Near-surface interactions and their etching-reaction model in metal plasma-assisted etching

Reactive interactions in plasma etching have been investigated. Simple gas-phase transport of etchants and the reaction by-products in the wafer near-surface area are discussed. A new reincidence parameter, determined with a proposed near-surface model, was used to formulate metal etch rates. The experimental results obtained from an electron cyclotron resonance microwave plasma etching system revealed that the measured etching rate agreed well with those obtained by the near-surface model. It was found that reaction by-products repeatedly arrived at the surface depending on the reincidence numbers for the metal etching. The reincidence is the result of the diffusional transport in the vicinity of the wafer and is given by the expression {(one-half of the wafer radius)/(mean-free path)}. The ratio of the by-product flux is expressed by the product of the etching-rate flux times the reincidence number. Then, the resulting ratio of the reaction products in the flux becomes very high when we compare it to those obtained by the residential time model. Based on the near-surface model, the reactive interactions between the wall near-surface and the wafer near-surface make it possible to relate the etching of the wall materials to side-etching width control. The effects of wall etching on the feature profile control are clarified through the inter-near-surface mechanism in metal etching. The use of an oxygen-free reactor inner wall and a C additive to the source gas are found to be effective for enabling highly selective metal etching with fine features.