Patent Publication Number: US-11020894-B2

Title: Safe separation for nano imprinting

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 14/632,125 filed Feb. 26, 2015, which is a divisional of U.S. application Ser. No. 13/095,514 filed Apr. 27, 2011, now U.S. Pat. No. 8,968,620, which claims priority to U.S. Provisional Application No. 61/328,353 filed Apr. 27, 2010; each of which is hereby incorporated by reference. 
    
    
     BACKGROUND INFORMATION 
     Nano-fabrication includes the fabrication of very small structures that have features on the order of 100 nanometers or smaller. One application in which nano-fabrication has had a sizeable impact is in the processing of integrated circuits. The semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate; therefore nano-fabrication becomes increasingly important. Nano-fabrication provides greater process control while allowing continued reduction of the minimum feature dimensions of the structures formed. Other areas of development in which nano-fabrication has been employed include biotechnology, optical technology, mechanical systems, and the like. 
     An exemplary nano-fabrication technique in use today is commonly referred to as imprint lithography. Exemplary imprint lithography processes are described in detail in numerous publications, such as U.S. Pat. No. 8,349,241, U.S. Patent Publication No. 2004/0065252, and U.S. Pat. No. 6,936,194, each of which is hereby incorporated by reference herein. 
     An imprint lithography technique disclosed in each of the aforementioned U.S. patent publication and patents includes formation of a relief pattern in a formable (polymerizable) layer and transferring a pattern corresponding to the relief pattern into an underlying substrate. The substrate may be coupled to a motion stage to obtain a desired positioning to facilitate the patterning process. The patterning process uses a template spaced apart from the substrate and a formable liquid applied between the template and the substrate. The formable liquid is solidified to form a rigid layer that has a pattern conforming to a shape of the surface of the template that contacts the formable liquid. After solidification, the template is separated from the rigid layer such that the template and the substrate are spaced apart. The substrate and the solidified layer are then subjected to additional processes to transfer a relief image into the substrate that corresponds to the pattern in the solidified layer. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       So that features and advantages of the present invention can be understood in detail, a more particular description of embodiments of the invention may be had by reference to the embodiments illustrated in the appended drawings. It is to be noted, however, that the appended drawings only illustrate typical embodiments of the invention, and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  illustrates a simplified side view of a lithographic system. 
         FIG. 2  illustrates a simplified side view of the substrate illustrated in  FIG. 1 , having a patterned layer thereon. 
         FIGS. 3A-3B  illustrate a simplified side view and magnified view of lateral strain (side motion) of a template and a substrate during an imprint lithography separation process. 
         FIGS. 4A-4B  illustrate a simplified side view and magnified view of lateral strain (side motion) of a template during an imprint lithography separation process. 
         FIG. 5  illustrates a graphical representation of lateral strain ratio of interfacing template and substrate as a function of thickness ratio and back pressure (absolute pressure). 
         FIG. 6  illustrates a graphical representation of lateral strain ratio of interfacing template and substrate having variable thicknesses and substantially similar back pressure. 
         FIG. 7  illustrates a graphical representation of lateral strain ratio of interfacing template and substrate having substantially similar thicknesses and variable back pressure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the figures, and particularly to  FIG. 1 , illustrated therein is a lithographic system  10  used to form a relief pattern on substrate  12 . Substrate  12  may be coupled to substrate chuck  14 . As illustrated, substrate chuck  14  is a vacuum chuck. Substrate chuck  14 , however, may be any chuck including, but not limited to, vacuum, pin-type, groove-type, electrostatic, electromagnetic, and/or the like. Exemplary chucks are described in U.S. Pat. No. 6,873,087, which is hereby incorporated by reference herein. 
     Substrate  12  and substrate chuck  14  may be further supported by stage  16 . Stage  16  may provide translational and/or rotational motion along the x, y, and z-axes. Stage  16 , substrate  12 , and substrate chuck  14  may also be positioned on a base (not shown). 
     Spaced-apart from substrate  12  is template  18 . Template  18  may include a body having a first side and a second side with one side having a mesa  20  extending therefrom towards substrate  12 . Mesa  20  having a patterning surface  22  thereon. Further, mesa  20  may be referred to as mold  20 . Alternatively, template  18  may be formed without mesa  20 . 
     Template  18  and/or mold  20  may be formed from such materials including, but not limited to, fused-silica, quartz, silicon, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal, hardened sapphire, and/or the like. As illustrated, patterning surface  22  comprises features defined by a plurality of spaced-apart recesses  24  and/or protrusions  26 , though embodiments of the present invention are not limited to such configurations (e.g., planar surface). Patterning surface  22  may define any original pattern that forms the basis of a pattern to be formed on substrate  12 . 
     Template  18  may be coupled to chuck  28 . Chuck  28  may be configured as, but not limited to, vacuum, pin-type, groove-type, electrostatic, electromagnetic, and/or other similar chuck types. Exemplary chucks are further described in U.S. Pat. No. 6,873,087. Further, chuck  28  may be coupled to imprint head  30  such that chuck  28  and/or imprint head  30  may be configured to facilitate movement of template  18 . 
     System  10  may further comprise a fluid dispense system  32 . Fluid dispense system  32  may be used to deposit formable material  34  (e.g., polymerizable material) on substrate  12 . Formable material  34  may be positioned upon substrate  12  using techniques, such as, drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), thin film deposition, thick film deposition, and/or the like. Formable material  34  may be disposed upon substrate  12  before and/or after a desired volume is defined between mold  22  and substrate  12  depending on design considerations. Formable material  34  may be functional nano-particles having use within the bio-domain, solar cell industry, battery industry, and/or other industries requiring a functional nano-particle. For example, formable material  34  may comprise a monomer mixture as described in U.S. Pat. No. 7,157,036 and U.S. Patent Publication No. 2005/0187339; both of which are herein incorporated by reference. Alternatively, formable material  34  may include, but is not limited to, biomaterials (e.g., PEG), solar cell materials (e.g., N-type, P-type materials), and/or the like. 
     Referring to  FIGS. 1 and 2 , system  10  may further comprise energy source  38  coupled to direct energy  40  along path  42 . Imprint head  30  and stage  16  may be configured to position template  18  and substrate  12  in superimposition with path  42 . System  10  may be regulated by processor  54  in communication with stage  16 , imprint head  30 , fluid dispense system  32 , and/or source  38 , and may operate on a computer readable program stored in memory  56 . 
     Either imprint head  30 , stage  16 , or both vary a distance between mold  20  and substrate  12  to define a desired volume therebetween that is filled by formable material  34 . For example, imprint head  30  may apply a force to template  18  such that mold  20  contacts formable material  34 . After the desired volume is filled with formable material  34 , source  38  produces energy  40 , e.g., ultraviolet radiation, causing formable material  34  to solidify and/or cross-link conforming to a shape of surface  44  of substrate  12  and patterning surface  22 , defining patterned layer  46  on substrate  12 . Patterned layer  46  may comprise a residual layer  48  and a plurality of features shown as protrusions  50  and recessions  52 , with protrusions  50  having a thickness t 1  and residual layer having a thickness t 2 . 
     The above-mentioned system and process may be further employed in imprint lithography processes and systems referred to in U.S. Pat. Nos. 6,932,934, 7,077,992, 7,179,396, and 7,396,475, each of which is hereby incorporated by reference in its entirety. 
     After formation of patterned layer  46 , template  18  or mold  20  and features  50  and  52  of patterned layer  46  may be separated. Generally, the separation effort includes application of force to separate two “plate-like” structures (i.e., template  18  and substrate  12 ). Separation generally needs to be performed without causing excessive stress and/or strain to template  18  or mold  20  and/or imprinted features  50  and  52  of patterned layer  46 . If template  18  and substrate  12  are pulled out in a relatively normal direction (e.g., without a tilting motion), the separation front moves inward (in radial) from a boundary of patterned layer  46 . If additional tilting motion is applied, the separation front may move fairly in-parallel lines starting from a remote side from the tilting axis. Exemplary separation front schemes are described in further detail in U.S. Pat. Nos. 7,701,112, 8,075,299, 7,635,445, and 7,635,263, which are hereby incorporated by reference in their entirety. 
     As illustrated in  FIG. 3A , template  18   a  and substrate  12   a  may form a small angle θ at a separation front, which is equal to the sum of the relative bending angles θ 1  of the template  18   a  and θ 2  of the substrate  12   a  with respect to un-deformed plane PL 1 . Here, P is the pressure at the gap between the template and substrate outside of the imprinted area, P t  and P b  represent the pressure, if any, applied to the template backside and the substrate backside, respectively. Relative bending angles θ 1  of the template  18   a  and θ 2  of the substrate  12   a  with respect to un-deformed plane PL 1  are functions of multiple variables including, but not limited to, thickness, Young&#39;s modulus, pressures, adhesion between template  18   a  and patterned layer  46 , and the like.  FIG. 3B  shows two lateral motions at the separation front between the template and substrate where d t  is the lateral displacement (or lateral strain) of the template features and d b  is the lateral displacement (or lateral strain) of the imprinted features on the substrate. 
       FIG. 4  illustrates strain d t  of template  18   a  with respect to substrate  12   a  where it is assumed that the substrate is rigid with no bending at all. Template  18   a  thus exhibits a lateral strain d t  but the substrate d b  has zero lateral strain. As illustrated, in such a case where the lateral strains are not matched between the template features and the substrate features, imprinted features  50   a  and  52   a  will be distorted or fail. In order to prevent the feature failure, it is advantageous to allow the substrate  12   a  to bend or stretch and its lateral strain d b  to be matched with that of the template (d t ). 
     The bending amounts of the template and substrates are inverse proportional to (ET 3 ), wherein E is Young&#39;s modulus of the template or substrate material and T is the template or substrate thickness. Subsequently, the strain is a function of the bending multiplied with the thicknesses (T). Therefore, strain magnitude is inverse proportional to (ET 2 ). Then, the ratio of two lateral strains (d t /d b ) at the interfacing surfaces of template  18   a  and substrate  12  is proportional to (E b T b   2 )/(E t T t   2 ). 
       FIGS. 5-7  illustrate graphic plots of lateral stain ratio (d t /d b ) in relation to thicknesses of template  18   a  and substrate  12   a  (T b /T t ). Generally, solid lines  70 - 70   b  represent the strain ratio of template  18   a  and substrate  12   a  under substantially similar boundary conditions (e.g., back pressure). Dashed lines  72 ,  72   b  and  74  represent template  18   a  and substrate  12   a  under substantially different boundary conditions (e.g., back pressure). 
       FIG. 5  illustrates a graphic plot  68  of lateral strain ratio (d t /d b ) for combinations of thicknesses during separation of template  18   a  and substrate  12   a . For example, under substantially similar boundary conditions (i.e., reference line  70 ), when thickness of thickness T t  template  18   a  is significantly less than thickness T b  substrate  12   a  (T t &lt;&lt;T b ), separation front may be formed mainly by bending of template  18   a . In this example, the ratio of the strain (d t /d b ) is larger than (E b /E t ). Alternatively, having thickness T b  of substrate  12   a  significantly less than thickness T t  of template  18   a  (T b &lt;&lt;T t ), the ratio of the strain (d t /d b ) is smaller than (E b /E t ). 
     An optimal case may exist wherein strain ratio (d t /d b ) becomes 1 for template  18   a  and substrate  12   a . When the template and the substrate have the same Young&#39;s modulus, the optimal configuration is when template  18   a  and substrate  12   a  have substantially similar thicknesses T t  and T b  respectively and is under near identical process conditions (e.g., back pressure, constraining boundary conditions). It should be noted that pressure is both positive and negative pressure (vacuum). 
     Having template  18   a  and substrate  12  constrained by means of different back supporting (i.e., adjusting the material stiffness) or through the application of back pressure (positive pressure and/or vacuum), however, may significantly influence stress and/or lateral strain. For example, as illustrated in  FIG. 5 , curves  72  and  74  illustrate lateral strain ratio (d t /d b ) when template  18   a  and substrate  12   a  are under different back pressure conditions. Curve  72  represents the relative lateral strain ratio (d t /d b ) when back pressure of substrate  12   a  is lower (e.g. −30 Kpa) than that of template  18   a  (e.g. 0 Kpa), and curve  74  represents the opposite case (i.e., where back pressure of substrate  12   a  is higher than that of template  18   a ). For example, having only substrate  12   a  vacuum chucked may influence bending geometry to cause excessive strain during the separation process. Based on the graphical representation, thickness T t  of template  18   a  may be configured (e.g., increased) greater than thickness T b  of substrate  12   a  such that bending stiffness of template  18   a  may be increased in order to compensate for a differences in backside pressure, separation force, and/or template geometry. 
     Thickness of substrate  12   a , however, is generally not a freely selectable variable. For example, semiconductor wafers of 8 inch or 12 inch diameters generally include an industry standard for thickness for substrate  12   a . For compensation, thickness T t  of template  18   a  may be determined based on pre-selected thickness T b  for substrate  12   a . Additionally, thickness T t  of template  18   a  may be determined based on material stiffness (e.g., Young&#39;s modulus), back pressure, and the like, such that lateral strain d t  may be minimized or eliminated. Alternatively, back pressure of template  18   a  can be controlled such that lateral strain ratio (d t /d b ) may be approximately 1. 
     More specifically, back pressure P t  and/or P b  applied to the template and/or the substrate (see  FIG. 3A ), can be adjusted in order to modify lateral strain d t  and/or lateral strain d b  to yield a lateral strain ratio (d t /d b ) of approximately 1. The amount and degree of back pressure P t  and/or P b  that is necessary to provide can be predetermined based on the Young&#39;s modulus, thickness of the template and substrate, and the separation force to be applied. Control and supply of such back pressure to a template can be provided using chucks and systems described in, for example, U.S. Pat. No. 7,019,819, incorporated herein by reference. Control and supply of such back pressure to a substrate can be provided using chucks and systems described in, for example, U.S. Pat. Nos. 7,635,263 and 7,635,445, each of which is incorporated herein by reference. 
       FIG. 6  illustrates a graphic plot  76  of lateral strain ratio (d t /d b ) for combinations of thicknesses. Graphic plot  76  provides an exemplary method for optimizing lateral strain ratio (d t /d b ) wherein thickness T t  and T b  of either template  18   a  or substrate  12   a  is a controllable variable. For example, substrate  12   a  may be formed of Si having a Young&#39;s modulus of approximately 150 GPa, thickness T b  of approximately 0.775 mm. Template  18   a  may be formed of fused silica having a Young&#39;s modulus of approximately 75 GPa. Then, lateral strain ratio (d t /d b ) is a quadratic function passing (0,0) and (1,2). As such, for an ideal lateral strain ratio (d t /d b ) of 1, thickness ratio should be the square root of 0.5 based on (E b T b   2 )/(E t T t   2 ). Therefore, thickness T t  of template  18   a  may need to be at approximately 1.1 mm. Substantially identical back pressure may need to be provided to both template  18   a  and substrate  12   a . For example, back pressure may be maintained at approximately −30 Kpa at both template  18   a  and substrate  12   a . A small variation of the back pressures can be optimized based on the separation force to be applied. Alternatively, when template  18   a  is under ambient pressure, at least a portion of substrate  12   a  may be under substantially the same back pressure (e.g., ambient) while the remaining portions of substrate  12   a  are subjected to a different back pressure. Systems and methods for providing differing levels of pressure are further described in U.S. Pat. Nos. 7,019,819, 7,635,263 and 7,635,445, each of which is hereby incorporated by reference in its entirety. 
       FIG. 7  illustrates a graphic plot  78  of lateral strain ratio (d t /d b ) wherein thicknesses are not controlled variables. Graphic plot  76  provides an exemplary method for optimizing lateral strain ratio (d t /d b ) wherein thickness T t  and T b  of either template  18   a  or substrate  12   a  is not a control variable. Material properties of template  18   a  and substrate  12   a  may be substantially similar. Thickness T t  and T b  of template  18   a  and substrate  12   a  may have a fixed ratio. For example, in one embodiment, the fixed ratio may be set to T b /T t =0.18. Generally, the “thicker” of template  18   a  or substrate  12   a  may need additional support of high back pressure while the “thinner” of template  18   a  or substrate  12   a  may need back pressure having a low pressure (e.g., vacuum). For example, for fused silica material, back pressure between approximately 40 Kpa to 90 Kpa may be used for the thicker of template  18   a  and substrate  12   a  and back pressure between approximately −40 Kpa to 0 Kpa may be used for the thinner of template  18   a  and substrate  12   a . Actual numbers may be determined using an analytical model and/or finite element analysis. Further, back pressure levels for template  18   a  and substrate  12   a  may be adjusted as separation propagates. 
     Control of lateral strain of template  18   a  and substrate  12   a  through the selection of thicknesses T t  and/or T b , control of back pressure, and/or selection of material stiffness may be applied to other separation methods including, but not limited to, those further described in U.S. Pat. Nos. 7,636,999, 7,701,112, 8,075,299, 7,635,445, and 7,635,263. 
     Further modifications and alternative embodiments of various aspects will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only. It is to be understood that the forms shown and described herein are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description. Changes may be made in the elements described herein without departing from the spirit and scope as described in the following claims.