Relationship between oxide density and charge trapping in SiO2 films

Abstract

Spectroscopic ellipsometry was used to determine the density of oxides thermally grown on Si substrates as a function of the oxidation temperature, and the time and temperature of postoxidation anneals. All the oxides were found to be denser than fused silica. The density of the as-grown oxides was found to decrease as the growth temperature was increased. Postoxidation anneals were found to reduce the oxide density; high temperature or long-time anneals caused the greatest reduction in density. Holes alone, or holes and electrons, were injected into the oxides by irradiating with vacuum ultraviolet light or x rays under electric field bias. Using capacitance–voltage measurements, it was found that low-density oxides trap charge more efficiently than high-density oxides. Electron spin resonance measurements indicated that, for most of these oxides, the number of paramagnetic defects was substantially smaller than the number of trapped charges. It is hypothesized that the additional, nonparamagnetic, charge is in the form of protons trapped near network oxygen atoms that have large Si–O–Si bond angles. The number of these large-angle bonds in the near-interfacial oxide increases as the oxide density decreases, explaining the observed correlation between the charge trapping and the oxide density.

Effects of rapid thermal annealing on nitrided gate oxide grown on 4H-SiC

“…In contrast, the increase in D it in nitrided oxide treated at T a = 900°C may, in part, contribute to the observed negative DV FB value. The induction of positive-oxide charge due to the increase in the annealing temperature has also been reported [27] in non-nitrided oxides on Si, after Aror N 2 -post-oxidation annealing.…”

“…In Si-SiO 2 system subjected to N 2 or vacuum RTA, the density of dangling-bond (P b centers) at Si(1 0 0)-and Si(1 1 1)-non-nitrided oxide interface were enhanced [24,25]. The increase in the defects is due to depassivation of hydrogen from the P b center and not the creation of additional interface state [24,25] or the changes in interface roughness [27]. These conclusions were based on evidences acquired from electron paramagnetic resonance and quasistatic capacitance-voltage analyses.…”

“…These conclusions were based on evidences acquired from electron paramagnetic resonance and quasistatic capacitance-voltage analyses. Further analysis using infrared spectroscopy and constantcurrent injection independently suggested that bulk oxide stress is relaxed [27] and trapping of electron in the bulk oxide is enhanced [26] in the RTA treated Si-based nonnitrided oxide. These factors accumulatively attributed to the improvement in the oxide reliability [26,28].…”

Model form uncertainty versus intrinsic atomic variability in amorphous silicon oxides and nitrides

“…As is well known, LDA suffers from a lack of core-valence repulsion and thus tends to overbind; GGA tends to over-correct this problem leading to underbinding, and this is observed all three systems. A comparison with experimental values provides further support to this observation; experimental densities for a-SiO 2 (2.20-2.27 g/cm 3 [41,42]) lie between the high-end tails of GGA and low-end tails of LDA. For a-Si 3 N 4 a wide range of densities have been reported depending on processing conditions: 2.60-3.20 g/cm 3 [43][44][45]; this range is consistent with our predictions but extends to lower values which could be the result of porosity in some of the experimental samples.…”

Effect of wet-chemical substrate smoothing on passivation of ultrathin-SiO2/n-Si(111) interfaces prepared with atomic oxygen at thermal impact energies

“…It is well known from investigations of metal-oxide-semiconductor (MOS) devices that the quality of thin thermal oxide films strongly depends on interface micro-roughness and oxide density [6][7][8] and that interfacial defects give rise to interface electronic charges such as interface-trapped charges and fixed oxide charge [8][9][10]. As shown by photoconductive decay (PCD) measurements, thermally prepared oxide layers can be applied to reduce near surface charge carrier recombination losses also on textured and multi-crystalline (mc-Si) solar cells substrates [11].…”