Correlation of Fixed Positive Charge and E′γ Centers as Measured via Electron Injection and Electron Paramagnetic Resonance Techniques

Abstract

It has long been believed that the electron paramagnetic resonance (EPR) signal identified as the E~ center is due to fixed positive charge generated by ionizing radiation in SiQ. This hypothesis has been studied in the past, with results consistent with this idea. However, the possibility that the generic E' center is related to neutral electron traps, which are also created with ionizing radiation, has not been examined since the earlier studies did not involve electron injection, and large neutral electron traps were not widely known to exist when the initial correlation was made. The present study examines this possibility, utilizing two different radiation dose levels, where the ratios of the densities of fixed positive charge and neutral electron traps are different, to differentiate the two possibilities. It involves correlations between actual insulated gate field effect transistors, whose oxides were irradiated the same as blanket oxides, used for EPR studies. By comparing the density of E~ centers with the densities of fixed positive charge and neutral electron traps, measured by a two-step electron injection sequence, as well as examining the ratios between the two radiation levels, two independent measures of the nature of the E~ center are obtained. It was found that the density of the E~ centers matches the density of the fixed positive charge, and that the ratio of the densities between the two different dose levels also follows the behavior of the fixed positive charge. The density of fixed positive charge plateaus at high radiation dose as does the EPR signal attributed to fixed positive charge. Conversely, the densities of neutral electron traps do not track the change in EPR signal as radiation level changes. Thus, we conclude that E4 centers are indeed fixed positive charge, and not neutral electron traps.It has long been suggested (1-6) that fixed positive charge created by ionizing radiation and the E~ center, detected with EPR, are one and the same. The presence of fixed positive charge is deduced from studies on either capacitors or insulated gate field effect transistors (IGFETs) where either flatband or threshold lowering, respectively, is observed following exposure to ionizing radiation. The EPR resonance which has been correlated to fixed positive charge has been observed on blanket SiO2 grown on silicon substrates. This correlation was made on the basis that fixed positive charge was detected in devices and the E~ resonance was observed in blanket oxides after exposure to ionizing radiation. At that time it was not widely known that large neutral electron traps (7, 8) are also created during exposure of SiO~ to ionizing radiation. Since the studies involving EPR had not been correlated with actual electron injectio n studies of devices, correlations of the E~ center with fixed positive charge were made without taking into account the presence of uncharged large neutral electron traps also created by ionizing radiation, and not detectable by either flatband or threshold voltage shifts...

E ′ centers and leakage currents in the gate oxides of metal oxide silicon devices

“…13 P b centers are silicon dangling bond centers precisely on the Si/SiO 2 boundary. [11][12][13][14][15][16][17][22][23][24] The spectrometer settings used to obtain the data in Fig. 3 are less than optimum for both the EЈ and P b spectra.…”

“…Positively charged EЈ centers may be generated by exposing oxides to modest (Ͻ10 14 holes/cm 2 ) fluences of holes, [11][12][13][14][15][16][17] for example, by exposing the oxides to a moderate dose ͑р10 Mrad͒ of ionizing radiation. Neutral EЈ centers can be generated by subjecting oxides to extended periods of vacuum ultraviolet illumination ͑VUV͒.…”

Predicting radiation response from process parameters: Verification of a physically based predictive model

“…A comprchensive physically based predictive model €or both major aspects of MOS radiation damage, oxide hole trapping aud SilSiO, interfacc trap gcneration, bas recently bccn proposcd 11-41, Tlie niodel is based 011 the principles or the statistical mechanics of solids and a knowledge of defects involvcd, obtaiiied through clcclron spin resonance (ESR) studies [15][16][17][18][19][20] Earlier work showed that the inodcl could predict hole trapping quite accurately for a narrow range o€ processing parameters[l,Z] and that lhc modcl's Di, predictions arc in at lcast semi-quaiititalive agreenicnt with nuincrous observations in the litcraturel3,4].…”

Radiation-induced leakage currents: atomic scale mechanisms

“…This defect state is created when an oxygen vacancy site (O Si-Si O ) captures a hole. Quite a few mutually corroborating studies have established that E′ centers dominate oxide hole trapping in gate oxides subjected to moderate levels of ionizing radiation [7]- [12], [17].…”

“…It is well established that these centers are generated in oxides by both ionizing radiation [7]- [13] and high electric fields [14]- [16]. Most ESR E′ studies have dealt with the positively charged variant (O Si Si O ) in which an electrically neutral silicon dangling bond orbital is closely coupled to a positively charged silicon [7]- [12], [17]- [22]. This defect state is created when an oxygen vacancy site (O Si-Si O ) captures a hole.…”