Fabrication and testing of nanomechanical <100> silicon beam structures using a scanning probe system

Abstract

Knowledge of the mechanical behavior of strategically important materials such as silicon at nano scale is the key for building next generation devices. In this paper, we investigate the Young’s Modulus of nanomechanical beams [1-8 mm long, 200-400 nm wide, and 193 & 255 nm in thickness] fabricated from silicon-on-insulator (SOI) wafers. The beams of different dimensions were defined in PMMA resist using e-beam lithography. A layer of chrome deposited using lift-off technique, acted as an etch-mask for silicon to fabricate the beams by using RIE. The samples were dipped in BOE (Buffered Oxide Etch) to etch the oxide underneath and the beams were released using critical point drying. Using a Scanning Probe System, nanomechanical beams were bent using AFM silicon tapping mode probes. A controlled amount of force was applied by varying the voltage applied to the Z-axis piezoactuator. The values of beam deflection and the net force applied enabled us to plot the Load vs. Displacement graph for the bending of the nanomechanical beams. Using Euler - Bernoulli beam bending equations, the Young’s Modulus of the Silicon beams was measured to be 174 GPa. This value agrees within 5% of the known value of bulk silicon Young’s modulus of 169GPa. Thus we conclude that the value of Young’s modulus of Si beams does not change when the size is reduced to nanometer regime.