P. M. Lenahan

Hole traps and trivalent silicon centers in metal/oxide/silicon devices

We report electron spin resonance (ESR) measurements of E′‐center (a ‘‘trivalent silicon’’ center in SiO2) density as well as capacitance versus voltage (C‐V) measurements on γ‐irradiated metal/oxide/silicon (MOS) structures. We also report a considerable refinement of earlier ESR measurements of the dependence of radiation‐induced Pb ‐center (a ‘‘trivalent silicon’’ center at the Si/SiO2 interface) occupation as a function of the Fermi level at the Si/SiO2 interface. These measurements indicate that the Pb centers are neutral when the Fermi level is at mid‐gap. Since the Pb centers are largely responsible for the radiation‐induced interface states, one may take ΔVmg Cox/e (where ΔVmg 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 ΔVmg Cox/e in oxides grown in both stream and dry oxygen. Etch‐back experiments demonstrate that the E′ centers are concentrated very near ...

What can electron paramagnetic resonance tell us about the Si/SiO2 system?

Electron paramagnetic resonance (EPR) measurements of Si/SiO2 systems began over 30 years ago. Most EPR studies of Si/SiO2 systems have dealt with two families of defects: Pb centers and E′ centers. Several variants from each group have been observed in a wide range of Si/SiO2 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 (MOS) 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 rele...

Electrically active point defects in amorphous silicon nitride: An illumination and charge injection study

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 ...

An electron spin resonance study of radiation‐induced electrically active paramagnetic centers at the Si/SiO2 interface

We have compared the generation of radiation‐induced Pb (‘‘trivalent silicon’’) centers at the Si/SiO2 interface with the radiation‐induced buildup of interface states. We observe a strong correlation between the density of Pb centers and radiation‐induced interface state density (Dit) and similar annealing behavior of radiation‐induced Pb and Dit. Furthermore, the Pb resonance intensity is strongly bias dependent; this indicates that the charge state of the Pb defect is bias dependent. We conclude that Pb defects account for a very large portion of radiation‐induced interface states.

The effect of interfacial layer properties on the performance of Hf-based gate stack devices

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.

Electron‐spin‐resonance study of radiation‐induced paramagnetic defects in oxides grown on (100) silicon substrates

We have used electron‐spin resonance to investigate radiation‐induced point defects in Si/SiO2 structures with (100) silicon substrates. We find that the radiation‐induced point defects are quite similar to defects generated in Si/SiO2 structures grown on (111) silicon substrates. In both cases, an oxygen‐deficient silicon center, the E’ defect, appears to be responsible for trapped positive charge. In both cases trivalent silicon (Pb centers) defects are primarily responsible for radiation‐induced interface states. In earlier electron‐spin‐resonance studies of unirradiated (100) substrate capacitors two types of Pb centers were observed; in oxides prepared in three different ways only one of these centers, the Pb0 defect, is generated in large numbers by ionizing radiation.

Effect of bias on radiation‐induced paramagnetic defects at the silicon‐silicon dioxide interface

Electron spin resonance measurements have been made on gamma‐irradiated (111) Si/SiO2 structures as a function of bias across the oxide. We observe a large change in the density of radiation‐induced paramagnetic Pb centers with bais. We conclude that Pb defects (trivalent silicons at the Si/SiO2 interface) account for a very large portion of the radiation‐induced interface states.

Electron spin resonance observation of trapped electron centers in atomic-layer-deposited hafnium oxide on Si

We observed two paramagnetic defects in thin films of HfO2 on silicon with electron spin resonance. Both appear after photoinjecting electrons into the dielectric. Strong spectroscopic evidence links one spectrum to an O2− defect. A second spectrum is likely due to an Hf+3 related defect.

Room temperature reactions involving silicon dangling bond centers and molecular hydrogen in amorphous SiO2 thin films on silicon

Exposing thin films of amorphous SiO2 to molecular hydrogen at room temperature converts some silicon dangling bond defects, E’ centers, into two hydrogen coupled complexes. These reactions may play important roles in radiation and hot carrier instabilities in metal/oxide/silicon devices.

Nature of the E’ deep hole trap in metal‐oxide‐semiconductor oxides

We have found through a sequence of ultraviolet illuminations, electron spin resonance measurements, and capacitance versus voltage measurements, that the E’ deep hole trap in metal‐oxide‐semiconductor silicon dioxide is a fundamentally reversible defect. Our results are totally consistent with an oxygen vacancy model for the E’ deep hole trap, but our results are inconsistent with the bond strain gradient model for the deep hole trap in metal‐oxide‐semiconductor silicon dioxide.