Abstract:
The present invention provides a method of planarizing a substrate with a template spaced-apart from the substrate having a liquid disposed therebetween, the method including: contacting the liquid with the template forming a first shape therein; and impinging radiation upon the liquid causing a reduction in volume of the liquid, with the first shape compensating for the reduction in volume such that upon impinging the actinic radiation upon the liquid, the liquid forms a contoured layer having a substantially planar shape.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The field of invention relates generally to semiconductor device processing. More particularly, the present invention is directed to a method of compensating for a volumetric shrinkage of a material disposed upon a substrate to form a substantially planar structure therefrom.  
         [0002]     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.  
         [0003]     As the minimum features size of structures formed on substrates is reduced, the need to form a substrate having a substantially planar surface is increased. A method of planarizing a substrate is disclosed in U.S. patent application Publication 2003/0184917 to Chang et al. Chang et al. describes a method of reducing step heights in the planarization of thin films carriers in an encapsulation system by utilizing an adhesive tape having a thinner adhesive thickness and stiffer tape for the film sealing the encapsulant on the carrier to result in a low step height surface transition between the carrier and the cured encapsulant. Also, the composition of the encapsulant may be altered to reduce the shrinkage thereof during curing. A first approach to alter the composition of the encapsulant is to include absorbents in the formulation of the encapsulant to absorb the irradiation and reducing the curing effect. A second approach to alter the composition of the encapsulant is to add a gas-emitting additive into the encapsulant, which will be converted into gaseous products upon irradiation.  
         [0004]     Another method of planarizing a substrate is disclosed in U.S. Pat. No. 6,218,316 to Marsh. Marsh describes a method of planarizing a substrate having a planarization material disposed thereon and bringing a substantially flat surface into contact therewith. The planarization material is exposed to radiation at a first wavelength of light to cure the planarization material and is exposed to radiation at a second wavelength of light to cause changes to the planarization material that facilitate separation of the substantially flat surface from the planarization material.  
         [0005]     It is desired, therefore, to provide an improved method of planarizing a substrate.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides a method of planarizing a substrate with a template spaced-apart from the substrate having a liquid disposed therebetween, the method including; contacting the liquid with the template forming a first shape therein; and impinging radiation upon the liquid causing a reduction in volume of the liquid, with the first shape compensating for the reduction in volume such that upon impinging the actinic radiation upon the liquid, the liquid forms a contoured layer having a substantially planar shape. These embodiments and others are described more fully below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a simplified elevation view of a multi-layered structure, having a substrate and a transfer layer, prior to polymerizing and cross-linking a material of the transfer layer;  
         [0008]      FIG. 2  is a simplified representation of the material from which the transfer layer, shown in  FIG. 1 , is comprised before being polymerized and cross-linked;  
         [0009]      FIG. 3  is a simplified representation of cross-linked polymer material into which the material shown in  FIG. 2  is transformed after being subjected to radiation;  
         [0010]      FIG. 4  is a simplified elevation view of the multi-layered structure, shown in  FIG. 1 , after the transfer layer is polymerized and cross-linked;  
         [0011]      FIG. 5  is a simplified elevation view of a multi-layered structure comprising a template and a imaging layer;  
         [0012]      FIG. 6  is a simplified elevation view of the multi-layered structure of  FIG. 5  prior to contact with the transfer layer of the multi-layered structure shown in  FIG. 1 ;  
         [0013]      FIG. 7  is a simplified elevation view of the multi-layered structure of  FIG. 5  in contact with the transfer layer of the multi-layered structure of  FIG. 1 ;  
         [0014]      FIG. 8  is a simplified elevation view of the multi-layered structure of  FIG. 5  after being exposed to radiation;  
         [0015]      FIG. 9  is a simplified elevation view of the multi-layered structure of  FIG. 5  in superimposition with the multi-layered structure of  FIG. 1  showing misalignment along one direction;  
         [0016]      FIG. 10  is a top down view of the multi-layered structure of  FIG. 5  and the multi-layered structure of  FIG. 1  showing misalignment along two transverse directions;  
         [0017]      FIG. 11  is a top down view of the multi-layered structure of  FIG. 5  and the multi-layered structure of  FIG. 1  showing angular misalignment;  
         [0018]      FIG. 12  is a simplified elevation view of the multi-layered structure of  FIG. 5  having a crown surface formed thereon;  
         [0019]      FIG. 13  is an exploded view of a region of the multi-layered structure of  FIG. 8 ;  
         [0020]      FIG. 14  is a simplified elevation view of the multi-layered structure of  FIG. 8  having a tilted surface;  
         [0021]      FIG. 15  is a top down view of the multi-layered structure shown in  FIG. 4 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Referring to  FIG. 1 , a multi-layered structure  10  is shown prior to exposure to radiation, described further below. Multi-layered structure  10  comprises a substrate  12  and a transfer layer  14 , with transfer layer  14  being disposed upon substrate  12 . Substrate  12  may be formed from materials including, but not limited to, silicon, gallium arsenide, quartz, fused-silica, sapphire, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers or a combination thereof. Transfer layer  14  may be deposited upon substrate  12  in a plurality of methods including, but not limited to, chemical vapor deposition (CVD), physical vapor deposition (PVD), sputter deposition, spin-coating, and dispensing of a liquid. Transfer layer  14  comprises a surface  15  and as shown in  FIG. 1 , surface  15  comprises a substantially planar profile. However, surface  15  may comprise a substantially non-planar profile.  
         [0023]     Substrate  12  may comprise a plurality of protrusions and recesses, however, only protrusions  16 ,  18 , and  20  and recesses  22 ,  24 ,  26 , and  28  are shown, with protrusions  16 ,  18 , and  20  and recesses  22 ,  24 ,  26 , and  28  forming a pattern on a surface  30  of substrate  12 . The pattern formed on surface  30  of substrate  12  may be formed by such techniques including, but not limited to, photolithography, e-beam lithography, x-ray lithography, ion beam lithography, and imprint lithography. Imprint lithography is described in detail in numerous publications, such as U.S. 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”; U.S. 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. published patent application 2004/0046271 field as U.S. patent application Ser. No. 10/235,314, entitled “Functional Patterning Material for Imprint Lithography Processes”, all of which are assigned to the assignee of the present invention. An exemplary lithographic system utilized in imprint lithography is available under the trade name IMPRIO 100™ from Molecular Imprints, Inc., having a place of business at 1807-C Braker Lane, Suite 100, Austin, Tex. 78758. The system description for the IMPRIO 100™ is available at www.molecularimprints.com and is incorporated herein by reference.  
         [0024]     Additionally, it has been found beneficial to deposit a primer layer (not shown) when forming transfer layer  14  upon substrate  12  which may or may not include any previously disposed patterned/unpatterned layer present on substrate  12 . The primer layer (not shown) may function, inter alia, to provide a standard interface with transfer layer  14 , thereby reducing the need to customize each process to the material upon which transfer layer  14  is to be deposited. In addition, the primer layer (not shown) may be formed from an organic material with the same etch characteristics as transfer layer  14 . The primer layer (not shown) is fabricated in such a manner so as to possess a continuous, smooth, if not planar, relatively defect-free surface that may exhibit excellent adhesion to transfer layer  14 . An exemplary material from which to form the primer layer (not shown) is available from Brewer Science, Inc. of Rolla, Mo. under the trade name DUV30J-6. The primer layer (not shown) may be deposited using any know technique with respect to patterned layer  14 .  
         [0025]     As mentioned above, substrate  12  comprises protrusions  16 ,  18 , and  20  and recesses  22 ,  24 ,  26 , and  28 . Protrusion  16  may be disposed between recess  22  and recess  24 ; protrusion  18  may be disposed between recess  24  and recess  26 ; and protrusion  20  may be disposed between recess  26  and recess  28 . Transfer layer  14  has a thickness ‘a’ defined between surface  15  and recess  24  and a thickness ‘b’ defined between surface  15  and protrusion  18 , with thickness ‘a’ being greater than thickness ‘b.’ In the present example, thickness ‘a’ may have a value of approximately 250 nm and thickness ‘b’ may have a value of approximately 50 nm. However, thicknesses ‘a’ and ‘b’ may have any value desired.  
         [0026]     Referring to  FIGS. 1 and 2 , transfer layer  14  may be formed from a material  32  forming a volume  34  within transfer layer  14 . An exemplary composition for material  32  is disclosed in U.S. patent application Ser. No. 10/463,396, filed on Jun. 16, 2003, entitled “Method to Reduce Adhesions between a Conformable Region and a Pattern of a Mold,” which is incorporated by reference in its entirety herein. Material  32  is shown in  FIG. 3  as being cross-linked at points  36 , forming a cross-linked polymer material  38 .  
         [0027]     Referring to  FIG. 4 , multi-layered structure  10  is shown after radiation is impinged thereupon. Referring to  FIGS. 1, 2 , and  4 , as a result, material  32  of transfer layer  14  is polymerized and cross-linked forming cross-linked polymer material  38 , shown in  FIG. 3 , and as a result, the composition of transfer layer  14  transforms from material  32  to cross-linked polymer material  38 , shown in  FIG. 3 , which is a solid.  
         [0028]     However, upon polymerization, e.g. curing, of material  32  to form cross-linked polymer material  38  within transfer layer  14 , volume  34  associated with transfer layer  14  is reduced by a shrinkage factor F 1 , forming a volume  40 , as shown in  FIG. 4 , within transfer layer  14 , wherein shrinkage factor F 1  is a property of material  32 . As a result, surface  15 , shown in  FIG. 1 , transforms to form a surface  17 , wherein surface  17  comprises a substantially non-planar profile, which is undesirable. As a result of forming volume  40  within transfer layer  14 , the thickness of transfer layer  14  with respect to substrate  12  is reduced. More specifically, thickness ‘a’ is reduced to form a thickness ‘c’ between surface  17  and recess  24 ; and thickness ‘b’ is reduced to form a thickness ‘d’ between surface  17  and protrusion  18 . Therefore, to minimize, if not prevent, forming surface  17  of multi-layered structure  10 , a multi-layered structure  42 , shown in  FIG. 5 , is utilized, described further below.  
         [0029]     Referring to  FIG. 5 , multi-layered structure  42  is shown. Multi-layered structure  42  comprises a substrate  44  and an imaging layer  46 . Substrate  44  may be formed from any of the materials mentioned above with respect to substrate  12 , shown in  FIG. 1 . Imaging layer  46  may be deposited upon substrate  44  in any of the methods mentioned above with respect to transfer layer  14 , shown in  FIG. 1 .  
         [0030]     Referring to  FIGS. 1, 4 , and  5 , as mentioned above, volume  34  associated with transfer layer  14  is reduced by a shrinkage factor F 1 , forming a volume  40 , as shown in  FIG. 4 , within transfer layer  14 , and thus surface  15  transforms to form a surface  17 , wherein surface  17  comprises a substantially non-planar profile, which is undesirable. To that end, a priori knowledge of the shrinkage factor F 1  may be beneficial in that multi-layered structure  42  may be formed to compensate for such a shrinkage factor F 1  of material  32 , shown in  FIG. 2 , of transfer layer  14  such that surface  17  may comprise a substantially planar profile after polymerization of material  32 , shown in  FIG. 2 , within transfer layer  14 . More specifically, a surface  48  of multi-layered structure  42  is formed to have a profile that is substantially the same as the profile of surface  17  of multi-layered structure  10 . To form substantially the same profile as surface  17  of multi-layered structure  10  on multi-layered structure  42 , imaging layer  46  may comprise a material such that when the same is subjected to radiation, a volume of the material is reduced by a shrinkage factor F 2 , with shrinkage factor F 2  being substantially the same as shrinkage factor F 1  of material  32  of transfer layer  14 , described further below.  
         [0031]     In a first embodiment, to have shrinkage factor F 2  be substantially the same as shrinkage factor F 1 , the material of imaging layer  46  may be selected such that the same comprises a component that reduces in volume in response to radiation being impinged thereupon. Therefore, an organic modified silicate may be utilized that comprises a functional group, wherein the percentage of reduction of volume of the material of imaging layer  46  depends upon the density of the functional group contained with the organic modified silicate. Exemplary materials from which to form imaging layer  46  are available from Microresist Technology GmbH located in Berlin, Germany under the trade names Ormocer® B59 and Ormocer® B66.  
         [0032]     In a further embodiment, to have shrinkage factor F 2  be substantially the same as shrinkage factor F 1 , the material of imaging layer  46  may be selected such that the same may comprise a first component that expands in volume in response to radiation impinged thereupon and a second component that reduces in volume in response to radiation impinged thereupon. By adjusting the ratio of the first and second components contained with the material of imaging layer  46 , the shrinkage factor F 2  of the material of imaging layer  46  may be matched to the shrinkage factor F 1  of material  32 , shown in  FIG. 2  of transfer layer  14 . A first composition for the material of imaging layer  46  consists of the following:  
       COMPOSITION 1  
     bisphenol A-glycidyl methacrylate 1,5,7,11-tetraoxaspiro[5.5]undecane 2-hydroxy-2-methyl-1-phenyl-propan-1-one triarylsulfonium hexafluoroantimonate salt  
       [0033]     The component bisophenol A-glycidyl methacrylate (Bis-GMA) has the following general structure:  
                         
 
 and comprises approximately 58% of COMPOSITION 1 by weight. 
 
         [0034]     The component 1,5,7,11-tetraoxaspiro[5.5] undecane (TOSU) has the following general structure:  
                         
 
 and comprises approximately 38.6% of COMPOSITION 1 by weight. 
 
         [0035]     The component 2-hydroxy-2-methyl-1-phenyl-propan-1-one comprises approximately 1.9% of COMPOSITION 1 by weight and is available from Ciba Geigy located in Basel, Switzerland under the trade name Darocur® 1173. The component triarylsulfonium hexafluoroantimonate salt comprises approximately 1.5% of COMPOSITION 1 by weight and is available from Dow Chemical located in Midland, Mich. under the trade name UVI® 6976. In COMPOSITION 1, the component Bis-GMA reduces in volume in response to radiation impinged thereupon while the component TOSU expands in volume in response to radiation impinged thereupon. By adjusting the ratio of Bis-GMA and TOSU contained in COMPOSITION 1, the shrinkage factor F 2  of the material of imaging layer  46  may be matched to the shrinkage factor F 1  of transfer layer  14 .  
         [0036]     A second composition for the material of imaging layer 46 consists of the following:  
       COMPOSITION 2  
     diglycidyl ether of bisphenol-A 1,5,7,11-tetraoxaspiro[5.5]undecane triarylsulfonium hexafluoroantimonate salt  
       [0037]     The component diglycidyl ether of bisphenol-A comprises approximately 67.3% of COMPOSITION 2 by weight and is available from Dow Chemical located in Midland, Mich. under the trade name DER® 332. The component 1,5,7,11-tetraoxaspiro[5.5]undecane (TOSU) comprises approximately 28.9% of COMPOSITION 2 by weight. The component triarylsulfonium hexafluoroantimonate salt comprises approximately 3.8% of COMPOSITION 2 by weight. In COMPOSITION 2, the component diglycidyl ether of bisphenol-A reduces in volume in response to radiation impinged thereupon while the component TOSU expands in volume in response to radiation impinged thereupon. By adjusting the ratio of diglycidyl ether of bisphenol-A and TOSU contained in COMPOSITION 2, the shrinkage factor F 2  of the material of imaging layer  46  may be matched to the shrinkage factor F 1  of transfer layer  14 . In a preferred embodiment, the material of imaging layer comprises COMPOSITION 1.  
         [0038]     Referring to  FIGS. 2 and 6 , multi-layered structure  42  is shown spaced-apart from multi-layered structure  10  defining a gap  50  therebetween. To that end, to make mechanical contact between multi-layered structures  10  and  42 , gap  50  is reduced, as shown in  FIG. 7 . Surface  15  of multi-layered structure  10  conforms to a profile of surface  48  of multi-layered structure  42 . After gap  50  is reduced, radiation is impinged upon material  32  of transfer layer  14  to polymerize and cross-link the same, forming cross-linked polymer material  38 , shown in  FIG. 3 , which is a solid. The radiation impinged upon multi-layered structure  10  may be ultraviolet, thermal, electromagnetic, visible light, heat, and the like. The selection of radiation impinged upon to initiate the polymerization of transfer layer  14  is known to one skilled in the art and typically depends on the specific application which is desired. Specifically, cross-linked polymer material  38 , shown in  FIG. 3 , is solidified to provide surface  15  of multi-layered structure  10  with a substantially planar profile. After transfer layer  14  is transformed to consist of cross-linked polymer material  38 , gap  50  is increased such that multi-layered structures  10  and  42  are spaced-apart, as shown in  FIG. 8 , wherein surface  15  of multi-layered is substantially planar.  
         [0039]     Surface  15  comprises a substantially planar profile as a result of surface  48  of multi-layered structure  42 . More specifically, imaging layer  46  makes a pattern in transfer layer  14  such that when material  32  of transfer layer  14  is exposed to actinic radiation, the reduction in volume of material  32  is such that surface  15  of multi-layered structure  10  comprises a substantially planar profile. To that end, surface  48  of multi-layered structure  42  is defined to facilitate in the formation of a planar profile in surface  15  of multi-layered structure  10 , as desired.  
         [0040]     Referring to  FIG. 6 , to properly form surface  15  of multi-layered structure  10  with a substantially planar profile, proper alignment of multi-layered structure  42  with respect to multi-layered structure  10  is needed. Ascertaining a proper alignment between multi-layered structure  42  and multi-layered structure  10  facilitates in compensating for the volumetric reduction in volume  34 , shown in  FIG. 1 , of transfer layer  14  such that surface  15  comprises a substantially planar profile.  
         [0041]     Referring to  FIGS. 9 and 10 , to facilitate the above-mentioned alignment of multi-layered structures  10  and  42 , multi-layered structure  42  may include multi-layered structure alignment marks, one of which is shown as  52 , and multi-layered structure  10  may include multi-layered structure alignment marks, one of which is shown as  54 . In the present example, it is assumed that desired alignment between multi-layered structures  10  and  42  occurs upon multi-layered alignment mark  52  being in superimposition with multi-layered structure alignment mark  54 . As shown in  FIG. 9 , desired alignment between multi-layered structures  10  and  42  has not occurred, shown by the two marks being offset a distance O. Further, although offset O is shown as being a linear offset in one direction, it should be understood that the offset may be linear along two directions shown as O 1  and O 2 , as shown in  FIG. 10 . In addition to, or instead of, the aforementioned linear offset in one or two directions, the offset between multi-layered structures  10  and  42  may also consist of an angular offset, shown in  FIG. 11  as angle θ. An exemplary embodiment for alignment marks  52  and  54  is disclosed in U.S. Pat. No. 5,414,514 entitled “On-Axis Interferometric Alignment of Plates using the Spatial Phase of Interference Patterns,” and U.S. Pat. No. 5,808,742 entitled “Optical Alignment Apparatus having Multiple Parallel Alignment Marks.” 
         [0042]     Referring to  FIG. 12 , in a further embodiment, multi-layered structure  10  may be subjected to a blanket etch such that a crown surface  60  is formed on multi-layered structure  10 , wherein crown surface  60  is defined by an exposed surface  62  of each of protrusions  16 ,  18 , and  20  and an upper surface of portions  64  that remain on transfer layer  14  after multi-layered structure  10  is subjected to the aforementioned blanket etch.  
         [0043]     Referring to  FIG. 13 , a portion  70  of multi-layered structure  10 , shown in  FIG. 8 , is depicted, wherein portion  70  displays a level of planarity of surface  15  that is preferred in the present invention. Surface  15  comprises a plurality of hills and valleys; however, only hill  72  and valley  74  are shown. The plurality of hills and valleys of surface  15  define an average plane of planarity, shown as plane ‘a,’ of surface  15 . However, the plurality of hills and valleys of surface  15  may deviate from plane ‘a’ by differing magnitudes and wherein, for simplicity, each deviation may be defined as Δ dev . More specifically, a zenith of hill  72  may deviate from plane ‘a’ a magnitude Δ 1  and a nadir of valley  74  may deviate from plane ‘a’ a magnitude Δ 2 . The values of the deviations of the plurality of hills and valleys of surface  15 , Δ dev , from plane ‘a’ are a function of a step height ‘h’ of protrusions  16 ,  18  and  20 . In the present invention, a preferred level of planarity of surface  15  is defined by the equation: 
 
Δ dev   ≦h/N,    (1) 
 
 wherein it is desirable to have N≧1. To that end, a more preferred level of planarity of surface  15  is defined by the equation: 
 
Δ dev   ≦h/ 5   (2) 
 
 and a most preferred level of planarity of surface  15  is defined by the equation: 
 
Δ dev   ≦h/ 10.   (3) 
 
         [0044]     Referring to  FIG. 14 , surface  15  of multi-layered structure  10  is shown tilted with respect to surface  30 . More specifically, an angle Φ is formed between surface  15  and surface  30 . The angle Φ is formed as a result in the difference in thickness of transfer layer  14  across multi-layered structure  10 . More specifically, a thickness ‘t 1 ’ is defined between protrusion  16  and surface  15  and a thickness ‘t 2 ’ is defined between protrusion  20  and surface  15 . The difference in magnitudes of thicknesses ‘t 1 ’ and ‘t 2 ’ define a thickness variation Δt.  
         [0045]     In the present invention, it may be preferable to minimize the angle Φ such that Δ t  may have a magnitude defined by the equation: 
 
Δ t ≦h,   (4) 
 
 wherein h, shown in  FIG. 13 , is the aforementioned step height of protrusions  16 ,  18 , and  20 . However, it may be more preferable to minimize the angle Φ such that Δ t  may be defined by the equation: 
 
Δ t   ≦h/ 5,   (5) 
 
 and it may be most preferable to minimize the Φ such that Δ t  may be defined by the equation: 
 
Δ t   ≦h/ 10,   (6) 
 
 To minimize the angle Φ, a compliant device may be employed, such as disclosed in U.S. patent application Ser. No. 10/858,100, filed Jun. 1, 2004 and entitled “A Compliant Device for Nano-scale Manufacturing,” which is incorporated by reference in its entirety herein. 
 
         [0046]     Referring to  FIGS. 4 and 15 , although the reduction in thickness of transfer layer  14  is shown along a single axis, the reduction in thickness of transfer layer  14  may be along two axes A 1  and A 2 , wherein axes A 1  and A 2  may be placed transverse to one another. As shown in  FIG. 14 , a reduction in thickness of transfer layer  14  may be along axis A 1 , resulting in a thickness ‘c,’ as mentioned above, and a reduction in thickness of transfer layer  14  along axis A 2 , resulting in a thickness ‘m.’ Therefore, the above-mentioned process for compensating for a volumetric reduction of a material disposed upon a substrate to from a substantially planar structure may be along two axes.  
         [0047]     While this invention has been described with references to various illustrative embodiments, the description is not intended to be construed in a limiting sense. As a result various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.