A new system has been constructed for electron cyclotron resonance (ECR) ion stream etching to fabricate metal–oxide–semiconductor (MOS) gates at the quarter‐micron level. It has three features: (i) a new ECR plasma source that generates a uniform plasma; (ii) a supplementary coil that makes the ion stream perpendicular over the whole surface of a 6‐ or 8‐in. wafer; and (iii) CF4 and O2 addition to reduce the influence of SiClx by‐products formed by the reaction between silicon and the Cl2 etching gas. We have found that reducing the amount of SiClx reaction products desorbed from the chamber wall is essential for significant improvement in etching characteristics. Using this new system, we attained (i) uniformity as good as ±1.6% over a 6 in. wafer with a Si etch rate of 0.17 μm/min; (ii) uniformly vertical profiles over the whole wafer, including the edges; and (iii) stable etching conditions with a high selectivity of over 100.

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