Patent Abstract:
The present invention provides a method of controlling the distribution of a fluid on a body that features compensating for varying distribution of constituent components of a composition that moved over a surface of a substrate. To that end, the method includes generating a sequence of patterns of liquid upon a substrate, each of which includes a plurality of spaced-apart liquid regions, with voids being defined between adjacent liquid regions. A second of the patterns of liquid of the sequence is arranged so that the liquid regions associated therewith are in superimposition with the voids of a first of the patterns of liquid of the sequence.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. published patent application 2006-0062922-A1, filed as U.S. patent application Ser. No. 10/948,511 on Sep. 23, 2004 entitled “Polymerization Technique to Attenuate Oxygen Inhibition of Solidification of Liquids and Composition Therefor,” which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The field of invention relates generally to nano-fabrication of structures. More particularly, the present invention is directed to methods for controlling distribution of fluid components on a body in imprint lithographic processes. 
     Nano-scale fabrication involves the fabrication of very small structures, e.g., having features on the order of one nanometer or more. A promising process for use in nano-scale fabrication is known as imprint lithography. Exemplary imprint lithography processes are described in detail in numerous publications, such as United States published patent application 2004/0065976 filed as U.S. patent application Ser. No. 10/264,960, entitled “Method and a Mold to Arrange Features on a Substrate to Replicate Features having Minimal Dimensional Variability”; United States published patent application 2004/0065252 filed as U.S. patent application Ser. No. 10/264,926, entitled “Method of Forming a Layer on a Substrate to Facilitate Fabrication of Metrology Standards”; and U.S. Pat. No. 6,936,194, issued Aug. 30, 2005 and entitled “Functional Patterning Material For Imprint Lithography Processes,” all of which are assigned to the assignee of the present invention. 
     Referring to  FIG. 1 , the basic concept behind imprint lithography is forming a relief pattern on a substrate that may function as, inter alia, an etching mask so that a pattern may be formed into the substrate that corresponds to the relief pattern. A system  10  employed to form the relief pattern includes a stage  11  upon which a substrate  12  is supported, and a template  14  having a mold  16  with a patterning surface  18  thereon. Patterning surface  18  may be substantially smooth and/or planar, or may be patterned so that one or more recesses are formed therein. Template  14  is coupled to an imprint head  20  to facilitate movement of template  14 . A fluid dispense system  22  is coupled to be selectively placed in fluid communication with substrate  12  so as to deposit polymerizable material  24  thereon. A source  26  of energy  28  is coupled to direct energy  28  along a path  30 . Imprint head  20  and stage  11  are configured to arrange mold  16  and substrate  12 , respectively, to be in superimposition, and disposed in path  30 . Either imprint head  20 , stage  11 , or both vary a distance between mold  16  and substrate  12  to define a desired volume therebetween that is filled by polymerizable material  24 . 
     Typically, polymerizable material  24  is disposed upon substrate  12  before the desired volume is defined between mold  16  and substrate  12 . However, polymerizable material  24  may fill the volume after the desired volume has been obtained. After the desired volume is filled with polymerizable material  24 , source  26  produces energy  28 , which causes polymerizable material  24  to solidify and/or cross-link, forming polymeric material conforming to the shape of the substrate surface  25  and mold surface  18 . Control of this process is regulated by processor  32  that is in data communication with stage  11  imprint head  20 , fluid dispense system  22 , and source  26 , operating on a computer-readable program stored in memory  34 . 
     An important characteristic with accurately forming the pattern in the polymerizable material is to reduce, if not prevent, adhesion to the mold of the polymeric material, while ensuring suitable adhesion to the substrate. This is referred to as preferential release and adhesion properties. In this manner, the pattern recorded in the polymeric material is not distorted during separation of the mold. Prior art attempts to improve the release characteristics employ a release layer on the surface of the mold. The release layer is typically hydrophobic and/or has low surface energy. The release layer adheres to the mold by covalent chemical bonding. Providing the release layer improves release characteristics. This is seen by minimization of distortions in the pattern recorded into the polymeric material that are attributable to mold separation. This type of release layer is referred to, for purposes of the present discussion, as an a priori release layer, i.e., a release layer that is solidified to the mold. 
     Another prior art attempt to improve release properties is described by Bender et al. in “Multiple Imprinting in UV-based Nanoimprint Lithography: Related Material Issues,” Microeletronic Engineering 61-62 (2002), pp. 407-413. Specifically, Bender et al. employ a mold having an a priori release layer in conjunction with a fluorine-treated UV curable material. To that end, a UV curable layer is applied to a substrate by spin-coating a 110 cPs UV curable fluid to form a UV curable layer. The UV curable layer is enriched with fluorine groups to improve the release properties. 
     A need exists, therefore, to improve the preferential release and adhesion properties of a mold employed in imprint lithography processes. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of controlling the distribution of a fluid on a body that features compensating for varying distribution of constituent components of a composition that move over a surface of a substrate. Specifically, the quantity of a surfactant component of a composition varied over the surface upon which the composition was spread to form a contiguous layer. Typically, the composition is deposited upon the surface as a plurality of spaced-apart droplets. It was discovered that the air-liquid interface of each droplet varied in dimension as the same was spread over the surface. This resulted in there being a depletion of surfactants, referred to as surfactant depletion regions (SDR) in the area of the contiguous layer proximate to the situs of the droplets and a surfactant rich region (SRR) in area of the layer located proximate to spaces between the droplets. This is believed to increase the probability that pitting of a solidified layer formed from the contiguous layer occurs. The pitting is believed to be attributable to, inter alia, from an uneven distribution of surfactant on the mold. A lamella layer is generated on the mold after each imprint. The lamella layer is formed primarily from surfactants present in the material disposed between the mold and the substrate during imprinting. An uneven distribution of surfactants in this material causes an uneven distribution of surfactants in the lamella layer. This in turn exacerbates the differences in surfactant quantities in the SDR and SRR as the number of imprints increases. To compensate for the varying distribution of surfactants in a given layer, the method includes generating a sequence of patterns of liquid upon a substrate, each of which includes a plurality of spaced-apart liquid regions, with interstices being defined between adjacent liquid regions. A second of the patterns of liquid of the sequence is arranged so that the liquid regions associated therewith are in superimposition with the interstices of a first of the patterns of liquid of the sequence. These and other embodiments are described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified plan view of a lithographic system in accordance with the prior art; 
         FIG. 2  is a simplified elevation view of a template and imprinting material disposed on a substrate in accordance with the present invention; 
         FIG. 3  is a top down view of a region of the substrate, shown in  FIG. 2 , upon which patterning occurs employing a pattern of droplets of polymerizable fluid disposed thereon; 
         FIG. 4  is a simplified elevation view of an imprint device spaced-apart from the patterned imprinting layer, shown in  FIG. 1 , after patterning in accordance with the present invention; 
         FIG. 5  is a detailed view of the template, shown in  FIG. 2  being removed after solidification of imprinting material in accordance with a second embodiment of the present invention; 
         FIG. 6  is a cross-sectional view of an imprinted layer showing varying thickness that the present invention is directed to reduce if not avoid; 
         FIG. 7  is a top down view of a region of the substrate, shown in  FIG. 2 , showing an intermediate pattern formed by the droplets of polymerizable fluid shown in  FIG. 3 , during spreading; 
         FIG. 8  is a detailed cross-sectional view of a portion of one droplet of imprinting material showing the change in shape of the same during formation of intermediate pattern in accordance with the present invention; 
         FIG. 9  is a detailed cross-sectional view of a portion of one droplet of imprinting material showing the change is surfactant molecule distribution as the shape of the same changes during formation of intermediate patterns; and 
         FIG. 10  is a partial top down view of  FIG. 3  showing a sequence of droplets deposited on a surface in furtherance of forming a sequence of contiguous layers of imprinting material in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 and 2 , a mold  36 , in accordance with the present invention, may be employed in system  10 , and may define a surface having a substantially smooth or planar profile (not shown). Alternatively, mold  36  may include features defined by a plurality of spaced-apart recessions  38  and protrusions  40 . The plurality of features defines an original pattern that forms the basis of a pattern to be formed on a substrate  42 . Substrate  42  may comprise a bare wafer or a wafer with one or more layers disposed thereon, one of which is shown as primer layer  45 . To that end, reduced is a distance “d” between mold  36  and substrate  42 . In this manner, the features on mold  36  may be imprinted into a conformable region of substrate  42 , such as an imprinting material disposed on a portion of surface  44  that presents a substantially planar profile. It should be understood that the imprinting material may be deposited using any known technique, e.g., spin-coating, dip coating and the like. In the present example, however, the imprinting material is deposited as a plurality of spaced-apart discrete droplets  46  on substrate  42 . 
     Referring to both  FIGS. 3 and 4 , droplets  46  are arranged in a pattern  49  to facilitate formation of a contiguous layer  50 . Imprinting material is formed from a composition that may be selectively polymerized and cross-linked to record the original pattern therein, defining a recorded pattern. Specifically, the pattern recorded in the imprinting material is produced, in part, by interaction with mold  36 , e.g., electrical interaction, magnetic interaction, thermal interaction, mechanical interaction or the like. In the present example, mold  36  is spaced-apart from substrate  42  with the area of surface  44  in superimposition therewith being shown by periphery  51 . Portions of surface  44  not covered by droplets  46  and within periphery  51  define voids  53 . Regions of mold  36  in superimposition with droplets  46  define deposition zones. It should be understood that for purposes of the present example, each side of periphery  51  is 25 millimeters in length, i.e., the area encompassed by periphery is 25×25 mm square. Droplets  46  are shown to reflect an accurate depiction of proportional size a diameter thereof compared to the length of one side of periphery  51 . Although droplets  46  are shown being different sizes, the present invention envisions an embodiment wherein all the droplets  46  are of the same size, i.e., contain the same quantity of liquid. Regions of mold  36  in superimposition with voids  53  define interstices. Mold  36  comes into mechanical contact with the imprinting material, spreading droplets  46 , so as to generate a contiguous layer  50  of the imprinting material over surface  44 . In one embodiment, distance “d” is reduced to allow sub-portions  52  of imprinting material to ingress into and fill recessions  38 . To facilitate filling of recessions  38 , before contact between mold  36  and droplets  46 , the atmosphere between mold  36  and droplets  46  is saturated with helium or is completely evacuated or is a partially evacuated atmosphere of helium. It may be desired to purge the volume, defined between mold  36 , surface and droplets  46 , shown in  FIG. 2 , for example with Helium gas flowed at 5 pounds per square inch (psi), before contact occurs. An exemplary purging technique is disclosed in U.S. Pat. No. 7,090,716 issued Aug. 15, 2006, entitled SINGLE PHASE FLUID IMPRINT LITHOGRAPHY, which is incorporated by reference herein. 
     The imprinting material is provided with the requisite properties to completely fill recessions  38  while covering surface  44  with a contiguous formation of the imprinting material. In the present embodiment, sub-portions  54  of imprinting material in superimposition with protrusions  40  remain after the desired, usually minimum, distance “d” has been reached. This action provides contiguous layer  50  with sub-portions  52  having a thickness t 1 , and sub-portions  54 , having a thickness t 2 . Thicknesses “t 1 ,” and “t 2 ” may be any thickness desired, dependent upon the application. Thereafter, contiguous layer  50  is solidified by exposing the same to the appropriate curing agent, e.g., actinic energy, such as broadband ultra violet energy, thermal energy or the like, depending upon the imprinting material. This causes the imprinting material to polymerize and cross-link. The entire process may occur at ambient temperatures and pressures, or in an environmentally-controlled chamber with desired temperatures and pressures. In this manner, contiguous layer  50  is solidified to provide side  56  thereof with a shape conforming to a shape of a surface  58  of mold  36 . 
     Referring to  FIGS. 1 ,  2  and  3 , the characteristics of the imprinting material are important to efficiently pattern substrate  42  in light of the unique patterning process employed. For example, it is desired that the imprinting material have certain characteristics to facilitate rapid and even filling of the features of mold  36  so that all thicknesses t 1  are substantially uniform and all thicknesses t 2  are substantially uniform. To that end, it is desirable that the viscosity of the imprinting material be established, based upon the deposition process employed, to achieve the aforementioned characteristics. As mentioned above, the imprinting material may be deposited on substrate  42  employing various techniques. Were the imprinting material deposited as a plurality of discrete and spaced-apart droplets  46 , it would be desirable that a composition from which the imprinting material is formed have relatively low viscosity, e.g., in a range of 0.5 to 30 centipoises (cPs). 
     Considering that the imprinting material is spread and patterned concurrently, with the pattern being subsequently solidified into contiguous layer  50  by exposure to radiation, it would be desired to have the composition wet surface of substrate  42  and/or mold  36  and to avoid subsequent pit or hole formation after polymerization. Were the imprinting material deposited employing spin-coating techniques, it would be desired to use higher viscosity materials, e.g., having a viscosity greater than 10 cPs and typically, several hundred to several thousand cPs, with the viscosity measurement being determined in the absence of a solvent. The total volume contained in droplets  46  may be such so as to minimize, or avoid, a quantity of the imprinting material from extending beyond the region of surface  44  in superimposition with mold  36 , while obtaining desired thicknesses t 1  and t 2 , e.g., through capillary attraction of the imprinting material with mold  36  and surface  44  and surface adhesion of the imprinting material. 
     In addition to the aforementioned characteristics, referred to as liquid phase characteristics, it is desirable that the composition provides the imprinting material with certain solidified phase characteristics. For example, after solidification of contiguous layer  50 , it is desirable that preferential adhesion and release characteristics be demonstrated by the imprinting material. Specifically, it is beneficial for the composition from which the imprinting material is fabricated to provide contiguous layer  50  with preferential adhesion to substrate  42  and preferential release of mold  36 . In this fashion, reduced is the probability of distortions in the recorded pattern resulting from the separation of mold  36  therefrom due to, inter alia, tearing, stretching or other structural degradation of contiguous layer  50 . 
     For example, with reference to  FIGS. 4 and 5 , upon separation of mold  36 , contiguous layer  50  is subjected to a separation force Fs. Separation force Fs is attributable to a pulling force F P  on mold  36  and adhering forces, e.g., Van der Waals forces, between contiguous layer  50  and mold  36 . Pulling force F P  is used to break vacuum seal. It is desired to decouple mold  36  from contiguous layer  50  without unduly distorting contiguous layer  50 . One manner in which to control distortion of contiguous layer  50  during separation of mold  36  therefrom is by providing the composition from which the imprinting material is formed with releasing agents, such as surfactants. 
     The constituent components of the composition that form the imprinting material and layer  45  to provide the aforementioned characteristics may differ. This results from substrate  42  being formed from a number of different materials, i.e. providing differing magnitudes of adhering forces F A . As a result, the chemical composition of surface  44  varies dependent upon the material from which substrate  42  is formed. For example, substrate  42  may be formed from silicon, plastics, gallium arsenide, mercury telluride, and composites thereof. As mentioned above, substrate  42  may include one or more layers shown as primer layer  45 , e.g., dielectric layer, metal layer, semiconductor layer, planarization layer and the like, upon which contiguous layer  50  is generated. To that end, primer layer  45  would be deposited upon a wafer  47  employing any suitable technique, such as chemical vapor deposition, spin-coating and the like. Additionally, primer layer  45  may be formed from any suitable material, such as silicon, germanium and the like. Additionally, mold  36  may be formed from several materials, e.g., fused-silica, quartz, indium tin oxide diamond-like carbon, MoSi, sol-gels and the like. 
     An exemplary composition that may be employed from which to form contiguous layer  50  is as follows: 
     Composition 
     
         
         
           
             isobornyl acrylate 
             n-hexyl acrylate 
             ethylene glycol diacrylate 
             2-hydroxy-2-methyl-1-phenyl-propan-1-one 
             R 1 R 2    
           
         
       
    
     An acrylate component of the bulk material, isobornyl acrylate (IBOA), has the following structure: 
                                
and comprises approximately 47% of COMPOSITION by weight, but may be present in a range of 20% to 80%, inclusive. As a result, the mechanical properties of solidified imprinting layer  134  are primarily attributable to IBOA. An exemplary source for IBOA is Sartomer Company, Inc. of Exton, Pa. available under the product designation SR 506.
 
     The component n-hexyl acrylate (n-HA) has the following structure: 
                                
and comprises approximately 25% of bulk material by weight, but may be present in a range of 0% to 40%, inclusive. Also providing flexibility to formation  50 , n-HA is employed to reduce the viscosity of the prior art bulk material so that bulk material, in the liquid phase, has a viscosity in a range 2-9 Centipoises, inclusive. An exemplary source for the n-HA component is the Aldrich Chemical Company of Milwaukee, Wis.
 
     A cross-linking component, ethylene glycol diacrylate, has the following structure: 
                                
and comprises approximately 15% of bulk material by weight, and may be present in a range of 10% to 50%, inclusive. EGDA also contributes to the modulus and stiffness buildup, as well as facilitates cross-linking of n-HA and IBOA during polymerization of the bulk material.
 
     An initiator component, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, is available from Ciba Specialty Chemicals of Tarrytown, N.Y. under the trade name DAROCUR® 1173, and has the following structure: 
                                
and comprises approximately 3% of the bulk material by weight, and may be present in a range of 1% to 5%, inclusive. The initiator is responsive to a broad band of ultra-violet radiation generated by a medium-pressure mercury lamp. In this manner, the initiator facilitates cross-linking and polymerization of the components of the bulk material. The constituent components of COMPOSITION, IBOA, n-HA, EGDA and 2-hydroxy-2-methyl-1-phenyl-propan-1-one form the bulk material of the same.
 
     A surfactant component, R 1 R 2 , is a non-ionic surfactant sold by Mason Chemical Company of Arlington Heights, Ill. under the product names MASURF® FS-2000. The surfactant component consists of approximately 2%, by weight, of the bulk material and acts as a release agent of COMPOSITION by facilitating preferential adhesion and release of contiguous layer  50 , once solidified. 
     The advantages of this patterning process are manifold. For example, the thickness differential between protrusions  40  and recessions  38  facilitates formation, in substrate  42 , of a pattern corresponding to the recorded pattern formed in contiguous layer  50 . Specifically, the thickness differential between t 1  and t 2  of protrusions  40  and recession  38 , respectively, results in a greater amount of etch time being required before exposing regions of substrate  42  in superimposition with protrusions  40  compared with the time required for regions of substrate  42  in superimposition with recession  52  being exposed. For a given etching process, therefore, etching will commence sooner in regions of substrate  42  in superimposition with recessions  38  than regions in superimposition with protrusions  40 . This facilitates formation of a pattern in substrate corresponding to the aforementioned recorded pattern. By properly selecting the imprinting materials and etch chemistries, the relational dimensions between the differing features of the pattern eventually transferred into substrate  42  may be controlled as desired. To that end, it is desired that the etch characteristics of the recorded pattern, for a given etch chemistry, be substantially uniform. 
     As a result, the characteristics of the imprinting material are important to efficiently pattern substrate  42  in light of the unique patterning process employed. As mentioned above, the imprinting material is deposited on substrate  42  as a plurality of discrete and spaced-apart droplets  46 . The combined volume of droplets  46  is such that the imprinting material is distributed appropriately over an area of surface  44  where the recorded pattern is to be formed. In this fashion, the total volume of the imprinting material in droplets  46  defines the distance “d”, to be obtained so that the total volume occupied by the imprinting material in the gap defined between mold  36  and the portion of substrate  42  in superimposition therewith once the desired distance “d” is reached is substantially equal to the total volume of the imprinting material in droplets  46 . To facilitate the deposition process, it is desired that the imprinting material provide rapid and even spreading of the imprinting material in droplets  46  over surface  44  so that all thicknesses t 1  are substantially uniform and all residual thicknesses t 2  are substantially uniform. 
     Referring to  FIGS. 3 and 6 , a problem recognized by the present invention involves varying characteristics of a contiguous layer of imprinting material. Specifically, formed on a substrate  142  was a layer  100  in the manner discussed above, i.e., except with a non-patterned mold (not shown) having a smooth surface, to spread droplets  46 . After spreading of droplets  46  the imprinting material was exposed for approximately 700 ms to actinic energy having a wavelength of approximate 365 nm a flux of 77 mW/cm 2  to solidify the same. After sequentially forming and solidifying several layers  100  employing mold  36 , observed were pits  102  over the area of layers  100  formed later in the sequence. Pits  102  were found to be a complete absence of layer  100  in superimposition with portions  104  of substrate  142  and located between portions  106  of layer  100  having a desired thickness. It is believed that pits  102  result from an uneven surfactant distribution over layer  100  that prevents the bulk material of COMPOSITION from being in superimposition with regions  104 . The difference becomes more pronounced as the number of layers  100  imprinted. 
     Referring to  FIGS. 3 ,  4  and  6 , the present invention overcomes these drawbacks by changing the position of droplets  46  in pattern  49  on sequential formation of contiguous layers, such as contiguous layer  50  or  100 . The present discussion concerns contiguous layer  100 , with the understanding that the same applies to contiguous layer  50 , as well. Specifically, it was found that the quantity of the surfactant component of COMPOSITION varied in contiguous layer  100  over the surface upon which the composition was spread to form solidified contiguous layer  100 . Typically, the composition is deposited upon surface  44  as a plurality of spaced-apart droplets  46 . It was discovered that the surfactant concentration in the air-liquid interface of each droplet varied as the droplet was spread over the surface. This resulted from several factors, including the viscosity differential between the surfactant component of COMPOSITION and the bulk material component of the same and the consumption of the surfactant component by clinging to the mold  36  surface in contact with the COMPOSITION. The presented as surfactant depletion regions (SDR) in the area of the contiguous layer proximate to the situs of the droplets  46 , regions  106 , and a surfactant rich region (SRR) in areas of the layer located proximate to spaces between the droplets, regions  104 . 
     Referring to  FIGS. 3 ,  8  and  9 , observing that surfactants have an affinity for the region of a liquid proximate to a liquid-air interface it was realized that during formation of a contiguous layer, surfactant molecules underwent redistribution due to the varying size of the liquid-air-interface. Upon deposition of droplets  46  on surface  44 , each of the droplets  46  generates an initial liquid-air interface  120 . Surfactant molecules  122  are packed tightly, after a predetermined time, at interface  120 . As mold  36  interacts with droplets  46 , liquid in droplets  46  moves with respect to substrate  42 , in direction of the movement shown by arrow  124  forming a series of intermediate patterns, such as pattern  110 , before droplets  46  merge to form contiguous layer  100 . As droplets  46  move the air-liquid interface  120  moves, shown by liquid-air interface  220 , which finally becomes ambient-air interface  108 , shown in  FIG. 7 . This results in the spacing between adjacent surfactant molecules  122  increasing, shown in  FIG. 9 , for the reasons discussed above. As a result, a greater number of surfactant molecules travel from regions of liquids in superimposition with deposition zones of mold  36 , creating SDR regions thereat, and an SRR region in areas of liquid in superimposition with interstices of mold  36 , shown in  FIG. 4 . 
     Referring to  FIGS. 4 ,  6 ,  8  and  9 , the presence of surfactant molecules  122  in contiguous layer  100  generates a lamella layer  150  on mold  36  after formation of each contiguous layer  100 . Lamella layer  150  comprises a densely packed fluid composition of surfactant molecules  122 . The distribution of surfactant molecules  122  in lamella layer  150  matches the distribution of surfactant molecules in contiguous layer  100 , i.e. SDR regions  102  and SRR region  104 . Thus, there is an uneven distribution of surfactant molecules  122  in lamella layer  150 . On formation of subsequent contiguous layers, the difference in surfactant molecule distribution in lamella layer  150  may become exacerbated, resulting in an increasing probability that voids may be present in contiguous layer  100 . To reduce, if not avoid an uneven distribution of surfactant molecules  122  in layers  100  and  150 , a subsequent layer formed by mold  36  would be generated by locating deposition zones of the same to be in superimposition with interstices of a previously formed contiguous layer  100  that includes regions  104 , shown more clearly in  FIG. 10 . 
     Referring again to  FIGS. 4 ,  6 ,  8  and  9 , in this manner, the existing surfactant molecule  122  distribution present in lamella  150  may be compensated for, at least in part, by the resulting surfactant molecule  122  distribution from spreading of droplets  46  to form contiguous layer  100 . This is referred to as a droplet pattern shift in which sequential contiguous layers formed from COMPOSITION is generated by shifting the droplets in the pattern for one of the contiguous layers in the sequence compared to the position of the droplets in the pattern employed to form the previous contiguous layer in the sequence. 
     Referring to  FIG. 10 , it should be understood, however, that it need not be necessary to shift the pattern  49  of droplets so that the entire area of droplets  46  are in superimposition with the interstices. Rather, it is within the spirit of the present invention that there may be an overlap between droplets  46  of one pattern and droplets  146  of the next pattern formed in a sequence. This may be repeated until a pattern is formed corresponding to a subsequent contiguous layer the area of which is entirely within a void  53  of an initial pattern and, therefore, the interstice. Moreover, it may be desirable to vary the quantity of surfactants in one or more of droplets  46 ,  146 ,  246  and  346  to avoid pitting of contiguous layer  100 , shown in  FIG. 6 . 
     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. The scope of the invention should not, therefore, be limited by the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Technology Classification (CPC): 1