Design of a Multi-Wafer Reactor for Supercritical Fluid Deposition of Cu in Mass Production: (2) Benchmarks for Single- and Multiple-Wafer Reactors

Abstract

The feasibility of a wafer-scale reactor for supercritical fluid deposition (SCFD) of Cu for interconnects in ultra-large-scale integration (ULSI) was evaluated for mass production based on two criteria: the throughput of the reactor (20 wafers/h) and the film-thickness uniformity on 12-inch wafers (>99%). The optimal configuration and size of a reactor adequate for mass production were determined using finite-element method (FEM) simulations with a reaction-rate equation and kinetic parameters from our previous study. Cu interconnects are conventionally fabricated by two processes: seed layer formation by sputtering, followed by gap filling by electroplating. SCFD can be used for seed-layer formation alone or for both seed-layer formation and gap filling. Here, the same conclusions were reached in both cases. A single-wafer reactor (SWR) was not suitable due to its low throughput, although excellent thickness uniformity could be expected. Stacking multiple wafers in a multi-wafer reactor (MWR) is thus preferable, where the throughput is a function of the number of stacked wafers. A closed MWR is acceptable due to its inherent film-thickness uniformity in addition to its high throughput. A continuous flow MWR imposes design issues on the reactor to achieve a uniform film-thickness distribution on the stacked wafers. A flow-channel MWR, where the precursor flows among the stacked wafers in parallel with the growing surfaces, was deemed suitable for mass production of ULSI Cu interconnects.