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Proceedings Paper

Effect of Fe and Cu contamination on the reliability of ultrathin gate oxides
Author(s): John D'Amico; Lubek Jastrzebski; Marshall Wilson; Alexandre Savtchouk
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Paper Abstract

The detrimental effect of heavy metal contamination on gate oxide reliability has been well documented for oxides thicker than 7 nm. This study offers evidence of the detrimental effect that metallic (Fe, Cu) contamination has on ultra-thin gate oxide reliability. Oxides grown at 850 degrees Celsius of 3.5 and 7 nm thickness were intentionally contaminated with Fe (pre-oxidation) or Cu (pre- and post-oxidation.) Bulk silicon FE concentrations of 5 X 1010 to 1 X 1013 atoms/cm3 were achieved through the spin doping of an aqueous FeCl3 solution on the wafer surface prior to oxidation. Pre-oxidation Cu contamination was attained through full wafer immersion in a 10:1 HF:H2O solution contaminated with CuSO4 of varying Cu concentrations (1 ppb to 100 ppb), while post-oxidation contamination results from a 30 minute 450 degree Celsius forming gas anneal which drives in Cu previously deposited on the backside of the wafer. A new corona-based technique was used to measure the stress-induced leakage current (SILC) characteristics of the contaminated and control oxides after various stress fluences, from 10-5 to 10-1 C/cm2, in either the Fowler-Nordheim or the direct tunneling regime for the 7 and 3.5 nm oxides respectively. This non-contact technique employing the COCOS (Corona Oxide Characterization of Semiconductor) methodology measures current flowing through the oxide as a function of the oxide electric field induced by corona. In addition, electrical measurements on MOS capacitors were performed and the results compared to COCOS SILC results. For the 7 nm oxides, COCOS measurements clearly showed enhanced SILC due to metallic contamination confirming previous findings. For the 3.5 nm oxides, two distinct features were established: (1) pre-stress I-V characteristics were consistent with a direct tunneling mechanism exhibiting a distinct shift to higher currents at lower electric fields and (2) the SILC was smaller in magnitude than that exhibited by the 7 nm oxides. Existing SILC models (i.e. trap-assisted tunneling) were used to interpret the I-V data. In addition, this stress resulted in oxide wearout, which produced noticeable flat-band shifts and an order of magnitude increase in interface state density, also measured using the COCOS technique. The effect of metallic contamination on these wearout issues was also investigated.

Paper Details

Date Published: 27 August 1999
PDF: 12 pages
Proc. SPIE 3884, In-Line Methods and Monitors for Process and Yield Improvement, (27 August 1999); doi: 10.1117/12.361352
Show Author Affiliations
John D'Amico, Univ. of South Florida (United States)
Lubek Jastrzebski, Univ. of South Florida (United States)
Marshall Wilson, Semiconductor Diagnostics, Inc. (United States)
Alexandre Savtchouk, Semiconductor Diagnostics, Inc. (United States)

Published in SPIE Proceedings Vol. 3884:
In-Line Methods and Monitors for Process and Yield Improvement
Sergio A. Ajuria; Jerome F. Jakubczak, Editor(s)

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