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Self-Assembled Monolayers as High-Resolution Resists

IP.com Disclosure Number: IPCOM000117604D
Original Publication Date: 1996-Apr-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 139K

Publishing Venue

IBM

Related People

Biebuyck, H: AUTHOR [+2]

Abstract

The potential for atomic-level manipulation of matter with the Scanning Tunneling Microscope (STM) has spurred significant interest in the use of STM as a nanofabrication tool. A significant obstacle in the progess of STM nanostructure fabrication is the transfer of a pattern into a usable metallic or semiconductor structure because STM modifies very thin layers of material that cannot withstand the process of actual pattern transfer. Finding a suitable "resist" for effective pattern transfer is, therefore, a major problem (1).

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Self-Assembled Monolayers as High-Resolution Resists

      The potential for atomic-level manipulation of matter with the
Scanning Tunneling Microscope (STM) has spurred significant interest
in the use of STM as a nanofabrication tool.  A significant obstacle
in the progess of STM nanostructure fabrication is the transfer of a
pattern into a usable metallic or semiconductor structure because STM
modifies very thin layers of material that cannot withstand the
process of actual pattern transfer.  Finding a suitable "resist" for
effective pattern transfer is, therefore, a major problem (1).

      A very different approach to lithography is based on contact
printing using Self-Assembled Monolayers (SAM) on gold.  Reaction of
gold or other metals with organosulfur compounds results in their
assembly in highly ordered, crystalline monolayers 0.1 to 3 nm thick
that are registered to the underlying surface (2).  Monolayers of
hexadecanethiol protect gold from attack by a cyanide based etching
solution: 10E6 differences in the rates of dissolution of the metal
occur between bare gold and gold protected by a SAM of
hexadecanethiol (3).  Elastomers of poly(dimethylsiloxane) (PDMS) are
used for stamps because these polymers are inert and allow excellent
replication of topographic features.  Together, these components form
a system capable  of massively parallel lithography on scales down to
100 nm in a technologically relevant material.

      Notice (4) that SAMs of dodecanethiol are atomically resolved
by STM at voltages between 0.9 to 1.4 V of either polarity, and
currents less than 10 pA.  Imaging with high resolution was extremely
sensitive to the conditions, stopping at currents above 10 pA.
Moreover, if the currents were increased to 100 pA and higher, the
tip or the surface was damaged irreversibly and high resolution was
no longer possible with the same tip or on the same surface.
Initially, it was not clear, whether structural changes in the SAM
were severe enough to allow a developing step in order to be used as
a resist material.  A key question was whether sufficient damage to
the monolayer occurred following its exposure to electrons so that an
etch solution could dissolve the underlying gold in that region.

      Tests with STM lithography on SAMs provided conditions for
three regimes of behavior: A "penup" condition (i.e., imaging
without writing etchable features) is met by currents in the range
from 1 to 10 pA and voltages in the range from 0.9 to 1.4 V.  A
"minimum linewidth" condition is met for currents of 20 pA and
voltages in the range from 1 to 2.5 V and speeds between 20 and 200
um/s which...