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

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.