A monitoring system and method for the spatial position of a droplet target in an extreme ultraviolet light source

Abstract

The present invention belongs to the technical field of extreme ultraviolet light sources, and particularly relates to a monitoring system and method for the spatial position of a droplet target in an extreme ultraviolet light source. By using a single CCD to simultaneously image the droplets on the XOZ plane and the YOZ plane, the real-time monitoring of the spatial position of the droplet tin target is realized. On this basis, two feedback control methods, manual control and automatic control, are developed to feedback-adjust the spatial position of the droplet generator, so that the movement path of the droplets always passes through the laser focus. The present invention can perform real-time feedback adjustment on the spatial position of the droplet target in the extreme ultraviolet lithography light source based on the droplet jet pictures taken by the CCD, and has the advantages of simple structure, high precision, and easy implementation. Moreover, it can effectively correct the offset of the target droplet path relative to the laser focus, which is beneficial to improving the generation efficiency of EUV light radiated by LPP.

Description

Technical Field

[0001] The present invention belongs to the technical field of extreme ultra-violet (EUV) light sources, and particularly relates to a monitoring system and method for the spatial position of a droplet target in an EUV light source. Background Technique

[0002] At present, with the continuous development of Moore's law, the most advanced integrated circuit process nodes have reached 5 nm or even 3 nm. Traditional near ultra-violet (NUV) light sources and deep ultra-violet (DUV) light sources can no longer meet the requirements of the above lithography processes, and a new generation of EUV light sources must be developed.

[0003] The mainstream method for generating EUV light is laser-produced plasma (LPP) radiation. By focusing a pulsed laser with a high peak power on a target tin droplet, it is ionized into a plasma, and the plasma will radiate EUV light with a wavelength of 13.5 nm. However, due to a certain degree of jitter in the path of the tin droplets ejected by the droplet generator, the target droplet deviates from the laser focus, resulting in the laser not hitting the target droplet or the interaction between the laser and the target droplet being insufficient, which is not conducive to the efficient generation of EUV light.

[0004] In a conventional monitoring and control system for the spatial position of a droplet tin target in an EUV light source, generally two mutually perpendicular charge-coupled devices (CCDs) are used to monitor the offsets of the droplet in the XOZ plane and the YOZ plane respectively, and then the spatial position of the droplet generator is feedback-regulated.

[0005] Through the above analysis, the problems and defects existing in the prior art are as follows:

[0006] (1) Multiple devices in the prior art will increase the complexity of the system, result in higher costs, and reduce stability.

[0007] (2) There are certain patent barriers in commercial applications. Summary of the Invention

[0008] Aiming at the problems existing in the prior art, the present invention provides a monitoring system for the spatial position of a droplet target in an EUV light source, which is used to monitor and control the spatial position of the droplet target by using single-camera imaging in the light source of an EUV lithography machine.

[0009] The present invention includes a droplet generator, a first detection light source, a second detection light source, a semi-reflective and semi-transmissive lens, a plane mirror, a CCD, a synchronization signal source, a computer, a two-dimensional electric control rotary table, and a two-dimensional electric control displacement table;

[0010] The droplet generator is used to heat and melt metallic tin and eject it in the form of droplets, and the movement path of the droplets is a ray.

[0011] Both the first detection light source and the second detection light source are connected to the synchronization signal source, receive pulse signals from the synchronization signal source, and generate pulsed light beam outputs with a certain repetition frequency to provide background light illumination for the CCD.

[0012] The plane mirror is parallel to the z-axis and placed on the optical paths of the two light beams to adjust the propagation direction of the light and change the distance of the light transmitted to the CCD.

[0013] The semi-reflective semi-transmissive lens is placed at the front end of the CCD lens, and the mirror surface is parallel to the z-axis to integrate the two light beams into the CCD camera.

[0014] The CCD is connected to the synchronization signal source, and takes pictures of the droplets when the detection light source emits light. The imaging area of the CCD can be finely adjusted through the mounting bracket.

[0015] The computer is connected to the CCD, receives the picture stream from the CCD, and performs real-time processing on the pictures through a program, can calculate the angles at which the droplet jet deviates from the laser focus in the x-direction and the y-direction, and outputs the angles as parameters.

[0016] The two-dimensional electrically controlled displacement stage is tightly fixed to the droplet generator, drives the droplet generator to displace in the XOZ plane and the YOZ plane, and adjusts the nozzle position directly above the laser focus.

[0017] The two-dimensional electrically controlled rotary stage is tightly fixed to the droplet generator, is connected to the computer through a signal transmission line, and drives the droplet generator to rotate in the XOZ plane and the YOZ plane according to the control parameters of the computer to perform feedback adjustment on the ejection angle of the droplet jet so that the droplets pass through the laser focus.

[0018] Further, the normal line of the mirror forms a 45° angle with the light beam transmission direction.

[0019] Further, the trigger signal waveforms received by the first detection light source and the second detection light source are the same, and the shooting time of the CCD covers the light emission time of the detection light source.

[0020] Further, the laser focus is defined as the coordinate origin.

[0021] Further, the light beam emitted by the first detection light source propagates along the negative x-axis through the vacuum chamber.

[0022] Four plane mirrors, namely mirror A, mirror B, mirror C, and mirror D, are placed in the optical path to adjust the optical path. After passing through the semi-reflective and semi-transmissive lens E, the light is transmitted to the CCD. The light beam emitted by the second detection light source propagates along the negative y-axis through the vacuum chamber, is reflected by the mirror F and the mirror G, and then is reflected by the semi-reflective and semi-transmissive lens E to the CCD. When adjusting the optical path, the path length of the light beam L1 should be the same as that of the light beam L2, and the droplet projections on the XOZ plane and the YOZ plane should be clearly imaged on the CCD.

[0023] Another object of the present invention is to provide a method for monitoring the spatial position of a droplet target in an extreme ultraviolet light source, including:

[0024] Using a single CCD to simultaneously image the droplets on the XOZ plane and the YOZ plane to realize real-time monitoring of the spatial position of the droplet tin target. On this basis, two feedback control methods, manual control and automatic control, are developed to feedback-adjust the spatial position of the droplet generator so that the movement path of the droplet always passes through the laser focus.

[0025] An operation method of this system is as follows (manual control mode):

[0026] (1) Mark the laser focus, turn on the CCD and set it to the continuous imaging mode, and finely adjust the position of the CCD so that the two images of the laser focus on the XOZ plane and the YOZ plane coincide and are located at the center of the photo.

[0027] (2) The droplet generator starts to work, turn on the synchronous signal source, trigger the first detection light source and the second detection light source to flash, and set the CCD to the trigger mode to take pictures synchronously with the light emission of the light source.

[0028] (3) When the droplet jet deviates, the images of the droplet jet captured by the CCD will have different characteristics. The judgment criterion is: on the photo, the positive directions of the x-axis and the y-axis both point to the left side of the photo, and the droplet ejection direction is from top to bottom. From this, the deviation direction of the droplet can be judged.

[0029] (4) Control the two-dimensional electric control rotary table to rotate in the XOZ plane and the YOZ plane, respectively adjust the two images of the droplet jet to be vertically downward, and distinguish which plane each of the two images belongs to during this process. At this time, the two images should be parallel to each other. After this operation, the direction deviation of the droplet jet is corrected, but the position deviation of the nozzle of the droplet generator still exists.

[0030] (5) Control the two-dimensional electric control displacement table to move in the XOY plane until the images of the droplet jet on the CCD coincide and pass through the laser focus. At this time, the position deviation of the nozzle of the droplet generator is corrected.

[0031] Another operation method of this system is as follows (automatic control mode):

[0032] (1) Mark the laser focus, adjust the two-dimensional electric control displacement stage to make the center of the nozzle directly above the laser focus, start the droplet generator, and turn on the synchronization signal source.

[0033] (2) Trigger the first detection light source, adjust the CCD to the trigger mode to image the droplet jet on the YOZ plane, and transmit the image information to the computer.

[0034] (3) After the computer receives the image information, use the thresholding algorithm to binarize the picture. By setting reasonable threshold conditions, search for the droplet boundary. Taking the Python language as an example, the OpenCV function library can be called. First, use the cv2.cvtColor function to convert the RGB image to a grayscale image, then use the THRESH_BINARY algorithm of the cv2.threshold function to binarize the image. Finally, use the cv2.findContours function to quickly and accurately identify the contour of the droplet.

[0035] (4) Calculate the centroid of each droplet respectively. Since the picture is binarized, for a single droplet, the centroid calculation formula is as follows:

[0036]

[0037] where, (x i , y i ) represents the pixel coordinates included in the droplet, and n is the total number of pixels contained in the droplet.

[0038] (5) Fit a straight line according to the centroid coordinates, find the equation expression of the projection of the droplet jet on the YOZ plane, and the angle α between the droplet jet and the z-axis on the YOZ plane can be deduced from the slope k of the straight line equation. The calculation method is as follows:

[0039]

[0040] (6) The computer outputs the parameter α to the two-dimensional electric control rotary table, so that the droplet generator rotates by an angle α around the nozzle center on the YOZ plane, so that the projection of the droplet jet on the YOZ plane passes through the laser focus;

[0041] (7) Turn off the first detection light source, trigger the second detection light source, the CCD images the droplet jet on the YOZ plane, and transmits the image information to the computer. Repeat the processing of the above steps (3), (4), and (5) to obtain the angle β between the droplet jet and the z-axis on this plane. The computer outputs the parameter β to the two-dimensional electric control rotary table, so that the droplet generator rotates by an angle β around the nozzle center on the YOZ plane, so that the projection of the droplet jet on the YOZ plane passes through the laser focus.

[0042] (8) Return to step (2) and repeat the above process until the monitoring and regulation process ends.

[0043] Combining the above technical solutions and the solved technical problems, the advantages and positive effects of the technical solution to be protected by the present invention are analyzed from the following aspects:

[0044] First, aiming at the technical problems existing in the above-mentioned prior art and the difficulty of solving this problem, closely combining the technical solution to be protected by the present invention and the results and data in the R & D process, etc., analyze in detail and profoundly how the technical solution of the present invention solves the technical problems and the creative technical effects brought after solving the problems. The specific description is as follows:

[0045] (1) In the optical path arrangement, the present invention realizes the simultaneous imaging of droplets on the XOZ plane and the YOZ plane by using the combination of two mutually perpendicular light beams and multiple reflectors;

[0046] (2) In the motion control of the droplet generator, the present invention combines a two-dimensional electric control displacement stage and a two-dimensional electric control rotation stage, and realizes the precise regulation of the droplet jet path through the motion control of 4 dimensions;

[0047] (3) In the operation mode, for the droplet target space position monitoring and regulation system in the present invention, two control modes, manual and automatic, are proposed. Among them, the manual control mode is more intuitive and has better handling of details in manual adjustment; while the automatic control mode can store and process the data generated during work faster and more conveniently.

[0048] Second, regarding the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by the present invention are specifically described as follows:

[0049] (1) The present invention provides a monitoring system for the space position of a droplet target in an extreme ultraviolet light source based on single-camera imaging. By reasonably arranging the optical path, the CCD can simultaneously image the droplets on the XOZ plane and the YOZ plane, realizing the real-time monitoring of the space position of the droplet jet in the vacuum chamber.

[0050] (2) Another object of the present invention is to provide a regulation system for the space position of a droplet target in an extreme ultraviolet light source. According to the droplet jet photos taken by the CCD, the offset of the droplet jet path relative to the laser focus can be calculated, and this is used as the adjustment basis for the two-dimensional electric control rotation stage and the two-dimensional electric control displacement stage to perform feedback adjustment on the space position of the droplet generator, ensuring that the movement path of the tin droplet always passes through the laser focus, which is beneficial to improving the generation efficiency of EUV light radiated by LPP.

[0051] (3) Another object of the present invention is to provide an extreme ultraviolet light source that implements the method for monitoring the spatial position of the droplet target in the extreme ultraviolet light source.

[0052] Thirdly, as the auxiliary evidence of the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0053] (1) The expected benefits and commercial value after the transformation of the technical solution of the present invention are:

[0054] In traditional extreme ultraviolet light sources, the monitoring and regulation of droplet tin jets are realized by using two mutually perpendicular CCDs. The present invention can bypass the established patent barriers and use a single CCD to monitor the position of the droplet tin jet. The present invention also combines computer machine vision with the motion regulation of the droplet generator, enabling the system to have the ability to automatically monitor and regulate the spatial position of the droplet jet.

[0055] (2) Whether the technical solution of the present invention overcomes technical prejudices:

[0056] The innovativeness of the present invention is reflected in the advantages of the present invention:

[0057] First of all, it breaks through the traditional method of using two mutually perpendicular CCDs to monitor the droplet jet in the extreme ultraviolet light source, and realizes the monitoring and regulation of the spatial position of the droplet target in the extreme ultraviolet light source based on the droplet jet pictures taken by a single CCD camera.

[0058] Secondly, the present invention combines a two-dimensional electric control displacement stage and a two-dimensional electric control rotation stage to achieve precise regulation of the droplet jet path through motion control in four dimensions. Brief Description of the Drawings

[0059] Figure 1 It is a schematic structural diagram of a monitoring system for the spatial position of the droplet target in the extreme ultraviolet light source provided by an embodiment of the present invention.

[0060] Figure 2 It is a top view of the optical path of the monitoring system for the spatial position of the droplet target in the extreme ultraviolet light source provided by an embodiment of the present invention.

[0061] Figure 3 It is a schematic diagram of the droplet jet deviating from the laser focus in an embodiment provided by an embodiment of the present invention (the nozzle deviates from the z-axis).

[0062] Figure 4 is a schematic diagram of the imaging of the droplet jet on the CCD in an embodiment provided by an embodiment of the present invention. Among them, Figure 4(a) is a schematic diagram of the image presented on the CCD14 when the first detection light source 11 and the second detection light source 12 are triggered simultaneously; Figure 4(b) is to adjust the two-dimensional electric control rotation stage so that the two images 30 yoz and 30 xozSchematic diagram all parallel to the z-axis.

[0063] Figure 5 In an embodiment provided by an embodiment of the present invention, it is a schematic diagram of the droplet jet deviating from the laser focus (the nozzle is located on the z-axis).

[0064] Figure 6 is a schematic diagram of the projections of the droplet jet in the YOZ plane and the XOZ plane in an embodiment provided by an embodiment of the present invention. Among them, Figure 6(a) is the imaging result diagram of triggering the first detection light source 11 to image the droplet jet on the YOZ plane; Figure 6(b) is the imaging result diagram of triggering the second detection light source 12 to image the droplet jet on the XOZ plane.

[0065] Figure 7 In an embodiment provided by an embodiment of the present invention, it is a schematic flow diagram of the method for monitoring the spatial position of the droplet target in the extreme ultraviolet light source.

[0066] Figure 8 It is a schematic diagram of the image processing flow of the monitoring system for the spatial position of the droplet target in the extreme ultraviolet light source provided by an embodiment of the present invention.

[0067] Figure 9(a) is a droplet jet diagram in the first quadrant provided by an embodiment of the present invention: both images are shifted to the left from top to bottom.

[0068] Figure 9(b) is a droplet jet diagram in the second quadrant provided by an embodiment of the present invention: from top to bottom, one image is shifted to the left and one is shifted to the right; if the two-dimensional electric control rotating table is adjusted to rotate in the XOZ plane, the slope of the image shifted to the right will change.

[0069] Figure 9(c) is a droplet jet diagram in the third quadrant provided by an embodiment of the present invention: both images are shifted to the right from top to bottom;

[0070] Figure 9(d) is a droplet jet diagram in the fourth quadrant provided by an embodiment of the present invention: from top to bottom, one image is shifted to the left and one is shifted to the right; if the two-dimensional electric control rotating table is adjusted to rotate in the XOZ plane, the slope of the image shifted to the left will change.

[0071] Figure 10 is a comparison diagram of droplet images during the processing; among them, Figure 10(a) is the original picture and the ROI selection (black frame); Figure 10(b) is the binary image; Figure 10(c) is the droplet contour, droplet center, and the fitted droplet path diagram.

[0072] In the figure: 11, the first detection light source; 12, the second detection light source; 13, the semi-reflective semi-transmissive lens; 14, the CCD; 15, the two-dimensional electric control rotating table; 16, the synchronous signal source; 17, the computer; 18, the two-dimensional electric displacement table; 19, the droplet generator; 20, the nozzle center; 30, the droplet jet; 30 yoz, the image of the droplet jet on the YOZ plane on the CCD; 30 xoz , the image of the droplet jet on the XOZ plane on the CCD; 100, laser focus; 101, the initial droplet jet photo taken by the CCD; 102, the droplet jet photo taken by the CCD after adjusting the angle; 201, the photo of the droplet jet on the YOZ plane taken by the CCD; 202, the photo of the droplet jet on the XOZ plane taken by the CCD; 400, vacuum chamber; L1, the light beam emitted by the first detection light source; L2, the light beam emitted by the second detection light source. Specific embodiments

[0073] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the following further elaborates on the present invention in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0074] I. Explanation of the embodiment. In order to enable those skilled in the art to fully understand how the present invention is specifically implemented, this part is an explanatory embodiment that expands and explains the technical solution of the claims.

[0075] Embodiment 1

[0076] As Figure 1 shown, the present invention provides a monitoring system for the spatial position of a droplet target in an extreme ultraviolet light source, mainly including: a first detection light source 11, a second detection light source 12, a semi-reflective and semi-transmissive lens 13, a CCD 14, a synchronization signal source 16, a computer 17, a two-dimensional electric displacement stage 18, and a droplet generator 19. The synchronization signal source 16 is connected to the first detection light source 11, the second detection light source 12, and the CCD 14; the computer 17 is connected to the CCD 14 and the two-dimensional electric displacement stage 18; the two-dimensional electric displacement stage 18 is connected to the droplet generator 19.

[0077] Figure 2 is the top view of the optical path of the droplet target spatial position monitoring and control system in the embodiment of the present invention; the light beam L1 emitted by the first detection light source 11 propagates along the negative x-axis direction through the vacuum chamber 400, and four plane mirrors A, B, C, and D are placed in the optical path to adjust the optical path, and then transmitted to the CCD 14 through the semi-reflective and semi-transmissive lens 13; the light beam L2 emitted by the second detection light source 12 propagates along the negative y-axis direction through the vacuum chamber 400, and is reflected by the mirrors F and G and then reflected by the semi-reflective and semi-transmissive lens 13 to the CCD 14; when adjusting the optical path, it should be ensured that the length of the path O-G-F-E-H is the same as the length of the path O-A-B-C-D-E-H, and the droplets on the XOZ plane and the YOZ plane can be clearly imaged on the CCD 14.

[0078] In one embodiment, the droplet jet 30 is offset from the laser focus 100 and intersects the XOY plane in the third quadrant, as Figure 3 shown. We use the manual operation mode for adjustment. After the optical path is aligned, the first detection light source 11 and the second detection light source 12 are triggered simultaneously. The image presented on the CCD14 is shown in the initial droplet jet photograph 101 taken by the CCD in Fig. 4(a) of Fig. 4; adjust the two-dimensional electric control rotating table to make the two images of the droplet jet on the CCD14 yoz and xoz both parallel to the z-axis, as shown in the droplet jet photograph 102 taken by the CCD after adjusting the angle in Fig. 4(b) of Fig. 4. At this time, the jet direction of the jet is vertically downward; finally, adjust the horizontal position of the droplet generator 19 through the two-dimensional electric displacement table 18 to make the images yoz and xoz coincide with the laser focus 100 to ensure that the movement path of the droplet jet 30 passes through the laser focus 100.

[0079] In another embodiment, the nozzle 20 has been adjusted to a position directly above the laser focus 100, but the droplet jet 30 is offset from the laser focus 100 and intersects the XOY plane in the third quadrant, as Figure 5 shown. We use the automatic operation mode for adjustment. The operation process is as Figure 7 shown. One operation cycle includes the following steps:

[0080] (1) Trigger the first detection light source 11 to image the droplet jet on the YOZ plane. The imaging result is shown in the droplet jet photograph 201 on the YOZ plane taken by the CCD in Fig. 6(a) of Fig. 6, and transmit the picture to the computer 17.

[0081] (2) After the computer 17 receives the image information, use the thresholding algorithm to binarize the picture. By setting reasonable threshold conditions, search for the droplet boundary. During this process, interference to the calculation result caused by factors such as background light and noise should be avoided, and the droplet boundaries that meet the requirements are screened out.

[0082] (3) Calculate the centroid of each droplet, and the equation expression of the projection of the droplet jet on the YOZ plane can be obtained by fitting a straight line. Based on this, the angle α between the droplet jet and the z-axis on the YOZ plane is obtained.

[0083] (4) The computer 17 outputs the parameter α to the two-dimensional electric control rotating table 15 to make the droplet generator 19 rotate by an angle α around the nozzle center 20 on the YOZ plane to ensure that the projection of the droplet jet on the YOZ plane passes through the laser focus 100.

[0084] (5) Trigger the second detection light source 12 to image the droplet jet on the XOZ plane. The imaging result is shown in the photo 202 of the droplet jet taken by the CCD in Fig. 6(b) of Fig. 6, and is transmitted to the computer for processing in the above processes (2) and (3) to obtain the angle β between the droplet jet and the z-axis on this plane, and control the two-dimensional electronically controlled rotating table 15 to rotate the droplet generator 19 by an angle β around the nozzle center 20 on the XOZ plane to ensure that the projection of the droplet jet on the XOZ plane passes through the laser focus 100.

[0085] Figure 8 It is the image processing flow chart of the monitoring system for the spatial position of the droplet target in the extreme ultraviolet light source provided by the embodiment of the present invention.

[0086] Embodiment 2

[0087] The present invention provides a method for monitoring the spatial position of a droplet target in an extreme ultraviolet light source, including:

[0088] Simultaneously image the droplets on the XOZ plane and the YOZ plane using a single CCD to realize real-time monitoring of the spatial position of the droplet tin target. On this basis, two feedback regulation methods, manual control and automatic control, are developed to feedback regulate the spatial position of the droplet generator so that the movement path of the droplet always passes through the laser focus.

[0089] Manual control mode:

[0090] (1) Mark the laser focus, turn on the CCD and set it to the continuous imaging mode, and finely adjust the position of the CCD so that the two images of the laser focus on the XOZ plane and the YOZ plane coincide and are located in the center of the photo.

[0091] (2) The droplet generator starts to work, turn on the synchronous signal source, trigger the first detection light source and the second detection light source to flash, and set the CCD to the trigger mode to take pictures synchronously with the light emission of the light source.

[0092] (3) When the droplet jet deviates, the images of the droplet jet taken by the CCD will have different characteristics. The judgment criterion is: on the photo, the positive directions of the x-axis and the y-axis both point to the left side of the picture, and the droplet ejection direction is from top to bottom. Thus, the deviation direction of the droplet can be judged.

[0093] (4) Control the two-dimensional electronically controlled rotating table to rotate on the XOZ plane and the YOZ plane, respectively adjust the two images of the droplet jet to be vertically downward, and distinguish which plane each of the two images belongs to during this process. At this time, the two images should be parallel to each other. After this operation, the direction deviation of the droplet jet is corrected, but the position deviation of the nozzle of the droplet generator still exists.

[0094] (5) Control the movement of the two-dimensional electronically controlled displacement stage in the XOY plane until the images of the droplet jets observed on the CCD overlap and pass through the laser focus. At this time, the position deviation of the nozzle of the droplet generator can be corrected.

[0095] Automatic control mode:

[0096] (1) Mark the laser focus, adjust the two-dimensional electronically controlled displacement stage so that the nozzle center is directly above the laser focus, start the droplet generator, and turn on the synchronization signal source.

[0097] (2) Trigger the first detection light source, adjust the CCD to the trigger mode to image the droplet jets on the YOZ plane, and transmit the image information to the computer.

[0098] (3) After the computer receives the image information, use the thresholding algorithm to binarize the picture. By setting reasonable threshold conditions, search for the droplet boundaries. Taking the Python language as an example, the OpenCV function library can be called. First, use the cv2.cvtColor function to convert the RGB image to a grayscale image, then use the THRESH_BINARY algorithm of the cv2.threshold function to binarize the image. Finally, use the cv2.findContours function to quickly and accurately identify the contours of the droplets.

[0099] (4) Calculate the centroid of each droplet respectively. Since the picture is binarized, for a single droplet, the centroid calculation formula is as follows:

[0100]

[0101] where (x i , y i ) represents the pixel coordinates included in the droplet, and n is the total number of pixels contained in the droplet.

[0102] (5) Fit a straight line according to the centroid coordinates, find the equation expression of the projection of the droplet jet on the YOZ plane, and the angle α between the droplet jet and the z-axis on the YOZ plane can be deduced from the slope k of the straight line equation. The calculation method is as follows:

[0103]

[0104] (6) The computer outputs the parameter α to the two-dimensional electronically controlled rotary stage, so that the droplet generator rotates by an angle of α around the nozzle center on the YOZ plane, so that the projection of the droplet jet on the YOZ plane passes through the laser focus;

[0105] (7) Turn off the first detection light source, trigger the second detection light source, and the CCD images the liquid droplet jet on the YOZ plane and transmits the image information to the computer. Repeat the processing in the above steps (3), (4), and (5) to obtain the angle β between the liquid droplet jet and the z-axis on this plane. The computer outputs the parameter β to the two-dimensional electric control rotary stage, causing the liquid droplet generator to rotate by an angle β around the nozzle center on the YOZ plane, so that the projection of the liquid droplet jet on the YOZ plane passes through the laser focus.

[0106] (8) Return to step (2) and repeat the above process until the monitoring and regulation process ends.

[0107] II. Application embodiments. To prove the creativity and technical value of the technical solution of the present invention, this part is the application embodiments of the technical solution of the claims on specific products or related technologies.

[0108] The present invention provides a liquid droplet target spatial position regulation system in an extreme ultraviolet lithography machine light source based on single-camera imaging, including a liquid droplet generator, a first detection light source, a second detection light source, a semi-reflective semi-transmissive lens, a plane mirror, a CCD, a synchronization signal source, a computer, a two-dimensional electric control rotary stage, and a two-dimensional electric control displacement stage.

[0109] Preferably, the liquid droplet generator is used to heat and melt metallic tin and spray it in the form of liquid droplets. At any moment, the movement path of the liquid droplet can be regarded as a ray.

[0110] Preferably, the first detection light source and the second detection light source are uniform parallel light sources, which are connected to the synchronization signal source, receive the pulse signal from the synchronization signal source, and generate a pulsed light beam output with a certain repetition frequency to provide background light illumination for the CCD.

[0111] Preferably, the plane mirror is parallel to the z-axis and is placed on the optical paths of the two beams of light. The normal of the mirror forms a 45° angle with the beam transmission direction, which is used to adjust the propagation direction of the light and change the distance of the light transmitted to the CCD. The semi-reflective semi-transmissive lens is placed in front of the CCD lens, and the mirror surface is parallel to the z-axis, which is used to integrate the two beams of light into the CCD camera.

[0112] Preferably, the CCD is connected to the synchronization signal source and takes pictures of the liquid droplets when the detection light source emits light. During the shooting process, ensure that the laser focus is within the field of view of the CCD, and the imaging focus of the lens is near the laser focus.

[0113] Preferably, the synchronization signal source generates three-way pulse signals, which are respectively used to trigger the first detection light source, the second detection light source, and the CCD. The waveforms of the trigger signals received by the first detection light source and the second detection light source are the same, and the shooting time of the CCD covers the light emission time of the detection light source.

[0114] Preferably, the computer is connected to the CCD, receives the picture stream from the CCD, and processes the picture in real time through a program to respectively calculate the angles at which the droplet jet deviates from the laser focus in the x direction and the y direction, and outputs this as a parameter.

[0115] Preferably, the two-dimensional electric control displacement stage is tightly fixed to the droplet generator, drives it to displace in the XOZ plane and the YOZ plane, and adjusts the nozzle position directly above the laser focus.

[0116] Preferably, the two-dimensional electric control rotary stage is tightly fixed to the droplet generator, is connected to the computer through a signal transmission line, and drives the droplet generator to rotate in the XOZ plane and the YOZ plane according to the control parameters of the computer, and performs feedback adjustment on the injection angle of the droplet jet to ensure that it passes through the laser focus.

[0117] III. Evidence of related effects of the embodiments. Some positive effects have been achieved during the research and development or use of the embodiments of the present invention, and it indeed has great advantages compared with the prior art. The following content will be described in combination with the data, charts, etc. of the test process.

[0118] There are two control methods, manual and automatic, during the use of the embodiments of the present invention. The test phenomena that will occur under the two different methods will be described separately below:

[0119] (1) Manual control method

[0120] Under the manual control method, the CCD simultaneously images the YOZ plane and the XOZ plane. Based on the deviation degree of the droplet jet, the following four situations may exist:

[0121] The first quadrant, as shown in Fig. 9(a), both images of the droplet jet deviate to the left from top to bottom;

[0122] The second quadrant, as shown in Fig. 9(b), of the two images of the droplet jet, one deviates to the left and one deviates to the right from top to bottom; the two-dimensional electric control rotary stage can be adjusted to rotate in the XOZ plane, and the slope of the image deviating to the right will change;

[0123] The third quadrant, as shown in Fig. 9(c), both images of the droplet jet deviate to the right from top to bottom;

[0124] The fourth quadrant, as shown in Fig. 9(d), of the two images of the droplet jet, one deviates to the left and one deviates to the right from top to bottom; the two-dimensional electric control rotary stage can be adjusted to rotate in the XOZ plane, and the slope of the image deviating to the left will change.

[0125] (2) Automatic control method

[0126] In a laboratory environment, the CCD background is illuminated by an LED backlight module. The droplets are darker in color in the figure, and their grayscale values are clearly distinguishable from the background light. However, due to problems such as the offset of the LED placement position and noise in the pictures, not all photos have a uniform background light distribution. Therefore, it is necessary to preprocess the pictures, including ROI selection, filtering and denoising, binarization, etc. At the same time, since the lighting conditions are not exactly the same for each experiment, the threshold parameters for picture processing need to be found and set manually multiple times. Figure 10 shows the comparison of droplet images during the processing, presenting the CCD imaging photos of the droplets in the XOZ plane and their processing results. The YOZ plane can be processed in the same way. The calculated results will be output as parameters to a two-dimensional electric control rotary table to adjust the position of the droplet jet. Among them, Figure 10(a) shows the original picture and the ROI selection (black frame); Figure 10(b) shows the image after binarization; Figure 10(c) shows the droplet contour, the droplet center, and the fitted droplet path diagram.

[0127] It should be noted that the embodiments of the present invention can be implemented through hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated designed hardware. Those of ordinary skill in the art can understand that the above devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code is provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and their modules of the present invention can be implemented by hardware circuits of programmable hardware devices such as very large scale integrated circuits or gate arrays, semiconductors such as logic chips and transistors, or programmable logic devices such as field programmable gate arrays, and can also be implemented by software executed by various types of processors, or can be implemented by a combination of the above hardware circuits and software, such as firmware.

[0128] As described above, the above are only the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A method for monitoring the spatial position of a droplet target in an extreme ultraviolet light source, characterized in that, the method for monitoring the spatial position of the droplet target in the extreme ultraviolet light source includes: using a single CCD to simultaneously image the droplets on the XOZ plane and the YOZ plane, realizing real-time monitoring of the spatial position of the droplet tin target, and using feedback regulation methods of manual control and automatic control to feedback-regulate the spatial position of the droplet generator, so that the movement path of the droplet always passes through the laser focus; When the droplet jet deviates, the droplet jet images captured by the CCD will have different characteristics. The judgment criterion is: on the photo, the positive directions of the x-axis and the y-axis both point to the left side of the picture, and the droplet ejection direction is from top to bottom. Thus, the deviation direction of the droplet can be judged; Control the two-dimensional electric control displacement stage to move within the XOY plane until the images of the droplet jet on the CCD coincide and pass through the laser focus. At this time, the position deviation of the nozzle of the droplet generator is corrected; Obtain the angle β between the droplet jet on the plane and the z-axis, and the computer outputs the parameter β to the two-dimensional electric control rotary stage, so that the droplet generator rotates by an angle β around the nozzle center on the YOZ plane, so that the projection of the droplet jet on the YOZ plane passes through the laser focus.

2. The method for monitoring the spatial position of a droplet target in an extreme ultraviolet light source according to claim 1, characterized in that, the manual control method includes: (1) Mark the laser focus, turn on the CCD and be in continuous imaging mode, and finely adjust the position of the CCD so that the two images of the laser focus on the XOZ plane and the YOZ plane coincide and are located in the center of the photo; (2) The droplet generator starts to work, turn on the synchronous signal source, trigger the first detection light source and the second detection light source to flash, and the CCD is adjusted to the trigger mode to take pictures synchronously with the light emission of the light source; (3) When the droplet jet deviates, the droplet jet images captured by the CCD will have different characteristics. The judgment criterion is: on the photo, the positive directions of the x-axis and the y-axis both point to the left side of the picture, and the droplet ejection direction is from top to bottom. Thus, the deviation direction of the droplet can be judged; (4) Control the two-dimensional electric control rotary stage to rotate in the XOZ plane and the YOZ plane, respectively adjust the two images of the droplet jet to be vertically downward, and distinguish which plane each of the two images belongs to during this process. At this time, the two images should be parallel to each other; after this operation, the direction deviation of the droplet jet is corrected, but the position deviation of the nozzle of the droplet generator still exists; (5) Control the two-dimensional electric control displacement stage to move within the XOY plane until the images of the droplet jet on the CCD coincide and pass through the laser focus. At this time, the position deviation of the nozzle of the droplet generator is corrected.

3. The method for monitoring the spatial position of a droplet target in an extreme ultraviolet light source according to claim 1, characterized in that, the automatic control method includes: (1) Mark the laser focus, adjust the two-dimensional electric control displacement stage so that the nozzle center is directly above the laser focus, the droplet generator starts to work, and turn on the synchronous signal source; (2) Trigger the first detection light source, and the CCD is adjusted to the trigger mode to image the droplet jet on the YOZ plane and transmit the image information to the computer; (3) After the computer receives the image information, it binarizes the picture using a thresholding algorithm. By setting reasonable threshold conditions, it searches for the droplet boundary. It calls the OpenCV function library. First, it uses the cv2.cvtColor function to convert the RGB image to a grayscale image, then uses the THRESH_BINARY algorithm of the cv2.threshold function to binarize the image. Finally, it uses the cv2.findContours function to quickly and accurately identify the contour of the droplet. (4) Calculate the centroid of each droplet respectively. Since the picture is binarized, for a single droplet, the formula for calculating its centroid is as follows: Among them, (x i , y i ) represents the pixel coordinates included in the droplet, and n is the total number of pixels contained in the droplet; (5) Fit a straight line according to the centroid coordinates to obtain the equation expression of the projection of the droplet jet on the YOZ plane. From the slope k of the straight line equation, the angle α between the droplet jet and the z-axis on the YOZ plane can be deduced. The calculation method is as follows: (6) The computer outputs the parameter α to the two-dimensional electric control rotating table, so that the droplet generator rotates by an angle α around the nozzle center on the YOZ plane, making the projection of the droplet jet on the YOZ plane pass through the laser focus. (7) Turn off the first detection light source, trigger the second detection light source, and the CCD images the droplet jet on the YOZ plane and transmits the image information to the computer. Repeat the processing of the above steps (3), (4), and (5) to obtain the angle β between the droplet jet and the z-axis on this plane. The computer outputs the parameter β to the two-dimensional electric control rotating table, so that the droplet generator rotates by an angle β around the nozzle center on the YOZ plane, making the projection of the droplet jet on the YOZ plane pass through the laser focus. (8) Return to step (2) and repeat the above process until the monitoring and regulation process ends.

4. A system for regulating the spatial position of a droplet target in an extreme ultraviolet light source of an extreme ultraviolet lithography machine, which implements the method for monitoring the spatial position of the droplet target according to any one of claims 1 to 3, characterized in that, the system for regulating the spatial position of the droplet target in the extreme ultraviolet light source of the extreme ultraviolet lithography machine includes a droplet generator, a first detection light source, a second detection light source, a semi-reflective semi-transmissive mirror, a plane mirror, a CCD, a synchronization signal source, a computer, a two-dimensional electric control rotating table, and a two-dimensional electric control displacement table; the droplet generator is used for heating and melting the droplets and spraying them in the form of droplets; both the first detection light source and the second detection light source are connected to the synchronization signal source, receive the pulse signal from the synchronization signal source, and generate a pulsed light beam output with a repetition frequency to provide background light illumination for the CCD; the plane mirror is parallel to the z-axis and is placed on the optical paths of the two beams of light, used for adjusting the propagation direction of the light and changing the distance of the light transmitted to the CCD; the semi-reflective semi-transmissive mirror is placed at the front end of the CCD lens, and the mirror surface is parallel to the z-axis, used for integrating the two beams of light into the CCD camera; the CCD is connected to the synchronization signal source and takes pictures of the droplets when the detection light source emits light; the computer is connected to the CCD, receives the picture stream from the CCD, and processes the pictures in real time through a program to respectively calculate the angles by which the droplet jet deviates from the laser focus in the x direction and the y direction, and outputs the angles as parameters. The two-dimensional electrically controlled displacement stage is tightly fixed to the droplet generator, driving the droplet generator to displace within the XOZ plane and the YOZ plane, and adjusting the nozzle position directly above the laser focus; The two-dimensional electrically controlled rotary stage is tightly fixed to the droplet generator and connected to a computer through a signal transmission line. According to the control parameters of the computer, it drives the droplet generator to rotate within the XOZ plane and the YOZ plane, and feedback-adjusts the ejection angle of the droplet jet so that the droplet passes through the laser focus.

5. The droplet target spatial position control system in the extreme ultraviolet lithography light source as described in claim 4, characterized in that, the droplet generator is used to heat and melt metallic tin and eject it in the form of droplets; the movement path of the droplets is a ray.

6. The droplet target spatial position control system in the extreme ultraviolet lithography light source as described in claim 4, characterized in that, the normal of the mirror forms a 45° angle with the beam transmission direction.

7. The droplet target spatial position control system in the extreme ultraviolet lithography light source as described in claim 4, characterized in that, the trigger signal waveforms received by the first detection light source and the second detection light source are the same, and the shooting time of the CCD covers the light-emitting time of the detection light source.

8. The droplet target spatial position control system in the extreme ultraviolet lithography light source as described in claim 4, characterized in that, the beam emitted by the first detection light source propagates through the vacuum chamber along the negative x-axis direction. Four plane mirrors, namely plane mirror A, plane mirror B, plane mirror C, and plane mirror D, are placed in the optical path to adjust the optical path, and then it is transmitted to the CCD after passing through a semi-reflective and semi-transmissive lens; the beam emitted by the second detection light source propagates through the vacuum chamber along the negative y-axis direction, and is reflected by the semi-reflective and semi-transmissive lens after passing through mirror F and mirror G to the CCD; when adjusting the optical path, the length of the x-axis path is made the same as that of the x-axis path, and the droplets in the XOZ plane and the YOZ plane can be clearly imaged on the CCD.

9. A computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the processor performs the following steps: using the CCD to simultaneously image the droplets on the XOZ plane and the YOZ plane, and performing real-time processing on the images, calculating the offset of the droplet jet path relative to the laser focus, and outputting the offset as a parameter to the two-dimensional electrically controlled rotary stage to perform feedback adjustment on the spatial position of the droplet generator so that the movement path of the droplets always passes through the laser focus.

10. An extreme ultraviolet light source, characterized in that, the extreme ultraviolet light source executes the monitoring method for the spatial position of the droplet target in the extreme ultraviolet light source as described in any one of claims 1 to 3.

Images