JP2006216820A - Laser beam machining method, laser processing apparatus and crystallization apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining method, a laser processing apparatus, and a crystallization apparatus which solve conventional problems. <P>SOLUTION: The machining method for radiating laser light to a transparent material to be processed mounted on a stage 25 includes steps of collecting laser light emitted from a laser light source by a condenser lens, radiating the collected laser light to the material, absorbing or passing the laser light transmitted through the material on the stage 25 when the material is to be processed, and diffusely reflecting the laser light on the surface of the stage 25. The laser processing apparatus and the crystallization apparatus characterized by the above method are also provided. Thus, the material can be well processed without abrasion (transpiration) occurring on the surface of the stage 25 and without an unintended part of the material machined. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  Processing technology using excimer laser, which is pulsed laser light, is widely used in process applications such as ablation (transpiration), heating, and melting. In recent years, the use of ablation techniques in a wide range such as soft organic materials such as plastic, ceramics and quartz called difficult-to-process materials, etc. has been studied. Since excimer laser has high photon energy (5 eV or more), it directly acts on the bond between molecules, so that high processing performance is realized. Examples of applications include quartz ablation for forming fiber gratings and nozzle processing for inkjet printers.

  Specifically, in laser processing technology, high power laser light of about several tens of watts to several hundreds of watts is used, and fine processing of several microns to several hundred microns is put into practical use. For example, in a processing apparatus using an excimer laser, there is an apparatus in which amorphous silicon is formed on a light-transmitting substrate such as a glass substrate and crystallized by laser irradiation. The illumination optical system of this apparatus emits excimer laser light by making the intensity of the light irradiation cross section uniform with a homogenizer and shaping it into a rectangular shape through a metal mask having an elongated rectangular opening (for example, the cross-sectional shape is 150 mm × 200 μm). . The emitted laser light is scanned in a direction perpendicular to the major axis direction of the laser rectangle shaped on the rectangle on the surface of the amorphous silicon thin film deposited on the glass substrate, and spaced by 10 μm in the minor axis direction. And is irradiated with a laser. The region of the silicon thin film that has absorbed the laser light is converted into crystalline silicon after passing through molten silicon. With this technology, even if a general glass or plastic substrate is used, the substrate is not thermally damaged. This is because the excimer laser is a pulse laser having a light emission time of about 20 ns, and crystallization is completed in about 50 to 100 ns. The crystal grain size depends on the laser energy density, and a polycrystalline thin film having a grain size of about 0.1 to 1 μm can be formed.

  Excimer laser annealing (in this case, laser processing is by heating) for polycrystallizing such an amorphous film is a technique for improving the performance of thin film transistors used in driving elements such as liquid crystal displays. It's being used.

  If the work material has a high absorption coefficient with respect to the wavelength of the laser light used for processing, most of the laser light is absorbed by the work material and hardly causes problems, but if the absorption is low (transparent to the laser wavelength) If), problems are likely to occur during processing. For example, when a glass substrate is used as a workpiece, there is only weak absorption (small absorption coefficient) with respect to the wavelength of the processing laser. The amount of absorption of laser light used for processing is determined by the absorption coefficient and thickness of the workpiece. Therefore, if there is a certain thickness (about 1 mm), the light reaching the back surface can be ignored, but if it becomes thinner, it cannot be absorbed completely. Since the thinning of the glass is progressing for weight reduction, the laser beam cannot be absorbed completely. As a result, it was found that the following problems occurred due to the transmitted light.

  Laser light that has passed through the substrate, which is a workpiece, and reached the stage on which the substrate is placed enters the stage surface. Since the wavelength of the laser beam does not pass through the stage, the stage surface is heated significantly, causing ablation (transpiration). The transpiration material scattered from the surface of the stage by ablation becomes a contaminant that stains the back surface of the substrate. Also, the surface of the substrate stage itself becomes rough due to ablation, and problems such as deteriorating the positional accuracy of the substrate and damaging the back surface of the substrate occur. Another problem is that laser light that reaches the substrate stage is reflected on the surface of the stage and is incident on the substrate again to cause unintended processing. Specifically, for example, in the process of crystallizing amorphous silicon, an unintended place is crystallized (processed) by the stage reflected light. When reflection on the substrate stage surface is considered, it is the same as when a mirror is placed, so how is the reflected light on the stage surface after passing through the substrate focused in addition to the optical system from the laser device to the substrate? Such complicated optical system traces are required.

  The present invention has been made in response to the above-described points, and processing of a substrate to be processed by unintentional reflection of laser light on the surface of the stage and laser processing for preventing contamination of the back surface of the substrate to be processed by ablation of the stage surface. It is an object of the present invention to provide a method, a laser processing apparatus, and a crystallization apparatus.

  Thus, a laser processing method for processing a laser beam emitted from a laser light source according to one embodiment of the present invention by condensing the laser beam on a workpiece placed on the surface of the stage is a transmitted laser beam transmitted through the workpiece. On the other hand, the method includes a step of performing at least one of absorption and transmission at the stage.

  The laser beam is preferably a laser beam in which the spatial intensity distribution of the laser beam is made uniform by a homogenizer element.

  Preferably, the method further includes a step of providing a phase modulation element in an output side optical path of the homogenizer element, and modulating a spatial intensity distribution with respect to the laser light made uniform by the homogenizer element.

  According to another aspect of the present invention, there is provided a laser processing apparatus for processing a workpiece placed on a stage surface by a laser beam emitted from a laser light source, wherein at least the surface of the stage on which the workpiece is placed is The laser beam is composed of at least one of a laser transmitting body and a laser absorbing body.

  An antireflection film is preferably provided on at least the surface of the stage on which the workpiece is placed.

  An uneven structure is preferably provided on at least the surface of the stage on which the workpiece is placed.

  Preferably, the optical path of the laser beam further includes a homogenizer for making the spatial intensity distribution of the laser beam uniform.

    A crystallization apparatus for crystallizing a crystallized substrate by irradiating the crystallized substrate placed on the stage surface by modulating the light intensity of a laser beam from a laser light source according to still another aspect of the present invention. The at least surface of the stage on which the crystallized substrate is placed is made up of at least one of a laser transmitting body and a laser absorbing body with respect to the laser.

  According to the present invention, a laser processing method and a laser processing apparatus that solve the conventional drawbacks, reduce the reflection of the laser beam on the stage surface and reduce the ablation of the stage surface, and do not contaminate the work material or the back surface of the crystallized substrate. And a crystallization apparatus.

  Further, the present invention provides a laser processing method, a laser processing apparatus, or a crystallization apparatus for preventing an unintended portion from being processed or crystallized due to reflection from a substrate surface.

  Next, embodiments of the present invention will be described with reference to the drawings. First, FIG. 1 and FIG. 2 show an outline of an excimer laser processing apparatus such as a crystallization apparatus 1 according to the present invention. As shown in FIG. 1, the crystallization apparatus 1 includes an illumination system 2, an optical element 13 provided on the optical axis of the illumination system 2, and a condensing provided on the optical axis of the optical element 13. A lens, for example, an imaging optical lens system 14, a workpiece 22 provided on the optical axis of the imaging optical lens system 14, and a stage 25, for example, an XYZ-θ stage for supporting the workpiece. .

  The illumination system 2 is, for example, the optical system shown in FIG. 2, and the configuration of the illumination system 2 will be described in a mimicry manner. The illumination system 2 includes, for example, a light source 11 and a homogenizer such as a homogenizing optical system 12. The light source 11 includes a XeCl excimer laser light source 11 that emits pulsed light having a wavelength of 308 nm. In addition to the XeCl excimer laser light source, other excimer lasers such as a KrF excimer laser that emits pulsed light with a wavelength of 248 nm and an ArF laser that emits pulsed light with a wavelength of 193 nm are also suitable as the light source 11. The light source 11 may be another laser light source such as a YAG laser light source. The light source 11 may be another appropriate light source that outputs energy for melting the non-single crystal semiconductor film 23, for example, an amorphous silicon film.

  The homogenizing optical system 12 includes, for example, a beam expander 12a, a first fly-eye lens 12b, a first condenser optical system 12c, and a second fly-eye, which are sequentially arranged on the optical axis of the laser light from the light source 11. It has a lens 12d and a second condenser optical system 12e. The homogenizing optical system 12 makes the light intensity of the laser light emitted from the light source 11 and the incident angle to the optical element 13 uniform in the cross section of the light beam, as will be described below.

  In the illumination system 2, the laser light incident from the light source 11 is magnified via the beam expander 12a and then enters the first fly-eye lens 12b. A plurality of light sources are formed on the rear focal plane of the first fly-eye lens 12b, and light beams from the plurality of light sources pass through the incident surface of the second fly-eye lens 12d via the first condenser optical system 12c. Illuminate in a superimposed manner. As a result, a larger number of light sources are formed on the rear focal plane of the second fly-eye lens 12d than on the rear focal plane of the first fly-eye lens 12b. Light beams from a number of light sources formed on the rear focal plane of the second fly-eye lens 12d are incident on the optical element 13 via the second condenser optical system 12e, and are illuminated in a superimposed manner.

  As a result, the first fly-eye lens 12b and the first condenser optical system 12c of the homogenizing optical system 12 constitute a first homogenizer, and perform a homogenization process on the incident angle of the laser light incident on the optical element 13. Further, the second fly-eye lens 12d and the second condenser optical system 12e constitute a second homogenizer, and the laser beam on the optical element 13 with respect to the laser beam whose incident angle from the first homogenizer is made uniform by the second homogenizer. The light intensity at each position in the plane is made uniform. In this way, the illumination system 2 forms laser light having a substantially uniform light intensity distribution, and this laser light irradiates the optical element 13.

  The optical element 13 is an optical component having a function of shaping the intensity distribution. For example, the optical element 13 has a rectangular opening for shielding the peripheral light of the laser light and transmitting the relatively uniform light of the central light. An optical mask based on a metal mask or quartz or the like obtained by evaporating a non-transmissive material on a transmissive optical component such as quartz and etching and removing the non-transmissive material in a rectangular shape may be used. Further, the optical element 13 may be a phase shifter that is a phase modulation element, for example. This phase shifter is an optical element that phase-modulates the light emitted from the homogenizing optical system 12 and emits a laser beam having a reverse peak-shaped minimum light intensity distribution. This phase shifter has a concavo-convex pattern formed on a transparent substrate such as quartz glass. The uneven pattern includes a line and space pattern and an area modulation pattern.

  The phase shifter is provided with an uneven step on a transparent body, for example, a quartz substrate, causes laser beam diffraction and interference at the step boundary, and imparts a periodic spatial distribution to the laser beam intensity. Some phase shifters have a phase difference of 180 ° on the left and right with the stepped portion x = 0 as a boundary, for example. In general, when a wavelength of laser light is λ, a transparent medium having a refractive index n is formed on a transparent substrate to give a phase difference of 180 °. The film thickness t of the transparent medium is t = λ / 2 (n -1).

  For example, assuming that the refractive index of the quartz substrate is 1.46, the wavelength of the XeCl excimer laser light is 308 nm. Therefore, in order to add a phase difference of 180 °, a step of 334.8 nm is formed by a method such as photoetching. Form.

  Also, when the SiNx film is used as a transparent medium, the refractive index of the SiNx film formed by PECVD, LPCVD, etc. is near 2, so that the SiNx film is formed on the quartz substrate at 154 nm and is stepped by photoetching. You can add. For example, the intensity of laser light that has passed through a phase shifter with a phase difference of 180 ° shows a pattern of periodic strength.

  In this embodiment, the width of the phase shift pattern and the distance between the patterns are both 3 μm, for example. The phase difference does not necessarily need to be 180 °, and may be any phase difference that can realize the strength of the laser beam.

  The laser light phase-modulated by the optical element 13 is condensed on the workpiece 22 via a condenser lens, for example, an imaging optical lens system 14. Here, the imaging optical lens system 14 optically conjugates the pattern surface of the optical element 13 and the workpiece 22. In other words, the height position of the stage 25 is corrected so that the workpiece 22 is set to a surface optically conjugate with the pattern surface of the optical element 13 (image surface of the imaging optical lens system 14). . The imaging optical lens system 14 includes a positive lens group 14a, a positive lens group 14b, and an aperture stop 14c provided therebetween. The imaging optical lens system 14 is an optical lens that forms an image on the workpiece 22 by reducing the image of the optical element 13 to the same magnification or variable magnification, for example, 1/5.

  The aperture stop 14c has a plurality of aperture stops having different sizes of openings (light transmission portions), and these aperture stops 14c are configured to be exchangeable with respect to the optical path. Alternatively, the aperture stop 14c may be one iris stop that can continuously change the size of the opening. In any case, the size of the aperture of the aperture stop 14c (and hence the image-side numerical aperture NA of the imaging optical lens system 14) generates a required light intensity distribution on the workpiece 22 as will be described later. Is set to The imaging optical lens system 14 may be a refractive optical system, a reflective optical system, or a refractive reflective optical system, and is restricted in form. Not.

  As shown in FIG. 1, the workpiece 22 is formed by applying a silicon oxide layer as a base insulating layer 22b on a glass substrate 22a which is a plate glass for a liquid crystal display, for example, by chemical vapor deposition (CVD) or sputtering. A non-single crystal semiconductor film 23, for example, an amorphous silicon film, and a silicon oxide layer as a cap film 22c are sequentially formed as a crystallization target layer. However, it is not limited to the glass substrate 22a, and may be, for example, a polyimide substrate, a plastic substrate, or a semiconductor substrate.

  The stage 25 is a stage for supporting the workpiece 22 and aligning the workpiece 22 with a machining position with high accuracy. The stage 25 is preferably an XYZ-θ stage 25. The XYZ-θ stage 25 is provided with an X table that moves in the X-axis direction, a Y table that moves in the Y-axis direction is provided on the X table, and moves in the Z-axis direction on the Y table. A Z table is provided, and a θ table that rotates in the θ direction is provided on the Z table. The material of the stage 25 is a material that has at least one characteristic of absorption and transmission by reducing reflected light when a transmission laser transmitted through the workpiece enters.

The base insulating layer 22b is formed, for example, with a SiO ₂ film thickness of 500 to 1000 nm. In the base insulating layer 22b, a non-single crystal semiconductor film 23 such as an amorphous silicon film and a glass substrate 22a are in direct contact, and foreign matters such as Na deposited from the glass substrate 22a are mixed into the amorphous silicon film 23. This prevents the melting temperature during the crystallization process of the amorphous silicon film 23 from being directly transferred to the glass substrate 22a, and contributes to crystallization of a large grain size by the heat storage effect of the melting temperature.

The amorphous silicon film 23 is an object to be actually processed and is a film to be crystallized. The amorphous silicon film 23 is selected to have a thickness of, for example, 30 to 260 nm. The cap film 22c stores heat generated when the amorphous silicon film 23 is melted during the crystallization process, and this heat storage action contributes to the formation of a crystallized region having a large grain size. The cap film is an insulating film such as a silicon oxide film (SiO ₂ ) and has a thickness of 100 to 400 nm, for example, 300 nm. The cap film may be laminated with an SiO _X layer that absorbs a part of the incident laser light and generates heat, and stores this heat.

  Below, the crystallization process of the to-be-processed material 22 which has a structure as shown in FIG. 1 is demonstrated. The workpiece 22 is automatically conveyed onto the stage 25 of the crystallization apparatus 1 by a known method, positioned and placed at a predetermined position, and held by a vacuum chuck or an electrostatic chuck. Is done.

  Next, fine alignment is performed based on the alignment marks provided on the workpiece 22.

  Next, an actual crystallization process will be described with reference to process flowchart 1 (process 2 to process 8) in FIG. In the following description, what is described as (process x, x is a numerical value) indicates each process code in FIG. Pulse laser light is emitted from the laser light source 11 (step 2), and the emitted pulse laser light is homogenized by the homogenizing optical system 12 so that the light intensity is uniform within the beam diameter and the incident angle to the optical element 13 is uniform. Done (step 3).

  The laser light is, for example, XeCl excimer laser light having a wavelength of 308 nm, and the pulse duration of one shot is 1 to 10 nsec. When the optical element 13 is irradiated with pulsed laser light under the above conditions, the pulsed laser light incident on the periodically formed optical element 13 such as a phase modulation element causes diffraction and interference at the stepped portion. As a result, the phase modulation element, which is the optical element 13, generates a strong and weak light intensity distribution in a reverse peak pattern that changes periodically (step 4).

  The intensity distribution of the intensity of the reverse peak pattern desirably outputs a laser beam intensity that melts the amorphous silicon film 23 from the minimum light intensity to the maximum light intensity. The pulsed laser light that has passed through the optical element 13 is focused on the workpiece 22 by the imaging optical lens system 14 (step 5) and is incident on the amorphous silicon film 23.

  The incident pulse laser light is almost transmitted through the silicon oxide layer of the cap film 22 c and absorbed by the amorphous silicon film 23. As a result, the irradiated region of the amorphous silicon film 23 is heated and melted. The heat at the time of melting is stored in the base insulating layer 22b and the cap film 22c.

  When the irradiation of the pulse laser beam is in the cut-off period, the irradiated region tries to cool down at high speed, but due to the heat stored in the cap film 22c provided on the front and back surfaces and the silicon oxide film of the base insulating layer 22b. The temperature drop rate becomes extremely gradual. At this time, the temperature of the irradiated region is lowered according to the light intensity distribution of the reverse peak pattern generated by the optical element 13, and the crystals are sequentially grown in the lateral direction (step 6).

  In other words, the solidification position in the melted region in the irradiated region gradually moves from the low temperature side to the high temperature side. That is, the crystal grows laterally from the crystal growth start position toward the crystal growth end position. The crystallized region thus crystal-grown is large enough to form one or more TFTs.

  In the workpiece 22 that is transparent to the irradiated laser light, the irradiated laser light passes through the workpiece 22 and reaches the surface of the stage 25. The stage 25 according to the embodiment of the present invention absorbs or transmits the transmitted laser light transmitted through the workpiece 22 (process 7), or diffusely reflects the transmitted laser light (process 8), and has a problem with the transmitted laser light. Is solved.

  The crystallization apparatus 1 automatically irradiates a crystallization region of the next amorphous silicon film 23 with a pulsed laser beam according to a program stored in advance to form a crystallization region. Movement to the next crystallization position can be performed by relatively moving the workpiece 22 and the light source 11, for example, by moving the stage 25.

  When a region to be crystallized is selected and alignment is completed, the next pulse laser beam is emitted. By repeating such laser beam shots, the workpiece 22 can be crystallized over a wide range. In this way, the crystallization process is completed.

  In the above, the crystallization process by a laser was demonstrated as an example as a laser processing process. However, laser processing is not limited to crystallization, but is performed by the intensity of light intensity of the laser, and includes ablation (heating), heating, melting, activation, and the like. In the crystallization process described above, the crystallization process of the amorphous silicon film 23 on the surface of the workpiece 22 has been described. However, the workpiece 22 itself may be processed, or the crystal of the amorphous silicon film may be processed. There is a case where only the surface 23 of the workpiece 22 is processed as in the process of forming. The processing of the surface 23 means a change in the surface form, for example, rough surface morphology or formation of irregularities, drilling, activation, physical properties (crystallization, formation of crystal grains, expansion of crystal grains, crystal structure) Change). The surface 23 may represent a mere surface of the workpiece 22 or may be formed by a method of depositing or depositing a substance or a film different from the main base material of the workpiece 22. Even in that case, the surface 23 is considered to be a part of the workpiece 22.

  Next, the case where the workpiece 22 is transparent to the wavelength of the laser irradiated will be described. Here, having transparency means that it is only necessary to transmit a part of the laser light, and does not mean to transmit all of the laser light. Further, since the transmission amount is determined by the transmission coefficient of the substance and its thickness, for example, even if the transmission coefficient of the material of the workpiece 22 is low, the workpiece 22 is thin and a part of the irradiated laser beam is covered. In the case where it is transmitted from the back surface of the workpiece 22, it has transparency. On the contrary, even if the material 22 has a high transmittance, the workpiece 22 is thick and absorbs and reflects most of the irradiated laser light so that the laser light does not pass through the back surface. It will not have.

  A processing step of the surface 23, for example, a crystallization step in the case where the workpiece 22 has transparency will be described with reference to FIG. The same reference numerals are given to the same parts in each figure, and the duplicate description for each figure is omitted. Here, the surface 23 (amorphous silicon film) that is the object to be processed of the workpiece 22 in FIG. 1 has a structure in which a silicon oxide layer is vertically provided as a base insulating layer 22b and a cap film 22c. The surface 23 is not necessarily limited to that having such a structure. Therefore, in the following description, an example in which the surface 23 of the workpiece 22 does not have the silicon oxide layer as the base insulating layer 22b and the cap film 22c will be described. In FIG. 4, a laser beam focused on a workpiece 23 placed on a stage 25 and a surface 23 of the workpiece 22, for example, an amorphous silicon film as a crystallized film is deposited. 21 is irradiated and processed to produce a crystallized region 24.

  If the workpiece 22 has a high absorption coefficient with respect to the wavelength of the laser beam 21 used for processing, or has a certain thickness (about 1 mm) even if the absorption coefficient is low, the workpiece 22 reaches the back surface of the workpiece 22. Prior to this, most of the laser beam 21 is absorbed by the workpiece 22 and no problem occurs (FIG. 4A). However, as shown in FIGS. 4 (b) and 4 (c), when the absorption is small (when it is nearly transparent with respect to the laser wavelength, for example, in the case of a glass substrate or a synthetic quartz substrate) and not according to the present invention Causes problems during machining.

  As shown in FIG. 4B, the laser beam that has passed through the workpiece 22 and reached the stage 25 is irradiated on the stage surface. The normal stage 25 is made of a material that does not transmit the wavelength of the laser light, and the laser light 21 irradiated on the stage surface remarkably heats the stage surface and causes ablation (transpiration). Ablation causes roughness 25a on the surface of the stage itself, which causes problems such as the positional accuracy of the workpiece 22 being distorted and the back surface being damaged. Further, the contaminant 25a 'scattered from the stage surface also causes a problem that the back surface of the workpiece 22 is soiled.

  Further, as shown in FIG. 4C, the laser light reaching the stage 25 is reflected on the surface of the stage to become reflected light 21a, and is incident on the amorphous silicon film on the surface 23 again to cause unintended crystallization. Region 24a is produced.

  Next, details of an embodiment that addresses the points shown in FIGS. 4B and 4C will be described below.

First embodiment
A first embodiment is shown in FIGS. 5 and 6A. The same reference numerals are given to the same parts in each figure, and the duplicate description for each figure is omitted. FIG. 5A shows a case where the stage itself is constituted by a laser absorber 25b. Here, the laser absorber is a material having a constant absorption coefficient with respect to the wavelength of the laser beam (referred to as an absorptive material), and may be any material that absorbs a certain amount of incident laser beam. A laser absorber that substantially absorbs 50% or more of the incident laser light with a thickness of 0.3 mm or more corresponds to the laser absorber.

  When the absorption coefficient is high and 50% or more of the incident laser beam is absorbed with a thickness of 0.3 mm or less, rapid heating due to the absorption of the laser beam occurs in the vicinity of the surface, which is ablation (transpiration). It leads to a phenomenon and cannot be used.

  As a material of the laser absorber 25b, for example, a glass material or a resin material containing particulate titanium oxide or zinc oxide is used. A glass material or a resin material formed by uniformly containing a certain amount of particulate titanium oxide or zinc oxide so as to satisfy the above-described conditions is used. The laser absorber is not limited to those containing finely divided titanium oxide or zinc oxide, but can be used as long as the material has a certain absorption characteristic that meets the above-mentioned conditions for the laser emission wavelength. I can do it.

  Further, as shown in FIG. 5B, in order to reduce the reflection of the laser beam on the surface of the laser absorber 25b and increase the absorption efficiency of the laser beam in the laser absorber 25b, the surface of the laser absorber 25b is arranged. What deposited the antireflection film 26a may be used.

  5A and 5B, the stage itself is configured by the laser absorber 25b. However, when the laser absorber 25b has a high absorption coefficient with respect to the laser beam, as shown in FIG. 5C, the stage Only the 25 incident surfaces may be integrated with the laser absorber 25b, or an antireflection film 26a deposited on the surface of the laser absorber 25b may be used.

  Thus, by using the laser absorber 25b for the stage 25, as shown in FIG. 6A, the condensed laser light 21 is transmitted through the transmissive workpiece 22, and the stage 25 or the stage 25 is used. Is absorbed by the laser absorber 25b which is a part of the above.

  Further, for example, when there is an antireflection film 26a deposited on the laser absorber 25b, the reflected light can be further reduced as much as possible, the surface of the stage 25 is processed (transpiration), or the reflected laser light is amorphous. Good processing can be provided without crystallizing unintended portions of the quality silicon film 23.

  When such a stage 25 is used, a laser beam condensed by a condensing lens represented by, for example, a multiplying optical lens system is incident on the workpiece 22 only once, and a desired portion is processed. . If it was a conventional stage, the laser beam was incident on the workpiece again due to reflection from the stage (second incidence), and an unintended portion was processed.

  According to the present embodiment, incidence on the workpiece 22 due to reflection from the stage 25 is significantly reduced, and the workpiece 22 cannot be processed with the light intensity, and only desired processing can be performed. Therefore, it is important in this embodiment that the incident is performed only once as originally planned. The second incident is incident by unintentional reflection from the stage surface, and the element design that simulates the incident due to the reflection and assumes the optical path (element design that does not cause a problem even if there is a second incident due to reflection). Is extremely complicated, it is important to reduce the second incidence.

  In the above embodiment, the example in which the reflection from the surface of the stage 25 is reduced has been described. However, it cannot be completely reduced to zero, and the reduced weak reflected light is incident on the back surface of the workpiece 22. Become. However, this does not already have the light intensity for processing the workpiece 22, and in this case, the second incidence is not counted. Therefore, the first incidence and the second incidence are only incident laser beams having light intensity for processing a workpiece.

Second embodiment
A second embodiment will be described with reference to FIG. The same reference numerals are given to the same parts in each figure, and the duplicate description for each figure is omitted. FIG. 6B shows a case where the stage 25 itself is constituted by a laser transmitting body 25c. The laser transmitting body is a material (referred to as a transmissive material) having a certain transmission coefficient with respect to the laser wavelength to be used, and it is sufficient that it transmits a certain amount of incident laser light.

In practice, a laser transmitting body corresponds to a case where 50% or more of the incident laser light remains as a transmission amount when transmitting through a thickness of 0.3 mm. Specifically, as a material having a certain transmission coefficient, glass, quartz glass, fused silica glass, synthetic quartz glass, sapphire (aluminum oxide crystal), KB ₅ O ₈ · 4H ₂ O, BeSO ₄ · 4H ₂ O, KD ₂ PO ₄ , Nd ₂ Ti ₂ O ₇ can be used. If it is hygroscopic but nitrogen atmosphere or the like, halides (LiF, NaF, KF, RbF, CsF, MgF ₂ , CaF ₂ , SrF ₂ , BaF ₂ , PbF ₂ , BaMgF ₄ , BaZnF ₄ , KCl, RbCl, CsCl, LiBr, NaBr, KBr, CsBr, LiI, KI, LiClO ₄ .3H ₂ O, etc.) can also be used because they exhibit good permeability.

  As shown in FIG. 6B, the stage 25 itself may be constituted by a laser transmitting body 25c, or a film obtained by depositing an antireflection film 26a on the surface of the laser transmitting body 25c, for example, may be used. good. By using the laser transmitting body 25c for the stage 25 in this way, the condensed laser light 21 is transmitted through the transparent workpiece 22 and further transmitted through the laser transmitting body 25c as the stage 25. Good processing can be provided without processing (evaporating) the surface of the stage or crystallizing an unintended portion of the amorphous silicon film 23 by the reflected laser light.

  Further, for example, when there is an antireflection film 26a deposited on the laser transmitting body 25c, the reflected light can be further reduced as much as possible, so that the above-mentioned problems caused by the reflected light are further reduced, and better processing is provided. I can do it. The laser transmitting body 25c does not need to have a transmittance of 100%, and has a transmittance that reduces the ablation of the stage surface and the generation of contaminants on the back surface of the workpiece 22 to a problem-free level. That's fine.

Third Embodiment A third embodiment will be described with reference to FIG. 6C, FIG. 6D, and FIG. FIG. 6C shows a case where the stage 25 itself is constituted by a laser absorber 25b. As shown in FIG. 6C, the surface of the laser absorber 25b has an uneven structure 26b. Although a considerable amount of laser light is absorbed by the laser absorber 25b, the laser light that is not absorbed and is reflected by the surface of the laser absorber 25b is reflected (diffuse reflection 21b) while being diffused over a wide range by the uneven structure 26b. Therefore, an unintended crystallization region 24a is not generated unlike the reflected light 21a in FIG. 4C, and good processing can be provided.

  FIG. 6C illustrates the case where the stage 25 is the laser absorber 25b. However, the stage 25 is not limited thereto. For example, even if the stage 25 is constituted by the laser transmitting body 25c, the surface has an uneven structure. 26b, the laser beam reflected by the surface of the laser transmitting body 25c without being transmitted by the laser transmitting body 25c is reflected (diffuse reflection 21b) while being diffused over a wide range by the uneven structure 26b. Good processing can be provided as in 6 (c).

  As the shape of the concavo-convex structure 26b, the structures shown in FIGS. 7A, 7B, 7C, and 7D are effective. FIG. 7A shows a structure in which the quadrangular pyramids 52 on which the surface of the stage 51 is continuous are arranged. Laser light is diffusely reflected on the side surfaces of the large number of quadrangular pyramids 52. This uneven structure is not limited to a quadrangular pyramid, and may be a polygonal pyramid such as a triangular pyramid, a pentagonal pyramid, a hexagonal pyramid, or a cone. In the case of a polygonal pyramid, it is not necessary to have a perfect polygonal pyramid shape, and a round may be provided on each side formed by the side surface. In the case of a polygonal pyramid and a cone, a structure in which a round is provided so that a back surface of the workpiece 22 is not damaged at a vertex portion in contact with the workpiece or a trapezoidal structure having a flat portion may be used.

  As shown in FIG. 7B, the stage 53 is partially provided with a quadrangular pyramid 54 on the surface, and the surface portion other than the quadrangular pyramid has an uneven structure 54a. The workpiece is supported by the quadrangular pyramid 54, and the laser beam is diffused and reflected by the side surface of the quadrangular pyramid 54 and the concave-convex structure 54a. The quadrangular pyramid 54 that supports the workpiece is not limited to a quadrangular pyramid, and may be, for example, a polygonal pyramid, a cone, a trapezoid, a polygonal column, a cylinder, or the like, and has a structure that can support the workpiece. Good.

  The uneven structure 54a may be a structure including a structure in which continuous polygonal cones, cones, etc. are made fine as shown in FIG. 7A, or a structure in which the surface is physically or chemically roughened.

  As a physical method, for example, there is a method of roughening the surface by blasting or sputtering. Blasting is a processing method in which sand (sand), shots (steel pieces), glass beads, plastic particles, ice particles, dry ice particles, or the like are sprayed at a high speed on the surface to be roughened.

  Sputtering is a process in which high-speed ion particles (mainly Ar ions, etc.) accelerated by an electric field in a vacuum are irradiated to cause atoms and molecules constituting the surface to jump out, resulting in wear of the surface. It is a method to do.

  The chemical method is a method of treating by an erosion reaction by immersing in a solution of strong alkali or strong acid having reactivity to the surface to be treated or a high temperature solution thereof. When the concavo-convex structure 54a is created by such a physical method or a chemical method, for example, the quadrangular pyramid 54 that is a support member of the workpiece is covered, and the physical method or the chemical method is not used. Need to be protected. Alternatively, it may be formed by deposition after the formation of the concavo-convex structure 54a.

  Thus, by separating the workpiece support portion such as the quadrangular pyramid 54 and the concavo-convex structure 54a, the concavo-convex structure 54a does not directly contact the workpiece. For this reason, wear due to contact does not occur, and the concavo-convex structure 54a that is stable for a long time can be maintained. Thereby, stable diffuse reflection can be realized, and generation of particles caused by wear can be suppressed.

  FIG. 7C shows a structure in which spherical concave structures 56 in which the surface of the stage 55 is continuous are arranged. FIG. 7D shows a structure in which spherical convex structures 58 in which the surface of the stage 57 is continuous are arranged. Both the spherical concave structure 56 and the spherical convex structure 58 do not need to have a perfect spherical shape, as long as they include an arcuate portion on the surface irradiated with the laser light. Each fine portion constituting the arc-shaped portion reflects the laser light in different directions, and diffuse reflection can be realized.

  As shown in FIG. 6 (d), the uneven structure 26b, specifically, an antireflection film 26a for laser light is further provided on the uneven structure shown in FIGS. 7 (a) to 7 (d). There may be. By doing so, the reflected light of the laser light is reduced to the limit of the antireflection film 26a, and the laser light irradiated on the stage is the laser absorber 25b or the laser transmitting body 25c (FIG. 6C shows a laser absorber). 25b only) is absorbed or transmitted, and even if there is reflected light, it is diffusely reflected by the concavo-convex structure 26b, so that better processing without problems caused by ablation and reflection can be realized.

Fourth embodiment
A fourth embodiment is shown in FIG. FIG. 8A shows a structure in which a portion of the stage 25 corresponding to the irradiation position of the laser beam is a through hole 27. As shown in FIG. 8A, the focused laser beam 21 passes through the transparent workpiece 22 and further passes through the through hole 27 of the stage 25 and is installed at a position where the laser beam is sufficiently spread. It is absorbed by a laser absorption mechanism (not shown).

  Thus, by providing the through hole 27 in the stage 25 portion, the laser beam is no longer incident on the stage surface, and therefore there is no ablation from the surface of the stage 25 or reflection from the surface of the stage 25 by the laser beam. Therefore, good processing can be provided without causing the problems caused by. The through-hole 27 has a through-portion that is larger than the range where the laser is irradiated at the laser irradiation position. This takes into account the alignment accuracy and multiple scattered light from the workpiece 22 and its surface 23 of the laser beam. However, since a through hole larger than necessary causes the deflection of the workpiece 22, for example, if an area of 1.5 to 10 times the irradiation area of the stage 25 of the laser beam is passed, Good processing without ablation or reflection and no problem of deflection can be realized.

  FIG. 8B shows an embodiment in which multiple scattered light from the workpiece 22 and its surface 23 is incident on a portion of the stage 25 around the through hole 27. When a portion of the stage 25 is irradiated with multiple scattered light, an antireflection film 26a for suppressing reflection, a laser absorber 25b that absorbs or transmits the irradiated laser light, and a laser transmission body 25c (FIG. 8B). May be a stage constituted by a laser absorber 25b).

  Moreover, the uneven structure 26b (FIG. 6C) shown in the third embodiment and the structure of the stage 25 having the antireflection film 26a (FIG. 6D) formed thereon may be used. By adopting such a structure, even when there is multiple scattered light, the multiple scattered light irradiated on the stage 25 is absorbed or transmitted by the laser absorber 25b or the laser transmitter 25c, and is deposited on the laser absorber 25b, for example. When the antireflection film 26a is provided, the reflected light can be further reduced as much as possible. As a result, the surface of the stage 25 is not processed (evaporated), and the reflected multiple scattered light does not crystallize an unintended portion of the amorphous silicon film 23, thereby providing good processing.

  As described above, according to the embodiment of the present invention, in the laser processing method for processing a workpiece having transparency to the laser light emitted from the laser light source, the workpiece is placed on the stage surface. A step of irradiating the workpiece with the laser beam by a condensing lens that collects the laser beam, processing the workpiece, and transmitting laser light transmitted through the workpiece; A step of absorbing or transmitting by a stage.

  The laser beam irradiated on the workpiece is preferably incident only once on the workpiece. Preferably, the method further includes a step of providing an antireflection film on the surface of the stage to reduce reflected light of the transmitted laser light from the stage to the workpiece. Preferably, the method further includes a step of providing a concavo-convex structure on the surface of the stage to diffusely reflect the reflected light of the transmitted laser light from the stage to the workpiece.

  The method further includes the step of installing a homogenizer element in the laser beam path to uniformize the spatial intensity distribution of the laser beam to the condenser lens. Preferably, the method includes a step of installing a phase modulation element to modulate the uniform spatial intensity distribution of the laser light.

  A laser processing apparatus for processing a workpiece having transparency to a laser beam according to another aspect of the present invention includes a laser light source that emits the laser beam, a stage on which the workpiece is placed, A condenser lens for condensing the emitted laser light and irradiating the workpiece, and a portion of the stage on which the workpiece is placed is transparent to the laser light. It has at least one of a laser transmitting body that is a material and a laser absorber that is an absorptive material.

  The laser beam applied to the workpiece is preferably incident only once on the workpiece. An antireflection film is preferably provided on the surface of the stage. The surface of the stage is preferably provided with an uneven structure. At least a part of the surface of the stage that supports the workpiece is a convex part of the concavo-convex structure.

  Preferably, the laser beam path further includes a homogenizer element for making the light intensity distribution of the laser beam uniform. Preferably, a phase modulation element for phase modulating the laser beam made uniform by the homogenizer element is further provided.

It is the schematic of the optical system of the laser processing apparatus which concerns on this invention. It is the schematic of the illumination system of the laser processing apparatus which concerns on this invention. It is a figure which shows the process flowchart of the laser processing method which concerns on this invention. It is the schematic for demonstrating the processing state when not based on this invention. It is the schematic for demonstrating the 1st Embodiment of this invention. (A) is the 1st Embodiment of this invention, (b) is 2nd Embodiment, (c) And (d) is the schematic for demonstrating 3rd Embodiment. It is the schematic for demonstrating the uneven structure which is the 3rd Embodiment of this invention. It is the schematic for demonstrating the 4th Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Laser light source, 12 ... Homogenizing optical system, 13 ... Optical element, 14 ... Imaging optical lens system, 21 ... Laser beam, 21a ... Reflected light, 24 ... Crystallization area | region, 22 ... Work material, 25 ... Stage, 25a ... contaminants, 25b ... laser absorber, 25c ... laser transmitting body, 26a ... antireflection film, 26b ... uneven structure, 27 ... through-hole, 56 ... spherical concave structure, 58 ... spherical convex structure.

Claims (8)

A laser processing method for condensing and processing laser light emitted from a laser light source on a workpiece placed on a stage surface,
A laser processing method comprising a step of performing at least one of absorption and transmission on the stage with respect to a transmitted laser beam transmitted through the workpiece.   2. The laser processing method according to claim 1, wherein the laser beam is a laser beam in which a spatial intensity distribution of the laser beam is made uniform by a homogenizer element.   3. The laser processing according to claim 2, further comprising a step of providing a phase modulation element in an output side optical path of the homogenizer element, and modulating a spatial intensity distribution with respect to the laser light uniformized by the homogenizer element. Method. A laser processing apparatus for processing a workpiece placed on a stage surface with a laser beam emitted from a laser light source,
The laser processing apparatus according to claim 1, wherein at least a surface of the stage on which the workpiece is placed is configured by at least one of a laser transmitting body and a laser absorbing body with respect to the laser light.   The laser processing apparatus according to claim 4, wherein an antireflection film is provided on at least a surface of the stage on which the workpiece is placed.   6. The laser processing apparatus according to claim 4, wherein an uneven structure is provided on at least a surface of the stage on which the workpiece is placed.   The laser processing apparatus according to any one of claims 4 to 6, further comprising a homogenizer for uniformizing a spatial intensity distribution of the laser light in an optical path of the laser light. A crystallization apparatus for crystallizing a crystallized substrate by irradiating the crystallized substrate placed on the stage surface by modulating the light intensity of a laser beam from a laser light source,
The crystallization apparatus according to claim 1, wherein at least a surface of the stage on which the crystallized substrate is placed is composed of at least one of a laser transmitting body and a laser absorbing body with respect to the laser.

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