Paper TF-WeM6
Conformality of Chemical Vapor Deposited Copper Oxide Thin Films in High Aspect Ratio Features for ULSI/MEMS Applications

Wednesday, October 22, 2008, 9:40 am, Room 302

Kinetics of chemical vapor deposition of copper oxide (Cu₂O) thin film using Cu(tmvs)(hfac) and H₂O₂ as precursors were investigated. Cu₂O films could be deposited at relatively low temperature, as low as 80°C, on various kinds of under-layers including thermal silicon oxide and TaN. Cu₂O films can be easily reduced to metallic copper thin films using formic acid (HCOOH) as reducing agent. This reduction process can be performed at low temperature of around 100°C. Thus, Cu₂O deposition and its reduction process combination can be a novel chemical route to make metallic copper film at low temperature. In this work, we examined the source precursor partial pressure dependencies of Cu₂O growth rate (G.R.) using cold wall type CVD reactor. G.R. showed non-linear behavior, know as Langmuir-Hinshelwood mechanism, against partial pressure of Cu precursor (P_Cu), while G.R. showed linear dependence against the partial pressure of H₂O₂ (P_H2O2). These kinetics suggest Cu₂O is formed via direct reaction of gas-phase H₂O₂ and adsorbed Cu precursor. The extendibility of this Cu₂O-CVD process to make conformal deposition onto high aspect ratio (HAR) features was systematically investigated. The film thickness profile within HAR-feature, like as trench, was analyzed by solving diffusion equation for precursor molecules. The consumption of the precursors by surface reaction, whose rate had been obtained from the above mentioned kinetic studies, was taken into account. The analysis suggested that film thickness non-uniformity was mainly derived from the consumption of H₂O₂. The Cu precursor concentration profile does exist in the HAR-features, however, due to the non-linear kinetic behavior of G.R. against P_Cu, its non-uniformity will not affect to the film thickness uniformity. Existence of gas-phase reaction to decompose H₂O₂ was also confirmed from the growth rate profile analysis. These kinetic information were integrated and extendibility of this Cu₂O-CVD process for conformal deposition onto HAR features was estimated. We could conclude that this process is suitable for ULSI interconnect and TSV applications with nearly 100% step coverage, but for MEMS applications, this process may have a limit. Step coverage of about 40% or less will be obtained for aspect ratio of 100, which may be sometimes required for MEMS applications.