Anisotropic dry etching of submicron W features using a Ti mask

Anisotropic dry etching of tungsten features has been achieved in SF 6 - or CF 4 -based plasmas using a Ti overlayer as the etch mask. Features down to 0.5 mu m have been demonstrated using this simple and robust method. Undercutting of the W sidewall is inhibited while any Ti remains on the feature, and the anisotropic nature of this etching technique occurs over a wide pressure range (1-140 mTorr) and at low DC bias (-100 V). The latter minimizes ion-induced damage to the underlying semiconductor. The Ti mask can be readily removed in dilute HF. High-quality GaAs/AlGaAs heterojunction bipolar transistors have been fabricated using Ti as a mask for dry etching the W emitter contact.