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

Paper PS2-TuM6
An Isotropic SiGe Etch Process for Fabrication of Silicon-on-Nothing Transistors

Tuesday, November 16, 2004, 10:00 am, Room 213B

Session: New Gate Conductor Etching
Presenter: T. Sparks, Freescale Semiconductor, France
Authors: T. Sparks, Freescale Semiconductor, France
S. Rauf, Freescale Semiconductor, France
G. Cunge, LTM-CNRS, France
L. Vallier, LTM-CNRS, France
Correspondent: Click to Email
As the device dimensions are shrinking, the development of new transistor structures is essential to meet the ITRS roadmap device performance specifications. One such device, the Si-on-nothing (SON) transistor, utilizes a sacrificial SiGe epitaxial layer underneath a thin transistor active channel region. The SiGe layer is removed using a lateral isotropic etch process. Isotropic chemical downstream etch processes for SiGe removal suffer from high etch rates, low selectivity to Si and lack of insitu monitoring processes such as optical emission analysis. An alternative approach for lateral SiGe etching has been developed utilizing an inductively coupled plasma (ICP) operating in the 'remote' plasma mode, and it is described in this presentation. The etch process was designed using a combination of computational modeling and experiments. The Hybrid Plasma Equipment Model (HPEM) from the University of Illinois was utilized for plasma modeling and process design, and experiments in a commercial ICP reactor were used to confirm the predicted conditions. The plasma model was also coupled to a string-based feature scale model, where the etch mechanism was based on blanket wafer etching experiments and information available in literature. Etching was conducted in CF@sub 4@ containing plasmas, which will generate SiGe etchants (e.g., F) as well as polymer precursors for Si (e.g., CF@sub 2@). Possible mechanisms were investigated to understand the observed high isotropic etch selectivity of SiGe to Si. Process modeling also identified an intermediate gas pressure regime where plasma was localized close to the inductive coils away from the substrate. If the plasma is operated in this gas pressure regime without RF bias, ion energy flux at the substrate was small while flux of neutral etchants and polymer deposition precursors was reasonable. The resulting SiGe process therefore offered good selectivity to Si and a controllable etch rate.