A novel thermal scanning probe lithography (tSPL) method based on the local removal of organic resist materials has been developed at the IBM Research Laboratory in Zurich [1-3]. A polymeric polyphthalaldehyde resist [2-4] responds to the presence of a hot tip by local material decomposition and desorption. Thereby arbitrarily shaped patterns can be written in the organic films in the form of a topographic relief, constrained only by the shape of the tip. The combination of the fast ‘direct development’ patterning of a polymer resist and the in-situ metrology capability of the AFM setup allows to reduce the typical turnaround time for nano-lithography to minutes.
Patterning rates of 500 kHz have been achieved. For this, the mechanics and drive waveform of the scan stage were optimized, achieving high speed linear scanning with an overall position accuracy of ± 10 nm over scan-ranges and scan-speeds of up to 50 μm and 20 mm/s, respectively. A pre-tension-and-release strategy was used to actuate the cantilever above its resonance frequency of 150 kHz. Fabrication of three dimensional patterns is done in a single patterning step by controlling the amount of material removal at each pixel position. The individual depths of the pixels are controlled by the force acting on the cantilever.
The structuring capability in the third dimension adds an entirely new feature to the lithography landscape and finds applications e. g. in multi-level data storage, nano/microoptic components and directed positioning of nanoparticles. For the latter, shapematching guiding structures for the assembly of nanorods of size 80nm × 25nm have been written by thermal scanning probe lithography . The nanorods were assembled into the guiding structures by means of capillary interactions. Following particle assembly, the polymer was removed cleanly by thermal decomposition and the nanorods are transferred to the underlying substrate without change of lateral position. As a result we demonstrate both the placement and orientation of nanorods with an overall positioning accuracy of ≈ 10 nm onto an unstructured target substrate.
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