AVS 51st International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session DI+PS-TuM

Paper DI+PS-TuM10
UV Activated Surface Preparation of Silicon for High-k Dielectric Deposition

Tuesday, November 16, 2004, 11:20 am, Room 304C

Session: High-k Dielectrics: Growth and Processing
Presenter: C.C. Finstad, University of Arizona
Authors: C.C. Finstad, University of Arizona
A.J. Muscat, University of Arizona
Correspondent: Click to Email
High-k gate materials, such as HfO@sub 2@, are unstable on silicon, readily forming a low permittivity interfacial oxide when heated. A single layer of silicon nitride grown prior to gate dielectric deposition could serve as a diffusion barrier to prevent oxide formation. Moreover the SiN layer should promote nucleation of the dielectric film, thereby acting as both a barrier and a seed layer. A monolayer film of surface amine groups will be chemically similar to the hydrogen atoms of surface hydroxyl groups; therefore a pin-hole free monolayer of amine groups should simultaneously serve as both a diffusion barrier and a seed layer. This study aims to deposit a thin, continuous layer of surface amines at low temperatures (<100°C) using atomic layer deposition (ALD). UV-Cl@sub 2@ exposures (0.1-100 Torr Cl@sub 2@ at 25-150°C, 2-10 min, 1000 W Xe lamp) were used to terminate Si with Cl atoms. Exposure to NH@sub 3@ (0.05-1000 Torr, 75°C, 5-20 min) replaced Cl atoms with amine groups. Cl atoms served as reactive leaving groups, lowering the overall activation energy barrier for nitridation; HCl formed as a by-product and desorbed from the surface. By providing a more reactive surface, ALD of silicon nitride occurs at lower temperatures (<100°C) and with better initial deposition rates compared to deposition on H-terminated Si.@footnote 1@ As measured by XPS, the amine surface coverage saturated at 0.35 monolayer (ML) at a NH@sub 3@ pressure of 10 Torr. Cl coverage decreased, but the surface reaction did not go to completion. Significant oxygen was observed due to competition by H@sub 2@O contamination. Alternatively, UV photons with energy >5.8 eV can photodissociate NH@sub 3@ molecules to yield NH@sub 2@ photofragments that react with H-terminated Si surfaces. With UV activation, N coverage increased with time and saturated at 1.7 ML. @FootnoteText@ @footnote 1@A. Nakajima et al., Appl. Phys. Lett. 80 (7), 1252 (2002).