We have studied the local atomic structure of silicon suboxide (SiOx, x<2) thin films using infrared (IR) spectroscopy. The films were prepared by plasma enhanced chemical vapor deposition (PECVD) of silane (SiH4) and nitrous oxide (N2O) mixtures, which were then diluted with He. The IR spectra were found to vary significantly with the degree of He dilution. Films grown with no He showed SiN, NH, and SiH bonding groups in addition to the three characteristic vibrations of the Si–O–Si linkage. The addition of He reduced the strength of the SiN, NH, and SiH absorption bands, and resulted in systematic increases in the frequency of the Si–O–Si asymmetric stretching vibration. The frequency of this Si–O–Si stretching vibration scales linearly with the oxygen concentration from approximately 940 cm−1 in oxygen doped amorphous silicon to 1075 cm−1 in stoichiometric noncrystalline SiO2. A deposition temperature of 350 °C and a He dilution of 50% gave a film composition close to SiO1.9. We propose a model for the deposition process that emphasizes the role of the He dilution.
An increasingly important issue in semiconductor device physics is understanding of how departures from ideal bonding at silicon-dielectric interfaces generate electrically active defects that limit performance and reliability. Building on previously established criteria for formation of low defect density glasses, constraint theory is extended to crystalline silicon-dielectric interfaces that go beyond Si-SiO 2 through development of a model that quantifies average bonding coordination at these interfaces. This extension is validated by application to interfaces between Si and stacked silicon oxide/nitride dielectrics demonstrating that as in bulk glasses and thin films, an average coordination, N av , greater than three yields increasing defective interfaces.
High resolution soft x-ray photoelectron spectroscopy with synchrotron radiation is used to study the interfaces of SiO 2 /Si(111), SiO 2 /Si(100), Si͑111͒/Si 3 N 4 , and SiO 2 /Si 3 N 4 for device-quality ultrathin gate oxides and nitrides. The thin oxides and nitrides were grown by remote plasma deposition at a temperature of 300°C. Aftergrowth samples were further processed by rapid thermal annealing for 30 s at various temperatures from 700 to 950°C. The Si͑111͒/Si 3 N 4 samples were air exposed and formed a thin ϳ6 Å SiO 2 layer with a Si(2p) core-level shift of 3.9 eV, thus allowing us to study both the Si͑111͒/Si 3 N 4 and SiO 2 /Si 3 N 4 interfaces with a single type of sample. We obtain band offsets of 4.54Ϯ0.06 eV for SiO 2 /Si(111) and 4.35Ϯ0.06 eV for SiO 2 /Si(100) with film thicknesses in the range 8-12 Å. The Si͑111͒/Si 3 N 4 nitrides show 1.78Ϯ0.09 eV valence-band offset for 15-21 Å films. This value agrees using the additivity relationship with our independent photoemission measurements of the nitride-oxide valence-band offset of 2.66Ϯ0.14 eV. However, we measure a substantially larger SiO 2 /Si 3 N 4 ⌬E V value of 3.05 eV for thicker ͑ϳ60 Å͒ films, and this indicates substantial differences in core-hole screening for films of different thickness due to additional silicon substrate screening in the thinner ͑15-21 Å͒ films.
The electron energy band alignment between (100)Si and several complex transition/rare earth (RE) metal oxides (LaScO 3 , GdScO 3 , DyScO 3 , and LaAlO 3 , all in amorphous form) is determined using a combination of internal photoemission and photoconductivity measurements. The band gap width is nearly the same in all the oxides ͑5.6-5.7 eV͒ yielding the conduction and valence band offsets at the Si/oxide interface of 2.0± 0.1 and 2.5± 0.1 eV, respectively. However, band-tail states are observed and these are associated with Jahn-Teller relaxation of transition metal and RE cations which splits their d* states.
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