AVS 45th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA5
A Study of the Relationship Between Si/SiO@sub 2@ Interface Charges and Roughness

Tuesday, November 3, 1998, 3:20 pm, Room 309

Session: Morton M. Traum Student Award Session
Presenter: L. Lai, University of North Carolina, Chapel Hill
Authors: L. Lai, University of North Carolina, Chapel Hill
K.J. Hebert, University of North Carolina, Chapel Hill
E.A. Irene, University of North Carolina, Chapel Hill
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This study examines the correlation between interface micro-roughness and charges. Atomic force microscopy (AFM) and a newly developed area roughness function, A(RMS,D@sub F@)@footnote 1@ which couples two roughness parameters, root mean square (RMS) and fractal dimension (D@sub F@), are used to reliably and accurately characterize surface micro-roughness. For the common surface area computation methods, this leads to large round-off errors. This new area roughness function obviates this problem, and it is not only a sensitive roughness parameter, but also a reliable area extracting tool for surfaces with micro-roughness. Micro-roughness has a small vertical magnitude relative to the large horizontal data sampling interval. Interface charges (D@sub it@ and Q@sub f@) are measured using high frequency and quasistatic capacitance-voltage methods. These charges are reported in per unit area, so in order to obtain reliable charges levels, one must know the area. This study is divided into three parts where smooth, purposely roughened, and purposely smoothened Si substrates are used to make MOS capacitors. For smooth samples, we found that interface charges decrease as the oxidation time increases. Purposely roughened substrates show that there is a correlation between interface roughness and charges. When the correct area, A(RMS,D@sub F@), is used, the excess interface charges due to roughness are accounted for. Roughened then smoothened substrates show that the rate of decrease of the corrected charges with respect to oxidation time become about the same as those from smooth substrates. We conclude that the increases of D@sub it@ and Q@sub f@ with Si roughness are due entirely to the area increase and orientation changes that result from roughness. @FootnoteText@ @footnote 1@ L. Lai and E. A. Irene, J. Vac. Sci. Technol. A. submitted (1998).