Abstract:
A nano-imprinting process is described, comprising: providing a substrate including an imprinting material layer covering a surface of the substrate; providing a mold including protruding features set on a surface of the mold covered with an anti-adhesion layer; forming a transferring material layer on a top surface of each protruding feature; embedding the transferring material layer into a first portion of the imprinting material layer; removing the mold and separating the mold and the transferring material layer simultaneously to transfer the transferring material layer into the first portion of the imprinting material layer and to expose a second portion of the imprinting material layer; using the transferring material layer as a mask to remove the second portion of the imprinting material layer and a portion of the substrate; and removing the first portion of the imprinting material layer and the transferring material layer.

Description:
RELATED APPLICATIONS 
     This application claims priority to Taiwan Application Serial Number 96119831, filed Jun. 1, 2007, which is herein incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a macro/nano-imprinting process, and more particularly, to a mask-embedded imprinting process. 
     BACKGROUND OF THE INVENTION 
     In typical imprinting techniques, such as a hot embossed or laser assisted nano-imprinting, an external high energy heating source is needed to heat imprinting material layers to melt the imprinting material layers. However, during the high temperature heating treatment of the imprinting material layer, a substrate is in a high temperature circumstance, so that circuit layout structures pre-formed in the substrate are damaged, and an ill effect of stress remaining on the surface of the substrate is caused by a large temperature difference. 
     In addition, an imprinting material adopted in an ultraviolet (UV) curing nano-imprinting technique is in a liquid state at room temperature. In the transferring of a pattern of a mold, the mold is pressed into the imprinting material, and then the imprinting material is cured by ultraviolet to transfer the pattern structure of the mold into the imprinting material. The mold adopted in the ultraviolet curing nano-imprinting technique has to be made of a material that is pervious to ultraviolet, such as a quartz mold, or a PDMS mold formed by a mold-making technique. However, the manufacturing processes of the quartz mold and the PDMS mold both are very complicated, and the quartz mold and the PDMS mold are difficult to be manufactured, so that the molds are expensive. 
     In a soft lithography nano-imprinting technique, special ink is adopted as a material for pattern definition. However, the special ink is very expensive, and the ink spreads when a feature pattern is defined to an imprinting material layer to cause a defect of the inaccurate definition of the feature pattern. 
       FIGS. 1A through 1F  are schematic flow diagrams showing a conventional imprinting process. In a typical imprinting process, a substrate  100  is firstly provided, and an imprinting material layer  102  is coated on a surface  108  of the substrate  100 , wherein the imprinting material layer  102  has to be made of a thermoplastic polymer material. Simultaneously, a mold  104  is provided, wherein a surface of the mold  104  is set with a pattern structure  106 . As shown in  FIG. 1A , in the step of providing the mold  104 , the surface of the mold  104  with the pattern structure  106  is opposite to the surface  108  of the substrate  100  coating with the imprinting material layer  102 . 
     Then, a heating step is performed to melt the imprinting material layer  102 . The mold  104  is pressed into the melted imprinting material layer  102  to transfer the pattern structure  106  of the mold  104  into the imprinting material layer  102 , such as shown in  FIG. 1B . Subsequently, a heating source is removed. After the temperature is reduced to the value below the glass transition temperature of the imprinting material layer  102 , a mold-releasing step is performed to separate the mold  104  and the imprinting material layer  102 , so as to transfer the pattern of the pattern structure  106  of the mold  104  onto the imprinting material layer  102 , such as shown in  FIG. 1C . 
     Next, the imprinting material layer  102  is etched to remove a portion of the imprinting material layer  102  until a portion of the surface  108  of the substrate  100  is exposed, such as shown in  FIG. 1D . When the exposed surface  108  of the substrate  100  is etched by using the imprinting material layer  102  remained on the surface  108  of the substrate  100  as an etching mask, a portion of the imprinting material layer  102  is easily removed to damage the transferring pattern. As a result, a distortion phenomenon occurs when the pattern is transferred onto the substrate  100 . Therefore, a mask layer  110  is additionally formed on the imprinting material layer  102  and the exposed surface  108  of the substrate  100 , such as shown in  FIG. 1E . 
     After the formation of the mask layer  110  is completed, the imprinting material layer  102  and the mask layer  110  on the imprinting material layer  102  are removed by a lift-off process to expose the underlying surface  108  of the substrate  100 . Then, the exposed surface  108  of the substrate  100  may be etched by using the remaining mask layer  110  as the etching mask to remove a portion of the substrate  100 , so as to form a pattern structure  112  on the surface  108  of the substrate  100  to further transfer the pattern of the imprinting material layer  102  onto the surface  108  of the substrate  100 . Subsequently, as shown in  FIG. 1F , the remaining mask layer  110  and the imprinting material layer  102  are removed to complete the imprinting process. 
     In the conventional imprinting process, the imprinting material layer  102  has to be etched until a portion of the surface  108  of the substrate  100  is exposed, and then the mask layer  110  as the etching mask is set on the exposed surface  108  of the substrate  100 . However, the step of setting the mask layer  110  is very complicated, and the procedures of firstly etching the imprinting material layer  102  and then setting the mask layer  110  increase the complexity of the process. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is to provide a nano-imprinting process, which can simplify the complicated steps required in typical nano-imprinting processes, so that the degradation of the accuracy caused by multiple processes can be reduced to rapidly and accurately define feature patterns to an imprinting material layer on a surface of a substrate desired to be imprinted, and to greatly reduce the contamination resulted from the processes. 
     Another aspect of the present invention is to provide a nano-imprinting process, in which the formation of an etching/exposure mask required in the definition of feature patterns on an imprinting material layer and a subsequent dry etching or exposure process can be completed by directly embedding the exposure/etching mask into the imprinting material layer, so that the time and the fabrication cost of the nano-imprinting process can be greatly reduced, to achieve low-cost, rapid and large-area imprinting. Therefore, the nano-imprinting process has great ability of mass production. 
     Still another aspect of the present invention is to provide a nano-imprinting process, which does not need an external heating source with high temperature during the imprinting process, so that the consumption of the energy can be saved to greatly reduce the production cost and to achieve an environment-friendly nano-imprinting process with low energy consumption. 
     Yet another aspect of the present invention is to provide a nano-imprinting process, which does not need an applied heating source with high temperature, so that electronic devices preset on a substrate will not be damaged by heat to enhance the process yield and the product reliability. 
     According to the aforementioned objectives, the present invention provides a nano-imprinting process, comprising: providing a substrate including an imprinting material layer covering a surface of the substrate; providing a mold including a plurality of protruding features and at least one indentation set on a surface of the mold, wherein the indentation is disposed between the protruding features, and the surface of the mold is covered with an anti-adhesion layer; forming a transferring material layer on a top surface of each protruding feature; pressing the surface of the mold into the imprinting material layer to make the transferring material layer embed in a first portion of the imprinting material layer; removing the mold and separating the mold and the transferring material layer simultaneously to transfer the transferring material layer into the first portion of the imprinting material layer and to expose a second portion of the imprinting material layer; using the transferring material layer as a mask to remove the second portion of the imprinting material layer and a portion of the substrate underlying the second portion of the imprinting material layer; and removing the first portion of the imprinting material layer and the transferring material layer. 
     According to a preferred embodiment of the present invention, the material of the substrate may be a silicon wafer, the material of the imprinting material layer may be PMMA, the material of the mold may be silicon, the material of the anti-adhesion layer may be 1H, 1H, 2H, 2H-perfluorooctyl-trichlorosilane, and the transferring material layer may be a chromium metal film. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention are more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIGS. 1A through 1F  are schematic flow diagrams showing a conventional imprinting process. 
         FIGS. 2A through 2F  are schematic flow diagrams showing a nano-imprinting process in accordance with a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention discloses a nano-imprinting process, which can directly embed an etching mask into an imprinting material layer, so that the process can be effectively simplified to rapidly and accurately complete the nano-imprinting process. In order to make the illustration of the present invention more explicit, the following description is stated with reference to  FIGS. 2A through 2F . 
       FIGS. 2A through 2F  are schematic flow diagrams showing a nano-imprinting process in accordance with a preferred embodiment of the present invention. In an exemplary embodiment, a substrate  200  is provided, wherein the substrate  200  includes a surface  204  and a surface  206  on opposite sides. The material of the substrate  200  is, for example, a semiconductor material, a plastic material, a piezoelectric material, a dielectric material, a glass material, a ceramic material, an electrically conductive material, metal or any combinations of the aforementioned materials. In an embodiment, a silicon wafer may be adopted as the substrate  200 . In a preferred embodiment, the substrate  200  can be further set with at least one pair of alignment marks to facilitate alignment in the following processes. The surface  204  of the substrate  200  is covered with an imprinting material layer  208 , wherein the imprinting material layer  208  may be formed on the surface  204  of the substrate  200  by, for example a spin coating method, to make the imprinting material layer  208  uniformly distribute on the surface  204  of the substrate  200 . The material of the imprinting material layer  208  may be a polymer-based material, such as a thermoplastic polymer material. The material of the imprinting material layer  208  may be composed of a photoresist material to facilitate the subsequent pattern definition. In an embodiment, the material of the imprinting material layer  208  may be PMMA, such as PMMA 950K (PMMA having a molecular weight of 950000) provided by MicroChem Co., Ltd.. In other embodiments, the material of the imprinting material layer  208  may be photoresist SAL-601 provided by Shipley Company, photoresist ZEP 520A provided by ZEON Co., Ltd., or photoresist NEB 31 provided by Sumitomo Chemical Co., Ltd. 
     When the substrate  200  is provided, a mold  202  for imprinting is provided, wherein the mold  202  includes surfaces  210  and  212  on opposite sides. The hardness of the mold  202  is larger than that of the imprinting material layer  208 , wherein the material of the mold  202  is, for example, a semiconductor material, a plastic material, a piezoelectric material, a dielectric material, a glass material, a ceramic material, an electrically conductive material, metal or any combinations of the aforementioned materials. In an embodiment, a silicon wafer may be adopted as the mold  202 . The surface  210  of the mold  202  is set with a pattern structure, wherein the pattern structure includes a plurality of protruding features  214  and at least one indentation  216 , wherein the protruding features  214  protrude on the surface  210  of the mold  202 , and the indentation  216  is disposed between the protruding features  214 . In an exemplary embodiment, the size of the protruding features  214  may be on the micrometer scale or the nanometer scale. In a preferred embodiment, the mold  202  is also set with a pair of alignment marks corresponding to the alignment marks on the substrate  200  to facilitate alignment in the following processes. An anti-adhesion layer  218  is formed to cover the surface  210  of the mold  202  set with the protruding features  214  by, for example, an evaporation method, to ensure that a transferring material layer  228  can be successfully and completely transferred to the imprinting material layer  208  when the mold  202  contacts with the imprinting material layer  208  under the applying of an external pressure. The anti-adhesion layer  218  includes any materials that can make the transferring material layer  228  subsequently formed on the anti-adhesion layer  218  come off the surface  210  of the mold  202  and be transferred onto the surface of the imprinting material layer  208 . In an exemplary embodiment, the material of the anti-adhesion layer  218  may be composed of 1H, 1H, 2H, 2H-perfluorooctyl-trichlorosilane while the material of the mold  202  is silicon. 
     Next, the transferring material layer  228  is formed on the surface  210  of the mold  202  by, for example, an evaporation method, such as an electron beam evaporation method. In an exemplary embodiment, because the transferring material layer  228  is formed by the evaporation process, the transferring material layer  228  is composed of two separated transferring material portions  220  and  222 , wherein the transferring material portions  220  are deposited on a top surface of each protruding feature  214 , and the transferring material portion  222  is deposited on a bottom surface of the indentation  216 , such as shown in  FIG. 2A . In another exemplary embodiment, the transferring material layer  228  is only deposited on the top surface of each protruding feature  214 , i.e. the transferring material layer  228  only consists of the transferring material portions  220  on the top surfaces of the protruding features  214 , by further using other definition technique, such as a photolithography and etching technique or a lift-off technique. The transferring material layer  228  is used as a mask structure in the subsequent process steps of exposing or etching the imprinting material layer  208  and etching the substrate  200 , so that the transferring material layer  228  is preferably composed of a material that cannot be exposed to an exposure light of the imprinting material layer  208 , or a material that has larger etching selectivity with the imprinting material layer  208  and the substrate  200 . The material of the transferring material layer  228  is, for example, a semiconductor material, a plastic material, a piezoelectric material, an oxide material, a dielectric material, a glass material, a ceramic material, an electrically conductive material, metal or any combinations of the aforementioned materials. In an embodiment, the transferring material layer  228  may be a metal film, preferably a chromium metal film. In addition, in an exemplary embodiment, a ration of the thickness of the imprinting material layer  208  to that of the transferring material layer  228  is controlled in a value less than 100, preferably in a value less than 10. When the mold  202  and substrate  200  are disposed, the surface  210  of the mold  202  including the protruding features  214  set thereon is opposite to the surface  204  of the substrate  200  including the imprinting material layer  208  formed thereon, such as shown in  FIG. 2A . 
     Then, a pressing step is performed on the mold  202  and the substrate  200 . In an embodiment, a pressure  230  may be applied in the pressing step to directly press the surface  210  of the mold  202  against the surface  204  of the substrate  200  to make the transferring material portion  220  on the top surface of each protruding feature  214  completely or partly be pressed into a portion of the imprinting material layer  208  on the substrate  200 , so as to make the transferring material portion  220  on the top surface of each protruding feature  214  completely or partly be embedded into some regions of the imprinting material layer  208 . For example, as shown in  FIG. 2B , the transferring material portions  220  on the top surfaces of the protruding features  214  are embedded in the some regions of the imprinting material layer  208  locally. However, in some embodiments, in the pressing step, the mold  202  is disposed on the substrate  200 , wherein the surface  210  of the mold  202  is opposite to the surface  204  of the substrate  200 , and the protruding features  214  on the surface  210  of the mold  202  closely adhere to the imprinting material layer  208  on the surface  204  of the substrate  200 ; and then the pressure  230  is applied to press the transferring material portions  220  on the top surfaces of the protruding features  214  of the mold  202  into a portion of the imprinting material layer  208  on the surface  204  of the substrate  200 . In the illustrated embodiment shown in  FIG. 2B , the pressure  230  is applied on the mold  202  from the surface  212  of the mold  202  to the surface  210 . However, in other embodiments, in the pressing step, the pressure may be applied on the substrate  200  from the surface  206  of the substrate  200  to the surface  204 ; or, the pressures may be simultaneously applied on the surface  206  of the substrate  200  and the surface  212  of the mold  202  to make the surface  204  of the substrate  200  be oppositely connected to the surface  210  of the mold  202 , so as to make the pressure distribution between the mold  202  and the imprinting material layer  208  on the substrate  200  more uniform. In the pressing step to connect the substrate  200  and the mold  202 , the alignment marks on the substrate  200  and the mold  202  may be used to determine the relative location between the substrate  200  and the mold  202  during pressing. 
     In the step of pressing and connecting the mold  202  and the substrate  200 , a baking treatment is selectively applied on the imprinting material layer  208  by heating the substrate  200 . In the baking treatment, a low-temperature heating method, such as a heating method with a heating temperature lower than about 120° C., is preferably adopted. Through the baking treatment, the diluted solvent within the imprinting material layer  208 , which is in a liquid state at room temperature, can be evaporated or volatilized, to increase the solidification rate of the imprinting material layer  208  so as to rapidly increase the viscosity of the imprinting material layer  208 . As a result, the adhesion force between the transferring material portions  220  pressed in the imprinting material layer  208  and the imprinting material layer  208  is larger than the adhesion force between the transferring material layer  228  and the anti-adhesion layer  218 . Accordingly, as shown in  FIG. 2C , in a mold-releasing step following the pressing step, when the mold  202  is removed, the transferring material portions  220  can successfully be separated from the anti-adhesion layer  218  on the mold  202  to embed into a portion of the imprinting material layer  208 , so as to be completely transferred into the imprinting material layer  208 . At present, the transferring material portions  220  have been successfully embedded into the imprinting material layer  208  and can be used as a photomask for the subsequent exposure and development step or as an etching mask for the subsequent etching step. The baking treatment of the imprinting material layer  208  may be performed by using an electrical resistance heating source, an eddy current heating source, an electromagnetic heating source or an optical heating source. After the mold  202  is removed, a portion of the imprinting material layer  208  that is not embedded by the transferring material portions  220  is exposed. 
     Next, the exposed portion of the imprinting material layer  208  is removed by an exposure and development method, or an etching method. In an exemplary embodiment, an exposure light source is used to expose the exposed portion of the imprinting material layer  208  composed of, for example, positive photoresist by using the transferring material portions  220  as the photomask, and then the exposed portion of the imprinting material layer  208  is removed by developing to expose a surface portion  224  of the underlying substrate  200  and to form an imprinting material layer  208   a  under the transferring material portions  220 , such as shown in  FIG. 2D . The exposure light source is, for example, deep UV light, UV light, a laser, a x-ray, an electron beam or an ion beam. The wavelength of the exposure light source is preferably between 0.05 Å to 100 μm. The laser among the exposure light sources may be an excimer laser, and the wavelength of the excimer laser is, for example, KrF-248 nm, ArF-193 nm, XeCl-308 nm or XeF-351 nm. In an embodiment, if the material of the imprinting material layer  208  is PMMA 950K A6, a suitable exposure light source may be deep UV light or electron beam. In another embodiment, if an electron beam is adopted as the exposure light source, the material of the imprinting material layer  208  may be PMMA, photoresist SAL-601, photoresist ZEP 520A or photoresist NEB 31. 
     In another exemplary embodiment, the exposed portion of the imprinting material layer  208  is removed by etching, so that two etching steps are used in the exemplary embodiment to respectively remove the exposed portion of the imprinting material layer  208  and the portion of the substrate  200  underlying the exposed portion of the imprinting material layer  208 . The exposed portion of the imprinting material layer  208  is etched by using the transferring material portions  220  as the etching mask, to remove a portion of the imprinting material layer  208  until the underlying surface portion  224  of the substrate  200  is exposed and to form the imprinting material layer  208   a  under the transferring material portions  220 , such as shown in  FIG. 2D . In the etching of the exposed portion of the imprinting material layer  208 , a dry etch method, such as a reactive ion etching (RIE) method or a deep reactive ion etching (DRIE) method, may be used, and O 2  plasma is used as the etchant for etching, for example. 
     After the exposed portion of the imprinting material layer is removed by an exposure and development process or an etching method, the exposed surface portion  224  of the substrate  200  is etched by using the transferring material portions  220  and the underlying imprinting material layer  208   a  as the etching mask structure, to remove a portion of the substrate  200 , so as to form a pattern structure  226  on the surface  204  of the substrate  200  to successfully transfer the pattern of the pattern structure of the mold  202  to the surface  204  of the substrate  200 , such as shown in  FIG. 2E . In the etching of the portion of the substrate  200 , a dry etching method, such as a reactive ion etching method or a deep reactive ion etching method, may be used, and SF 6  plasma is used as the etchant for etching, for example. 
     Subsequently, as shown in  FIG. 2F , the remaining imprinting material layer  208   a  and the overlying transferring material portions  220  are removed by, for example, a lift-off method, to expose the other portion of the surface  204  of the substrate  200 , so as to complete the nano-imprinting process of the surface  204  of the substrate  200 . 
     In an exemplary embodiment, the imprinting process can be repeatedly performed on the same imprinting substrate, such as different regions of a wafer, until the imprinting procedures of the desired regions of the entire substrate are completed; or the imprinting process can be repeatedly performed on different layers on the same region of the same imprinting substrate so as to form a structure including multiple imprinting layers. In addition, the imprinting process can be performed in an automatic imprinting stage to further speed up the imprinting process. 
     According to the aforementioned embodiments, the nano-imprinting process of one exemplary embodiment of the present invention can simplify the complicated steps required in typical nano-imprinting processes, so that the degradation of the accuracy caused by multiple processes can be reduced to rapidly and accurately define feature patterns to an imprinting material layer on a surface of a substrate desired to be imprinted, and to further lighten the burden on the environment caused by the processes. 
     According to the aforementioned embodiments, the nano-imprinting process of one exemplary embodiment of the present invention can complete the formation of an etching/exposure mask required in the definition of feature patterns on an imprinting material layer and a subsequent dry etching or exposure process by directly embedding the photo/etching mask into the imprinting material layer, so that the time and the fabrication cost of the nano-imprinting process can be greatly reduced, to achieve low-cost, rapid and large-area imprinting. Therefore, the nano-imprinting process of one exemplary embodiment has great ability of mass production. 
     According to the aforementioned embodiments, the nano-imprinting process of one exemplary embodiment of the present invention does not need an external heating source with high temperature during the imprinting process, so that the consumption of the energy can be saved to greatly reduce the production cost and to achieve an environment-friendly nano-imprinting process with low energy consumption. 
     According to the aforementioned embodiments, the nano-imprinting process of one exemplary embodiment of the present invention does not need an applied heating source with high temperature, so that electronic devices preset on a substrate will not be damaged by heat to enhance the process yield and the product reliability. 
     As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.