AVS 57th International Symposium & Exhibition
    Surface Science Monday Sessions
       Session SS2+EM-MoM

Paper SS2+EM-MoM9
Monolayer Passivation of Ge(100) Surface via Nitridation and Oxidation

Monday, October 18, 2010, 11:00 am, Room Santa Ana

Session: Semiconductor Surfaces and Interfaces
Presenter: J.S. Lee, University of California at San Diego
Authors: J.S. Lee, University of California at San Diego
S. Bishop, University of California at San Diego
T. Kaufman-Osborn, University of California at San Diego
A.C. Kummel, University of California at San Diego
Correspondent: Click to Email
The monolayer passivation of Ge(100) surface via formation of Ge-N and Ge-O surface species was studied using scanning tunneling microscopy (STM) and density functional theory (DFT) to develop a process of minimizing interface defect density between Ge and a high-k dielectric layer in a highly scaled device. Direct nitridation was performed on a Ge(100) surface using an electron cyclotron resonance (ECR) plasma source with pure N2 gas. It was hypothesized that plasma nitridation at elevated temperature (500oC) would form an ordered nitride structure that would combine the low defect density of GeO2 with the higher thermal stability of GeON via formation of a Ge-N ordered structure. Experimental and theoretical modeling showed that bandgap states are produced from the ordered nitride structure resulting in Fermi level pinning of the surface; however, it is predicted that H-passivation on the nitride structure would unpin the Fermi level by reducing the dangling bonds and the bond strain. The best method to passivate a Ge(100) surface is to form a layer of GeO2 which is free of suboxides. However, this process is difficult to scale using thermal oxidation by O2, so alternative oxidants, H2O and GeO2, were studied. At room temperature, the H2O-dosed Ge surface showed Ge-OH sites with very few Ge adatoms, while the e-beam deposition of GeO2 formed semi-ordered Ge-O structures and Ge ad-species. It is likely the H2O dosing produces an ideal passivation layer since it displaces few surface Ge atoms. Nevertheless, annealing above 300oC converts the surface oxides into suboxide rows on both H2O and GeO2 dosed Ge surfaces due to the reactivity of GeO2 with Ge. Scanning tunneling spectroscopy (STS) shows that the Fermi level of the n-type Ge surfaces covered by suboxides is near the valence band edge, consistent with formation of Ge suboxide rows likely causing Fermi level pinning. The atomic layer deposition (ALD) of GeON and SiO2 are being studied to form a monolayer or bilayer of passivation with a minimum defect density and the improved thermal stability.