Thermally induced interface degradation in (111) Si/SiO2traced by electron spin resonance

Abstract

Thermal post-oxidation interface degradation in ͑111͒ Si/SiO 2 has been isolated by electron-spin resonance ͑ESR͒ as a permanent P b ͑SiwSi 3 ͒ interface defect creation. This process, initiating from ϳ640°C onward, reveals interface breakdown on an atomic scale as interfacial SiO bond rupture. The crucial creation step has been isolated as thermal cycling in an O-free ambient. Once created, the new P b system exhibits similar fully reversible H passivation-depassivation kinetics as the preexisting one, naturally introduced during oxidation. ESR is herewith raised to a powerful probe for Si/SiO 2 degradation.

Analysis of Pb centers at the Si(111)/SiO2 interface following rapid thermal annealing

“…Given the final thermal treatment, the sample underwent, i.e., RTA at 1040°C ͓effectively a postoxidation anneal ͑POA͒ in inert ambient͔, this result may not come as a surprise. Indeed, as demonstrated previously, 13 POA in a vacuum or N 2 at elevated temperature may result in strong creation of additional P b defect sites; e.g., at 1040°C, P b densities of ϳ1.5ϫ10 13 cm Ϫ2 may be attained within minutes. 13 The value found in the present work is lower, for which there may be several reasons.…”

“…Indeed, as demonstrated previously, 13 POA in a vacuum or N 2 at elevated temperature may result in strong creation of additional P b defect sites; e.g., at 1040°C, P b densities of ϳ1.5ϫ10 13 cm Ϫ2 may be attained within minutes. 13 The value found in the present work is lower, for which there may be several reasons. It may be related to the very short POA time ͑20 s͒ and/or ambient conditions.…”

“…It is well documented, 12,13 that the interface of as-grown standard thermal Si(111)/SiO 2 is invariably characterized by an inherent P b density N 0 ϭ(4.9Ϯ0.4)ϫ10 12 cm Ϫ2 for the oxidation range ϳ300-950°C. Interestingly, we find here a markedly higher P b density, indicating additional creation of P b centers.…”

“…8,9 The measured density of states ͑DOS͒ across the energy gap following the RTA or RTO processes, extracted from the quasistatic-C -V (QS-C -V) response, yields a peak value located at 0.85-0.88 eV above the valence band for the oxidized Si͑100͒ orientation. The location of the peak in the band gap, and the extracted peak densities (5.5ϫ10 12 to 1.7ϫ10 13 cm Ϫ2 eV Ϫ1 ), 7 suggest that the defects are due to unpassivated P b0 /(P b1 ) centers for the oxidized Si͑100͒ surface. Moreover, an experiment using Si(111)/SiO 2 structures exposed to RTA (1040°C, 20 s in N 2 ) as the final process step, yielded the two well established peaks in the DOS profile for the P b center of the oxidized Si͑111͒ orientation.…”

“…Second, the identification of the interface defects as P b centers by ESR, will provide an unambiguous explanation for the peaklike features widely observed in the C -V response of polysilicon/oxide/Si͑100͒ structures measured following RTA in N 2 . For this experiment, the Si͑111͒ orientation was selected, as the oxidized Si͑111͒ surface has a well characterized single P b center 12,13 as well as clear peaks in the DOS profile in the upper and lower regions of the energy gap. 14 …”