SiCl4/Cl2 plasmas: A new chemistry to etch high-k materials selectively to Si-based materials

Abstract

Plasma etching of ultrathin layers of high-k materials is one critical step in the fabrication of gate transistors. The main challenge in this process is to achieve an infinite etching selectively between the high-k and the Si (or SiO2 covered silicon) substrate to prevent damaging the source and drain regions of the transistor. State of the art high-k etching plasmas use BCl3 chemistries, sometime at high wafer temperature. However, the process window in which an infinite high-k/Si selectivity can be achieved is very narrow and several issues remain associated with these processes. In this work, we introduced a new high-k plasma etching chemistry: SiCl4/Cl2. It can be used to etch Hf-based and Al-based high-k materials with an infinite selectivity towards Si, SiO2 and SiON, and with a much wider process window than BCl3 plasmas. XPS analyses indicate that the selectivity mechanism relies on the formation of a SiClx deposit selectively on Si-containing materials, which prevent them from being etched. By contrast SiClx radicals and ions are directly involved in the etching of the metallic oxide layer by forming volatile products (most probably SiOClx and HfClx). This new chemistry may replace valuably BCl3-based plasmas for future high-k etching processes and it may also be interesting for other applications.