Abstract:
An imprint process of a thermosetting material is described, comprising: providing a mold including pattern structures, wherein convex portions and concave portions of the pattern structures are covered with a transferred material layer; providing a substrate, wherein a thermosetting material layer and a sacrificial layer cover the substrate in sequence; performing an imprint step to transfer the transferred material layer on the convex portions onto a first portion of the sacrificial layer; etching a second portion of the sacrificial layer and the underlying thermosetting material layer by using the transferred material layer as a mask; and performing a wet stripping step by using a stripper to completely etch the sacrificial layer and the overlying transferred material layer, wherein the stripper has a first etching rate and a second etching rate to the thermosetting material layer and the sacrificial layer respectively, and a ratio of the second etching rate to the first etching rate is greater than or equal to 30.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to Taiwan Application Serial Number 98100535, filed Jan. 8, 2009, which is herein incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to an imprint process, and more particularly to an imprint process of a thermosetting material. 
       BACKGROUND OF THE INVENTION  
       [0003]    A thermosetting material, such as polyimide (PI), is a material with high heat resistance, a great mechanical property, a superior optical property and a low dielectric constant, so that the thermosetting material has been widely applied in flexible printed circuit (FPC) boards, electronic packages, optical waveguides, alignment films of liquid crystal displays (LCD) and microfluidic devices. In the application, the thermosetting material typically needs to be patterned by a pattern definition technology to form the desired pattern structure for use. 
         [0004]    Several technologies, such as laser machining technology, conventional photolithography technology, new photolithography technology, and nano-imprint technology including, for example soft imprint technology and hot-embossing technology, have been developed to pattern the thermosetting material. When the laser machining technology patterns the thermosetting material, the laser directly irradiates the thermosetting material layer through a mask to remove a portion of the thermosetting material layer to complete the thermosetting material pattern structures. However, when the laser machining technology patterns the thermosetting material, irradiation of many laser shots is required, so that the process is time-consuming and consumes large amounts of laser energy, thereby increasing the cost. Moreover, due to the size of the laser beam and the optical diffraction limit, the laser machining technology cannot produce the pattern with too small size, such as the thermosetting material pattern structures with the nanometer scale. 
         [0005]    When the conventional photolithography technology is used to pattern a thermosetting material layer, a photoresist layer is firstly coated on the thermosetting material layer, the photoresist layer is patterned by the exposure and development technology, and then the thermosetting material layer is etched with tile patterned photoresist layer as the etching mask to complete the thermosetting material pattern structures. However, due to the wavelength limit of the exposure light source, the feature size of the thermosetting material pattern strictures produced by the conventional photolithography technology has a limit, so that the pattern structures with a smaller size cannot be produced. 
         [0006]    When the new photolithography technology is used to pattern the thermosetting material, a photosensitive thermosetting material is needed, the bonding link in parts of directions of the thermosetting material is destroyed by directly using the light source, such as deep ultraviolet, and the exposed thermosetting material layer is developed to complete the pattern structures of the thermosetting material. However, the surface roughness of the thermosetting material pattern structure formed by the new photolithography technology is poor, there still exists many issues in the positive tone and negative tone photosensitive thermosetting materials, such as that the adjustment of the ingredients of the material is difficult, and the control of the process parameters and the machining precision of the thermosetting material is difficult to result in the poor fidelity and the reliability of pattern transferring. In addition, similarly, due to the wavelength limit of the exposure light source, the new photolithography technology cannot produce the thermosetting material pattern structures with a smaller size. Furthermore, the negative tone photosensitive thermosetting material is swelling after the developing process, so that the fidelity of the pattern transferring is further decreased. 
         [0007]    When the soft nanoimprint technology is used to pattern the thermosetting material, such as polyimide, and the imprint mold is pressed into the liquid poly(amic acid) (PAA) that has not been heated to form the solid polyimide, it is easy for bubbles to form between the pattern structures of the imprint mold and the liquid poly(amic acid) after heating, and these bubbles are formed on the surface of the polyimide. Therefore, the surface of the pattern structures of the thermosetting material formed by the soft nanoimprint technology has many holes, so that the surface roughness of the thermosetting material pattern structures is poor, and the mechanical strength of the thermosetting material pattern structures is reduced. Moreover, when the liquid poly(amic acid) is heated to solidify the liquid poly(amic acid) to form the polyimide before the mold is removed, the solvent of the poly(amic acid) is evaporated, so that the volume of the thermosetting material pattern structures is decreased to lower the fidelity of the pattern transferring. 
         [0008]    When the hot embossing nanoimprint technology is used to pattern the thermosetting material, the imprint temperature needs to be raised to more than the glass transition temperature (Tg) 300° C. of the thermosetting material. In addition, due to the heat, the remaining thermal stress, the expansion and the shrink effects occur on the mold and the substrate simultaneously, thereby seriously affecting the substrate material and the size of the thermosetting material pattern structures to reduce the reliability of the pattern transferring. 
       SUMMARY OF THE INVENTION 
       [0009]    Therefore, one objective of the present invention is to provide an imprint process of a thermosetting material, which can accurately transfer a pattern on an imprint mold to a thermosetting material layer, thereby effectively increasing the accuracy and the reliability of the pattern transferred to the thermosetting material layer. 
         [0010]    Another objective of the present invention is to provide an imprint process of a thermosetting material, which can successively define the pattern of the thermosetting material with low thermal budget and under relatively lower temperatures compared with the hot embossing nanoimprint process, thereby reducing the process cost and preventing the feature size of the transferred pattern of the thermosetting material from being distorted. Furthermore, the remaining thermal stress formed on the substrate and the thermosetting material layer due to high temperature can be decreased, and the substrate and the thermosetting material layer can be prevented from being damaged. 
         [0011]    According to the aforementioned objectives, the present invention provides an imprint process of a thermosetting material, comprising: providing a mold including a pattern structure, wherein the pattern structure comprises a plurality of convex portions and a plurality of concave portions; forming a transferred material layer on the convex portions and the concave portions; providing a substrate, wherein a surface of the substrate is covered with a thermosetting material layer and a sacrificial layer in sequence; performing an imprint step to transfer the transferred material layer on the convex portions onto a first portion of the sacrificial layer and to expose a second portion of the sacrificial layer; dry etching the second portion of the sacrificial layer and a second portion of the underlying thermosetting material layer to remain the first portion of the sacrificial layer and a first portion of the underlying thermosetting material layer by using the transferred material layer as a mask; and performing a wet stripping step by using a stripper to completely etch the first portion of the sacrificial layer and to lift off the overlying transferred material layer, wherein the stripper has a first etching rate and a second etching rate to the thermosetting material layer and the sacrificial layer respectively, and a ratio of the second etching rate to the first etching rate is greater than or equal to 30. 
         [0012]    According to a preferred embodiment of the present invention, the material of the sacrificial layer may be PMMA 950K A6 provided by MicroChem Corp., Newton, Mass., U.S.A. or photoresist S1818 provided by Shipley Company, L.L.C., Marlborough, Mass., U.S.A., the stripper may be acetone, such as TAIMAX acetone provided by Taiwan Maxwave Co., Ltd. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    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: 
           [0014]      FIGS. 1A through 1H  are schematic flow diagrams showing an imprint process of a thermosetting material in accordance with a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]      FIGS. 1A through 1H  are schematic flow diagrams showing an imprint process of a thermosetting material in accordance with a preferred embodiment of the present invention. In an exemplary embodiment, when the imprint process of a thermosetting material is performed, a mold  100  may be provided to perform the imprint process. A pattern structure  104  is set in a surface  102  of the mold  100 , wherein the pattern structure  104  comprises a plurality of concave portions  108  and a plurality of convex portions  106 . The feature size of the pattern structure  104  may be micrometer scale or nanometer scale. Next, such as shown in  FIG. 1A , an anti-stick layer  110  is selectively formed to cover the pattern structure  104  of the mold  100  by, for example, a thermal evaporation method, wherein the anti-stick layer  110  includes two portions  110   a  and  110   b,  the portion  110   a  of the anti-stick layer  110  covers on bottoms of the concave portions  108  of the pattern structure  104 , and the portion  110   b  of the anti-stick layer  110  covers on top surfaces of the convex portions  106  of the pattern structure  104 . In another exemplary embodiment, when the material of the mold  100  itself has an anti-stick property, such as ethylene tetrafluoroethylene [—(C2H4-C2F4)-] provided by DuPont Company, the anti-stick layer  110  does not need to be formed additionally. 
         [0016]    Next, such as shown in  FIG. 1B , a transferred material layer  112  is formed on the anti-stick layer  110  by using, for example a thermal evaporation method, an e-beam evaporation method, a chemical vapor deposition method or a physical vapor deposition method cooperating with a typical pattern definition technique, wherein the transferred material layer  112  also includes portions  112   a  and  112   b,  the portions  112   a  of the transferred material layer  112  are located on the portion  110   a  of the anti-stick layer  110  within the concave portions  108  of the pattern structure  104 , and the portions  112   b  of the transferred material layer  112  are located on the portion  111   b  of the anti-stick layer  110  on the top surfaces of the convex portions  106  of the pattern structure  104 . In another exemplary embodiment, when the material of the mold  100  itself has an anti-stick property and the anti-stick layer  110  is not formed, the transferred material layer  112  directly covers the pattern structure  104  of the mold  100 , wherein the portions  112   a  of the transferred material layer  112  are directly located on die bottoms of the concave portions  108  of the pattern structure  104 , and the portions  112   b  of the transferred material layer  112  are directly located on the top surfaces of the convex portions  106  of the pattern structure  104 . The material of the transferred material layer  112  may be metal, oxide or a dielectric material. In one embodiment, the material of the transferred material layer  112  may be chromium (Cr). In another embodiment, the material of the transferred material layer  112  may be a dielectric material and oxide, such as silicon dioxide (SiO 2 ). By disposing the anti-stick layer  110  or adopting the mold  100  having an anti-stick property, the portions  112   b  of the transferred material layer  112  on the convex portions  106  of the mold  100  can be successively separated from the convex portions  106  of the mold  100 . 
         [0017]    Simultaneously, a substrate  114  desired to be imprinted is provided, wherein the substrate  114  is preferably composed of a material that can resist the etching of the stripper  130  (referring to  FIG. 1G ). The material of the substrate  114  may be, for example, silicon wafer, glass, quartz or metal. A thermosetting material layer  118  is formed to cover a surface  116  of the substrate  114  by, for example, a physical vapor deposition method, a chemical vapor deposition method or a coating method. In some embodiments, the material of the thermosetting material layer  118  may be, for example, polyimide or polyethersulfone (PES), wherein each polyimide and polyethersulfone is a material having a high glass transition temperature. In an exemplary embodiment, the material of the thermosetting material layer  118  may be RN-1349 polyimide provided by Nissan Chemical Industries. Next, the thermosetting material layer  118  may be baked to dry the solvent in the thermosetting material layer  118 . Then, such as shown in  FIG. 1C , a sacrificial layer  120  is formed to cover the thermosetting material layer  118  by, for example, a deposition method or a coating method. In an exemplary embodiment, the material of the sacrificial layer  120  may be polymethylmethacrylate (PMMA) or photoresist S1818 provided by Shipley Company, L.L.C., Marlborough, Mass., U.S.A. The material of the sacrificial layer  120  also may be PMMA 950K A6 provided by MicroChem Corp., Newton, Mass., U.S.A. The choice of the materials of the thermosetting material layer  118  and the sacrificial layer  120  is in relation to the stripper  130  (referring to  FIG. 1G ), wherein the stripper  130  has two different etching rates to the thermosetting material layer  118  and the sacrificial layer  120  respectively, and the etching rate of the stripper  130  to the sacrificial layer  120  is much larger than that of the stripper  130  to the thermosetting material layer  118 . Therefore, when the sacrificial layer  120  is completely removed by the stripper  130 , the thermosetting material layer  118  may hardly be etched by the stripper  130  and is kept. In an exemplary embodiment, the ratio of the etching rate of the stripper  130  to the sacrificial layer  120  to the etching rate of the stripper  130  to the thermosetting material layer  118  may be preferably larger than or equal to 30, more preferably be larger than or equal to 40, and further more preferably be larger than or equal to 50. 
         [0018]    Next, referring to  FIG. 1D , an imprint step is performed, wherein the surface  102  of the mold  100  is oppositely pressed on the surface  116  of the substrate  114  to press the portions  112   b  of the transferred material layer  112  on the convex portions  106  of the pattern structure  104  of the mold  100  on the liquid status of the sacrificial layer  120  on the substrate  114  and contact with the sacrificial layer  120 . After the portions  112   b  of the transferred material layer  112  on the mold  100  are pressed on the sacrificial layer  120  on the substrate  114 , the sacrificial layer  120  is baked at substantially 95° C. in substantially five minutes to dry the sacrificial layer  120 . After the temperature is lowered to room temperature, the mold  100  is removed from the sacrificial layer  120 . At this time, the convex portions  106  of the pattern structure  104  of the mold  100  are covered with the anti-stick layer  110  to make the anti-stick layer  110  be located between the surface  102  of the mold  100  and the transferred material layer  112 , or the mold  100  itself has an anti-stick property, so that the portions  112   b  of the transferred material layer  112  on the convex portions  106  of the pattern structure  104  of the mold  100  can be successfully separated from the mold  100  to transfer to the surface of the sacrificial layer  120  to complete the imprint step. After the imprint step is completed, the portions  112   b  of the transferred material layer  112  are only transferred to a first portion  122  of the sacrificial material layer  120 , and a second portion  124  of the sacrificial layer  120  is exposed, such as shown in  FIG. 1E . 
         [0019]    Next, referring to  FIG. 1F , the second portion  124  of the sacrificial layer  120  uncovered by the portions  112   b  of the transferred material layer  112  and the portion of the thermosetting material layer  118  underlying the second portion  124  are removed until a portion of the surface  116  of the substrate  114  underlying the second portion  124  of the sacrificial layer  120  is exposed, and the first portion  122  of the sacrificial layer  120  and a first portion  126  of the thermosetting material layer  118  underlying the first portion  122  are maintained. In another embodiment, according to the difference of the applications of the products, the removal step may only remove the second portion  124  of the sacrificial layer  120  and a portion of the thermosetting material layer  118  underlying the second portion  124  of the sacrificial layer  120  to keep the first portion  122  of the sacrificial layer  120 , the other portion of the thermosetting material layer  118  underlying the second portion  124  of the sacrificial layer  120 , and the first portion  126  of the thermosetting material layer  118  underlying the first portion  122 . Accordingly, the surface  116  of the substrate  114  underlying the second portion  124  of the sacrificial layer  120  is not exposed. In a preferred embodiment, in the removal of a portion of the sacrificial layer  120  and a portion of the thermosetting material layer  118 , an etching method, such as a dry etching method, may be adopted, and the portions  112   b  of the transferred material layer  112  on the first portion  122  of the sacrificial layer  120  may be used as the etching mask to etch and remove the portion of the sacrificial layer  120  and the portion of the thermosetting material layer  118 . The dry etching method may be, for example, a reactive ion etching (RIE) technique or an inductively coupled plasma (ICP) ion etching technique. In some embodiments, when the dry etching method, such as the reactive ion etching method or the inductively coupled plasma ion etching method, is used to perform the etching of the sacrificial layer  120  and the thermosetting material layer  118 , oxygen may be used as the main reactive gas. For example, oxygen, or oxygen and argon of specially designated ratio may be used as the etching reactive gas. In the present exemplary embodiment, the adjacent portions  112   b  of the transferred material layer  112  pressed on the first portion  122  of the sacrificial layer  120  have a pitch  134 . 
         [0020]    According to the experiment discovery, the photosensitive photoresist material is used as the etching mask to pattern the thermosetting material layer in the conventional photolithography technique, and the photoresist layer swells due to that the photoresist layer absorbing a portion of the developer during the development process, so that the volume of the photoresist layer is expanded. Therefore, when the photoresist layer with the expanded volume is used as the etching mask to etch the pattern of the underlying material layer, the feature size of the formed pattern structure of the material layer is distorted. However, in a preferred embodiment of the present invention, the portions  112   b  of the transferred material layer  112  on the first portion  122  of the sacrificial layer  120  are used as the etching mask without using the photoresist layer as the etching mask, and the transferred material layer  112  does not experience the exposing and developing process, so that the transferred material layer  112  will not swell due to the developer. Therefore, by using the transferred material layer  112  as the dry etching mask, it can ensure that the pattern structures of the etched sacrificial layer  120  and the thermosetting material layer  118  are not distorted to greatly increase the fidelity of the achieved pattern structures of the sacrificial layer  120  and the thermosetting material layer  1118 . 
         [0021]    Then, referring to  FIG. 1G , a stripping tank  128  that can resist the etching of the stripper  130  is provided, wherein the stripping tank  128  is filled with the stripper  130  for the wet stripping step. Next, the substrate  114 , and the portions  112   b  of the transferred material layer  112 , the first portion  122  of the sacrificial layer  120  and the first portion  126  of the thermosetting material layer  118  on the substrate  114  are entirely immersed in the stripper  130  in the stripping tank  128  to use the stripper  130  to completely etch and remove the first portion  122  of the sacrificial layer  120  and to lift off the portions  112   b  of the transferred material layer  112  on the first portion  122  of the sacrificial layer  122  while the thermosetting material layer  118  may hardly be etched by the stripper  130 . Therefore, the etching rate of the stripper  130  to the first portion  122  of the sacrificial layer  120  must be far larger than that of the stripper  130  to the first portion  126  of the thermosetting material layer  118 . In one embodiment, the ratio of the etching rate of the stripper  130  to the sacrificial layer  120  to the etching rate of the stripper  130  to the thermosetting material layer  118  may be, for example, larger than or equal to 30, more preferably be larger than or equal to 40, and further more preferably be larger than or equal to 50. 
         [0022]    In a preferred embodiment, the thermosetting material layer  118  may be composed of, for example, RN-1349 polyimide provided by Nissan Chemical Industries, the sacrificial layer  120  may be composed of, for example, PMMA, such as PMMA 950K A6 provided by MicroChem Corp., Newton, Mass., U.S.A., and the stripper  130  may be composed of TAIMAX acetone provided by Taiwan Maxwave Co., Ltd. In another preferred embodiment, the thermosetting material layer  118  may be RN-1349 polyimide provided by Nissan Chemical Industries, the sacrificial layer  120  may be photoresist S1818 provided by Shipley Company, L.L.C., Marlborough, Mass., U.S.A., and the stripper  130  may be acetone, such as TAIMAX acetone provided by Taiwan Maxwave Co., Ltd. After the etching of the first portion  122  of the sacrificial layer  120  is completed, the substrate  114  and the first portion  126  of the thermosetting material layer  118  on the substrate  114  are removed from the stripping tank  128  and are rinsed with the deionized water, and then a heating and baking treatment is performed to bake under substantially 100° C. for substantially three minutes. The first portion  126  of the thermosetting material layer  118  remained on the substrate  114  is the pattern structure  132  with the desired pattern, and the pattern of the pattern structure  132  are completely and reliably transferred from the pattern of the pattern stricture  104  of the mold  100 . 
         [0023]    The etching rate of the stripper  130  to the thermosetting material layer  118  is very small, and the etching rate of the stripper  130  to the sacrificial layer  120  is much larger than that of the stripper  130  to the thermosetting material layer  118 , so that the sacrificial layer  120  can be completely etched by the stripper  130  in a very short time. Therefore, when the sacrificial layer  120  has been completely removed by the stripper  130 , the first portion  126  of the thermosetting material layer  118  is hardly etched by the stripper  130  and is almost retained entirely, so as to precisely and exactly transfer the pattern of the pattern structure  104  of the mold  100  to the thermosetting material layer  118  to obtain the pattern structure  132  with the desired pattern. Accordingly, the pattern of the imprint mold  100  can be reliably transferred to the thermosetting material layer  118  with low thermal budget. Therefore, the fidelity and the reliability of the pattern transferred from the mold  100  to the thermosetting material layer  118  can be increased, and the process cost can be greatly reduced due to the decrease of the thermal budget. 
         [0024]    According to the aforementioned embodiments of the present invention, one advantage of the present invention is that an imprint process of a thermosetting material of the present invention can accurately transfer a pattern on an imprint mold to a thermosetting material layer, thereby effectively increasing the accuracy and the reliability of the pattern transferred to the thermosetting material layer. Furthermore, the imprint process can be completed under the relatively lower temperature compared with the hot embossing nanoimprint process, so that the remaining thermal stress formed on the substrate and the thermosetting material layer due to high temperature can be decreased, and the substrate and the thermosetting material layer can be prevented from being damaged. 
         [0025]    According to the aforementioned embodiments of the present invention, another advantage of the present invention is that an imprint process of a thermosetting material of the present invention can successively define the pattern of the thermosetting material with low thermal budget, thereby reducing the process cost and preventing the feature size of the transferred pattern of the thermosetting material from being distorted. 
         [0026]    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.