This Small Business Innovation Research Phase I project will determine the feasibility of making foundry-quality MEMS starter wafers composed of ultrananocrystalline diamond (UNCD) on SiO2 and on Si (diamond-on-insulator, DOI) in a strategy similar to silicon-on-insulator (SOI) wafers. The research team has solved problems of thickness uniformity, sp3/sp2 ratio uniformity, grain size uniformity, adhesion, and roughness (<30 nm rms), but problems remain with the stress level, particle density (>102 cm-2 particles >1 um mainly due to non-clean room processing), and limited uniformity of the acoustic velocity (14-16 km/s). Phase 1 will 1) implement a novel method for stress reduction to bring it down to -50 to + 100 MPa and prove the resulting level is conserved through subsequent thermal processing (deposition of oxide and nitride layers by LPCVD, PECVD), 2) prove that particle density on the device layer can be reduced to under 10/cm2 (for particles of size >1 um) while backside contamination can be eliminated by special seeding conditions and cleaning, and 3) optimize the deposition conditions to bring the acoustic velocity to the 16 km/s range with a 10% confidence level on 4" and 6 " diameter DOI wafers.
UNCD has proven its advantages for MEMS components through its exceptional hardness, Young's modulus, toughness, acoustic velocity, smoothness, uniformity, bio-compatibility, and tunable conductivity. The commercialization of diamond MEMS products is inhibited by limited (high) quality diamond production capabilities, little experience with diamond by end users, and concerns that the seeding process (precursor of diamond growth) may lead to contamination issues. The present DOI product targets users at various levels (small companies, foundries, research centers) who want to enter the diamond MEMS realm. Diamond MEMS has great potential in RF-MEMS (resonators, filters, oscillators for wireless communication and information technology), bio-implantable chips (artificial retina, cochlear implants, implantable ID chips), electronics and material research (AFM probes, data storage devices, x-ray and electron optics), sensors (SAW sensors, vibrating cantilever sensors, etc).
