High resolution electron beam lithography using ZEP-520 and KRS resists at low voltageSingle crystal and polycrystalline silicon films have been patterned and etched with a novel high-selectivity process using self-assembled monolayer resists of octadecylsiloxanes ͑ODS͒. The highest resolution patterning of sub-10 nm features has been demonstrated by scanning force microscopy imaging of ODS layers patterned with a focused electron beam. An all-dry UV/ozone developer has been used to remove residual carbon from the electron beam exposed regions to improve etch selectivity. The positive tone pattern transfer process consisted of a short buffered hydrofluoric acid wet etch to remove the silicon native oxide followed by a high-selectivity, low ion energy etch using Cl 2 and BCl 3 in an electron cyclotron resonance reactive ion etch. Features have been etched up to 90 nm deep into Si͑100͒ wafers and minimum feature sizes obtained are ϳ25 nm. Poly-Si films on SiO 2 insulator layers have been similarly patterned and have been used in a combined process with photolithographic definition of microbridges to form narrow conducting channels in the poly-Si.

A set of processes has been explored that enhances the utility of self-assembled-monolayer electron-beam resists for patterning silicon. A self-assembled monolayer resist of octadecylsiloxane was exposed using a scanning electron microscope with a 20 keV beam energy and dose of 320 μC/cm2. After the patterned monolayer was developed using ultraviolet light and ozone, it served as a wet etch mask for the underlying native oxide. Linewidths of ∼30 nm were etched in silicon using the patterned oxide as a reactive ion etch mask. The maximum etch depth achieved in silicon was 90 nm using this process.

Novel processes have been developed for transferring patterns using self-assembled monolayer (SAM) electron beam resists. Because the SAMs are very thin, high-selectivity processes are required for effective substrate modification. Two separate techniques have been studied for patterning intermediate layers for use as reactive ion etch (RIE) masks. A bilayer process using the native oxide as an intermediate etch mask has been used to etch into both crystalline and polycrystalline silicon. The native oxide is patterned with the SAM resist and the oxide is then used as a mask in an electron cyclotron resonance RIE. This process has been used to produce ∼25 nm etched features in silicon. Instead of its selective removal, an alternative technique for forming the intermediate etch mask layer is the selective deposition of the layer. Thin nickel layers have been formed with an electroless plating technique on silicon. The electroless deposition is highly selective for producing nickel plating on silicon as opposed to the silicon oxide. These novel high-selectivity techniques demonstrate the ability for ultrathin SAM resist layers to pattern silicon and other materials.

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