High spatial resolution and high precision detection method for lithography machine exposure accuracy

Abstract

The present invention provides a high spatial resolution and high precision detection method for the exposure accuracy of a lithography machine, which divides the exposure area of ​​the mask into several detection areas, and transfers the characteristic pattern to the wafer after the photolithography etching process to form several patterns on the entire wafer, and outputs an unbalanced voltage between another group of metal electrodes by inputting an electrical signal to a group of metal electrodes on the pattern, thereby drawing a Mapping diagram of the unbalanced voltage according to the coordinates of the entire wafer, and reflecting the consistency of the exposure accuracy of the lithography machine according to the distribution of the Mapping diagram. The entire exposure area of ​​the wafer is divided into a dot matrix distribution with patterns as units, which can effectively improve the spatial resolution of the uniformity of the exposure accuracy of the lithography machine, and the smaller the pattern size, the higher the spatial resolution; in addition, through the evaluation method of the electrical performance of the pattern, the measurement accuracy of the unbalanced voltage can reach less than 1‰, achieving the purpose of high-precision detection of exposure.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for detecting exposure accuracy of a photolithography machine with high spatial resolution and high precision. Background Art

[0002] Photolithography machines are widely used in the manufacturing process of micro-nano structures of micrometers and above. Exposure accuracy is an important parameter for measuring the performance of photolithography machines. Exposure accuracy refers to the error in the width of a line template of a certain width after exposure and development, reflecting the accuracy of the line. Because its absolute deviation will be affected by subsequent development and other processes, the more critical indicator is the uniformity of the line width error. In other words, the deviation of the exposed lines does not matter much, and the degree to which the deviation changes with position in the same line is the key to the accuracy of photolithography. Therefore, the level of exposure accuracy will directly affect the uniformity of the processing accuracy of semiconductor devices, and with the development of integrated circuits becoming more dense and miniaturized, the consistency of exposure accuracy in the photolithography process has a more prominent impact on process consistency during wafer preparation.

[0003] The current method for measuring the exposure accuracy and distribution of the optical system of a lithography machine is to expose a specific series of narrow lines, develop them, and then observe them under a microscope to obtain the exposure line width error and its distribution. However, this method can only roughly obtain the exposure line width accuracy and distribution. Because the line width of a lithography machine is in the micron or submicron order, its line width error is usually tens to several nanometers. It is difficult to accurately distinguish this difference under a microscope. Often, the resolvable exposure width error is only a dozen times the line resolution limit of the lithography machine, which cannot meet the needs of more accurate optical exposure accuracy and consistency detection. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a high spatial resolution and high precision detection method for the exposure accuracy of a lithography machine, so as to solve the problem of low spatial resolution and precision detection of the consistency of the exposure accuracy of a lithography machine in the prior art.

[0005] To achieve the above object, the present invention provides a high spatial resolution and high precision detection method for exposure accuracy of a lithography machine, the detection method comprising:

[0006] Providing a mask, wherein the exposure area of ​​the mask is divided into a plurality of detection areas;

[0007] Forming the same characteristic pattern in each of the detection areas, wherein the characteristic pattern is a Wheatstone bridge pattern;

[0008] Expose the wafer based on the mask; wherein the wafer includes a substrate layer and an epitaxial layer in sequence along a thickness direction;

[0009] Performing development and etching on the wafer to transfer the characteristic pattern on the mask to the epitaxial layer, thereby forming a plurality of patterns;

[0010] Two identical sets of metal electrodes facing each other are formed on the four end surfaces of all the patterns, wherein one set of the metal electrodes is a signal input end, and the other set of the metal electrodes is a signal output end;

[0011] measuring the unbalanced voltage of all the patterns on the wafer;

[0012] The measured unbalanced voltage of each of the patterns is plotted into a Mapping diagram according to the device coordinates, and the exposure accuracy and consistency of the lithography machine are reflected according to the distribution of the Mapping diagram.

[0013] Optionally, the plurality of detection areas divided by the exposure area of ​​the mask are of the same size, and each of the characteristic patterns is arranged at the same position of the detection area where it is located.

[0014] Optionally, the Wheatstone bridge pattern is a four-end pattern in the shape of a cross, a rectangle, a square, or a four-leaf clover; the two groups of metal electrodes cover the tail ends of the four ends of the Wheatstone bridge pattern.

[0015] Optionally, the material of the epitaxial layer of the wafer includes a material that can generate resistance.

[0016] Optionally, the Mapping diagram is a Mapping diagram that can reflect the regional distribution of unbalanced voltages.

[0017] Optionally, a wafer electrical performance tester is used to measure the unbalanced voltages of all the patterns.

[0018] Optionally, the substrate layer in the wafer structure is an insulating layer, and the epitaxial layer is an active layer.

[0019] Optionally, when etching the wafer after the exposure process, an over-etching process is used to achieve complete etching.

[0020] As described above, the high spatial resolution and high precision detection method for the exposure accuracy of the lithography machine of the present invention specifically divides the exposure area of ​​the mask into a number of detection areas with specific characteristic patterns (Wheatstone bridge patterns), and transfers the characteristic patterns to the wafer after a photolithography and etching process to form a number of Wheatstone bridge patterns on the entire wafer. By inputting an electrical signal to a set of relative metal electrodes on the pattern, an unbalanced voltage will be output between another set of relative metal electrodes, thereby drawing a Mapping diagram of the unbalanced voltage according to the coordinates of the entire wafer, and the uniformity of the exposure accuracy of the lithography machine can be reflected according to the distribution of the Mapping diagram. Since the pattern size distributed in various areas of the wafer is determined by the exposure accuracy of the photolithography machine in each area, when preparing the pattern, the optical path distortion and optical path asymmetry at a small scale will cause the characteristic pattern distortion on the mask, which is an axisymmetric pattern in both vertical directions, to be transferred to the characteristic pattern, destroying the symmetry of the pattern, thereby generating a voltage difference on the pattern, i.e., an unbalanced voltage. The unbalanced voltage reflects the tiny unevenness of the exposure lines. Currently, this tiny unevenness is a measure of optical path distortion and optical path asymmetry, and is caused by the phase unevenness of the optical path system. It is currently difficult to detect this tiny unevenness in the industry because the method is to measure the optical path distortion and optical path asymmetry in the optical path system. A preparation method for patterns spread all over a wafer, wherein each pattern is taken as an exposure point, is equivalent to dividing the entire exposure area of ​​the wafer into a dot matrix distribution based on patterns, thereby effectively improving the spatial resolution of the uniformity of exposure accuracy of a lithography machine, and the smaller the pattern size, the higher the spatial resolution. For example, for a dot matrix distribution display of no less than 100,000 patterns formed on a single exposure area of ​​a 4-inch exposure surface, a high-resolution dot matrix distribution map can be formed; in addition, the evaluation method of the electrical properties of the pattern is more accurate than other physical or optical methods of measuring the size of the graphic, and the measurement accuracy of the unbalanced voltage can reach less than 1‰, thereby achieving the purpose of high-precision detection of exposure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Shown is a schematic diagram of the structure of the mask in the high spatial resolution and high precision detection method for the consistency of exposure accuracy of the lithography machine of the present invention.

[0022] Figure 2 Shown is a schematic diagram of the structure of the detection area in the high spatial resolution and high precision detection method for the exposure accuracy of the lithography machine of the present invention.

[0023] Figures 3 to 7 Shown are several exemplary structural schematic diagrams of characteristic patterns in the detection area of ​​the high spatial resolution and high precision detection method for the exposure accuracy of the lithography machine of the present invention.

[0024] Figure 8It shows a structural schematic diagram of the relative positions of various structures when the stepper lithography machine is exposed in the high spatial resolution and high precision detection method of the lithography machine exposure accuracy of the present invention.

[0025] Fig. 9 Shown is a schematic diagram of the cross-sectional structure of a wafer in the high spatial resolution and high precision detection method of the exposure accuracy of a lithography machine of the present invention.

[0026] Fig.10 It is a schematic diagram showing uneven imaging during exposure of a photolithography machine in the method for detecting exposure accuracy of a photolithography machine with high spatial resolution and high precision of the present invention.

[0027] Fig.11 It shows a schematic top view of a pattern structure formed in the method for high spatial resolution and high precision detection of exposure accuracy of a lithography machine of the present invention, wherein the pattern is not distorted.

[0028] Fig.12 It shows a schematic top view of a pattern structure formed in the method for high spatial resolution and high precision detection of exposure accuracy of a lithography machine of the present invention, wherein the pattern is distorted.

[0029] Fig.13 It shows a schematic diagram of a top-view structure after a metal electrode is formed on a pattern in the high spatial resolution and high-precision detection method for exposure accuracy of a lithography machine of the present invention, wherein the pattern is not distorted.

[0030] Fig.14 It shows a schematic diagram of a top-view structure after a metal electrode is formed on a pattern in the high spatial resolution and high-precision detection method for exposure accuracy of a lithography machine of the present invention, wherein the pattern is distorted.

[0031] Fig.15 Shown is a schematic diagram of the cross-sectional structure after a metal electrode is formed on a pattern in the high spatial resolution and high precision detection method for the exposure accuracy of a lithography machine of the present invention.

[0032] Figures 16 to 19 Shown are schematic diagrams of top-view structures of several examples after a metal electrode is formed on a pattern in the high spatial resolution and high-precision detection method for exposure accuracy of a lithography machine of the present invention.

[0033] Fig. 20 Shown is a schematic diagram of the arrangement of patterns on a wafer in the high spatial resolution and high precision detection method for the exposure accuracy of a lithography machine of the present invention.

[0034] Fig.21 Shown is a color scale distribution diagram of unbalanced voltage formed by a single shot of a stepper lithography machine in a high spatial resolution and high precision detection method for exposure accuracy of a lithography machine in an experimental example of the present invention.

[0035] Fig. 22 It shows the unbalanced voltage mapping diagram formed on the wafer after the stepper lithography is performed in the high spatial resolution and high precision detection method of the exposure accuracy of the lithography machine in the experimental example of the present invention.

[0036] Fig.23 Shown is a schematic flow chart of the high spatial resolution and high precision detection method for the exposure accuracy of the lithography machine of the present invention.

[0037] Component number description

[0038] 10 mask, 100 exposure area of ​​the mask, 101 detection area, 102 feature pattern, 11 prism, 12 wafer, 121 substrate layer, 122 epitaxial layer, 123 photoresist layer, 124 metal electrode, 125 pattern, 13 clear imaging point, 14 larger blurred imaging point, 15 smaller blurred imaging point. DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0040] See also Figures 1 to 23 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0041] This embodiment provides a high spatial resolution and high precision detection method for the exposure precision of a lithography machine, which is used to improve the resolution of the uniformity of the exposure precision of the lithography machine, such as Fig.23 As shown, the detection method comprises the following steps:

[0042] S1. Providing a mask, and dividing the exposure area of ​​the mask into a plurality of detection areas;

[0043] S2, forming the same characteristic pattern in each of the detection areas, wherein the characteristic pattern is a Wheatstone bridge pattern;

[0044] S3, performing exposure processing on the wafer based on the mask; wherein the wafer includes a substrate layer and an epitaxial layer in sequence along a thickness direction;

[0045] S4, developing and etching the wafer to transfer the characteristic pattern on the mask to the epitaxial layer, thereby forming a plurality of patterns;

[0046] S5, forming two identical sets of metal electrodes facing each other on the four end surfaces of all the patterns, wherein one set of the metal electrodes is a signal input end, and the other set of the metal electrodes is a signal output end;

[0047] S6, measuring the unbalanced voltage of all the patterns on the wafer;

[0048] S7. Plotting the measured unbalanced voltage of each of the patterns into a Mapping diagram according to device coordinates, and reflecting the exposure accuracy and consistency of the lithography machine (Wheatstone bridge pattern) according to the distribution of the Mapping diagram.

[0049] The high spatial resolution and high precision detection method for the exposure accuracy of the lithography machine of the present embodiment specifically divides the exposure area of ​​the mask into a number of detection areas with specific characteristic patterns, and transfers the characteristic patterns to the wafer after a photolithography and etching process to form a number of Wheatstone bridge patterns on the entire wafer. By inputting an electrical signal to a set of relative metal electrodes on the pattern, an unbalanced voltage will be output between another set of relative metal electrodes. Thus, a Mapping diagram of the unbalanced voltage is drawn according to the coordinates of the entire wafer, and the uniformity of the exposure accuracy of the lithography machine can be reflected according to the distribution of the Mapping diagram. Since the pattern size distributed in various areas of the wafer is determined by the exposure accuracy of the photolithography machine in each area, when preparing the pattern, the optical path distortion and optical path asymmetry at a small scale will cause the characteristic pattern on the mask, which is an axisymmetric pattern in two vertical directions, to be distorted and transferred to the characteristic pattern, destroying the symmetry of the pattern, thereby generating a voltage difference on the pattern, i.e., an unbalanced voltage. The unbalanced voltage reflects the tiny unevenness of the exposure lines. Currently, this tiny unevenness is a measure of optical path distortion and optical path asymmetry, and is caused by the phase unevenness of the optical path system. It is currently difficult to detect this tiny unevenness in the industry because this method is to spread the pattern all over the wafer. The method for preparing a pattern, each pattern is used as an exposure point, which is equivalent to dividing the entire exposure area of ​​the wafer into a dot matrix distribution with patterns as units, thereby effectively improving the spatial resolution of the uniformity of the exposure accuracy of the lithography machine, and the smaller the pattern size, the higher the spatial resolution. For example, for a dot matrix distribution display of no less than 100,000 patterns formed on a single exposure area of ​​a 4-inch exposure surface, a high-resolution dot matrix distribution map can be formed, and the resolution can reach no more than 100μm; in addition, the evaluation method of the electrical properties of the pattern is more accurate than other physical or optical methods of measuring the size of the graphic, and the measurement accuracy of the unbalanced voltage can reach less than 1‰, thereby achieving the purpose of high-precision detection of exposure.

[0050] The high spatial resolution and high precision detection method for the exposure accuracy of the lithography machine of this embodiment will be described in detail below with reference to the specific drawings.

[0051] like Figure 1 As shown, step S1 is first performed to provide a mask 10 and divide the exposure area 100 of the mask into a plurality of detection areas 101 .

[0052] It should be noted here that, under the premise that the existing exposure technology can achieve, the more the detection area 101 is divided, the more patterns will be formed on the wafer subsequently, and the higher the resolution of the corresponding exposure accuracy consistency will be.

[0053] The shape of the mask 10 is not limited and can be selected according to actual needs. For example, it can be a square, a rectangle, a circle, a regular hexagon, a regular octagon, etc. In addition, the size of the mask 10 is not limited and can be selected according to actual needs. For example, different lithography methods such as contact lithography, proximity lithography or projection lithography can be used to select the corresponding size of the mask 10.

[0054] As a preferred example, the exposure area 100 of the mask is divided into a plurality of detection areas 101 of the same size, so that the pattern formed subsequently can be spread more evenly on the wafer.

[0055] like Figure 2 As shown, step S2 is then performed to form the same characteristic pattern 102 in each of the detection areas 101, wherein the characteristic pattern 102 is a Wheatstone bridge pattern.

[0056] like Figures 3 to 7 As shown, the characteristic pattern 102 is an axisymmetric pattern along the vertical X direction and Y direction, that is, it is a symmetrical pattern about the BB axis in the X direction and a symmetrical pattern about the AA axis in the Y direction.

[0057] As a preferred example, the characteristic pattern 102 of each detection area 101 is set at the same position of the detection area 101 where it is located. More preferably, the exposure area 100 of the mask is divided into a plurality of detection areas 101 of the same size, and the characteristic pattern 102 of each detection area 101 is set at the same position of the detection area 101 where it is located, so that the subsequently formed pattern can be evenly distributed in an array on the wafer (such as Fig. 20 as shown).

[0058] As an example, the characteristic pattern 102 may be set as a Hall device pattern, such as Figure 3 and Figure 4 A cross-shaped pattern, Figure 3 The corners are right angles, Figure 4The corners are rounded; Figure 5 It is a rectangular pattern; Figure 6 It is a square pattern; Figure 7 It is a four-leaf clover pattern, in which Figure 7 The corners can be right angles or rounded.

[0059] like Figure 8 and Fig. 9 As shown, step S3 is then performed to expose the wafer 12 based on the mask 10; wherein, Fig. 9 As shown, the wafer 12 includes a substrate layer 121 and an epitaxial layer 122 in sequence along the thickness direction. In addition, a photoresist layer 123 needs to be formed on the epitaxial layer 122 before exposure processing.

[0060] The photoresist layer 123 may be a positive photoresist or a negative photoresist. In this embodiment, positive photoresist is taken as an example for description.

[0061] It should be noted that the positional relationship between the mask 10 and the wafer 12 is set based on the adopted photolithography method. Figure 8 In the process, step-by-step lithography is used, so the exposure method is projection type, and a focusing lens, such as a prism 11, is arranged between the mask 10 and the wafer 12, that is, the mask 10 is placed above the wafer 12, and each exposure realizes one shot exposure on the wafer 12. For contact lithography, the mask 10 is placed on the surface of the wafer 12.

[0062] As an example, the substrate layer 121 in the wafer structure is an insulating layer, and the epitaxial layer 122 is an active layer.

[0063] As an example, the material of the epitaxial layer 122 of the wafer 12 can be any semiconductor material suitable for preparing semiconductor devices, such as III-V compound materials such as gallium arsenide or indium antimonide, silicon, germanium, aluminum oxide, graphene, etc. Preferably, when the characteristic pattern 102 in the detection area 101 of the mask 10 is set as a Hall device pattern, the material of the epitaxial layer 122 is preferably a material that can produce a Hall effect, such as III-V compound materials such as gallium arsenide or indium antimonide, silicon-based materials or graphene, etc. The material of the substrate layer 121 is selected to be a material suitable for being a substrate, which can be an insulating material or a semiconductor material, preferably a material with a small lattice match and thermal mismatch with the epitaxial layer 122, for example, when the material of the epitaxial layer 122 is gallium arsenide or indium antimonide, the material of the substrate layer 121 is selected to be silicon.

[0064] like Fig.10As shown, when the exposure accuracy during the photolithography process is uneven, for example, the exposure light path has a certain angle deviation in the Z direction (i.e., the direction perpendicular to the wafer surface), that is, there is a certain local distortion, which will cause the surface imaging of the wafer 12 to be locally "blurred", such as Fig.10 The relatively large blurred point 14 and the relatively small blurred point 15 relative to the clear imaging point 13, this "blurred" imaging will have different degrees of influence on the photoresist layer 123 on the surface of the wafer 12 during the exposure reaction process. For example, the clear imaging point 13 will make the photoresist react with normal size during the exposure process, the relatively large blurred point 14 may cause the photoresist to react with a relatively large size during the exposure process, and the relatively small blurred point 15 may cause the photoresist to react with a relatively small size during the exposure process, resulting in a difference in the graphic size of the pattern 125 when the feature pattern on the subsequent mask 10 is transferred to the epitaxial layer 122 to form the pattern 125, thereby causing the generation of unbalanced voltage.

[0065] Then, step S4 is performed to develop and etch the wafer 12 to transfer the characteristic pattern 102 on the mask 10 to the epitaxial layer 122, thereby forming a plurality of patterns 125, that is, forming a plurality of patterns 125 on the epitaxial layer 122 of the wafer 12, such as Fig.11 As shown, the photoresist layer 123 is then removed.

[0066] As an example, the process of development and etching includes: developing the wafer 12 after exposure, using the difference in chemical properties between the exposed area and the unexposed area, selectively retaining the exposed area (negative photoresist) or the unexposed area (positive photoresist) in the required chemical solution; after development, using the required etching method (including dry etching or wet etching), in this embodiment, preferably dry etching is used to etch the epitaxial layer 122, etching away the part of the epitaxial layer 122 not covered by the photoresist layer 123, and only retaining the part of the epitaxial layer 122 protected by the photoresist layer 123. Preferably, during the etching process, an over-etching process is used to etch to a preset thickness range below the surface of the substrate layer 121 to ensure electrical insulation between adjacent patterns 125.

[0067] like Fig.11 As shown, when the exposure accuracy is locally uniform during the exposure process, the feature pattern 102 on the mask 10 is uniformly transferred to the pattern 125 formed by the epitaxial layer 122. Fig.12 As shown, when the exposure precision is partially uneven during the exposure process, the characteristic pattern 102 on the mask 10 is transferred to the pattern 125 formed by the epitaxial layer 122 and the width D1 of the pattern on the left is smaller than the width D2 of the pattern on the right. It should be noted that Fig.12This is only an example of a possible distortion of the pattern 125. In practice, the distortion may take many different forms. However, as long as the distortion occurs, an unbalanced voltage may be formed, which indicates that the exposure pattern in the region has deviated. Here, the degree of pattern deviation caused by the uneven local exposure accuracy is referred to as exposure accuracy, which reflects the local exposure accuracy and uniformity of the lithography machine.

[0068] Fig.11 and Fig.12 The pattern 125 is based on the feature pattern 102 on the mask 10. Figure 3 The cross-shaped feature pattern 102 shown is formed by transfer. Of course, when the feature pattern 102 on the mask 10 is Figures 4 to 7 The shape of will also be transferred to the epitaxial layer 122 to form a corresponding pattern 125, which can be referred to in the subsequent Figures 16 to 19 The pattern in 125. Figures 13 to 15 As shown, Fig.13 The pattern and Fig.11 correspond, Fig.14 The pattern and Fig.12 Correspondingly, step S5 is then performed to form two identical sets of metal electrodes 124 facing each other on the four end surfaces of all the patterns 125, wherein one set of the metal electrodes 124 is a signal input end, and the other set of the metal electrodes 124 is a signal output end.

[0069] like Fig. 20 As shown, after forming the pattern 125, a plurality of patterns 125 are closely arranged on the wafer 12, and each pattern 125 is used as a pixel point for exposure light intensity determination. The smaller the size of the pattern 125, the higher the spatial resolution of the detection.

[0070] like Fig.13 In the embodiment, if a group of metal electrodes 124 opposite to each other in the up-down direction are used as signal input terminals, then a group of metal electrodes 124 opposite to each other in the left-right direction are used as signal output terminals; vice versa, that is, if a group of metal electrodes 124 opposite to each other in the up-down direction are used as signal output terminals, then a group of metal electrodes 124 opposite to each other in the left-right direction are used as signal input terminals.

[0071] The driving signal input to the signal input end can be a current signal or a voltage signal, which is selected according to actual needs. For example, when the material of the epitaxial layer 122 is gallium arsenide, the driving signal input to the signal input end is a constant current signal; when the material of the epitaxial layer 122 is indium antimonide, the driving signal input to the signal input end is a constant voltage signal.

[0072] The material of the metal electrode 124 is not limited, and any metal suitable for forming an electrode can be used, such as gold, copper, aluminum, etc.

[0073] As a preferred example, the metal electrode 124 needs to cover the entire tail end of the four ends of the entire pattern 125, that is, the size of the metal electrode 124 is at least not less than the tail end size of the four ends of the pattern 125. Fig.13 and Fig.16 As shown, the pattern 125 is a cross-shaped pattern, and the metal electrode 124 completely covers the tail ends of the four ends, without exposing the pattern 125; Fig.17 As shown, the pattern 125 is a rectangular pattern, and the metal electrode 124 completely covers the tail ends of the four ends (ie, the four vertices of the rectangle), without exposing the pattern 125; Fig.18 As shown, the pattern 125 is a square pattern, and the metal electrode 124 completely covers the tail ends of the four ends (ie, the four vertices of the square), without exposing the pattern 125; Fig.19 As shown, the pattern 125 is a four-leaf clover-shaped pattern, and the metal electrode 124 completely covers the ends of the four leaves, without exposing the pattern 125.

[0074] As another preferred example, Figures 16 to 19 As shown, the shape of the metal electrode 124 is set to be an axisymmetric figure to facilitate process preparation.

[0075] like Fig. 20 As shown, the next step S6 is to measure the unbalanced voltage of all the patterns 125 on the wafer 12. The unbalanced voltage is the voltage difference between the two opposite metal electrodes at the signal output end. The unbalanced voltage is obtained by pattern differential operation, which can reflect the influence of the exposure accuracy of the pattern 125.

[0076] Generally, a wafer electrical performance tester is used to measure the unbalanced voltages of all the patterns 125 .

[0077] Finally, step S7 is performed to plot the measured unbalanced voltage of each of the patterns 125 into a Mapping diagram according to the device coordinates, and the exposure accuracy and consistency of the lithography machine are reflected according to the distribution of the Mapping diagram.

[0078] As an example, when using step lithography, the wafer 12 will be divided into different areas for step lithography, so that the wafer 12 will be divided into multiple exposure areas. By superimposing these exposure areas and calculating the average value of each point, the accuracy of the exposure accuracy consistency data can be reflected.

[0079] As another example, the specific form of the Mapping diagram is not limited, and any Mapping diagram that can reflect the distribution of unbalanced voltage areas can be used. Generally, the Mapping diagram often adopts a Mapping color scale diagram, but it is not limited to other feasible Mapping diagrams, such as a Mapping vertical distribution diagram, a Mapping ladder diagram, a Mapping grayscale diagram, etc.

[0080] The following uses a gallium arsenide epitaxial wafer as an experimental example to illustrate the high spatial resolution and high precision detection method and effect of the exposure accuracy of the lithography machine of this embodiment.

[0081] 1. Use gallium arsenide material to prepare the epitaxial layer of the wafer;

[0082] 2. Use organic solutions such as xylene, methanol, acetone, isopropanol, etc. to soak and shake the wafer for cleaning;

[0083] 3. After cleaning, use a glue coating machine to coat the surface of the epitaxial layer with positive photoresist (temporary glue, used for etching). After spin coating, perform pre-baking on a hot plate to dry out some of the moisture in the glue on the surface of the epitaxial layer;

[0084] 4. Use a stepper lithography machine that needs to measure the consistency of exposure accuracy to expose the wafer coated with photoresist. After exposure, immerse and shake the wafer in the developer to leave the pattern circuit on the surface of the epitaxial layer in the form of photoresist.

[0085] 5. After development, the wafer is hardened on a hot plate to further dry the moisture in the photoresist and ensure the bonding strength between the photoresist and the surface of the underlying epitaxial layer to be suitable for subsequent etching processes;

[0086] 6. For the epitaxial layer material, configure the corresponding etching solution. Here, the gallium arsenide epitaxial layer material uses a phosphoric acid hydrogen peroxide solution. The epitaxial layer is corroded according to the shape of the photoresist pattern. The corrosion depth needs to be monitored during the corrosion process to ensure that the epitaxial layer is corroded through to the substrate layer under the epitaxial layer. After the corrosion is completed, the wafer is immersed in the degumming solution to remove the photoresist on the surface of the epitaxial layer;

[0087] 7. After the epitaxial layer pattern circuit etching is completed, the metal electrode needs to be prepared by depositing metal in the coating machine. Before depositing the metal electrode, the area where no metal deposition is required needs to be isolated and protected with photoresist. Specifically, negative photoresist (temporary glue for lift) is coated on the surface of the epitaxial layer using a coating machine. off metal stripping), after spin coating, pre-baking treatment is performed on a hot plate to dry part of the moisture in the negative photoresist on the surface of the epitaxial layer; overlay is performed using a photolithography machine to prepare electrode patterns, and after exposure, intermediate baking treatment is performed on a hot plate to cause a "cross-linking" reaction in the exposed area, and the area that produces the "cross-linking" reaction will be retained during the development process, while the area that does not produce the "cross-linking" reaction will be removed during the development process; the wafer after light exposure is immersed and shaken in the developer to isolate and protect the area where no metal deposition is required, and the developed wafer is placed in the coating machine cavity for metal electrode deposition; after metal deposition is completed, the wafer is placed in a negative photoresist removal solution to strip off the negative photoresist on the surface of the epitaxial layer together with the metal on the negative photoresist, so that only the deposited metal is left at the electrode on the surface of the epitaxial layer after stripping; after metal stripping is completed, the wafer is annealed to form an ohmic contact between the deposited metal and the material below it;

[0088] 8. After completing the above process preparation, the wafer is arranged on the wafer electrical performance tester for electrical performance test. The unbalanced voltage value of each pattern measured is plotted into a Mapping color scale diagram according to the device coordinates. The distribution of the Mapping color scale diagram can reflect the consistency of the exposure accuracy of the lithography machine.

[0089] like Fig.21 This is a color scale diagram of Mapping in a single Shot. It can be seen from the figure that the color distribution in a single Shot is polarized (red in the lower left corner and blue in the lower right corner), which shows that the consistency of the accuracy of the lithography machine in exposing a single shot is poor. Fig. 22 This is the Mapping color scale diagram on the entire wafer. It can be seen from the figure that the polarization distribution degree of shots at different positions in the wafer is also different, but the mapping diagrams of multiple shots have good repeatability, which shows that this is a problem of the spatial distribution (consistency) of the local (micron level) exposure accuracy of a single shot on the entire shot surface. It can only be caused by the lithography exposure system, which also verifies the reliability of the method of this embodiment and the authenticity and effectiveness of the detection results. Here, the colors in the Mapping color scale diagram are defined as: red indicates that the unbalanced voltage is positive, and blue indicates that the unbalanced voltage is negative.

[0090] The unbalanced voltage data of the pattern in the center area of ​​the wafer prepared in the above experimental example are summarized in Table 1 below.

[0091] Table 1: Unbalanced voltage of the pattern in the center area of ​​the wafer

[0092] Serial number X Y <![CDATA[V OS (Unit: mV)]]> Serial number X Y <![CDATA[V OS (Unit: mV)]]> Serial number X Y <![CDATA[V OS (Unit: mV)]]> 1 29 -71 -0.466 41 -10 -72 0.033 81 10 -72 0.042 2 28 -71 -0.158 42 -10 -73 -0.132 82 10 -73 -0.111 3 27 -71 -0.492 43 -9 -72 -0.232 83 11 -72 0.144 4 26 -71 -0.194 44 -9 -73 -0.032 84 11 -73 0.142 5 25 -71 -0.501 45 -8 -72 -0.244 85 12 -72 -0.024 6 24 -71 -0.158 46 -8 -73 -0.134 86 12 -73 -0.003 7 23 -71 -0.462 47 -7 -72 -0.143 87 13 -72 -0.039 8 22 -71 -0.324 48 -7 -73 0.330 88 13 -73 -0.055 9 21 -71 -0.529 49 -6 -72 -0.292 89 14 -72 -0.181 10 20 -71 -0.202 50 -6 -73 -0.191 90 14 -73 0.066 11 19 -71 -0.070 51 -5 -72 -0.229 91 15 -72 -0.102 12 18 -71 -0.121 52 -5 -73 -0.239 92 15 -73 -0.350 13 17 -71 -0.322 53 -4 -72 -0.092 93 16 -72 -0.305 14 16 -71 -0.041 54 -4 -73 -0.109 94 16 -73 -0.285 15 15 -71 -0.223 55 -3 -72 -0.151 95 17 -72 -0.196 16 14 -71 -0.225 56 -3 -73 -0.289 96 17 -73 -0.368 17 13 -71 -0.219 57 -2 -72 0.017 97 18 -72 -0.392 18 12 -71 0.078 58 -2 -73 -0.251 98 18 -73 -0.075 19 11 -71 -0.075 59 -1 -72 -0.317 99 19 -72 -0.187 20 10 -71 -0.039 60 -1 -73 -0.002 100 19 -73 -0.261 21 9 -71 -0.061 61 0 -72 -0.411 101 20 -72 -0.042 22 8 -71 -0.064 62 0 -73 -0.363 102 20 -73 -0.239 23 7 -71 -0.125 63 1 -72 -0.486 103 21 -72 -0.446 24 6 -71 0.109 64 1 -73 -0.105 104 21 -73 -0.135 25 5 -71 0.328 65 2 -72 -0.140 105 22 -72 -0.508 26 4 -71 0.014 66 2 -73 -0.061 106 22 -73 -0.438 27 3 -71 -0.006 67 3 -72 -0.387 107 23 -72 -0.374 28 2 -71 -0.119 68 3 -73 -0.133 108 23 -73 -0.453 29 1 -71 -0.254 69 4 -72 0.088 109 24 -72 -0.370 30 0 -71 -0.170 70 4 -73 -0.111 110 24 -73 -0.389 31 -1 -71 -0.151 71 5 -72 -0.073 111 25 -72 -0.448 32 -2 -71 -0.296 72 5 -73 0.108 112 25 -73 -0.243 33 -3 -71 0.154 73 6 -72 0.368 113 26 -72 -0.198 34 -4 -71 -0.454 74 6 -73 -0.067 114 26 -73 -0.376 35 -5 -71 -0.222 75 7 -72 0.127 115 27 -72 -0.564 36 -6 -71 -0.101 76 7 -73 0.146 116 27 -73 -0.512 37 -7 -71 -0.191 77 8 -72 -0.148 117 28 -72 0.081 38 -8 -71 -0.019 78 8 -73 0.092 118 28 -73 -0.022 39 -9 -71 -0.071 79 9 -72 -0.011 119 29 -72 -0.233 40 -10 -71 -0.116 80 9 -73 -0.087 120 29 -73 -0.449

[0093] The data in Table 1 above show that the standard deviation value STD of the light intensity uniformity is 0.193, the median value MED is -0.150, the average value AVG is -0.165, the minimum negative unbalanced voltage value MIN is -0.564, and the maximum positive unbalanced voltage value MAX is 0.368.

[0094] Since the pattern size is no more than 100 μm, the exposure range has a high spatial resolution. At the same time, since the accuracy of the unbalanced voltage value can reach 0.0005 mV, the unbalanced voltage in the above table is converted into a detection accuracy of 0.9‰ (voltage value accuracy / maximum unbalanced voltage), reflecting the high-precision detection capability of this embodiment.

[0095] In summary, the high spatial resolution and high precision detection method for the exposure accuracy of the lithography machine of the present invention is specifically to divide the exposure area of ​​the mask into a number of detection areas with specific characteristic patterns (Wheatstone bridge patterns), and transfer the characteristic patterns to the wafer after the photolithography etching process to form a number of Wheatstone bridge patterns on the entire wafer, and by inputting an electrical signal to a group of relative metal electrodes on the pattern, an unbalanced voltage will be output between another group of relative metal electrodes, thereby drawing a Mapping diagram of the unbalanced voltage according to the coordinates of the entire wafer, and the uniformity of the exposure accuracy of the lithography machine can be reflected according to the distribution of the Mapping diagram. Since the pattern size distributed in various areas of the wafer is determined by the exposure accuracy of the photolithography machine in each area, when preparing the pattern, the optical path distortion and optical path asymmetry at a small scale will cause the characteristic pattern on the mask, which is an axisymmetric pattern in two vertical directions, to be distorted and transferred to the pattern, destroying the symmetry of the pattern, thereby generating a voltage difference on the pattern, i.e., an unbalanced voltage. The unbalanced voltage reflects the tiny unevenness of the exposure lines. Currently, this tiny unevenness is a measure of optical path distortion and optical path asymmetry, and is caused by the phase unevenness of the optical path system. It is currently difficult to detect this tiny unevenness in the industry because this method is to spread it all over the wafer. The method for preparing a pattern, in which each pattern is taken as an exposure point, is equivalent to dividing the entire exposure area of ​​the wafer into a dot matrix distribution based on the pattern, thereby effectively improving the spatial resolution of the uniformity of the exposure accuracy of the lithography machine, and the smaller the pattern size, the higher the spatial resolution. For example, for a dot matrix distribution display of no less than 100,000 patterns formed on a 4-inch wafer, a high spatial resolution dot matrix distribution map can be formed, and the resolution can reach no more than 100μm; in addition, the evaluation method of the electrical properties of the pattern is more accurate than other physical or optical methods of measuring the size of the graphic, and the measurement accuracy of the unbalanced voltage can reach less than 1‰, thereby achieving the purpose of high-precision detection of exposure.

[0096] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A high spatial resolution and high precision detection method for exposure accuracy of a lithography machine, characterized in that: The detection method comprises: Providing a mask, wherein the exposure area of ​​the mask is divided into a plurality of detection areas; Forming the same characteristic pattern in each of the detection areas, wherein the characteristic pattern is a Wheatstone bridge pattern; Expose the wafer based on the mask; wherein the wafer includes a substrate layer and an epitaxial layer in sequence along a thickness direction; Performing development and etching on the wafer to transfer the characteristic pattern on the mask to the epitaxial layer, thereby forming a plurality of patterns; Two identical sets of metal electrodes facing each other are formed on the four end surfaces of all the patterns, wherein one set of the metal electrodes is a signal input end, and the other set of the metal electrodes is a signal output end; measuring the unbalanced voltage of all the patterns on the wafer; The measured unbalanced voltage of each of the patterns is plotted into a Mapping diagram according to the device coordinates, and the exposure accuracy and consistency of the lithography machine are reflected according to the distribution of the Mapping diagram.

2. The high spatial resolution and high precision detection method for exposure accuracy of a lithography machine according to claim 1, characterized in that: The plurality of detection areas divided by the exposure area of ​​the mask have the same size, and each of the characteristic patterns is arranged at the same position of the detection area where it is located.

3. The high spatial resolution and high precision detection method for exposure accuracy of a lithography machine according to claim 1, characterized in that: The Wheatstone bridge pattern is a four-end pattern in a cross shape, a rectangle shape, a square shape, or a four-leaf clover shape; the two groups of metal electrodes cover the tail ends of the four ends of the Wheatstone bridge pattern.

4. The high spatial resolution and high precision detection method for exposure accuracy of a lithography machine according to claim 1, characterized in that: The material of the epitaxial layer of the wafer includes a material that can generate resistance.

5. The high spatial resolution and high precision detection method for exposure accuracy of a lithography machine according to claim 1, characterized in that: The mapping diagram is a mapping diagram that can reflect the regional distribution of unbalanced voltages.

6. The high spatial resolution and high precision detection method for exposure accuracy of a lithography machine according to claim 1, characterized in that: The unbalanced voltages of all the patterns are measured using a wafer electrical performance tester.

7. The high spatial resolution and high precision detection method for exposure accuracy of a lithography machine according to claim 1, characterized in that: The substrate layer in the wafer structure is an insulating layer, and the epitaxial layer is an active layer.

8. The high spatial resolution and high precision detection method for exposure accuracy of a lithography machine according to claim 1, characterized in that: When etching the wafer after the exposure process, an over-etching process is used to achieve complete etching.

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