Thermal Scanning Probe Lithography (t-SPL) for Nano-Fabrication

Thermal scanning probe lithography (t-SPL) is a direct-write patterning method that creates high-resolution features with a heated scanning probe tip in an organic resist material. It is able to produce dense high-resolution patterns with sub-20 nm half-pitch at ambient conditions which can be transferred into silicon substrates using a hard-mask patterning stack and reactive ion etching (RIE). Feature sizes of transferred lines can be as small as 7 nm. Linear write speeds of up to 20 mm/s can be achieved. Different from e-beam lithography (EBL), in t-SPL proximity effects are absent and substrate damage of sensitive materials caused by high energy electrons is avoided. A direct inspection of the patterned area is provided during the writing process. Overlay patterning without additional alignment marks onto pre-existing structures is another feature of the t-SPL method. Existing device structures can be located precisely under a resist stack with the local probe tip and the additional target structures can then be generated with $\lt 5$ nm-precise overlay alignment. One further strength of tSPL is the capability of producing 3D patterns. The process can be controlled to produce 3D structures with $\approx 1$ nm $(1 \sigma)$ depth accuracy. Examples of unique devices fabricated by tSPL will be discussed.