Patent Publication Number: US-2021165329-A1

Title: Method for making photolithography mask plate

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 16/734,441, filed on Jan. 6, 2020, entitled, “METHOD FOR MAKING MICROSTRUCTURES AND PHOTOLITHOGRAPHY MASK PLATE”, which is a continuation application of U.S. patent application Ser. No. 15/684,428, filed on Aug. 23, 2017, entitled, “PHOTOLITHOGRAPHY MASK PLATE”, which claims all benefits accruing under 35 U.S.C. § 119 from China Patent Application No. 201611093541.9, filed on Dec. 1, 2016, in the China National Intellectual Property Administration, the contents of which are hereby incorporated by reference. The disclosures of the above-identified applications are incorporated herein by reference. 
    
    
     FIELD 
     The subject matter herein generally relates to a photolithography mask plate. 
     BACKGROUND 
     At present, with in depth studies on microstructures, microstructures can be applied to multiple fields, such as special surfaces of optical devices, hydrophobic material, anti-reflection surfaces. For example, a microstructure is generally provided in a light guide plate in order to improve the light emission efficiency in the optical devices. The main methods for making the microstructures are photolithography, etching and so on. Photolithography is widely used because of the simple process, easy operation and preparation in a large area. However, the mask material in photolithography are generally plastic, glass or pattern metal. The microstructures obtained by these mask material have low dimensional accuracy. Also it is difficult to obtain microstructures in nanoscale. 
     What is needed, therefore, is to provide a photolithography mask plate for solving the problem discussed above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with references to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. Implementations of the present technology will now be described, by way of example only, with reference to the attached figures, wherein: 
         FIG. 1  is a flow chart of one embodiment of a method of making microstructure. 
         FIG. 2  is a Scanning Electron Microscope (SEM) image of the drawn carbon nanotube film. 
         FIG. 3  is a Scanning Electron Microscope (SEM) image of a carbon nanotube structure consisting of a plurality of stacked drawn carbon nanotube precursor films. 
         FIG. 4  is a flow chart of a method of disposing the carbon nanotube layer on the second substrate. 
         FIG. 5  is a structural schematic view of a patterned photoresist microstructure. 
         FIG. 6  is a structural schematic view of a patterned photoresist microstructure. 
         FIG. 7  is a flow chart of a lift-off method of making micro-nanostructure. 
         FIG. 8  is a flow chart of one embodiment of a method of making micro-nanostructure. 
         FIG. 9  is a structural schematic view of a photolithography mask plate. 
         FIG. 10  is a structural schematic view of a photolithography mask plate. 
         FIG. 11  is a flow chart of one embodiment of the method of making micro-nanostructure. 
         FIG. 12  is a flow chart of one embodiment of the method of making micro-nanostructure. 
         FIG. 13  is a structural schematic view of a photolithography mask plate used in the method of  FIG. 11 . 
         FIG. 14  is a flow chart of one embodiment of a method of making the lithographic mask of  FIG. 13 . 
         FIG. 15  is a flow chart of one embodiment of the method of making micro-nanostructure. 
         FIG. 16  is a structural schematic view of a photolithography mask plate used in the method of  FIG. 15 . 
         FIG. 17  is a flow chart of one embodiment of a method of making the lithographic mask of  FIG. 16 . 
         FIG. 18  is a flow chart of one embodiment of the method of making micro-nanostructure. 
         FIG. 19  is a structural schematic view of a photolithography mask plate used in the method of  FIG. 18 . 
         FIG. 20  is a flow chart of one embodiment of the method of making the lithographic mask of  FIG. 19 . 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to better illustrate details and features. The description is not to be considered as limiting the scope of the embodiments described herein. 
     Several definitions that apply throughout this disclosure will now be presented. 
     The connection can be such that the objects are permanently connected or releasably connected. The term “substantially” is defined to be essentially conforming to the particular dimension, shape or other word that substantially modifies, such that the component need not be exact. The term “comprising” means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series and the like. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     Referring to  FIG. 1 , an embodiment of a method of making microstructures comprises:
         S 11 , providing a first substrate  150 , setting a photoresist layer  160  on a surface of the first substrate  150 ;   S 12 , covering a surface of the photoresist layer  160  with a photolithography mask plate  100 , wherein the photolithography mask plate  100  includes a second substrate  110  and a composite layer  140  located on a surface of the second substrate  110 ;   S 13 , exposing the photoresist layer  160  by irradiating the photoresist layer  160  through the photolithography mask plate  100  with ultraviolet light  180 , wherein the ultraviolet light  180  reach the photoresist layer  160  through the second substrate  110  and the composite layer  140 ;   S 14 , removing the photolithography mask plate  100  from the photoresist layer  160 , and developing the photoresist layer  160  to obtain a patterned photoresist microstructures  170 .       

     In step S 11 , the first substrate  150  can be insulating materials such as silica or silicon nitride. The first substrate  150  can also be conductive materials such as gold, aluminum, nickel, chromium, or copper. Also the first substrate  150  can be semiconductor materials such as silicon, gallium nitride, or gallium arsenide. In one embodiment, the first substrate  150  is a silicon wafer. 
     The type of the photoresist layer  160  can be negative or positive. The photoresist layer  160  can be S9912 positive photoresist or SU8 negative photoresist. The photoresist layer  160  can be directly applied to the surface of the first substrate  150  by spin coating. The thickness of the photoresist layer  160  can be in a range of about 50 nm to about 200 nm. When the thickness of the photoresist layer  160  is too thin, graphic contrast after photolithography decreases. When the thickness of the photoresist layer  160  is too thick, patterned photoresist can easily create slopes near the edge of the pattern. In one embodiment, the photoresist layer  160  is S9912 positive photoresist, and the thickness of the photoresist layer  160  is about 100 nm. 
     In step S 12 , the photolithography mask plate  100  provides a patterned mask. The photolithography mask plate  100  includes at least a second substrate  110  and a composite layer  140  located on the surface of the second substrate  110 . The composite layer  140  includes a carbon nanotube layer  120  and a cover layer  130 . The carbon nanotube layer  120  is directly located on the surface of the second substrate  110 . The cover layer  130  covers the carbon nanotube layer  120  so that the carbon nanotube layer  120  is sandwiched between the cover layer  130  and second substrate  110 . The cover layer  130  is continuously and directly attached to a surface of the carbon nanotube layer  120 . The cover layer  130  is bonded to the carbon nanotube layer  120  to form the composite layer  140 . Due to portions of the cover layer  130  can extend through the holes of the carbon nanotube layer  120  to be in direct contact with the second substrate  110 , the cover layer  130  can fix the carbon nanotube layer  120  on the second substrate  110 . 
     The photolithography mask plate  100  covers the photoresist layer  160 . The photolithography mask plate  100  is located on the surface of the photoresist layer  160  away from the first substrate  150 . In one embodiment, the composite layer  140  is in direct contact with the surface of the photoresist layer  160  away from the first substrate  150 . The second substrate  110  is spaced from the photoresist layer  160 . In one embodiment, the second substrate  110  can be in direct contact with the photoresist layer  160  so that the second substrate  110  sandwiched between the composite layer  140  and the photoresist layer  160 . The composite layer  140  is spaced from the photoresist layer  160 . When the composite layer  140  is located on the surface of the photoresist layer  160 , the composite layer  140  is not completely in direct contact with the surface of the photoresist layer  160 , and there may be air gaps between partial surfaces of the composite layer  140  and surfaces of the photoresist layer  160 . 
     The second substrate  110  serves as a support. Materials of the second substrate  110  can be rigid materials (e.g., p-type or n-type silicon, quartz, silicon with a silicon dioxide layer formed thereon, crystal, crystal with an oxide layer formed thereon), or flexible materials (e.g., plastic or resin). The second substrate  110  material can be polyethylene terephthalate, polyethylene naphthalate two formic acid glycol ester (PEN), or polyimide. The second substrate  110  has a high transmittance to UV light, for example more than 60%. In one embodiment, the second substrate  110  material is quartz. 
     The carbon nanotube layer  120  includes a plurality of carbon nanotubes parallel to the surface of the carbon nanotube layer  120 . The plurality of carbon nanotubes along an extending direction joined end to end by van der Waals attraction forces. The carbon nanotube layer  120  is a free-standing structure. The term “free-standing structure” includes the carbon nanotube layer  120  that can sustain the weight of itself when it is hoisted by a portion thereof without any significant damage to its structural integrity. Thus, the carbon nanotube layer  120  can be suspended by two spaced supports (not shown). The plurality of carbon nanotubes can be single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes. The length and diameter of the plurality of carbon nanotubes can be selected according to need. The diameter of the single-walled carbon nanotubes can be from about 0.5 nanometers to about 10 nanometers. The diameter of the double-walled carbon nanotubes can be from about 1.0 nanometer to about 15 nanometers. The diameter of the multi-walled carbon nanotubes can be from about 1.5 nanometers to about 50 nanometers. In one embodiment, the length of the carbon nanotubes can be from about 200 micrometers to about 900 micrometers. 
     The carbon nanotube layer  120  can include at least one carbon nanotube film, at least one carbon nanotube wire, or combination thereof. In one embodiment, the carbon nanotube layer  120  can be pure carbon nanotube layer. In one embodiment, the carbon nanotube layer  120  can include a single carbon nanotube film or two or more carbon nanotube films stacked together. Thus, the thickness of the carbon nanotube layer  120  can be controlled by the number of the stacked carbon nanotube films. In one embodiment, the carbon nanotube layer  120  is formed by folding a single carbon nanotube wire. In one embodiment, the carbon nanotube layer  120  can include a layer of parallel and spaced carbon nanotube wires. Also, the carbon nanotube layer  120  can include a plurality of carbon nanotube wires crossed or weaved together to form a carbon nanotube net. The carbon nanotube net defines a plurality of holes. The plurality of holes extend throughout the carbon nanotube layer  120  along the thickness direction of the layer. It is understood that any carbon nanotube structure described can be used with all embodiments. 
     Referring to  FIG. 2 , in one embodiment, the carbon nanotube layer  120  includes at least one drawn carbon nanotube film. A drawn carbon nanotube film can be drawn from a carbon nanotube array that is able to have a film drawn therefrom. The drawn carbon nanotube film includes a plurality of successive and oriented carbon nanotubes joined end-to-end by van der Waals attraction forces therebetween. The drawn carbon nanotube film is a free-standing film. Each drawn carbon nanotube film includes a plurality of successively oriented carbon nanotube segments joined end-to-end by van der Waals attraction forces therebetween. Each carbon nanotube segment includes a plurality of carbon nanotubes parallel to each other, and combined by van der Waals attraction forces therebetween. As can be seen in  FIG. 2 , some variations can occur in the drawn carbon nanotube film. The carbon nanotubes in the drawn carbon nanotube film are oriented along a preferred orientation. The drawn carbon nanotube film can be treated with an organic solvent to increase the mechanical strength and toughness and reduce the coefficient of friction of the drawn carbon nanotube film. A thickness of the drawn carbon nanotube film can range from about 0.5 nanometers to about 100 micrometers. The drawn carbon nanotube film defines a plurality of holes between adjacent carbon nanotubes. 
     Referring to  FIG. 3 , the carbon nanotube layer  120  can include at least two stacked drawn carbon nanotube films. In other embodiments, the carbon nanotube layer  120  can include two or more coplanar carbon nanotube films, and can include layers of coplanar carbon nanotube films. Additionally, when the carbon nanotubes in the carbon nanotube film are aligned along one preferred orientation (e.g., the drawn carbon nanotube film), an angle can exist between the orientation of carbon nanotubes in adjacent films, whether stacked or adjacent. Adjacent carbon nanotube films can be combined by only the van der Waals attraction forces therebetween. As can be seen in  FIG. 3 , an angle between the aligned directions of the carbon nanotubes in two adjacent carbon nanotube films can range from about 0 degrees to about 90 degrees. When the angle between the aligned directions of the carbon nanotubes in adjacent stacked drawn carbon nanotube films is larger than 0 degrees, a plurality of holes is defined by the carbon nanotube layer  120 . In one embodiment, the carbon nanotube layer  120  is shown with the aligned directions of the carbon nanotubes between adjacent stacked drawn carbon nanotube films at 90 degrees. Stacking the carbon nanotube films will also add to the structural integrity of the carbon nanotube layer  120 . 
     The carbon nanotube wire can be untwisted or twisted. Treating the drawn carbon nanotube film with a volatile organic solvent can form the untwisted carbon nanotube wire. Specifically, the organic solvent is applied to soak the entire surface of the drawn carbon nanotube film. During soaking, adjacent parallel carbon nanotubes in the drawn carbon nanotube film will bundle together, due to the surface tension of the organic solvent as it volatilizes, and thus, the drawn carbon nanotube film will be shrunk into an untwisted carbon nanotube wire. The untwisted carbon nanotube wire includes a plurality of carbon nanotubes substantially oriented along a same direction (i.e., a direction along the length of the untwisted carbon nanotube wire). The carbon nanotubes are substantially parallel to the axis of the untwisted carbon nanotube wire. More specifically, the untwisted carbon nanotube wire includes a plurality of successive carbon nanotube segments joined end to end by van der Waals attraction forces therebetween. Each carbon nanotube segment includes a plurality of carbon nanotubes substantially parallel to each other, and combined by van der Waals attraction forces therebetween. The carbon nanotube segments can vary in width, thickness, uniformity, and shape. The length of the untwisted carbon nanotube wire can be arbitrarily set as desired. A diameter of the untwisted carbon nanotube wire ranges from about 0.5 nanometers to about 100 micrometers. 
     The twisted carbon nanotube wire can be formed by twisting a drawn carbon nanotube film using a mechanical force at two opposite ends of the drawn carbon nanotube film in opposite directions. The twisted carbon nanotube wire includes a plurality of carbon nanotubes helically oriented around an axial direction of the twisted carbon nanotube wire. More specifically, the twisted carbon nanotube wire includes a plurality of successive carbon nanotube segments joined end to end by van der Waals attraction forces therebetween. Each carbon nanotube segment includes a plurality of carbon nanotubes parallel to each other, and combined by van der Waals attraction forces therebetween. The length of the carbon nanotube wire can be set as desired. A diameter of the twisted carbon nanotube wire can be from about 0.5 nanometers to about 100 micrometers. Further, the twisted carbon nanotube wire can be treated with a volatile organic solvent after being twisted to bundle the adjacent paralleled carbon nanotubes together. The specific surface area of the twisted carbon nanotube wire decreases while the density and strength of the twisted carbon nanotube wire increases. 
     The carbon nanotube layer  120  can be located directly on the surface of the second substrate  110 . As carbon nanotube layer  120  defines a plurality of holes, a partial surface of the second substrate  110  is exposed through the plurality of holes. 
     Furthermore, referring to  FIG. 4 , disposing the carbon nanotube layer  120  on the second substrate  110  comprises solvent treating the second substrate  110  with the carbon nanotube layer  120  thereon. Because there is an air gap  112  between the carbon nanotube layer  120  and the surface of the second substrate  110 , the solvent can exhaust air while allowing the carbon nanotube layer  120  to be closely and firmly adhered on the surface of the second substrate  110 . The solvent can be water or volatile organic solvent such as ethanol, methanol, acetone, dichloroethane, chloroform, or mixtures thereof. In one embodiment, the organic solvent is ethanol. 
     The material of the cover layer  130  can be metal, metal oxide, metal nitride, metal carbide, metal sulfide, silicon oxide, silicon nitride, or silicon carbide. The metal can be gold, nickel, titanium, iron, aluminum, chromium, or alloy thereof. The metal oxide can be alumina, magnesium oxide, zinc oxide, or hafnium oxide. The material of the cover layer  130  is not limited above and can be any material as long as the material can be deposited on the carbon nanotube layer  120  and have a high transmittance to UV light, for example more than 60%. 
     The cover layer  130  can be deposited on the surface of the carbon nanotube layer  120  by atomic layer deposition (ALD). The method of depositing the cover layer  130  can also be physical vapor deposition (PVD), chemical vapor deposition (CVD), magnetron sputtering, or spaying. The method of depositing the cover layer  130  is not limited above and can be any method as long as the cover layer  130  can be continuously deposited on the carbon nanotube layer  120  surface and the structure of the carbon nanotube layer  120  is not destroyed. The thickness of the cover layer  130  is 5 nm-20 nm. If the thickness of the cover layer  130  is more than 20 nm, the transmittance to UV light of the cover layer  130  would be seriously reduced. In one embodiment, the material of the cover layer  130  is alumina, and the thickness of the cover layer  130  is 5 nm. 
     Furthermore, when the carbon nanotube layer  120  is a free-standing structure, the composite layer  140  is also free-standing and can be used alone as a lithographic pattern and the second substrate  110  is not optional. 
     In step S 13 , when the ultraviolet light  180  irradiates on the photolithography mask plate  100 , due to the second substrate  110  and the cover layer  130  having high transmittance, the loss of the ultraviolet light  180  is negligible as the light  180  passes through the second substrate  110  and the cover layer  130 . As the carbon nanotubes is capable of strongly absorbing the ultraviolet light, the ultraviolet light irradiated on the carbon nanotube structure is almost completely absorbed and the ultraviolet light irradiated at the holes between carbon nanotubes can pass directly through the carbon nanotube layer  120 . The photoresist layer  160  is exposed by irradiating the surface of the photoresist layer  160  through the photolithography mask plate  100  with the ultraviolet light  180 . The surface of the photoresist layer  160  corresponding to the holes between the carbon nanotubes is exposed to the ultraviolet light  180 . The surface of the photoresist layer  160  corresponding to the carbon nanotube structure is not exposed to the ultraviolet light  180 . The exposure time of the photoresist layer  160  is about 2 s-7 s. In one embodiment, the exposure time of the photoresist layer  160  is about 2 s. 
     In step S 14 , the photoresist layer  160  physically contacts the photolithography mask plate  100 , and the bonding force between the photoresist layer  160  and the composite layer  140  is less than the bonding force between the composite layer  140  and the second substrate  110 . Thus, the photolithography mask plate  100  can be separated from the photoresist layer  160  by applying a force to the second substrate  110 , and the structure of the photolithography mask plate  100  would not be strongly affected. After the photolithography mask plate  100  is separated from the surface of the photoresist layer  160 , the structure of the photolithography mask plate  100  remains intact. So the photolithography mask plate  100  can be reused as a mask, and can be used repeatedly in steps S 12 -S 13 . 
     The photoresist layer  160  is subjected to a developing process by placing the photoresist layer  160  in a developer for a period of time. The developer is a solution containing 0.4% NaOH and 1% NaCl solution. The developing time of the photoresist layer  160  is about 20 s. The developing time can be determined by the developer composition, the concentration, and the like. The developer is not limited to above and can be any solution as long as the photoresist layer  160  can be developed. 
     The developer can be a mixed solution of NaOH solution and NaCl solution. The mass content of NaOH in the mixed solution is about 0.2%-1%, and the mass content of NaCl is about 0.5%-2%. The patterned photoresist microstructures  170  are obtained after developing the photoresist layer  160 . The pattern of the patterned photoresist microstructures  170  is consistent with the pattern of the carbon nanotube layer  120 . As can be seen in  FIG. 5  and  FIG. 6 , the patterned photoresist microstructures  170  include a plurality of ribs  171  and a plurality of micropores  172  between adjacent ribs  171 , and the micropores  172  are holes or gaps. The width of the ribs  171  and the diameter of the micropores  172  are related to the diameter of the carbon nanotubes and the diameter of the holes in the carbon nanotube layer  120 . The size of the micropore is the diameter of the hole or width of the gap. The plurality of micropores  172  extend throughout the patterned photoresist microstructures  170  along the thickness direction. The thickness of the ribs  171  and the depths of the micropores  172  is consistent with the thickness of the photoresist layer  160 . The width of each ribs  171  is about 20 nm-200 nm, and the diameter of each microspore is about 20 nm-300 nm. 
     Referring to  FIG. 7 , microstructures  152  formed by other non-photoresist materials can be further obtained according to the patterned photoresist microstructures  170 . The microstructures  152  can be made by a lift-off method, etching, or a combination thereof. The method for making the microstructures  152  is not limit the aforementioned methods and can be any method as long as the microstructures  152  can be obtained. In one embodiment, the microstructures  152  are made by the lift-off method. 
     The lift-off method of making the microstructures  152  includes following steps: step  1 , depositing a preformed layer  190  on a surface of the patterned photoresist microstructures  170  away from the first substrate  150  and an exposed surface of the first substrate  150 ; step  2 , immersing the whole structure above in acetone, and removing the patterned photoresist microstructures  170  to obtain the microstructures  152  on the first substrate  150 . 
     In step  1 , the preformed layer  190  material can be metal, insulating materials, or semiconductor materials. The metal can be gold, silver, nickel, titanium, iron, aluminum, chromium, or alloy thereof. The insulating materials can be silicon oxide, silicon nitride. The semiconductor materials can be silicon, gallium nitride, gallium arsenide. The material of the preformed layer  190  is not limit above and can be any material as long as the material does not react with acetone. The preformed layer  190  can be deposited by magnetron sputtering, vapor deposition, CVD method, or the like. The preformed layer  190  on the patterned photoresist microstructures  170  is not continuous so that both lateral sides of the patterned photoresist microstructures  170  are not completely covered by the preformed layer  190 . Thus, the acetone can be contact and react with the patterned photoresist microstructures  170 . In one embodiment, the preformed layer  190  material is aluminum, and the preformed layer  190  is made by vapor deposition method. 
     In step  2 , as both lateral sides of the patterned photoresist microstructures  170  are not completely covered by the preformed layer  190 , the acetone can react with the photoresist to remove the patterned photoresist microstructures  170 . At the same time, portions of the preformed layer  190  that are deposited on the patterned photoresist microstructures  170  surface can also be removed. The other portions of the preformed layer  190  that are deposited on the first substrate  150  forms the microstructures  152 . 
     In one embodiment, the carbon nanotube layer  120  includes two crossed drawn carbon nanotube films, and the microstructures  152  is a vertical crossed strips structure. The width of each strip in the direction perpendicular to the extension direction is set to be 1, and the size of/is about 20 nm-200 nm, the width of spacing between two adjacent strips is about 20 nm-300 nm. The thickness of the microstructures  152  can be determined in accordance with the thickness of the preformed layer  190 . 
     The microstructures  152  can also be formed by dry etching. The exposed surface of the first substrate  150  is etched with the patterned photoresist microstructures  170  as a mask. The dry etching can be plasma etching or reactive ion etching (RIE). In one embodiment, the dry etching is performed by applying plasma energy on the entire or partial surface of the first substrate  150  surface via a plasma device. The plasma gas can be an inert gas and/or etching gases, such as argon (Ar), helium (He), chlorine (Cl 2 ), hydrogen (H 2 ), oxygen (O 2 ), fluorocarbon (CF 4 ), ammonia (NH 3 ), or air. 
     When etching the first substrate  150 , the etching gas can react with the first substrate  150  and may not react with the patterned photoresist microstructures  170 . The reaction rate between the etching gas and the patterned photoresist microstructures  170  is much less than the reaction rate between the etching gas and the first substrate  150 . The pattern of the microstructures  152  is substantially identical to the pattern of the patterned photoresist microstructures  170 . 
     Furthermore, method of making the microstructures  152  comprises removing the patterned photoresist microstructures  170 . The method of removing the patterned photoresist microstructures  170  can be ultrasonic method, tearing method, oxidation method and so on. In one embodiment, the patterned photoresist microstructures  170  are removed by ultrasonic method. 
     Referring to  FIG. 8 , an embodiment of a method of making microstructures comprises:
         S 21 , providing a first substrate  150 , setting a photoresist layer  160  on a surface of the first substrate  150 ;   S 22 , covering a surface of the photoresist layer  160  with a photolithography mask plate  200 , wherein the photolithography mask plate  200  includes at least two second substrates  110  and at least two composite layers  140 , each composite layer  140  is located on one second substrate  110  to form a photolithography mask plate unit;   S 23 , exposing the photoresist layer  160  by irradiating the photoresist layer  160  through the photolithography mask plate  200  with the ultraviolet light  180 , wherein the ultraviolet light  180  reach the photoresist layer  160  through the second substrate  110  and the composite layer  140 ;   S 24 , removing the photolithography mask plate  200  from the photoresist layer  160 , and developing the photoresist layer  160  to obtain a patterned photoresist microstructures  170 .       

     The method of making microstructures is similar to the above method of making microstructures of  FIG. 1  except that the photolithography mask plate  200  includes a plurality of second substrates and a plurality of composite layers  140 . Each second substrate and each composite layer  140  locating on the second substrate  110  can be treated as a photolithography mask plate unit. The photolithography mask plate  200  includes a plurality of photolithography mask plate units. The plurality of photolithography mask plate units are stacked, and the carbon nanotubes in the photolithography mask plate unit can be arranged in parallel in one direction, or intersected in a plurality of directions. 
     The mask pattern of the photolithography mask plate  200  can be adjusted by selecting photolithography mask plate units having different arrangements of carbon nanotubes. If the mask pattern of the photolithography mask plate  200  is a network pattern, the mask pattern can be obtained by directly selecting a photolithography mask unit having intersected carbon nanotubes. Also the mask pattern can be obtained by selecting two photolithography mask units having parallel carbon nanotubes, and the two photolithography mask units are stacked and the carbon nanotubes in the two units are arranged in different directions. As can be seen in  FIG. 9 , the angle α of the two units can be selected as desired. As can be seen in  FIG. 10 , if the mask pattern of the photolithography mask plate  200  includes a plurality of parallel strips and an interval distance of each adjacent strips is l, the mask pattern can be obtained by selecting two photolithography mask units having parallel strips and the interval distance of each adjacent strips is 2l, wherein the two photolithography mask units are stacked and the strips in the two photolithography mask units are in the same direction, and the strips of the two photolithography mask units alternates in positions. 
     Referring to  FIG. 11 , an embodiment of a method of making microstructures comprises:
         S 31 , providing a first substrate  150 , setting a photoresist layer  160  on a surface of the first substrate  150 ;   S 32 , covering a surface of the photoresist layer  160  with a photolithography mask plate  300 , wherein the photolithography mask plate  300  includes a second substrates  110 , a third substrate  109 , and a carbon nanotube layer  120  sandwiched between the two substrates;   S 33 , exposing the photoresist layer  160  by irradiating the photoresist layer  160  through the photolithography mask plate  300  with ultraviolet light  180 , wherein the ultraviolet light  180  reach the photoresist layer  160  through the photolithography mask plate  300 ;   S 34 , removing the photolithography mask plate  300  from the photoresist layer  160  and developing the photoresist layer  160  to obtain a patterned photoresist microstructures  170 .       

     The method of making microstructures is similar to the above method of making microstructures of  FIG. 1  except that the photolithography mask plate  300  includes a second substrates  110 , a third substrate  109 , and a carbon nanotube layer  120  sandwiched between the two substrates. The use of the third substrate  109  is the same as that of the second substrate  110 , and the material of the third substrate  109  can be the same as that of the second substrate  110 . As the carbon nanotube layer  120  is sandwiched between the third substrate  109  and the second substrate  110 , the third substrate  109  and the second substrate  110  can fix and grip the carbon nanotube layer  120 . Due to the carbon nanotube layer  120  is fixed, it can not move on the plane and the direction perpendicular to the plane. The method for making the photolithography mask plate  300  is simple, and the photolithography mask plate  300  having a fixed carbon nanotube layer is obtained without the step of depositing a cover layer. In one embodiment, the carbon nanotube layer  120  is a pure carbon nanotube layer and only comprises a plurality of carbon nanotubes. 
     Referring to  FIG. 12 , an embodiment of a method of making microstructures comprises:
         S 41 , providing a first substrate  150 , setting a photoresist layer  160  on a surface of the first substrate  150 ;   S 42 , covering a surface of the photoresist layer  160  with a photolithography mask plate  400 , wherein the photolithography mask plate  400  includes a second substrates  110 , a first patterned chrome layer  122 , a carbon nanotube layer  120 , and a cover layer  130 ;   S 43 , exposing the photoresist layer  160  by irradiating the photoresist layer  160  through the photolithography mask plate  400  with ultraviolet light  180 , wherein the ultraviolet light  180  reach the photoresist layer  160  through the photolithography mask plate  400 ;   S 44 , removing the photolithography mask plate  400  from the photoresist layer  160  and developing the photoresist layer  160  to obtain a patterned photoresist microstructures  170 .       

     The method of making microstructures is similar to the above method of making microstructures of  FIG. 1  except that the photolithography mask plate  400  includes a second substrates  110 , a first patterned chrome layer  122 , a carbon nanotube layer  120  and a cover layer  130 . The pattern of the first patterned chrome layer  122  coincides with the pattern of the carbon nanotube layer  120 . The photolithography mask plate  400  can be used as a photolithography mask unit, and a plurality of units are used in combination. Since the absorption rate of chromium to the ultraviolet light is high, the photolithography mask plate  400  has a better effect of absorbing ultraviolet light compared to a mask with only carbon nanotubes. The microstructures obtained by the photolithography mask plate  400  have higher accuracy compared to a mask with only carbon nanotubes. 
     Referring to  FIG. 13 , the photolithography mask plate  400  above comprises: the second substrate  110 , the first patterned chrome layer  122 , the carbon nanotube layer  120 , and the cover layer  130 . The first patterned chrome layer  122  is located on the surface of the second substrate  110 . The carbon nanotube layer  120  is located on a surface of the first patterned chrome layer  122  away from the second substrate  110 . The pattern of the first patterned chrome layer  122  is the same with the pattern of the carbon nanotube layer  120 . The cover layer  130  is located on the carbon nanotube layer  120  surface away from the second substrate  110 . The cover layer  130  is continuously and directly attached to the carbon nanotube layer  120  surface. Because the cover layer  130  can cover the entire carbon nanotube layer  120 , the entire first patterned chrome layer  122 , and a portion of the second substrate  110 , the cover layer  130  can fix the carbon nanotube layer  120  on the second substrate  110 . 
     The photolithography mask plate  400  is similar to the photolithography mask plate  100  except that the photolithography mask plate  400  includes the first patterned chrome layer  122  between the carbon nanotube layer  120  and the second substrate  110 . The pattern of the first patterned chrome layer  122  coincides with the pattern of the carbon nanotube layer  120 . Since the absorption rate of chromium to the ultraviolet light is high, the photolithography mask plate  400  has a better effect of absorbing ultraviolet light. The microstructures obtained by the photolithography mask plate  400  have higher accuracy. 
     Referring to  FIG. 14 , an embodiment of a method of making the photolithography mask plate  400  comprises:
         S 51 , providing a second substrate  110 , setting a chrome layer  121  on a surface of the second substrate  110 ;   S 52 , locating a carbon nanotube layer  120  on a surface of the chrome layer  121  to expose a partial surface of the chrome layer  121 ;   S 53 , etching the chrome layer  121  with the carbon nanotube layer  120  as a mask to obtain a first patterned chrome layer  122 ;   S 54 , depositing a cover layer  130  on a surface of the carbon nanotube layer  120  away from the second substrate.       

     In step S 51 , the chrome layer  121  can be deposited by electron beam evaporation, ion beam sputtering, atomic layer deposition, magnetron sputtering, vapor deposition, chemical vapor deposition, etc. The chrome layer  121  is continuous and deposited on the second substrate  110 . The thickness of the chrome layer  121  is from about 10 nm to about 50 nm. In one embodiment, the chrome layer  121  is deposited on the second substrate  110  by vapor deposition, and the thickness of the chrome layer  121  is 20 nm. 
     In step S 52 , the method of disposing the carbon nanotube layer  120  can be the same with the method above. The method can make the carbon nanotube layer  120  closely and firmly adhered on the chrome layer  121  surface. Partial surfaces of the chrome layer  121  corresponding to the holes of the carbon nanotube layer  120  are exposed. 
     In step S 53 , the etching method can be same with the method of etching the first substrate  150  above. The etching gases can be determined by the material which is etched. And the etching gases can not react with the carbon nanotube layer  120 . 
     In step S 54 , the method of making the cover layer  130  is the same with the method above. The cover layer  130  is directly attached to the surface of the carbon nanotube layer  120  to form a continuous layer structure, and cover the first patterned chrome layer  122  at the same time. The carbon nanotube layer  120  is fixed on the second substrate  110  by the cover layer  130 . 
     Referring to  FIG. 15 , an embodiment of a method of making microstructures comprises:
         S 61 , providing a first substrate  150 , setting a photoresist layer  160  on a surface of the first substrate  150 ;   S 62 , covering the surface of the photoresist layer  160  with a photolithography mask plate  500 , wherein the photolithography mask plate  500  includes a second substrate  110 , a first patterned chrome layer  122 , a carbon nanotube layer  120 , and a cover layer  130 ;   S 63 , exposing the photoresist layer  160  by irradiating the photoresist layer  160  through the photolithography mask plate  500  with ultraviolet light  180 , wherein the ultraviolet light  180  reach the photoresist layer  160  through the photolithography mask plate  500 ;   S 64 , removing the photolithography mask plate  500  from the photoresist layer  160 , and developing the photoresist layer  160  to obtain a patterned photoresist microstructures  170 .       

     The method of making microstructures is similar to the method of making microstructures of  FIG. 1  except that the first patterned chrome layer  122  is located between the carbon nanotube layer  120  and the cover layer  130 . The pattern of the first patterned chrome layer  122  coincides with the pattern of the carbon nanotube layer  120 . Since the absorption rate of chromium and carbon nanotube to the ultraviolet light is high, the microstructures obtained by the photolithography mask plate  500  have higher accuracy. 
     Referring to  FIG. 16 , the photolithography mask plate  500  above comprises: the second substrate  110 , the carbon nanotube layer  120 , the first patterned chrome layer  122 , and the cover layer  130 . The carbon nanotube layer  120  is located on the surface of the second substrate  110 . The first patterned chrome layer  122  is located on the surface of the carbon nanotube layer  120  away from the second substrate  110 . The pattern of the first patterned chrome layer  122  is the same with the pattern of the carbon nanotube layer  120 . The cover layer  130  covers on the surface of the first patterned chrome layer  122  away from the second substrate  110 . 
     The photolithography mask plate  500  is similar to the photolithography mask plate  400  except that the first patterned chrome layer  122  is located on the carbon nanotube layer  120  surface away from the second substrate  110 . The pattern of the first patterned chrome layer  122  coincides with the pattern of the carbon nanotube layer  120 . The microstructures obtained by the photolithography mask plate  500  have higher accuracy. 
     Referring to  FIG. 17 , an embodiment of a method of making the photolithography mask plate  500  comprises:
         S 71 , providing a fourth substrate  101 , setting a carbon nanotube layer  120  on the fourth substrate  101 ;   S 72 , locating a chrome layer  121  on the surface of the carbon nanotube layer  120  away from the fourth substrate  101 , wherein the chrome layer  121  includes a first patterned chrome layer  122  and a second patterned chrome layer  123 , the first patterned chrome layer  122  is located on the surface of carbon nanotubes of the carbon nanotube layer  120 , and the second patterned chrome layer  123  is deposited on a surface of the fourth substrate  101  corresponding to holes of the carbon nanotube layer  120 ;   S 73 , transferring the carbon nanotube layer  120  with the first patterned chrome layer  122  thereon from the surface of the fourth substrate  101  to the surface of the second substrate  110 , and the carbon nanotube layer  120  being in contact with the surface of the second substrate  110 ;   S 74 , depositing a cover layer  130  on the surface of the first patterned chrome layer  122  away from the second substrate  110 .       

     In step S 72 , when the thickness of the chrome layer  121  is smaller than the thickness of the carbon nanotube layer  120 , the chrome layer  121  is a discontinuous structure. The chrome layer  121  is divided into the first patterned chrome layer  122  and the second patterned chrome layer  123  away from each other. The first patterned chrome layer  122  is located only on the surface of the carbon nanotubes. The second patterned chrome layer  123  is located on partial surfaces of the fourth substrate  101 , and the partial surfaces corresponds to and is exposed from the holes of the carbon nanotube layer  120 . 
     In step S 73 , since the chrome layer  121  is a discontinuous layered structure, the carbon nanotube layer  120  can be directly detached from the fourth substrate  101  surface. After the first patterned chrome layer  122  and the carbon nanotube layer are transferred, the structure of the second patterned chrome layer  123  remains unchanged. The fourth substrate  101  and the second patterned chrome layer  123  can also be used as a photolithography mask. 
     Referring to  FIG. 18 , an embodiment of a method of making microstructures comprises:
         S 81 , providing a first substrate  150 , setting a photoresist layer  160  on a surface of the first substrate  150 ;   S 82 , covering a surface of the photoresist layer  160  with a photolithography mask plate  600 , wherein the photolithography mask plate  500  includes a second substrate  110 , a carbon nanotube composite structure  141  and a cover layer  130 ;   S 83 , exposing the photoresist layer  160  by irradiating the photoresist layer  160  through the photolithography mask plate  600  with ultraviolet light  180 , wherein the ultraviolet light  180  reach the photoresist layer  160  through the photolithography mask plate  600 ;   S 84 , removing the photolithography mask plate  600  from the photoresist layer  160 , and developing the photoresist layer  160  to obtain a patterned photoresist microstructures  170 .       

     The method of making microstructures is similar to the method of making microstructures of  FIG. 1  except that the carbon nanotube composite structure  141  is located on the surface of the second substrate  110  and comprises a carbon nanotube layer  120 , and a chrome layer  121  wraps the carbon nanotube layer  120 . The chrome layer  121  completely covers each of carbon nanotubes in the carbon nanotube layer  120 . 
     The features of the method of making microstructures includes the following points. Since the carbon nanotubes and chromium have the high absorption of ultraviolet light and the low transmittance to ultraviolet light, the transmittance to ultraviolet light of holes is very high, then it is easy to obtain patterned microstructures. The cover layer can fix the carbon nanotube layer on the second substrate to form a mask, and the mask is easy to disassemble and can be used repeatedly to cut costs. Also the mask can be produced in a large scale. 
     Referring to  FIG. 19 , the photolithography mask plate  600  above comprises: the second substrate  110 , the carbon nanotube composite structure  141 , and the cover layer  130 . The carbon nanotube composite structure  141  is located on the surface of the second substrate  110 . The carbon nanotube composite structure  141  comprises a carbon nanotube layer  120  and a chrome layer  121  wrapped the carbon nanotube layer  120 . The cover layer  130  covers the surface of the carbon nanotube composite structure  141  away from the second substrate  110 . 
     The photolithography mask plate  600  is similar to the photolithography mask plate  500  except that the chrome layer  121  is wrapped only on the surface of the carbon nanotubes in the carbon nanotube layer  120  and the holes between the carbon nanotubes are not covered by the chrome layer  121 . The microstructures obtained by the photolithography mask plate  600  have a high precision. 
     Referring to  FIG. 20 , an embodiment of a method of making the photolithography mask plate  600  comprises:
         S 91 , providing the carbon nanotube composite structure  141 , wherein the carbon nanotube composite structure  141  comprises a carbon nanotube layer  120  and a chrome layer  121  wraps the carbon nanotube layer  120 ;   S 92 , locating the carbon nanotube composite structure  141  on the surface of the second substrate  110  to expose partial surfaces of the second substrate  110 ;   S 93 , depositing a cover layer  130  on the surface of the carbon nanotube composite structure  141  away from the second substrate  110 .       

     The method of making the photolithography mask plate  600  is similar to the method of making the photolithography mask plate  500  except that the chrome layer  121  wraps the entire surface of the carbon nanotubes in the carbon nanotube layer  120 . When the ultraviolet light passes through the photolithography mask plate  600 , the ultraviolet light can pass through the chrome layer twice. The photolithography mask plate  600  has a higher absorption of UV light. 
     The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including in matters of shape, size, and arrangement of the parts within the principles of the present disclosure up to, and including, the full extent established by the broad general meaning of the terms used in the claims. 
     Depending on the embodiment, certain of the steps of methods described may be removed, others may be added, and the sequence of steps may be altered. The description and the claims drawn to a method may comprise some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.