Role of Nucleation on the Growth of Nanocrystalline Diamond (NCD) Films: a Particular Study in the Fabrication of Micro-Cantilevers

Abstract

The effect of ultrasonic method of seeding on the growth of nanocrystalline diamond (NCD) films has been studied by investigating the nucleation densities of two nanodiamond slurries- 1) nanodiamond powder suspended in acetone 2) mixture of titanium nanopowder and nanodiamond powder suspended in acetone. The former has resulted in a lower nucleation density on the order of 108 cm−2 while the later has increased the nucleation density by over two orders (>1010 cm−2) of magnitude. NCD films were grown on Si(100) substrates in a Cyrannus I Iplas microwave plasma enhanced chemical vapor deposition (MPECVD) reactor using 0.5% CH₄, 1% H₂ and 98.5% Ar gas chemistry at a substrate temperature of ∼ 750°C, pressure of 135 T and a microwave power of 1.8 kW. The double anchored cantilever structures with NCD as structural material have been fabricated by conventional photolithography. It was observed that the films grown after pre-treating the substrates in pure nanodiamond slurry have not provided a complete coverage at the anchor regions of the cantilevers due to the lower nucleation density. Hence during the sacrificial oxide etch, the anchor regions did not adhere well to the substrate and the entire structures got detached from the substrate. But on the other hand, the films grown by seeding the substrates in a suspension of titanium nanopowder and diamond nanopowder showed complete film coverage and consequently very good bonding to the Si substrate at the anchor pads. In this case, the cantilevers have been successfully released without any problems at the anchor pads. Further the mechanical properties of the films were conducted by evaluating the Young’s modulus and the hardness by nano-indentation technique.

Keywords:chemical vapor deposition (CVD)(deposition), nucleation & growth, microelectro-mechanical (MEMS)