Tungsten etching using an electron cyclotron resonance plasma

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Abstract
Electron cyclotron resonance (ECR) plasma etching is one of the most suitable methods to realize a highly selective and highly anisotropic etching because the ECR is able to generate a high density plasma at low pressure. We applied this technique to W etching using sulfur hexafluoride (SF6) and octafluoro cyclobutane (C4F8) mixture gases at the etching chemistry. The characteristics of the W etching using ECR plasma were investigated. Consequently, high selectivity to photoresist is obtained without biasing rf power. Furthermore, it is clear that the addition of C4F8 to the plasma decreases the reactive ion etching lag effect in W etching. Both our simulations and mass spectral analysis with changing orifice aspect ratios show the surface reaction coefficients of the precursors to increase with increasing molecular weight. For example, the surface reaction coefficient of the parent species of the C4F+9 fragment is estimated to be about 0.12. Furthermore, in our simulation, the flux of these parent species is lowered below 60% in the 2.5‐aspect‐ratio trench pattern.

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