'Thin films & coatings' Roadmap - Nano Mahidol

2.3.3 Patterning methods
Patterning methods have been widely used in the semiconductor industry and some
other applications could benefit from these technologies. Their main objectives are to
provide the coated substrate with the required pattern and they involve both
techniques for removing or adding material. Main bottlenecks lie on the size of the
area to be patterned, the feature size of these patterns (depending on the
wavelength or the size of the tip/stamp) and the chemical specificity required.
2.3.3.1 Optical Lithography
This is the main mass-production patterning method used by the semiconductor
industry. It uses light to transfer a pattern onto a surface. The surface is coated with
a polymer thin film (e.g. normally over a semiconductor substrate) that acts as a
resist. The light passes through a mask containing the desired patterning and the
pattern is transferred to the resist. The exposed parts of the resist change chemically
and can then be selectively removed, exposing the underlying surface in the desired
pattern. This surface can then be selectively treated (e.g. etching, doping). The
resolution of the patterning process (already under 90 nm in commercial production)
depends on the wavelength of the radiation and the numerical aperture of the lens.
Using shorter wavelengths is one way of increasing resolution.
Main barriers to success and research paths
According to the experts this is a well-understood technology limited by the size of
patterns that can be achieved. Recent research is exploring the use of extreme UV to
downsize the patterns. Main technical barriers are related to the resist (polymer thin
film). The adhesion to the substrate has been largely solved, according to the
experts.
With regard to cost factors, this process requires very expensive equipment for
features below 100nm. High production runs are needed to spread these costs.
19 Roadmap report on
Thin films and coatings