 Step and
Flash® imprint lithography (S-FIL®) was developed
at the University of Texas at Austin. The technique is based on
the ancient craft of embossing, with an adaptation to modern semiconductor
needs. The technique uses a fused silica imprint mask (template) with a circuit
pattern etched into it.
The fused silica surface, coated with a release layer, is gently
pressed into a thin layer of low viscosity, silicon-containing
monomer. When illuminated by a UV lamp, the surface is polymerized
into a solid layer. Upon separation of the fused silica template,
the circuit pattern is left on the wafer surface. A residual layer of
polymer between features is eliminated by an etch process, and
a perfect replica of the pattern is ready to be used in semiconductor
processing for etch or deposition. Only the template fabrication
process, typically accomplished with an e-beam writer, limits
the resolution of the features. Sub-20 nm have
been made to date that exceed the present requirements in the
International Technology Roadmap Semiconductors (ITRS).
The S-FIL process has
several important advantages over conventional optical lithography
and EUV lithography. The parameters in the classic photolithography
resolution formula (k1, NA, and lambda) are not relevant to S-FIL applications,
because this technology does not use reduction lenses. Investigations
by MII and others in the sub-100 nm regime indicate that the
resolution is only limited by the pattern resolution on the template.
The resolution of the S-FIL process is a direct function of the resolution
of the template fabricating process. Therefore, S-FIL tools
are multi-generational and should have longer life than optical lithography tools, which have to be replaced when the
exposure wavelength is decreased. S-FIL templates are typically
fabricated using conventional optical phase-shift mask technology.
Electron beam writers that provide high resolution, but lack the
throughput required for mass production, are used. The S-FIL process, therefore, takes advantage of the resolution offered by e-beam technology,
without compromising throughput and tool life.
To
receive more information on S-FIL technology, click here.
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