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Topic Name: Develop lultrasmal low-cost recipe for patterning microchips

Category: Nanocharacterization

Research persons: Stephen Y. Chou,William B. Russel

Location: NanoStructure Laboratory at Princeton UniversityEngineering Quadrangle, Olden Street,Princeton, NJ 08544, United States

Details

Creating ultrasmall grooves on microchips -- a key part of many modern technologies -- is about to become as easy as making a sandwich, using a new process invented by Princeton engineers.
The simple, low-cost technique results in the self-formation of periodic lines, or gratings, separated by as few as 60 nanometers -- less than one ten-thousandth of a millimeter -- on microchips. Features of this size have many uses in optical, biological and electronic devices, including the alignment of liquid crystals in displays. The researchers will publish their findings Sept. 2 in the online version of Nature Nanotechnology.
“It’s like magic,” said electrical engineer Stephen Chou, the Joseph C. Elgin Professor of Engineering. “This is a fundamentally different way of making nanopatterns.”
The process, called fracture-induced structuring, is as easy as one-two-three. First, a thin polymer film is painted onto a rigid plate, such as a silicon wafer. Then, a second plate is placed on top, creating a polymer sandwich that is heated to ensure adhesion. Finally, the two plates are pried apart. As the film fractures, it automatically breaks into two complementary sets of nanoscale gratings, one on each plate. The distance between the lines, called the period, is four times the film thickness.
The ease of creating these lines is in marked contrast to traditional fabrication methods, which typically use a beam of electrons, ions, or a mechanical tip to “draw” the lines into a surface. These methods are serial processes which are extremely slow and therefore only suitable for areas one square millimeter or smaller. Other techniques suitable for larger areas have difficulties achieving small grating periods or producing a high yield, or they require complex and expensive processes. Fracture-induced structuring is not only simple and fast, but it enables patterning over a much larger area. The researchers have already demonstrated the ability of the technique to create gratings over several square centimeters, and the patterning of much large areas should be possible with further optimization of the technique.
“It’s remarkable – and counterintuitive – that fracturing creates these regular patterns,” said chemical engineering professor and dean of Princeton’s graduate school William Russel. Russel and his graduate student Leonard Pease III teamed with Chou and his graduate students Paru Deshpande and Ying Wang to develop the technique.
A patent application has been filed on the process, which the researchers say is economically feasible for large-scale use in industry. The gratings generated by the fracturing process also could be used in conjunction with existing patterning methods. For example, the nanoimprinting method invented by Chou in the 1990s can use the gratings generated by fracture-induced structuring to create a mold that enables mass duplication of patterns with high precision at low cost.
As with many scientific discoveries, the fracture-induced structuring process was happened upon accidentally. Graduate students in the Chou and Russel groups were trying to use instabilities in various molten polymers (in essence, melted plastic) to create patterns when they discovered instead that fracturing a solid polymer film can generate the gratings automatically. The team seized upon this finding and established the optimal conditions for grating formation.
Next, the group plans to explore the fundamental science behind the process and investigate the interplays of various forces at such a small scale, according to Chou.
“And, we want to push the limit and see how small we can go,” he said.
Abstract: Self-formation of sub-60-nm half-pitch gratings with large areas through fracturing
Periodic micro- and nanostructures (gratings) have many significant applications in electronic, optical, magnetic, chemical and biological devices and materials. Traditional methods for fabricating gratings by writing with electrons, ions or a mechanical tip are limited to very small areas and suffer from extremely low throughput. Interference lithography can achieve relatively large fabrication areas, but has a low yield for small-period gratings. Photolithography, nanoimprint lithography, soft lithography and lithographically induced self-construction all require a prefabricated mask, and although electrohydrodynamic instabilities can self-produce periodic dots without a mask, gratings remain challenging. Here, we report a new low-cost maskless method to self-generate nano- and microgratings from an initially featureless polymer thin film sandwiched between two flat relatively rigid plates. By simply prying apart the plates, the film fractures into two complementary sets of nonsymmetrical gratings, one on each plate, of the same period. The grating period is always four times the thickness of the glassy film, regardless of its molecular weight and chemical composition. Periods from 120 nm to 200 mm have been demonstrated across areas as large as two square centimeters.
About Researcher:

Stephen Y. Chou,
Joseph C. Elgin Professor of Engineering and the head of the NanoStructure Laboratory at Princeton University, is a world leader, pioneer, and inventor in a broad range of nanotechnologies. Dr. Chou received his PhD from MIT in 1986. He was a Research Associate and Acting Assistant Professor at Stanford University (1986--1989), and a faculty member at the University of Minnesota (1989-1991, Assistant Prof, 1991-1994, Associate Prof, and 1994-1997 Full Prof), and joined Princeton University in 1998. As an entrepreneur, Dr. Chou founded Nanonex (1999) and NanoOpto (2000) Corporations.
Dr. Chou's pioneering research and inventions in a broad spectrum of nanotechnologies and nanodevices has helped shape new paths in the fields of nanofabrication, nanoscale electronics, optoelectronics, magnetics, and materials. Dr. Chou's graduate work used X-ray lithography to scale MOSFETs to the 60 nm range, and since 1985 he has demonstrated various ultra-small MOSFETs, quantum devices, and single electron transistors. In early 1990's, he began pioneering work in exploring sub-wavelength optical elements (SOEs) and bringing nanofabrication into magnetic data storage media. He originated quantized magnetic disks(QMDs), a new paradigm in magnetic data storage in 1993. In 1995, he pioneered his best-known work, nanoimprint lithography (NIL), a revolutionary nanoscale patterning method that allows sub-10 nm patterning over large areas with high throughput and low cost. He is also a key inventor of lithographically induced self-assembly (LISA) and 10 emerging technologies that will change the world(LADI) and applications of NIL, LISA and LADI in a wide range of disciplines, from electronics and optics to magnetics, biotech, and materials. Since 1999, he has been applying unique and extensive expertise in nanofabrication, nanoelectronics, nanooptics, nanomagnetics and nanomaterials to biology for developing innovative biological manipulators, separators, detectors and analyzers for DNAs, proteins and cells.
Dr. Chou's inventions and pioneer work have brought significant impacts to industry. Nanoimprint lithography is regarded as one of the "10 emerging technologies that will change the world" (MIT Technology Review); is selected as a next generation lithography for semiconductor ICs; and is becoming an enabling manufacturing platform for multiple multi-billion-dollar industries ranging from semiconductor ICs, magnetic data storage, displays, optics, biotech to nanomaterials. Furthermore, SOEs and QMDs are being developed by industries aggressively as a future of integrated optics and magnetic data storage.
 

William B. Russel
Arthur W. Marks '19 Professor
Dean of the Graduate School
B.A., Rice University, 1969
M.Ch.E., Rice University, 1969
Ph.D., Stanford University, 1973
NATO Postdoctoral Fellow, Cambridge University, 1974
Room: A-225 Engineering Quadrangle
Phone: (609) 258-4590
E-mail: wbrussel@princeton.edu
Webpage: Russel Research Group
Research Interests
Formation of Thin Films from Colloidal Dispersions
Horizontal drying fronts during solvent evaporation from latex films”, AIChE Journal, 44 2088-98 (1998)[with A.F. Routh].
“A process model for latex film formation: limiting regimes for individual driving forces”, Langmuir 15 7762-7773 (1999) [with A.F. Routh].
“Deformation mechanisms during latex film formation: experimental evidence”, Industrial and Engineering Chemistry: Research 40 4302-4308 (2001) [with A.F. Routh].
“Role of capillary stresses in latex film formation”, Langmuir 20 2947-2961 (2004) [with M. Tirumkudulu].
“Cracking in drying latex films”, Langmuir 21 4938-48 (2005) [with M. Tirumkudulu].

Electrohydrodynamic Patterning of Thin Polymer Films [with S.Y. Chou]
“Electrostatically induced submicron patterning of thin perfect and leaky dielectric films: a generalized linear stability analysis”, Journal of Chemical Physics 118 3790-3803 (2003) [with L.F. Pease III].
“Limitations on length scales for electrostatically induced submicron pillars and holes”, Langmuir 20 795-804 (2004) [with L.F. Pease III].
“Cylindrically symmetric electrohydrodynamic patterning”, Physical Review E 70 041601 (2004) [with P. Deshpande, L. Chen, S.Y. Chou, and L.F. Pease III].
“Dynamics of the formation of polymeric microstructures induced by electrohydrodynamic instability”, Applied Physics Letters 86 241912 (2005) [with N. Wu].
“Electric-field induced thin polymer film patterns: weakly nonlinear and fully nonlinear evolution” Langmuir 21 12290-12302 (2005) [with N. Wu and L.F. Pease III].
“Electrohydrodynamic instability of dielectric bilayers: kinetics and thermodynamics” Industrial and Engineering Chemistry Research 45 5455-65 (2006) [with N. Wu].
“Charge driven, electrohydrodynamic patterning of thin films”, Journal of Chemical Physics 125 184716 (2006) [with L.F. Please III].
“Toward large-scale alignment of electrohydrodynamic patterning of thin polymer films”, Advanced Functional Materials 16 1992-1999 (2006) [with N. Wu and L.F. Pease III].
& Graduate student -Cho, Theresa '04 tcho@princeton.edu
In The Images:
1.William B. Russel
2.Stephen Y. Chou
3.Fracture-induced structuring results in the self-formation of periodic lines, or gratings, separated by as few as 60 nanometers -- less than one ten-thousandth of a millimeter -- on microchips. First, a thin polymer film is painted onto a rigid plate, such as a silicon wafer. Then, a second plate is placed on top, creating a polymer sandwich that is heated to ensure adhesion. Finally, the two plates are pried apart. As the film fractures, it automatically breaks into two complementary sets of nanoscale gratings, one on each plate.