Evaluation of Plasma Strip Induced Substrate Damage

Abstract

High dose, ultra shallow junction implant resist strip requires minimal substrate loss and dopant loss. Silicon recess (silicon loss) under the source/drain (S/D) extensions increases the S/D extension resistance and decreases drive currents by changing the junction profile. ITRS surface preparation technology roadmap [1] targets silicon loss to be 0.4Å per cleaning step for 45nm and 0.3Å for 32nm generation. Fluorine-containing chemistries which are often used to enhance implanted resist strip and residue removal result in unacceptable substrate loss. A non-fluorine plasma strip was developed in earlier work and is qualified for 45nm logic production [2]. The objective of this work is to study the substrate damage that is induced by the resist strip plasma process. Silicon surface oxidation and silicon loss of different plasma strip chemistries were evaluated with various metrologies such as optical ellipsometry, electrical oxide measurement, XPS, TEM and mass measurement. The impact of different strip chemistries on dopant retention and distribution is also discussed.