Ziyuan Liu

Influence of H2-annealing on the hydrogen distribution near SiO2/Si(100) interfaces revealed by in situ nuclear reaction analysis

Employing hydrogen depth-profiling via 1H(15N,αγ)12C nuclear reaction analysis (NRA), the “native” H concentration in thin (19–41.5 nm) SiO2 films grown on Si(100) under “wet” oxidation conditions (H2+O2) was determined to be (1–2)×1019 cm−3. Upon ion-beam irradiation during NRA this hydrogen is redistributed within the oxide and accumulates in a ∼8-nm-wide region centered ∼4 nm in front of the SiO2/Si(100) interface. Annealing in H2 near 400 °C introduces hydrogen preferentially into the near-interfacial oxide region, where apparently large numbers of hydrogen trap sites are available. The amount of incorporated H exceeds the quantity necessary to H-passivate dangling Si bonds at the direct SiO2/Si(100) interface by more than one order of magnitude. The H uptake is strongly dependent on the H2-annealing temperature and is suppressed above 430 °C. This temperature marks the onset of hydrogen desorption from the near-interfacial oxide trap sites, contrasting the thermal stability of the native H, which pre...

A hydrogen storage layer on the surface of silicon nitride films

Composition, layer structure, and H-retaining stability of 980°C N2-annealed silicon nitride-oxide (ON) stacks were analyzed using high resolution rutherford backscattering, synchrotron x-ray specular reflectometry, and nuclear reaction analysis. The formation of a Si2N2O layer in the near-surface part of N2-annealed nitride films was discovered. The Si2N2O layer can store hydrogen species that are resistant against energetic electron damage due to their reduced diffusion mobility. Although degrading in air, the Si2N2O layer thus provides reliable hydrogen species, which are desirable in the integrated circuit processing of silicon transistors and silicon ONO trap memories.

Influence of Hydrogen Permeability of Liner Nitride Film on Program/Erase Endurance of Split-Gate Type Flash EEPROMS

The paper demonstrates that H atoms diffused into the CVD tunnel oxide degrade the endurance of split-gate type flash EEPROMs. The authors observed that F-N stress application generates high trap densities at the tunnel-oxide/FG interface as well as negative charges in the tunnel oxide. The density of FN-induced traps and charges was found to strongly depend on the liner nitride (SiN) film quality. Nuclear reaction analysis revealed a difference in H permeability between LPCVD-SiN and plasma SiN liner films, allowing us to correlate H atoms and the endurance degradation.

Hydrogen redistribution induced by negative-bias-temperature stress in metal–oxide–silicon diodes

Poly-Si/SiO2/Si diodes in which oxides were grown thermally under wet oxidation conditions and subsequently treated by a post-oxidation anneal (POA) have been characterized electrically and chemically before and after applying negative-bias-temperature stress (NBTS). It was confirmed that NBTS produces interface states and that POA suppresses the interface state production. Nuclear reaction analysis indicated that NBTS results in hydrogen redistribution within the oxide layer. POA was shown to partly suppress such hydrogen accumulation. Hydrogen is thus clearly shown to influence the stability against NBTS.

Current Understanding of the Transport Behavior of Hydrogen Species in MOS Stacks and Their Relation to Reliability Degradation

We review recent experiments that suggest a comprehensive model for the reversible hydrogen (H) transport between the poly-Si interface and the oxide/Si interface of MOS stacks. The H diffusion in intact model MOS structures is probed by H depth profiling via resonant N-H nuclear reaction analysis (NRA). It is demonstrated that MOS device degradation correlates with H accumulation in the oxide/Si interface region. A specific ultra-thin oxynitride is discovered in the poly-Si/oxynitride interface as well as in the near-surface region of N2-annealed nitride films and shown to function as a potential H-storage layer. The interfacial storage layer between the poly-Si gate and the oxynitride dielectric of MOS transistors is found to contain two kinds of H species, which are mobile and stable, respectively, versus irradiationinduced relocation. The mobile H, if stimulated by energetic carriers, migrates across the gate films and relocates to the SiO2/Si interface, causing device instabilities. Understanding this basic hydrogen transport behavior allows conceiving fabrication countermeasures to improve the device reliability.

SIMS characterization of hydrogen transport through SiO2 by low-temperature hydrogen annealing

The variation of hydrogen distribution at the SiO 2 /Si interface by low-temperature hydrogen annealing was investigated using secondary ion mass spectrometry (SIMS). As the amount of hydrogen atoms incorporated at SiO 2 /Si is considered to be comparable to the silicon dangling bond density (1 x 10 10 to 1 x 10 12 atoms/cm 2 ), an analytical method with a high sensitivity is necessary for the detection of hydrogen at SiO 2 /Si. In this study, the experimental conditions of SIMS were optimized in order to obtain a sufficient reproducibility of interfacial hydrogen ion intensity. There are two main causes that influence the measurement reproducibility: (1) misalignment of the relative irradiation areas of the electron beam and ion beam and (2) the contribution of background hydrogen from surface contaminants and residual gas. We obtained a high measurement reproducibility within a 5.5% relative standard deviation (2σ). This enabled us to observe an increase of hydrogen at SiO 2 /Si by hydrogen annealing at 400 °C, which resulted from the incorporation of hydrogen from the ambient. From the results of nuclear reaction analysis (NRA) and thermal desorption spectroscopy (TDS), it was also found that the incorporated hydrogen had two chemical states.

Mobile and stable hydrogen species in the interface layer between poly silicon and gate oxynitride

The diffusion behavior of hydrogen contained in the surface layer of oxynitrides serving as models for poly-Si/oxynitride interfaces in MOS transistors was studied with H depth profiling by nuclear reaction analysis. The poly-Si/oxynitride interface is found to contain mobile and stable H species. The mobile H species tends to desorb in vacuum at room temperature. A TDDB improvement caused by resting in air for more than 24 h prior to the post nitridation annealing is attributed to the reduction of mobile H species. Eliminating the mobile H from the gate interface is thus suggested to improve the reliability of oxynitride dielectrics.

Indications for an ideal interface structure of oxynitride tunnel dielectrics

Interface characteristics with respect to nitrogen-distribution and hydrogen-diffusion behavior were evaluated for two model tunnel oxides nitrided by NO and N2O gas, respectively. Nuclear reaction analysis reveals a different resistance of the two interfaces against the approach by H, which allows us to correlate the characteristic N-distribution of the tunnel oxide with a H-diffusion barrier. From the relation between the interface structure and the electrical properties of the tunnel oxynitrides, we thus propose that the ideal interface structure of reliable tunnel oxynitride features a N-rich H-diffusion barrier layer in front of the oxynitride/Si interface.

Hydrogen distribution in oxide-nitride-oxide stacks and correlation with data retention of MONOS memories

We demonstrate that hydrogen (H) atom penetration into the bottom oxide (BTO) of ONO stacks degrades the retention reliability of MONOS memory. We observe that post-nitride (SiN) N2-annealing improves the retention through a suppression of the H atom diffusion in ONO stacks. Nuclear reaction analysis revealed the presence of an ultra thin H-storage layer in the top oxide/SiN interface, which can effectively shield the BTO from H diffusion, and in turn provides H species resistant against energetic electron damage.

FORMATION MECHANISM OF METAL-OXIDES ON PLASMA-EXPOSED WSIX/POLY SI GATE STACKS

The formation mechanism of WOx (x=2, 3), which breaks down the insulating SiO2 layer covering of WSix/poly Si gate electrodes, has been investigated. Plasma exposure was found to introduce oxygen into the surface of WSix films and caused the WOx formation during the subsequent thermal oxidation. It was revealed that the oxidation product on plasma-exposed WSix films depends on the grain orientation and no WOx was formed on c-axis oriented grains. This observation was substantiated by growing WSix films with preferred c-orientation and no evidence of WOx was found.