easy. If this is attempted to be solidified using a YAG laser or the like, there are problems such as large interference in beam shaping and low pulse energy.

There is a technical disclosure example regarding a laser annealing method and apparatus capable of easily irradiating laser light with a simple configuration (Patent Document 1). In this technical disclosure example, laser light from a laser oscillator is transmitted through an optical fiber, and the transmitted laser light is irradiated onto a glass substrate through an optical waveguide connected to the optical fiber. However, with this configuration, coherence is large and interference fringes are easily generated in the synthesized laser beam, and it is difficult to obtain a uniform intensity distribution.
JP 2007-88050 A

  Provided are a laser processing apparatus that is easy to maintain and capable of coherence control, a laser processing method using the same, and an electronic device using the laser processing method.

  According to one aspect of the present invention, a seed light source that emits seed light in an infrared wavelength band, a first fiber amplifier that is supplied with the seed light and emits first laser light, and the seed light is supplied. A second fiber amplifier that emits a second laser light; a first wavelength converter that converts the wavelength of the first laser light into a wavelength range of ultraviolet light to visible light; and the second laser light. A second wavelength conversion unit that converts the wavelength of the light into a wavelength range of ultraviolet light to visible light, and an optical irradiation unit that combines the wavelength-converted first and second laser lights to form a combined beam. The laser processing apparatus is characterized in that the first laser beam and the second laser beam are synthesized in a state where at least one of a center wavelength, an optical path length, a phase, and an emission timing is different. Provided.

  According to another aspect of the invention, seed light is supplied to the fiber amplifier to emit the first and second laser lights, and the first and second laser lights are respectively emitted using a nonlinear crystal. A laser processing method that performs wavelength conversion, combines the wavelength-converted first and second laser beams to form a combined beam, and irradiates a workpiece with the combined beam, the first and first laser beams The laser processing method is characterized in that the two laser beams are synthesized in a state in which at least one of the center wavelength, the optical path length, the phase, and the emission timing is different.

  According to yet another aspect of the present invention, there is provided an electronic device formed using the laser processing method described above.

  Provided are a laser processing apparatus that is easy to maintain and capable of coherence control, a laser processing method using the same, and an electronic device using the laser processing method.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of a laser processing apparatus according to an embodiment of the present invention.
The laser processing apparatus includes a seed light source 10, a fiber amplifier 12, a wavelength conversion unit 14, an irradiation optical unit 16, and a stage 18. For example, pulse seed light G10 having an infrared light wavelength is emitted from the seed light source 10. The pulse seed light G10 is divided into, for example, three parts and is incident on the fiber amplifier 12 respectively. The fiber amplifier 12 outputs amplified laser beams G11, G21, and G31. The wavelength conversion unit 14 emits laser beams G12, G22, and G32 obtained by wavelength-converting the amplified laser beams G11, G21, and G31, respectively. The irradiation optical unit 16 generates a combined beam GT using the laser beams G12, G22, and G32. The composite beam GT is irradiated onto the workpiece 20 on the stage 18 and laser processing is performed.

FIG. 2 is a configuration diagram of the fiber amplifier.
The fiber amplifier 12 includes a preamplifier 12a (A1, A3, A5) including a Yb (ytterbium) -doped optical fiber 54 and a pumping light source 58, and a main amplifier 12b (A2, A4, A6) including a Yb-doped optical fiber 56 and a pumping light source 62. Are connected in three series. The pumping light sources 58 and 62 are semiconductor lasers, and the pumping light is synthesized by the combiners 60 and 64 and transmitted to the optical fibers 54 and 56. P1, P2, P3, P4, and P5 represent fusion points between the fibers. The pulse seed light G10 is branched into three and is incident on the preamplifiers A1, A3, and A5, respectively. Amplified laser beams G11, G21, and G31 are emitted from the main amplifiers A2, A4, and A6, respectively. It should be noted that only the main amplifiers A2, A4, and A6 may be used if there is a margin in the amplification gain and laser light output.

  In the cores of the optical fibers 54 and 56, Yb excited by a high-power semiconductor laser or the like causes stimulated emission by the incidence of the pulse seed light G10 having an infrared light wavelength, and the pulse seed light G10 is amplified. For example, assuming that the pulse width of the pulse seed light G10 is about 100 ns and the average output is several W, the preamplifier 12a and the main amplifier 12b respectively obtain laser lights G11, G21, and G31 having an average output of about 200W. Such a fiber amplifier 12 is called a MOPA (Master Oscillator Power Amplifier). Although the number of series connected in parallel is at least two, in the case of laser annealing processing that requires a high energy pulse, it can be 10 series or more.

  The light emission spectrum of Yb, which is a rare earth element added to the core, has a wide wavelength range having local maxima in the vicinity of 975 and 1030 nm. In addition to Yb, Tm (thulium) or the like may be added. The wavelength of the excitation light is, for example, 800 to 1100 nm.

As shown in FIG. 1, the wavelength converter 14 includes a lens 30, a SHG (Second Harmonic Generation) element 32 made of a nonlinear crystal, a lens 34, and a THG (Third Harmonic Generation: third made of a nonlinear crystal). (Second harmonic generation) element 36 and lens 38 are provided. The nonlinear crystal is made of, for example, LBO: LiB ₃ O ₅ , and the SHG element 32 converts the wavelength converted light into half of the wavelengths of the amplified lights G11, G21, and G31 that are incident light. The THG element 36 converts the wavelength-converted light from the SHG element 32 into a wavelength that is one third of the original incident light wavelength. That is, the pulse seed light G10 having a wavelength of infrared light is converted into laser beams G12, G22, and G32 that are wavelength converted light having a wavelength of ultraviolet light to visible light. In this case, the conversion efficiency by the two-stage wavelength conversion can be set to 20% or more, for example. Further, the THG element 36 can be omitted depending on the application.

  In addition, infrared light has a wavelength range of 700 nm to 100 μm, but in the laser processing, the vicinity of about 1000 nm is often used. Further, ultraviolet light has a wavelength range of 10 to 400 nm, and visible light has a wavelength range of 400 to 700 nm. In laser annealing of silicon material, it is preferable to use ultraviolet light having a large absorption coefficient.

  FIG. 3 is a schematic diagram illustrating an irradiation optical unit. That is, FIG. 3A shows the irradiation optical unit 16 of a thin rectangular callide method. The laser beams G12, G22, and G32 from the wavelength conversion unit 14 are transmitted by a guide fiber or transmitted by space, and are combined into a line-shaped combined beam GT1 by a lens system. The cross-sectional shape of the combined beam GT is not limited to a line shape, and may be a spot shape (GT2 represented by a broken line) or a rectangular shape. FIG. 3B shows a multistage array lens type irradiation optical unit 16. In the irradiation optical unit 16, the combined beam GT is formed by an array lens.

 In the laser processing apparatus according to this embodiment, the laser beams G12, G22, and G32 to be combined are adjusted so that at least one of the center wavelength, the optical path length, the phase, and the emission timing is different to suppress interference. First, in FIG. 1, the fiber amplifier 12 including the preamplifier A1 and the main amplifier A2, and the fiber amplifier 12 including the optical path length of the laser light passing through the first series of the wavelength converter 14 connected thereto and the preamplifier A3 and the main amplifier A4. And the optical path length of the laser light passing through the second series of the wavelength conversion unit 14 connected thereto, K2, and the optical path length of the laser light passing through the fiber amplifier 12 including the preamplifier A5 and the main amplifier A6 and the third series connected thereto as K3. To do.

  In this case, at least two optical path lengths are set to different values to suppress interference when laser beams are combined. It is more preferable that the optical path lengths of all the laser beams are all different values. FIG. 4 is a diagram for explaining the coherence due to the deviation of the optical path length. According to the inventor's experiment, when the above seed light was synthesized after being branched into two, when the optical path length deviation was zero, interference fringes were generated as shown in FIG. 4A, but the optical path length deviation was 0. When the thickness is 0.5 mm, the interference fringes can be suppressed as shown in FIG.

The coherence length L of the laser light that has been amplified by a fiber amplifier using a seed light source equipped with a fiber laser oscillator and wavelength-converted by an SHG element and a THG element is as short as several millimeters, for example. The coherence length L (or coherence length) is expressed by the following equation.

L = c / Δf

Where c is the speed of light and 3 × 10 ⁸ m in vacuum
Δf is the frequency spectrum width of the light source (Hz)

In the semiconductor laser, Δf is several to several hundred MHz, the coherence length L is in the range of about 1 to 100 m, and is longer than several mm, which is the coherence length of the amplified light from the fiber amplifier.

  The optical path length difference (between K1 and K2) expressed by the optical distance (physical distance × refractive index) from the seed light exit to the position where the laser light is synthesized through the fiber amplifier 12 and the wavelength converter 14. , Between K2 and K3, and between K3 and K1) is more than the coherence length L, which is more preferable because interference fringes can be reliably suppressed. In the present embodiment, Δf is as wide as 10 to 100 GHz, for example, and the coherence length L can be shortened. Therefore, the optical path length difference can be shortened compared to a light source using YAG or a semiconductor laser, and the laser processing apparatus can be downsized. When the optical path length difference is sufficiently longer than the coherence length, interference fringes are hardly generated at any position on the optical path, and a combined beam GT having a uniform intensity distribution can be realized.

Further, interference can be suppressed even if the center wavelength of the laser beam is changed.
First, FIG. 5 shows a seed light source, FIG. 5A is a configuration diagram of a fiber laser oscillator, and FIG. 5B is a diagram of a semiconductor laser. In FIG. 5A, the optical fiber 40 can be, for example, a Yb-doped optical fiber, like the fiber amplifier 12 constituting FIG. Yb is excited by the semiconductor laser 42.

  FBGs (Fiber Bragg Grating) are provided on both sides of the optical fiber 40 and the AO (Acousto-Optic) switch 50. The FBG includes a diffraction grating in which the refractive index of the core portion of the optical fiber is periodically changed. The FBG 48 highly reflects light having the Bragg wavelength of the diffraction grating and transmits other wavelengths. The FBG 46 transmits and reflects light having a Bragg wavelength.

The AO switch 50 changes the direction of polarization by periodically changing the refractive index by ultrasonic waves generated by applying a high-frequency voltage to the AO material. When the polarization direction of the AO switch 50 is matched with the optical axes of the FBG 46 and FBG 48, an optical resonator is formed and seed light G10, which is oscillation light that matches the Bragg wavelength of the FBGs 46, 48, is emitted from the FBG 48 to the outside. On the other hand, when the polarization direction of the AO switch 50 does not coincide with the optical axes of the FBGs 46 and 48, no resonator is configured and no light is emitted. In this way, the pulse seed light G10 can be obtained. Examples of the AO material include LiTaO ₃ , LiNbO ₃ , TeO ₂ , and CdS.

  Between the FBG 46 and the optical fiber 40, the pumping light from the pumping light source 42 enters the optical fiber 40 via the two-stage combiners 44a and 44b. In order to obtain a high output pulse seed light G10, for example, several tens of pumping semiconductor lasers may be connected.

  When the length of the optical fiber and the concentration of the added rare earth element such as Yb are changed, the wavelength at which the amplification gain is maximized can be changed. When the common seed light source 10 shown in FIG. 1 is configured as shown in FIG. 5, the wavelength range of the excitation spectrum width of the rare earth element is larger than the wavelength range of the pulse seed light. The wavelength at which the amplification gain becomes maximum between the series can be set to different values. For this reason, interference can be suppressed by changing the center wavelength of the laser light. If the central wavelengths of the first, second, and third series are all different values, interference can be more easily suppressed.

  Note that the length or the rare earth element concentration of at least one of the preamplifier 12a and the main amplifier 12b may be changed. Further, as indicated by a broken line in FIG. 1, the preamplifier 12a and the main amplifier 12b may be connected to each other.

  FIG. 5B shows a case where the semiconductor laser 52 is used as a seed light source. Compared with the fiber laser oscillator, the operating life is short, but the configuration is simple and the size can be easily reduced.

  Furthermore, interference can be suppressed even if the phase of the laser beam is changed. In FIG. 1, a phase plate (or a phase modulator) 70 that shifts the phase is provided between the preamplifier A3 and the main amplifier A4, and the phase is shifted and interfered between the amplified laser beam G11 and the amplified laser beam G21. Suppress. Further, when the amplified laser beam G31 having a phase different from the amplified laser beams G11 and G21, which are further provided with a phase plate (or phase modulator) 71 between the preamplifier A5 and the main amplifier A6, is assumed. , Interference can be further suppressed. These phase plates (or phase modulators) 70 and 71 may be inserted anywhere between the seed light source 10 and the irradiation optical unit 16.

FIG. 6 is a configuration diagram of a laser processing apparatus according to a modification of the present embodiment.
Pulse seed lights G10, G20, and G30 are provided for each series. In FIG. 5A, the Bragg wavelength of the FBGs 46 and 48 can be changed and the center wavelength can be changed by changing the interval of the diffraction grating. Note that the seed light from one fiber laser oscillator shown in FIG. 5A can be spatially propagated, separated by using a dichroic mirror whose cutoff wavelength is slightly shifted, and then incident on each fiber amplifier. In FIG. 5B, the center wavelength can be changed by changing the composition of the active layer of the semiconductor laser. Thus, in this modification, it can be easily set as a different center wavelength.

  In the laser processing apparatus shown in FIGS. 1 and 6, the emission timing of the laser beam G12 and the emission timing of the laser beam G22 are shifted by a time (second) represented by 1 / Δf, and interference can be suppressed. . However, Δf represents the frequency spectrum width (Hz) of the laser beam.

  Even if the modulation pulse width is changed, the irradiation timing can be shifted to suppress interference. For example, the modulation timing of the semiconductor laser used for the seed light source 10 is made even 1 / Δf or more, or the modulation timing is shifted by 1 / Δf or more using a Q switch that controls the emitted light of the fiber laser oscillator constituting the seed light source 10. Therefore, the irradiation timing can be shifted to suppress interference. These are mainly means for controlling electrical timing.

  In the laser processing apparatus shown in FIGS. 1 and 6, different values among the optical path length, the center wavelength, the phase, and the emission timing may not be the same. For example, the optical path length may be different between the laser beam G12 and the laser beam G22, and the center wavelength may be different between the laser beam G22 and the laser beam G32. Further, the phase may be different between the laser beam G22 and the laser beam G32, or the emission timing may be different. Regardless of the configuration, it is easier to suppress interference if the laser light to be synthesized has at least any one of the optical path length, the center wavelength, the phase, and the emission timing.

  Since the laser processing apparatus according to the present embodiment is a solid-state laser system and does not use halogen gas, maintenance such as gas exchange and chamber exchange is easy, and no toxic gas is required and it is safe. The pulse width of the excimer laser is substantially fixed at about 30 ns, but in this embodiment, the modulation timing can be changed to make the pulse width variable. For this reason, for example, a pulse width of 100 nm or more is possible, and the degree of freedom of laser processing can be increased.

FIG. 7 is a flowchart of the laser processing method according to the present embodiment.
For example, pulse seed light G10 having an infrared light wavelength is emitted from the seed light source 10. The pulse seed light G10 divided into three is incident on the fiber amplifier 12 and amplified (S100). The laser beams G11, G21, and G31 are converted into shorter wavelength laser beams G12, G22, and G32 by the wavelength conversion unit 14 (S102).

  The laser beams G12, G22, and G32 are converted into a combined beam GT having a line-shaped or spot-shaped cross-sectional shape by the irradiation optical unit 16 (S106). By irradiating the workpiece 20 placed on the stage 18 with the composite beam GT, laser processing becomes possible. The synthesized beam GT is scanned to collectively process a predetermined area on the surface of the workpiece 20 (S106). Moving the stage 18 on which the workpiece 20 is placed is the same as scanning the composite beam GT.

  In the case of beam shaping in a line shape, for example, the line beam width W is about several μm to 50 μm, and the line beam length BL is 500 mm. The combined beam GT is irradiated onto the workpiece 20, and the workpiece 20 can be processed with high throughput.

  In the laser processing method of the present embodiment, a combined beam GT that is optically combined while suppressing interference between at least two laser beams is used. For this reason, interference fringes, that is, nonuniformity of beam intensity can be suppressed in beam shaping, and laser processing of the workpiece can be performed using the uniform composite beam GT.

  Furthermore, the processed object 20 can be processed with a high throughput, for example, by irradiating the semiconductor with a combined beam GT such as a spot or a line. For this reason, it is possible to rationalize the laser annealing process such as converting amorphous silicon into polycrystalline silicon. Similarly, the annealing process of the semiconductor layer after ion implantation can be rationalized. Thus, the laser processing method of the present embodiment can increase the productivity of the manufacturing process of electronic devices such as liquid crystal display devices and semiconductor devices.

  The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to these embodiments. Even if a person skilled in the art changes the design regarding the material, size, shape, arrangement, etc. of the seed light source, fiber amplifier, wavelength converter, irradiation optical system, optical fiber, and semiconductor laser constituting the present invention, It is included in the scope of the present invention without departing from the gist of the invention.

The block diagram of the laser processing apparatus concerning embodiment of this invention Fiber amplifier configuration diagram Schematic diagram showing the irradiation optics Diagram explaining coherence due to optical path length deviation Configuration diagram of seed light source The block diagram of the laser processing apparatus concerning the modification of this embodiment Flow chart of laser processing method according to this embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Seed light source, 12 Fiber amplifier, 14 Wavelength conversion part, 16 Irradiation optical part, 18 stage, 20 Work piece, 40, 54, 56 Optical fiber, 52 Semiconductor laser, 70 Phase plate (phase modulator), 50 Q switch ,
G10, G20, G30 Pulse seed light, G11, G21, G31 Laser light, G12, G22, G32 Laser light, GT, GT1, GT2 Composite beam, K1, K2, K3 Optical path length

Claims (12)

A seed light source that emits seed light in the infrared wavelength band;
A first fiber amplifier that is supplied with the seed light and emits a first laser light;
A second fiber amplifier that is supplied with the seed light and emits a second laser light;
A first wavelength converter that converts the wavelength of the first laser light into a wavelength range of ultraviolet light to visible light;
A second wavelength converter for converting the wavelength of the second laser light into a wavelength range of ultraviolet light to visible light;
An optical irradiation unit that combines the wavelength-converted first and second laser beams to form a combined beam;
With
The laser processing apparatus, wherein the first laser beam and the second laser beam are synthesized in a state in which at least one of a center wavelength, an optical path length, a phase, and an emission timing is different.   The laser processing apparatus according to claim 1, wherein the first and second wavelength conversion units generate second harmonics of the first and second laser beams using a nonlinear crystal.   The difference in optical path length between the first laser beam and the second laser beam is larger than any of the coherence lengths of the first and second laser beams. Laser processing equipment. The seed light source wavelength-separates the seed light from one fiber laser oscillator and supplies it to the first and second fiber amplifiers, respectively.
The laser processing apparatus according to claim 1, wherein a center wavelength of the first laser light and a center wavelength of the second laser light are different.   The optical fiber included in the first fiber amplifier and the optical fiber included in the second fiber amplifier are different in at least one of the length and the concentration of the added rare earth element, so that the wavelength at which the amplification gain is maximized is increased. The laser processing apparatus according to claim 1, wherein the laser processing apparatuses are different from each other. The seed light source comprises at least two lasers having different center wavelengths;
The laser processing apparatus according to claim 1, wherein a center wavelength of the first laser light is different from a center wavelength of the second laser light.   7. The apparatus according to claim 1, further comprising at least one of a phase plate and a phase modulator that relatively shift the phases of the first laser beam and the second laser beam. The laser processing apparatus as described.   The emission timing of the first laser light and the second laser light is different from each other by (1 / Δf) seconds or more when the spread width of the emission spectrum of the laser light is Δf (hertz). The laser processing apparatus as described in any one of 1-3. The seed light source includes first and second lasers;
The laser processing apparatus according to claim 1, wherein the modulation timings of the first and second lasers are different by (1 / Δf) seconds or more. Supplying seed light to the fiber amplifier to emit the first and second laser light;
Wavelength conversion of the first and second laser beams using a nonlinear crystal,
Combining the wavelength-converted first and second laser beams to form a combined beam;
A laser processing method for irradiating a workpiece with the combined beam,
The laser processing method, wherein the first and second laser beams are synthesized in a state where at least one of a center wavelength, an optical path length, a phase, and an emission timing is different.   The laser processing method according to claim 10, wherein the semiconductor included in the workpiece is irradiated with the synthetic beam and laser annealing of the semiconductor is performed.   An electronic device formed using the laser processing method according to claim 10.