JP4610201B2 - Laser irradiation device - Google Patents

Description

  The present invention relates to a laser irradiation apparatus, and more particularly to a laser irradiation apparatus that can irradiate a workpiece with laser light emitted from a plurality of laser light sources.

  Laser annealing is performed on a substrate having an amorphous silicon film formed on the surface by repeatedly irradiating laser light intermittently to polycrystallize the amorphous silicon film. The amorphous silicon film is temporarily melted by laser irradiation, and polycrystallization is performed. Note that crystal grains can be further grown by intermittently repeating laser light irradiation on a substrate on which a polycrystalline silicon film is formed. A substrate on which a polycrystalline silicon film is formed is used, for example, in an active matrix liquid crystal display device.

  While scanning the laser beam in which the cross section is elongated in one direction and the light intensity distribution in the cross section is uniform in the long direction in the direction orthogonal to the long direction of the beam cross section on the substrate surface, A laser annealing technique for irradiating a substrate is known. If the entire surface to be processed is not irradiated with laser once such scanning is performed, the substrate is moved in the longitudinal direction of the beam cross section so that the laser can be irradiated to the unirradiated region after the scanning is completed. Then, beam scanning is performed again in a direction orthogonal to the longitudinal direction of the beam cross section, and beam irradiation is performed on a region in contact with the region irradiated with the laser in the first scanning. By repeating such scanning as many times as necessary, the entire surface to be processed is irradiated with laser. However, it is difficult to improve the quality of the polycrystalline silicon film at the boundary between regions irradiated with laser in each scanning.

  The longer the length of the beam cross section on the substrate, the smaller the number of laser light scans required to irradiate the entire workpiece surface with laser (reducing the number of boundaries as described above). Is preferable. However, in order to perform the annealing process, the power density in the beam cross section must be equal to or higher than a threshold value. Increasing the power of the laser light applied to the work surface can make the beam cross section longer.

  For example, a beam homogenizer using an array lens is used in order to make the light intensity distribution in the cross section of the laser light irradiated to the surface to be processed uniform. This beam homogenizer divides incident laser light into a plurality of beams within the beam cross section by an array lens, and expands the divided beams with a focus lens and superimposes them on the cross section of the beam on the homogenization surface. The light intensity distribution inside is made uniform. For example, in the laser irradiation apparatus disclosed in Patent Document 1, such a beam homogenizer is used in order to uniformize the light intensity distribution of pulsed laser light emitted from an excimer laser light source.

  Patent Document 2 describes a laser irradiation apparatus including a diffractive optical element (DOE) as another apparatus for uniformizing the light intensity distribution. In this laser irradiation apparatus, the light intensity distribution is made uniform as follows. The incident beam is branched into a plurality of beams by the diffractive optical element, and each of the branched beams is collected by a condenser lens. The beam spots of the beams branched by the diffractive optical element are discretely arranged on the focal plane of the condenser lens. The image plane is set on a defocus plane out of the focus of the condenser lens. Since the beams branched by the diffractive optical element overlap each other on the defocus surface, the light intensity distribution on the defocus surface can be made uniform.

  Patent Document 3 has four solid-state laser light sources, and the laser light emitted from these laser light sources can be spatially superimposed to increase the power of the laser light irradiated onto the processing surface. A laser irradiation device is described. Hereinafter, this apparatus will be further described.

  The laser beams emitted from the first and second laser light sources are adjusted so that their polarization planes are orthogonal to each other, and then superimposed on the same optical axis by the first polarization beam splitter. The laser beams emitted from the third and fourth laser light sources are adjusted so that their polarization planes are orthogonal to each other, and then superimposed on the same optical axis by the second polarization beam splitter. The two laser beams emitted from the first and second polarizing beam splitters approach each other and travel in parallel.

  When both laser beams are incident on the telescope optical system and the beam diameter is enlarged, the cross sections of both laser beams almost overlap each other. The laser light thus spatially superimposed is incident on a beam homogenizer using an array lens, and the light intensity distribution in the cross section is made uniform. Laser light emitted from the beam homogenizer is irradiated onto the processing surface.

JP 9-36060 A JP 2003-114400 A JP 2002-176006 A

  A beam homogenizer using an array lens does not function well for laser light having high coherence (for example, laser light emitted from a solid-state laser light source such as a YAG laser). Due to the fact that the laser beams incident on the beam homogenizer and split in the beam cross section interfere with each other, a pattern with a strong and weak light intensity distribution is formed in the beam cross section on the homogenization surface.

  The laser irradiation apparatus described in Patent Document 3 requires a telescope optical system to spatially superimpose laser beams, and a beam homogenizer to make the light intensity distribution uniform. With a simpler configuration, laser beams emitted from multiple laser light sources can be spatially overlapped (that is, the same area on the processing surface can be irradiated with laser beams emitted from multiple laser light sources) If there is a laser irradiation apparatus that can uniformize the light intensity distribution in the beam cross section, it is preferable from the viewpoint of easy adjustment of the optical system. In the laser irradiation apparatus described in Patent Document 3, the light intensity distribution of the laser light emitted from the solid-state laser light source is uniformed by a beam homogenizer using an array lens. .

  An object of the present invention is to provide a laser irradiation apparatus that can achieve uniform light intensity distribution even when the coherence of laser light emitted from a laser light source is high.

  Another object of the present invention is to provide a laser irradiation apparatus capable of uniformizing the light intensity distribution in the beam cross section with a novel configuration.

  Another object of the present invention is to irradiate a laser beam emitted from a plurality of laser light sources to the same region on the processing surface with a simple configuration, and the light intensity within the beam cross section on the processing surface. It is an object of the present invention to provide a laser irradiation apparatus that can make the distribution uniform.

  Another object of the present invention is to provide a laser irradiation apparatus capable of irradiating laser light emitted from a plurality of laser light sources to the same region on a processing surface with a novel configuration.

According to one aspect of the present invention, a first laser light source that emits a first laser beam that is a continuous wave, a second laser light source that emits a second laser beam that is a continuous wave, and a diffractive optical element A laser beam emitted from only one laser light source is incident, and a beam cross section of the laser beam incident on the diffractive optical element has a shape that is long in the first direction on the imaging plane of the diffractive optical element. performs shaping to the light intensity distribution in the beam cross section at said imaging plane of the laser beam emitted from the diffraction optical element, with respect to the first direction, the laser light beam incident on the diffraction optical element A diffractive optical element designed to make the light intensity distribution uniform so as to approach a more uniform distribution than the light intensity distribution in the cross section, and the first and second light emitted from the first and second laser light sources. The laser light of the surface of the diffractive optical element To different positions of, and the cross-sectional surface on the optical axis parallel to each other is incident to have no overlap with each other, the first and second laser beam emitted from the diffraction optical element, the imaging A laser irradiation apparatus for irradiating the same region on the surface is provided.

Laser light emitted from the first and second laser light sources irradiates a common area on the imaging surface of the diffractive optical element . Thereby, the power in a light irradiation area | region can be raised. When the diffractive optical element makes the light intensity distribution uniform, the light intensity distribution is made uniform even if the coherence of the laser light source is high.

  First, a diffractive optical element used in a laser irradiation apparatus according to an embodiment of the present invention will be described. This diffractive optical element can be manufactured by forming a predetermined pattern consisting of fine steps (1 to several depths of recesses) on a substrate such as quartz using a photoetching process. The laser light incident on the diffractive optical element is diffracted by this fine step pattern and propagates as described below.

  Consider an XYZ orthogonal coordinate system having a Z axis parallel to the traveling direction of laser light incident on the diffractive optical element. The cross section of the incident laser beam is, for example, circular, and the light intensity distribution in the cross section is, for example, a Gaussian distribution. Laser light diffracted at various positions in the step pattern on the diffractive optical element propagates in the Z-axis direction so that it does not spread in the X-axis direction and spreads in the Y-axis direction. Overlapping in a light irradiation region that is elongated in the Y-axis direction and narrow in the X-axis direction on a virtual plane (this is called an imaging plane) that is a predetermined distance away from the element. The inside of the light irradiation region is irradiated with a substantially uniform light intensity in the longitudinal direction of the light irradiation region. In this way, the cross-sectional shape of the laser beam is shaped to be long on the imaging plane, and the light intensity distribution in the beam cross-section is made uniform in the long direction.

  By the way, the diffractive optical element is designed so that laser light emitted from one laser light source is incident thereon. For this reason, it is not assumed that laser light emitted from two or more laser light sources is simultaneously incident on one diffractive optical element and used, and it is known whether such use is possible. There wasn't. With an optical system such as a lens or mirror that uses light refraction or reflection, the behavior of outgoing light relative to incident light can be understood relatively easily. However, a diffractive optical element is an optical element that utilizes light diffraction, and it is not easy to understand the behavior of outgoing light with respect to incident light.

  If the laser beam emitted from two or more laser light sources is incident on one diffractive optical element at the same time, both laser beams cause unexpected interference with each other, and the diffractive optical element is desired. It is possible that the function is not performed.

  Next, an experiment in which laser beams emitted from two laser light sources are simultaneously incident on one diffractive optical element will be described with reference to FIGS. 1A and 1B are schematic views showing two types of optical systems used in the experiment. First, an experiment corresponding to FIG.

  The laser light sources 31a and 31b are YAG lasers that emit continuous wave laser light of the second harmonic (wavelength 532 nm). The coherence of the laser light emitted from the YAG laser light source is high. The laser light emitted from the laser light source 31 a is rotated on the plane of polarization by the half-wave plate 32 and is changed to S-polarized light with respect to the polarization beam splitter 34. The laser light emitted from the half-wave plate 32 is reflected by the folding mirror 33 and enters the polarization beam splitter 34. The laser light source 31 b emits P-polarized light with respect to the polarizing beam splitter 34, and the P-polarized light enters the polarizing beam splitter 34.

  The polarizing beam splitter 34 reflects the incident S-polarized light and transmits the incident P-polarized light, so that both laser beams emitted from the polarizing beam splitter 34 are superimposed on the same optical axis. Laser beams superimposed on the same optical axis enter a beam expander 35 that expands the beam diameter.

  Laser light emitted from the beam expander 35 enters the diffractive optical element 36. A beam cross section on the imaging surface 36 a of the diffractive optical element 36 is reduced and projected onto the imaging surface 37 a by the imaging lens 37. The light intensity distribution of the image on the image plane 37a (which corresponds to the light intensity distribution of the beam cross section on the image plane 36a of the diffractive optical element 36) is observed by the beam profiler 39 through the objective lens 38.

  The graph of FIG. 2A shows the observed light intensity distribution. The horizontal axis indicates the relative position corresponding to the position in the longitudinal direction of the beam cross section, and the vertical axis indicates the relative light intensity (light intensity expressed in arbitrary units). The light intensity is a value integrated in the short direction of the beam cross section (the width direction of the beam cross section).

  The graph L1 shows the light intensity distribution when the laser light emitted only from the laser light source 31a in FIG. 1A is incident on the diffractive optical element 36. The graph L2 shows the light intensity distribution when the laser light emitted only from the laser light source 31b is incident on the diffractive optical element. The graph La shows the light intensity distribution when the laser beams emitted from the laser light sources 31a and 31b are simultaneously incident on the diffractive optical element. A graph Lb shows a (calculated) light intensity distribution obtained by adding the values of the graphs L1 and L2.

  As can be seen from the graphs L1 and L2, when the laser light emitted from one laser light source is incident on the diffractive optical element 36, the light intensity is high at both ends in the longitudinal direction of the beam cross section, and from both ends to the inside. It decreases and becomes almost uniform inside except for both ends. As can be seen from the graph La, even when the laser beams of two laser light sources are simultaneously incident, the light intensity is high at both ends in the longitudinal direction of the beam cross section, decreases from both ends toward the inside, It becomes almost uniform inside. From this experiment, even when laser beams emitted from two laser light sources are simultaneously incident on the diffractive optical element, the beam section can be elongated and the light intensity distribution in the beam section can be made uniform. all right.

  The graph La substantially matches the graph Lb that is the sum of the light intensities of the graphs L1 and L2. This indicates that when the laser beams emitted from the two laser light sources are simultaneously incident on the diffractive optical element, the powers of the laser beams emitted from the respective laser light sources can be added with almost no loss.

  In the optical system shown in FIG. 1B, the optical axes of the laser beams emitted from the laser light sources 31 a and 31 b are made parallel by the polarization beam splitter 34. A difference from the optical system of FIG. 1A is that the optical axes of the two laser beams do not coincide.

  FIG. 1C is a front view showing the beam incident surface of the diffractive optical element 36. Since the optical axes of the two laser beams emitted from the polarization beam splitter 34 do not coincide with each other, the positions of the two beam sections LBa and LBb on the diffractive optical element 36 are different from each other. In this case, the total area of the beam cross section on the diffractive optical element 36 is wider than in the case where the optical axes of the two laser beams coincide. Therefore, as indicated by the hatched portion in the figure, the light at the edge of the beam cross-section may protrude from the beam incident surface of the diffractive optical element 36.

  As shown in FIG. 1B, if the aperture 40 is arranged between the beam expander 35 and the diffractive optical element 36, the edge of the cross section of the beam incident on the aperture 40 is shielded, and the diffractive optical element 36 The cross-section of the laser beam incident on can be reduced. As a result, the beam cross section can be kept within the beam incident surface of the diffractive optical element 36. With respect to the optical system of FIG. 1B, two experiments were conducted, with and without the aperture 40 being arranged.

  The graph of FIG. 2B shows the result when the aperture 40 is not arranged. The graph L1 shows the light intensity distribution when the laser light emitted only from the laser light source 31a of FIG. 1B is incident on the diffractive optical element 36. The graph L2 shows the light intensity distribution when the laser light emitted only from the laser light source 31b is incident on the diffractive optical element. The graph La shows the light intensity distribution when the laser beams emitted from the laser light sources 31a and 31b are simultaneously incident on the diffractive optical element. A graph Lb shows a (calculated) light intensity distribution obtained by adding the values of the graphs L1 and L2.

  As can be seen from the graphs L1 and L2, when laser light emitted from one laser light source is incident on the diffractive optical element 36, the light intensity is high at one end and from one end to the inside in the longitudinal direction of the beam cross section. It decreases toward the other end and becomes almost uniform. In the graphs L1 and L2, the light intensity at the opposite ends is high. As can be seen from the graph La, when the laser beams of two laser light sources are simultaneously incident, the light intensity is high at both ends in the longitudinal direction of the beam cross section, and decreases from both ends toward the inside. It becomes almost uniform inside. From this experiment, it has been found that when two parallel laser beams are incident on the diffractive optical element at the same time, the beam cross section can be elongated and the light intensity distribution in the beam cross section can be made uniform.

  The graph La substantially matches the graph Lb that is the sum of the light intensities of the graphs L1 and L2. This indicates that when the laser beams emitted from the two laser light sources are simultaneously incident on the diffractive optical element, the powers of the laser beams emitted from the respective laser light sources can be added with almost no loss.

  In this experiment, the beam cross sections of the two laser beams incident on the beam incident surface of the diffractive optical element 36 do not coincide with each other. However, on the imaging surface 36a of the diffractive optical element 36, the beam cross sections of the two laser beams coincide. That is, the diffractive optical element 36 irradiates the common region with the two laser beams. From this experiment, it was found that the diffractive optical element can be used for the synthesis of two laser beams. Even when three or more laser beams are incident, the diffractive optical element can be synthesized so as to irradiate a common region.

  The graph of FIG. 2C shows the result when the aperture 40 is arranged. The graph L1 shows the light intensity distribution when the laser light emitted only from the laser light source 31a of FIG. 1B is incident on the diffractive optical element 36. The graph L2 shows the light intensity distribution when the laser light emitted only from the laser light source 31b is incident on the diffractive optical element. The graph La shows the light intensity distribution when the laser beams emitted from the laser light sources 31a and 31b are simultaneously incident on the diffractive optical element. A graph Lb shows a (calculated) light intensity distribution obtained by adding the values of the graphs L1 and L2.

  The graph of FIG. 2C corresponds to a portion excluding both ends in the longitudinal direction of the graph of FIG. By arranging the aperture 40 in front of the diffractive optical element 7 (on the laser light source side), the light intensity can be made uniform so that there are few portions with high light intensity at the end.

  When the aperture 40 is not arranged, as described with reference to FIG. 1C, the light at the edge of the cross section of the laser light incident on the diffractive optical element 36 may protrude from the beam incident surface of the diffractive optical element 36. is there. The light travels as it is and is mixed with the laser light shaped by the diffractive optical element 36. By arranging the aperture 40, such a problem can be prevented.

  Next, a laser irradiation apparatus according to an embodiment of the present invention will be described with reference to FIG. This laser irradiation apparatus can be used, for example, for annealing a substrate on which an amorphous or polycrystalline silicon film is formed.

This laser irradiation apparatus has four laser light sources 1a to 1d that emit continuous wave laser light. When the annealing process is performed, the wavelength of the continuous wave laser beam is desirably a wavelength that is absorbed by the amorphous and polycrystalline silicon films, that is, an ultraviolet wavelength to a visible wavelength. As such laser light, for example, the fundamental wave or second harmonic of an Ar laser or Kr laser, the second harmonic or the third harmonic of an Nd: YAG laser, Nd: YVO ₄ laser, or Nd: YLF laser is used. be able to. Considering the output size and stability, it is desirable to use the second harmonic of an LD (laser diode) pumped Nd: YAG laser or an LD pumped Nd: YVO ₄ laser. The wavelength of the second harmonic of the Nd: YAG laser and the Nd: YVO ₄ laser is 532 nm.

  The laser light sources 1a and 1b, the half-wave plate 25a, the folding mirror 26a, and the polarization beam splitter 27a are respectively the laser light sources 31a and 31b, the half-wave plate 32, the folding mirror 33, and the polarization shown in FIG. It functions in the same manner as the beam splitter 34. Laser beams emitted from the laser light sources 1a and 1b are superimposed on the same optical axis by the polarization beam splitter 27a. The laser beam LB1 superimposed on the same optical axis by the polarization beam splitter 27a is reflected by the folding mirrors 28a and 28b and enters the shutter 2.

  The laser light sources 1d and 1c, the half-wave plate 25b, the folding mirror 26b, and the polarization beam splitter 27b are respectively the laser light sources 31a and 31b, the half-wave plate 32, the folding mirror 33, and the polarization shown in FIG. It functions in the same manner as the beam splitter 34. Laser beams emitted from the laser light sources 1c and 1d are superimposed on the same optical axis by the polarization beam splitter 27b. The laser beam LB2 superimposed on the same optical axis by the polarization beam splitter 27b enters the shutter 2. The optical axes of the laser beams LB1 and LB2 incident on the shutter 2 are parallel to each other.

  The shutter 2 is disposed in the optical path from the laser light sources 1a to 1d to the ND filter 3, and switches between a state in which the laser light enters the ND filter 3 and a state in which the laser light does not enter. The ND filter 3 changes the power of the laser light by continuously changing the transmittance. Even if the shutter 2 is not disposed, whether or not the laser light is incident on the ND filter 3 can be controlled by changing the outputs of the laser light sources 1a to 1d. However, if it does so, it will become difficult to ensure the stability of the output of each laser light source. Therefore, it is desirable to arrange the shutter 2.

  The laser beam that has passed through the ND filter 3 is incident on the shutter 4 disposed on the optical path from the ND filter 3 to the folding mirror 5. The shutter 4 switches between a state in which the laser light is incident on the folding mirror 5 and a state in which the laser light is not incident. The shutter 4 includes, for example, an acousto-optic modulator and a damper. The acousto-optic modulator can deflect the laser beam incident thereon by applying a predetermined high-frequency signal. When no high frequency signal is applied, the laser beam is not deflected. One of the laser light deflected by the acousto-optic modulator and the laser light not deflected is made incident on the folding mirror 5, and the other is made incident on the damper. By controlling the signal applied to the shutter 4, a laser beam having a desired irradiation time width (pulse width) can be cut out from the continuous wave laser beam at a desired timing and irradiated onto the workpiece.

  The laser beams LB1 and LB2 emitted from the shutter 4 and reflected by the folding mirror 5 are adjusted in beam cross-sectional size by a beam expander (or beam reducer) 6 and transmitted through an aperture 29. The aperture 29 has a light shielding region and an opening formed in the light shielding region, and makes the beam cross section of the laser light incident on the diffractive optical element 7 in a shape and size corresponding to the opening. Laser light emitted from the aperture 29 enters the diffractive optical element 7. Since the optical axes of the two laser beams are parallel, the incident positions of the laser beams LB1 and LB2 on the diffractive optical element 7 are different from each other. The diffractive optical element 7 shapes the cross section of the laser light to be long on the image plane 7a, and makes the light intensity distribution in the long direction in the beam cross section uniform. The laser light emitted from the four laser light sources 1a to 1d and transmitted through the diffractive optical element 7 irradiates the same region on the imaging surface 7a.

  A slit 8 is disposed on the image plane 7 a of the diffractive optical element 7. The slit 8 has a light shielding region and a rectangular opening formed therein. As described with reference to the graph in FIG. 2B, the light intensity distribution in the longitudinal direction within the beam cross section shaped by the diffractive optical element 7 is uniform, but the non-uniformity increases at both ends. Have The slit 8 shields light at both ends in the longitudinal direction of the beam cross section (the portion where the uniformity of the light intensity distribution is low), and the inside excluding both ends in the length direction of the beam cross section (the portion where the uniformity of the light intensity distribution is high) ) Only. If necessary, also in the short direction of the beam cross section, both ends of the beam cross section can be shielded from light and the inside other than both ends can be transmitted.

  The laser light transmitted through the opening of the slit 8 is converged by the imaging lens 10 and enters the substrate 11. An amorphous or polycrystalline silicon film is formed on the surface of the substrate 11. The imaging lens 10 is arranged at a position where the opening of the slit 8 forms an image on the surface of the substrate 11. Thereby, a laser beam is irradiated to a region similar to the opening of the slit 8 on the substrate surface. If the slit 8 is removed, the beam cross section shaped by the diffractive optical element 7 forms an image on the surface of the substrate 11.

  It is difficult to produce a diffractive optical element capable of condensing laser light in a range of several times the wavelength or less with the current photoetching technology (that is, the length in the short direction of the laser light that can be shaped by the diffractive optical element). (Beam cross-sectional width) has a lower limit). For example, when the wavelength of the laser beam is 532 nm, it is not easy to obtain a beam cross section having a width of about 5 μm or less using only the diffractive optical element. However, there is a case where it is desired to irradiate the object to be processed by making the width of the beam cross section narrower than that.

  By using the imaging lens 10, it becomes easy to reduce the width of the beam cross section on the substrate surface, as will be described below. The width of the beam cross section shaped by the diffractive optical element 7 and the width of the opening of the slit 8 are approximately the same. The imaging lens 10 can reduce and project the beam cross section (or the opening of the slit 8) on the imaging surface 7 a onto the surface of the substrate 11. For example, when it is desired to set the width of the beam cross section on the substrate surface to 3 μm, if the imaging lens 10 having a magnification of 5 is used, the width of the beam cross section on the imaging surface 7a may be about 15 μm. When the imaging lens 10 having a magnification of several times to several tens of times is used, the width of the beam cross section shaped by the diffractive optical element 7 may be several times to several tens of times the width of the beam cross section on the substrate surface. That's fine.

  Note that the substrate 11 may be arranged so that the processed surface is arranged on the imaging surface 7a as long as the width of the beam cross section can be reduced to a desired width only by the diffractive optical element 7. At this time, if a slit 8 that shields the edge of the beam cross section is necessary, it may be arranged so as to be close to the imaging plane 7a.

  The substrate 11 is held on an XY stage 12, and the XY stage 12 can move the substrate 11 in a two-dimensional direction parallel to the surface of the substrate 11. By moving the substrate 11 with the XY stage 12, the incident position of the laser beam on the substrate surface moves (the laser beam is scanned on the substrate surface). The amorphous or polycrystalline silicon film is annealed by scanning the laser beam in a direction orthogonal to the longitudinal direction of the beam cross section on the substrate surface.

  If necessary, an image rotator 9 is disposed in the optical path from the slit 8 to the imaging lens 10. By rotating the image rotator 9 about the optical axis of the laser beam, the beam cross section can be rotated within the surface of the substrate 11. As a result, the scanning direction of the laser light (the direction perpendicular to the longitudinal direction of the beam cross section) can be made to coincide with an arbitrary direction on the substrate surface.

  In the laser irradiation apparatus described above, the diffractive optical element 7 lengthens the cross section of the laser light and makes the light intensity distribution in the cross section uniform. Even when laser light having high coherence is used, the light intensity distribution is made uniform.

  In the laser irradiation apparatus described above, the diffractive optical element 7 can irradiate a plurality of laser beams incident on the diffractive optical element 7 onto a common region on the substrate surface, and further the laser irradiated on the substrate surface. The light intensity distribution in the light section can be made uniform. There is no need to separately arrange an optical system for irradiating a common area on the substrate surface with a plurality of laser beams and an optical system for homogenizing the light intensity distribution in the cross section of the laser beams. The configuration of the laser irradiation apparatus is simplified, and the adjustment of the optical system is facilitated.

  In the laser irradiation apparatus described above, the outputs of the laser beams emitted from the four laser light sources can be added together and irradiated onto the same region on the processing surface. Since the power irradiated onto the surface to be processed can be improved, the length of the cross section of the laser beam to be annealed can be extended. Note that the number of laser light sources may be reduced according to the power required for the annealing process (or the output per unit may be reduced).

  If, for example, the laser light source 1a, the half-wave plate 25a, the folding mirror 26a, and the polarization beam splitter 27a are removed from the laser irradiation apparatus of FIG. 3, a configuration example of the laser irradiation apparatus having three laser light sources 1b to 1d is obtained. . Further, if the laser light source 1b and the folding mirrors 28a and 28b are removed, a configuration example of a laser irradiation apparatus having two laser light sources is obtained. In this apparatus, the laser beams emitted from the two laser light sources 1c and 1d are superimposed on the same optical axis and enter the diffractive optical element 7.

  Further, if the laser light sources 1a and 1d, the half-wave plates 25a and 25b, the folding mirrors 26a and 26b, and the polarization beam splitters 27a and 27b are removed from the laser irradiation apparatus of FIG. 3, a laser irradiation apparatus having two laser light sources is obtained. This is another configuration example. In this apparatus, the laser beams emitted from the two laser light sources 1 b and 1 c travel along optical axes parallel to each other and enter the diffractive optical element 7.

  By the way, as will be described below, the light intensity distribution of the laser light on the surface of the substrate changes with variations in the divergence angle, the incident position, and the beam diameter of the laser light incident on the diffractive optical element.

  The output of the laser light source changes with time. When the output of the laser light source fluctuates, the divergence angle of the emitted laser light fluctuates (generally, the output decreases due to the deterioration of the laser light source over time, and the divergence angle increases due to the decrease in output). The position of the imaging plane of the diffractive optical element (the distance from the diffractive optical element to the imaging plane) varies depending on the divergence angle of the incident laser light. It is assumed that the distance from the diffractive optical element to the imaging lens and the distance from the imaging lens to the substrate surface are constant. If the position of the imaging surface of the diffractive optical element changes due to the change in the divergence angle, the surface on which the shaped beam cross-section is imaged by the imaging lens does not coincide with the substrate surface. A desired light intensity distribution cannot be obtained on the substrate surface. The distance between the position where the shaped beam section is imaged by the imaging lens and the substrate surface is called the defocus amount.

  FIG. 4A and FIG. 4B are graphs showing the results of a simulation examining the relationship between the defocus amount and the light intensity distribution on the substrate surface. The result when the defocus amount is changed by 100 μm is shown. In this simulation, laser light having a wavelength of 532 nm, a beam cross-sectional shape of a circle, and an intensity distribution in the beam cross-section having a Gaussian distribution was incident on the diffractive optical element. The conditions for the incident light are the same for the simulation described below with reference to FIGS.

  In both graphs, the horizontal axis indicates the defocus amount, and the vertical axis indicates the light intensity. The horizontal axis shows the case where the imaging surface is shifted to the side farther from the substrate surface when viewed from the diffractive optical element, and the negative side of the horizontal axis is imaged closer to the substrate surface when viewed from the diffractive optical element. The case where the surface has shifted is shown. A light intensity distribution corresponding to the defocus amount is shown at a position indicating each defocus amount. 4A shows the light intensity distribution in the long direction, and FIG. 4B shows the light intensity distribution in the short direction (width direction of the beam cross section).

  As can be seen from FIGS. 4A and 4B, when no defocus occurs (when the defocus amount is zero), the light intensity is uniform in the long direction and the width in the short direction is narrow. Distribution is obtained. When defocusing occurs (when the magnitude of the defocus amount is 100 μm or more), the light intensity on the substrate surface rapidly decreases. In addition, the distribution shape changes due to defocusing, for example, the width of the beam cross section becomes thick.

  The direction of laser light emitted from the laser light source varies within a certain range (pointing stability). As a result, the incident position of the laser light incident on the diffractive optical element 7 varies. When the incident position of the laser light incident on the diffractive optical element varies, the light intensity distribution of the beam cross section on the imaging plane of the diffractive optical element changes.

  FIG. 5 shows the longitudinal direction of the beam cross section on the imaging surface of the diffractive optical element when the incident position of the laser beam is deviated from the predetermined position by a certain distance (30 μm) within the incident surface on the diffractive optical element. It is a graph which shows the result of the simulation which investigated what kind of shape the light intensity distribution of became. The horizontal axis indicates the relative position corresponding to the position in the longitudinal direction of the beam cross section, and the vertical axis indicates the relative light intensity (light intensity expressed in arbitrary units). The diffractive optical element is designed so that the light intensity on the imaging surface of the diffractive optical element is constant from one end to the other end of the beam cross-section when the laser light is incident on a predetermined position (this result is shown in FIG. Not shown).

  As can be seen from FIG. 5, when the incident position is deviated, the light intensity gradually increases from one end (right end in the figure) to the other end (left end in the figure) of the beam cross section. Thus, when the incident position of the laser beam on the diffractive optical element varies, the light intensity distribution on the imaging surface changes.

  The output of the laser light source changes with time. When the output of the laser light source fluctuates, the size of the beam cross section of the emitted laser light fluctuates (generally, the output decreases due to the deterioration of the laser light source with time, and the beam diameter decreases due to the decrease in output). The light intensity distribution of the beam cross section on the imaging surface of the diffractive optical element also changes when the size of the beam cross section of the laser light incident on the diffractive optical element changes.

  FIGS. 6A and 6B show a long beam cross section on the imaging plane of the diffractive optical element when the size of the cross section of the incident light on the diffractive optical element varies from a predetermined size. It is a graph which shows the result of the simulation investigated about how the light intensity distribution of a direction changes. In both graphs, the horizontal axis indicates the relative position corresponding to the position in the longitudinal direction of the beam cross section, and the vertical axis indicates the relative light intensity (light intensity expressed in arbitrary units).

  When the incident beam diameter is 2 mm, the diffractive optical element is designed so that the light intensity on the imaging surface of the diffractive optical element is constant from one end to the other end of the beam cross section (this result is not shown). ). 6A shows the light intensity distribution when the incident beam diameter is 1.9 mm, and FIG. 6B shows the light intensity distribution when the incident beam diameter is 2.1 mm.

  As can be seen from FIGS. 6A and 6B, when the incident beam diameter becomes thinner than the design value, the light intensity at the center of the beam cross section relatively increases (distribution becomes convex). When the incident beam diameter is thicker than the design value, the light intensity at the center of the beam cross section is relatively lowered (the distribution becomes concave). As described above, when the size of the cross section of the laser light incident on the diffractive optical element changes, the light intensity distribution on the imaging surface changes.

  Next, referring to FIG. 7, the laser irradiation apparatus capable of suppressing the change in the light intensity distribution accompanying the fluctuation of the divergence angle, the incident position, and the beam diameter of the laser light incident on the diffractive optical element as described above. Will be described.

  The laser irradiation apparatus shown in FIG. 7A has a configuration in which optical devices 15a to 15d capable of adjusting the spread angle are added to the laser irradiation apparatus shown in FIG. The optical devices 15a to 15d are arranged so that the laser beams emitted from the laser light sources 1a to 1d are incident on the optical devices 15a to 15d, respectively. Each optical device 15a-15d has an equivalent function.

  FIG. 7B shows a configuration example of the optical device 15b as an example. The laser light emitted from the laser light source 1b passes through the concave lens 16a and the convex lens 16b, and its beam diameter is enlarged to be (almost) parallel light. The convex lens 16 is held by a lens moving mechanism 16c including, for example, a voice coil mechanism. The lens moving mechanism 16c displaces the convex lens 16b in a direction parallel to the optical axis of the laser light, thereby adjusting the beam diameter enlargement ratio. The control device 16i controls the lens moving mechanism 16c.

  When the beam diameter is enlarged by the concave lens 16a and the convex lens 16b, the divergence angle of the laser light is reduced. For example, when the beam diameter is expanded by a factor of 2, the divergence angle becomes ½ compared to that before the beam diameter expansion. By adjusting the expansion ratio of the beam diameter, the divergence angle of the laser light after the beam diameter expansion can be adjusted.

  The laser beam emitted from the convex lens 16b is incident on the partial reflection mirror 16d. The partial reflection mirror 16d transmits most of the incident light (for example, 99%) and reflects the remaining (for example, 1%). The laser light transmitted through the partial reflection mirror 16d enters the polarization beam splitter 27a, and the laser light reflected by the partial reflection mirror 16d passes through the aperture 16e and enters the lens 16f and is converged. The partial reflection mirror 16d reflects most of the incident light and transmits the remaining light, so that the reflected light is incident on the polarization beam splitter 27a and the transmitted light is incident on the lens 16f via the aperture 16e. I do not care.

  The diameter of the laser beam incident on the lens 16f is defined by the aperture 16e. The laser beam that has passed through the lens 16f passes through the filter 16g that attenuates the power of the laser beam and enters the CCD camera 16h. The CCD camera 16h is disposed at a position where the beam diameter of the laser beam converged by the lens 16f is the smallest (beam waist position). The filter 16g can prevent excessively high power laser light from entering the CCD camera 16h.

Data of an image captured by the CCD camera 16h is sent to the control device 16i. This image data corresponds to the light intensity distribution in the cross section of the laser light incident on the CCD camera 16h. The control device 16i obtains the cross-sectional thickness of the laser light from this image data. The cross-sectional thickness of the laser beam can be defined by, for example, the full width at half maximum of the light intensity distribution or a width in a range where the intensity is 1 / e ² times or more of the peak intensity (e is the base of natural logarithm). In accordance with the principle described below, the divergence angle of the laser beam can be obtained based on the thickness of the beam cross section detected using the CCD camera 16h.

With reference to FIG. 8, the relationship between the thickness of the laser light transmitted through the lens 16f and the divergence angle will be described. The focal length on the laser beam incident side (left side in the figure) of the lens 16f and the focal length on the laser beam emission side (right side in the figure) are both f. The distance from the focal position on the incident side to the beam waist of the incident light (position where the beam diameter becomes the smallest) is z, and the distance from the focal position on the emission side to the beam waist of the emitted light is z _a . The radius of the incident light at the beam waist is W ₀ , and the radius of the emitted light at the beam waist is W.

  When the wavelength of the laser beam is λ and the circumference is π,

と表され、

And

と表される。

It is expressed.

と表される（定義される）。 The spread angle θ of the laser beam is

Expressed (defined).

と表される。 Substituting equation (3) into equation (1),

It is expressed.

  From equation (4), it can be seen that the larger the divergence angle θ, the smaller the denominator of the right side of equation (4), and the larger the radius W at the beam waist of the emitted light. By measuring the radius W with the CCD camera 16h in FIG. 7B, the divergence angle θ can be obtained based on the equation (4).

  When the divergence angle of the laser light changes (when the thickness of the laser light observed by the CCD camera 16h changes), the position of the imaging surface 7a of the diffractive optical element 7 is shifted as described above. When the divergence angle of the laser beam varies from a predetermined value, the control device 16i operates the lens moving mechanism 16c so as to cancel the variation of the divergence angle. Thereby, it is possible to prevent the position of the image plane 7a of the diffractive optical element 7 from being shifted due to the fluctuation of the spread angle of the laser light. In the above description, the divergence angle of the laser beam is adjusted by displacing the convex lens 16b by the lens moving mechanism 16c. However, the divergence angle may be adjusted by other methods.

  Returning to FIG. 7A, the description will be continued. The laser beams emitted from the laser light sources 1a to 1d pass through the optical devices 15a to 15d, respectively, and two lasers are used by the polarization beam splitters 27a and 27b in the same manner as described for the laser irradiation device of FIG. After being combined into light and passing through the shutter 2 and the like, the light enters the aperture 29.

  As described with reference to FIG. 3, the laser light transmitted through the aperture 29 enters the diffractive optical element 7. If the aperture 29 is disposed close to the diffractive optical element 7 (for example, within 10 mm), the laser light is incident on the diffractive optical element 7 at the position where the aperture 29 is disposed, and the irradiation region is the aperture. It can be made to be almost congruent with 29 openings. The closer the distance between the aperture 29 and the diffractive optical element 7 is, the better.

  The aperture of the aperture 29 has a shape and a size corresponding to a predetermined region where the laser on the surface of the diffractive optical element 7 is desired to enter. The cross section of the laser light incident on the aperture 29 is made larger than the opening. Laser light outside the predetermined area is shielded, and the laser light enters the predetermined area. As shown in FIG. 1C, when two laser beams whose beam cross sections are not in contact with each other are incident on the surface of the diffractive optical element 7, an aperture may be provided for each laser beam.

  In this way, even if the direction of the laser light emitted from the laser light sources 1a to 1d fluctuates or the size of the cross section of the laser light emitted from the laser light sources 1a to 1d fluctuates, the diffractive optical element 7 The laser beam can be incident on the predetermined region.

  As described above, the laser irradiation apparatus shown in FIG. 7A has the light intensity on the substrate surface due to the divergence angle, the incident position, and the beam diameter of the laser light incident on the diffractive optical element 7. It can suppress that distribution changes.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

FIG. 1A is a schematic diagram showing one optical system used in an experiment in which laser beams emitted from two laser light sources are incident on a diffractive optical element, and FIG. It is the schematic which shows the other optical system used for the experiment which makes the laser beam radiate | emitted from the laser beam source of a stand enter, FIG.1 (C) is a front view of a diffractive optical element. 2A is a graph of a light intensity distribution showing experimental results corresponding to the experimental optical system of FIG. 1A, and FIG. 2B is an aperture in the experimental optical system of FIG. 1B. FIG. 2C is a light intensity distribution graph showing experimental results corresponding to the case where the aperture is not arranged, and FIG. 2C is a light intensity distribution showing experimental results corresponding to the case where the aperture is arranged in the experimental optical system of FIG. It is a graph of. It is the schematic which shows the laser irradiation apparatus by the Example of this invention. FIG. 4A is a graph showing a simulation result (intensity distribution in the longitudinal direction of the beam cross section) for examining how the light intensity distribution on the substrate surface changes due to defocusing. B) is a graph showing simulation results (intensity distribution in the short direction of the beam cross section) for examining how the light intensity distribution on the substrate surface changes due to defocusing. It is a graph which shows the simulation result investigated about how the light intensity distribution on the image plane of a diffractive optical element changes with the fluctuation | variation of the incident position of the laser beam which injects into a diffractive optical element. FIG. 6A shows a simulation result of examining how the light intensity distribution on the imaging surface of the diffractive optical element changes due to the change in the beam diameter of the laser light incident on the diffractive optical element (the beam diameter is FIG. 6B is a graph showing how the light intensity distribution on the imaging surface of the diffractive optical element changes due to the variation of the beam diameter of the laser light incident on the diffractive optical element. It is a graph which shows the simulation result (when a beam diameter becomes thick) investigated about whether to do. FIG. 7A is a schematic diagram illustrating a laser irradiation apparatus according to a modification, and FIG. 7B is a schematic diagram illustrating a configuration example of an optical apparatus (which can adjust the divergence angle). It is a figure for demonstrating the relationship between the thickness of the laser beam which permeate | transmits a lens, and a divergence angle.

Explanation of symbols

1, 1a, 1b, 1c, 1d Laser light source 2 Shutter 3 ND filter 4 Shutter 5 Folding mirror 6 Beam expander 7 Diffraction optical element 7a (Diffraction optical element) Imaging surface 8 Slit 9 Image rotator 10 Imaging lens 11 Substrate 12 XY stages 15a, 15b, 15c, 15d (adjustable divergence angle) optical devices 25a, 25b half-wave plates 26a, 26b, 28a, 28b folding mirrors 27a, 27b polarization beam splitter 29 aperture

Claims (5)

A first laser light source that emits a first laser beam that is a continuous wave;
A second laser light source that emits a second laser light that is a continuous wave;
A diffractive optical element, in which laser light emitted from only one laser light source is incident, and a beam cross section of the laser light incident on the diffractive optical element is expressed in a first direction on the imaging surface of the diffractive optical element A laser that is shaped into a long shape, and the light intensity distribution in the beam cross section at the imaging plane of the laser light emitted from the diffractive optical element is incident on the diffractive optical element in the first direction. A diffractive optical element designed to homogenize a light intensity distribution that is closer to a more uniform distribution than a light intensity distribution in a beam cross-section of light;
The first and second laser beams emitted from the first and second laser light sources are arranged at mutually different positions on the surface of the diffractive optical element so that the optical axes are parallel to each other and the cross sections do not overlap each other. A laser irradiation apparatus that irradiates the same region on the imaging surface with the first and second laser beams incident on the diffractive optical element and emitted from the diffractive optical element. further,
A holding table for holding the workpiece;
2. The laser irradiation according to claim 1, further comprising: a lens disposed at a position capable of reducing and projecting a beam cross section on the imaging plane of the diffractive optical element onto the surface of the object to be processed held on the holding table. apparatus. Further, other than the specific region, the laser beam is arranged in an optical path between the first and second laser light sources and the diffractive optical element so that the laser beam is incident on the specific region on the surface of the diffractive optical element. The laser irradiation apparatus of Claim 1 or 2 which has a light-shielding apparatus which light-shields the laser beam of. further,
A divergence angle adjusting device that changes a divergence angle of laser light emitted from the first or second laser light source based on a control signal input from the outside;
A detector capable of detecting the divergence angle of the laser beam emitted from the divergence angle adjusting device;
Based on the divergence angle detected by the detector, when the divergence angle deviates from a predetermined value, the control device controls the divergence angle adjusting device so as to reduce the deviation. the divergence angle adjusting device the laser light emitted from the laser irradiation apparatus according to any one of claims 1 to 3, incident on the diffractive optical element. It said first and second laser light sources, laser irradiation apparatus according to any one of claims 1 to 4, which is a solid-state laser oscillator.

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