Abstract Electron cycloton resonance (ECR) plasmas are different from glow dischargeplasmas and introduce new complexities and possibilities. For dry etching processes (reactive ion etching), the operation in a low pressure regime and the high etch rates achievable at low ion energies,which can be controlled by an independently adjustable r.f. bias voltage, are some of the essential advantages. Etching of SiO 2 and silicon by an ECR plasma stream using CF 4 and O 2 as etching gases shows no loading effect, a reasonable selectivity mostly influenced by the etching chemistry (ratio of CF 4 to O 2 ) and isotropic profiles which depend on the applied r.f. bias voltage.