AVS 49th International Symposium
    Plasma Science Monday Sessions
       Session PS-MoM

Paper PS-MoM7
HBr Outgassing and Condensation from Silicon and Polysilicon Wafers after Plasma Etching

Monday, November 4, 2002, 10:20 am, Room C-105

Session: Conductor Etch I
Presenter: H. Singh, Lam Research Corporation
Authors: H. Singh, Lam Research Corporation
D. Outka, Lam Research Corporation
J.D. Daugherty, Lam Research Corporation
Correspondent: Click to Email
HBr gas is commonly used in dry etching of poly-silicon gate structures and in shallow trench etching since HBr-rich etch chemistry provides good profile control and high selectivity to gate oxide. As a result, the surface of wafers in many silicon etch processes are bromine terminated at the end of plasma etching. Subsequently, HBr outgasses from etched wafers upon exposure to atmosphere. HBr also condenses on the etched wafer and neighboring wafers in the form of HBr-hydrate and bromine-hydrate. HBr and bromine hydrates crystals are stable at ambient conditions. The timescale for HBr outgassing and condensation varies from few seconds to days, depending on the etch and ambient conditions (e.g. humidity). HBr outgassing and condensation also occurs on bare silicon wafers commonly used to condition plasma etchers before etching production wafers. The re-use of these bare silicon wafers results in micro-masking of the wafer by the HBr-hydrate crystals, resulting in formation of silicon pillars on the wafer. The micro-masking of the wafer results in formation of so-called @super "@black silicon@super "@ rendering the wafer unusable. Various methods investigated to minimize the outgassing and condensation of HBr on wafers, including the heating of the wafer in vacuum, heating the wafer after exposure to atmosphere, and treating the wafer with oxygen plasmas, show limited success in removing bromine from the wafer surface. Separation of unetched and etched wafers on the etcher is the most effective method of eliminating micro-masking of unetched wafers. For bare silicon wafers, post treatment of the wafer with fluorine plasma is an effective way to remove the bromine from the wafer. A phenomenological model explaining the processes involved is presented, elucidating the role of chemisorbed and physisorbed bromine on the wafer.