Study on electrical characteristics of HfO2 treated by Nf3 plasma

Abstract

Summary form only given. Plasma process was used widely to manufacture semiconductor device due to low temperature and good performance. In particular, capacitively coupled plasma (CCP) and inductively coupled plasma (ICP) system were commonly used for dry etch, deposition and plasma treatment process in semiconductor device. In this paper, the fluorine plasma treatment process on high-k dielectric HfO2 was studied for improvement of dielectric performance. Fluorine can recover the trap due to passivation into oxygen vacancy of HfO2 dielectric. Plasma treatment is one of promising candidates to inject the ionized fluorine atom into oxygen vacancy of HfO2 effectively. Both CCP system with low density plasma (LDP, ~0.01%) and ICP system with high density plasma (HDP, ~1%) with NF3 gas were used for fluorine ionization. Composition and structure of the fluorinated-HfO2 treated by plasma were analyzed with TEM, XPS and Tof-SIMS. Electrical characteristics of I-V and C-V were measured with semiconductor device analyzer. Interfacial layer (IL) thickness of the fluorinated-HfO2 increasingly increased under the condition of ICP system, which led to the decrease of capacitance and degradation of dielectric. Also, crystallization and agglomeration of HfO2 was observed at TEM image. These result from fluorine ion bombardment and high temperature induced by plasma with high energy. Fluorine ionized by ICP system collides with HfO2. Bombardment of ionized fluorine can convert from HfO bond to Hf-F bond partially due to thermal energy and ion bombardment. Dissociated oxygen diffuses out surface or into silicon substrate, and then oxygen piled up on silicon substrate is combined with silicon. This results in the increase of IL thickness. Also, High thermal energy (>;550°C) generated from ion bombardment by ICP system can crystallize and agglomerate HfO2 dielectric sufficiently. Based on this model, we suggest that the fluorine treatment with low temperature and low density plasma can incorporate fluorine into oxygen vacancy of HfO2 without the damage of HfO2 and the increase of IL thickness on substrate silicon. We improved electrical characteristics of fluorinated-HfO2 without degradation of dielectric at the condition of low temperature (>;250°C) and low power with HFRF in CCP system. VBD (breakdown voltage) and IG (gate leakage current) of fluorinated-HfO2 were sharply improved about 10% and 50% compared to that of conventional HfO2. Stress induced leakage current (SILC) of fluorinated-HfO2 was improved in terms of dielectric reliability.