Sodium passivation in Al-SiO2-Si structures containing chlorine

Abstract

Experiments have been done to measure the trapping and neutralization kinetics of sodium ions in Al-SiO2-Si structures using oxides grown with HCl-Ar/O mixtures. The trapping of sodium at the Si-SiO2 interface was quantified by thermally stimulated ionic current (TSIC) measurements made at negative applied electric fields following positive bias temperature stress. There were three distinct types of behavior depending on the chlorine content of the oxide. For chlorine contents ≳3.0×1015 atoms cm−2 the TSIC results showed two sodium peaks, with maxima at about 0.8 and 1.5 eV, corresponding to states at the Si-SiO2 interface in which the ions were on the whole charged and neutral, respectively. Complete neutralization of the sodium, and good stability with respect to detrapping from the Si-SiO2 interface under typical device operating conditions, was possible only in samples containing ≳3.0×1015 Cl atoms cm−2. A Schottky-type variation of the neutral peak trap energy with applied field was measured, with coefficient (19±1)×10−5 eV V−1/2 cm1/2. For chlorine contents in the range (0.9–2.8)×1015 cm−2 the TSIC spectra showed two overlapping peaks, with maxima at 0.8 and about 1.25 eV. In this case only part of the second peak at energies above 1.25 eV corresponded to ions which were completely neturalized. For chlorine contents <0.8×1015 cm−2, the TSIC spectra showed only one sodium peak, at about 0.8 eV, similar to that observed in dry-grown oxides which do not contain chlorine. It was found that a fraction of the ions, about 20%, were neutralized even in dry-grown oxides. The amount of sodium neutralization was measured as a function of time and temperature of positive-bias stress, magnitude of applied electric field, and oxide chlorine content. A method was used which separated the rate of neutralization at the Si-SiO2 interface from the overall process. For samples with chlorine content ≳3.0×1015 cm−2, the time dependence of the interfacial neutralization process was consistent with a model in which lateral diffusion of sodium, to chlorine-containing ’’islands’’ at the Si-SiO2 interface, is the rate-limiting process. The activation energy of the interfacial neutralization process, (0.87±0.15)eV, is in agreement with that of lateral diffusion, (0.8±0.2)eV.

Cl Incorporation at the Si / SiO2 Interface during the Oxidation of Si in HCl / O 2 Ambients

“…Chlorine incorporation.--The results for the total chlorine incorporated as a function of time or HC1 concentration are generally consistent with those previously reported (2,5,8). However, a rapid increase in the so-called "threshold" region is not apparent as in our earlier results (2).…”

“…According to these authors, the samples belonging to the agglomerated phase regime contain C1 higher than 3 • 10'5/cm 2 for all the oxidation temperatures (5). However, in addition to the agglomerates we have observed individual particle microstructures for samples with C1 content higher than 3.0 x 1015/cm 2.…”

“…2). For several oxidation conditions, phase separated regions have been observed (4)(5)(6). It has been asserted that both chlorine incorporation and sodium neutralization are related to the development of the Cl-rich phase formed at the Si/SiO2 interface (3)(4)(5).…”

Ion transport phenomena in oxide layer on the silicon surface and electron–ion exchange effects at the SiO2/Si interface

“…Moreover, the values of calculation parameters-the potential well depth ͑0.5 eV͒ and the preexponential factor in the expression for jump probability (10 6 s Ϫ1 )-are not in agreement with previously reported data for activation energy of ion mobility 9 and oscillation frequency of ions in the potential well ͑ϳphonon frequency͒. 18,19 The qualitative form change for the quasistatic capacitance-voltage (C -V) characteristics caused by sample polarization is direct evidence of significant ion neutralization at the SiO 2 /Si IF. After ion move to IF the C -V curve essentially spreads ͑Fig.…”

“…Actually depending on the experimental technique used by various authors the observed results are ascribed to the effect of free ion drift ͑transit-time experiments, 9,10 dynamic currentvoltage (I -V) characteristics͒, [11][12][13][14][15] or as the manifestation of ion trap emptying ͑isothermal or thermostimulated polarization and depolarization of insulator͒. [16][17][18][19][20][21] The influence of semiconductor electrons on the ion migration in the insulator has not been considered at all. Opposing opinions have been reported concerning the ion neutralization possibility, owing to electron capture from the semiconductor on traps formed by ions and their dielectric environment.…”