Plasma etching of HfO_2 in metal gate CMOS devices

摘要

With the introduction of new materials in the CMOS gate stacks, such as metal and high-k materials, plasma etching has to address new challenges. The authors present a study dedicated to the etching of thin HfO_2 layers in BCl_3 plasmas. This etching process must be selective with respect to Si and SiO_2 since the underlying silicon substrate must not be damaged. In this work, it is shown that HfO_2 etching with infinite selectivity can be achieved by adjusting the bias power in pure BCl_3 plasma, by diluting BCl_3 in argon, and by conditioning the reactor walls with a carbon coating before BCl_3 process. However, the etch process has to minimize the deposition rate of boron polymers on silicon surfaces in order to prevent the formation of HfO_2 residues. The anisotropic profile of the gate is maintained during the BCl_3 plasma step. The c-Si surface presents no contamination (Hf or B) after HfO_2 etching process and wet post-treatment. Reactor wall cleaning issues are also addressed.