US 20060062922 A1
The present invention includes a method of solidifying a polymerizable liquid to form a film on a substrate that features minimizing inhibition of the polymerization process by oxygen contained in the atmosphere surrounding the polymerizable liquid. To that end, the polymerizable liquid includes, inter alia, an initiator that consumes oxygen that interacts with the polymerizable liquid and generates additional free radicals to facilitate the polymerization process.
1. A method for solidifying a polymerizable liquid disposed in an atmosphere and having a plurality of molecules, said method comprising:
creating a primary group of free radicals;
forming a secondary group of free radicals by interaction of molecules of said atmosphere with a subset of the free radicals of said primary group; and
generating a tertiary group of free radicals by interaction of said plurality of molecules with the free radicals of said secondary group to link together a subset of molecules of said plurality of molecules.
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8. A method for solidifying a polymerizable liquid disposed in an oxygen-containing atmosphere and having a plurality of molecules, said method comprising:
disposing a volume of said liquid on a substrate, said volume having a boundary defining a interface with said atmosphere; and
initiating polymerization of said molecules while minimizing inhibition of polymerization of said molecules by oxygen proximate to said boundary.
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16. A method for solidifying a polymerizable liquid disposed in an oxygen-containing atmosphere and having a plurality of molecules including photoinitiators and chemical initiators, said method comprising:
exposing said photoinitiators to actinic radiation to create a plurality of radicals to initiate linking of said plurality of molecules; and
accelerating linking of said plurality of molecules by creating additional radicals through combining said photoinitiators with oxygen.
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23. A method of polymerizing a liquid, said method comprising:
combining isobornyl acrylate, n-hexyl acrylate, ethylene glycol diacrylate and 2-hydroxy-2-methyl-1-phenyl-propan-1-one with an oxygen scavenging initiator, defining a composition; and
exposing said composition to actinic radiation.
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26. A composition having a plurality of molecules, said composition comprising:
a polymerizable composition including a photoinitiator and an oxygen scavenging element to react with oxygen and facilitate cross-linking of said plurality of molecules.
27. The composition as recited in
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30. A composition having a plurality of molecules, said composition comprising:
isobornyl acrylate n-hexyl acrylate ethylene glycol diacrylate 2-hydroxy-2-methyl-1-phenyl-propan-1-one and an oxygen scavenging element to react with oxygen and facilitate cross-linking of said plurality of molecules.
31. The composition as recited in
32. A composition having a plurality of molecules, said composition comprising:
isobornyl acrylate n-hexyl acrylate ethylene glycol diacrylate 2-hydroxy-2-methyl-1-phenyl-propan-1-one, R1CH2CH2O(CH2CH2O)XH and an oxygen scavenging element to react with oxygen and facilitate cross-linking of said plurality of molecules.
33. The composition as recited in
The field of invention relates generally to micro-fabrication of structures. More particularly, the present invention is directed to a polymerization technique suited for use in imprint lithography.
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.
An exemplary micro-fabrication technique is commonly referred to as imprint lithography and is described in detailed in numerous publications, such as United States published patent applications 2004/0065976 entitled METHOD AND A MOLD TO ARRANGE FEATURES ON A SUBSTRATE TO REPLICATE FEATURES HAVING MINIMAL DIMENSIONAL VARIABILITY, 2004/0065252, entitled METHOD OF FORMING A LAYER ON A SUBSTRATE TO FACILITATE FABRICATION OF METROLOGY STANDARDS, 2004/0046271, entitled METHOD AND A MOLD TO ARRANGE FEATURES ON A SUBSTRATE TO REPLICATE FEATURES HAVING MINIMAL DIMENSIONAL VARIABILITY, all of which are assigned to the assignee of the present invention. The fundamental imprint lithography technique as shown in each of the aforementioned published patent applications includes formation of a relief pattern in a polymerizable layer and transferring the relief image into an underlying substrate forming a relief image in a structure. To that end, a template is employed spaced-apart from a substrate, with a formable liquid present between the template and the substrate. The liquid is solidified forming a solidified layer that has a pattern recorded therein that is conforming to a shape of the surface of the template in contact with the liquid. The substrate and the solidified layer are then subjected to processes to transfer, into the substrate, a relief structure that corresponds to the pattern in the solidified layer.
On manner in which the polymerizable liquid is located between the template and the substrate is by depositing a plurality of droplets of liquid on the substrate. Thereafter, contact is made with the polymerizable liquid by the template to spread the polyermizable liquid over the surface of the substrate and subsequently record a pattern therein. It is highly desirable to avoid trapping of gases, such as air, when the polymerizable liquid spreads over the substrate.
It is desired, therefore, to provide a method for forming a fluid layer on a substrate while minimizing the trapping of gases therein.
The present invention includes a method of solidifying a polymerizable liquid to form a film on a substrate that features minimizing inhibition of the polymerization process by oxygen contained in the atmosphere surrounding the polymerizable liquid. To that end, the polyermizable liquid includes, inter alia, an initiator or additive that consumes oxygen that interacts with the polyermizable liquid and generates additional free radicals to facilitate the polyermization process. Specifically, the method includes creating a primary group of free radicals by exposing the polymerizable liquid to actinic radiation to initiate linking together of a plurality of molecules. A secondary group of free radicals is generated by interaction of molecules of an atmosphere surrounding the liquid by a subset of the free radicals of the primary group. A tertiary group of free radicals is generated by interaction of the plurality of molecules with the free radicals of the secondary group to link together additional molecules of the plurality of molecules. These and other embodiments are discussed more fully below.
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Radiation source 22 is located so that mold 26 is positioned between radiation source 22 and substrate 32, with actinic radiation generated by radiation source 22 propagating through mold 26. As a result, it is desired that mold 26 be fabricated from material that is substantially transparent to the actinic radiation. Exemplary materials from which mold 26 may be fabricated include fused-silica, quartz, silicon, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal, and combinations of the above dependent upon the actinic radiation employed. An exemplary 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.
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In the present embodiment, sub-portions 48 of recorded pattern 134 in superimposition with projections 30 remain after the desired, usually minimum distance “d”, has been reached, leaving sub-portions 46 with a thickness t1, and sub-portions 48 with a thickness, t2. Thickness t2 is referred to as a residual thickness. Thicknesses “t1” and “t2” may be any thickness desired, dependent upon the application. The total volume contained in droplets 38 may be such so as to minimize, or avoid, a quantity of the imprinting material from extending beyond the region of surface 36 in superimposition with mold 26, while obtaining desired thicknesses t1 and t2, i.e., through capillary attraction of the imprinting material with mold 26 and surface 36 and surface adhesion of the imprinting material.
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The advantages of this patterning process are manifold. For example, the thickness differential between protrusions 54 and recessions 52 facilitates formation, in substrate 32, of a pattern corresponding to the recorded pattern 134. Specifically, the thickness differential between t1 and t2 of protrusions 54 and recession 52, respectively, results in a greater amount of etch time being required before exposing regions of substrate 32 in superimposition with protrusions 54 compared with the time required for regions of substrate 32 in superimposition with recession 52 being exposed. For a given etching process, therefore, etching will commence sooner in regions of substrate 32 in superimposition with recessions 52 than regions in superimposition with protrusions 54. This facilitates formation of a pattern in substrate corresponding to recorded pattern 134. By properly selecting the imprinting materials and etch chemistries, the relational dimensions between the differing features of the pattern eventually transferred into substrate 32 may be controlled as desired. To that end, it is desired that the etch characteristics of recorded pattern 134, for a given etch chemistry, be substantially uniform.
As a result, the characteristics of the imprinting material are important to efficiently pattern substrate 32 in light of the unique patterning process employed. As mentioned above, the imprinting material is deposited on substrate 32 as a plurality of discrete and spaced-apart droplets 38. The combined volume of droplets 38 is such that the imprinting material is distributed appropriately over an area of surface 36 where recorded pattern 134 is to be formed. In this fashion, the total volume of the imprinting material in droplets 38 defines the distance “d”, to be obtained so that the total volume occupied by the imprinting material in the gap defined between mold 26 and the portion of substrate 32 in superimposition therewith once the desired distance “d” is reached is substantially equal to the total volume of the imprinting material in droplets 38. To facilitate the deposition process, it is desired that the imprinting material provide rapid and even spreading of the imprinting material in droplets 38 over surface 36 so that all thicknesses t1 are substantially uniform and all residual thicknesses t2 are substantially uniform.
with R1R2 being a surfactant. 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. In surfactant R1R2, R1═F(CF2CF2)y, with y being in a range of 1 to 7, inclusive, and R2═CH2CH2O(CH2CH2O)XH, with X is in a range of 0 to 15, inclusive. An exemplary surfactant is available under the trade name ZONYL® FSO-100 from DUPONT™. It was believed that during the polymerization reaction the PRIOR ART COMPOSITION formed peroxide radicals proximate to the material-gas boundaries. This slows the rate of, if not prevents, polymerization of the imprinting material. As a result, for a given polymerization process, film 300 is provided with varying degrees of solidification over the volume thereof.
The present invention overcomes these drawbacks by including in the composition, which forms the imprinting material, a scavenger material that consumes molecules in the ambient that would inhibit the curing process. Specifically, it was found that by including an additive with the initiator, the inhibition of polymerization at material-gas boundaries could be minimized. To that end, included in the PRIOR ART COMPOSITION is an amine-containing additive to provide the following composition:
The acrylate component isobornyl acrylate (IBOA) has the following structure:
The surfactant component provides suitable wetting properties of COMPOSITION 1 when in the liquid phase, as well as desired release characteristics in the solid phase. An amine component N-methyldiethanolamine has the following structure:
In addition to reactions 1-3 above, additional reactions occur proximate to boundary 202 where the ambient is present. An exemplary reaction occurs between the radical initiator R. and oxygen O2 as follows:
In addition, the amine radical reacts with the acrylates M to facilitate further polymerization thereof as follows:
Also, the amine group reacts with oxygen present in the ambient to reduce the formation of the RO2. type of peroxide radicals, as follows:
Although the radical DO2. is undesirable, the same may interact with other amine groups present in COMPOSITION 1 as follows:
where 2-Methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one is available from Ciba Specialty Chemicals Corporation of Tarrytown N.Y. under the trade name IRGACURE® 907; and
where 2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone is available from Ciba Specialty Chemicals Corporation of Tarrytown, N.Y. under the trade name IRGACURE® 369; and
where 2-(4-methyl-benzyl)-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone is available from Ciba Specialty Chemicals Corporation of Tarrytown, N.Y. under the trade name IRGACURE® 379.
To reduce the probability that solidified primer layers 96 and 196 adhere to planarization mold 80 the same may be treated with a low surface energy coating 98. Low surface energy coating 98 may be applied using any known process. For example, processing techniques may include chemical vapor deposition method, physical vapor deposition, atomic layer deposition or various other techniques, brazing and the like. In a similar fashion a low surface energy coating (not shown) may be applied to mold 26, shown in
In addition to the aforementioned surfactants and low surface energy coatings, fluorinated additives may be employed to improve release properties of the imprinting material. Fluorinated additives, like surfactants, have a surface energy associated therewith that is lower than a surface energy of the imprinting material. An exemplary process by which to employ the aforementioned fluorinated additive is discussed by Bender et al. in MULTIPLE IMPRINTING IN UV-BASED NANOIMPRINT LITHOGRAPHY:RELATED MATERIAL ISSUES, Microelectronic Engineering pp. 61-62 (2002). The low surface energy of the additive provides the desired release properties to reduce adherence of cross-linked and polymerized imprinting material molds 26 and 80.
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. For example, the ratio of the components of each of the aforementioned COMPOSITIONs may be varied. The scope of the invention should, therefore, not be limited by the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.