AVS 52nd International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS-WeM

Paper PS-WeM10
Evaluation of Several Plasma Etching and Boron Cleaning Processes for Hafnium Oxide Thin Films on Silicon

Wednesday, November 2, 2005, 11:20 am, Room 304

Session: Advanced Gate Stack Fabrication
Presenter: C. Wang, University of Houston
Authors: C. Wang, University of Houston
V.M. Donnelly, University of Houston
Correspondent: Click to Email
At present, BCl@sub 3@-containing plasmas are commonly used to etch high dielectric constant ("high-k") materials such as HfO@sub 2@ and aluminum oxide. However, a boron residue is left on underlying surfaces during the overetch period. Boron is a p-type dopant; its presence is undesirable in subsequent processing. Previously, we reported that pure H@sub 2@ plasmas were effective in removing B from Si surfaces after HfO@sub 2@/Si and Al-oxide/Si samples were overetched in high density BCl@sub 3@ plasmas for 60 s. The underlying Si substrate, however, was etched about 15 nm. Here we report that dilute H@sub 2@/Ar plasmas (1 to 5% of H@sub 2@) are also effective in removal B, but in a more controlled fashion, such that the etching of the Si substrate can be minimized. After 60 s overetch in BCl@sub 3@ plasmas, HfO@sub 2@ samples were transferred under vacuum to an ultrahigh vacuum (UHV) for X-ray photoelectron spectroscopy surface analysis. B deposited during BCl@sub 3@ plasma etching was removed from the reactor walls in a pure H@sub 2@ plasma, and the samples were then returned to the plasma chamber and exposed to a dilute H@sub 2@/Ar cleaning plasma, and then re-examined by XPS. Under the best conditions (1% H@sub 2@/Ar plasma), > 90% of B was removed from Si in 20 s, while etching away <3 nm of Si. We also explored B cleaning in dilute I@sub 2@/Ar (2 to 20% of I@sub 2@) plasmas. ~90% of the B was removed in 10 s, but more of the Si substrate was etched (~8 nm) compared with the dilute H@sub 2@/Ar plasma cleaning process. Several B-free plasmas were also examined for HfO@sub 2@ etching. The etching rate of HfO@sub 2@ in I@sub 2@/Ar, H@sub 2@/Ar or CH@sub 4@-containing plasmas was not observable (<10Å/min). A CHF@sub 3@ plasma was found to be the most promising non-boron containing gas, with an etching rate for HfO@sub 2@ of 30 Å/min. Supported by SRC and AMD Inc.