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A novel approach for measuring ultra‐thin, buried SiO 2 film thickness
Author(s) -
Jiang Z. X.,
Sieloff D. D.
Publication year - 2009
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.3111
Subject(s) - oxide , analytical chemistry (journal) , ion beam , thin film , ion , materials science , oxygen , stoichiometry , silicon , stack (abstract data type) , secondary ion mass spectrometry , chemistry , optoelectronics , nanotechnology , organic chemistry , chromatography , computer science , metallurgy , programming language
Accurate measurement of physical thickness of thin SiO 2 films is of great interest to the semiconductor industry. Existing inspection techniques are subject to large error when the oxide thickness falls below 2 nm. This work explored a new approach with improved accuracy to the measurement of thickness of thin oxide films. The new method utilizes dynamic SIMS with a primary ion beam of one isotope of oxygen ( 16 O or 18 O) at normal incidence and detecting negative secondary ions of another isotope ( 18 O or 16 O, respectively) inside SiO 2 . The experiment was performed by using an 16 O 2 + primary beam and detecting 18 O − as characteristic secondary ions for SiO 2 . We substantiated that the matrix effect was eliminated during profiling through the SiO 2 /Si interface in a poly Si/SiO 2 /Si stack with an O 2 + beam at normal incidence, which is crucial for reliable quantification of oxygen amount inside SiO 2 . The high ion yield of 18 O − and negligible contribution from the mass interference of 16 OH 2 − ensured measurement of the total amount of oxygen inside an SiO 2 film with good sensitivity. By assuming that the silicon oxide is in the form of stoichiometric SiO 2 , which is the case for those layers grown with dry oxidation, the measured amount of oxygen can be readily converted into the thickness of SiO 2 . This technique provides reproducible measurement of the thickness of SiO 2 films and potentially a good accuracy if a reference material is well calibrated. Copyright © 2009 John Wiley & Sons, Ltd.