JP2006049635A - Method and apparatus for laser irradiation and method for laser annealing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser irradiation method capable of bringing the distribution of exposure quantity in a light irradiation area in which interference stripes are generated near to uniform distribution during the irradiation period of one shot of a pulse laser. <P>SOLUTION: One shot of a pulse laser beam is made incident on an optical system for irradiating a common light irradiation area with components passed through mutually different areas in the cross section of the incident laser beam. In the period of incidence, the components passed through the mutually different areas in the cross section of the pulse laser beam made incident on the optical system interfere with each other in the light irradiation area, generating interference stripes. In the repeated direction of the interference stripes, the interference stripes are moved only by a distance corresponding to the period of the interference stripes or more to perform laser irradiation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser irradiation method, a laser irradiation apparatus, and a laser annealing method, and in particular, a component that passes through different regions in a cross section of a laser beam is superimposed on a common light irradiation region, and laser is irradiated onto a laser irradiation object. The present invention relates to a laser irradiation method for irradiating a beam, a laser irradiation apparatus, and a laser annealing method.

  Laser beams are used for various processes. If the light intensity distribution in the light irradiation region is made uniform, the processing uniformity in the light irradiation region can be improved. In order to make the light intensity distribution close to uniform, for example, a homogenizer having an array lens is used. This homogenizer divides a laser beam into a plurality of components in a cross section by an array lens, and superimposes the divided components on a common light irradiation region by a condenser lens. Within this light irradiation region, the light intensity distribution is made close to uniform.

  Patent Document 1 discloses an exposure apparatus using such a homogenizer. This exposure apparatus is used for manufacturing a semiconductor device. The exposure apparatus will be described in detail below. A pulsed laser beam emitted from a laser light source, which is an excimer laser, passes through an expander, etc., is reflected by a swayable scanning mirror, and then enters an array lens to be divided into a plurality of components within the beam cross section. Is done. Each component emitted from the array lens passes through the two condensing lenses and is superimposed on a common area on the surface of the reticle on which the circuit pattern is formed. The laser beam that has passed through the reticle passes through the projection lens and is irradiated onto the wafer. In this way, the circuit pattern is transferred to the wafer. In order to transfer the circuit pattern to the wafer, the reticle is irradiated with a plurality of shot pulse laser beams.

  In the light irradiation area on the surface of the reticle, the components divided by the array lens overlap. Since the excimer laser beam has coherence, components divided by the array lens interfere with each other, and interference fringes are generated in the light irradiation region. When the interference fringes are generated, the uniformity of the light intensity distribution in the light irradiation region is lowered.

  Patent Document 1 discloses a method capable of compensating for a decrease in uniformity of light intensity distribution caused by interference fringes as described below. Assume that the array lens divides the laser beam into n in one direction in the cross section of the laser beam, and the n-divided components overlap to generate interference fringes. While moving the interference fringes on the surface of the reticle by 1 / n of the period of the interference fringes in the repetition direction of the interference fringes, an n-shot pulse laser is irradiated. That is, the n-shot pulse laser is irradiated so that the position of the interference fringes at the time of irradiation of each shot is shifted by 1 / n of the period of the interference fringes in the repetition direction of the interference fringes. On the reticle surface, the light intensity distribution of one shot is accumulated for n shots within the irradiation period of n shots, whereby the exposure dose distribution becomes uniform. The interference fringes are moved by swinging the scanning mirror.

  The laser beam is used for, for example, a laser annealing process for growing silicon crystal grains in addition to the wafer exposure process. For example, Patent Document 2 describes a laser irradiation apparatus that can perform laser annealing.

JP-A-8-330225 JP 2003-59859 A

  A homogenizer using an array lens is also used in laser annealing. When used for laser annealing, the homogenizer shapes the cross section of the laser beam into a shape that is long in one direction, and at least makes the light intensity distribution in the long direction in the cross section uniform. For example, a laser annealing process is performed on a substrate having an amorphous or polycrystalline silicon film formed on the surface as described below.

  While moving the light irradiation region on the substrate surface in the direction perpendicular to the longitudinal direction of the light irradiation region within the surface of the substrate, the irradiation with the pulse laser beam is repeated. The moving speed of the light irradiation region with respect to the substrate is set such that the light irradiation region irradiated with one shot of the pulse laser and the light irradiation region irradiated with the next one shot partially overlap each other. In this way, laser annealing is performed on the entire surface to be processed.

  A solid-state laser may be used as a laser light source used for laser annealing. Solid-state lasers have higher coherence than excimer lasers and the like. For this reason, when the laser beam emitted from the solid-state laser is incident on the homogenizer, it is difficult to make the light intensity distribution in the light irradiation region uniform.

  When interference fringes are generated in the light irradiation region irradiated with the laser beam emitted from the homogenizer, the laser annealing process has a different problem from the wafer exposure process. As described above, in the exposure process, the distribution of the exposure amount on the reticle surface may be made uniform within a period in which the reticle is irradiated with a plurality of shots. However, in the laser annealing process, the silicon film is melted and crystallized for each shot. For this reason, it is necessary to make the distribution of the exposure amount in the light irradiation region close to uniform during the irradiation period of one shot of the pulse laser. If the uniformity of the exposure dose distribution in the light irradiation region is low, the uniformity of the quality of the silicon film in which crystal grains are grown by laser irradiation cannot be improved.

  One object of the present invention is to use a laser irradiation method capable of making the exposure dose distribution within a light irradiation region where interference fringes are generated uniform even during the irradiation period of one shot of a pulse laser, and the method thereof. It is providing the laser irradiation apparatus which can be performed.

  Another object of the present invention is to provide a laser annealing method that does not deteriorate the uniformity of the quality of a silicon film even when a laser beam having interference fringes in the cross section is irradiated.

  According to one aspect of the present invention, a period during which one shot of a pulsed laser beam is incident on an optical system that irradiates a common light irradiation region with components that pass through different regions in the cross section of the incident laser beam. The interference fringes generated by the interference between the components that have passed through different regions in the cross section of the pulse laser beam incident on the optical system in the light irradiation region are represented by the period of the interference fringes with respect to the repetition direction of the interference fringes. A laser irradiation method for moving the above distance is provided.

  According to another aspect of the present invention, an array lens that divides a laser beam in a beam cross section and a condensing lens that irradiates each component of the laser beam divided by the array lens to a common region are configured. During the period in which one shot of the pulse laser beam is incident on the homogenizer, the interference fringes generated by the interference of each component of the laser beam divided by the array lens on the homogenization surface of the homogenizer A laser irradiation method for moving an incident direction of a pulsed laser beam incident on a homogenizer with respect to a repetition direction of the interference fringes, wherein a plurality of lenses constituting an array lens of the homogenizer are arranged in a first direction. And the width of each of the lenses in the first direction is h, and the pulse width of the pulsed laser beam is When the wavelength of the pulse laser beam is λ, the component of the angular velocity at which the incident direction of the pulse laser beam incident on the homogenizer is swung is equal to or greater than λ / (th). There is provided a laser irradiation method in which the incident direction of a pulsed laser beam incident on the homogenizer is changed.

  During the irradiation period of one shot of the pulsed laser, the distribution of the exposure amount irradiated in the light irradiation region approaches uniformly. If the laser irradiation method according to one aspect or the other aspect of the present invention is used for, for example, a laser annealing process for growing silicon crystal grains, the quality of the silicon film on which the crystal grains have grown by pulse laser beam irradiation can be made uniform. .

  FIG. 1 schematically shows a laser irradiation apparatus according to an embodiment of the present invention. Hereinafter, description will be given by taking as an example a case where this laser irradiation apparatus is used for laser annealing for growing crystal grains of a silicon film formed on a substrate surface.

  The laser light source 1 emits a pulse laser beam. When laser annealing is performed, the wavelength of the laser beam is preferably in the range of 340 nm to 900 nm. The laser light source 1 is, for example, a solid laser including a harmonic generation unit. The control device 3 controls the laser light source 1 so that the pulse laser beam is emitted at a desired pulse period. The laser beam emitted from the laser light source 1 is incident on the beam scanner 2 that swings the traveling direction of the laser beam in at least a one-dimensional direction. For example, an electro-optic deflector or a polygon mirror can be used as the beam scanner 2. The control device 3 controls the beam scanner 2 so that the traveling direction of the laser beam is swung in a desired direction at a desired timing.

  The laser beam emitted from the beam scanner 2 enters the homogenizer 4. The homogenizer 4 includes an array lens 4a that divides an incident laser beam into a plurality of components within the beam cross section, and a condenser lens 4b that irradiates a component divided by the array lens 4a to a common region. The The homogenizer 4 shapes the cross-sectional shape of the laser beam into a shape that is long in one direction on the homogenized surface.

  The laser beam emitted from the homogenizer 4 is reflected by the folding mirror 5 and irradiated onto the substrate 6 on the surface of which an amorphous or polycrystalline silicon film is formed. The surface of the substrate 6 is disposed on the homogenization surface of the homogenizer 4. The XY stage 7 holds the substrate 6. The XY stage 7 can move the substrate 6 in a two-dimensional direction parallel to the surface of the substrate 6.

  The irradiation of the pulse laser beam is repeated while moving the substrate 6 so that the light irradiation region irradiated with one shot of the pulse laser moves on the substrate in a direction perpendicular to the longitudinal direction. The moving speed of the substrate 6 is set such that the light irradiation region irradiated with one shot of the pulse laser and the light irradiation region irradiated with the next one shot partially overlap each other. In this way, laser annealing is performed on the entire surface to be processed.

  During the period in which each shot of the pulse laser is irradiated onto the substrate 6, the beam scanner 2 swings the traveling direction of the laser beam, so that the light irradiation region on the substrate becomes a minute distance in the longitudinal direction (for example, several tens of μm). ) Just move.

  Next, the homogenizer 4 will be further described with reference to FIGS. 2 (A) and 2 (B). When the beam scanner does not swing the traveling direction of the laser beam (when the laser beam is not deflected), the traveling direction of the laser beam incident on the homogenizer 4 is the Z-axis positive direction, and the beam scanner swings the traveling direction of the laser beam. Consider an XYZ orthogonal coordinate system whose direction is the Y-axis direction (the beam scanner moves the laser beam in a direction parallel to the YZ plane). 2A and 2B are a schematic view of the path of the laser beam passing through the homogenizer 4 as viewed with a line of sight parallel to the X axis and a schematic view as viewed from a line of sight parallel to the Y axis, respectively. is there.

  As shown in FIG. 2A, the array lens 4a includes seven equivalent lenses 4aa to 4ag. The lenses 4aa to 4ag are columnar elongated in the X-axis direction, and the lenses 4aa to 4ag are arranged in the Y-axis direction. The widths of the lenses 4aa to 4ag in the Y-axis direction are h.

  A laser beam is incident on the array lens 4a from the negative side of the Z axis (left side in the figure). The light intensity distribution in the cross section of the incident laser beam is approximated by, for example, a Gaussian distribution. The relative position of the laser beam and the array lens 4a is adjusted so that the central portion of the beam cross section passes through the lens 4ad disposed at the center of the array lens 4a.

  In the figure, only the path of the component incident on the lens 4ad disposed at the center of the array lens 4a and the lenses 4aa and 4ag disposed at both ends is shown as a representative. A path when the beam scanner does not deflect the laser beam is indicated by a solid line, and a path when the beam scanner deflects the laser beam by an angle θ with respect to the Z axis is indicated by a dotted line.

  Each of the lenses 4aa to 4ag converges the incident component in the YZ plane. As a result, the laser beam incident on the array lens 4a is divided into seven convergent beam bundles corresponding to the lenses 4aa to 4ag. In the XZ plane, the lenses 4aa to 4ag do not affect the convergence and divergence of the incident component.

  The seven convergent light bundles emitted from the array lens 4a minimize the width in the Y-axis direction in front of the condenser lens 4b. This position is closer to the lens than the incident side focal point of the condenser lens 4b. For this reason, the seven light fluxes transmitted through the condenser lens 4b become divergent light fluxes in the YZ plane. Seven divergent light bundles that have passed through the condenser lens 4b overlap on the homogenizing surface 4c. The homogenizing surface 4c is defined at the position of the rear focal point of the condenser lens 4b. In the laser irradiation apparatus shown in FIG. 1, the length of the optical path from the condenser lens 4b of the homogenizer 4 to the surface of the substrate 6 through the folding mirror 5 is the rear side (on the image space side) of the condenser lens 4b. The focal length f is adjusted. Thereby, the substrate surface is arranged on the homogenized surface.

  The homogenizer 4 also has an array lens 4d that converges the laser beam in the XZ plane. The array lens 4d does not affect the convergence and divergence of the laser beam in the YZ plane.

  As shown in FIG. 2B, the array lens 4d is composed of seven columnar lenses elongated in the Y-axis direction and arranged in front of the condenser lens 4b (on the laser light source side). Is done. The laser beam incident on the homogenizer 4 is divided into seven convergent beam bundles corresponding to the lenses constituting the array lens 4d. In the figure, only the light beams at the center and both ends are shown as representatives. Each of these convergent light bundles becomes a divergent light bundle after entering the condenser lens 4b as a divergent light bundle after minimizing the width in the X-axis direction in front of the incident side focal point of the condenser lens 4b. The beam bundles that have passed through the condenser lens 4b become convergent beam bundles. These convergent light bundles transmitted through the condenser lens 4b overlap on the homogenizing surface 4c.

  The length Ly in the Y-axis direction of the light irradiation region on the homogenized surface 4c is the width h of each lens of the array lens 4a in the Y-axis direction, the focal length fa of each lens of the array lens 4a, and the focal length of the condenser lens 4b. Using f,

The length Lx in the X-axis direction of the light irradiation region on the homogenized surface 4c is the width hd in the X-axis direction of each lens of the array lens 4d, the focal length fd of each lens of the array lens 4d, and the condenser lens Using the focal length f of 4b,

It is expressed.

  H, fa, hd, and fd are set so that the light irradiation region of the homogenized surface 4c has a long and narrow shape in the Y-axis direction (Ly is long) and narrow in the X-axis direction (Lx is short). In this way, the homogenizer 4 shapes the beam cross section into a shape that is long in one direction.

  The light intensity distribution in the Y-axis direction in the light irradiation region on the homogenized surface 4c is expanded in the Y-axis direction so that the light intensity distributions of the components incident on the lenses 4aa to 4ag respectively correspond to the light irradiation regions. The distribution is overlaid.

  The lenses 4aa and 4ag, the lenses 4ab and 4af, and the lenses 4ac and 4ae are arranged at an equal distance from the lens 4ad through which the central portion of the cross section of the incident light passes. As a result, the light intensity distributions of the light bundles incident on the lenses 4aa and 4ag have a relationship reversed with respect to the Y-axis direction, and the light intensity distributions of the light bundles incident on the lenses 4ab and 4af, respectively, The light intensity distributions of the light bundles incident on the lenses 4ac and 4ae are reversed with respect to the Y-axis direction. When the light intensity distributions of these light bundles overlap, the light intensity distribution in the Y-axis direction in the light irradiation region on the homogenized surface 4c approaches uniformly.

  Note that the light intensity distribution in the X-axis direction in the light irradiation region on the homogenized surface 4c is also made uniform by the action of the array lens 4d and the condensing lens 4b for converging the laser beam on the XZ plane.

  As described above, the homogenizer 4 makes the light intensity distribution in the light irradiation region uniform, but the uniformity of the light intensity distribution is lowered as described below due to the coherence of the laser beam. In the light irradiation region on the homogenization surface 4c, components that have passed through different regions in the cross section of the laser beam incident on the homogenizer 4 overlap. Due to the coherence of the laser beam, when the components that have passed through different regions in the cross section of the laser beam interfere with each other, interference fringes are generated in the light irradiation region. When interference fringes are generated, the intensity in the light irradiation region fluctuates in a vibrational manner.

  FIG. 3 shows that a laser beam having a particularly high coherence (for example, a laser beam emitted from a YAG laser having a particularly high coherence among solid-state lasers (for example, a second harmonic of a YAG laser)) is incident on the homogenizer 4. Of the light intensity distribution indicating interference fringes (interference fringes in which the repeating direction coincides with the long direction) generated in the long direction of the light irradiation region (Y-axis direction in FIG. 2A) on the homogenized surface. It is a graph. The horizontal axis of the graph indicates the (relative) position in the longitudinal direction in the light irradiation region expressed in μm units, and the vertical axis indicates the intensity expressed in arbitrary units. The intensity increases and decreases with a period of 20 μm.

  A component that passes through a certain region in the cross section of the laser beam easily interferes with a component that passes through a region relatively close to that region, and hardly interferes with a component that passes through a region relatively far from that region. For example, the component that passes through the lens 4aa shown in FIG. 2A is most likely to interfere with the component that passes through the lens 4ab that is the lens closest to the lens 4aa. Compared with that, it is hard to interfere with the component which permeate | transmits the lens 4ac which adjoins the lens 4aa and the lens 4ab.

  In the light irradiation region on the homogenized surface 4c, the interference fringes formed by components transmitted through the lenses closest to each other among the lenses 4aa to 4ag, and the adjacent lenses with one lens among the lenses 4aa to 4ag are transmitted. Interference fringes and the like formed by the components overlapped. Considering the amplitude of the intensity of each interference fringe, the amplitude of the interference fringe formed by the components transmitted through the lenses closest to each other among the lenses 4aa to 4ag is the largest.

  The period p of interference fringes formed by components that have passed through the lenses that are closest to each other (that is, the interval between the positions where the intensity reaches a peak) is defined as h in the Y-axis direction of the lenses 4aa to 4ag, and the condenser lens 4b. When the focal length on the rear side (image space side) is f and the wavelength of the laser beam is λ,

と表される。

It is expressed.

  The denominator on the right side of Equation (1) indicates the distance between the centers of adjacent lenses in the Y-axis direction. For example, the period of interference fringes formed by components transmitted through adjacent lenses across one lens can be obtained by substituting 2h that is twice h for the denominator of the right side of Equation (1). This period is half of the period of interference fringes formed by components transmitted through the closest lens. Thus, the longer the distance between the lenses through which the components that interfere with each other are transmitted, the shorter the period of the interference fringes.

  The interference fringes in the light irradiation region on the homogenized surface are formed by overlapping a plurality of interference fringes having different periods and different peak intensities. For this reason, as shown in FIG. 3, the intensity distribution of the interference fringes in the light irradiation region has a complicated shape. Among the individual interference fringes to be superimposed, the interference fringes formed by the components transmitted through the lenses closest to each other have the longest period and the highest peak intensity. Other interference fringes have a shorter period and lower peak intensity than that. The period of the interference fringes (in which the individual interference fringes are superimposed) in the light irradiation region coincides with the period p of the interference fringes formed by the components transmitted through the lenses closest to each other.

  In the graph of FIG. 3, the peak position where the intensity is about 450 to 500 corresponds to the peak position of the intensity of the interference fringes formed by the components transmitted through the lenses closest to each other among the lenses 4aa to 4ag. From the equation (1), the period p of the interference fringes shown in FIG. 3 can be obtained. The interference fringes shown in FIG. 3 correspond to the case where the lens width h is 5 mm, the focal length f is 188 mm, and the wavelength λ is 532 nm, and the period p is obtained as 20 μm from the equation (1).

  Exposure amount when the interference fringes generated in the light irradiation region on the homogenized surface are moved by one period of the interference fringes in the repetition direction of the interference fringes during the period when one shot of the pulse laser is irradiated Consider. At this time, the intensity of light irradiated to a certain light irradiation position on the homogenized surface changes according to the light intensity distribution for one cycle of the interference fringes. As a result, the value obtained by temporally averaging the intensity of the light applied to this position becomes substantially equal to the value obtained by spatially averaging the intensity of one period of the interference fringes. Similarly, for other light irradiation positions on the homogenized surface, the value obtained by temporally averaging the intensity of light applied thereto is approximately equal to the value obtained by spatially averaging the intensity of one period of the interference fringes. Become.

  In this way, by moving the interference fringes during the irradiation period of one shot, the average intensity with respect to time of the light irradiated to each position in the light irradiation region on the homogenized surface becomes a constant value. Get closer. That is, the distribution of the exposure amount in the light irradiation region approaches uniform (is made uniform) during the one-shot irradiation period. It should be noted that the distance for moving the interference fringes during the one-shot irradiation period does not have to coincide with one period of the interference fringes. Done.

  As described above, a plurality of interference fringes are superimposed in the light irradiation region, but the period of each interference fringe superimposed in the light irradiation region is an interference in which the individual interference fringes are superimposed. Since the period is less than the period of the fringes, if the interference fringes are moved by a distance equal to or longer than one period of the interference fringes on which the individual interference fringes are superimposed, the distribution of the exposure amount becomes uniform for each of the individual interference fringes.

  When the traveling direction of the laser beam incident on the homogenizer is swung by a minute angle, the light irradiation region on the homogenization surface moves, and the interference fringes in the light irradiation region also move without changing the shape. As shown in FIG. 2A, when the traveling direction of the laser beam is swung by a minute angle θ with respect to the Z axis in the YZ plane, the light irradiation region on the homogenized surface 4c and the interference generated in the light irradiation region. The stripe moves by ftanθ in the Y-axis direction.

  If the interference fringes generated in the longitudinal direction (Y-axis direction) of the light irradiation region during the one-shot irradiation period of the pulse laser are moved in the Y-axis direction by a distance equal to or longer than the period p, the homogenized surface The distribution of the exposure amount in the Y-axis direction on 4c can be made uniform. In the following, the conditions under which this can be done will be considered.

  The movement distance of the interference fringes when the traveling direction of the laser beam is swung by θ is f tan θ. Here, assuming that θ is very small, the movement distance of the interference fringes is approximated to fθ.

  The moving speed v of the interference fringes is expressed as follows:

と表される。

It is expressed.

  The condition for uniform exposure dose distribution is that the pulse width of the pulse laser beam is t,

It is expressed. Substituting Equation (1) and Equation (2) into Equation (3) and rearranging them as a condition for uniformizing the exposure dose distribution,

Is guided. If the traveling direction of the laser beam is changed at an angular velocity ω satisfying the equation (4) during the pulse width t, the interference fringes can be moved by a distance equal to or longer than the period p.

  For example, when the wavelength λ of the laser beam is 500 nm, the pulse width is 100 ns, and the lens width h is 5 mm, these are substituted into equation (4),

The condition is obtained. In addition, the unit of both sides of Formula (5) is rad / s. If the traveling direction of the laser beam is changed at an angular velocity of 1000 rad / s during a pulse width of 100 ns, the interference fringes move by one period (distance p). At this time, the traveling direction of the laser beam is swung by 100 μrad. Note that tan θ may be approximated to θ because the angle at which the traveling direction of the laser beam is swung is very small.

  More specifically, a method of using an electro-optic deflector or a polygon mirror as a beam scanner to move interference fringes and make the exposure dose distribution uniform will be described below. As in the case of the expression (5), it is assumed that the wavelength λ of the laser beam is 500 nm, the pulse width is 100 ns, and the lens width h is 5 mm. Further, it is assumed that the pulse period is 1 ms (pulse frequency is 1 kHz).

  First, a case where an electro-optic deflector is used as a beam scanner will be described. The electro-optic deflector includes an electro-optic crystal whose refractive index changes when a voltage is applied, and swings the traveling direction of the incident laser beam by an angle proportional to the voltage applied to the electro-optic crystal. A voltage is applied to the electro-optic deflector via a driver.

For example, Model 311A of CONOPTICS is used as an electro-optic deflector, and Model 301 of the company is used as a driver. This electro-optic deflector oscillates the traveling direction of the laser beam by 3.0 μrad each time a unit voltage (1 V) is applied. Further, when this driver is used, the applied voltage of the electro-optic deflector can be changed from -200 V to 200 V at maximum (up to 400 V as the maximum voltage difference) in a minimum of 80 ns. When these electro-optic deflector and driver are used, the maximum angular velocity ω _{MAX at which} the traveling direction of the laser beam is swung is

It becomes.

  In order to move the interference fringes by one period, as can be seen from Equation (5), the traveling direction of the laser beam may be swung by 100 μrad during the pulse width of 100 ns (angular velocity is 1000 rad / s). Therefore, if the applied voltage of the electro-optic deflector is changed by 33.3 V during the pulse width of 100 ns, the traveling direction of the laser beam can be swung by 100 μrad, and the interference fringes can be moved by one period (distance p). it can.

  If the applied voltage of the electro-optic deflector is changed by 33.3 × N (N is a natural number) V during the pulse width of 100 ns, the traveling direction of the laser beam fluctuates by 100 × N μrad, and the interference fringes are N It can be moved by a period (distance p × N). However, since the difference between the maximum voltage and the minimum voltage that can be generated by the driver is 400 V (= 33.3 × 12 V), the maximum value of N is 12. That is, when the electro-optic deflector and the driver as described above are used, the interference fringes can be moved up to 12 periods within a pulse width of 100 ns. Note that the movement distance of the interference fringes during the one-shot irradiation period may not be an integral multiple of the period p.

  The pulse laser beam is incident on the electro-optic deflector every 1 ms. The control device 3 shown in FIG. 1 controls the driver so that the traveling direction of the laser beam is swung in synchronization with the pulse period. For example, the driver applies a triangular wave to the electro-optic deflector so that the voltage increases for a predetermined period at a rate of 33.3 V per 100 ns and then decreases for a predetermined period at a rate of 33.3 V per 100 ns. To do.

  For example, the first shot of the pulse laser beam is irradiated during the period in which the applied voltage is increasing, and the second shot that is the next shot of the first shot is in the period in which the applied voltage is decreasing. The period of the triangular wave is set so that is irradiated. At this time, the applied voltage increases by 33.3 V during the irradiation period of the first shot. As a result, the interference fringe moves, for example, by one cycle of the interference fringe in the positive Y-axis direction of FIG. Also, the applied voltage decreases by 33.3 V during the second shot irradiation period. As a result, the interference fringe moves, for example, by one cycle of the interference fringe in the negative Y-axis direction of FIG.

  Further, for example, the period of the triangular wave is set so that the first and second shots are irradiated during the period in which the applied voltage is increasing. At this time, the applied voltage increases by 33.3 V during the irradiation period of each of the first and second shots. As a result, during each irradiation period of the first and second shots, the interference fringes move, for example, by one cycle of the interference fringes in the positive Y-axis direction of FIG.

  Next, a case where a polygon mirror is used as the beam scanner will be described. The polygon mirror is a regular polygonal columnar structure whose side is a mirror. When the polygon mirror rotates around the central axis of the regular polygonal column, the traveling direction of the laser beam reflected by the side surface of the polygon mirror changes.

When the polygon mirror is rotated by an angle theta _p, the traveling direction of the laser beam reflected by the side surfaces of the polygon mirror is swung by an angle 2 × θ _p. When the angular velocity of the polygon mirror and the omega _p, the traveling direction of the laser beam is deflected at an angular velocity 2 × ω _p. In order to make the exposure dose distribution uniform, the equation (5):

Need to be met. The rotation speed R of the polygon mirror is

Therefore, substituting equation (7) into equation (8),

The condition is derived. By rotating the polygon mirror at a rotational speed of 79.6 round / s or higher (angular speed of 500 rad / s or higher) and swinging the traveling direction of the laser beam, interference fringes are generated for one cycle or more during the irradiation period of one shot of the pulse laser. Can be moved by a distance of.

  The pulse laser beam is incident on the polygon mirror every 1 ms. If the operation of the polygon mirror is not synchronized with the pulse period, the traveling direction of each shot reflected by the polygon mirror varies, and all shots cannot enter the homogenizer (some shots do not enter the homogenizer). By setting as follows, the operation of the polygon mirror can be synchronized with the pulse period.

When the number of side surfaces of the polygon mirror (the number of reflection surfaces) is M, the rotational speed is R, and therefore the number of times (frequency) f _p that the polygon mirror can swing the traveling direction of the laser beam per unit time is

It is expressed. Frequency f _p is, to match the 1kHz a pulse frequency, by setting the rotational speed R and the surface number M of the polygon mirror, the operation of the polygon mirror is synchronized with the pulse period. By doing so, the ranges in which the reflection surfaces of the polygon mirrors swing the traveling direction of the shot of the pulse laser coincide with each other. The control device 3 shown in FIG. 1 controls the driving mechanism of the polygon mirror so that the polygon mirror rotates at the rotation speed R satisfying the equation (10). The frequency f _p is not necessary to match the pulse frequency, it may be set to be an integral multiple of the pulse frequency. Thus setting the frequency f _p, it can be so does not vary the traveling direction of each shot that is reflected.

  Substituting equation (8) into equation (10), for the number M of polygon mirror surfaces,

Is obtained. When the frequency f _p is 1 kHz and the angular velocity ω _{p of the} polygon mirror is 500 rad / s (the angular velocity at which the interference fringes move exactly one cycle during the irradiation period of one shot), the equation (11)

Is obtained. Since 12.6 on the rightmost side of equation (12) is a non-integer, it is inappropriate as the number of polygon mirror surfaces. Therefore, for example, the number M of polygon mirrors is set to 12, and the angular velocity ω _p is set to about 524 rad / s so as to correspond to the number (so that equation (11) is satisfied). With this setting, the interference fringes can be moved by about 1.05 periods during the irradiation period of each shot.

If it is desired to move the interference fringes for about two cycles during the one-shot irradiation period, the following may be performed. The angular velocity ω _p at which the interference fringes move exactly two periods during the irradiation period of one shot is 1000 rad / s, which is twice the 500 rad / s. Assuming that the temporary value of the angular velocity ω _p is 1000 rad / s,

From this equation, for example, the number of faces of the polygon mirror is set to 6, and the angular velocity ω _p is set to about 1047 rad / s so as to correspond thereto. With this setting, the interference fringes can be moved by about 2.09 periods during the irradiation period of each shot.

  As described above, when the interference fringes are generated in the longitudinal direction of the light irradiation region, the method of moving the interference fringes in the longitudinal direction and uniformizing the exposure amount distribution has been described. In addition, it is preferable that the repetition direction of the interference fringes generated in the light irradiation region coincide with the direction in which the interference fringes are moved, but the interference fringe repetition direction and the movement direction may be slightly shifted. . If the moving direction includes a component parallel to the repeating direction of the interference fringes, the interference fringes can be moved with respect to the repeating direction. For example, in FIG. 2A, if the direction in which the laser beam travels varies includes a component parallel to the direction in which the lenses 4aa to 4ag of the array lens 4a are aligned (Y-axis direction), Interference fringes generated in the longitudinal direction can be moved in the longitudinal direction. If the component parallel to the direction in which the lenses 4aa to 4ag are arranged is equal to or larger than λ / (th) shown in the equation (4), the angular velocity for oscillating the traveling direction of the laser beam is within the irradiation period of one shot of the pulse laser. In addition, the interference fringes can be moved one period or more in the longitudinal direction. Note that when the interference fringe repetition direction matches the interference fringe movement direction, the interference fringe movement speed in the interference fringe repetition direction can be maximized.

  Note that interference fringes can also occur in the short direction of the light irradiation region. In such a case, if a beam scanner that changes the traveling direction of the laser beam is arranged so that the interference fringes move in the short direction of the light irradiation region, the distribution of the exposure amount in the short direction can be made uniform.

  As described above, even when a laser beam having high coherence is incident on the homogenizer by changing the traveling direction of the laser beam incident on the homogenizer during the irradiation period of one shot of the pulse laser, light irradiation is performed. The distribution of the exposure amount in the region can be made close to uniform. If this is used for laser annealing, the quality of the silicon film on which crystal grains are grown by irradiation with a pulse laser can be made closer to uniform.

  In the laser annealing treatment, the light irradiation region on the substrate is moved in the short direction, and the light irradiation region irradiated by one shot of the pulse laser and the light irradiation region irradiated by the next one shot are partially divided. Overlap. Even when interference fringes are generated in the short direction of the light irradiation region, the quality of the silicon film in the short direction of the light irradiation region can be made uniform by adjusting the width in which the light irradiation regions overlap each other. it can. When doing so, the interference fringes need not be moved in the short direction by the beam scanner.

  In the above description, an electro-optic deflector or a polygon mirror is used as the beam scanner. However, other devices may be used as the beam scanner. For example, an acousto-optic deflector may be used. It would also be possible to use a galvano scanner. Further, the tuning fork to which the mirror is attached may be a device that swings the traveling direction of the laser beam incident on the mirror by minutely vibrating the tuning fork with a piezoelectric element, for example.

  Processing other than the laser annealing treatment may be performed using the method for uniformizing the exposure amount distribution described above. In addition, even if it is an optical system other than a homogenizer, if it is an optical system that irradiates a common light irradiation region with components that pass through different regions in the cross section of the laser beam, due to the coherence of the laser beam, Interference fringes can occur in the light irradiation region. When it is desired to improve the uniformity of the exposure amount distribution in the light irradiation region irradiated with one shot of the pulse laser, the interference fringes in the light irradiation region during the irradiation period of one shot are longer than the period in the repetition direction. It is only necessary to move the distance.

  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.

It is a figure which shows schematically the laser irradiation apparatus by an Example. 2A and 2B are diagrams schematically showing the configuration of the homogenizer. It is a graph which shows the light intensity distribution of the interference fringe produced in the light irradiation area | region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Beam scanner 3 Control apparatus 4 Homogenizer 4a Array lens 4b Condensing lens 5 Folding mirror 6 Substrate 7 XY stage

Claims (8)

A component that passes through different regions in the cross section of the incident laser beam is incident on the optical system during the period when one shot of the pulse laser beam is incident on the optical system that irradiates the common light irradiation region. Laser irradiation method for moving interference fringes generated by interference of components passing through different regions in a cross section of a pulse laser beam in the light irradiation region by a distance equal to or longer than the period of the interference fringes with respect to the repetition direction of the interference fringes . The optical system is a homogenizer configured to include an array lens that divides a laser beam in a beam cross section, and a condenser lens that irradiates each component of the laser beam divided by the array lens to a common area. ,
The interference fringes generated by the interference of each component of the laser beam divided by the array lens on the homogenization surface of the homogenizer are moved by swinging the incident direction of the pulse laser beam incident on the homogenizer. The laser irradiation method as described. One pulse laser beam is supplied to a homogenizer that includes an array lens that divides the laser beam in the beam cross section and a condenser lens that irradiates each component of the laser beam divided by the array lens to a common region. During the period in which the shot is incident, the interference of the laser beam divided by the array lens interferes on the homogenizer surface of the homogenizer, and the pulse laser beam is incident on the homogenizer. A laser irradiation method for moving the direction of the interference fringes by moving the direction,
The plurality of lenses constituting the array lens of the homogenizer are arranged in a first direction, and the width of each of the lenses in the first direction is h, and the pulse width of the pulse laser beam Where t is the wavelength of the pulse laser beam and λ is the wavelength of the pulsed laser beam, the component of the angular velocity at which the incident direction of the pulsed laser beam incident on the homogenizer is swung is greater than or equal to λ / (th). Thus, the laser irradiation method which shakes the incident direction of the pulse laser beam incident on the homogenizer. A laser light source for emitting a pulsed laser beam;
A beam scanner that swings a traveling direction of a pulsed laser beam emitted from the laser light source based on a control signal input from the outside;
The pulse laser beam emitted from the beam scanner is arranged to be incident, and an array lens that divides the incident pulse laser beam in the beam cross section and each component divided by the array lens are shared on the homogenized surface. A homogenizer having a condenser lens that irradiates the area;
During the period in which one shot of the pulsed laser beam is incident on the homogenizer, the beam scanner divides the incident direction of the pulsed laser beam incident on the homogenizer so that the pulses divided by the array lens of the homogenizer Control for controlling the beam scanner so that the interference fringes generated on the homogenization surface of the homogenizer due to interference between the components of the laser beams are moved by a distance equal to or longer than the period of the interference fringes in the repetition direction of the interference fringes. A laser irradiation apparatus. The beam scanner is a polygon mirror that is rotated by a driving mechanism, where M is the number of reflection surfaces of the polygon mirror, and R is the number of rotations per unit time of the polygon mirror. The laser irradiation apparatus according to claim 4, wherein the controller controls the drive mechanism so that the polygon mirror rotates so as to coincide with a pulse frequency of a pulse laser beam emitted from a laser light source. A laser light source for emitting a pulsed laser beam;
A beam scanner that swings a traveling direction of a pulsed laser beam emitted from the laser light source based on a control signal input from the outside;
The pulse laser beam emitted from the beam scanner is arranged to be incident, and an array lens that divides the incident pulse laser beam in the beam cross section and each component divided by the array lens are shared on the homogenized surface. A homogenizer having a condensing lens for irradiating a region, wherein a plurality of lenses constituting the array lens are arranged in a first direction, and the width of each of the lenses in the first direction is h The homogenizer which is
When the pulse width of the pulsed laser beam emitted from the laser light source is t and the wavelength of the pulsed laser beam is λ, the first angular velocity at which the incident direction of the pulsed laser beam incident on the homogenizer is swung. And a control device that causes the beam scanner to change the traveling direction of the pulsed laser beam so that the component related to the direction of λ is equal to or greater than λ / (th). The beam scanner is a polygon mirror that is rotated by a driving mechanism, where M is the number of reflection surfaces of the polygon mirror, and R is the number of rotations per unit time of the polygon mirror. The laser irradiation apparatus according to claim 6, wherein the controller controls the drive mechanism so that the polygon mirror rotates so as to coincide with a pulse frequency of a pulse laser beam emitted from a laser light source. A substrate having an amorphous or polycrystalline silicon film formed on its surface is irradiated with a pulsed laser beam whose cross section is shaped into a long shape in one direction. A laser annealing method including a step of moving a beam cross section on the surface of the substrate by a distance equal to or longer than a first length in a longitudinal direction of the beam cross section, wherein the first length is equal to the beam cross section. A laser annealing method in which a repetition direction is an interference fringe period that coincides with the longitudinal direction.

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