Alignment mark and method for monitoring three-dimensional effects of a reticle

Abstract

The application discloses an alignment mark for monitoring three-dimensional effect of a mask and a method. The alignment mark for monitoring three-dimensional effect of a mask comprises at least one identification unit, wherein the identification unit comprises multiple groups of identification rod pairs; the multiple groups of identification rod pairs are arranged along a scanning axis of the corresponding identification unit at intervals, and there is a spacing between the identification rod pairs of adjacent groups along the scanning axis; two identification rods in each group of identification rod pairs are symmetrically distributed on both sides of the scanning axis, and a clamping angle is formed between the two identification rods. By using the provided alignment mark, the three-dimensional effect of the mask can be effectively monitored, and the actual deviation value of the actual pattern area can be detected. Based on the monitored three-dimensional effect data, the deviation can be corrected, so that the yield and reliability of the photolithography process are improved.

Description

TECHNICAL FIELD

[0001] The present application relates generally to the field of integrated circuit lithography process. More particularly, the present application relates to an alignment mark and method for lithography process, especially an alignment mark and method for monitoring mask three-dimensional effect. BACKGROUND

[0002] In the process of integrated circuit design, exposure and development is an essential step, which is currently widely carried out by lithography technology, mainly using exposure machine to project the pattern on the mask onto the photoresist layer on the wafer, and then finally copying the pattern of the mask on the wafer through the developing machine. That is, the mask is used for pattern transfer in integrated circuits. With the improvement of process nodes, after 28 nanometers, the three-dimensional effect of the mask caused by the mask manufacturing process begins to appear. Such effects include non-ideal flatness of mask pattern in three dimensions (e.g. non-vertical sidewall) caused by mask etching, shadow effect caused by oblique incident light shining on the mask, etc. These three-dimensional effects can be approximately equivalent to the spherical aberration of the optical system.

[0003] In the prior art, the general idea of monitoring spherical aberration is to use ring-shaped patterns. However, the circular formation of ring-shaped patterns can be affected by the process, resulting in non-standard ring-shaped patterns that interfere with the accurate determination of spherical aberration. Moreover, when using ring-shaped images to monitor spherical aberration, only one direction can be monitored, while spherical aberration can occur in multiple directions. Therefore, monitoring a single direction can miss spherical aberration information in other directions, resulting in the inability to meet the monitoring requirements. In the prior art, there is also a way to monitor astigmatism through a special mask during the equipment adjustment stage of the lithography process, and then monitor the spherical aberration effect. However, since the special mask only monitors spherical aberration during the equipment adjustment stage of the lithography process, it does not monitor spherical aberration in other stages of the lithography process. Therefore, even if the mask process is error-free, it is not possible to effectively adjust the error in the actual lithography exposure stage. This is because under different target sizes, different film layer stacks on the wafer, and different L / S (Line / Space) patterns, the actual critical dimension (CD) differences caused by the optical spherical aberration in the horizontal and vertical directions are not consistent.

[0004] Therefore, there is an urgent need to provide a solution for monitoring mask three-dimensional effect, so as to detect the actual deviation of the actual pattern area, and then correct the deviation based on the monitored three-dimensional effect data, thereby improving the yield and reliability of the lithography process. SUMMARY

[0005] To at least solve one or more of the above-mentioned technical problems, the present application proposes, in multiple aspects, an alignment mark and a method for monitoring a three-dimensional effect of a reticle.

[0006] In a first aspect, the present application provides an alignment mark for monitoring a three-dimensional effect of a reticle, comprising: at least one identification unit; wherein the identification unit comprises a plurality of groups of identification rod pairs; the plurality of groups of identification rod pairs are arranged along a scanning axis of the corresponding identification unit with a spacing between adjacent groups of identification rod pairs along the scanning axis; two identification rods in each group of identification rod pairs are symmetrically distributed along both sides of the scanning axis, and a included angle is formed between the two identification rods.

[0007] In some embodiments, the spacing is set according to the line size and gap size of the reticle peripheral pattern where the identification rods are located.

[0008] In some embodiments, the included angle is between 30° and 160°.

[0009] In some embodiments, the alignment mark comprises a plurality of the identification units, and the scanning directions of the plurality of identification units are different from each other.

[0010] In some embodiments, the plurality of identification units are distributed in a circumferential radial manner, a plurality of corresponding scanning axes intersect at a center, and the scanning direction is from the center along each scanning axis outward.

[0011] In some embodiments, the plurality of identification units comprise at least one inner layer identification unit and at least one outer layer identification unit arranged with a spacing, wherein the inner layer identification unit is closer to the center than the outer layer identification unit.

[0012] In some embodiments, the size of each identification rod in the outer layer identification unit is greater than the size of each identification rod in the inner layer identification unit.

[0013] In some embodiments, the size of the identification rods of the inner layer identification unit is proportionally reduced relative to the size of the identification rods of the outer layer identification unit, and the proportion is set according to a size parameter of the inner layer identification unit and the outer layer identification unit at corresponding positions of the reticle, respectively.

[0014] In some embodiments, the size parameter comprises a critical dimension and a size period.

[0015] In a second aspect, the present application provides a method for monitoring three-dimensional effect of a mask, the method comprising: placing one or more alignment marks on the mask at different positions; performing scanning on the alignment marks in a scanning direction along a scanning axis of the alignment mark to collect a monitoring signal; and adjusting a related parameter of an alignment system based on the monitoring signal.

[0016] In some embodiments, the monitoring signal comprises offset information of the alignment mark relative to a reference position, and shape information of the alignment mark.

[0017] In some embodiments, the offset information of the alignment mark relative to a reference position comprises offset information of each identification rod in each identification unit in the alignment mark relative to its corresponding reference position in a first direction and in a second direction.

[0018] In some embodiments, the first direction is X direction, and the second direction is Y direction perpendicular to the X direction.

[0019] In some embodiments, the shape information of the alignment mark comprises shape information of each identification rod in each identification unit in the alignment mark.

[0020] Compared with the prior art, the present application has the unexpected technical effect that: by using the provided alignment mark, the three-dimensional effect of the mask can be effectively monitored, and the actual deviation value of the actual pattern area can be detected. Based on the monitored three-dimensional effect data, the deviation can be further corrected, thereby improving the yield and reliability of the photolithography process.

[0021] The alignment mark provided by the embodiments of the present application can be adapted to various areas, and thus can be placed in various areas of the mask (including the periphery of the photolithography layer and the exposure area), so that various pattern design rules can be filled into the corresponding positions under the premise that the signal is identifiable, thereby the data of the three-dimensional effect of the mask received by the mask at different positions can be collected. Further, the L / S of the identification rod in the alignment mark is controllable to adapt to the offset and deformation collected in different pattern environments. In some embodiments, data for judging spherical aberration can be provided, and the spherical aberration can be corrected by converting and adjusting the parameters of the illumination system through the Zernike formula. BRIEF DESCRIPTION OF DRAWINGS

[0022] The above and other objects, features and advantages of the example embodiments of the present application will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which several embodiments of the present application are shown by way of example, and wherein like reference numerals refer to like elements throughout. In the drawings:

[0023] Figure 1 A schematic diagram showing the working principle of a lithographic apparatus to which the alignment mark of embodiments of the application can be applied is shown;

[0024] Figure 2A A schematic diagram showing an alignment mark comprising one identification unit for monitoring three-dimensional effects of a reticle according to embodiments of the application is shown;

[0025] Figure 2B A schematic diagram showing another alignment mark comprising one identification unit for monitoring three-dimensional effects of a reticle according to embodiments of the application is shown;

[0026] Figure 2C A schematic diagram showing an alignment mark comprising eight identification units for monitoring three-dimensional effects of a reticle according to embodiments of the application is shown;

[0027] Figure 2D A schematic diagram showing an alignment mark comprising sixteen identification units for monitoring three-dimensional effects of a reticle according to embodiments of the application is shown;

[0028] Figure 3 A schematic diagram showing a flow chart of a method for monitoring three-dimensional effects of a reticle according to embodiments of the application is shown;

[0029] Figure 4 A schematic diagram showing an alignment mark according to embodiments of the application disposed on a reticle is shown;

[0030] Figure 5 A schematic diagram showing the shift of an alignment mark relative to a reference position according to embodiments of the application is shown;

[0031] Figure 6 A schematic diagram showing the waveform of a light intensity signal of an identification bar according to embodiments of the application is shown.

[0032] Legend of the figures:

[0033] lithographic apparatus 100; light source system 110; reticle stage 120; projection system 130;

[0034] wafer stage 140; reticle 121; wafer 141; alignment mark 200; identification unit 210;

[0035] identification bar pair 211; scanning axis 212; exposure area 1210. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0037] It should be understood that the terms "comprising" and "including" used in the specification and claims of the present application indicate the presence of the described features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0038] It should also be understood that the terms used in the specification of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. As used in the specification and claims of the present application, the singular forms "a", "an" and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. It should be further understood that the term "and / or" used in the specification and claims of the present application means any combination of one or more of the associated listed items and all possible combinations thereof, and includes these combinations.

[0039] It should also be understood that, for the convenience of description, spatial relative terms such as "under", "below", "lower", "above", "upper" and the like can be used herein to describe the relationship of one element or component to another (or other) element or component as shown in the drawings. When an element or layer is referred to as "on", "adjacent to", "connected to" or "coupled to" other elements or layers, it can be directly on, adjacent to, connected or coupled to other elements or layers, or there can be intervening elements or layers. In contrast, when an element is referred to as "directly on", "directly adjacent to", "directly connected to" or "directly coupled to" other elements or layers, there are no intervening elements or layers.

[0040] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0041] Figure 1 The working principle of a photolithography apparatus to which the alignment mark of the embodiments of the present application can be applied is shown.

[0042] The photolithography apparatus is a key device in the semiconductor manufacturing process, which is used to transfer the chip circuit pattern on the mask plate to the wafer. As shown in Figure 1 The photolithography apparatus 100 can include a light source system 110, a mask table 120, a projection system 130 and a wafer table 140.

[0043] The light source system 110 is used to provide light energy with a stable frequency and energy, and may include a light source and various types of optical components or combinations of optical components for guiding, shaping or controlling the irradiation beam. The light beam emitted by the light source is typically ultraviolet (UV) or deep ultraviolet (DUV) light, which, after being shaped and homogenized by various optical components, irradiates the mask plate 121 located on the mask stage 120.

[0044] The mask stage 120 supports the mask 121 and is adjustable with multiple degrees of freedom. In the step-scan exposure mode, the mask stage 120 works in conjunction with the wafer stage 140 to achieve highly precise synchronous stepping and scanning of the mask 121 and the wafer 141. The mask 121 has the desired chip circuit pattern.

[0045] The projection system 130 is located below the mask stage 120 and is used to project the pattern imparted by the photomask 121 to the illumination beam onto the wafer 141 located on the wafer stage 140. The wafer stage 140, which supports the wafer 141 and is located below the projection system 130, can move synchronously with the mask stage 120 during exposure to ensure that the pattern on the mask 121 is accurately transferred onto the wafer 141.

[0046] In this embodiment of the application, the lithography equipment 100 further includes: a stepper ( Figure 1 (Not shown in the image) During the exposure process, the mask stage 120 and the wafer stage 140 are moved synchronously by the stepper to expose different areas of the wafer 141 on the wafer stage 140, forming multiple photolithographic product patterns on the surface of the wafer 141. After that, other semiconductor processes such as development and etching can be performed to pattern the surface material (i.e., photosensitive layer) of the wafer 141.

[0047] In the integrated circuit manufacturing process, as the process node advances, the three-dimensional effect of the mask 121 becomes apparent at nodes beyond 28 nanometers due to the mask fabrication process. To monitor this three-dimensional effect, this embodiment of the application can set alignment marks on the mask 121 to effectively monitor the three-dimensional effect and detect the actual deviation value of the actual patterned area. Based on the monitored three-dimensional effect data, the deviation can be corrected, thereby improving the yield and reliability of the photolithography process.

[0048] Figure 2A A schematic diagram of an alignment mark 200 including an identification unit 210 for monitoring the three-dimensional effect of a mask 121 according to an embodiment of this application is shown.

[0049] like Figure 2AAs shown, the alignment mark 200 comprises: at least one identification unit 210; wherein the identification unit 210 comprises a plurality of groups of identification rod pairs 211; the plurality of groups of identification rod pairs 211 are arranged at intervals along a scanning axis 212 of the corresponding identification unit 210, and there is a spacing between adjacent groups of identification rod pairs 211 along the scanning axis 212; two identification rods in each group of identification rod pairs 211 are symmetrically distributed on both sides of the scanning axis 212, and an included angle is formed between the two identification rods.

[0050] In the embodiment of the present application, one identification unit 210 comprises a plurality of groups of identification rod pairs 211, for example, 5 pairs or 8 pairs, and the number of identification rod pairs 211 contained in each identification unit 210 is not specifically limited in the embodiment of the present application, and can be determined according to actual process requirements.

[0051] In the embodiment of the present application, each group of identification rod pairs 211 comprises two identification rods, and the shape of the identification rods in the identification rod pairs 211 can be rectangular or other shapes, for example, triangular, polygonal, etc., which are not specifically limited in the embodiment of the present application, and the embodiment of the present application is only described by taking the shape of the identification rods as rectangular.

[0052] In the embodiment of the present application, there is a spacing between adjacent groups of identification rod pairs 211 along the scanning axis 212, as shown in the figure. Figure 2A As shown, in the direction from left to right along the scanning axis 212, the spacing between the first group of identification rod pairs 211 and the second group of identification rod pairs 211 along the scanning axis 212 is d1, the spacing between the second group of identification rod pairs 211 and the third group of identification rod pairs 211 along the scanning axis 212 is d2, the spacing between the third group of identification rod pairs 211 and the fourth group of identification rod pairs 211 along the scanning axis 212 is d3, and the spacing between the fourth group of identification rod pairs 211 and the fifth group of identification rod pairs 211 along the scanning axis 212 is d4.

[0053] In the embodiment of the present application, the above d1, d2, d3 and d4 can be set according to the line size and gap size of the peripheral pattern of the mask plate 121. The line size refers to the width of the line of the pattern on the mask plate 121, and the gap size refers to the spacing between adjacent lines on the mask plate 121. Specifically, d1, d2, d3 and d4 can be determined according to the ratio of the line size to the gap size, for example, if the ratio of the line size to the gap size is large (for example, greater than 10 ), then d1, d2, d3 and d4 are set to a smaller value; if the ratio of the line size to the gap size is small (for example, greater than 1 ), then d1, d2, d3 and d4 are set to a larger value.

[0054] The embodiment of the present application sets the distance between the adjacent groups of the marker rod pairs 211 along the scanning axis 212 on the identification unit 210 by identifying the line size and gap size of the peripheral pattern of the mask 121, so that different density patterns on the mask 121 can be simulated, and the actual displacement of the peripheral pattern of the mask 121 can be better represented.

[0055] In the embodiment of the present application, the included angle between the two marker rods in each group of marker rod pairs 211 may be between 30° and 160°, and may be 30°, 50°, 70°, 90°, 100°, 120°, 140°, 160°, or other values within the above range, which are not limited herein.

[0056] For example, Figure 2A the included angle between the two marker rods in the marker rod pair 211 shown in is 90 degrees, Figure 2B the included angle between the two marker rods in the marker rod pair 211 shown in is 60 degrees.

[0057] The alignment mark provided by the embodiment of the present application can be adapted to various regions, and thus can be placed in various regions of the mask (including the peripheral of the photolithography layer and the exposure area), so that various pattern design rules can be filled into the corresponding positions under the premise that the signal is identifiable, so that the data of the mask three-dimensional effect suffered by the mask at different positions can be collected. Further, the L / S of the marker rod in the alignment mark is controllable to adapt to the offset and deformation collected under different pattern environments.

[0058] Figure 2C FIG. 2 shows a schematic diagram of an alignment mark including eight identification units for monitoring the mask three-dimensional effect according to some embodiments of the present application. Figure 2D FIG. 3 shows a schematic diagram of an alignment mark including 16 identification units for monitoring the mask three-dimensional effect according to some other embodiments of the present application.

[0059] As an optional embodiment of the present application, as Figure 2C shown, the above alignment mark 200 includes a plurality of identification units 210, and the scanning directions of the plurality of identification units 210 are different from each other.

[0060] For example, the alignment mark 200 shown in Figure 2C includes eight identification units 210 (i.e., four large identification units 210 and four small identification units 210). For another example, Figure 2DThe alignment mark 200 shown includes 16 identification units 210 (i.e., 8 large identification units 210 and 8 small identification units 210). The number of identification units 210 included in the alignment mark 200 is not specifically limited in the embodiments of the present application, and can be determined according to actual processes.

[0061] It should be noted that when the alignment mark 200 includes multiple identification units 210, the number of identification rods 211 included in different identification units 210 can be the same or different, which is not specifically limited in the embodiments of the present application, and can be determined according to actual processes.

[0062] In the embodiments of the present application, the scanning directions of the multiple identification units 210 are different from each other, specifically, the multiple identification units 210 are distributed in a circular radial manner, and the multiple scanning axes 212 correspondingly intersect at the center of the circle, and the scanning direction is from the center to the outside along each scanning axis 212. For example, Figure 2C The 8 scanning axes 212 of the alignment mark 200 shown extend from the center in 8 directions; for another example, Figure 2D The 16 scanning axes 212 of the alignment mark 200 shown extend from the center in 16 directions. As for the scanning direction of each identification unit, it can be determined according to actual processes.

[0063] As an optional embodiment of the present application, the multiple identification units 210 include at least one inner layer identification unit and at least one outer layer identification unit arranged at intervals, wherein the inner layer identification unit is closer to the center than the outer layer identification unit.

[0064] Exemplarily, in the embodiments of the present application, the size of each identification rod in the outer layer identification unit is larger than the size of each identification rod in the inner layer identification unit. Specifically, the size of the identification rod of the inner layer identification unit is reduced in proportion to the size of the identification rod of the outer layer identification unit, and the proportion can be set according to the size parameters of the inner layer identification unit and the outer layer identification unit at the corresponding positions of the mask plate 121.

[0065] In the embodiments of the present application, the size parameters include a critical dimension and a size period. The critical dimension (CD) refers to a special line pattern reflecting the width of a feature line of an integrated circuit in integrated circuit photomask manufacturing and photolithography processes, specifically, the critical dimension refers to a feature size on a chip. The size period refers to the center-to-center distance between adjacent circuit features in an integrated circuit. The reduction of the size period can improve the integration of the integrated circuit, thereby improving performance and reducing power consumption.

[0066] In a specific implementation, if the critical dimension of the inner layer at the mask position is CD1 and the critical dimension of the outer layer at the mask position is CD2, the size ratio of the inner-outer layer marker stick can be set according to CD1:CD2; for example, the larger the size period, the larger the ratio, and so on.

[0067] The embodiment of the present application sets the size of the inner layer identification unit to be proportionally reduced relative to the size of the outer layer identification unit, thereby improving the alignment accuracy of the alignment mark 200 and adapting to complex manufacturing processes.

[0068] Based on the above description of the alignment mark 200, the method for monitoring the three-dimensional effect of the mask using the alignment mark 200 is described below.

[0069] Figure 3 A flowchart of the method 300 for monitoring the three-dimensional effect of the mask according to the embodiment of the present application is shown. As shown in the left side of the figure, Figure 3 The method 300 for monitoring the three-dimensional effect of the mask uses the alignment mark described in the above embodiment to monitor the mask. The method includes: step S310, setting one or more alignment marks at different positions of the mask; step S320, performing scanning on the alignment mark in the scanning direction along the scanning axis of the identification unit of the alignment mark to collect a monitoring signal; and step S330, adjusting the related parameters of the alignment system based on the monitoring signal.

[0070] Exemplarily, in the embodiment of the present application, in step S310, the alignment mark can be set at different positions of the mask, for example, the exposure area, the periphery of the lithography layer, and so on, and the present application does not make specific limitations on the setting position of the alignment mark.

[0071] Figure 4 A schematic diagram of the alignment mark according to the embodiment of the present application deployed on the mask is shown. As shown in the left side of the figure, Figure 4 As shown in the left side of the figure, the alignment mark 200 is located at the periphery of the lithography layer, and as shown in the right side of the figure, Figure 4 As shown in the right side of the figure, the alignment mark 200 is located at the exposure area 1210.

[0072] In this embodiment, in step S320, the alignment mark is scanned along the scanning axis of the marking unit in the alignment mark in the scanning direction. Specifically, the alignment mark is scanned along the scanning axis in the scanning direction, thereby acquiring monitoring signals along the X direction and the Y direction, as well as monitoring signals that can acquire deformation information of the alignment mark. Specifically, in this embodiment, the monitoring signals may include offset information of the alignment mark relative to the reference position (including offset information in the X direction and offset information in the Y direction) and shape information of the alignment mark. Here, the reference position can be pre-set. Specifically, the alignment mark is pre-set on the wafer, and the position of the alignment mark set on the wafer is the aforementioned reference position.

[0073] In this embodiment, the offset information of the alignment mark relative to the reference position may include the offset information of each pair of marker bars in each marker unit of the alignment mark relative to its corresponding reference position in a first direction (i.e., the X direction) and in a second direction (i.e., the Y direction). In specific implementation, the offset information in the first direction and the offset information in the second direction can be determined by the coordinates of any point on the pair of marker bars (e.g., the center point of one of the marker bars) and the coordinates of its corresponding reference position.

[0074] Specifically, such as Figure 5 As shown, dark gray marker bars are used to indicate the actual position of the marker bars, while light gray marker bars are used to indicate the reference position of the marker bars. From Figure 5 It can be seen that the actual position of each marker bar in the alignment marks is offset to varying degrees relative to the reference position, from which we can obtain the following... Figure 5 The offsets of each marker bar relative to the reference position in the X direction (i.e., X1, X2, X3, X4, X5) and in the Y direction (i.e., Y1, Y2, Y3, Y4, Y5) are shown.

[0075] In this embodiment of the application, the shape information of the alignment mark may include the shape information of each marker bar in each marker unit of the alignment mark. For example... Figure 6 As shown, different shapes of marker bars result in different waveforms in the marker bar light intensity signal. For example, the waveform corresponding to a trapezoid has a longer period than the waveform corresponding to a rectangle, and it is not a smooth sine wave; similarly, the waveform of a parallelogram also has a slightly longer period than the waveform corresponding to a rectangle, and it is also not a smooth sine wave. Therefore, if the shape of the marker bar changes after scanning, this can be reflected in the waveform of the marker bar light intensity signal. Thus, in this embodiment, the shape information of the alignment mark is acquired by collecting the waveform of the marker bar light intensity signal.

[0076] Exemplarily, in the embodiment of the present application, in the step S330, the related parameters of the alignment system are adjusted based on the monitoring signal. In actual implementation, the collected monitoring signal can be fed back to a failure detection and classification (FDC) system, and the FDC system analyzes the monitoring signal, and then adjusts the related parameters of the alignment system (for example, the parameters of the illuminator system of the exposure machine) according to the analysis result. In the embodiment of the present application, the related parameters of the alignment system can be calculated by a Zernike polynomial.

[0077] Specifically, in the embodiment of the present application, the shift in the X direction and the shift in the Y direction in the monitoring signal can be used to reflect the degree of tilt of the optical element, and such tilt can cause the propagation direction of the light to change, thereby introducing aberration. In the Zernike polynomial, the shift in the X direction and the shift in the Y direction are mainly related to low-order terms. Specifically, Z1 and Z2 in the Zernike polynomial correspond to the tilt in the X direction and the tilt in the Y direction, respectively.

[0078] Based on the above description, in the embodiment of the present application, the related parameters of the alignment system calculated based on the Zernike polynomial can be as follows: the shift in the X direction and the shift in the Y direction are respectively input into the Zernike polynomial, and the corresponding Zernike coefficients (namely, Z1 and Z2) are obtained, and then other aberration terms (for example, Z8 of spherical aberration) are combined to adjust the related parameters of the alignment system.

[0079] In the embodiment of the present application, the shape information of the alignment mark in the monitoring signal is used to adjust the related parameters of the alignment system in the following manner: the collected shape information (namely, two-dimensional coordinates or three-dimensional coordinates) of the alignment mark is converted to polar coordinates to adapt to the orthogonality of the Zernike polynomial. A suitable Zernike polynomial order (for example, Z8 of spherical aberration) is selected according to the complexity of the deformation of the alignment mark, and then the related parameters of the alignment system are adjusted according to the calculated Zernike coefficient (namely, Z8).

[0080] Specifically, the Zernike polynomial is a commonly used mathematical tool for describing wavefront aberration in an optical system. In the Zernike polynomial, each order term corresponds to a different type of aberration. In the embodiment of the present application, Z1, Z2 and Z8 represent the following types of aberration, respectively:

[0081] Z1: represents the overall tilt of the wavefront in the X direction, and corresponds to the shift of the light beam in the X direction.

[0082] Z2: represents the overall tilt of the wavefront in the Y direction, and corresponds to the shift of the light beam in the Y direction.

[0083] Z8 (spherical aberration): represents the aberration of the wavefront in the radial symmetric direction, corresponding to the focusing deviation of the light beam caused by the three-dimensional effect of the mask.

[0084] In the specific calculation of Z1 and Z2:

[0085] The average offset ΔX in the X direction can be calculated based on the offsets of the respective identification rods in the X direction relative to the reference position (for example, X1, X2, X3, X4, X5 in the above table), and the average offset ΔY in the Y direction can be calculated based on the offsets of the respective identification rods in the Y direction relative to the reference position (for example, Y1, Y2, Y3, Y4, Y5 in the above table). Figure 5 Figure 5

[0086] Then the average offset ΔX in the X direction and the average offset ΔY in the Y direction are input into the Zernike polynomial to calculate the coefficient Z1 and the coefficient Z2:

[0087] Z1 = k1 × ΔX

[0088] Z2 = k2 × ΔY

[0089] Wherein, k1 and k2 are calibration coefficients related to the optical system, which can be obtained by system calibration.

[0090] In the specific calculation of Z8:

[0091] The shape information (i.e. two-dimensional coordinates or three-dimensional coordinates) of the collected alignment marks is converted to polar coordinates, and then the average deformation ΔS equivalent to the shape of the alignment marks is calculated, and Z8 is calculated by Zernike polynomial:

[0092] Z8 = k8 × ΔS

[0093] Wherein, k8 is a calibration coefficient related to the optical system, which can be obtained by system calibration.

[0094] After Z1, Z2, and Z8 are calculated, Z1, Z2, and Z8 are input into the illumination control system of the exposure machine, and the device parameters are adjusted according to Z1, Z2, and Z8 by the illumination control system, specifically:

[0095] Z1 is used to adjust the X-axis tilt compensation parameter of the exposure machine. When Z1 > 0, the mask plate is offset along the positive direction of the X-axis, and the mask table of the exposure machine is adjusted in the negative direction of the X-axis. When Z1 < 0, the mask plate is offset along the negative direction of the X-axis, and the mask table of the exposure machine is adjusted in the positive direction of the X-axis. As for the amount of adjustment each time, it can be proportional to |Z1|, for example, |Z1| increases by 1, and the mask table is adjusted by 0.01 μrad.

[0096] ​​Z2 is used to adjust the Y-axis tilt compensation parameter of the exposure machine. When Z2 > 0, the reticle is offset in the positive Y-axis direction, and the reticle stage of the exposure machine is adjusted in the negative Y-axis direction. When Z2 < 0, the reticle is offset in the negative Y-axis direction, and the reticle stage of the exposure machine is adjusted in the positive Y-axis direction. As for the amount of adjustment each time, it can be proportional to |Z2|, for example, |Z2| increases by 1, and the reticle stage is adjusted by 0.01 μrad.

[0097] Z8 is used to adjust the spherical aberration compensation parameter of the exposure machine. When Z8 > 0 (indicating under-correction of spherical aberration), the outer radius of the aperture stop of the illumination system of the exposure machine needs to be reduced to reduce the proportion of edge light, so that the focal points of light in different radius regions tend to be consistent. When Z8 < 0 (indicating over-correction of spherical aberration), the outer radius of the aperture stop needs to be increased to increase the proportion of edge light. As for the amount of adjustment each time, it can be proportional to |Z8|, for example, |Z8| increases by 1, and the radius is adjusted by 0.1 nm.

[0098] The embodiments of the present disclosure can quantitatively analyze the deformation and offset characteristics by applying the deformation and offset of the alignment mark to the Zernike polynomial, and adjust the related parameters of the alignment system accordingly, thereby improving the alignment accuracy and the robustness of the system.

[0099] Although the embodiments of the present application have been shown and described herein, it will be apparent to those skilled in the art that many modifications, changes and substitutions can be made thereto without departing from the spirit and scope of the present application. It is to be understood that various alternatives to the embodiments of the present application described herein can be employed in practicing the present application. The appended claims are intended to cover all such alternatives and equivalents.

Claims

1. An alignment mark for monitoring three-dimensional effects of a reticle, characterized in that, The alignment mark comprises: at least one identification unit; wherein the identification unit comprises a plurality of identification rod pairs; the plurality of identification rod pairs are arranged along the scanning axis of the corresponding identification unit with a spacing between adjacent identification rod pairs along the scanning axis, and the spacing is set according to the line size and gap size of the peripheral pattern of the mask plate, wherein the line size refers to the width of the line of the pattern on the mask plate; and the gap size refers to the spacing between adjacent lines on the mask plate; two identification rods in each group of identification rod pairs are symmetrically distributed along the two sides of the scanning axis, and a included angle is formed between the two identification rods.

2. The alignment mark of claim 1, wherein The included angle is between 30° and 160°.

3. The alignment mark of any of claims 1-2, wherein, The plurality of identification units are arranged in a circular radial distribution, and the corresponding plurality of scanning axes intersect at the center of the circle, and the scanning direction is from the center of the circle along each scanning axis outward.

4. The alignment mark of claim 3, wherein, The plurality of identification units comprise at least one inner layer identification unit and at least one outer layer identification unit arranged in a spacing, wherein the inner layer identification unit is closer to the center of the circle than the outer layer identification unit.

5. The alignment mark of claim 4, wherein, The size of each identification rod in the outer layer identification unit is larger than that of each identification rod in the inner layer identification unit.

6. The alignment mark of claim 5, wherein, The size of the identification rod of the inner layer identification unit is proportionally reduced relative to the size of the identification rod of the outer layer identification unit, and the proportion is set according to the size parameters of the inner layer identification unit and the outer layer identification unit at the corresponding positions of the mask plate.

7. The alignment mark of claim 6, wherein, The size parameters include critical dimensions and size periods.

8. The alignment mark of claim 7, wherein, The alignment mark according to any one of claims 1-8 is used to monitor the mask plate, and the method comprises:

9. A method for monitoring three-dimensional effects of a reticle, characterized in that, one or more alignment marks are arranged at different positions of the mask plate; scanning is performed on the alignment marks in the scanning direction along the scanning axis of the identification unit in the alignment mark to collect a monitoring signal; based on the monitoring signal, relevant parameters of an alignment system are adjusted, and the relevant parameters include parameters of an exposure machine illumination system, and the parameters of the exposure machine illumination system include X-axis tilt compensation parameters of the exposure machine, Y-axis tilt compensation parameters of the exposure machine, and spherical aberration compensation parameters of the exposure machine. The monitoring signal comprises offset information of the alignment mark relative to a reference position and shape information of the alignment mark.

10. The method of claim 9, wherein, The offset information of the alignment mark relative to the reference position comprises offset information of each identification rod pair in each identification unit in the alignment mark relative to the corresponding reference position in a first direction and a second direction.

11. The method of claim 10, wherein, The first direction is the X direction, and the second direction is the Y direction perpendicular to the X direction.

12. The method of claim 11, wherein, The shape information of the alignment mark comprises shape information of each identification rod in each identification unit in the alignment mark.

13. The method of claim 10, wherein, ​

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