Metal‐insulator‐semiconductor (MIS) diodes with an electron‐beam‐deposited and oxygen‐annealed thin (≊80 nm) Y2O3 dielectric layer on p‐Si(100) show metal‐oxide‐semiconductor capacitor action. As‐deposited Y2O3 films are oxygen‐deficient amorphous and show low 5×10−9 A leakage currents for a capacitor area of 0.785 mm2 and breakdown fields of 1.0 MV/cm. Amorphous Y2O3 film crystallizes to a bcc phase by annealing at 400 °C causing increased conduction due to asperities related localized high‐field regions at contacts while its dielectric constant increases from a low value of 9.0e0 to 27e0. Annealing the Y2O3 film on Si above the crystallization temperature in the range 425 °C<Ts < 650 °C leads to growth of an about 5‐nm‐thick intermediate SiO2 layer at the Y2O3/SiO2 interface. A remarkable two orders of magnitude decrease in leakage current to 2×10−11 A and increase in breakdown field to 2.0 MV/cm is observed for MIS diodes with composite Y2O3/SiO2 dielectric. Current‐voltage behavior in the inversion mo...

Structural and electrical characteristics of metal-insulator-semiconductor diodes based on Y2O3 dielectric thin films on silicon

An effective permeation reduction of gaseous hydrogen isotopes into a metal wall by introducing a barrier is essential in two main fields: prevention of hydrogen-embrittlement in steels and control of the tritium inventory in future nuclear fusion reactors. By far the most important advances and relevant studies originate from the Nuclear Fusion Community where tritium retention is an important issue, influencing safety issues. Stable permeation barriers are searched among materials with the lowest bulk hydrogen solubility and diffusivity. Besides a few specific pure metals, like beryllium and tungsten, dense oxides, nitrides and carbides have been mostly investigated. Coating techniques for preparation of well adhered and perfect barriers are evidently of the same importance as the material selection itself. Most attractive are the techniques where an ad-layer is formed simply by oxidation. Other methods require specific gas environments with strong electric and magnetic fields, which may represent a limit for the ad-layers uniform coverage over large and uneven areas. Evaluation of the achieved barrier performances is another challenging task. Several new methods, which can trace hydrogen isotopes in bulk at very low concentrations, often miss in the determination of their mobility. Also, they do not reveal the role of barrier defects. The classical gas permeation rate method through coated membranes is still the most reliable option to determine the actual Hydrogen Permeation Barrier (HPB) efficiency. At elevated temperature, the hydrogen permeation rate is recorded at the downstream side of a coated membrane exposed to a substantially higher hydrogen upstream pressure. By using modern vacuum instrumentation techniques, even the most effective barriers can be well characterised.

Hydrogen permeation barriers: Basic requirements, materials selection, deposition methods, and quality evaluation

Support for this work from the Australian Research
Council ARC Discovery Grant No. DP0664357 is gratefully
acknowledged.

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Improved silicon surface passivation achieved by negatively charged silicon nitride films

As-deposited (AD) and annealed (500, 750, and 900°C) borophosphosilicate glass (BPSG) films were characterized during aging, baking, and etching using transmission Fourier transform infrared spectroscopy and ellipsometry. BPSG films contained oxides such as Si-O, P=O, P-O, and B-O as well as hydroxyl groups such as SiO-H, HOH, PO-H, and BO-H in a variety of local bonding environments, which became more uniform as the annealing temperature was increased. The water content in the BPSG films increased steadily during storage at ambient conditions. Based on bond strength, polarity, thermodynamics, and FTIR data, the B-O bond is the primary site for water adsorption on the surface of the film. Water absorption within the film was consistent with a reaction-limited model. Water reacted readily with P-O groups forming P=O and PO-H, which H bonds strongly within the film. The slower reaction with P=O moieties is proposed as the rate-limiting step for water absorption. Annealing after deposition strengthened the Si-O lattice, which reduced the affinity to absorb water. Etching rates ranged from 1 to 10 A/s on the films studied. A 200°C bake desorbed water from the surface layer of the films and increased the reaction rate between water and P=O and B-O to form PO-H and BO-H groups. The bulk etching rate was not affected by baking, but the induction time needed to start etching increased to 31 ± 1, 22 ± 2, and 74 ± 24 s for the AD, 500 and 750°C annealed films, respectively, and increased from 45 ± 5 to 72 ± 5 s for the 900°C annealed film.

Moisture Absorption and Reaction in BPSG Thin Films

We have investigated the crystallization of amorphous equiatomic NiTi thin films sandwiched between two protective silicon nitride barrier films using optical, atomic force, and transmission electron microscopies. Crystallite nucleation occurs homogeneously inside the NiTi films because small composition shifts at the interfaces between NiTi and surrounding layers suppress heterogeneous nucleation at these interfaces. The crystallite growth rate is independent of film thickness for films thicker than 600nm. Below 600nm, the growth rate decreases rapidly and has an apparent activation energy that increases with decreasing film thickness. We suggest that diffusion of hydrogen from the film interfaces may be responsible for this unusual behavior.

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Crystallization kinetics of amorphous equiatomic NiTi thin films: Effect of film thickness

Hydrogen concentration depth profiles in silicon nitride films deposited by low‐pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) techniques were studied. Quantitative hydrogen profiling was carried out using the resonant nuclear reaction 15N+1H→12C+4He+γ ray. Hydrogen concentration in as‐deposited LPCVD silicon nitride films was ∼2.5×1021 atoms/cm3 and was stable even after a furnace anneal at 450 °C in 3% H2/Ar for 30 min or a rapid thermal anneal at 1000 °C in oxygen for 30 s. These nitride films thus appear to be good hydrogen diffusion barriers. In contrast, hydrogen concentration in as‐deposited PECVD silicon nitride films was ∼1.75×1022 atoms/cm3 and dropped to ∼7.5×1021 atoms/cm3 after rapid thermal annealing at 1000 °C in oxygen for 30 s. During high‐temperature anneals, the hydrogen diffused from PECVD silicon nitride film into the underlying SiO2 layer. A comparison of the hydrogen concentration in these deposited oxides under the nitrides with those previously reported for as‐deposited, but uncovered, SiO2 films points out that the observed threshold voltage shifts in nitride covered metal–oxide semiconductor capacitors are related to the loss of hydrogen from the silicon oxide during vacuum processing for nitride deposition and to the subsequent diffusion in SiO2 from the PECVD nitride films.

Stability of hydrogen in silicon nitride films deposited by low‐pressure and plasma enhanced chemical vapor deposition techniques

Hydrogen concentration depth profiles in as‐deposited and annealed chemical vapor deposited silicon oxide [2% P glass, 8% P glass, tetraethylorthosilicate (TEOS), phosphorous‐doped TEOS and plasma oxide] films were measured using the nuclear reaction profiling technique with a 6.4 MeV 15N ion beam. The H2/Ar annealing of 450 °C for 60 min in furnace and the rapid thermal annealing at 1000 °C for 60 s in O2 or H2/Ar were carried out. It is found that hydrogen concentration is in the range 1021–1022 per cm3 in as‐deposited films. Annealing at high temperatures, even in hydrogen containing medium, lowers the hydrogen concentration in all films. The hydrogen concentration gradually increased with time when the films were left in the room environment. The electrical properties of the oxide are found to be related to the presence of hydrogen. The observed correlation between the flatband voltage and the hydrogen concentration is presented and discussed.

An investigation of hydrogen concentration profiles in as‐deposited and annealed chemical vapor deposited SiO2 films

Hydrogen concentration depth profiles in as‐deposited and annealed phosphorus‐doped silicon dioxide films were measured using the nuclear reaction profiling technique with 6.4 MeV 15N ion beam. The H2/Ar annealing of 450 °C for 60 min in furnace and the rapid thermal annealing at 1000 °C for 60 s in O2 or H2/Ar were carried out. It is found that hydrogen concentration is in the range of 1021–1022 per cm3 in as‐deposited films. Annealing at high temperatures, even in a hydrogen containing medium, lowers the hydrogen concentration in all films. The hydrogen concentration gradually increased with time when the films were left in the room environment. The electrical properties of the oxide are found to be related to the presence of hydrogen. The observed correlation between the flatband voltage and the hydrogen concentration is presented and discussed.

Hydrogen concentration profiles in as‐deposited and annealed phosphorus‐doped silicon dioxide films

Polycrystalline silicon–silicon dioxide–silicon capacitors were annealed in argon and argon containing oxygen ambients in a rapid thermal annealer. Capacitance–voltage (C–V) characteristics were determined before and after anneal as a function of annealing time at 1100 and 1200 °C. C–V characteristics of the capacitors annealed in argon degraded with increased annealing time and temperature. At 1100 °C oxide capacitance decreased and oxide leakage occurred. At 1200 °C the annealing resulted in catastrophe, capacitance decreased by more than factor of ten. Careful examination of the thin oxide layer, after selective removal of the polysilicon film, showed holes in the oxide, hole density increasing with time and temperature. On the other hand, C–V characteristics of capacitors, annealed in argon containing oxygen, had no significant change after anneal at 1100 °C. Also defect density was extremely low. The C–V characteristics of capacitors annealed in pure argon can be recovered by the anneal in oxygen amb...

Rapid thermal processing of silicon dioxide films in metal–oxide semiconductor capacitors: High‐temperature SiO2 decomposition at the SiO2–Si interfaces in inert ambient

Joseph Z. Xie

Papers

Stability of hydrogen in silicon nitride films deposited by low‐pressure and plasma enhanced chemical vapor deposition techniques

An investigation of hydrogen concentration profiles in as‐deposited and annealed chemical vapor deposited SiO2 films

Hydrogen concentration profiles in as‐deposited and annealed phosphorus‐doped silicon dioxide films

Rapid thermal processing of silicon dioxide films in metal–oxide semiconductor capacitors: High‐temperature SiO2 decomposition at the SiO2–Si interfaces in inert ambient