AVS 53rd International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS1-ThA

Paper PS1-ThA3
Effects of Low Energy Nitrogen Plasma on the Removal of HfSiON

Thursday, November 16, 2006, 2:40 pm, Room 2009

Session: Plasma Processing for High-K/III-V’s and Smart Materials
Presenter: W.S. Hwang, National University of Singapore
Authors: W.S. Hwang, National University of Singapore
W.J. Yoo, Sungkyunkwan University, Korea
B.J. Cho, National University of Singapore
D.S.H. Chan, National University of Singapore
Correspondent: Click to Email
HfSiON high-k dielectric is being studied extensively to improve the electrical properties of conventional SiON dielectric since it can attain low leakage current especially for low standby power application. The removal of high-k dielectric using a wet etching technique is more frequently used than dry etching techniques which result in poor etching selectivity over underlying Si. Dilute hydrofluoric acid (DHF) solution etches amorphous HfSiON easily without the loss of the underlying Si. However, crystallized HfSiON shows strong resistance in DHF after post-deposition anneal, posing challenges in the integration involving the removal of high-k dielectric at the active transistor regions of source and drain. In this work, the DHF wet removal of HfSiON assisted by N@sub 2@ ion bombardment is investigated. The anisotropic and undercut-free profile is achieved by this technique. An as-deposited amorphous HfSiON of 4 nm can be removed by 1% DHF in 15s, whereas the annealed crystallized HfSiON cannot be removed. N@sub 2@ plasma treatment helps the crystallized HfSiON to be etched in DHF. The ion assisted wet removal is made feasible via changing the structure of the crystallized HfSiON to the mixture of metallic Hf and amorphous HfSiON. We found a correlation between ion energy and formation energy of HfSiON; the ions having energy less than 9eV do not penetrate HfSiON, whereas ions having energy higher than its formation energy of ~ 9.3eV penetrate HfSiON and participate in the formation of SiN. The low energy ion assisted wet removal method results in lower threshold voltage than the conventional DHF wet etching method which causes lateral encroachment of HfSiON that lowers gate oxide capacitance. This plasma assisted method can be applied extensively to various removals of high-k material constrained by low crystallization temperature and thereby high etching resistance in conventional DHF.