In Situ Deposition Monitoring by a Tilted Fiber Bragg Grating Optical Probe: Probing Nucleation in Chemical Vapour Deposition of Gold

Abstract

Abstract The gold(I) compound [Au(N i Pr) 2 CNMe 2 ] 2 was used as a chemical vapour deposition precursor to deposit gold metal films between 200 – 225 °C on both flat silicon substrates as well as on silica optical fibers. The deposited gold film was nanocrystalline with a preferred (111) orientation and had marginal conductivity. The film shows good purity and has a very high growth rate of 222 nm/min (37 A/s) when measured on the optical fiber. The growth of the gold film on the optical fiber was monitored by the attenuation of a guided light mode diffracted into the fiber's cladding by a tilted Bragg grating (TFBG) inscribed in the fiber core. The initiation of the gold film growth was found to coincide with an increase in the attenuation of polarized light propagating in the fiber and monitored at wavelengths near 1559 nm. This attenuation peaked when the film granularity maximized losses to the cladding mode and then disappeared when the film became thicker and continuous. Further evidence of a continuous film was indicated by a wavelength shift of 0.2 nm of the cladding mode resonance wavelengths. A growth rate of 222 nm/min (37 A/s) was found during the first 50 seconds of deposition, tapering off to an overall growth rate of 39 nm/min (6.5 A/s). The use of a TFBG as a sensor was shown to be a valuable method to monitor film nucleation, growth and uniformity.