Abstract:
The present invention provides a method of forming recesses on a substrate, the method including forming on the substrate a patterning layer having first features; trim etching the first features to define trimmed features having a shape; and transferring an inverse of the shape into the substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is a continuation of U.S. patent application Ser. No. 10/946,570, filed on Sep. 21, 2004 now U.S. Pat. No. 7,186,656 entitled “Method of Forming a Recessed Structure Employing a Reverse Tone Process,” which is a continuation-in-part of U.S. patent application Ser. No. 10/850,876 filed on May 21, 2004 now abandoned entitled “A Method of Forming a Recessed Structure Employing a Reverse Tone Process,” both of which are incorporated by reference herein. 

   BACKGROUND OF THE INVENTION 
   The field of the invention relates generally to micro-fabrication of structures. More particularly, the present invention is directed to creating recessed structures utilizing a trim etch process followed by reverse toning of the recessed structures. 
   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 have been employed include biotechnology, optical technology, mechanical systems and the like. 
   A method of reducing the minimum feature dimension of structures formed from micro-fabrication is disclosed in U.S. Pat. No. 6,541,360 to Plat et al. Plat et al. describes a bi-layer trim etch process to form integrated circuit gate structures having small critical dimensions. More specifically, Plat et al. describes forming a multi-layered structure by depositing an organic underlayer over a layer of polysilicon, depositing an imaging layer over the organic underlayer, and patterning the imaging layer. The imaging layer is then utilized as a hard mask to selectively trim etch the organic underlayer to form a pattern smaller than that produced by the imaging layer. The hard mask imaging layer is then removed, and finally, the portions of the polysilicon layer are etched using the pattern formed by the organic underlayer. This allows for formation of a gate pattern with widths less than the widths of the pattern of the imaging layer. 
   What is desired, however, is a technique to form a structure having holes/trenches of a reduced critical dimension. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method of forming recesses on a substrate, the method including forming on the substrate a patterning layer having first features; trim etching the first features to define trimmed features having a shape; and transferring an inverse of the shape into the substrate. These embodiments and others are described more fully below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified elevation view of a multi-layered structure; 
       FIG. 2  is a simplified elevation view of a multi-layered structure formed by imprint lithography; 
       FIG. 3  is a simplified elevation view of the multi-layered structure, shown in  FIG. 1 , after the multi-layered structure is exposed to a trim etching process; 
       FIG. 4  is a simplified elevation view of the multi-layered structure, shown in  FIG. 3 , after selectively etching the multi-layered structure; 
       FIG. 5  is a simplified elevation view of the multi-layered structure, shown in  FIG. 4 , after the multi-layered structure has been exposed to a dip etch; 
       FIG. 6  is a simplified elevation view of the multi-layered structure, shown in  FIG. 5 , after deposition of a conformal layer; 
       FIG. 7  is a simplified elevation view after a blanket etch of the multi-layered structure, shown in  FIG. 6 , and formation of a crown surface; 
       FIG. 8  is a simplified elevation view of the multi-layered structure, shown in  FIG. 7 , after subjecting the crown surface to an etch process to expose regions of a substrate; 
       FIG. 9  is a simplified elevation view of the substrate, shown in  FIG. 8 , after transferring a pattern of the multi-layered structure therein; 
       FIG. 10  is a simplified elevation view of the multi-layered structure, shown in  FIG. 5 , after deposition of a conformal layer in accordance with an alternate embodiment of the present invention; 
       FIG. 11  is a simplified elevation view of a multi-layered structure in accordance with an alternate embodiment of the present invention; 
       FIG. 12  is a simplified elevation view of the multi-layered structure, shown in  FIG. 11 , after the multi-layered structure is exposed to a trim etching process; 
       FIG. 13  is a simplified elevation view of the multi-layered structure, shown in  FIG. 12 , after post processing in accordance with an alternate embodiment of the present invention; 
       FIG. 14  is a simplified elevation view of a multi-layered structure in an alternate embodiment of the present invention; and 
       FIG. 15  is a simplified elevation view of a multi-layered structure in an alternate embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a multi-layered structure  40  is shown having a substrate  30 , a transfer layer  37 , and an imaging layer  43 , with transfer layer  37  being positioned between imaging layer  43  and substrate  30 . Substrate  30  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  37  and imaging layer  43  may be formed using any known techniques, dependent upon the materials and application desired. For example, the etching process that may be employed to remove material from transfer layer  37  and imaging layer  43 , as well as substrate  30 , may be any known in the semiconductor processing art. The etching process employed is dependent upon the materials employed and the application desired. Techniques that may be employed to deposit transfer layer  37  and imaging layer  43  include, but are not limited to, chemical vapor deposition (CVD), physical vapor deposition (PVD), sputter deposition, spin-coating and dispensing of a liquid. 
   Transfer layer  37  may be an anti-reflective coating (BARC) layer, such as DUV30J-6 available from Brewer Science, Inc. of Rolla, Mo. Additionally, transfer layer  37  may be a silicon-containing low-k layer, or a BCB layer, for example. In an alternative embodiment, a composition for transfer layer  37  may be silicon-free and consists of the following: 
   COMPOSITION 1 
   isobornyl acrylate 
   n-hexyl acrylate 
   ethylene glycol diacrylate 
   2-hydroxy-2-methyl-1-phenyl-propan-1-one 
   In COMPOSITION 1, isobornyl acrylate comprises approximately 55% of the composition, n-hexyl acrylate comprises approximately 27%, ethylene glycol diacrylate comprises approximately 15% and the initiator 2-hydroxy-2-methyl-1-phenyl-propan-1-one comprises approximately 3%. The initiator is sold under the trade name DAROCUR® 1173 by CIBA® of Tarrytown, N.Y. The above-identified composition also includes stabilizers that are well known in the chemical art to increase the operational life of the composition. 
   Imaging layer  43  has a plurality of features  44  and  45  to provide imaging layer  43  with etch properties that differ from the etch properties of transfer layer  37 . Features  44  and  45  may be formed by such techniques including, but not limited to, photolithography (various wavelengths including G line, I line, 248 nm, 193 nm, 157 nm, and 13.2-13.4 nm), e-beam lithography, x-ray lithography, ion-beam lithography, atomic beam lithography, and imprint lithography. Imprint lithography is described 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 United States published patent application 2004/0046271 filed 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 and are incorporated by reference herein. An exemplary lithographic system 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. 
   Referring to  FIGS. 1 and 2 , employing imprint lithography to form features  44  and  45  may result in the formation of residual portions  11  of imaging layer  43  in superimpositions with features  44 . Thus, to remove residual portions  11 , a break-through each may be employed such that multi-layered structure  40  shown in  FIG. 1  is formed. 
   Referring to  FIG. 1 , as mentioned above, features  44  and  45  provide imaging layer  43  with each properties that differ from the etch properties of transfer layer  37 . To that end, the etch properties of imaging layer  43  enable imaging layer  43  to serve as a hard mask for transfer layer  37 . To that end, imaging layer  43  may be formed from a silicon organic material having a silicon content laying in the range of 3% to 40% be weight or other materials that may be photo-image capable. Imaging layer  43  may be deposited by spin-coating onto transfer layer  37  a silicon-containing material with sufficient thickness so that the desired etch differential characteristics with respect to transfer layer  37  are obtained for given etch processes. Exemplary material from which to form imaging layer  43  include COMPOSITION 2 and COMPOSITION 3, discussed more fully below. After patterning features  44  and  45  into imaging layer  43 , multi-layered structure  40  is exposed to a trim etch process. In a further embodiment, imaging layer  43  and transfer layer  37  may be formed by the SiBER™ DUV bi-layer resist platform available from Rohm and Haas of Philadelphia, Pa. The description for the SiBER™ DUV bi-layer resist platform is available at http://electronicmaterials.rohmhaas.com/businesses/micro/lithography/248photo.asp?caid=240 and is incorporated herein by reference. 
   Referring to  FIG. 3 , the trim etch process forms protrusions  42  in multi-layered structure  40 . Each of protrusions  42  includes features  45  and a portion of transfer layer  37  in superimposition therewith, referred to as a body  47 . The width ‘a 1 ,’ shown in  FIG. 1 , of features  45  may be reduced by the trim etch process to provide features  45  with a width ‘a 2. ’ Specifically, material is removed from features  45  during the trim etch process so that width ‘a 1 ,’ shown in  FIG. 1 , is greater than width ‘a 2 .’ Similarly, material is removed from transfer layer  37 . Specifically, transfer layer  37  is partially exposed to the trim etch process so that portions of transfer layer  37  in superimposition with features  44 , shown in  FIG. 1 , are removed. This results from imaging layer  43  functioning as a mask for transfer layer  37  during the trim etch process. The portions of transfer layer  37  in superimposition with features  45  are partially etched as well. In this manner, body  47  has varying dimensions over the length thereof. The width ‘b 1 ’ of body  47  at an interface of body  47  and substrate  30  is greater than the width ‘b 2 ’ of body  47  at the interface of body  47  and imaging layer  43 . Width ‘b 1 ’ may be substantially the same as width ‘a 2 ’ or smaller and width ‘b 2 ’ may be less than width ‘a 2 .’ 
   Referring to  FIGS. 3 and 4 , after subjecting multi-layered structure  40  to the above-mentioned trim etch process, multi-layered structure  40  is subsequently exposed to a second etching process to provide remaining portions of transfer layer  37  with uniform dimensions. Specifically, transfer layer  37  is selectively etched using the remaining portions of imaging layer  43  as a mask. In this manner, a multi-layered structure  140  is formed. Multi-layered structure  140  has protrusions  42  with a width ‘c 1 .’ Width ‘c 1 ’ may be substantially the same as width ‘b 2 .’ In a further embodiment, width ‘c 1 ’ may be less than width ‘b 2 .’ As a consequence of exposing multi-layered structure  140  to the above-mentioned etching process, features  45  become faceted, referred to as faceted material. It is desired to remove the faceted portions. The manner in which the faceted portions may be removed is dependent upon the material from which the same is formed. To that end, one manner in which to remove the faceted material is by exposing the same to a hydrofluoric acid (HF) dip. Alternatively, the material from which the faceted portions is formed may be photo-responsive in that the same may be exposed to radiation and subsequently exposed to a chemical to remove the faceted portions, not unlike a photo-resist material. It is desired, however, that the process for removing the faceted portions minimize or avoid faceting of the remaining portions of protrusions  42  to form protrusions  54 , shown in  FIG. 5 . 
   Referring to  FIGS. 5 and 6 , after removal of the faceted portions, the reverse tone of protrusions  54  are transferred into substrate  30 . To that end, a conformal layer  46  may be deposited over protrusions  54  forming multi-layered structure  340 . This may be achieved by methods including, but not limited to, spin-on techniques, contact planarization, and the like. To that end, conformal layer  46  may be formed from a polymerizable material. Exemplary compositions from which to form conformal layer  46  are as follows: 
   COMPOSITION 2 
   hydroxyl-functional polysiloxane 
   hexamethoxymethylmelamine 
   toluenesulfonic acid 
   methyl amyl ketone 
   COMPOSITION 2 
   hydroxyl-functional polysiloxane 
   hexamethoxymethylmelamine 
   gamma-glycidoxypropyltrimethoxysilane 
   toluenesulfonic acid 
   methyl amyl ketone 
   In COMPOSITION 2, hydroxyl-functional polysiloxane comprises approximately 4% of the composition, hexamethoxymethylmelamine comprises approximately 0.95%, toluenesulfonic acid comprises approximately 0.05% and methyl amyl ketone comprises approximately 95%. In COMPOSITION 3, hydroxyl-functional polysiloxane comprises approximately 4% of the composition, hexamethoxymethylmelamine comprises approximately 0.7%, gamma-glycidoxypropyltrimethoxysilane comprises approximately 0.25%, toluenesulfonic acid comprises approximately 0.05%, and methyl amyl ketone comprises approximately 95%. 
   Conformal layer  46  includes first and second opposed sides. First side  48  faces substrate  30 . The second side faces away from substrate  30 , forming normalization surface  50 . Normalization surface  50  is provided with a substantially normalized profile by ensuring that the distances k 1 , k 3 , k 5 , k 7 , and k 9  between protrusions  54  and normalization surface  50  are substantially the same and that the distance k 2 , k 4 , k 6 , and k 8  between recessions  58  and normalization surface  50  are substantially the same. 
   One manner in which to provide normalization surface  50  with a normalized profile is to contact conformal layer  46  with a planarizing mold  60  having a planar surface  62 . Thereafter, planarizing mold  60  is separated from conformal layer  46  and radiation impinges upon conformal layer  46  to polymerize and, therefore, to solidify the same. The radiation impinged upon conformal layer  46  may be ultraviolet, thermal, electromagnetic, visible light, heat, and the like. In a further embodiment, the radiation impinged upon conformal layer  46  may be impinged before planarizing mold  60  is separated from conformal layer  46 . To ensure that conformal layer  46  does not adhere to planarizing mold  60 , a low surface energy coating  64  may be deposited upon planarizing mold  60 . 
   Alternatively, release properties of conformal layer  46  may be improved by including in the material from which the same is fabricated a surfactant. The surfactant provides the desired release properties to reduce adherence of conformal layer  46  to planarizing mold  60 . For purposes of this invention, a surfactant is defined as any molecule, one tail of which is hydrophobic. Surfactants may be either fluorine containing, e.g., include a fluorine chain, or may not include any fluorine in the surfactant molecule structure. An exemplary surfactant is available under the trade name ZONYL® FSO-100 from DUPONT™ that has a general structure of R 1 R 2 , where R 1 =F(CF 2 CF 2 ) Y , with y being in a range of 1 to 7, inclusive and R 2 =CH 2 CH 2 O(CH 2 CH 2 O) X H, where X being in a range of 0 to 15, inclusive. It should be understood that the surfactant may be used in conjunction with, or in lieu of, low surface energy coating  64  that may be applied to planarizing mold  60 . 
   Referring to  FIGS. 6 and 7 , a blanket etch is employed to remove portions of conformal layer  46  to provide multi-layered structure  340  with a crown surface  66 . Crown surface  66  is defined by an exposed surface  68  of each of protrusions  54  and upper surfaces of portions  70  that remain on conformal layer  46  after the blanket etch. The blanket etch may be a wet etch or dry etch. In a further embodiment, a chemical mechanical polishing/planarization may be employed to remove portions of conformal layer  46  to provide multi-layered structure  340  with crown surface  66 . 
   Referring to  FIGS. 6 ,  7  and  8 , crown surface  66  is subjected to an anisotropic plasma etch. The etch chemistry of the anisotropic etch is selected to maximize etching of protrusions  54 , while minimizing etching of portions  70 . In the present example, advantage was taken of the distinction of the silicon content between protrusions  54  and conformal layer  46 . Specifically, employing a plasma etch with an oxygen-based chemistry, it was determined that an in-situ hardened mask  72  would be created in the regions of portions  70  proximate to crown surface  66 , forming a multi-layered structure  440 . This results from the interaction of the silicon-containing polymerizable material with the oxygen plasma. As a result of hardened mask  72  and the anisotropy of the etch process, regions  74  in superimposition with protrusions  54  are exposed. 
   Referring to  FIGS. 8 and 9 , the pattern defined by multi-layered structure  440  may form the basis of a pattern transferred into substrate  30 . Specifically, the shape of the structure defined by multi-layered structure  440  may be transferred into substrate  30  by employing an anisotropic fluorine plasma etch. The benefit of this process is that recesses may be formed in substrate  30  with much smaller dimensions than the patterned layer, such as imaging layer  43 , shown in  FIG. 1 , which forms the basis of the shapes of recesses. Also, were conformal layer  46 , shown in  FIG. 6 , formed from a silicon-containing photo-responsive material, the removal of the conformal layer  46 , shown in  FIG. 6 , may be achieved in a manner consistent with the removal of photo-resist material. As a result, it would not be necessary to employ a blanket fluorine etch. 
   Referring to  FIGS. 4 and 10 , another embodiment is shown that avoids having to employ the HF dip discussed above. Specifically, after formation of protrusions  42 , conformal layer  46  is deposited. To that end, conformal layer  46  and the faceted regions of protrusions  42  are made from material having similar etch characteristics. Specifically, it is desired that the etch rate associated with the faceted regions be no greater than the etch rate associated with conformal layer  46 . In this manner, a blanket etch may be performed as discussed above with respect to  FIGS. 6 and 7 . However, it should be understood that the surface need not be planar as shown above with respect to crown surface  66 , shown in  FIG. 7 . Thereafter, recesses in regions  74  are formed in substrate  30  as discussed above in  FIGS. 7 ,  8 , and  9 . 
   Referring to  FIG. 11 , an additional embodiment of the present invention is described demonstrating that the foregoing process may be employed to form recessed structures in an existing layer on substrate  30 . To that end, a multi-layered structure  540  is shown having substrate  30 , an underlayer  141 , a transfer layer  137 , and an imaging layer  143 , with underlayer  141  being positioned between transfer layer  137  and substrate  30  and transfer layer  137  being positioned between imaging layer  143  and underlayer  141 . Transfer layer  137  and imaging layer  143  may be formed by the materials mentioned above with respect to transfer layer  37  and imaging layer  43 , shown in  FIG. 1 , respectively, and may be formed as mentioned above with respect to transfer layer  37  and imaging layer  43 , shown in  FIG. 1 , respectively. 
   Underlayer  141  may be formed from low-k materials such as silicon-containing low-k, BCB, silicon dioxide, spin-on-glass, FSG, and polysilicon. Underlayer  141  may be formed employing any of the techniques discussed above with respect to transfer layer  37  and imaging layer  43 , shown in  FIG. 1 . In an exemplary embodiment, underlayer  141  may be deposited upon substrate  30  utilizing spin-coating techniques and consists of a low-k silicon-containing dielectric. 
   Referring to  FIGS. 12 and 13 , as mentioned above with respect to imaging layer  43  and transfer layer  37 , shown in  FIG. 1 , imaging layer  143  has etch properties associated therewith differing from etch properties of transfer layer  137 . In this manner, a trim etch procedure is employed to form protrusions  142 . As shown, protrusions  142  are formed in a manner discussed above with respect to  FIG. 3 , excepting that unlike body  47 , shown in  FIG. 3 , which extends between substrate  30  and features  45 , shown in  FIG. 3 , body  147  extends between features  145  and underlayer  141 . After subjecting multi-layered structure  540  to the above-mentioned trim etch process, additional processing may be undertaken as discussed above with respect to  FIGS. 4 ,  5 ,  6 ,  7 ,  8  and  9  to obtain recessed structures  174  in underlayer  141 . Although not shown, recessed structures  174  may extend completely through underlayer  141  and terminate at substrate  30 . 
   Referring to  FIG. 14 , in a further embodiment, imaging layer  43  may be positioned upon substrate  30  forming multi-layered structure  640 . Imaging layer  43  may be formed from an organic resist, such I-line, 193 nm, and 248 nm photolithography resists available from Rohm and Haas of Philadelphia, Pa. The description for I-line, 193 nm, and 248 nm photolithography resists is available from http://electronicmaterials.rohmhaas.com/businesses/micro/lithography/248photo.asp?caid=235 and is incorporated by reference herein. Imaging layer  43  may also be formed from an electron beam organic resist available from Zeon Corporation of Tokyo, Japan. The description for an electron beam organic resist is available from http://www.zeon.co.jp/business_e/enterprise/imagelec/zep7000.html and is incorporated by reference herein. To reduce the width ‘a 1 ’ of features  45 , imaging layer  43  may be subjected to an organic etch with an isotropic etch component. However, this may lead to features  45  becoming faceted, referred to as faceted material. Additional processing may be undertaken as discussed above with respect to  FIGS. 4 ,  5 ,  6 ,  7 ,  8 , and  9  to transfer the shape of the structure defined by multi-layered structure  640  into substrate  30 . However, employing the blanket etch mentioned above with respect to  FIGS. 6 and 7  on multi-layered structure  640  may require an over-etch to eliminate the above-mentioned faceted material. 
   Referring to  FIG. 15 , in a further embodiment, imaging layer  143  may be positioned upon underlayer  141  to form multi-layered structure  740 , wherein multi-layered structure  740  may be subjected to the process mentioned above with respect to multi-layered structure  640  such that the shape of the structure defined by multi-layered structure  740  is transferred into underlayer  141 . 
   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, therefore, be determined with reference to the appended claims along with their full scope of equivalents.