Low-stress silicon carbonitride for the machining of high-frequency nanomechanical resonators

Abstract

The synthesis of silicon carbonitride by low-temperature plasma-enhanced chemical vapor deposition and the machining of nanomechanical resonators in this material are reported. Films with thickness of 1μm, 200nm, and 50nm were deposited using ammonia, nitrogen, and diethylsilane as precursors. X-ray photoelectron spectroscopy indicated that usage of higher NH3:DES gas flow ratios results in higher nitrogen and low carbon contents in the deposited films. In addition, annealing of the material enabled the full tunability of its residual stress from the compressive to the tensile range. Infrared spectroscopy indicated that desorption of incorporated hydrogen was responsible for those changes. Assaying of resonant cantilevers fabricated from 200-nm-thick films yielded root-modulus-over-density values as high as √(E∕ρ)=8.35×103m∕s, comparable to those of silicon. Doubly clamped beams were also fabricated from 50-nm-thick films of low (σ=80MPa) and high (σ=220MPa) tensile stresses. Beam resonators fabricated in the lower stress material showed resonance qualities ranging between 3000 and 5000, and resonant frequencies between f=6.1MHz and f=16MHz. Beam resonators machined in the higher stress material experienced quality factors between 8000 and 23 000 and frequencies between f=7.6 and 24MHz. These values correspond to fQ products as high as of 1.5×1011s−1, exceeding the performance of previously reported silicon resonators.