Structural Changes of La2O3-doped Hf-based High-k Dielectrics during Aqueous HF Treatment

Abstract

The wet removal of La2O3-doped Hf-based dielectrics is examined for future high-k metal-insulator-semiconductor field-effect-transistor (MIS-FET) processing. XPS observations reveal that aqueous HF treatment removes Hf and Si components from La2O3-doped HfSiON, and LaFx residue remains on the processed wafer surface. It is shown that the sequential treatment of strong acid and HF is effective to reduce unfavorable LaFx adhesion. It is pointed out that HF-treatment fluorinates La in HfO2 film with no-film-dissolution and reactive-ion-etching (RIE) must be selected to remove La2O3-doped HfO2 film. To clarify the effect of removal processing on actual MIS-FET structure, SEM and high resolution STEM observations are carried out. The observations suggest that both the side etching of HfSiON dielectrics during HF-treatment and the substrate recess during HfO2 film removal with RIE are serious issues for the manufacturing of La2O3-doped high-k MIS-FETs.