JP2006119210A - Focal point adjustment apparatus, laser irradiation device and light irradiation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focal point adjustment apparatus by which a laser beam can easily focus on a processed face regardless of an increase in the size of a processed object. <P>SOLUTION: The focal position adjustment apparatus includes: a light transmission member on which light converging or diverging is made incident and whose thickness can be varied in the direction where incident light advances; and a drive mechanism for varying the thickness of the light transmission member. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a focal position adjusting device, a laser irradiation device, and a light irradiation method, and in particular, it is possible to adjust the size of a cross section on the surface of a light irradiation object of convergent or diverging light irradiated to the light irradiation object. The present invention relates to a focus position adjusting device, a laser irradiation device, and a light irradiation method.

  Laser beams are used for various processes. For example, the processing target is irradiated with a laser beam that has been converged so that the beam cross-section is minimized on the surface to be processed (so as to be focused). In addition, for example, a process of irradiating a processing target with a laser beam so that a beam cross section shaped by a mask forms an image on a processing surface by a lens is also performed. A technique is known in which a workpiece to be processed held on an XY stage is moved in a direction parallel to a processing surface to move a laser beam incident position on the processing surface (scanning a laser beam on the processing surface). It has been.

  As an object to be irradiated with a laser beam, for example, there is a glass substrate that is a main component of a flat panel display. An amorphous silicon film is formed on the surface of the glass substrate before laser irradiation. By performing laser irradiation on the amorphous silicon film, the amorphous silicon film is polycrystallized. For example, such a workpiece tends to be enlarged in recent years.

  When the workpiece becomes large, it becomes difficult to obtain a flat work surface. When scanning the laser beam on the work surface, if the work surface is not a perfect flat surface and has undulations, the surface of the object to be processed has a height direction corresponding to the shape of the undulations (the progress of the incident laser beam). Direction).

  Along with this, for example, the optical path length from the lens for forming an image of the beam cross section shaped by the mask on the processing surface to the surface of the processing object varies. As described above, it is impossible to scan the laser beam on the processing surface while maintaining the state where the beam cross section forms an image on the processing surface.

  For example, Patent Document 1 discloses a laser irradiation apparatus provided with an elevating drive device that moves a workpiece in the traveling direction of a laser beam so as to compensate for the displacement as described above. If this laser irradiation apparatus is used, the state in which the beam cross section shaped by the mask forms an image on the surface to be processed can be maintained during the scanning of the laser beam. In addition, the laser beam can be scanned while maintaining a state where the laser beam is focused on the surface to be processed.

JP 2003-282477 A

  In the technique disclosed in the document disclosed in Patent Document 1, the larger the workpiece is, the more difficult it is to position the workpiece at a high speed with respect to the traveling direction of the laser beam. For this reason, it is not easy to keep the laser beam focused on the surface to be processed.

  An object of the present invention is to provide a focus position adjusting device, a laser irradiation device, and a light irradiation method that can easily maintain a state in which a laser beam is focused on a surface to be processed even when a workpiece is enlarged. It is.

  According to an aspect of the present invention, light that converges or diverges is incident, and the thickness of the light transmissive member is variable with respect to the first direction in which the incident light travels, and the thickness of the light transmissive member is changed. A focus position adjustment device having a drive mechanism is provided.

  According to another aspect of the present invention, a holder for holding a light irradiation object, a laser light source that emits a laser beam, a lens that converges or diverges the laser beam emitted from the laser light source, and the lens, A light transmissive member disposed on a path of a laser beam between the light irradiation object held on the holding table and having a variable thickness in a first direction in which the incident laser beam travels; and the light transmission There is provided a laser irradiation apparatus having a focal position adjusting device having a drive mechanism for changing the thickness of a member.

  According to another aspect of the present invention, (a) the light converged by the lens is transmitted through the first medium, and further transmitted through the second medium having a refractive index different from the refractive index of the first medium. And (b) changing the thickness of the first medium with respect to the direction in which the light converged by the lens travels, and changing the thickness of the light converged by the lens. And a light irradiation method including a step of changing a position where the cross section is minimized.

  For example, when convergent light is incident on the light transmissive member, if the thickness of the light transmissive member changes, the position where the convergent light transmitted through the light transmissive member is focused (the position where the cross section of the convergent light is minimized) is Move in the direction of travel. Thereby, the magnitude | size of the cross section of the light irradiated to the surface of a light irradiation target object can be changed. For example, the irradiated light can be focused on the surface of the light irradiation object.

  FIG. 1 is a schematic view of a laser irradiation apparatus according to a first embodiment of the present invention. The laser light source 1 emits a laser beam. The laser beam emitted from the laser light source 1 is reflected by the folding mirror 2 and enters the condenser lens 3 that converges the laser beam. The laser beam emitted from the condenser lens 3 enters the focal position adjusting device 4.

The focal position adjusting device 4 includes a wedge substrate 4a1, a wedge substrate 4a2, and a drive mechanism 4b. The wedge substrates 4a1 and 4a2 are made of a material that transmits and refracts a laser beam such as synthetic quartz (SiO ₂ ). For example, the refractive index of synthetic quartz for light having a wavelength of 308 nm is 1.485. The wedge substrate 4a1 has an incident surface p1 orthogonal to the traveling direction of the laser beam emitted from the condenser lens 3, and an emission surface p2 inclined (not parallel or perpendicular) to the incident surface p1. The wedge substrate 4a2 has an incident surface p3 parallel to the emission surface p2 of the wedge substrate 4a1, and an emission surface p4 parallel to the incident surface p1 of the wedge substrate 4a1. The wedge substrate 4a1 and the wedge substrate 4a2 are arranged so that the emission surface p2 and the incidence surface p3 are in contact with each other, and constitute the light transmission member 4a. The laser beam emitted from the condenser lens 3 is incident on the entrance surface p1 of the wedge substrate 4a1, passes through the interface where the exit surface p2 and the entrance surface p3 are in contact with each other, and exits from the exit surface p4 of the wedge substrate 4a2.

  Each of the wedge substrates 4a1 and 4a2 is not uniform in thickness in the laser beam traveling direction, but the thickness of the portion of the light transmitting member 4a in which both the wedge substrates 4a1 and 4a2 are sandwiched between the incident surface p1 and the emission surface p4 is It becomes uniform. The thickness of the portion of the light transmission member 4a sandwiched between the incident surface p1 and the emission surface p4 is referred to as the thickness of the light transmission member 4a.

  The drive mechanism 4b holds the wedge substrate 4a2 in a movable manner. The drive mechanism 4b moves the wedge substrate 4a2 in a direction parallel to the emission surface p2 and in a direction in which the inclination angle with respect to the incident surface p1 is maximized. At this time, the relative position of the wedge substrate 4a2 with respect to the wedge substrate 4a1 moves while the emission surface p2 of the wedge substrate 4a1 and the incident surface p3 of the wedge substrate 4a2 are in contact with each other. The control device 8 controls the drive mechanism 4b.

  If the wedge substrate 4a2 is moved so that the relatively thick portion of the wedge substrate 4a1 and the relatively thick portion of the wedge substrate 4a2 approach each other, the light transmitting member 4a Thickness increases. If the wedge substrate 4a2 is moved so that the relatively thin portion of the wedge substrate 4a1 and the relatively thin portion of the wedge substrate 4a2 approach each other, the light transmitting member 4a The thickness becomes thinner.

  The relative position of the wedge substrate 4a1 with respect to the condensing lens 3, the moving range of the wedge substrate 4a2, and both wedges so that the laser beam emitted from the condensing lens 3 is transmitted through a portion having a uniform thickness of the light transmitting member 4a. The size of the board is set.

  The laser beam incident on the condenser lens 3 is converged, and the beam cross section is minimized (focused) at a certain position. The position where the cross section of the laser beam emitted from the condenser lens 3 is minimum is called the focal position. The light transmitting member 4 a is disposed on the optical path between the focal position when the light transmitting member 4 a is not present and the condenser lens 3.

  With reference to FIG. 2, the operation of the light transmitting member 4a will be described. FIG. 2 schematically shows a path of a laser beam converged by the condenser lens 3 and transmitted through the light transmitting member 4a to focus. The left figure shows a case where the thickness of the light transmission member 4a is relatively thin (the thickness in this case is t1), and the right figure shows that the thickness of the light transmission member 4a is relatively small. The case where it is thick (the thickness in this case is assumed to be t2) is shown. Here, it is assumed that the refractive index of the medium through which the laser beam is transmitted other than the condenser lens 3 and the light transmitting member 4a is smaller than the refractive index of the light transmitting member 4a.

  Of the components in the cross section of the laser beam incident on the light transmitting member 4a, the component that does not enter the incident surface p1 perpendicularly is refracted on the incident surface p1. The component refracted on the incident surface p1 is refracted again on the exit surface p4 and exits from the light transmitting member 4a, and travels in a direction parallel to the traveling direction when entering the entrance surface p1. The light transmitting member 4a refracts the laser beam, so that the focal position of the laser beam is shifted away from the laser light source with respect to the focal position when the light transmitting member 4a is not disposed.

In the figure on the left, the distance from the focal position f ₀ when the light transmitting member 4a is not disposed to the focal position f ₁ when the light transmitting member 4a having the thickness t ₁ is disposed (the focal position of the focal position). The movement amount d ₀ is approximately calculated by using the thickness t ₁ of the light transmission member 4 a and the refractive index n of the light transmission member 4 a.

It is expressed. Here, the angle at which the component refracted on the incident surface p1 is incident on the incident surface p1 (the angle formed by the traveling direction of the component incident on the incident surface p1 and the normal direction of the incident surface p1) is expressed as θ. The angle θ is small enough to approximate sin θ to θ and to approximate cos θ to 1−θ ² . Further, the refractive index of the medium around the light transmitting member 4a was set to 1.

As shown in the drawing on the right side, when the thickness of the light transmitting member 4a is increased, the distance traveled by the light refracted on the incident surface p1 until it reaches the output surface p4 becomes longer. Thereby, the focal position is further away from the laser light source as the thickness of the light transmitting member 4a is larger. From the focal point _{f 1, d 1} (the amount of movement of the focal position) length of the thickness of the light transmitting member 4a is to the focal position _{f 2} in the case of _{t 2,} the difference in thickness of the light transmission member 4a _{(t 2} - Using t ₁ ) and the refractive index n of the light transmitting member 4a,

It is expressed. The conditions of the approximation is similar to that that for determining the distance d _0.

  As described above, the focal position can be moved with respect to the traveling direction of the laser beam by changing the thickness of the light transmitting portion of the light transmitting member 4a.

  Note that when the angle formed by the incident surface p1 and the output surface p2 and the angle formed by the incident surface p3 and the output surface p4 is α and the moving distance of the wedge substrate 4a2 is L, the wedge substrate 4a2 moves by the distance L. The change Δt in the thickness of the light transmitting member 4a due to the

It is expressed.

  From Equation (3) and Equation (2),

It is expressed. Since the magnitudes of sin α and (1-1 / n) are both smaller than 1, the moving distance d ₁ of the focal position is smaller than the moving distance L of the wedge substrate 4a2. Thereby, the precision of a focus position can be made higher than the position precision of the moving direction of the wedge board | substrate 4a2. By appropriately setting at least one of the angle α and the refractive index n, the accuracy of the focal position can be sufficiently increased with respect to the positional accuracy of the wedge substrate 4a2 in the moving direction.

  Note that a method of moving the focal point by moving the condenser lens 3 in the traveling direction of the laser beam is also conceivable. In this method, the moving distance of the condenser lens 3 is equal to the moving distance of the focal position. Therefore, in order to increase the accuracy of the focal position, it is necessary to increase the positional accuracy of the condenser lens 3 to the same extent.

  Returning to FIG. 1, the description will be continued. A laser beam emitted from the light transmitting member 4 a is irradiated on the surface of the workpiece 5. The XY stage 6 holds the workpiece 5 and moves the workpiece 5 in a direction parallel to a plane that intersects the traveling direction of the laser beam incident on the workpiece surface. When the XY stage 6 moves the workpiece 5, the laser beam incident position on the processing surface moves. The control device 8 controls the XY stage 6 so that a laser beam is irradiated to a desired processing point.

  Hereinafter, a case where the surface of the workpiece 5 is not completely flat but has undulations will be considered. When the XY stage 6 moves the workpiece 5, the surface of the workpiece 5 at the laser beam incident position is displaced in the height direction (laser beam traveling direction) corresponding to the shape of the swell.

  The focal length of the condenser lens 3 and the light transmitting member are set so that when the laser beam is irradiated to the processing point arranged at the reference position in the height direction, the laser beam is focused on the processing point. A standard thickness of 4 is set.

  A displacement sensor 7 is disposed in a space above the surface of the workpiece 5. The displacement sensor 7 is a laser displacement meter, for example. The displacement sensor 7 measures how much the processing point arranged at the measurement position is displaced from the reference position in the height direction. A signal corresponding to the measured displacement of the workpiece point is sent from the displacement sensor 7 to the control device 8.

  The processing point whose displacement is measured by the displacement sensor 7 is moved to a position where the laser beam is incident. Based on the amount of displacement of the workpiece point, the control device 8 controls the drive mechanism 4b of the focal length adjusting device 4 so that the laser beam is focused on the workpiece point. Change the height.

  For example, a laser beam can be irradiated onto a linear workpiece region as follows. As shown in FIG. 3, one end of the processing region C is along a straight line connecting the laser beam incident position A and the measurement position B of the displacement sensor 7 arranged on the surface of the processing object 5. Is located on the measurement position B of the displacement sensor 7 and the processing area C is arranged so that the other end is on the side opposite to the laser beam incident position A.

  The workpiece 5 is moved in parallel with the length direction of the processing area C so that the displacement amount of each processing point is measured from one end of the processing area C to the other end. The processing point whose displacement amount is measured by the displacement sensor 7 reaches a laser beam incident position A after moving a predetermined distance. Adjust the focal position according to the amount of displacement of each processing point, and maintain the state where the laser beam is focused on the processing surface so that laser irradiation is performed from one end of the processing region C to the other end. I do. Note that the emission of the laser beam from the laser light source is controlled so that the laser irradiation is performed only in the processing area C.

  In this way, the displacement sensor 7 can be arranged such that the measurement position B is arranged before the laser beam incident position A with respect to the moving direction of the workpiece 5. In addition, when it is desired to move the workpiece 5 in a plurality of directions and perform laser irradiation, a plurality of displacement sensors may be arranged corresponding to the movement direction of the workpiece 5.

  As described above, the focal position adjusting device 4 can adjust the focal position of the laser beam by changing the thickness of the light transmitting member 4a. In order to adjust the focal position of the laser beam, it is not necessary to move the workpiece 5 in the traveling direction of the laser beam. The displacement sensor 7 is used to measure the position of the processing point with respect to the traveling direction of the laser beam, and based on this, the laser beam can be focused at the processing point. Even if the surface to be processed is not a perfect plane but a shape having waviness, the conditions of laser irradiation to each processing point can be made uniform, so that it is possible to suppress problems that the processing quality varies within the surface to be processed.

  In the above embodiment, the focal position is adjusted so that the laser beam is focused on the processing surface. However, the size of the beam cross section at the laser beam incident position on the processing surface using the focal position adjusting device 4 is used. The focal position may be adjusted so that is a desired size. For example, the beam cross section on the processing surface can be increased by moving the focal position away from the processing surface. If the size of the beam cross section on the processing surface is made constant, for example, there is an advantage that the power density of light applied to the processing surface can be made constant. When the laser beam is always focused on the processing surface, the size of the beam cross section on the processing surface is kept constant.

  Next, a laser irradiation apparatus according to the second embodiment will be described with reference to FIG. The laser irradiation apparatus shown in FIG. 4 has a configuration in which a homogenizer 9 and a mask 10 are inserted on the optical path between the laser light source 1 and the folding mirror 2 of the laser irradiation apparatus shown in FIG.

  The homogenizer 9 makes the light intensity distribution in the cross section of the laser beam emitted from the laser light source 1 uniform on the homogenization surface. The laser beam emitted from the homogenizer 9 enters a mask 10 having a through hole having a predetermined shape (for example, a square or a rectangle). The mask 10 transmits light in a portion corresponding to the through-hole in the beam cross section and shields light in other portions. The mask 10 is arranged so that the through hole of the mask 10 is positioned on the homogenization surface of the homogenizer 9.

  The optical path length from the mask 10 to the condenser lens 3, the focal length of the condenser lens 3, and the light transmission so that the through hole of the mask 10 forms an image on the processing surface arranged at the reference position in the height direction. The reference thickness of the member 4a and the optical path length from the condenser lens 3 to the processing surface are determined. Since the light intensity distribution in the cross section of the laser beam at the position passing through the through hole of the mask 10 is made uniform by the homogenizer 9, the light intensity distribution in the cross section of the beam on the processing surface is also made uniform.

  In this laser irradiation apparatus, even if the processing surface is displaced from the reference position in the height direction, the focus position adjusting device 4 is maintained so that the through-hole of the mask 10 is imaged on the processing surface. Adjusts the focal position.

  By using the laser irradiation apparatus of the second embodiment, it is possible to perform processing while maintaining the cross-sectional shape of the laser beam irradiated to the processing surface in a desired shape corresponding to the through hole of the mask 10. Further, it is possible to irradiate the processing surface with a laser beam having a uniform light intensity distribution in the beam cross section.

  The laser irradiation apparatus of the second embodiment can be used for annealing for performing laser irradiation on a glass substrate having an amorphous silicon film formed on the surface thereof, for example. Since the light intensity distribution in the beam cross section on the surface to be processed is uniform, a polycrystalline silicon film with little quality variation in the beam cross section can be formed.

  In the above embodiment, the two wedge substrates 4a1 and 4a2 included in the light transmitting member 4a are brought into contact with each other. However, both the wedge substrates are arranged so that the emission surface p2 and the incident surface p3 are spaced apart from each other. It doesn't matter. However, the exit surface p2 and the entrance surface p3 are preferably arranged so as to be parallel to each other.

  In the above embodiment, in order to change the thickness of the light transmitting member 4a, the wedge substrate 4a2 is arranged in a direction parallel to the emission surface p2 and having the maximum inclination angle with respect to the incidence surface p1 (incidence surface p1). The direction of movement of the wedge substrate 4a2 is not limited to this direction. If the wedge substrate 4a2 is moved in a direction that intersects the traveling direction of the laser beam that passes through the light transmitting member 4a and is not parallel to the virtual intersecting line of the incident surface p1 and the emitting surface p2, the light transmitting member 4a The thickness of the portion through which light is transmitted can be changed.

  In the above embodiment, the wedge substrate 4a2 is moved. However, if at least one of the wedge substrates 4a1 and 4a2 is moved, the thickness of the light transmitting member 4a can be changed.

  In the above embodiment, the light transmitting member 4a is a stack of two wedge substrates, and the thickness of the light transmitting member 4a is changed by changing the relative position of both wedge substrates. In addition, as the light transmissive member having a variable thickness, for example, a member made of a material that transmits light and having a structure in which a fluid that transmits and refracts light is filled between two opposing flat plates may be used. I do not care. As this fluid, a fluid having a refractive index different from that of the medium around the light transmitting member is selected. By changing the distance between the two flat plates, the focal position can be adjusted based on the same principle as adjusting the focal position by changing the thickness of the light transmitting member 4a of the above embodiment.

  In the above embodiment, the condensing lens 3 for converging the laser beam is used. However, the lens for diverging the laser beam is used, and the diverging light emitted from the lens is transmitted through the light transmitting member 4a to be processed. 5 may be incident. If the focal position adjusting device 4 is used, for example, the size of the beam cross section on the processing surface can be adjusted.

  In the above embodiment, the case where the measurement position of the displacement sensor is separated from the laser beam incident position has been described. However, the measurement position and the laser beam incident position may be matched.

  In the above embodiment, the displacement sensor that measures the displacement in the height direction of the surface of the workpiece 5 is used. However, the distance to measure the distance to the surface of the workpiece 5 instead of the displacement sensor. A meter may be used.

  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.

1 is a schematic view of a laser irradiation apparatus according to a first embodiment of the present invention. It is a figure which shows roughly the path | route of the light which permeate | transmits a light transmissive member. It is a top view of the processing target object for demonstrating the laser irradiation method. It is the schematic of the laser irradiation apparatus by a 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Folding mirror 3 Condensing lens 4 Focus position adjustment apparatus 4a Light transmissive member 4a1, 4a2 Wedge board | substrate 4b Drive mechanism 5 Process target 6 XY stage 7 Displacement sensor 8 Control apparatus 9 Homogenizer 10 Mask

Claims (12)

A light transmissive member in which light that converges or diverges is incident and the thickness of the incident light in the first direction is variable;
A focus position adjusting device having a driving mechanism for changing a thickness of the light transmitting member; The light transmitting member is in contact with the second surface and a first wedge substrate having a first surface intersecting the first direction and a second surface inclined with respect to the first surface. Or a third surface oppositely spaced in parallel and a second wedge substrate having a fourth surface parallel to the first surface;
2. The focus position adjusting apparatus according to claim 1, wherein the drive mechanism moves at least one of the first and second wedge substrates so that a thickness of a light transmission portion changes. The focus position adjusting apparatus according to claim 2, wherein the driving mechanism moves at least one of the first and second wedge substrates in a direction parallel to the second surface. The drive mechanism changes the thickness of the light transmission member based on the positional information on the light irradiation target irradiated with the light transmitted through the light transmission member with respect to the traveling direction of the light transmitted through the light transmission member. The focal position adjusting device according to any one of claims 1 to 3. A holding table for holding a light irradiation object;
A laser light source for emitting a laser beam;
A lens that converges or diverges the laser beam emitted from the laser light source;
A light transmissive member disposed on a path of a laser beam between the lens and a light irradiation object held on the holding table, and having a variable thickness in a first direction in which the incident laser beam travels; And a focal position adjusting device having a drive mechanism for changing the thickness of the light transmitting member. The light transmitting member of the focal position adjustment device includes a first surface that intersects the first direction, and a first wedge substrate having a second surface that is inclined with respect to the first surface; A third surface in contact with or parallel to the second surface and spaced in parallel; and a second wedge substrate having a fourth surface parallel to the first surface;
The laser irradiation apparatus according to claim 5, wherein the driving mechanism included in the focal position adjustment device moves at least one of the first and second wedge substrates so that a thickness of a light transmission portion changes. Furthermore, a sensor for measuring position information regarding the traveling direction of the laser beam incident on the light irradiation target object, which is held on the holding table,
A control device that controls the drive mechanism of the focal position adjustment device based on the position information measured by the sensor to change the thickness of the light transmission member in the first direction. Or the laser irradiation apparatus of 6. The holding table moves the light irradiation object held by the holding table in a direction parallel to a plane intersecting the traveling direction of the laser beam incident on the light irradiation object,
When the holding table moves the light irradiation target object, the control device may move the surface of the light irradiation target object even if the surface of the light irradiation target object at the laser beam incident position is displaced in the traveling direction of the laser beam. The laser irradiation apparatus according to claim 7, wherein the thickness of the light transmission member is changed by controlling the drive mechanism so that the size of the beam cross section of the laser beam does not change. The holding table moves the light irradiation object held by the holding table in a direction parallel to a plane intersecting the traveling direction of the laser beam incident on the light irradiation object,
When the holding table holds the light irradiation target object at a certain position, the first position in the laser beam path between the laser light source and the lens becomes an object point, and the light irradiation target object is placed on the surface of the light irradiation target object. The focal length of the lens, the thickness of the light transmission member, and the optical path length from the lens to the surface of the light irradiation object are set so that the image point is located,
When the holding table moves the light irradiation object, the control device is configured to display the image of the first position even if the surface of the light irradiation object at the laser beam incident position is displaced in the traveling direction of the laser beam. The laser irradiation apparatus according to claim 7, wherein the thickness of the light transmission member is changed by controlling the driving mechanism so that a point is maintained on the surface of the light irradiation object. (A) The light converged by the lens passes through the first medium, and further passes through the second medium having a refractive index different from the refractive index of the first medium, and enters the light irradiation object. Process,
(B) changing the thickness of the first medium in the direction in which the light converged by the lens travels, and changing the position where the cross section of the light converged by the lens is minimized. Light irradiation method. further,
(C1) a step of moving the light irradiation object in a direction parallel to a plane intersecting a traveling direction of the light incident on the light irradiation object, and moving the light irradiation object; In the step (b), the size of the light irradiation region on the surface of the light irradiation object does not change even if the surface of the light irradiation object at the incident position is displaced in the traveling direction of the incident light. The light irradiation method according to claim 10, wherein the thickness of the first medium is changed. further,
(C2) a step of moving the light irradiation object in a direction parallel to a plane intersecting a traveling direction of light incident on the light irradiation object, and when the light irradiation object is moved, Even if the surface of the light irradiation object at the incident position is displaced in the traveling direction of the incident light, the first position in the path of light incident on the lens becomes an object point, and the surface of the light irradiation object is The light irradiation method according to claim 10, wherein in the step (b), the thickness of the first medium is changed so that the state where the image point is located is maintained.

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