Analysis of Cu traces in Si using Transient Ion Drift combined with Rapid Thermal Annealing.
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Analysis of Cu traces in Si using Transient Ion Drift combined with Rapid Thermal Annealing. T.Heiser, A. Belayachi, E. Pihan, A.Kempf1, S.Bourdais2, P.Bloechl1, A.Huber1, and B. Semmache2 Laboratoire de Physique et Applications des Semiconducteurs, CNRS, Strasbourg, France 1 Wacker Siltronic AG, Burghausen, Germany 2 JIPELEC, MEYLAN, France
ABSTRACT Copper trace analysis using Transient Ion Drift (TID) combined with a Rapid Thermal Annealing (RTA) process is investigated. A double pulse method is implemented to allow unambiguous identification of the copper-induced capacitance signal. Use of a mercury probe as sensing Schottky barrier enhances the flexibility of the method and allows mapping of the contaminant. The method is evaluated on quantitatively contaminated silicon wafers and compared to Total X-ray fluorescence (TXRF). It is shown that in Czochralski grown material, the RTA is sufficient to dissolve most copper atoms into interstitial sites independently of their initial configuration. As a result, both, the surface and bulk contamination can be monitored by RTA/TID with a bulk detection limit close to 1011cm-3. In Float Zone material mapping of the quenched interstitial copper revealed the existence of defect reactions involving presumably vacancy clusters.
INTRODUCTION Introduction of copper interconnects in the semiconductor industry increases the risk for copper contamination and resulting device degradation. The impact of copper impurities on device properties such as gate oxide integrity or stress induced leakage current has been shown to occur1,2 for copper concentrations as low as 1012 cm-2. The need for monitoring copper contamination in silicon and silicon oxide during device fabrication has triggered considerable research efforts for the development of highly sensitive and flexible detection tools. Total X-ray fluorescence (TXRF) is a standard technique used mostly for surface contamination control. The sensitivity of 109 cm-2 was recently reported by Yamada et al3. The bulk silicon contamination level may be assessed by TXRF if the copper impurities diffuse toward the surface during an extended room temperature storage or a low temperature anneal.4,5 However, trapped copper impurities escape detection by TXRF. Copper contamination may as well be investigated using spectroscopic methods such as graphite furnace atomic absorption spectroscopy or inductively coupled plasma mass spectroscopy (ICPMS)4,6. These methods are generally combined with a vapor phase decomposition of either the silicon oxide or the near surface silicon layer. The corresponding detection limit is close to 1010 cm-2. They do not allow for the lateral mapping of the contaminant. The electrical characterization techniques based on minority carrier diffusion length or lifetime measurements7 are hindered by the complex behavior of copper impurities in silicon. The electrical activity of copper impurities is mostly due to secondary defects involving one or F13.12.1
several copper atoms (copper clusters or copper silicide parti
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