1. Field of the Invention
This invention generally relates to the area of low cost, high-resolution, high-throughput lithography with the potential to make structures that are below 100 nm in size.
2. Description of the Relevant Art
Optical lithography techniques are currently used to make microelectronic devices. However, these methods are reaching their limits in resolution. Sub-micron scale lithography has been a critical process in the microelectronics industry. The use of sub-micron scale lithography allows manufacturers to meet the increased demand for smaller and more densely packed electronic components on chips. The finest structures producible in the microelectronics industry are currently on the order of about 0.13 μm. It is expected that in the coming years, the microelectronics industry will pursue structures that are smaller than 0.05 μm (50 nm). Further, there are emerging applications of nanometer scale lithography in the areas of opto-electronics and magnetic storage. For example, photonic crystals and high-density patterned magnetic memory of the order of terabytes per square inch require nanometer scale lithography.
For making sub-50 nm structures, optical lithography techniques may require the use of very short wavelengths of light (for instance 13.2 nm). At these short wavelengths, few, if any, materials are optically transparent and therefore imaging systems typically have to be constructed using complicated reflective optics [1]. Furthermore, obtaining a light source that has sufficient output intensity at these wavelengths of light is difficult. Such systems lead to extremely complicated equipment and processes that appear to be prohibitively expensive. High-resolution e-beam lithography techniques, though very precise, typically are too slow for high-volume commercial applications.
One of the main challenges with current imprint lithography technologies is the need to establish direct contact between the template (master) and the substrate. This may lead to defects, low process yields, and low template life. Additionally, the template in imprint lithography typically is the same size as the eventual structures on the substrate (1X), as compared to 4X masks typically used in optical lithography. The cost of preparing the template and the life of the template are issues that may make imprint lithography impractical. Hence there exists a need for improved lithography techniques that address the challenges associated with optical lithography, e-beam lithography and imprint lithography for creating very high-resolution features.
The present invention is directed to an apparatus for patterning a liquid on a substrate, with the apparatus including, a template having a pair of spaced-apart recessions with a protrusion disposed therebetween, with the protrusion being spaced-apart from the substrate a first distance and each of the pair of spaced-apart recessions being spaced-apart from the substrate a second distance, with the second distance being greater than the first distance; and a source of voltage in electrical communication with the template to produce an electric field between the template and the substrate, with a strength of the electrical field being inversely proportional to the first and second distances. These and other embodiments are discussed below.
A curing agent 24, shown in
In
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Next, at step 34, the spacing between the template and the substrate is controlled so that a relatively uniform gap is created between the two layers permitting the type of precise orientation required for successful imprinting. The present invention provides a device and a system for achieving the type of orientation (both course and fine) required at step 34. At step 36, a liquid is dispensed into the gap between the template and the substrate. Preferably, the liquid is a UV curable organosilicon solution or other organic liquids that become a solid when exposed to UV light. The fact that a liquid is used eliminates the need for high temperatures and high pressures associated with prior art lithography techniques.
At step 38, the gap is closed with fine orientation of the template about the substrate and the liquid is cured resulting in a hardening of the liquid into a form having the features of the template. Next, the template is separated from the substrate, step 40, resulting in features from the template being imprinted or transferred onto the substrate. Finally, the structure is etched, step 42, using a preliminary etch to remove residual material and a well-known oxygen etching technique to etch the transfer layer.
As mentioned above, recent imprint lithography techniques with UV curable liquids [2, 3, 4, 5] and polymers [6] have been described for preparing nanoscale structures. These techniques may potentially be significantly lower cost than optical lithography techniques for sub-50 nm resolution. Recent research [7, 8] has also investigated the possibility of applying electric fields and van der Waals attractions between a template that possesses a topography and a substrate that contains a polymeric material to form nanoscale structures. This research has been for systems of polymeric material that may be heated to temperatures that are slightly above their glass transition temperature. These viscous polymeric materials tend to react very slowly to the electric fields (order of several minutes) making them less desirable for commercial applications.
The embodiments described herein may potentially create lithographic patterned structures quickly (in a time of less than about 1 second). The structures may have sizes of tens of nanometers. The structures may be created by curing a poiymerizable composition (e.g., a spin-coated UV curable liquid) in the presence of electric fields. Curing the polymerizable composition then sets the pattern of structures on the substrate. The pattern may be created by placing a template with a specific nanometer-scale topography at a carefully controlled nanoscale distance from the surface of a thin layer of the liquid on a substrate. If all or a portion of the desired structures are regularly repeating patterns (such as an array of dots), the pattern on the template may be considerably larger than the size of the desired repeating structures. The template may be formed using direct write e-beam lithography. The template may be used repeatedly in a high-throughput process to replicate nanostructures onto substrates. In one embodiment, the template may be fabricated from a conducting material such as Indium Tin Oxide that is also transparent to UV light. The template fabrication process is similar to that of phase shift photomasks for optical lithography; phase shift masks require an etch step that creates a topography on the template.
The replication of the pattern on the template may be achieved by applying an electric, field between, the template and the substrate. Because the liquid and air (or vacuum) have different dielectric constants and the electric field varies locally due to the presence of the topography of the template, an electrostatic force may be generated that attracts regions of the liquid toward the template. At high electric field strengths, the polymerizable composition may be made to attach to the template and dewet from the substrate at certain points. This polymerizable composition may be hardened in place by polymerization of the composition. The template may be treated with a low energy self-assembled monolayer film (e.g., a fluorinated surfactant) to aid in detachment of the template the polymerized composition.
It may be possible co control the electric field, the design of the topography of the template and the proximity of the template to the liquid surface so as to create a pattern in the poiymerizable composition that does not come into contact with the surface of the template. This technique may eliminate the need for mechanical separation of the template from the polymerized composition. This technique may also eliminate a potential source of defects in the pattern. In the absence of contact, however, the liquid may not form sharp, high-resolution structures that are as well defined as in the case of contact. This may be addressed by first creating structures in the poiymerizable composition that are partially defined at a given electric field. Subsequently, the gap may be increased between the template and substrate while simultaneously increasing the magnitude of the electric field to “draw-out” the liquid to form clearly defined structures without requiring contact.
The polymerizable composition may be deposited on top of a hard-baked resist material to lead to a bi-layer process. Such a bi-layer process allows for the formation of low aspect ratio, high-resolution structures using the electrical fields followed by an anisotropic etch that results in high-aspect ratio, high-resolution structures. Such a bi-layer process may also be used to perform a “metal lift-off process” to deposit a metal on the substrate such that the metal is left behind after lift-off in the trench areas of the originally created structures.
By using a low viscosity polymerizable composition, the pattern formation due to the electric field may be fast (e.g., less than about 1 sec), and the structure may be rapidly cured. Avoiding temperature variations in the substrate and the polymerizable composition may also avoid undesirable pattern distortion that makes nano-resolution layer-to-layer alignment impractical. In addition, as mentioned above, it is possible to quickly norm a pattern without contact with the template, thus eliminating defects associated with imprint methods that require direct contact.
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Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein arc to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.
The following references are specifically incorporated herein by reference:
1. “Getting More from Moore's,” Gary Stix, Scientific American, April 2001.
2. “Step and Flash Imprint Lithography: An alternative approach to high resolution patterning,” M. Colburn, S. Johnson, M. Stewart, S. Damle, B. J. Choi, T. Bailey, M. Wedlake, T. Michaelson, S. V. Sreenivasan, J. Skerdt, C. G. Nillson, Proc. SPIE Vol.3676, 379-383,1999.
3. “Design of Orientation Stages for Step and Flash Imprint Lithography,” B. J. Choi, S. Johnson, M. Colburn, S. V. Sreenivasan, C. G. Willson, To appear in J. of Precision Engineering.
4. U.S. patent application Ser. No. 09/266,663 entitled “Step and Flash Imprint Lithography” to Grant Willson and Matt Colburn.
5. U.S. patent application Ser. No. 09/698,317 entitled “High Precision Orientation Alignment and Gap Control Stages for Imprint Lithography Processes” to B. J. Choi, S.V. Sreenivasan and Steve Johnson.
6. “Large area high density quantized magnetic disks fabricated using nanoimprint lithography,” W. Wu, B. Cui, X. Y. Sun, W. Zhang, L. Zhunag, and S. Y. Chou., J. Vac Sci Technol B 16 (6) 3825-3829 Nov-Dec 1998
7. “Lithographically- induced Self-assembly of Periodic Polymer Micropillar Arrays,” S. Y. Chou, L. Zhuang, J Vac Sci Tech B 17 (6), 3197-3202, 1999
8. “Large Area Domain Alignment in Block Copolymer Thin Films Using Electric Fields,” P. Mansky, 1. DeRouchey, J. Mays, M. Pitsikalis, T. Morkved, H. Jaeger and T. Russell, Macromolecules 13,4399 (1998).
The present application is a divisional of U.S. patent application Ser. No. 09/905,718 filed on May 16, 2001 entitled “Method and System for Fabricating Nanoscale Patterns in Light Curable Compositions using an Electric Field,” which is incorporated by reference herein.
Number | Date | Country | |
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Parent | 09905718 | May 2001 | US |
Child | 10776881 | US |
Number | Date | Country | |
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Parent | 10776881 | Feb 2004 | US |
Child | 12052099 | US |