Focal plane test method, test system and photoetching machine

Abstract

According to the focal plane test method, the test system and the photoetching machine provided by the invention, the reflectivity of the different focal planes of each test point in the exposure field is obtained by testing the reflectivity of the photoresist pattern on the substrate; performing quadratic fitting on the reflectivity of different focal planes of each test point in the exposure field to obtain an optimal focal length, and obtaining the optimal focal lengths of all test points in the exposure field; and performing least square method plane fitting on the optimal focal length of each test point in the exposure field to obtain the optimal focal plane height and the optimal focal plane inclination. The photoetching machine is integrated with a reflectivity test unit, so that the cost of introducing a higher node technology, the cost of purchasing a high-precision critical dimension scanning electron microscope and overlay measurement equipment, and the cost of special reflectivity test equipment are remarkably reduced. Compared with size microscopic measurement and microscope manual judgment, the reflectivity testing efficiency is high. The field curvature and astigmatism of the exposure field can be calculated, and the method is used for testing the primary aberration.

Description

Technical Field

[0001] The present invention relates to the field of photolithography technology, and in particular to a focal plane testing method, a testing system and a photolithography machine. Background Art

[0002] The photolithography machine is the core equipment that undertakes the circuit transfer function in the chip manufacturing process. The imaging level of the photolithography machine is the top priority of chip manufacturing. There are four main types of detection methods for the imaging level of the photolithography machine in the industry: first, the pupil plane detection technology that does not require glue coating and exposure, and uses high-precision photoelectric sensors to directly test the interference phase of the spatial image; second, the image plane detection technology that does not require glue coating and exposure, and uses high-precision photoelectric sensors to directly test the position, shape, and light intensity of the exposure image; third, the image plane detection technology that requires glue coating and exposure, forms a photoresist pattern on the silicon wafer surface, and further calculates by testing the key size and overlay position of the pattern; fourth, the macroscopic detection technology that requires glue coating and exposure, forms a regularly distributed photoresist pattern on the silicon wafer surface, and further calculates by testing the reflectivity and transmittance of the pattern. The first two types of technology are mainly used for advanced technology node photolithography machines, and the third and fourth types and the methods derived from them are widely used and suitable for photolithography machines of various nodes.

[0003] The best focal plane of the lithography machine is an important parameter that can be freely set in the exposure program of the lithography machine, and it is also a basic parameter used in many evaluation items of the imaging level. From the perspective of end users, the best focal plane of the lithography machine includes the focal plane height Z and the focal plane inclination Rx and Ry. If the best focal plane deviates, the lithography pattern will change in size, the steepness of the sidewall will change, and it may even deform or become unresolvable, which will affect product performance and yield.

[0004] The definition of the best focal plane of a lithography machine can be mainly divided into two types: one is the best focal plane to measure the equipment status; the other is the best focal plane of the user's production conditions. If the best focal plane of the user's product conditions deviates from the best focal plane due to process factors such as the front layer structure of the substrate, exposure pattern, and photoresist absorption and reflection, the focal plane offset is generally added to the exposure program.

[0005] Therefore, the real needs of users are: when maintaining equipment, the best focal plane test method of the equipment is simple, low-cost, high-efficiency, and accurate enough; when producing products, the best focal plane difference caused by substrate differences, pattern differences, and photoresist differences, the test method is simple, low-cost, high-efficiency, accurate focal plane and large focal depth, and the product uniformity is good and meets the specifications. When troubleshooting product abnormalities, the image plane performance changes caused by product characteristics or thermal effects of the objective lens, etc., the test method and data have a certain reference value for troubleshooting. Summary of the invention

[0006] The object of the present invention is to provide a focal plane testing method, a testing system and a photolithography machine to solve the problem of optimal focal plane offset.

[0007] In order to solve the above technical problems, the present invention provides a focal plane testing method, comprising:

[0008] Providing a substrate, on which a photoresist pattern is formed;

[0009] Performing a reflectivity test on the photoresist pattern on the substrate to obtain the reflectivity of different focal planes of each test point in the exposure field;

[0010] Perform quadratic fitting on the reflectivity of different focal planes at each test point in the exposure field to obtain the best focal length, and obtain the best focal length of all test points in the exposure field;

[0011] The optimal focal length of each test point in the exposure field is fitted by the least squares plane to obtain the optimal focal plane height and the optimal focal plane tilt.

[0012] Optionally, before performing a reflectivity test on the substrate, the process includes:

[0013] The test point is moved under the light beam for testing the reflectivity, an alignment mark at a fixed offset of the test point is captured, and the center of the photoresist layer pattern is located by locating the alignment mark.

[0014] Optionally, a reflectivity testing unit is used to test the reflectivity of the substrate, and the testing steps include:

[0015] The light source module emits parallel incident light, which is reflected by the first reflecting prism, the beam splitting prism, and the second reflecting prism, and then is incident on the photoresist pattern on the substrate surface and diffusely reflected. The diffusely reflected light in different directions carrying the photoresist pattern information is reflected by the second reflecting prism and transmitted by the beam splitting prism, and then is received by the detector, and the reflectivity of different focal planes of each test point in the exposure field is obtained through conversion.

[0016] Optionally, a quadratic fit is performed on the reflectivity of different focal planes at each test point in the exposure field to obtain a quadratic curve, and the focal length corresponding to the peak value or valley value of the quadratic curve is the optimal focal length.

[0017] Optionally, the photoresist pattern includes a one-dimensional grating structure photoresist pattern and a two-dimensional grating structure photoresist pattern.

[0018] Optionally, the two-dimensional grating structure photoresist pattern is one of a circle, a regular octagon, a regular hexagon or a square, the arrangement of the two-dimensional grating structure photoresist pattern is a regular hexagon, an orthogonal arrangement or a non-orthogonal arrangement, and the two-dimensional grating structure photoresist pattern is a column or a hole.

[0019] Optionally, the one-dimensional grating structure photoresist pattern is a four-directional composite one-dimensional grating structure photoresist pattern arranged in four angular directions.

[0020] Optionally, the detector in the off-axis alignment unit includes four detection areas to detect the reflectivity of the four-way composite one-dimensional grating structure photoresist pattern, and calculate the aberration based on the reflectivity of the four-way composite one-dimensional grating structure photoresist pattern, wherein the aberration includes field curvature and astigmatism.

[0021] Optionally, the astigmatism includes 0 degree astigmatism and 45 degree astigmatism.

[0022] Optionally, the reflectivity testing unit is an off-axis alignment unit.

[0023] Based on the same concept, the present invention provides a focal plane testing system, comprising:

[0024] An exposure unit, used for transferring the mask pattern onto the substrate to form a photoresist pattern;

[0025] A reflectivity testing unit, used for testing the reflectivity of the photoresist pattern on the substrate to obtain the reflectivity of different focal planes of each test point in the exposure field;

[0026] The calculation unit is used to perform quadratic fitting on the reflectivity of different focal planes at each test point in the exposure field to obtain the best focal length, and perform least squares plane fitting on the best focal length of each test point in the exposure field to obtain the best focal plane height and the best focal plane tilt.

[0027] Optionally, the reflectivity testing unit is an off-axis alignment unit, which includes a light source module, a first reflecting prism, a beam splitting prism reflection, a second reflecting prism and a detector, the light source module is used to emit light, the first reflecting prism and the second reflecting prism are used to change the path of the light, the beam splitting prism is used to reflect or transmit the light, and the detector is used to detect diffusely reflected light in different directions carrying the photoresist graphic information.

[0028] Optionally, the mask pattern includes a one-dimensional pattern and a two-dimensional pattern, which are transferred to the photoresist pattern to form a one-dimensional grating structure photoresist pattern and a two-dimensional grating structure photoresist pattern.

[0029] Optionally, the two-dimensional figure is one of a circle, a regular octagon, a regular hexagon or a square, and the arrangement of the two-dimensional figure is a regular hexagon, an orthogonal arrangement or a non-orthogonal arrangement.

[0030] Optionally, the one-dimensional pattern is a four-directional composite one-dimensional pattern arranged in four angular directions, so as to be transferred to the photoresist pattern to form a four-directional composite one-dimensional grating structure photoresist pattern.

[0031] Optionally, the detector in the off-axis alignment unit includes four detection areas to detect the reflectivity of the four-way composite one-dimensional grating structure photoresist pattern, and the reflectivity of the four-way composite one-dimensional grating structure photoresist pattern is used to calculate the aberration.

[0032] Based on the same concept, the present invention provides a lithography machine, comprising a focal plane testing system as described in any one of the above items.

[0033] In the focal plane test method, test system and lithography machine provided by the present invention, the reflectivity test is performed on the photoresist pattern on the substrate, and the optimal focal length of all test points in the exposure field is calculated. The optimal focal plane height and the optimal focal plane tilt are obtained by performing the least squares plane fitting according to the optimal focal length of each test point in the exposure field. The lithography machine integrates a reflectivity test unit, that is, the lithography machine integrates an off-axis alignment unit. The reflectivity measurement can be achieved using the structural elements of the lithography machine itself, without adding elements or using other measuring equipment, which significantly reduces the cost of customers introducing higher node technology and the cost of purchasing high-precision critical dimension scanning electron microscopes, overlay measurement equipment, and special reflectivity test equipment. Compared with microscopic measurement of size and manual judgment by microscope, the reflectivity test efficiency is higher. The present invention solves the problem that the macroscopic test method using product grading can only test the entire piece, cannot distinguish a certain point in the exposure field, and cannot calculate the focal plane tilt in the exposure field.

[0034] Furthermore, the photoresist pattern includes a one-dimensional grating structure photoresist pattern and a two-dimensional grating structure photoresist pattern. The photoresist pattern is a micro-nano grating structure. The reflectivity of the photoresist micro-nano grating structure pattern mainly utilizes the characteristic that the diffuse reflection of the micro-nano grating pattern on the substrate surface carries the grating structure information. Therefore, the characteristics that the pattern size and side wall angle will change regularly when the focal plane of the lithography machine deviates and the changes in the shape, size, height and side wall angle of the grating pattern on the substrate surface will lead to regular changes in reflectivity can be utilized. The reflectivity is used to detect the best focal plane in the image plane of the lithography machine, which has better adaptability to complex working conditions other than lithography machines with non-advanced technology nodes and relatively high test accuracy.

[0035] Furthermore, the present invention designs a variety of photoresist patterns with grating structures that are close to the graphic structures of user products for image plane detection, including single one-dimensional grating patterns in different directions for focal plane testing, single two-dimensional grating patterns arranged in different ways, and composite grating photoresist patterns for primary aberration testing. The primary aberration includes field curvature and astigmatism, and the astigmatism includes 0-degree astigmatism and 45-degree astigmatism, which is more in line with the working conditions of user products and reduces the time cost from the optimal focal plane of the lithography machine to the optimal focal plane of the product working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Those skilled in the art will appreciate that the accompanying drawings are provided for a better understanding of the present invention and do not constitute any limitation on the scope of the present invention.

[0037] Figure 1 It is a flow chart of a focal plane testing method according to an embodiment of the present invention.

[0038] Figure 2 It is a flow chart of a method for forming a photoresist pattern on a substrate according to an embodiment of the present invention.

[0039] Figure 3 4 is a distribution diagram of test points in the reflectivity exposure field of an embodiment of the present invention.

[0040] Figure 4 These are the area requirements for the reflectivity test light spot and reflectivity test point graphic area of ​​the embodiment of the present invention.

[0041] Figure 5 It is a schematic diagram of the arrangement of reflectivity test patterns according to an embodiment of the present invention.

[0042] Figure 6 It is a schematic diagram of the reflectivity test pattern period of an embodiment of the present invention.

[0043] Figure 7 It is a schematic diagram of two-dimensional graphics of different shapes of the mask according to an embodiment of the present invention.

[0044] Figure 7a-7c It is a schematic diagram of dense graphics of different two-dimensional arrangements of masks according to an embodiment of the present invention.

[0045] Figure 8 It is a schematic diagram of a photoresist pattern of a columnar two-dimensional grating structure according to an embodiment of the present invention.

[0046] Fig. 9 It is a schematic diagram of a photoresist pattern of a hole-shaped two-dimensional grating structure according to an embodiment of the present invention.

[0047] Fig.10 It is a schematic diagram of a one-dimensional dense pattern of a mask according to an embodiment of the present invention.

[0048] Fig.11 It is a schematic diagram of a one-dimensional grating structure photoresist pattern after development according to an embodiment of the present invention.

[0049] Fig.12 Schematic diagram of the reflectivity exposure field zoom plane layout of an embodiment of the present invention.

[0050] Fig.13 It is a schematic diagram of a photoresist pattern of a two-dimensional grating structure after development according to an embodiment of the present invention.

[0051] Fig.14It is a schematic diagram of another photoresist pattern of a two-dimensional grating structure after development according to an embodiment of the present invention.

[0052] Fig.15 It is a reflectivity test flow chart of an embodiment of the present invention.

[0053] Fig.16 Schematic diagram of a single-point reflectivity test point and a positioning mark according to an embodiment of the present invention.

[0054] Fig.17 It is a schematic diagram of the position of the off-axis alignment unit in the lithography machine according to an embodiment of the present invention.

[0055] Fig.18 It is a schematic diagram of the off-axis alignment unit structure and reflectivity test principle of an embodiment of the present invention.

[0056] Fig.19 It is a schematic diagram of quadratic curve fitting of reflectivity under multiple focal planes at a single test point in the exposure field of an embodiment of the present invention.

[0057] Fig. 20 It is a plane schematic diagram of optimal focal length fitting of multiple test points in an exposure field according to an embodiment of the present invention.

[0058] Fig.21 It is a one-dimensional dense line schematic diagram of a mask pattern of a reflectivity experiment case according to an embodiment of the present invention.

[0059] Fig. 22 It is a schematic diagram of a PSS graphic of a reflectivity experimental case mask graphic according to an embodiment of the present invention.

[0060] Fig.23 Schematic diagram of line width quadratic curve fitting according to an embodiment of the present invention.

[0061] Fig.24 Schematic diagram of quadratic curve fitting of reflectivity in an embodiment of the present invention.

[0062] Fig.25 It is a three-dimensional topography diagram for determining the best focal plane according to an embodiment of the present invention.

[0063] Fig.26 It is a schematic diagram of a one-dimensional dense pattern of a mask according to another embodiment of the present invention.

[0064] Fig. 27 It is a schematic diagram of a one-dimensional grating structure photoresist pattern after development according to another embodiment of the present invention.

[0065] Fig.28 It is a schematic diagram of the off-axis alignment unit structure and reflectivity test principle according to another embodiment of the present invention.

[0066] In the attached figure:

[0067] 10-test point; 10a-graphic area; 10b-gap area; 11-test spot; 12-exposure field; 13-alignment mark;

[0068] 20-substrate; 21-one-dimensional grating structure photoresist pattern; 21a-four-way composite one-dimensional grating structure photoresist pattern; 22-two-dimensional grating structure photoresist pattern;

[0069] 31-mask plate; 31a-mask pattern; 32-optical axis; 33-objective lens;

[0070] 40-reflectivity test unit; 41-off-axis light beam; 42-light source module; 43-first reflecting prism; 44-beam splitting prism; 45-second reflecting prism; 46-detector;

[0071] 50- workpiece table; 51- workpiece table base plate. DETAILED DESCRIPTION

[0072] In order to make the purpose, advantages and features of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and are not drawn to scale, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In addition, the structure shown in the drawings is often a part of the actual structure. In particular, the emphasis of each drawing is different, and sometimes different scales are used.

[0073] As used in the present invention, the singular forms "one", "an" and "the" include plural objects, the term "or" is usually used to include the meaning of "and / or", the term "several" is usually used to include the meaning of "at least one", and the term "at least two" is usually used to include the meaning of "two or more". In addition, the terms "first", "second" and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined as "first", "second" and "third" can explicitly or implicitly include one or at least two of the features. In addition, as used in the present invention, an element is arranged on another element, which usually only indicates that there is a connection, coupling, matching or transmission relationship between the two elements, and the connection, coupling, matching or transmission between the two elements can be direct or indirect through an intermediate element, and cannot be understood as indicating or implying the spatial position relationship between the two elements, that is, an element can be in any orientation such as inside, outside, above, below or on one side of another element, unless the content clearly indicates otherwise. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0074] Figure 1FIG. 1 is a flow chart of a method for testing a focal plane according to an embodiment of the present invention. Figure 1 As shown, this embodiment provides a focal plane testing method, including:

[0075] Step S10, providing a substrate, wherein a photoresist pattern is formed on the substrate;

[0076] Step S20, performing a reflectivity test on the photoresist pattern on the substrate to obtain the reflectivity of different focal planes of each test point in the exposure field;

[0077] Step S30, performing a quadratic fit on the reflectivity of different focal planes at each test point in the exposure field to obtain an optimal focal length, and obtaining the optimal focal lengths of all test points in the exposure field;

[0078] Step S40, performing least squares plane fitting on the optimal focal length of each test point in the exposure field to obtain the optimal focal plane height and the optimal focal plane tilt.

[0079] Figure 2 1 is a flow chart of a method for forming a photoresist pattern on a substrate according to an embodiment of the present invention. In step S10, the step of forming a photoresist pattern on the substrate 20 includes:

[0080] Step S11, coating a photoresist layer on the substrate 20, the photoresist layer is, for example, a positive photoresist, and the thickness of the photoresist layer is, for example, 0.35 microns to 10 microns. The substrate type, substrate size, photoresist type, photoresist film thickness, baking, etc. are determined according to the requirements of the photoresist manufacturer and the user's product requirements, and this embodiment does not limit this. Test the best focal plane of the user's product working condition, using the working conditions of the specific product. In other words, the thickness of the photoresist is determined according to the actual situation of the product.

[0081] Step S12, performing an exposure process to transfer the mask pattern 31a to the photoresist layer to form a photoresist pattern. The optimal dose, zoom plane exposure and focal plane spacing of the exposure process are determined according to the target lithography machine. The test points in the exposure field are arranged in an array.

[0082] Figure 3 : is a distribution diagram of test points in the reflectivity exposure field of an embodiment of the present invention. Figure 3 As shown, according to the required test point density and reflectivity test efficiency when fitting the optimal focal plane height and the optimal focal plane tilt, the test point distribution in the exposure field 12 is to set i columns and j rows of test points 10 in the exposure field 12, with a column spacing of Cs and a row spacing of Rs.

[0083] Figure 4 The reflectivity test spot and reflectivity test point graphic area requirements of the embodiment of the present invention. Figure 4As shown, the size of the graphic area of ​​the single test point 10 is a predetermined multiple (eg, 10 times) of the size of the reflectivity test light spot 11. The circular diameter within the graphic area of ​​the single test point 10 is, for example, 0.35 microns to 10 microns.

[0084] Figure 5 Schematic diagram of the arrangement of reflectivity test patterns according to an embodiment of the present invention. Figure 5 As shown, the graphic design of a single test point is circular, and is arranged into a uniformly distributed dense graphic area according to a regular hexagon. For example, a circular graphic area 10a is the center, and six adjacent graphic areas 10a around the graphic area 10a constitute a regular hexagon. The circle is arranged in a regular hexagon and includes directions A1, A2 and A3. The directions A1, A2 and A3 are emitted from the center of the regular hexagon and pass through the direction where one of the vertices of the regular hexagon is located; and the three directions are not collinear. The angle between the A1 direction and the A2 direction is 60 degrees, the angle between the A3 direction and the A2 direction is 60 degrees, and the gap widths in the three array directions are equal. The graphic area 10a can be a light-transmitting or light-impermeable area, and the light transmittance of the gap area 10b is opposite to that of the graphic area 10a.

[0085] Figure 6 1 is a schematic diagram of a reflectivity test pattern cycle according to an embodiment of the present invention. Figure 6 As shown, in a single test point 10 pattern, the pattern area 10a and the gap area 10b are arranged repeatedly along one direction as a period. The period of the single test point 10 pattern is, for example, 1:1 to 1:2 or 2:1.

[0086] Figure 7 It is a schematic diagram of two-dimensional graphics of different shapes of the mask according to an embodiment of the present invention. Figure 7a-7c Schematic diagram of dense graphics of different two-dimensional arrangements of masks according to an embodiment of the present invention. Figure 7 As shown, the mask pattern 31a may be a circle, or may be a regular octagon, a regular hexagon or a square. Figure 7a-7c As shown, the mask pattern 31a may be arranged in a regular hexagonal shape, an orthogonal shape, or a non-orthogonal shape.

[0087] Figure 8 It is a schematic diagram of a photoresist pattern of a columnar two-dimensional grating structure according to an embodiment of the present invention. Fig. 9 FIG. 1 is a schematic diagram of a photoresist pattern of a hole-shaped two-dimensional grating structure according to an embodiment of the present invention. Figure 8 and Fig. 9 As shown, after exposure and development, a two-dimensional grating structure photoresist pattern 22 consisting of "pillars" or "holes" of different shapes is formed on the photoresist.

[0088] Fig.10It is a schematic diagram of a one-dimensional dense pattern of a mask according to an embodiment of the present invention. Fig.11 3 is a schematic diagram of a one-dimensional grating structure photoresist pattern after development according to an embodiment of the present invention. In another embodiment, the mask pattern 31a is a one-dimensional dense line pattern, the line width of the dense line is, for example, 0.35 microns to 10 microns, the period of the dense line is the ratio of the line width to the space, and the period of the dense line is, for example, 1:1 to 1:2 or 2:1. Fig.10 The one-dimensional dense lines are arranged in different directions, and a one-dimensional grating structure is formed on the photoresist after exposure and development. The side wall angle of the column 21 in the photoresist pattern is 90 degrees or the side wall angle of the column is less than 90 degrees, such as Fig.11 shown.

[0089] Fig.12 FIG. 1 is a schematic diagram of the layout of the reflectivity exposure field zoom plane of an embodiment of the present invention. Fig.12 As shown, the exposure field is arranged to sequentially set n exposure fields 12 on the substrate 20, wherein n is an integer, and the value of n is, for example, 7 to 9, that is, generally 7 to 9 exposure fields 12 can be set on the substrate 20. Taking the nominal best focal plane 0 μm as the reference, the focal plane offset is set for each exposure field 12 according to the fixed focal plane step x, and the focal plane inclination Rx and Ry are 0 by default. The nominal best focal plane refers to the focal plane position calibrated by the process exposure test when the workpiece stage is moved in the photolithography process, which is set as the nominal best focal plane position. The focal plane and step length are set according to the required test point density and reflectivity test efficiency when fitting the best focal plane height and the best focal plane inclination. The focal plane step length x can be a predetermined ratio of the focal depth of the target pattern of the photolithography machine, for example, between one seventh and one ninth, that is, the quadratic curve fitting of the single-point best focal plane in the exposure field 12 usually uses 7 to 9 points.

[0090] Step S13, performing a development process to form a photoresist pattern. Fig.13 It is a schematic diagram of a photoresist pattern of a two-dimensional grating structure after development according to an embodiment of the present invention. Fig.14 2 is another schematic diagram of a two-dimensional grating structure photoresist pattern after development according to an embodiment of the present invention. A developing machine is used to perform a developing process to develop the photoresist pattern on the substrate 20. The developing conditions are set according to the requirements of the photoresist manufacturer and the product requirements of the user. Affected by the performance of the photolithography machine, the performance of the photoresist, and the focal plane offset, the photoresist pattern after development forms a two-dimensional grating structure photoresist pattern 22 arranged in a regular hexagon by cylinders or cones, such as Fig.13 and Fig.14 shown.

[0091] Fig.15: is a reflectivity test flow chart of an embodiment of the present invention. In step S20, a reflectivity test unit 40 is used to perform a reflectivity test on the substrate 20 to obtain the reflectivity of different focal planes of each test point 10 in the exposure field 12. In this embodiment, an off-axis alignment unit is preferably used to perform a reflectivity test on the substrate 20. The off-axis alignment unit in the existing lithography machine tests the mark contour position, grating light intensity and grating diffraction signal of the photoresist for silicon wafer alignment. The off-axis alignment unit in this embodiment adds a function of testing the reflectivity of the micro-nano size grating structure pattern of the photoresist for image plane detection. The off-axis alignment unit is used in this embodiment, so that the test equipment is simple, the user's test equipment procurement cost is reduced, the test efficiency is high, and the adaptability to complex working conditions is better.

[0092] Specifically, step S20 includes:

[0093] Step S21, substrate alignment: at least one pair of alignment marks 13 is selected to perform global alignment of the substrate 20, or more than three alignment marks 13 in the exposure field 12 are aligned field by field, to establish a coordinate relationship between the substrate 20 and the lithography machine.

[0094] Step S22: positioning a single test point. Fig.16 Schematic diagram of a single-point reflectivity test point and positioning mark in an embodiment of the present invention. Fig.16 As shown, according to the nominal coordinates of the test points recorded by the measurement program, the workpiece stage 50 moves, and the test points are moved to the off-axis light beam 41 of the reflectivity test unit 40 in turn, and the large-size alignment mark 13 at the fixed offset of the test point 10 is captured by the detector 46. By locating the alignment mark 13, the center of the photoresist graphic area which is much smaller than the resolution of the alignment system is accurately located to ensure the horizontal coordinate accuracy of the test point in the exposure field 12.

[0095] Step S23, single test point reflectivity test: According to the measurement program, the reflectivity of the test point in the exposure field under different conditions is tested.

[0096] Fig.17 It is a schematic diagram of the position of the reflectivity testing unit in the lithography machine according to an embodiment of the present invention. Fig.18 Schematic diagram of the reflectivity test unit structure and reflectivity test principle of an embodiment of the present invention. In step S23, a single test point reflectivity test is performed using the reflectivity test unit. The reflectivity test unit 40 is preferably an off-axis alignment unit with an integrated reflection function, and the reflectivity test unit 40 is installed on one side of the objective lens 33 of the lithography machine and is located above the work stage 50. A work stage reference plate 51 can be provided on the work stage 50 for locating the position of the substrate 20.

[0097] Further, the reflectivity testing unit 40 includes a light source module 42, a first reflecting prism 43, a beam splitting prism 44, a second reflecting prism 45 and a detector 46. The light source module 42 includes an alignment light source for emitting an off-axis light beam 41. The first reflecting prism 43 and the second reflecting prism 45 are used to change the path of the light. The beam splitting prism 44 is used to reflect and lens the off-axis light beam 41. The detector 46 is, for example, a CCD detector, which is used to detect the reflectivity of the photoresist pattern carried by the off-axis light beam 41.

[0098] Among them, the reflectivity test principle is: the light source module 42 emits parallel incident light of the required band, which is reflected by the first reflectivity prism 43, the beam splitting prism 44, and the second reflective prism 45, and then hits the micro-nano size grating structure pattern on the surface of the substrate 10, and diffuse reflection occurs; the diffusely reflected light of different directions carrying the grating structure information is received by the detector 46 after being reflected by the second reflective prism 45 and transmitted by the beam splitting prism 44, and the reflectivity of different bands of the single test point 10 is obtained after conversion. As a specific embodiment, the wavelength of the alignment light source is the ultraviolet-visible light-near infrared band, and the wavelength of the alignment light source is, for example, 190nm to 1000nm. Due to the large differences in grating structures and photoresists, it is generally preferred to select a band interval with a relatively high reflectivity peak but a relatively small difference, and each user's working condition is also differentiated. The standard is determined by the actual situation and is not limited here. After testing the reflectivity data, the reflectivity data is processed. The reflectivity data processing includes extracting the reflectivity data of the corresponding band interval that meets the tolerance range according to the user's working condition standard.

[0099] In step S30, a quadratic fit is performed on the reflectivity of different focal planes at each test point in the exposure field to obtain an optimal focal length, and the optimal focal lengths of all test points in the exposure field are calculated.

[0100] Fig.19 It is a schematic diagram of quadratic curve fitting of reflectivity under multiple focal planes at a single test point in the exposure field of an embodiment of the present invention. Fig.19 The horizontal axis is the focal length, the vertical axis is the reflectivity, and the curve is a quadratic curve fitted by the reflectivity. Specifically, the method for calculating the optimal focal length of a single point in the exposure field includes: taking the nominal focal plane of the exposure field as the x-axis and the reflectivity as the y-axis, performing a quadratic fit on the reflectivity of n focal planes at each test point in the exposure field, and obtaining a quadratic curve y=ax 2 +bx+c, where the reflectivity peak or valley of the quadratic curve is -b / 2a, which is the corresponding optimal focal length. Fig.19 Similarly, calculate the optimal focal length Z of all test points in the exposure field ij .

[0101] In step S40, the optimal focal length of each test point in the exposure field is subjected to least squares plane fitting to obtain an optimal focal plane height and an optimal focal plane tilt.

[0102] Fig. 20 It is a plane schematic diagram of optimal focal length fitting of multiple test points in an exposure field according to an embodiment of the present invention. Fig. 20 In the figure, the horizontal axis is the optimal focal length at different test points, the vertical axis is the focal plane height, and the curve is the plane of the least squares plane fitting. The method for calculating the optimal focal plane height and the optimal focal plane tilt includes: performing the least squares plane fitting on the optimal focal length of each test point in the exposure field to obtain the plane equation:

[0103] z(x,y)=Ax+By+C (1)

[0104] According to the plane equation, we know that the optimal focal plane height Z = C, the optimal focal plane inclination Optimal focal tilt

[0105] Wherein, z(x,y) is the plane of focal height fitting of each test point, x is the x-axis coordinate of the test point, y is the y-axis coordinate of the test point, A, B, and C are all fitting coefficients; Z is the optimal focal plane height, Rx is the inclination of the optimal focal plane around the X-axis, and Ry is the inclination of the optimal focal plane around the Y-axis.

[0106] After the steps of calculating the optimal focal plane height and the optimal focal plane tilt, the optimal focal plane height and the optimal focal plane tilt of the lithography machine are compensated. Specifically, the new optimal focal plane height Z and the optimal focal plane tilt Rx and Ry are updated to the relevant machine constants of the lithography machine to complete the focal plane maintenance of the lithography machine or the focal plane determination of the user product working condition. If the user product working condition optimal focal plane is tested, the focal plane tilt generally remains unchanged, and the optimal focal plane height Z is updated to the relevant exposure program.

[0107] Fig.21 It is a one-dimensional dense line schematic diagram of a mask pattern of a reflectivity experiment case according to an embodiment of the present invention. Fig. 22 It is a schematic diagram of a PSS graphic of a reflectivity experimental case mask graphic according to an embodiment of the present invention. Fig.23 Schematic diagram of line width quadratic curve fitting according to an embodiment of the present invention. Fig.24 Schematic diagram of quadratic curve fitting of reflectivity in an embodiment of the present invention. Fig.25It is a three-dimensional morphology diagram for determining the best focal plane of an embodiment of the present invention. In the PSS (patterned sapphire substrate) industry, the same photolithography machine is used to expose one-dimensional dense lines and PSS patterns at the best focal plane. The mask pattern 31a is a one-dimensional dense line, and the photoresist pattern formed is a one-dimensional grating structure photoresist pattern 21. The line width of the dense line is, for example, 0.7μm, and the gap of the dense line is, for example, 0.7μm. The film thickness of the photoresist is, for example, 1.1μm, and the model of the photoresist is, for example, the AZ703 model. The mask pattern 31a is a PSS pattern, and the photoresist pattern formed is a two-dimensional grating structure photoresist pattern 22. The PSS pattern is a cylinder, the diameter of the cylinder is, for example, 2.3μm, the gap is, for example, 0.7μm, the PSS pattern is a dense cylinder arranged in a regular hexagon, the model of the photoresist is, for example, the AZ601 model, and the thickness of the photoresist is 2.5μm. The exposure focal plane step size is 0.5 microns. The line width is tested using a critical dimension scanning electron microscope, and the reflectivity is tested using a white light interferometer film thickness meter. The reflectivity test band selected the 515nm-535nm range with a higher peak value, and 8 pieces were tested repeatedly to take the average value. The best focal plane calculated by fitting the line width and reflectivity is compared with the most rigorous graphic sidewall morphology to confirm the best focal plane. According to the current PSS industry focal plane setting accuracy of 0.1μm, the critical dimension fitting and reflectivity fitting differ by 0.002μm, which is very close and fully meets the best focal length for three-dimensional morphology judgment. As shown in Table 1, and Figure 23 to Figure 25 shown.

[0108] Table 1 Comparison of best focal plane calculations for reflectivity experimental cases

[0109]

[0110] Fig.23 The horizontal axis is the focal length, the vertical axis is the line width, and the curve is a quadratic curve fitted by the line width. Fig.24 The horizontal axis is the focal length, the vertical axis is the reflectivity, and the curve is a quadratic curve fitted by the reflectivity. Fig.25 As can be seen from Table 1, the results of the best focal length determined by reflectivity are as accurate as those determined by line width and three-dimensional morphology. In other words, the experimental case in this embodiment confirms that the best focal length calculated by the reflectivity of a single test point is as accurate as the line width test and microscopic morphology judgment. Similarly, it is technically feasible to increase the test points in the exposure field, replace the lithography machine to automatically test the reflectivity, calculate the best focal length of each point in the exposure field, and then calculate the best focal plane height Z and the best focal plane inclination Rx and Ry according to the least squares method to fit the plane equation.

[0111] Fig.26 It is a schematic diagram of a one-dimensional dense pattern of a mask according to another embodiment of the present invention. Fig. 27Schematic diagram of a one-dimensional grating structure photoresist pattern after development according to another embodiment of the present invention. In another embodiment, the mask pattern 31a is a one-dimensional dense line pattern, the line width of the dense line is, for example, 0.35 microns to 10 microns, the period of the dense line is the ratio of the line width to the gap, and the period of the dense line is, for example, 1:1 to 1:2 or 2:1. The one-dimensional dense line pattern in the mask pattern 31a is arranged in four angular directions, and a four-way composite one-dimensional grating structure photoresist pattern 21a is formed on the photoresist after exposure and development. The four angular directions are respectively 0 degree direction, 90 degree direction, 45 degree direction, and 135 degree direction.

[0112] Fig.28 It is a schematic diagram of the reflectivity test unit structure and reflectivity test principle of another embodiment of the present invention. The reflectivity test unit 40 includes a light source module 42, a first reflecting prism 43, a beam splitting prism 44, a second reflecting prism 45 and a detector 46. The light source module 42 includes an aiming light source for emitting an off-axis light beam 41. The first reflecting prism 43 and the second reflecting prism 45 are used to change the path of the light. The beam splitting prism 44 is used to reflect and lens the off-axis light beam 41. The detector is, for example, a CCD detector, which is used to detect the reflectivity of the photoresist pattern carried by the off-axis light beam 41. The detector 46 includes four detection areas, namely, area 1, area 2, area 3 and area 4. The four detection areas of the detector 46 respectively detect the reflectivity of the photoresist pattern 21a corresponding to the four-way composite one-dimensional grating structure, as shown in FIG. Fig.28 As shown. The light source module 42 emits parallel incident light of the required wavelength band, which is reflected by the first reflectivity prism 43, the beam splitting prism 44, and the second reflection prism 45, and then hits the micro-nano-size grating structure photoresist pattern on the surface of the substrate 20, and undergoes diffuse reflection. Four groups of diffusely reflected light in different directions carrying information of the grating structure in four directions are respectively received by the four detection areas of the detector 46 after being reflected by the second reflection prism 45 and transmitted by the beam splitting prism 44, and the reflectivity of the four directional gratings and different wavelength bands of a single test point is obtained after conversion.

[0113] In step S30, quadratic fitting is performed on the reflectivity of different focal planes at each test point in the exposure field to obtain the optimal focal length, and the optimal focal length of all test points in the exposure field is calculated. Specifically, the method for calculating the optimal focal length of a single point in the exposure field includes: taking the nominal focal plane of the exposure field as the x-axis and the reflectivity as the y-axis, quadratic fitting is performed on the reflectivity of the four-directional composite one-dimensional grating structure photoresist pattern 21a and n focal planes at each test point in the exposure field, and obtaining quadratic curves y=ax in four directions respectively. 2 +bx+c, the peak or valley value of the quadratic curve reflectivity is -b / 2a, which is the corresponding optimal focal length. Similarly, the optimal focal lengths of the four-way composite one-dimensional grating structure photoresist pattern 21a of all test points in the exposure field are calculated and recorded as Z0 ij 、Z90 ij、Z45 ij and Z135 ij .

[0114] In step S40, the optimal focal length of each test point in the exposure field is fitted by the least square method to obtain the optimal focal plane height and the optimal focal plane tilt. The optimal focal plane height and the optimal focal plane tilt calculation method includes: first taking the average of the reflection of the four-way composite one-dimensional grating structure photoresist pattern 21a at each point, and then calculating the optimal focal plane height and the optimal focal plane tilt. The optimal focal length of each test point in the exposure field is fitted by the least square method to obtain a plane z(x,y)=Ax+By+C. According to the plane equation, the optimal focal plane height Z=C and the optimal focal plane tilt Optimal focal tilt Wherein, z(x,y) is the plane of focal height fitting of each test point, x is the x-axis coordinate of the test point, y is the y-axis coordinate of the test point, A, B, and C are all fitting coefficients; Z is the optimal focal plane height, Rx is the inclination of the optimal focal plane around the X-axis, and Ry is the inclination of the optimal focal plane around the Y-axis.

[0115] In this embodiment, it can also be used to test aberrations, where the aberrations include field curvature and astigmatism, wherein the astigmatism includes 0-degree astigmatism and 45-degree astigmatism.

[0116] The field curvature calculation in this embodiment specifically includes: the best focal length of the four-way composite one-dimensional grating structure photoresist pattern 21a at each test point in the exposure field is deducted from the corresponding best focal plane tilt to form the best focal length after deducting the best focal plane tilt, which is recorded as Z0′ ij 、Z90' ij 、Z45' ij and Z135' ij , and then take the average value Z ij-reTiltMean , forming the optimal focal length distribution after each test point in the exposure field is tilted to the optimal focal plane, and taking the maximum absolute value as the field curvature of the exposure field.

[0117] The astigmatism calculation in this embodiment specifically includes: the calculation method of 0 degree astigmatism includes: the astigmatism AST formed by the optimal focal plane difference between the one-dimensional grating structure in the 90 degree direction and the one-dimensional grating structure in the 0 degree direction at each test point in the exposure field ij The calculation method of 45 degree astigmatism includes: the astigmatism AST45 formed by the best focal plane difference between the one-dimensional grating structure in the 135 degree direction and the one-dimensional grating structure in the 45 degree direction at each test point in the exposure field ij The maximum absolute value of each distribution is taken as the astigmatism value.

[0118] This embodiment also provides a focal plane testing system, including:

[0119] An exposure unit, used for transferring the mask pattern 31 onto the substrate 20 to form a photoresist pattern;

[0120] A reflectivity testing unit, used to perform a reflectivity test on the photoresist pattern on the substrate 20 to obtain the reflectivity of different focal planes of each test point 10 in the exposure field 12;

[0121] The calculation unit is used to calculate the reflectivity of different focal planes at each test point in the exposure field by quadratic fitting to obtain the optimal focal length, and calculate the optimal focal length of all test points in the exposure field; and perform least squares plane fitting on the optimal focal length of each test point in the exposure field to obtain the optimal focal plane height and the optimal focal plane tilt.

[0122] The exposure unit includes an illumination unit, a homogenizing unit, a mask 31 and an objective lens 33. The illumination unit is used to emit a light beam. The homogenizing unit collimates and homogenizes the light beam. The light beam passes through the mask 31 along the optical axis 32 and enters the objective lens 33 to irradiate the photoresist layer of the substrate 20, transferring the mask pattern 31a on the mask 31 to the photoresist layer to form a photoresist pattern.

[0123] The reflectivity testing unit 40 is preferably an off-axis alignment unit, which includes a light source module 42, a first reflecting prism 43, a beam splitting prism 44, a second reflecting prism 45 and a detector 46. The light source module 42 is used to emit an off-axis light beam 41, that is, the off-axis light beam 41 is not coaxial with the optical axis 32. The first reflecting prism 43 and the second reflecting prism 45 are used to change the path of the off-axis light beam 41. The beam splitting prism 44 is used to reflect or transmit the off-axis light beam 41. The detector 46 is used to detect diffusely reflected light in different directions carrying the photoresist graphic information.

[0124] In another embodiment, the detector 46 in the reflectivity testing unit includes four detection areas to detect the reflectivity of the four-way composite one-dimensional grating structure photoresist pattern 21a.

[0125] The mask pattern 31a includes a one-dimensional pattern and a two-dimensional pattern. The two-dimensional pattern is one of a circle, a regular octagon, a regular hexagon or a square, and the arrangement of the two-dimensional pattern is a regular hexagon, an orthogonal arrangement or a non-orthogonal arrangement. After an exposure process, the mask pattern 31a is transferred to the photoresist layer, and a one-dimensional grating structure photoresist pattern 21 and a two-dimensional grating structure photoresist pattern 22 are formed on the photoresist layer.

[0126] Furthermore, the one-dimensional pattern is a four-directional composite one-dimensional pattern arranged in four angular directions, so as to be transferred onto the photoresist pattern to form a four-directional composite one-dimensional grating structure photoresist pattern 21a.

[0127] This embodiment also provides a lithography machine, comprising the focal plane testing system described in any one of the above items.

[0128] From the above, it can be seen that in the focal plane test method, test system and lithography machine provided by the embodiment of the present invention, the reflectivity test is performed on the photoresist pattern on the substrate, and the optimal focal length of all test points in the exposure field is calculated. The optimal focal plane height and the optimal focal plane tilt are obtained by performing the least squares plane fitting according to the optimal focal length of each test point in the exposure field. The lithography machine integrates a reflectivity test unit, that is, the lithography machine integrates an off-axis alignment unit, that is, the structural elements of the lithography machine itself can be used to measure the reflectivity, without adding elements or using other measuring equipment, which significantly reduces the cost of customers introducing higher node technology and the cost of purchasing high-precision critical dimension scanning electron microscopes, overlay measurement equipment, and special reflectivity test equipment. Compared with microscopic measurement of size and manual judgment by microscope, the reflectivity test efficiency is higher. The present invention solves the problem that the macroscopic test method using product grading can only test the entire piece, cannot distinguish a certain point in the exposure field, and cannot calculate the focal plane tilt in the exposure field.

[0129] Furthermore, the photoresist pattern includes a one-dimensional grating structure photoresist pattern and a two-dimensional grating structure photoresist pattern. The photoresist pattern is a micro-nano grating structure. The reflectivity of the photoresist micro-nano grating structure pattern mainly utilizes the characteristic that the diffuse reflection of the micro-nano grating pattern on the substrate surface carries the grating structure information. Therefore, the characteristics that the pattern size and side wall angle will change regularly when the focal plane of the lithography machine deviates and the changes in the shape, size, height and side wall angle of the grating pattern on the substrate surface will lead to regular changes in reflectivity can be utilized. The reflectivity is used to detect the best focal plane in the image plane of the lithography machine, which has better adaptability to complex working conditions other than lithography machines with non-advanced technology nodes and relatively high test accuracy.

[0130] Furthermore, the present invention designs a variety of photoresist patterns with grating structures that are close to the graphic structures of user products for image plane detection, including single one-dimensional grating patterns in different directions for focal plane testing, single two-dimensional grating patterns arranged in different ways, and composite grating photoresist patterns for primary aberration testing. The primary aberration includes field curvature and astigmatism, and the astigmatism includes 0-degree astigmatism and 45-degree astigmatism, which is more in line with the working conditions of user products and reduces the time cost from the optimal focal plane of the lithography machine to the optimal focal plane of the product working conditions.

[0131] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other. In addition, the different parts between the various embodiments can also be used in combination with each other, and the present invention is not limited to this.

[0132] In addition, it should be recognized that although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belongs to the scope of protection of the technical solution of the present invention.

Claims

1. A method for testing a focal plane, characterized in that: include: Providing a substrate, on which a photoresist pattern is formed; Performing a reflectivity test on the photoresist pattern on the substrate to obtain the reflectivity of different focal planes of each test point in the exposure field; Perform quadratic fitting on the reflectivity of different focal planes at each test point in the exposure field to obtain the best focal length, and obtain the best focal length of all test points in the exposure field; The optimal focal length of each test point in the exposure field is fitted by the least squares plane to obtain the optimal focal plane height and the optimal focal plane tilt.

2. The focal plane testing method according to claim 1, characterized in that: Before the reflectivity test of the substrate is performed, the method includes: The test point is moved under the light beam for testing the reflectivity, an alignment mark at a fixed offset of the test point is captured, and the center of the photoresist layer pattern is located by locating the alignment mark.

3. The focal plane testing method according to claim 1, characterized in that: The reflectivity test unit is used to test the reflectivity of the substrate, and the test steps include: The light source module emits parallel incident light, which is reflected by the first reflecting prism, the beam splitting prism, and the second reflecting prism, and then is incident on the photoresist pattern on the substrate surface and diffusely reflected. The diffusely reflected light in different directions carrying the photoresist pattern information is reflected by the second reflecting prism and transmitted by the beam splitting prism, and then received by the detector, and the reflectivity of different focal planes of each test point in the exposure field is obtained through conversion.

4. The focal plane testing method according to claim 1, characterized in that: A quadratic fit is performed on the reflectivity of different focal planes at each test point in the exposure field to obtain a quadratic curve, and the focal length corresponding to the peak value or valley value of the quadratic curve is the optimal focal length.

5. The focal plane testing method according to claim 1, characterized in that: The photoresist pattern includes a one-dimensional grating structure photoresist pattern and a two-dimensional grating structure photoresist pattern.

6. The focal plane testing method according to claim 5, characterized in that: The two-dimensional grating structure photoresist pattern is one of a circle, a regular octagon, a regular hexagon or a square, the arrangement of the two-dimensional grating structure photoresist pattern is a regular hexagon, an orthogonal arrangement or a non-orthogonal arrangement, and the two-dimensional grating structure photoresist pattern is a column or a hole.

7. The focal plane testing method according to claim 5, characterized in that: The one-dimensional grating structure photoresist pattern is a four-directional composite one-dimensional grating structure photoresist pattern arranged in four angular directions.

8. The focal plane testing method according to claim 7, characterized in that: The detector in the reflectivity testing unit includes four detection areas to detect the reflectivity of the four-way composite one-dimensional grating structure photoresist pattern, and calculates the aberration according to the reflectivity of the four-way composite one-dimensional grating structure photoresist pattern, wherein the aberration includes field curvature and astigmatism.

9. The focal plane testing method according to claim 8, characterized in that: The astigmatism includes 0 degree astigmatism and 45 degree astigmatism.

10. The focal plane testing method according to claim 3 or 8, characterized in that: The reflectivity testing unit is an off-axis alignment unit.

11. A focal plane testing system, characterized in that: include: An exposure unit, used for transferring the mask pattern onto the substrate to form a photoresist pattern; A reflectivity testing unit, used for testing the reflectivity of the photoresist pattern on the substrate to obtain the reflectivity of different focal planes of each test point in the exposure field; The calculation unit is used to perform quadratic fitting on the reflectivity of different focal planes at each test point in the exposure field to obtain the best focal length, and perform least squares plane fitting on the best focal length of each test point in the exposure field to obtain the best focal plane height and the best focal plane tilt.

12. The focal plane testing system according to claim 11, characterized in that: The reflectivity testing unit is an off-axis alignment unit, which includes a light source module, a first reflecting prism, a beam splitting prism reflection, a second reflecting prism and a detector. The light source module is used to emit light, the first reflecting prism and the second reflecting prism are used to change the path of the light, the beam splitting prism is used to reflect or transmit the light, and the detector is used to detect diffusely reflected light in different directions carrying the photoresist pattern information.

13. The focal plane testing system according to claim 11, characterized in that: The mask pattern includes a one-dimensional pattern and a two-dimensional pattern, which are transferred to the photoresist pattern to form a one-dimensional grating structure photoresist pattern and a two-dimensional grating structure photoresist pattern.

14. The focal plane testing system according to claim 13, characterized in that: The two-dimensional figure is one of a circle, a regular octagon, a regular hexagon or a square, and the arrangement of the two-dimensional figure is a regular hexagon, an orthogonal arrangement or a non-orthogonal arrangement.

15. The focal plane testing system according to claim 13, characterized in that: The one-dimensional pattern is a four-directional composite one-dimensional pattern arranged in four angular directions, so as to be transferred to the photoresist pattern to form a four-directional composite one-dimensional grating structure photoresist pattern.

16. The focal plane testing system according to claim 15, characterized in that: The detector in the off-axis alignment unit includes four detection areas to detect the reflectivity of the four-way composite one-dimensional grating structure photoresist pattern, and the reflectivity of the four-way composite one-dimensional grating structure photoresist pattern is used to calculate the aberration.

17. A photolithography machine, characterized in that: A focal plane testing system comprising the focal plane as claimed in any one of claims 11 to 16.

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