A method and system for identifying a source of contamination in an overlay contact area of a photolithographic mask

Abstract

This invention relates to the field of photolithography contamination identification technology, and discloses a method and system for identifying contamination sources in the overlapping contact area of ​​photolithography masks. The method includes: acquiring the contact footprint area; collecting and differentiating images before and after passing through each contact node to obtain the location of newly added particles; when located in the overlapping contact footprint area, identifying ambiguous contact nodes and selecting target contact nodes; controlling two verification photolithography masks to pass through the target contact nodes respectively, and determining this as contact displacement; collecting and differentiating images of the two verification photolithography masks before and after passing through the ambiguous contact nodes to obtain the location of newly added particles; matching two sets of newly added particle locations and converting them to the local coordinate system of each ambiguous contact node; when the displacement direction is the same, the displacement distance does not exceed the position tolerance, and the local position condition is met, the target contact node is determined as the contamination source contact node. This invention reduces the scope of accidental cleaning and downtime for investigation, and lowers the risk of subsequent mask contamination.

Description

Technical Field

[0001] This invention relates to the field of photolithography contamination identification technology, and more specifically, to a method and system for identifying contamination sources in the overlapping contact area of ​​a photolithography mask. Background Technology

[0002] Photolithography equipment uses a photomask to carry patterns and transfers these patterns to a substrate coated with a photosensitive material. During loading, transport, pre-positioning, and exposure, the photomask needs to sequentially contact the transport fixture, support components, and photomask platform. Over time, particles may adhere to these contact components. When these particles re-contact the photomask, they may transfer to the photomask surface, affecting photomask adhesion, positioning stability, and pattern transfer quality. With increasing demands for pattern precision and continuous operation capabilities in photolithography, timely identification of contamination sources along the photomask transport path has become crucial for controlling particle propagation, reducing equipment maintenance time, and preventing subsequent photomask contamination.

[0003] In the prior art, Chinese invention patent application CN118591773A discloses a system and method for inspecting parts of a lithography equipment. This system employs an inspection body that can be transported by the lithography equipment's conveyor, and an image capture device is installed on the inspection body to acquire images of the mask conveyor, turntable holder, mask platform fixture, or related components. The presence of contaminants in the inspected area is then determined based on these images. This approach reduces equipment disassembly and manual inspection time, but the focus is on observing specific components and confirming the presence of contaminants. When a mask sequentially passes through multiple contact components, the same particle anomaly may be associated with multiple contact components, especially when multiple contact components act on adjacent areas. Based solely on contamination images or the particle position on the mask surface, it is difficult to accurately determine the actual contact component causing particle transfer, easily leading to expanded downtime for investigation and cleaning, or continued contamination of subsequent masks before the source of contamination is eliminated.

[0004] Therefore, it is necessary to design a method and system for identifying contamination sources in the overlapping contact area of ​​a photomask to solve the problems existing in the current technology. Summary of the Invention

[0005] In view of this, the present invention proposes a method and system for identifying contamination sources in overlapping contact areas of photolithographic masks, aiming to solve the problem of difficulty in determining the actual source of particulate contamination when the contact footprints of multiple contact nodes overlap.

[0006] This invention proposes a method for identifying contamination sources in the overlapping contact area of ​​a photomask, comprising: The contact footprint area of ​​each contact node is obtained, and the images of the photomask before and after passing through each contact node are acquired and differentiated to obtain the location of the newly added particles. When the location of the newly added particle is in the overlapping area of ​​the contact footprint, the contact node involved is identified as an ambiguous contact node, and the target contact node is selected. Two verification photomasks are controlled to pass through the target contact node at a reference contact position and an offset contact position, respectively, while keeping the contact position of the remaining ambiguous contact node unchanged, and the displacement from the reference contact position to the offset contact position is determined as the contact displacement; Images of two verification photomasks before and after passing through the ambiguous contact nodes are acquired and differencing is performed to obtain the first set of new particle positions and the second set of new particle positions; the two sets of new particle positions are matched and transformed to the local coordinate system of each ambiguous contact node; When the displacement direction of the matching particle in the photomask coordinate system is the same as the contact displacement direction, the difference between the displacement distance and the contact displacement distance does not exceed the position tolerance, and the local position condition is met, the target contact node is determined to be the pollution source contact node.

[0007] Furthermore, the calibration process of the contact footprint area includes: acquiring the actual contact contours of each contact node and the calibration photomask; converting the actual contact contours to the coordinate system of the photomask; and expanding outward along the actual contact contours according to the sum of the upper limits of the errors of repeatability positioning error, contact position control error and image registration error to obtain the contact footprint area.

[0008] Furthermore, the setting of the offset contact position includes: setting the offset contact position along the direction of reducing the overlapping area of ​​the contact footprints of the target contact node and the remaining ambiguous contact node, and making the distance between the reference contact position and the offset contact position greater than the position tolerance.

[0009] Furthermore, when controlling the two verification photomasks to pass through the target contact node at the reference contact position and the offset contact position respectively, the following is included: except for the contact position of the target contact node, the two transfers use the same transfer path, movement direction, transfer speed and image acquisition parameters, and all remaining ambiguous contact nodes maintain the same contact position.

[0010] Furthermore, the process of determining the matching particles includes: obtaining the particle size, particle outline, and nearest neighbor particle spacing of two sets of newly added particles; and determining the particles whose particle size difference does not exceed the size tolerance, whose particle outline overlap is not lower than the outline threshold, and whose nearest neighbor particle spacing difference does not exceed the spacing tolerance as the matching particles.

[0011] Furthermore, the local coordinate transformation process for matching particle positions includes: establishing a local coordinate system based on the installation positioning reference of each ambiguous contact node; and converting the matching particle positions into a first local particle position and a second local particle position according to the contact pose of each ambiguous contact node in two contacts.

[0012] Furthermore, determining the position tolerance includes: determining the sum of the upper limits of the errors of image registration error, repetitive positioning error, contact position control error, and particle boundary extraction error as the position tolerance.

[0013] Furthermore, the particle displacement prediction process includes: translating the matching particle position in the first group of newly added particle positions according to the contact displacement to obtain the predicted particle position; when the distance between the matching particle position in the second group of newly added particle positions and the predicted particle position does not exceed the position tolerance, and the displacement direction of the matching particle is the same as the contact displacement direction, it is determined that the matching particle meets the displacement condition.

[0014] Furthermore, the process for identifying the sequence of ambiguous contact nodes includes: The position difference between the first local particle position and the second local particle position of the same matching particle in the local coordinate system of the target contact node does not exceed the position tolerance, and the position difference in the local coordinate system of each remaining ambiguous contact node exceeds the position tolerance, is determined as a local position condition. When at least two matching particles with a positional spacing greater than the positional tolerance and both satisfying the displacement condition and the local positional condition can be selected, the target contact node is determined to be the pollution source contact node. When there are at least two matching particles, but at least two matching particles that simultaneously satisfy the displacement condition and the local position condition cannot be selected, the reference contact position is restored, the target contact node is excluded, and the unidentified ambiguous contact node is selected. When there are fewer than two matching particles, the locations of the newly added particles in the first group and the locations of the newly added particles in the second group are re-acquired; when all ambiguous contact nodes are excluded, the result of no pollution source contact node is output.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: When the newly added particle is located in the overlapping area of ​​the contact footprint where multiple contact nodes act together, the ambiguous contact nodes are first identified, and then only the contact position of the target contact node relative to the verification photomask is changed, while keeping the contact position of the remaining ambiguous contact nodes unchanged, thereby establishing a single-variable active identification condition; subsequently, two sets of newly added particle positions are obtained through the difference results of the images before and after the two verification photomasks, and the displacement direction and displacement distance of the matching particle in the photomask coordinate system are compared with the contact displacement of the target contact node, and combined with the matching particle Cross-validation of the positional relationships in the local coordinate system of each ambiguous contact node ensures that particles truly transferred from the target contact node move synchronously in the photolithography mask coordinate system as the contact position changes, while maintaining a stable position in the local coordinate system of the target contact node. This eliminates remaining ambiguous contact nodes that are misjudged simply because of overlapping contact areas. It enables the identification of actual contamination source contact nodes without disassembling the photolithography equipment or expanding the scope of downtime investigation, reducing repeated inspections and cleaning of uncontaminated contact nodes, shortening equipment downtime, and preventing the contamination source from continuously contaminating subsequent photomasks.

[0016] On the other hand, this application also provides a contamination source identification system for overlapping contact areas of photomasks, used to apply the above-mentioned contamination source identification method for overlapping contact areas of photomasks, including: The acquisition module is used to acquire the contact footprint area of ​​each contact node, acquire images of the photomask before and after passing through each contact node, and perform differential processing to obtain the location of the newly added particles. The ambiguous node determination module is used to determine the contact node forming the contact footprint overlap area as an ambiguous contact node when the location of the newly added particle is located in the contact footprint overlap area, and to select the target contact node. The contact position control module is used to control the two verification photomasks to pass through the target contact node at the reference contact position and the offset contact position respectively, while keeping the contact position of the remaining ambiguous contact node unchanged; The particle processing module is used to acquire images of two verification photomasks before and after passing through the ambiguous contact nodes and perform differential processing to obtain the first set of newly added particle positions and the second set of newly added particle positions, match the two sets of newly added particle positions, and transform the matched particle positions to the local coordinate system of each ambiguous contact node. The pollution source identification module is used to determine whether the target contact node is a pollution source contact node based on the relationship between the displacement of the matching particle in the photomask coordinate system and the contact displacement from the reference contact position to the offset contact position, as well as the position difference of the matching particle in the local coordinate system of each ambiguous contact node.

[0017] It is understandable that the above-mentioned method and system for identifying contamination sources in the overlapping contact area of ​​photolithographic masks have the same beneficial effects, and will not be elaborated further here. Attached Figure Description

[0018] The accompanying drawings are used to illustrate the technical solutions of the present invention and do not constitute a limitation on the scope of protection of the present invention. The process nodes, regional relationships, and functional block diagrams in the drawings are used to illustrate the implementation methods of the embodiments of the present invention. In the drawings: Figure 1 A flowchart illustrating the method for identifying contamination sources in the overlapping contact area of ​​a photomask according to an embodiment of the present invention; Figure 2 A flowchart for pollution source identification provided in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the principle of pollution source identification in the overlapping contact area provided in an embodiment of the present invention. Figure 4 This is a functional block diagram of a contamination source identification system for overlapping contact areas of photomasks provided in an embodiment of the present invention.

[0019] Wherein, 101 represents the reference contact position state, 102 represents the offset contact position state, 103 represents the particle displacement response state, and 104 represents the local coordinate system verification state. Detailed Implementation

[0020] The specific embodiments of the present invention will now be described with reference to the accompanying drawings. These embodiments are used to illustrate the technical solutions of the present invention and do not limit the scope of protection of the present invention. Unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0021] In some embodiments of this application, see Figure 1-2 As shown, this application proposes a method for identifying contamination sources in the overlapping contact area of ​​a photomask, including: S100: Obtain the contact footprint area of ​​each contact node, acquire images of the photomask before and after passing through each contact node and perform differential analysis to obtain the location of the newly added particles.

[0022] S200: When the location of a newly added particle is in the overlapping area of ​​the contact footprint, the contact node involved is identified as an ambiguous contact node, and the target contact node is selected.

[0023] S300: Control the two verification photomasks to pass through the target contact node at the reference contact position and the offset contact position respectively, keep the contact position of the remaining ambiguous contact node unchanged, and determine the displacement from the reference contact position to the offset contact position as the contact displacement.

[0024] S400: Acquire images of two verification photomasks before and after passing through ambiguous contact nodes and perform differential analysis to obtain the first set of newly added particle positions and the second set of newly added particle positions; match the two sets of newly added particle positions and transform them to the local coordinate system of each ambiguous contact node.

[0025] S500: When the displacement direction of the matching particle in the photomask coordinate system is the same as the contact displacement direction, the difference between the displacement distance and the contact displacement distance does not exceed the position tolerance, and the local position condition is met, the target contact node is determined as the pollution source contact node.

[0026] Local position conditions are used to uniformly determine the positional consistency of matched particles in different local coordinate systems of contact nodes. The determination criteria include: the difference between the two local positions of the same matched particle in the local coordinate system of the target contact node does not exceed the position tolerance, and the difference between the local positions in the local coordinate system of any remaining ambiguous contact node is greater than the position tolerance. Local position conditions are used as the sole unified determination criterion in this invention and do not depend on the image segmentation method or particle morphology changes.

[0027] In some embodiments of this application, the contact nodes within the lithography equipment include a robotic gripper for holding, supporting, or positioning the photomask, a pre-positioning support, a buffer support, and a photomask platform contact portion. Different lithography equipment have different transport structures. In practical applications, contact nodes are defined according to the positions where the photomask makes physical contact during loading, transport, pre-positioning, and exposure positioning. Components that only perform non-contact detection or non-contact transport are not included in the contact nodes.

[0028] The matching of two sets of newly added particle locations, as referred to in this application, means selecting candidate particle pairs from the first and second sets of newly added particle locations, and determining whether the particles formed in the two contacts originate from the same contamination attachment location based on the particle size, particle outline, and nearest neighbor distance of the candidate particle pairs; particles in candidate particle pairs that meet the particle matching conditions are determined as matched particles. Matched particles are not limited to the same physical particle, but rather represent particles formed by the transfer of the same contamination attachment location or contamination accumulation area during the two contacts. In this invention, matched particles, as logical mapping objects, are essentially the characterization results of the same contamination attachment location in different contact experiments, and do not depend on the physical particle continuity in a single imaging.

[0029] Before step S100, a calibration photomask is used to calibrate the contact footprint area of ​​each contact node. The size, thickness, and edge structure of the calibration photomask are the same as those of the photomask to be tested. The non-patterned contact surface of the calibration photomask has a removable low-precipitation color layer that can display contact traces. Individual contact nodes are controlled to contact the calibration photomask according to the normal contact pressure and contact time of the photolithography equipment. Images before and after contact are acquired. The contact trace boundary is extracted through image registration and grayscale difference, and the area enclosed by the contact trace boundary is determined as the actual contact contour. For contact nodes where a color layer cannot be used, the actual contact contour can also be formed based on the structural dimensions, installation position, and actual indentation image of the contact component. However, the deviation between the structural dimensions and the actual contact position needs to be corrected through at least one real contact result.

[0030] A photomask coordinate system is established using two fixed positioning marks on the calibration photomask. The center of the first positioning mark is taken as the origin, the direction pointing from the first positioning mark to the second positioning mark is taken as the horizontal coordinate direction, and the direction perpendicular to the horizontal coordinate direction is taken as the vertical coordinate direction. Based on the positioning marks in the pre-contact and post-contact images, the images are translated and rotated for registration, transforming the actual contact contours of each contact node into the photomask coordinate system. The actual contact contours can be represented by several boundary points or closed polygons.

[0031] To avoid actual contaminant particles falling outside the calibrated contour due to contact position fluctuations, the area is extended outward along the normal direction of the actual contact contour, calculated as the sum of the upper limits of the repeatability error, contact position control error, and image registration error. The extended area is designated as the contact footprint region. Repeatability error is obtained by performing at least 10 consecutive loading and positioning operations on the same photomask and statistically analyzing the maximum positional deviation of the positioning mark in the photomask coordinate system. Contact position control error is obtained by performing at least 10 consecutive contact actions on the same contact node and statistically analyzing the maximum deviation of the actual contact contour center relative to the set contact position. Image registration error is obtained by continuously acquiring at least 10 sets of images on the same photomask and statistically analyzing the maximum residual deviation of the same positioning mark after registration. When the upper limit of error given by the equipment manufacturer is greater than the upper limit of the measured error, the upper limit given by the equipment manufacturer is used to avoid the contact footprint region being smaller than the actual possible contact range.

[0032] After calibrating the contact footprint region, images of the photomask to be tested before and after passing through each contact node are acquired. The image acquisition position, illumination angle, exposure time, magnification, and focal plane remain unchanged. The images before and after contact are registered and differencing to extract particle regions that appear only in the images after contact. For each particle region, the geometric center of the particle contour is used as the location of the new particle; when the particle contour is irregular, the average position of the pixel coordinates within the particle contour is used as the location of the new particle. The difference threshold is determined based on the background difference images continuously acquired by the same clean photomask before passing through contact nodes. Preferably, the mean gray value of the background difference plus three times the standard deviation is used as the difference threshold, and connected regions with an area smaller than the minimum resolvable area of ​​the imaging system are excluded.

[0033] When a newly added particle location is simultaneously situated within the overlapping portion of at least two contact footprint regions, the overlapping portion is defined as the contact footprint overlap area, and the contact node forming the contact footprint overlap area is defined as an ambiguous contact node. There must be two or more ambiguous contact nodes. Prioritize selecting the contact node from the ambiguous contact nodes that allows independent adjustment of its contact position within the non-patterned area of ​​the photomask as the target contact node; when multiple ambiguous contact nodes allow adjustment, prioritize selecting the contact node that, after adjustment, maximizes the reduction in the contact footprint overlap area.

[0034] In some embodiments of this application, two cleaned and inspected verification photomasks are used to perform target contact node identification. The two verification photomasks have identical dimensions, thickness, edge structure, and surface material, and no particles located within the overlapping area of ​​the contact footprint were detected during inspection. The two verification photomasks serve as the first verification photomask and the second verification photomask, respectively.

[0035] The term "matching particles" in this application does not require them to be the same solid particles transferred in two contacts. Rather, it refers to particles that form at the same contamination attachment location or in the same contamination accumulation area at the contact node during the two contacts, and whose particle size, particle profile, and spatial relationship meet the matching conditions. This embodiment applies to situations where the contact node contains particle aggregates, residual films, or attached contaminants capable of repeatedly releasing, imprinting, or continuously precipitating contaminants. If the second contact does not form sufficient matching particles, the current identification result is determined to be insufficient evidence, and the target contact node is not excluded based on the current identification result.

[0036] The insufficient evidence state is an intermediate judgment state. In this state, the target contact node is neither confirmed as a pollution source contact node nor excluded from the ambiguous contact node set. It is only used as a trigger condition for subsequent re-collection and verification.

[0037] Specifically, firstly, the first verification photomask is controlled to pass through the ambiguous contact nodes along a preset transport path. The target contact node contacts the first verification photomask according to the reference contact position, while all remaining ambiguous contact nodes contact the first verification photomask according to the normal contact position. Then, the second verification photomask is controlled to pass through the ambiguous contact nodes along the same transport path, moving the target contact node from the reference contact position to an offset contact position, while all remaining ambiguous contact nodes maintain their original contact positions. Both transports use the same direction of movement, transport speed, dwell time, contact pressure, and image acquisition parameters, thus using the contact position of the target contact node as the main change between the two transports. The displacement direction and displacement distance from the reference contact position to the offset contact position are jointly determined as the contact displacement.

[0038] The offset contact position is set along the direction that reduces the overlap area between the contact footprint area of ​​the target contact node and the contact footprint area of ​​the remaining ambiguous contact nodes. When determining the offset direction, the contact footprint area of ​​the target contact node is moved trial-shifted according to the device's allowed movement direction. The overlap area between the target contact node and the contact footprint area of ​​the remaining ambiguous contact nodes after the trial shift is calculated, and the movement direction with the largest reduction in overlap area is selected. The offset distance must be greater than the position tolerance, and the offset contact footprint area must still be located within the non-patterned area that the verification photomask allows contact with. The initial offset distance can be set to 1.5 to 3 times the position tolerance. If the reduction in the overlap area of ​​the contact footprint after the initial offset is less than 30% of the original overlap area, the offset distance is increased incrementally within the device's allowed range, with each increase not less than half of the position tolerance, until the reduction in overlap area reaches more than 30% of the original overlap area, or reaches the maximum allowed movement distance of the target contact node.

[0039] 30% is an optional calibration value. In actual use, it is determined that the contact footprint area of ​​the offset target contact node forms a non-overlapping region with a width greater than the position tolerance, and the distance between the predicted particle position generated by the target contact node and the predicted particle position generated by the remaining ambiguous contact nodes is greater than the position tolerance. If the above conditions are still not met after the target contact node reaches the maximum allowable movement distance, the target contact node is not selected for the current round of identification, and a new target contact node is selected from other ambiguous contact nodes with adjustable contact positions.

[0040] Images of the first and second verification photomasks before and after passing through the ambiguous contact node were acquired. Using the same registration and differencing methods as in Example 1, the locations of the first and second groups of newly added particles were obtained. In addition to particle locations, the particle size, particle outline, and nearest neighbor distance for each newly added particle were extracted. The particle size was represented by the equivalent diameter of the particle outline; the particle outline was represented by a normalized set of outline points; and the nearest neighbor distance was the distance between the nearest particle to the target particle in the same group of newly added particles.

[0041] Particle pairs are selected from the first and second groups of newly added particles. A particle pair is considered a matched particle if the particle size difference does not exceed the size tolerance, the particle contour overlap is not lower than the contour threshold, and the nearest neighbor particle distance difference does not exceed the distance tolerance. The particle contour overlap is obtained as follows: the geometric centers of two candidate particles are aligned, and the contours of the two candidate particles are converted into binary regions of the same pixel scale; the ratio between the overlapping area and the union area of ​​the two binary regions is calculated, and this ratio is determined as the particle contour overlap. If there are fewer than two newly added particles in a single group, the nearest neighbor particle distance is not calculated, and the current result is transferred to the insufficient identification evidence processing. The size tolerance is obtained by continuously imaging the same standard particle at least 10 times and statistically analyzing the maximum measurement difference of the equivalent diameter; the contour threshold is obtained by calculating the overlap of repeated imaging contours of the same standard particle, preferably using the lowest value of the repeated imaging contour overlap; the distance tolerance is obtained by statistically analyzing the maximum measurement difference of the nearest neighbor particle distance after continuously imaging the same group of standard particles. When the optical magnification, illumination method, or image acquisition position changes, the size tolerance, contour threshold, and spacing tolerance are redefined.

[0042] In some embodiments of this application, a local coordinate system for each ambiguous contact node is established based on its mounting and positioning reference. The mounting and positioning reference can be the center of a positioning hole on the contact node mounting base, a mechanical zero point, or a calibrated fixed mark. The origin of the local coordinate system is set at the mounting and positioning reference, the local lateral coordinate direction is set along the main allowable movement direction of the contact node, and the local longitudinal coordinate direction is perpendicular to the local lateral coordinate direction. The contact pose of each ambiguous contact node during two contacts includes the translational position and rotation angle of the contact node relative to the photomask.

[0043] The contact pose is obtained from the set position and position feedback value in the motion control record of the photolithography equipment, and corrected by calibrating the actual contact contour on the photolithography mask. Contact position control errors include translational position control error, rotational angle error, the maximum linear position error generated at the boundary of the contact footprint area, and the contact pose feedback residual. When determining the position tolerance, the largest contact position control error among all ambiguous contact nodes is used.

[0044] Based on the contact poses of each ambiguous contact node during two contacts, the positions of matching particles in the first group of newly added particles are converted into first local particle positions, and the positions of matching particles in the second group of newly added particles are converted into second local particle positions. During the conversion, the translation of the contact node relative to the photomask is first eliminated, and then the particle positions are rotated to the local coordinate system of the contact node according to the rotation angle of the contact node relative to the photomask. The straight-line distance between the first local particle position and the second local particle position is taken as the position difference of the matching particle in the local coordinate system of the ambiguous contact node.

[0045] The position tolerance is determined by the sum of the upper limits of the following errors: image registration error, photomask repetition positioning error, contact position control error of the target contact node, and particle boundary extraction error. The particle boundary extraction error is obtained by processing the same particle image continuously under the same segmentation conditions at least 10 times and statistically analyzing the maximum positional deviation of the particle's geometric center. The position tolerance is re-measured after equipment maintenance, camera reinstallation, optical magnification adjustment, or contact node recalibration. All errors are expressed in µm and are compared using the same physical length unit after coordinate transformation.

[0046] Based on the direction and distance of the contact displacement, the positions of the matching particles in the first group of newly added particle locations are translated to obtain the predicted particle positions. When the distance between the matching particle position and the predicted particle position in the second group of newly added particle locations does not exceed the position tolerance, and the direction in which the matching particle moves from the first group of newly added particle positions to the second group of newly added particle positions is the same as the contact displacement direction, the matching particle is determined to meet the displacement condition. The processing shows that the movement of the matching particle in the photomask coordinate system is affected by changes in the target contact node position.

[0047] For the same matching particle, the matching particle is considered to satisfy the local position condition when the position difference between the first local particle position and the second local particle position in the local coordinate system of the target contact node does not exceed the position tolerance, and the position difference in the local coordinate system of each remaining ambiguous contact node also exceeds the position tolerance. When the target contact node is the actual source of contamination, the attachment position of the contaminant particle remains stable relative to the target contact node. Therefore, after the contact position changes, the particle moves with the target contact node in the photomask coordinate system, but remains in approximately the same position after transformation to the target contact node local coordinate system. After transformation to the remaining ambiguous contact node local coordinate system where no position change occurs, a position difference greater than the position tolerance is formed between the two local particle positions.

[0048] When at least two matching particles with a distance greater than the positional tolerance and both satisfying the displacement and local positional conditions can be selected, the target contact node is identified as the pollution source contact node. Requiring at least two matching particles with a distance greater than the positional tolerance reduces the possibility of misjudgment caused by a single sporadic particle, particle boundary fluctuations, or local image noise. When there are at least two matching particles, but it is impossible to select at least two that simultaneously satisfy both the displacement and local positional conditions, the baseline contact position of the target contact node is restored, the target contact node is excluded, and a new target contact node is selected from the unidentified ambiguous contact nodes.

[0049] When there are at least two matching particles, and at least two matching particles that simultaneously satisfy both displacement and local position conditions can be selected, but the positional spacing between the matching particles that satisfy the conditions is not greater than the positional tolerance, it is considered that multiple matching particles may originate from the contour segmentation results of the same particle region, and the spatial independence of the current identification evidence is insufficient. At this point, it is uncertain whether the target contact node is a contamination source contact node, nor is it ruled out that it is a target contact node. The verification photolithography mask is replaced, and the positions of the first set of newly added particles and the second set of newly added particles are re-acquired.

[0050] When fewer than two matching particles are found, the current identification evidence is considered insufficient, and the target contact node is not ruled out. Two verification photomasks are replaced, and the positions of the first and second sets of newly added particles are re-acquired. The number of re-acquisitions is preset based on the number of verification photomasks and the equipment's allowed diagnostic time, preferably 2 to 3 times. Each re-acquisition uses another set of verification photomasks that have completed the initial inspection. If, after reaching the preset number of verifications, two matching particles with a positional distance greater than the positional tolerance cannot be selected, the result of insufficient evidence for target contact node identification is output, the identification of the current target contact node ends, and the target contact node is not identified as an excluded ambiguous contact node. When all ambiguous contact nodes are excluded, the result of no identified contamination source contact node is output, and the process proceeds to the subsequent investigation of non-contact deposition contamination or detection errors.

[0051] The number of re-acquisitions for the same target contact node is preset to 2 to 3 times. If, after reaching the preset number of re-acquisitions, at least two matching particles with a positional distance greater than the positional tolerance and simultaneously satisfying the displacement and local positional conditions cannot be obtained, the result of insufficient evidence for target contact node identification is output, and the identification of the current target contact node ends. Insufficient identification evidence is not used as a basis for excluding target contact nodes.

[0052] See Figure 3As shown, in the reference contact position state 101, the target contact node and the remaining ambiguous contact node each form contact footprint regions on the verification photomask. The two contact footprint regions overlap, forming a contact footprint overlap area. After passing through the target contact node and the remaining ambiguous contact node, the first verification photomask obtains the location of the first newly added particle within the contact footprint overlap area. Since the location of the first newly added particle is located within both contact footprint regions, the particle origin cannot be determined solely based on the location of the first newly added particle.

[0053] In offset contact position state 102, the target contact node is moved from the reference contact position to the offset contact position along the direction of reducing the overlap area of ​​the two contact footprint regions, while keeping the contact position of the remaining ambiguous contact node unchanged. After the second verification photomask passes through the target contact node and the remaining ambiguous contact node, the second newly added particle position is obtained. The displacement from the reference contact position to the offset contact position is the contact displacement.

[0054] In particle displacement response state 103, the positions of the first and second newly added particles are matched. When the displacement direction of the second newly added particle position relative to the first newly added particle position is the same as the contact displacement direction, and the difference between the particle displacement distance and the contact displacement distance does not exceed the position tolerance, the matched particles are determined to meet the displacement condition. The displacement condition indicates that the position of the newly added particle changes synchronously with the contact position of the target contact node.

[0055] In local coordinate system verification state 104, the positions of the first and second newly added particles are transformed to the local coordinate system of the target contact node and the local coordinate system of the remaining ambiguous contact node, respectively. In the local coordinate system of the target contact node, the positional difference between the first and second local particle positions does not exceed the positional tolerance; in the local coordinate system of the remaining ambiguous contact node, the positional difference between the first and second local particle positions exceeds the positional tolerance. This indicates that the particles maintain the same contamination attachment position relative to the target contact node, but do not maintain a consistent position relative to the remaining ambiguous contact node.

[0056] When at least two matched particles separated by each other satisfy the displacement condition, and simultaneously satisfy the positional consistency condition in the local coordinate system of the target contact node and the positional inconsistency condition in the local coordinate system of the remaining ambiguous contact nodes, the target contact node is identified as the pollution source contact node. Through this processing, when the contact footprints of multiple contact nodes overlap, the actual pollution source can be determined by utilizing the particle displacement response generated by the controlled offset of the target contact node, avoiding indiscriminate investigation of multiple contact nodes based solely on static particle positions.

[0057] In one specific embodiment, the contact footprint areas of the first and second contact nodes form an overlapping area of ​​contact footprints in the non-patterned area at the edge of the photomask. After repeated calibration, the upper limit of image registration error is 1.5µm, the upper limit of photomask repeatability error is 2µm, the upper limit of contact position control error of the first contact node is 2.5µm, and the upper limit of particle boundary extraction error is 1µm, thereby determining the position tolerance to be 7µm.

[0058] After calibration using standard particle repeat imaging, the size tolerance was set to 0.5µm, the contour threshold to 0.80, and the spacing tolerance to 2µm. The particle size differences between the two candidate particle pairs selected from the first and second groups of newly added particles were 0.2µm and 0.3µm, respectively; the particle contour overlap rates were 0.91 and 0.88, respectively; and the nearest neighbor particle spacing differences were 0.7µm and 1.1µm, respectively. Both candidate particle pairs met the particle matching conditions.

[0059] The first contact node is selected as the target contact node. It is moved 18µm laterally from the reference contact position to the offset contact position, while the second contact node remains in its original position. Two matching particles are obtained from the first group of newly added particles, with a distance of 42µm between them, which is greater than 7µm. In the second group of newly added particles, the displacement distances of the two matching particles relative to the first group of newly added particles are 17.2µm and 18.6µm, respectively. The displacement directions are both the same as the contact displacement direction. The differences between these displacement distances and 18µm are 0.8µm and 0.6µm, respectively, both not exceeding 7µm.

[0060] After transforming the two matched particles to the local coordinate system of the first contact node, the positional differences between the first and second local particle positions are 1.1µm and 1.7µm, respectively, both not exceeding 7µm. After transforming the two matched particles to the local coordinate system of the second contact node, the positional differences are 16.4µm and 18.1µm, respectively, both exceeding 7µm. Since both matched particles satisfy both the displacement condition and the local position condition, the first contact node is determined as the pollution source contact node.

[0061] This embodiment actively generates identifiable particle displacement responses within overlapping contact footprints that were previously indistinguishable by static particle positions by altering the contact position of a single target contact node. The particle displacement is then verified in both the photomask coordinate system and the local coordinate system of the ambiguous contact node. Therefore, even if multiple contact nodes form identical or highly overlapping contact areas on the photomask, the actual contact node where particle transfer occurred can be determined by utilizing the relationship between particle movement with the target contact node in the photomask coordinate system and stability in the local coordinate system of the contamination source contact node. Compared to contamination source localization, this embodiment further addresses situations where the degree of contact footprint overlap is high and static image differentiation and location attribution cannot distinguish the contamination source. It establishes position tolerance through an error upper limit and identification conditions through multi-particle consistency, distinguishing the actual particle displacement generated by contact position adjustment from image noise, repeated positioning fluctuations, and sporadic particles. This reduces the need to inspect and clean uncontaminated contact nodes, preventing further contamination of subsequent photomasks due to unresolved contamination sources.

[0062] Based on another preferred embodiment described above, see [link to preferred embodiment]. Figure 4 As shown, this embodiment provides a contamination source identification system for the overlapping contact area of ​​a photomask, used to apply the above-described contamination source identification method for the overlapping contact area of ​​a photomask, including: The acquisition module is used to acquire the contact footprint area of ​​each contact node, acquire images of the photomask before and after passing through each contact node, and perform differential processing to obtain the location of the newly added particles. The ambiguous node determination module is used to identify the contact nodes that form the contact footprint overlap area as ambiguous contact nodes when the location of a newly added particle is in the contact footprint overlap area, and to select the target contact node. The contact position control module is used to control the two verification photomasks to pass through the target contact node at the reference contact position and the offset contact position respectively, while keeping the contact position of the remaining ambiguous contact node unchanged; The particle processing module is used to acquire images of two verification photomasks before and after passing through ambiguous contact nodes and perform differential processing to obtain the first set of newly added particle positions and the second set of newly added particle positions. The two sets of newly added particle positions are matched and the matched particle positions are transformed to the local coordinate system of each ambiguous contact node. The pollution source identification module is used to determine whether a target contact node is a pollution source contact node based on the relationship between the displacement of the matching particle in the photomask coordinate system and the contact displacement from the reference contact position to the offset contact position, as well as the position difference of the matching particle in the local coordinate system of each ambiguous contact node.

[0063] In this embodiment, the acquisition module includes an imaging device positioned at the photolithography mask inspection location and a storage device for storing contact footprint areas and image data; the contact position control module is connected to the motion controller of the photolithography equipment and is used to issue the reference contact position and offset contact position of the target contact node; the ambiguous node determination module, particle processing module, and contamination source identification module are implemented by the processor executing instructions in the storage device. The processor reads the image formed by the imaging device, the contact pose recorded by the motion controller, and the pre-calibrated error data, and outputs the contamination source contact node identification result.

[0064] When the above system executes the aforementioned method, it can achieve the same technical effect as the aforementioned method.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for identifying contamination sources in the overlapping contact area of ​​a photomask, characterized in that, include: The contact footprint area of ​​each contact node is obtained, and the images of the photomask before and after passing through each contact node are acquired and differentiated to obtain the location of the newly added particles. When the location of the newly added particle is in the overlapping area of ​​the contact footprint, the contact node involved is identified as an ambiguous contact node, and the target contact node is selected. Two verification photomasks are controlled to pass through the target contact node at a reference contact position and an offset contact position, respectively, while keeping the contact position of the remaining ambiguous contact node unchanged, and the displacement from the reference contact position to the offset contact position is determined as the contact displacement; Images of two verification photomasks before and after passing through the ambiguous contact nodes are acquired and differencing is performed to obtain the first set of new particle positions and the second set of new particle positions; the two sets of new particle positions are matched and transformed to the local coordinate system of each ambiguous contact node; When the displacement direction of the matching particle in the photomask coordinate system is the same as the contact displacement direction, the difference between the displacement distance and the contact displacement distance does not exceed the position tolerance, and the local position condition is met, the target contact node is determined to be the pollution source contact node.

2. The method for identifying contamination sources in the overlapping contact area of ​​a photomask according to claim 1, characterized in that, The calibration process for the contact footprint area includes: The actual contact contours of each contact node and the calibrated photomask are collected; the actual contact contours are transformed to the coordinate system of the photomask; the contact footprint area is obtained by expanding outward along the actual contact contours according to the sum of the upper limits of the errors of repeatability positioning error, contact position control error and image registration error.

3. The method for identifying contamination sources in the overlapping contact area of ​​a photomask according to claim 2, characterized in that, The setting of the offset contact position includes: setting the offset contact position along the direction of reducing the overlapping area of ​​the contact footprints of the target contact node and the remaining ambiguous contact node, and making the distance between the reference contact position and the offset contact position greater than the position tolerance.

4. The method for identifying contamination sources in the overlapping contact area of ​​a photomask according to claim 3, characterized in that, When controlling two verification photomasks to pass through the target contact node at a reference contact position and an offset contact position respectively, the following are included: except for the contact position of the target contact node, the two transfers use the same transfer path, movement direction, transfer speed and image acquisition parameters, and all remaining ambiguous contact nodes maintain the same contact position.

5. The method for identifying contamination sources in the overlapping contact area of ​​a photomask according to claim 1, characterized in that, The process of determining the matching particles includes: obtaining the particle size, particle outline, and nearest neighbor particle spacing of two sets of newly added particles; and determining the particles whose particle size difference does not exceed the size tolerance, whose particle outline overlap is not lower than the outline threshold, and whose nearest neighbor particle spacing difference does not exceed the spacing tolerance as the matching particles.

6. The method for identifying contamination sources in the overlapping contact area of ​​a photomask according to claim 5, characterized in that, The local coordinate transformation process for matching particle positions includes: establishing a local coordinate system based on the installation positioning reference of each ambiguous contact node; and converting the matching particle positions into a first local particle position and a second local particle position according to the contact pose of each ambiguous contact node in two contacts.

7. The method for identifying contamination sources in the overlapping contact area of ​​a photomask according to claim 6, characterized in that, Determining the position tolerance includes: determining the position tolerance as the sum of the upper limits of the image registration error, the repetitive positioning error, the contact position control error, and the particle boundary extraction error.

8. The method for identifying contamination sources in the overlapping contact area of ​​a photomask according to claim 7, characterized in that, The particle displacement prediction process includes: translating the matching particle position in the first group of newly added particle positions according to the contact displacement to obtain the predicted particle position; when the distance between the matching particle position in the second group of newly added particle positions and the predicted particle position does not exceed the position tolerance, and the displacement direction of the matching particle is the same as the contact displacement direction, it is determined that the matching particle meets the displacement condition.

9. The method for identifying contamination sources in the overlapping contact area of ​​a photomask according to claim 8, characterized in that, The process of identifying the sequence of the ambiguous contact nodes includes: The position difference between the first local particle position and the second local particle position of the same matching particle in the local coordinate system of the target contact node does not exceed the position tolerance, and the position difference in the local coordinate system of each remaining ambiguous contact node exceeds the position tolerance, is determined as a local position condition. When at least two matching particles with a positional spacing greater than the positional tolerance and both satisfying the displacement condition and the local positional condition can be selected, the target contact node is determined to be the pollution source contact node. When there are at least two matching particles, but at least two matching particles that simultaneously satisfy the displacement condition and the local position condition cannot be selected, the reference contact position is restored, the target contact node is excluded, and the unidentified ambiguous contact node is selected. When there are fewer than two matching particles, the locations of the newly added particles in the first group and the locations of the newly added particles in the second group are re-acquired; when all ambiguous contact nodes are excluded, the result of no pollution source contact node is output.

10. A contamination source identification system for overlapping contact areas of photomasks, used to apply the contamination source identification method for overlapping contact areas of photomasks as described in any one of claims 1-9, characterized in that, include: The acquisition module is used to acquire the contact footprint area of ​​each contact node, acquire images of the photomask before and after passing through each contact node, and perform differential processing to obtain the location of the newly added particles. The ambiguous node determination module is used to determine the contact node forming the contact footprint overlap area as an ambiguous contact node when the location of the newly added particle is located in the contact footprint overlap area, and to select the target contact node. The contact position control module is used to control the two verification photomasks to pass through the target contact node at the reference contact position and the offset contact position respectively, while keeping the contact position of the remaining ambiguous contact node unchanged; The particle processing module is used to acquire images of two verification photomasks before and after passing through the ambiguous contact nodes and perform differential processing to obtain the first set of newly added particle positions and the second set of newly added particle positions, match the two sets of newly added particle positions, and transform the matched particle positions to the local coordinate system of each ambiguous contact node. The pollution source identification module is used to determine whether the target contact node is a pollution source contact node based on the relationship between the displacement of the matching particle in the photomask coordinate system and the contact displacement from the reference contact position to the offset contact position, as well as the position difference of the matching particle in the local coordinate system of each ambiguous contact node.

Images