Jenny Zhang

Mechanism for the generation of interface state precursors

The generation of interface states plays an important role in the degradation of submicrometer devices. Previous attention was mainly focused on the conversion between interface states and their precursors. The total number of defects, which is the sum of precursors and interface states, is often implicitly assumed to be constant. However, recent work indicates that this number could be increased. The mechanism for the generation of new precursors is still not clear and the objective of this article is to throw light on it. The work is concentrated on investigating the roles played by hydrogen and the holes trapped in the oxide. It is found that, although the H2 or the trapped hole alone does not create precursors, their simultaneous presence causes the damage. The hydrogen species can be either supplied externally or released within the device. The generation is thermally activated, but saturates at a defect-limited level. The generation kinetics is studied and the rate limiting mechanism is discussed. E...

Continuing degradation of the SiO2/Si interface after hot hole stress

This article reports new experimental results on the continuing interface trap generation post-hot hole injection and investigates the generation mechanism. The generation post-hole injection is found to be two orders of magnitude slower than that post-irradiation and cannot be satisfactorily explained by the transportation of hydrogen species across the gate oxide. The role played by the recombination of trapped holes with free electrons is examined. There is a lack of correlation between the trapped hole removal and the interface trap creation, which is against the prediction of the trapped hole conversion model. The results indicate that the interface traps generated during and post-stress originate from two different defects. The defect responsible for post-stress generation is excited by hole injection and then converted into an interface trap if a positive gate bias is applied. It is found that generation in a poly-Si gated metal–oxide–semiconductor field effect transistor behaves differently from that in an Al-gated device. The possible causes for this difference are discussed.

Behavior of hot hole stressed SiO2/Si interface at elevated temperature

The behavior of hot hole stressed SiO2/Si interface at elevated temperature is investigated. Although an exposure to an elevated temperature does not affect a fresh device, considerable damages occur in a stressed device for temperature above 300u2009°C. The damage is caused by two thermally activated processes, which are triggered by hole injection and continued after the injection. One of them is the post-stress interface state generation and the other is the unexpected creation of interface state precursors. These new precursors can only be electrically detected when the device is stressed again. The effects of temperature, exposure time and hole injection time on these processes are studied. At 400u2009°C, annealing of interface states is also significant. It is found that the annealing of the states created post-stress is much faster than the annealing of the states generated during the hole injection, indicating these two have different structures. Roles played by electron injection and hydrogen in the anne...

On the interface states generated under different stress conditions

After dry oxidation and when annealing in a hydrogen environment is carefully avoided, the energy distribution of interface states has two peaks, one in the lower and one in the upper half of the silicon band gap. Following hydrogen passivation, however, the interface states created by irradiation or electron injection typically have only one peak in the upper half of the gap. This letter investigates how to generate a double peak distribution by electrical stress and we attempt to link the distribution with the generation mechanism.

Defects Generation in SIO2/HFO2 Studied with Variable TCHARGE-TDIScharge Charge Pumping (VT2CP)

A variable t_CHARGE-t_DISCHARGE charge pumping (VT²CP) is used to investigate the creation of traps in the SiO₂ and HfO₂ separately in an ALD SiO₂/HfO₂ metal gate stack. It is shown that by independently controlling the pulse low timing discharging time and high level timing charging time, we are able to separate the traps in the interfacial SiO₂ from the traps in the HfO₂ and observe the creation of new traps in both constituent layers. During degradation the increase of traps, both in the SiO₂ as well as in the HfO₂, follows a power law behavior as a function of time with an exponent ~0.32 and ~0.34 respectively independent of stress voltage. The voltage acceleration of creation of HfO₂ traps (-30) found using VT²CP is nearly identical of the TDDB (-27) confirming the earlier published model that TDDB occurs when the density of traps in the HfO₂ reaches a critical value. VT²CP can accurately detect degradation down to a much lower voltage than the dielectric breakdown measurement range and only one stress experiment combined with VT²CP is sufficient to determine the degradation at a given voltage, while a TDDB test requires many measurements in order to construct an accurate distribution of failure times.

On the mechanism of electron trap generation in gate oxides

Abstract This paper investigates the applicability of the proposed models for electron trap generation in gate oxides. It is found that neither the electron–hole recombination nor the high oxide field itself is the main source for the generation. Although the hole injection alone can generate traps, the electron injection leads to additional generation, which is significant during the typical breakdown test.

On the hot hole induced post-stress interface trap generation in MOSFET's

The recently reported post-stress degradation of MOSFETs is investigated in more detail in this paper. The interface trap generation post hole injection is found to be two orders of magnitude slower than that post-irradiation and cannot be satisfactorily explained by the transportation of hydrogen species across the bulk of oxide. There is a lack of correlation between the trapped hole removal and the interface trap creation, which is against the prediction of the trapped hole conversion model. It is found that the interface traps generated during and post the stress originate from two different defects. The defect responsible for the post-stress generation is excited by the hole injection and then converted into an interface trap if a positive gate bias is applied post-stress.

Relation between hydrogen and the generation of interface state precursors

Plasma charging and electrical stresses create new interface state precursors, which accelerate the device degradation during the subsequent stress. This paper investigates the mechanism responsible for the precursor generation. The attention is focused on the roles played by the hydrogen species and the holes trapped in the oxide. The properties of the generated precursor are studied and compared with those of precursors originally existed in the device.

Dependence of energy distributions of interface states on stress conditions

Abstract This paper reports that the energy distribution of interface states has one peak in each half of the bandgap, when they are generated without supplying hydrogen to the SiO2–Si interface. By contrast, when hydrogen is available during the stress, only a single peak in the upper half of the gap is formed.

Generation of hole traps in silicon dioxides

Oxide breakdown is a potential showstopper for future CMOS technology. Defect generation is responsible for the breakdown. Previous work (Degraeve et al., 2000; Stathis and DiMaria, 1999; Zhang et al, 1992) was focused on electron trap generation, while little information is available on hole trap generation. This paper unambiguously shows that a significant amount of hole traps can be created.