Doping effects in reactive plasma etching of heavily doped silicon

Etch rates of heavily doped silicon films (n and p type) and undoped polycrystalline silicon film were studied during plasma etching and also during reaction ion etching in a CF4/O2 plasma. The etch rate of undoped Si was lower than the n+-Si etch rate, but higher than the p+-Si etch rate, when the rf inductive heating by the eddy current was minimized by using thermal backing to the water-cooled electrode. This doping effect may be explained by the opposite polarity of the space charge present in the depletion layer of n+-Si and p+-Si during reactive plasma etching.