Transcript Lotus Effect

Nanolithography
CHE 5480 Summer 2005
Maricel Marquez
Scanning Probe Lithography
(SPL)
•The Semiconductor Industry Association's 1997 National
Technology Roadmap for Semiconductors predicts that
critical dimensions will shrink to 150 nm by 2001, to 100
nm in 2006, and to 50 nm by 2012.
The conventional photolithography used for printing
integrated circuit features is approaching fundamental
limitations. An alternative lithography technology may be
required within the next five years.
Scanning probe lithography (SPL) could be a viable
alternative for patterning 100 nm feature sizes and
below.
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4 Factors in SPL
(1) Resolution,
(2) Alignment accuracy,
(3) Reliability, and
(4) Throughput (wafers/hour).
High Resolution (SPL)
 Scanning tunneling microscope (STM) or the
atomic force microscope (AFM) is used to
pattern nanometer-scale features.
 When a voltage bias is applied between a
sharp probe tip and a sample, an intense
electric field is generated in the vicinity of the
tip. This concentrated field is the enabling two
effects:
 Field enhanced oxidation (of silicon or metals)
and electron exposure of resist materials.
Schematic of the process:
Oxidation of
Single-Crystal Silicon
Electron Exposure of Resist
(Organic Polymer Films)
Force Feedback. One loop maintains a constant small force
(typically 10 nN) between the tip and the electron-sensitive resist.
Current Control. The other feedback loop maintains a constant
field emission current through the resist during exposure
(generally in the range of 20 pA to 1 nA).
Cross-sectional SEM images of etched silicon features patterned
by scanning probe lithography. (a) 50-nm-wide line written in
SAL601 and etched 300 nm into the silicon using an HBr+O2 high
density plasma (6:1 aspect ratio). (b) 26-nm-wide line written in
PMMA and transferred through lift-off and anisotropic etching
(NF3) into the silicon substrate. The etch depth is 260 nm, giving
the line an aspect ratio of 10:1.
High Speed Patterning of Siloxene
Spin-on-Glass
 In order to pattern large areas
in reasonable times, it is
imperative to increase SPL
writing speeds. For that
purpose a resist material
suitable for high speed writing
has been identified.
 The material is siloxene, a Si-O
polymer with attached methyl
groups, commonly known as
Spin-on-Glass (SOG).
 SOG can be easily patterned
High Speeds Patterns of 100 nm in
with electrons emanating from SOG written using the AFM
a scanning tip.
scanning at 1 mm/s. Other patterns
have been written at 3 mm/s.
Note: Dr. Quate’s website:
http://www.stanford.edu/group/quat
e_group/LithoFrame.html