Silicon dioxide etching technology for deep-submicron ultralarge scale integration has been developed using an electron cyclotron resonance (ECR) plasma etcher. The optimum conditions for silicon dioxide etching are obtained in terms of etch rate, geometrical controllability, and radiation damage by fully utilizing such advantages of the ECR plasma etcher as low-pressure operation, high plasma density, and independent control of ion energy and plasma discharge. High selectivity is also found at low pressures with C4F8/CH3F. The technology has been successfully applied to the formation of 0.35 mu m contact holes with an aspect ratio of 4 without a decrease in etch rate.