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 w afer near-surface area are discussed. A new reincidence parameter, det ermined with a proposed near-surface model, was used to formulate meta l etch rates. The experimental results obtained from an electron cyclo tron resonance microwave plasma etching system revealed that the measu red etching rate agreed well with those obtained by the near-surface m odel. It was found that reaction by-products repeatedly arrived at the surface depending on the reincidence numbers for the metal etching, T he reincidence is the result of the diffusional transport in the vicin ity of the wafer and is given by the expression {(one-half of the wafe r radius)/(mean-free path)}. The ratio of the by-product flux is expre ssed by the product of the etching-rate flux times the reincidence num ber. Then, the resulting ratio of the reaction products in the flux be comes very high when we compare it to those obtained by the residentia l time model. Based on the near-surface model, the reactive interactio ns between the wall near-surface and the wafer near-surface make it po ssible to relate the etching of the wall materials to side-etching wid th control, The effects of wall etching on the feature profile control are clarified through the inter-near-surface mechanism in metal etchi ng. The use of an oxygen-free reactor inner wall and a C additive to t he source gas are found to be effective for enabling highly selective metal etching with fine features, (C) 1998 American Vacuum Society.