AVS 51st International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS2-TuM

Paper PS2-TuM1
Study of Refractory Metal Nitrides/HfO@sub 2@ Gate Stack Etching Using Inductively Coupled Plasma

Tuesday, November 16, 2004, 8:20 am, Room 213B

Session: New Gate Conductor Etching
Presenter: W.J. Yoo, National University of Singapore, Singapore
Authors: J.H. Chen, National University of Singapore, Singapore
W.S. Hwang, National University of Singapore, Singapore
W.J. Yoo, National University of Singapore, Singapore
S.H.D. Chan, National University of Singapore, Singapore
D.-L. Kwong, University of Texas, Austin
Correspondent: Click to Email
Metal gates/high-K gate stacks are expected to be used for 45nm and beyond MOSFETs, replacing conventional Poly-Si/SiON gate stacks. Refractory metal nitrides (RMNs) including TaN, TiN, and HfN are being studied extensively as the promising candidates for future metal gates, because of good thermal stabilities, and suitable work functions on hafnium based high-K dielectric for CMOS devices. In this work, we investigated the etching properties of RMNs (TaN, TiN and HfN) on HfO@sub 2@ using inductive coupled plasma (ICP) of HBr/Cl@sub 2@/O@sub 2@. Results show that the etch rate of ~2800Å/min for TaN, ~2500Å/min for TiN and ~4000Å/min for HfN can be achieved at 10mTorr in HBr/Cl@sub 2@ plasma (inductive power of 400W and DC bias of 144V). Etch rates of RMNs increase rapidly with increasing ion density and energy. The dependences of etch rates of TaN, TiN and HfN on ICP parameters are different, but all are more sensitive than that of poly-Si. Etch electivity of RMNs with respect to HfO@sub 2@ was lower, comparing to poly-Si/SiO@sub 2@ gate stack structure. Adding small amount of O@sub 2@ into Cl@sub 2@ or HBr plasma enhanced the etch selectivity of RMNs with respect to HfO@sub 2@, because it can suppress the etch rate of HfO@sub 2@, without a significant change the etch rates of RMNs. Improvement of etch selectivity can be also achieved by reducing ion energy and increasing pressure. Very anisotropic profile of these three RMNs metal gates can be acquired by reducing pressure, increasing ion energy and adding more Cl@sub 2@ in the gas mixture. Optical emissions at 400-800nm wavelength were observed from RMNs etch byproducts in Cl@sub 2@ or HBr plasma, providing sharp etch end point signal. X-ray photoelectron spectroscopy analysis of etched surfaces shows that most of etch byproducts of these three RMNs etched by Cl@sub 2@ or HBr plasma are volatile at 10mTorr and 100°C, and residues are found to be mainly bromides and chlorides.