Stability of HSQ nanolines defined by e-beam lithography for Si nanowire field effect transistors

Multiple instability states, e.g., grouped collapse, single collapse, wavy, and grouped wavy states, have been observed in hydrogen silses quioxane (HSQ) nanolines defined by electron beam lithography (EBL). Experimental data show that the critical aspect ratio of the HSQ lines dramatically increase when the line pitch reduced to sub-100-nm, which is opposite to theoretical models for capillary forces and swelling strain. Such contradiction can be well explained only if Young's modulus is considered as a significantly varying factor. Further, experimental data show a dramatic decrease in swelling strain and increase in oxygen contents in HSQ with increasing EBL dose, indicating that it is the change in Young's modulus rather than the capillary force or swelling strain that dominates the instability behaviors at the nanoscale. Stable high aspect ratio HSQ nanolines over metal pads were used to make working Si nanowire transistors on Si on insulator substrates. 12-14 nm HSQ lines with aspect ratios of 11-14 have been obtained. Fabricated field effect transistors using back-gate configuration has shown expected performance towards biosensing applications.