Sep 26, 2012
Resist layer correlation joins up nanopatterns
Maskless lithography is a versatile approach for prototyping and fabricating nanostructures and devices. To create highly resolved nanopatterns over a large area, individually written fields are typically stitched together like a quilt. This requires distinct alignment marks, which can take up a significant amount of space between the useful structures. Now, IBM scientists in Zurich working in the field of scanning probe lithography have developed a method for aligning the write fields that gets around this issue. The technique exploits the fingerprint-like properties of the local surface roughness of the resist layer used to create the pattern templates.
The desktop-sized probe lithography tool works by locally evaporating a polymer resist layer without the usual need for a separate development step. In combination with the system’s built-in topography imaging feature, individual fields can be stitched together by imaging a margin around a written field. After shifting the sample with the coarse stage, the nominal stitching margin is read again, and a correlation between the two roughness images determines the precise offset position.
A surprising result from the theoretical analysis is that the stitching accuracy depends more heavily on the size of the area used for stitching rather than on the imaging resolution. The latter contributes mainly to the signal-to-noise ratio. Theoretically it is possible to determine the position of the fields to fractions of a nanometre – in other words by tens of atoms, even with significantly larger pixels. In practice, however, positioning is limited to the accuracy of the mechanical setup, which is in the range of ±10 nm.
The stitching feature for scanning probe lithography was a crucial aspect in creating a competitive low-cost nanopatterning solution that is fully compatible with standard microchip fabrication methods. Previous work published in Nanotechnology 22 275306 demonstrated a patterning rate of 500,000 pixels per second, which approaches the throughput values achieved by the de-facto standard patterning method using a Gaussian electron beam.
Originally, the thermal probe methods were developed for the IBM Probe Storage Technology. The data storage device used thousands of these heated tips to store data as indentations in polymers rather than removing the material completely as required for lithography.
More information can be found in the journal Nanotechnology.
About the author
The authors are members of the probe nanopatterning group led by Dr Michel Despont at IBM Research–Zurich. Dr Philip Paul is a postdoctoral researcher in the group, Felix Holzner is reading materials science at ETH Zurich towards his PhD degree. Dr Armin Knoll and Dr Urs Duerig are research staff members at IBM. Two of the authors, Philip Paul and Felix Holzner, have recently founded a start-up company – SwissLitho (http://www.swisslitho.com) – to bring this versatile tool to the market.