Electrical and optical properties of rf triode-sputtered Au films

Abstract

A large number of Au films with different nominal film thicknesses (NFT) from 12 to 960 Å, were rf triode sputtered with 2.5 kV in a single pumpdown in 1-mTorr argon, at a deposition rate of about 1.5 Å/sec, onto amorphous SiO2 at 120 °C. The film substructure, as determined by transmission electron microscopy, showed that the island particles became metallically connected at a NFT of about 30 Å. This small value was attributed to the high nucleation density (about 1.2×1012 nucleated particles/ cm2 at a NFT of 12.7 Å) and to the fact that the island particles grow as flattened platelets. Microscopy also revealed that the islands were composed of small single crystallites with mean dimensions less than 50 Å for a NFT of 20 Å. The surface coverage increased with NFT to about 100% at 100 Å. The mean crystallite increased to about 85 Å and then tended to remain constant for NFT's above 100 Å. The electrical resistivity of films with an NFT greater than 30 Å was measured over the temperature range 77–300 K. In the NFT range 30–40 Å, the films were found to have a very small positive temperature coefficient of resistance (TCR) that increased linearly with NFT from 0.0002 to 0;0004 K−1 and a large sheet resistance that decreased rapidly from 1000 Ω/□ (30 Å) to 100 Ω/□ (40 Å). Films greater than 100 Å had resistivities 3–4 times that reported for single-crystal Au. This increase was mainly attributed to polycrystalline grain boundary scattering. Optical properties were studied by measuring the reflectance and transmission of films over an incident wavelength range from 0.18 to 2.0 μ. Films with NFT's less than 50 Å were found to behave optically according to the Maxwell-Garnett theory for an array of particles, even though the island particles of these films were irregularly shaped. Optical indices were calculated for films thicker than 12 Å.