A technique for the measurement of brittle thin film toughness has been developed. It is based on the mechanics of channel cracking in thin films. Dielectric films including CVD silicon oxide and silicon nitride films were studied using this technique. To prevent channel cracks from propagating into silicon substrates, an aluminum layer was deposited prior to the deposition of the dielectric layer. By using a specially made bending fixture, the cracks were observed in situ when the samples were subject to well controlled stresses. It was observed that for each film, a well defined critical film stress level existed, beyond which the crack velocity accelerated very rapidly. The critical film stresses were obtained by superposition of the critical applied stresses and the residual stresses in the films due to deposition and thermal expansion mismatch. It was shown that this technique was highly consistent in critical stress measurement. A simple shear-lag model was used to obtain the film toughness values using the measured critical film stress data.
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.
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.
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.
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