A laser energy measurement device

Abstract

The present application discloses a laser energy measurement device. The laser energy measurement device includes: a first light homogenizing component, a light spatial distribution adjusting element, and a photodetector, which are sequentially arranged along the light output direction of the laser discharge cavity; the light spatial distribution adjusting element is used to perform light intensity spatial adjustment on the laser irradiated on the photodetector. The solution of the present application reduces the influence of beam distribution non-uniformity, pointing and position stability on the energy measurement result through the light spatial distribution adjusting element, improves the energy stability of the laser, and solves the energy measurement error caused by the change of laser beam non-uniformity, pointing and position stability.

Description

Technical Field

[0001] The present application relates to the field of optical technologies, and particularly to a laser energy measurement device. Background Art

[0002] Lasers are widely used in various industrial fields due to their high energy, high brightness, and good monochromaticity. Among them, deep ultraviolet excimer lasers are commonly used light sources for high-end lithography machines and are used for the processing of semiconductor chips. Common excimer lasers include argon fluoride (ArF) and krypton fluoride (KrF) excimer lasers, with central wavelengths of 193 nm and 248 nm respectively.

[0003] For excimer lasers used in the field of chip processing, high requirements are placed on the stability of their energy and spectrum. However, an excimer laser is a gas laser pumped by discharge, with poor single-pulse energy stability and large energy variations between each pulse. Therefore, an excimer laser requires a built-in energy measurement device to measure the laser energy of each pulse in real time and perform real-time closed-loop feedback through the control of the high-voltage power supply to obtain a laser output with stable energy.

[0004] The beam quality of excimer lasers is poor, and the spot distribution is uneven and unstable, resulting in great difficulty in accurately measuring the energy of excimer lasers. It is necessary to homogenize the laser beam during energy measurement. The homogenized beam is incident on a photodetector to obtain the laser intensity signal, and the homogenization effect directly affects the accuracy of energy measurement. How to solve the energy measurement error caused by the uneven laser beam has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The present application provides a laser energy measurement device to solve the above problems of the prior art. The present application also provides an excimer laser and its aperture.

[0006] The present application provides a laser energy measurement device, including: a first beam homogenization component, a light spatial distribution adjustment element, and a photodetector, which are sequentially arranged along the light output direction of the laser discharge cavity; the light spatial distribution adjustment element is used to perform spatial adjustment of the light intensity of the laser incident on the photodetector.

[0007] Optionally, the light spatial distribution adjustment element is one of a spatially adjustable aperture, a spatial light modulator, or a microlens array.

[0008] Optionally, the light spatial distribution adjustment element is a spatially adjustable aperture; the spatially adjustable aperture includes: a first aperture and a second aperture, and different groups of small holes are circumferentially distributed at different radii from the center to the outside on the first aperture and the second aperture;

[0009] The first diaphragm and the second diaphragm are stacked together, and the small holes at corresponding positions are aligned, allowing the maximum light intensity to pass through. By adjusting the relative angle between the first diaphragm and the second diaphragm, the small holes at corresponding positions are displaced, and the light intensity distribution passing through the light space distribution adjustment element can be adjusted.

[0010] Optionally, the small holes at the same radius position on each of the first diaphragm and the second diaphragm are of the same size, and the size of the small holes at a position far from the center of the diaphragm is larger than that of the small holes close to the center position.

[0011] Optionally, the shapes of the small holes on the first diaphragm and the second diaphragm are different.

[0012] Optionally, the small holes on the first diaphragm are circular holes, and the small holes on the second diaphragm are square holes.

[0013] Optionally, the device of the present application further includes a second light homogenizing component, which is arranged between the light space distribution adjustment element and the photodetector.

[0014] Optionally, a first beam splitter and a second beam splitter with orthogonal distribution are further arranged on one side of the first light homogenizing component in the light incident direction.

[0015] The first light homogenizing component is a frosted glass or a phase light homogenizing component.

[0016] On the other hand, the present application discloses an excimer laser, including the above-mentioned laser energy measurement device.

[0017] On the other hand, the present application discloses a diaphragm, in which different groups of small holes are distributed circumferentially at different radius positions from the center to the outside on the diaphragm, the small holes at the same radius position are of the same size, and the size of the small holes at a position far from the center is larger than that of the small holes close to the center position.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] The laser energy measurement device provided by the present application includes: a first light homogenizing component, a light space distribution adjustment element, and a photodetector, which are sequentially arranged along the light output direction of the laser discharge cavity; the light space distribution adjustment element is used to adjust the light intensity space of the laser irradiating on the photodetector.

[0020] The laser energy measurement device provided by this application uses a light space distribution adjustable aperture to select the proportion of the light intensity in the energy measurement device that shines on the photodetector, so as to eliminate the energy measurement errors caused by the uneven laser beam, changes in pointing and position stability. It can be used not only for the energy detection of excimer lasers, but also for other lasers with uneven gas or energy distribution and poor beam quality. The device provided by this application realizes the elimination of the influence of laser spot non-uniformity on energy measurement, improves the accuracy of laser energy measurement, solves the problem of energy measurement error, and improves the accuracy and stability of laser energy measurement, and enhances the energy stability of the laser. Description of the Drawings

[0021] Figure 1 It is a schematic structural diagram of a laser with an internal laser energy measurement device according to an embodiment of this application;

[0022] Figure 2 It is a schematic diagram of a laser energy measurement device according to an embodiment of this application;

[0023] Figure 3 It is an example diagram of the working principle of a laser energy measurement device with a beam splitter with orthogonal distribution provided by this application;

[0024] Figure 4 It is an example diagram of the selection of a beam by a light space distribution adjustable aperture provided by this application;

[0025] Figure 5 It is a schematic structural diagram of a light space distribution adjustable aperture according to an embodiment of this application;

[0026] Figure 6 Is Figure 5 It is a schematic structural diagram showing the structures of two apertures of a light space distribution adjustable aperture;

[0027] Figure 7 Is Figure 6 It is an example diagram of adjusting the relative angle after two apertures are stacked;

[0028] Figure 8 It is a schematic diagram of the exemplary small hole distribution on a light space distribution adjustable aperture according to an embodiment of this application; Detailed Embodiments

[0029] Many specific details are set forth in the following description in order to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of this application. Therefore, this application is not limited by the specific embodiments disclosed below.

[0030] As described above, lasers are widely used due to their high energy, high brightness, and good monochromaticity. Among them, in the semiconductor manufacturing process, the line width of the chip depends on various physical indicators such as the central wavelength and energy of the laser in the lithography machine. The excimer laser in the deep ultraviolet band is a commonly used light source for high-end lithography machines. Since the stability of the output energy and spectrum of the laser is particularly important for the process consistency in semiconductor processing, it is particularly important to measure only the pulse energy of the laser and control the laser pump power through the measurement results to obtain a laser output with stable energy. Based on this, the following embodiments of the present application provide an energy measurement device applied to a laser. This energy measurement device can be built into the laser and form a part of the laser, or can be placed outside the laser as a detection component for measuring the beam energy of the laser. The present application does not limit this.

[0031] The laser energy measurement device according to the embodiment of the present application includes: a first light homogenizing component, a light spatial distribution adjusting element, and a photodetector sequentially arranged along the light output direction of the laser discharge cavity; the light spatial distribution adjusting element is used for adjusting the spatial light intensity of the laser irradiating on the photodetector.

[0032] The following will describe in detail the laser energy measurement device according to the embodiment of the present application in conjunction with the accompanying drawings, and will also describe each step of the method.

[0033] For the convenience of understanding, this embodiment first describes the laser with an energy measurement device.

[0034] Please refer to Figure 1 , which shows a schematic diagram of a laser structure according to this embodiment. Figure 1 In, it includes: The laser includes a discharge cavity 1, a pump high-voltage power supply 2, an output coupling mirror 6, a line width narrowing device 5, and an energy measurement device 7. Among them, the discharge cavity is a sealed cavity, and the cavity is filled with a working substance gas, such as a mixture of inert gas and halogen gas. For a 193nm wavelength laser, the inside is a mixture of F2 and Ar, and for a 248nm wavelength laser, the inside is a mixture of F2 and Kr. Two relatively placed discharge electrodes 4 are also arranged inside the chamber of the discharge cavity 1, and the high-voltage power supply 2 is connected to the discharge electrodes 4. After the discharge electrodes 4 are energized, under the action of the high voltage, population inversion occurs, and F2 and Ar are converted into the excimer state of ArF (F2 and Kr are converted into the KrF excimer state). The electrons of the excimer state of ArF transition to the lower energy level, generating deep ultraviolet laser. The laser oscillates and amplifies in the resonant cavity, forming a laser with good monochromaticity and high energy concentration, and finally outputs through the output coupling mirror.

[0035] In this embodiment, the two sides of the discharge chamber 1 are sealed with window plates 3 made of CaF2 or fused silica. The angle between the window plate 3 and the discharge chamber 1 is the Brewster angle, which helps to reduce the reflection of the P-polarized light by the window plate, so as to improve the energy and polarization degree of the laser.

[0036] In this embodiment, a linewidth narrowing device 5 is further provided on one side of the discharge chamber 1 to narrow the linewidth of the laser beam and improve the laser monochromaticity. The linewidth narrowing device 5 can adopt any structure in the prior art and will not be elaborated here.

[0037] The energy measurement device 7 is provided on the other side of the discharge chamber 1 for measuring the light intensity of the beam output from the discharge chamber 1. The spot of the laser beam emitted from the discharge chamber 1 is approximately rectangular in distribution, with a length of about 12 mm and a width of about 2 mm. This beam enters the energy measurement device 7 through the output coupling mirror 6 and the beam splitter.

[0038] Please refer to Figure 2 , which is a schematic structural diagram of a laser energy measurement device provided in this embodiment. In Figure 2 , the laser energy measurement device includes a first beam homogenizing component 11, a light spatial distribution adjusting element 13, and a photodetector 16 arranged in sequence along the light output direction of the laser discharge chamber 1. Among them, the light spatial distribution adjusting element 13 is used to adjust the light intensity space of the laser irradiating on the photodetector 16.

[0039] As mentioned above, the beam quality of the excimer laser is poor, the spot distribution is uneven and unstable, resulting in great difficulty in accurately measuring the energy of the excimer laser. It is necessary to homogenize the beam of the laser during energy measurement. The homogenized beam is irradiated on the photodetector to obtain the laser light intensity signal. The homogenization effect directly affects the accuracy of energy measurement. Because the beam homogenization optical path cannot completely homogenize the spot of the laser, when the spot distribution, pointing or position of the laser changes, even if the total energy of the laser remains unchanged, the energy irradiated on the photodetector will change, thus affecting the accuracy of the laser energy measurement and the energy stability of the excimer laser.

[0040] Please continue to refer to Figure 2 , in this embodiment, the energy measurement device 7 includes at least two sets of beam homogenizing components - the first beam homogenizing component 11 and the second beam homogenizing component 14, whose function is to homogenize the spot of the laser and reduce the influence of the unevenness of the laser spot on energy measurement. However, it is not necessary to set two sets of beam homogenizing components. Fewer or more beam homogenizing components can also be set, and the number of beam homogenizing components to be set can be selected according to actual needs, such as the attenuation of light intensity, etc.

[0041] The first light homogenizing component 11 and the second light homogenizing component 14 can be multilayer frosted glasses that have been sufficiently polished. Since the uneven microstructures on the surface of the frosted glass can modulate the beam phase of the laser, making its distribution uniform. The first light homogenizing component 11 and the second light homogenizing component 14 can also be diffractive optical elements with specific phase structures, and the beam homogenization is achieved by using their phase distributions.

[0042] The materials of the first light homogenizing component 11 and the second light homogenizing component 14 are preferably fused silica or calcium fluoride, which have a relatively high transmittance in the deep ultraviolet band. The spot size after homogenization by the light homogenizing component is generally larger than the size of the incident spot, ranging from a dozen millimeters to dozens of millimeters. Only a part of the light in this beam is received by the photodetector 16 and converted into an electrical signal. After being amplified by the circuit, a voltage or current signal is obtained, and the magnitude of the signal is proportional to the incident light intensity. Therefore, the energy of the laser can be obtained by measuring the magnitude of the electrical signal of the photodetector 16 and fed back to the high-voltage power supply 2 for closed-loop feedback to maintain a stable output of the laser energy.

[0043] As mentioned above, during the process of the beam passing through the first light homogenizing component 11 and the second light homogenizing component 14, since the light homogenizing component cannot completely homogenize the beam, the proportion of the light at different positions of the laser beam hitting the photodetector 16 is not consistent. Generally, the homogenized spot is similar to a Gaussian distribution in terms of angular and spatial distribution. As Figure 2 shown, at this time, the vertically emitted beam is relatively strong, while the obliquely emitted beam is relatively weak. Therefore, after passing through the light homogenizing component, the light in the middle position hits the photodetector 16 in a larger proportion than the light at the edge position, as shown in Figure 4 Figure A in

[0044] Because the proportion of each point on the laser spot hitting the photodetector 16 is inconsistent, when the spot distribution of the laser changes, even if the total energy of the laser remains unchanged, different light intensities are still received by the photodetector 16, thus causing an energy measurement error and affecting the stability of the laser energy. For this reason, in the embodiments of the present application, an optical spatial distribution adjustment element 13 is provided to select the light at different positions of the laser beam, reduce the proportion of the middle beam hitting the photodetector, and increase the proportion of the edge beam hitting the photodetector 16. As Figure 4 Figure B in shows the radial light intensity transmission curve of the optical spatial distribution adjustment element; after passing through the spatially adjustable aperture, the proportion of the light at each point on the spot hitting the photodetector 16 is equal or approximately equal, as shown in Figure 4 Figure C in ; Using the optical spatial distribution adjustment element 13 can eliminate the influence of the uneven laser spot on energy measurement and improve the accuracy of laser energy measurement.

[0045] In this embodiment, the optical spatial distribution adjustment element can be a spatially adjustable aperture, asFigure 5 The front view and side view of the spatially distributed adjustable aperture of this embodiment are shown; the spatially distributed adjustable aperture includes: a first aperture 13a and a second aperture 13b. On each of the first aperture 13a and the second aperture 13b, different groups of small holes are respectively arranged circumferentially at different radius positions from the center outwards; the first aperture 13a and the second aperture 13b are stacked together, and the small holes at corresponding positions are aligned, allowing the maximum light intensity to pass through. By adjusting the relative angle between the first aperture 13a and the second aperture 13b, the small holes at corresponding positions are misaligned, and the light intensity distribution passing through the light spatial distribution adjustment element 13 can be adjusted.

[0046] Figure 5 and Figure 6 The structural schematic diagrams of the first aperture 13a and the second aperture 13b are respectively shown in Figure 5 and Figure 6 As shown, the first aperture 13a and the second aperture 13b are circular or approximately circular. Of course, they can also have other shapes. Different groups of small holes are arranged circumferentially at different radii (such as r1, r2) from the center (the center in other shapes) of the first aperture 13a and the second aperture 13b outwards. The shape of the small holes can be circular, square or other shapes. For example, several circular holes are arranged circumferentially along r1 on the second aperture 13b (for clarity, only 4 small holes are drawn in the figure), and several circular holes are arranged circumferentially along r2. Square holes are arranged on the first aperture 13a in the same way. Among them, the radius r1 is less than r2, the circular holes are evenly distributed on the radius r1, and their diameter is d1. The diameter of the circular holes on the radius r2 is d2. d2 is greater than d1. That is, the sizes of the small holes at the same radius position are the same, and the sizes of the small holes at positions farther from the center of the aperture are larger than those of the small holes at positions closer to the center. In this embodiment, only the case of arranging small holes at two different radii is shown. It should be understood that the small holes arranged circumferentially can be arranged at different radial positions. The small holes at corresponding positions of the two apertures can be the same, or the small holes on one aperture can be larger than the sizes of the small holes at the corresponding positions on the other aperture.

[0047] Stack the first aperture 13a and the second aperture 13b together and make them coaxial. At this time, the small holes at corresponding positions are aligned, and the maximum light intensity can be ensured to pass through the spatially distributed adjustable aperture. Rotate one of the apertures along the axis of the two, so that the small holes at corresponding positions are misaligned to a certain extent, so that the originally completely corresponding small holes are partially corresponding and partially blocked by the other aperture, and the light transmission gap is reduced, thereby reducing the light intensity passing through. By rotating to change the relative angle between the two apertures, the light transmission degree of the spatially distributed adjustable aperture can be changed, and thus the light intensity of the transmitted light can be changed. For easy understanding, the cases of small hole occlusion at different angles of the two apertures are respectively shown in Figures A, B, and C in Figure 7 The small hole occlusion at different angles of the two apertures is respectively shown in Figures A, B, and C in

[0048] As described above, the small hole with a radius of r1 is close to the center of the aperture. Therefore, it determines a greater proportion of the middle beam hitting the photodetector. When d1 increases, more of the middle beam will pass through the optical space distribution adjustment element 13 and hit the photodetector 16. When d1 decreases, more of the middle beam will be blocked by the optical space distribution adjustment element 13, and less light will hit the photodetector 16. The small hole with a radius of r2 is far from the center of the aperture. Therefore, the small hole with a radius of r2 determines a greater proportion of the edge-side beam hitting the photodetector 16. When d2 increases, more of the edge beam will pass through the optical space distribution adjustment element 13 and hit the photodetector 16. When d2 decreases, more of the edge beam will be blocked by the optical space distribution adjustment element 13, and less light will hit the photodetector 16.

[0049] During the actual debugging of the energy measurement device 7, it is necessary to adjust the light transmission ratio at different positions of the optical space distribution adjustment element 13 and compare the signal intensities of the photodetector 16 when the beam hits the center and the edge of the energy measurement device. When the intensity of the light hitting the center is greater than that of the edge, the light transmission ratio of the center can be reduced or the light transmission ratio of the edge can be increased. At this time, the aperture 13a can be rotated. The aperture 13a has a series of small holes, and their sizes are larger than those of the small holes in 13b. As Figure 7 shown, when the aperture 13a is rotated clockwise, the middle small hole in 13b will be blocked by 13a, while the small holes at the edge remain unchanged. Therefore, the light transmission ratio in the middle is reduced. When the aperture 13a is rotated counterclockwise, the small holes at the edge of 13b will be blocked by 13a, while the small hole in the center remains unchanged. Therefore, the light transmission ratio at the edge is reduced. By experimentally rotating the angle of the aperture 13a so that the signal intensities of the photodetector 16 are equal or approximately equal when the center and edge lights hit the energy measurement device 7, the influence of the uneven light intensity distribution, pointing, and stability of the laser on the energy measurement device 7 can be eliminated, the energy measurement accuracy can be improved, and the energy stability of the laser can be enhanced. The way that the blocking situations of the holes at the center position (inner side) and the edge (outer side) are inconsistent when the two apertures are rotated clockwise and counterclockwise as described above is achieved by the following method: when the small holes at the corresponding positions on the two apertures are aligned, the position of the small hole set on the inner side of one aperture moves slightly counterclockwise on the aperture, while the position of the small hole set on the outer side moves slightly clockwise. When the two apertures are stacked, as Figure 7 shown in Figure A, the inner circular hole of one aperture approaches the edge of the square hole of the other aperture counterclockwise, while the outer circular hole approaches the edge of the square hole clockwise. This makes the changes in the light transmission gaps on the inner and outer sides not exactly the same when the two apertures rotate relative to each other.

[0050] The optical space distribution adjustment element 13 is an important element for distributing the light transmission ratios of the middle and edge beams. It is adjusted during the laser debugging process, rather than adjusting the aperture during the laser operation. Therefore, the online adjustment function of the optical space distribution adjustment element 13 is not necessary and can be achieved by replacing the aperture with a specific distribution during the laser debugging process. That is to say, apertures with multiple small holes of different sizes, different shapes, and different distributions can be set, and two or more apertures can be selected and used together according to needs. As Figure 8 shown in, three different apertures are shown. When it is necessary to reduce the light transmission ratio of the edge light, the diameter of the edge small holes can be reduced, as shown by the aperture 13d; when it is necessary to reduce the light transmission ratio of the middle light, the diameter of the middle small holes can be reduced, as shown by the aperture 13e. It should be noted that in practice, in order to achieve a uniform light filtering effect of the aperture, the small holes on the aperture can be set very small and the number is very large. Moreover, the radial distribution of the small holes is not limited to two layers and can be multi-layer distributed.

[0051] In order to reduce the influence of the beam splitter on the energy measurement, as an implementation manner, a first beam splitter 8 and a second beam splitter 9 with an orthogonal distribution are further provided on the light incident direction side of the first light homogenizing component 11. As Figure 3 shown, the first beam splitter 8 and the second beam splitter 9 are preferably orthogonally distributed. The first beam splitter 8 is located in the YZ plane and forms an angle of 45 degrees with the Y axis. The second beam splitter 9 is located in the XY plane and forms an angle of 45 degrees with the Y direction. The light incident on the first beam splitter 8 that is p-polarized becomes s-polarized after reaching the second beam splitter 9, while the light incident on the first beam splitter 8 that is s-polarized becomes p-polarized after incident on the second beam splitter 9. When the incident laser light intensity is Ein, where the proportion of P light is k and the proportion of S light is 1-k, the reflected light intensity Eout after reflection by the first beam splitter 8 and the second beam splitter 9 is:

[0052] E out =E in kR p ·R s +E in (1-k)R p ·R s =E in R p ·R s

[0053] It can be seen that at this time, the reflected light intensity is independent of the polarization state of the laser. However, when the laser operates for a long time, the polarization state will change slightly. The beam splitters with an orthogonal distribution will not cause measurement errors in the energy measurement device 7, improving the long-term stability of the energy measurement device 7 for energy measurement.

[0054] The laser energy measurement device 7 of the embodiments of the present application includes a spatially adjustable aperture, which selects the proportion of the light intensity in the energy measurement device 7 that irradiates on the photodetector 16, so as to eliminate the energy measurement error caused by the uneven laser beam, the changes in the pointing and position stability. It can be used not only for the energy detection of excimer lasers, but also for other gas lasers or lasers with uneven energy distribution and poor beam quality.

[0055] In addition, other components can be used to achieve the function of the spatially adjustable aperture, such as a spatial light modulator or a micromirror array, etc., which will not be elaborated here.

[0056] Based on the above-disclosed energy measurement device, the present application further discloses an excimer laser, which solves the problems of poor beam quality, uneven spot distribution, and unstable beam pointing and position of the excimer laser, resulting in great difficulty in accurately measuring the energy of the excimer laser.

[0057] Although the present application is disclosed above in preferred embodiments, it is not intended to limit the present application. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application should be subject to the scope defined by the claims of the present application.

Claims

1. A laser energy measurement device, characterized in that, Comprising: A first light homogenizing component, a light spatial distribution adjusting element, and a photodetector sequentially arranged along the light output direction of the laser discharge cavity; The light spatial distribution adjusting element is used for performing light intensity spatial adjustment on the laser irradiated on the photodetector; Wherein, the light spatial distribution adjusting element is a light aperture with adjustable spatial distribution; the light aperture with adjustable spatial distribution includes: a first aperture and a second aperture, and different groups of small holes are circumferentially distributed at different radius positions from the center outwards on the first aperture and the second aperture; the small holes at the same radius position on each of the first aperture and the second aperture are of the same size, and the size of the small holes at a position far from the center of the aperture is larger than the size of the small holes at a position close to the center; the first aperture and the second aperture are stacked together, and the small holes at corresponding positions are aligned, allowing the maximum light intensity to pass through. By adjusting the relative angle between the first aperture and the second aperture, the small holes at corresponding positions are misaligned, and the light intensity distribution passing through the light spatial distribution adjusting element can be adjusted.

2. The laser energy measurement device according to claim 1, wherein The shapes of the small holes on the first aperture and the second aperture are different.

3. The laser energy measurement device according to claim 1, wherein The small holes on the first aperture are circular holes, and the small holes on the second aperture are square holes.

4. The laser energy measurement device according to claim 1, wherein It further includes a second light homogenizing component, and the second light homogenizing component is arranged between the light spatial distribution adjusting element and the photodetector.

5. The laser energy measurement device according to claim 1, wherein A first beam splitter and a second beam splitter with orthogonal distribution are further arranged on the side of the first light homogenizing component in the direction of the incident light.

6. The laser energy measurement device according to claim 1, characterized in that, The first light homogenizing component is a frosted glass or a phase light homogenizing component.

7. An excimer laser, characterized in that, Comprising the laser energy measurement device according to any one of claims 1-6 above.

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