Thermal scanning probe lithography

Thermal scanning probe lithography (t-SPL) is a form of scanning probe lithography (SPL) whereby material is structured on the nanoscale using scanning probes, primarily through the application of thermal energy.

Related fields are thermo-mechanical SPL (see also Millipede memory), thermochemical SPL (or thermochemical nanolithography) where the goal is to influence the local chemistry, and thermal dip-pen lithography as an additive technique.

History

Scientists around Daniel Rugar and John Mamin at the IBM research laboratories in Almaden have been the pioneers in using heated AFM (atomic force microscope) probes for the modification of surfaces. In 1992, they used microsecond laser pulses to heat AFM tips to write indents as small as 150 nm into the polymer PMMA at rates of 100 kHz. In the following years, they developed cantilevers with resonance frequencies above 4 MHz and integrated resistive heaters and piezoresistive sensors for writing and reading of data. This thermo-mechanical data storage concept formed the basis of the Millipede project which was initialized by Peter Vettiger and Gerd Binnig at the IBM Research laboratories Zurich in 1995. It was an example of a memory storage device with a large array of parallel probes, which was however never commercialized due to growing competition from non-volatile memory such as flash memory. The storage medium of the Millipede memory consisted of polymers with shape memory functionality, like e.g. cross-linked polystyrene, in order to allow to write data indents by plastic deformation and erasing of the data again by heating. However, evaporation instead of plastic deformation was necessary for nanolithography applications to be able to create any pattern in the resist.