Abstract:
The present invention is directed toward a method for reducing pattern distortions in imprinting layers by reducing gas pockets present in a layer of viscous liquid deposited on a substrate. To that end, the method includes varying a transport of the gases disposed proximate to the viscous liquid. Specifically, the atmosphere proximate to the substrate wherein a pattern is to be recorded is saturated with gases that are either highly soluble, highly diffusive, or both with respect to either the viscous liquid, the substrate, the template, or a combination thereof. Additionally, or in lieu of saturating the atmosphere, the pressure of the atmosphere may be reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation-in-part of U.S. patent application Ser. No. 10/898,034 filed on Jul. 23, 2004 entitled “Method for Creating a Turbulent Flow of Fluid Between a Mold and a Substrate” which is a divisional of U.S. Pat. No. 7,090,716 filed on Oct. 2, 2003 entitled “Single Phase Fluid Imprint Lithography Method,” all of which are incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    The field of invention relates generally to imprint lithography. More particularly, the present invention is directed to a system for controlling a flow of a substance over an imprinting material. 
         [0003]    Micro-fabrication involves the fabrication of very small structures, e.g., having features on the order of micro-meters or smaller. One area in which micro-fabrication has had a sizeable impact is in the processing of integrated circuits. As the semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate, micro-fabrication becomes increasingly important. Micro-fabrication provides greater process control while allowing increased reduction of the minimum feature dimension of the structures formed. Other areas of development in which micro-fabrication has been employed include biotechnology, optical technology, mechanical systems and the like. 
         [0004]    An exemplary micro-fabrication technique is shown in U.S. Pat. No. 6,334,960 to Willson et al. Willson et al. disclose a method of forming a relief image in a structure. The method includes providing a substrate having a transfer layer. The transfer layer is covered with a polymerizable fluid composition. A mold makes mechanical contact with the polymerizable fluid. The mold includes a relief structure, and the polymerizable fluid composition fills the relief structure. The polymerizable fluid composition is then subjected to conditions to solidify and polymerize the same, forming a solidified polymeric material on the transfer layer that contains a relief structure complimentary to that of the mold. The mold is then separated from the solid polymeric material such that a replica of the relief structure in the mold is formed in the solidified polymeric material. The transfer layer and the solidified polymeric material are subjected to an environment to selectively etch the transfer layer relative to the solidified polymeric material such that a relief image is formed in the transfer layer. The time required and the minimum feature dimension provided by this technique is dependent upon, inter alia, the composition of the polymerizable material. 
         [0005]    U.S. Pat. No. 5,772,905 to Chou discloses a lithographic method and apparatus for creating ultra-fine (sub-25 nm) patterns in a thin film coated on a substrate in which a mold having at least one protruding feature is pressed into a thin film carried on a substrate. The protruding feature in the mold creates a recess of the thin film. The mold is removed from the film. The thin film then is processed such that the thin film in the recess is removed, exposing the underlying substrate. Thus, patterns in the mold are replaced in the thin film, completing the lithography. The patterns in the thin film will be, in subsequent processes, reproduced in the substrate or in another material which is added onto the substrate. 
         [0006]    Yet another imprint lithography technique is disclosed by Chou et al. in  Ultrafast and Direct Imprint of Nanostructures in Silicon , Nature, Col. 417, pp. 835-837, June 2002, which is referred to as a laser assisted direct imprinting (LADI) process. In this process. a region of a substrate is made flowable, e.g., liquefied, by heating the region with the laser. After the region has reached a desired viscosity, a mold, having a pattern thereon, is placed in contact with the region. The flowable region conforms to the profile of the pattern and is then cooled, solidifying the pattern into the substrate. A concern with this technique involves pattern distortions attributable to the presence of gases in the flowable region. 
         [0007]    It is desired, therefore, to provide a system to reduce distortions in patterns formed using imprint lithographic techniques. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a lithographic system in accordance with the present invention; 
           [0009]      FIG. 2  is a simplified elevation view of a lithographic system shown in  FIG. 1 ; 
           [0010]      FIG. 3  is a simplified representation of material from which an imprinting layer, shown in  FIG. 2 , is comprised before being polymerized and cross-linked; 
           [0011]      FIG. 4  is a simplified representation of cross-linked polymer material into which the material shown in  FIG. 3  is transformed after being subjected to radiation; 
           [0012]      FIG. 5  is a simplified elevation view of a mold spaced-apart from the imprinting layer, shown in  FIG. 1 , after patterning of the imprinting layer; 
           [0013]      FIG. 6  is a simplified elevation view of an additional imprinting layer positioned atop the substrate shown in  FIG. 5  after the pattern in the first imprinting layer is transferred therein; 
           [0014]      FIG. 7  is a detailed perspective view of a print head shown in  FIG. 1 ; 
           [0015]      FIG. 8  is a cross-sectional view of a chucking system in accordance with the present invention; 
           [0016]      FIG. 9  is detailed cross-sectional view of an imprint head shown in  FIG. 7 ; and 
           [0017]      FIG. 10  is a bottom-up perspective view of the imprint head shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  depicts a lithographic system  10  in accordance with one embodiment of the present invention that includes a pair of spaced-apart bridge supports  12  having a bridge  14  and a stage support  16  extending therebetween. Bridge  14  and stage support  16  are spaced-apart. Coupled to bridge  14  is an imprint head  18 , which extends from bridge  14  toward stage support  16  and provides movement along the Z-axis. Disposed upon stage support  16  to face imprint head  18  is a motion stage  20 . Motion stage  20  is configured to move with respect to stage support  16  along X- and Y-axes. It should be understood that imprint head  18  may provide movement along the X- and Y-axes, as well as in the Z-axis, and motion stage  20  may provide movement in the Z-axis, as well as in the X and Y axes. An exemplary motion stage device is disclosed in U.S. patent application Ser. No. 10/194,414, filed Jul. 11, 2002, entitled “Step and Repeat Imprint Lithography Systems,” assigned to the assignee of the present invention, and which is incorporated by reference herein in its entirety. A radiation source  22  is coupled to lithographic system  10  to impinge actinic radiation upon motion stage  20 . As shown, radiation source  22  is coupled to bridge  14  and includes a power generator  23  connected to radiation source  22 . Operation of lithographic system  10  is typically controlled by a processor  25  that is in data communication therewith. 
         [0019]    Referring to both  FIGS. 1 and 2 , connected to imprint head  18  is a template  26  having a mold  28  thereon. Mold  28  includes a plurality of features defined by a plurality of spaced-apart recessions  28   a  and protrusions  28   b . The plurality of features defines an original pattern that is to be transferred into a substrate  30  positioned on motion stage  20 . To that end, imprint head  18  and/or motion stage  20  may vary a distance “d” between mold  28  and substrate  30 . In this manner, the features on mold  28  may be imprinted into a flowable region of substrate  30 , discussed more fully below. Radiation source  22  is located so that mold  28  is positioned between radiation source  22  and substrate  30 . As a result, mold  28  is fabricated from a material that allows it to be substantially transparent to the radiation produced by radiation source  22 . 
         [0020]    Referring to both  FIGS. 2 and 3 , a flowable region, such as an imprinting layer  34 , is disposed on a portion of a surface  32  that presents a substantially planar profile. A flowable region may be formed using any known technique, such as a hot embossing process disclosed in U.S. Pat. No. 5,772,905, which is incorporated by reference in its entirety herein, or a laser assisted direct imprinting (LADI) process of the type described by Chou et al. in  Ultrafast and Direct Imprint of Nanostructures in Silicon , Nature, Col. 417, pp. 835-837, June 2002. In the present embodiment, however, a flowable region consists of imprinting layer  34  being deposited as a plurality of spaced-apart discrete droplets  36  of a material  36   a  on substrate  30 , discussed more fully below. An exemplary system for depositing droplets  36  is disclosed in U.S. patent application Ser. No. 10/191,749, filed Jul. 9, 2002, entitled “System and Method for Dispensing Liquids,” assigned to the assignee of the present invention, and which is incorporated by reference herein in its entirety. Imprinting layer  34  is formed from material  36   a  that may be selectively polymerized and cross-linked to record the original pattern therein, defining a recorded pattern. An exemplary composition for material  36   a  is disclosed in U.S. patent application Ser. No. 10/463,396, filed Jun. 16, 2003, and entitled “Method to Reduce Adhesion Between a Conformable Region and a Pattern of a Mold,” which is incorporated by reference in its entirety herein. Material  36   a  is shown in  FIG. 4  as being cross-linked at points  36   b , forming a cross-linked polymer material  36   c.    
         [0021]    Referring to  FIGS. 2 ,  3  and  5 , the pattern recorded in imprinting layer  34  is produced, in part, by mechanical contact with mold  28 . To that end, distance “d” is reduced to allow droplets  36  to come into mechanical contact with mold  28 , spreading droplets  36  so as to form imprinting layer  34  with a contiguous formation of material  36   a  over surface  32 . In one embodiment, distance “d” is reduced to allow sub-portions  34   a  of imprinting layer  34  to ingress into and fill recessions  28   a.    
         [0022]    To facilitate filling of recessions  28   a , material  36   a  is provided with the requisite properties to completely fill recessions  28   a , while covering surface  32  with a contiguous formation of material  36   a . In the present embodiment, sub-portions  34   b  of imprinting layer  34  in superimposition with protrusions  28   b  remain after the desired, usually minimum, distance “d” has been reached, leaving sub-portions  34   a  with a thickness t 1 , and sub-portions  34   b  with a thickness, t 2 . Thicknesses “t 1 ” and “t 2 ” may be any thickness desired, dependent upon the application. Typically, t 1  is selected so as to be no greater than twice the width u of sub-portions  34   a , i.e., t 1 ≦2u, shown more clearly in  FIG. 5 . 
         [0023]    Referring to  FIGS. 2 ,  3  and  4 , after a desired distance “d” has been reached, radiation source  22  produces actinic radiation that polymerizes and cross-links material  36   a , forming cross-linked polymer material  36   c . As a result, the composition of imprinting layer  34  transforms from material  36   a  to cross-linked polymer material  36   c , which is a solid. Specifically, cross-linked polymer material  36   c  is solidified to provide side  34   c  of imprinting layer  34  with a shape conforming to a shape of a surface  28   c  of mold  28 , shown more clearly in  FIG. 5 . After imprinting layer  34  is transformed to consist of cross-linked polymer material  36   c , shown in  FIG. 4 , imprint head  18 , shown in  FIG. 2 , is moved to increase distance “d” so that mold  28  and imprinting layer  34  are spaced-apart. 
         [0024]    Referring to  FIG. 5 , additional processing may be employed to complete the patterning of substrate  30 . For example, substrate  30  and imprinting layer  34  may be etched to transfer the pattern of imprinting layer  34  into substrate  30 , providing a patterned surface  32   a , shown in  FIG. 6 . To facilitate etching, the material from which imprinting layer  34  is formed may be varied to define a relative etch rate with respect to substrate  30 , as desired. The relative etch rate of imprinting layer  34  to substrate  30  may be in a range of about 1.5:1 to about 100:1. 
         [0025]    Alternatively, or in addition to, imprinting layer  34  may be provided with an etch differential with respect to photo-resist material (not shown) selectively disposed thereon. The photo-resist material (not shown) may be provided to further pattern imprinting layer  34 , using known techniques. Any etch process may be employed, dependent upon the etch rate desired and the underlying constituents that form substrate  30  and imprinting layer  34 . Exemplary etch processes may include plasma etching, reactive ion etching, chemical wet etching and the like. 
         [0026]    Referring to  FIGS. 7 and 8 , template  26 , upon which mold  28  is present, is coupled to an imprint head housing  18   a  via a chucking system  40  that includes a chuck body  42 . Chuck body  42  is adapted to retain template  26  upon which mold  28  is attached employing vacuum techniques. To that end, chuck body  42  includes one or more recesses  42   a  that are in fluid communication with a pressure control system, such as a fluid supply system  70 . Fluid supply system  70  may include one or more pumps to provide both positive and negative pressure, as well as a supply of fluid to facilitate reducing, if not preventing, trapping of gases, such as air, in imprinting layer  34 , shown in  FIG. 5 . An exemplary chucking system is disclosed in U.S. patent application Ser. No. 10/293,224, entitled “Chucking System For Modulating Shapes of Substrates,” assigned to the assignee of the present invention, and which is incorporated by reference in its entirety herein. 
         [0027]    As discussed above, during imprinting template  26  and, therefore, mold  28 , is brought into proximity with substrate  30  before patterning imprinting material  36   a , shown in  FIG. 3 , is disposed on a region  77  of substrate  30 . Specifically, template  26  is brought within microns of substrate  30 , e.g., 15 microns more or less. It has been found desirable to perform localized control of the atmosphere  78  that is proximate to both template  26  and region  77 . For example, to avoid the deleterious effects of gases present in imprinting material  36   a , shown in  FIG. 3 , and/or subsequently trapped in the patterned imprinting layer  34 , shown in  FIG. 2 , it has been found beneficial to control the consistency of fluid in atmosphere  78  and/or the pressure of atmosphere  78 . 
         [0028]    Referring to  FIG. 9 , to facilitate control of atmosphere  78 , chuck body  42  is designed to facilitate the passage of fluids proximate to mold  28  and imprint head  18  includes a baffle  100  surrounding template  26 . Specifically, baffle  100  extends from imprint head  18 , terminating in a nadir  102  that lies in a plane in which a surface  26   a  lies. In this fashion, mold  28  extends beyond nadir  102  to facilitate contact with region  77 . Chuck body  42  includes one or more throughways, two of which are shown as  104  and  106 . Apertures  104   a  and  106   a  of throughways  104  and  106 , respectively, are disposed in a surface of chuck body  42  disposed between template  26  and baffle  100 , referred to as a peripheral surface  100   a . Throughways  104  and  106  place apertures  104   a  and  106   a  in fluid communication with fluid supply system  70 , shown in  FIG. 8 . Baffle  100  functions to slow the movement of fluid exiting apertures  104   a  and  106   a  away from mold  28 . To that end, baffle  100  includes first and second opposed surfaces  102   a  and  102   b . First opposed surface  102   a  extends from nadir  102  away from substrate  30  and faces template  26 . Second opposed surface  102   b  extends from nadir  102  away from substrate  30  and faces away from mold  28 . Although it is not necessary, first opposed surface  102   a  is shown extending obliquely with respect to second opposing surface  102   b . With this configuration, atmosphere  78  may be controlled by introduction or evacuation of fluid through apertures  104   a  and  106   a . However, first and second opposed surfaces  102   a  and  102   b  may extend parallel to one another from nadir  102 . 
         [0029]    Referring to  FIGS. 3 ,  8  and  9 , in one embodiment, atmosphere  78  is established so that the transport of the gases present therein to either imprinting material  36   a  in region  77 , substrate  31 , template  26 , mold  28 , or a combination thereof is increased. The term transport is defined to mean any mechanism by which the propagation of gases through either imprinting material  36   a , substrate  31 , template  26 , mold  28 , or a combination thereof is increased, e.g., increased solubility, increased diffusion and the like. To that end, fluid supply system  70  may include a supply of imprinting material  36   a . Under control of processor  25 , which is in data communication with fluid supply system  70 , imprinting material  36   a  may be introduced through apertures  104   a  and  106   a  to saturate atmosphere  78  with imprinting material  36   a . This was found to reduce, if not completely do away with, the quantity of gases, such as air, trapped in the imprinting layer  34 , shown in  FIG. 5 , during imprint processes. This is beneficial as it was found that the presence of air in imprinting layer  34 , shown in  FIG. 5 , creates undesirable voids. Alternatively, it was found that by saturating atmosphere  78  with carbon dioxide and/or helium the quantity of air trapped in imprinting layer  34 , shown in  FIG. 5 , was substantially reduced if not avoided. It should be understood that a mixture of imprinting material  36   a , carbon dioxide and/or helium may be introduced into atmosphere  78  to reduce the quantity of air trapped in imprinting layer  34 , shown in  FIG. 5 . 
         [0030]    Referring to  FIGS. 2 ,  9  and  10 , a difficulty encountered with respect to introducing fluids was to ensure that the molecules in the fluid streams  104   b  and  106   b  exiting apertures  104   a  and  106   a , respectively, traveled to a region of the atmosphere positioned between mold  28  and droplets  36 , and before contact of droplets  36  with mold  28 . This region of atmosphere  78  is referred to as a processing region  78   a . As shown, apertures  104   a  and  106   a  are disposed about peripheral surface  100   a , which is spaced-apart from processing region  78   a . Given that the separation of mold  28  from region  77  is on the order of microns, the relative dimensions of the molecules in fluid streams  104   b  and  106   b  and the spacing between mold  28  and region  77  makes difficult the ingression of the aforementioned molecules into processing region  78   a.    
         [0031]    Referring to  FIGS. 8 and 9 , one manner in which to overcome the aforementioned difficulty is to have fluid supply system  70  under control of processor  25 . A memory (not shown) is in data communication with processor  25 . The memory (not shown) comprises a computer-readable medium having a computer-readable program embodied therein. The computer-readable program includes instructions to pulse fluid streams  104   b  and  106   b  into atmosphere  78  having a desired mixture of molecules, discussed above. In this manner, laminar flow of fluid streams  104   b  and  106   b  may be avoided. It is believed that by providing fluid streams  104   b  and  106   b  with turbulent flow, the probability will be increased that a sufficient quantity of the molecules contained therein will reach processing region  78   a  to reduce, if not avoid, the presence of gases being trapped in imprinting layer  34 . To that end, fluid may be pulsed through both apertures  104   a  and  106   a , concurrently, or sequentially pulsed through the same, i.e., first fluid is introduced through aperture  104   a  and subsequently through aperture  106   a  and then again through  104   a , with the process being repeated for a desired time or during the entire imprinting process. Furthermore, the timing of the flow of gas into processing region  78   a  is important because it is desired that a sufficient quantity of molecules contained therein reach processing region  78   a  before contact is made between mold  28  and droplets  36 . 
         [0032]    Referring to  FIG. 9 , alternatively, fluid may be pulsed through one of the apertures, e.g., aperture  104   a , and then evacuated through the remaining aperture, e.g., aperture  106   a . In this manner, fluid would be drawn across processing region  78   a . It may also be advantageous to pulse the fluid through both apertures  104   a  and  106   a , concurrently, then evacuate through both apertures  104   a  and  106   a  concurrently. It is desired, however, that the flow rate of fluid be established to minimize, if not avoid, movement of droplets  36 , shown in  FIG. 2 . 
         [0033]    To ensure that the fluids exiting apertures  104   a  and  106   a  crosses through processing region  78   a , it may be advantageous to concurrently pulse fluid through both apertures  104   a  and  106   a  concurrently and then alternatingly evacuate through one of apertures  104   a  or  106   a . Concurrently introducing the fluid through both apertures  104   a  and  106   a  minimizes the time required to saturate atmosphere  78 . Alternatingly evacuating the fluid through one of apertures  104   a  and  106   a  ensures that the fluid travels through processing region  78   a . For example, a first step would include introducing fluid into atmosphere  78  through both apertures  104   a  and  106   a . A second step would include evacuating the fluid through one of apertures  104   a  and  106   a , e.g., aperture  104   a . Thereafter, at a third step, fluid would be introduced into atmosphere  78  through both apertures  104   a  and  106   a , concurrently. At a fourth step, fluid would be evacuated through one of apertures  104   a  and  106   a  that was not employed in the previous step to remove fluid, e.g., aperture  106   a . It should be understood that evacuation may occur through one of apertures  104   a  and  106   a , while fluid is being introduced through the remaining aperture of apertures  104   a  and  106   a . Alternatively, evacuation may occur in the absence of a fluid flow into atmosphere  78 . The desired result is that fluid ingression into atmosphere  78  and fluid evacuation therefrom occurs so that the desired concentration of fluid is present. 
         [0034]    Referring to  FIGS. 9 and 10 , in another embodiment, a plurality of apertures may be disposed about peripheral surface  100   a  so that each of the apertures of a pair is disposed opposite one another on opposite sides of template  26 . This is shown by aperture pair  104   a  and  106   a  being disposed opposite one another on opposite sides of template  26 . A second aperture pair is shown as  108   a  and  110   a . Apertures  108   a  and  110   a  are disposed opposite one another on opposite sides of template  26 . 
         [0035]    As shown, each of apertures  104   a ,  106   a ,  108   a  and  110   a , are arranged to lie on a common circle with adjacent apertures being spaced-apart therefrom by 90°. In this manner, each of apertures  104   a ,  106   a ,  108   a  and  110   a  are arranged to facilitate fluid flow in/out of a different quadrant of chuck body  42 . Specifically, aperture  104   a  facilitates fluid flow in/out of quadrant I; aperture  106   a  facilitates fluid flow in/out of quadrant II; aperture  108   a  facilitates fluid flow in/out of quadrant III; and aperture  110   a  facilitates fluid flow in/out of quadrant IV. However, any number of apertures may be employed, e.g., more than one per quadrant with differing quadrants having differing numbers of apertures and arranged in any spatial arrangement desired. Each of these arrangements should facilitate introduction and/or evacuation of a plurality of flows of fluid streams into atmosphere  78 , with a subset of the plurality of flows being introduced to differing regions about template  26 . It is believed that introduction of the multiple flows of fluid streams provides a turbulent flow of fluid in atmosphere  78 . This, it is believed, increases the probability that molecules in the fluid streams would reach processing region  78   a . However, fluid flow into atmosphere  78  through each of the apertures  104   a ,  106   a ,  108   a  and  110   a  and evacuation of fluid from atmosphere  78  therethrough may occur in any manner discussed above. 
         [0036]    In another embodiment, a fluid stream may be introduced through each of apertures  104   a ,  106   a ,  108   a  and  110   a  sequentially so that a flow cell  112  may be created between template  26  and region  77 . Flow cell  112  would facilitate ingression of molecules in the fluid streams into processing region  78   a  to provide the benefits mentioned above. For example, first a fluid flow may be introduced through aperture  104   a  and then terminated. After termination of fluid flow through aperture  104   a , fluid flow through aperture  106   a  is commenced to introduce fluid into atmosphere  78 . Subsequently, fluid flow through aperture  106   a  is terminated. After termination of fluid flow through aperture  106   a , fluid flow through aperture  108   a  is commenced to introduce fluid into atmosphere  78 . Fluid flow in through aperture  108   a  is subsequently terminated. After termination of fluid flow through aperture  108   a , fluid flow through aperture  110   a  is commenced to introduce fluid into atmosphere  78 . In this manner, fluid is introduced into atmosphere  78  through a single quadrant at any given time. However, it may be desirable to introduce fluid into more than one quadrant. Although this may frustrate creation of flow cell  112 , it is within confines of the present invention. 
         [0037]    Alternatively, sequential introduction and evacuation through apertures  104   a ,  106   a ,  108   a  and  110   a  may be undertaken to create flow cell  112 . This would include introducing fluid through one or more of apertures  104   a ,  106   a ,  108   a  and  110   a , concurrently. Subsequently, sequential evacuation may occur through each of apertures  104   a ,  106   a ,  108   a  and  110   a  to create flow cell  112 . For example, fluid may be introduced through all apertures in chuck body  42 , concurrently. Thereafter, fluid may be evacuated from each of apertures  104   a ,  106   a ,  108   a  and  110   a , one at a time. Before, the concentration in atmosphere  78  of fluid introduced through apertures  104   a ,  106   a ,  108   a  and  110   a  went below a desired level due to evacuation. The fluid may then be reintroduced through one or all of apertures  104   a ,  106   a ,  108   a  and  110   a  again and the process repeated to create and/or maintain flow cell  112 . 
         [0038]    The embodiments of the present invention described above are exemplary. Many changes and modifications may be made to the disclosure recited above, while remaining within the scope of the invention. Therefore, the scope of the invention should not be limited by the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.