Electron paramagnetic resonance ͑EPR͒ measurements of Si/SiO 2 systems began over 30 years ago. Most EPR studies of Si/SiO 2 systems have dealt with two families of defects: P b centers and EЈ centers. Several variants from each group have been observed in a wide range of Si/SiO 2 samples. Some of the most basic aspects of this extensive, body of work remain controversial. EPR is an extraordinary powerful analytical tool quite widely utilized in chemistry, biomedical research, and solid state physics. Although uniquely well suited for metal-oxide-silicon ͑MOS͒ device studies, its capabilities are not widely understood in the MOS research and development community. The impact of EPR has been limited in the MOS community by a failure of EPR spectroscopists to effectively communicate with other engineers and scientists in the MOS community. In this article we hope to, first of all, ameliorate the communications problem by providing a brief but quantitative introduction to those aspects of EPR which are most relevant to MOS systems. We review, critically, those aspects of the MOS/EPR literature which are most relevant to MOS technology and show how this information can be used to develop physically based reliability models. Finally, we briefly review EPR work dealing with impurity defects in oxide thin films.

Interaction of molecular hydrogen with trapped hole E' centers in irradiated and high field stressed metal/oxide/silicon oxides Dependence of radiationinduced interface traps on gate Al thickness in metal/SiO2/Si structures We report electron spin resonance (ESR) measurements of E' -center (a "trivalent silicon" center in SiOz) density as well as capacitance versus voltage (C-V) measurements on y-irradiated metal! oxide/silicon (MOS) structures. We also report a considerable refinement of earlier ESR measurements of the dependence of radiation-induced P b -center (a "trivalent silicon" center at the SiiSiO z interface) occupation as a function of the Fermi level at the SiiSiO z interface. These measurements indicate that the P b centers are neutral when the Fermi level is at mid-gap. Since the P b centers are largely responsible for the radiation-induced interface states, one may take L1 V mg Cox / e (where L1 V mg is the "mid-gap" C-V shift, Cox is the oxide capacitance, and e is the electronic charge) as the density of holes trapped in the oxide. We find that radiation-induced E' density equals L1 V mg Cox / e in oxides grown in both stream and dry oxygen. Etch-back experiments demonstrate that the E' centers are concentrated very near the SilSi0 2 interface (as are the trapped holes). Furthermore, we have subjected irradiated oxide structures to a sequence of isochronal anneals and find thatthe E ' density and L1 V mg annealing characteristics are virtually identical. We conclude that theE' centers are largely responsible for the deep hole traps in thermal Si0 2 on silicon. This observation coupled with observations regarding theP b center indicates that two intrinsic centers, both involving silicon atoms lacking one bond to an oxygen atom, are largely responsible for the two electrically significant aspects of radiation damage in MOS devices: charge buildup in the oxide and interface-state creation at the SiiSiO z interface.

The influence of Hf-based dielectrics on the underlying SiO2 interfacial layer (IL) in high-k gate stacks is investigated. An increase in the IL dielectric constant, which correlates to an increase of the positive fixed charge density in the IL, is found to depend on the starting, pre-high-k deposition thickness of the IL. Electron energy-loss spectroscopy and electron spin resonance spectra exhibit signatures of the high-k-induced oxygen deficiency in the IL consistent with the electrical data. It is concluded that high temperature processing generates oxygen vacancies in the IL responsible for the observed trend in transistor performance.

In this study, we utilize electrically detected magnetic resonance (EDMR) techniques and electrical measurements to study defects in SiC based metal oxide semiconductor field effect transistors (MOSFETs). We compare results on a series of SiC MOSFETs prepared with significantly different processing parameters. The EDMR is detected through spin dependent recombination (SDR) in most cases. However, in some devices at a fairly high negative bias, the EDMR likely also involves spin dependent trap-assisted tunneling (SDT) between defects on both sides of the SiC/SiO2 interface. At least three different defects have been detected in the magnetic resonance measurements. The defects observed include two at the SiC/SiO2 interface or on the SiC side of the SiC/SiO2 interface: one is very likely a vacancy center with a distribution which extends into the bulk of the SiC and the other is likely a “dangling bond” defect. A third defect, located on the SiO2 side of the SiC/SiO2 interface, has a spectrum very similar to that previously reported for an oxygen deficient silicon coupled to a hydrogen atom. In nearly all cases, we observe a strong dominating single line EDMR spectrum with an isotropic g≈2.0027. In some samples, this strong central line is accompanied by two pairs of considerably weaker side peaks which we link to hyperfine interactions with nearby Si and C atoms. The pattern is physically reasonable for a silicon vacancy in SiC. We therefore tentatively assign it to a silicon vacancy or silicon vacancy associated defect in the SiC. In one set of devices with very high interface trap density we observe another dominating spectrum with g∥=2.0026 and g⊥=2.0010 with the symmetry axis coincident with the [0001] and nearly the SiC/SiO2 interface normal. We ascribe this EDMR spectrum to a “dangling bond” defect. A third EDMR spectrum shows up in some devices at a fairly large negative gate bias. The phase of this spectrum is quite consistently opposite to that of the SDR detected EDMR at other biases. Part of this inverted phase spectrum involves two narrow lines which are separated by ≈10.5 G. Since the center responsible for this spectrum is almost certainly in the SiO2, it is likely due to the so called 10.4 G doublet center, an unpaired electron residing on an oxygen deficient silicon atom coupled to a hydrogen in SiO2. The likely presence of one oxygen deficient silicon defect suggests that other oxygen deficient silicon atom defect sites in the oxide may also be important in SiC/SiO2 devices. Oxygen deficient silicon defects in SiO2 are typically called E′ centers. Our results collectively demonstrate considerable complexity in both the chemical composition and physical distribution of performance limiting defects in SiC transistors, with defects observed on both sides of the SiC/SiO2 interface. Our results most strongly indicate that fairly high densities of intrinsic deep-level defects, likely due to a Si vacancy or a closely related defect, extend into the bulk of the SiC in all but one of the devices prepared utilizing a fairly wide range of processing parameters.

We observe a strong correlation between changes in the density of paramagnetic silicon ‘‘dangling-bond’’ centers and changes in the space-charge density in amorphous silicon nitride films subjected alternately to illumination and both positive- and negative-charge injection. We demonstrate that ultraviolet illumination annihilates space charge and creates stable paramagnetic centers in silicon nitride. These centers can be passivated with a 1-h anneal at 250 °C. Our results provide the first direct experimental evidence associating a specific point defect with the trapping phenomena in amorphous silicon nitride. We also demonstrate both directly and for the first time the amphoteric nature of the silicon nitride dangling-bond center. Furthermore, our ability to cycle the defect between its paramagnetic neutral state and both its charged diamagnetic states suggests that the optical generation of dangling bonds in amorphous silicon nitride involves no complex structural rearrangement, but simply changes in the charge and spin states of the defect.