Characterization of plasma-enhanced chemically-vapor-deposited silicon-rich silicon dioxide/thermal silicon dioxide dual dielectric systems

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Abstract
Plasma enhanced chemically‐vapor‐deposited silicon‐rich oxides (200 Å and 500 Å in thickness) of various excess silicon content were deposited onto thermal silicon dioxide (SiO2) layers (103, 207, and 530 Å in thickness) grown on a p‐type silicon (Si) substrate. The dielectric constant, electron injection efficiency, current‐voltage (I‐V) reproducibility, and breakdown property of these composite structures were examined. The dielectric constants of Si‐rich oxide were observed to increase with Si content from 3.8 for films deposited at a gas phase ratio (R0) of the concentration of nitrous oxide (N2O) to silane (SiH4) of 150 to ∼10 for films deposited with R0=0. The Si‐rich oxides with R0≤5 were found to work as electron injectors. The average oxide field needed to induce a current of 4.8×10−7 A/cm2 through the SiO2 (530 Å in thickness) decreased about 40% in magnitude by adding a Si‐rich oxide layer with the optimized R0(=1) compared to that of a control sample which had no Si‐rich oxide layer. For thin SiO2 (103 Å and 207 Å in thickness) samples, the decrease of the average field was only 2% and 10% in magnitude with the optimized R0 (=2) layer, respectively, due to the relatively large voltage drop (≊−1 V) across the Si‐rich oxide compared to that across the thermal oxide layer. The voltage drop across the oxide is discussed in terms of a dual dielectric model. The yeild, which was defined as the percentage of capacitors that required a field larger than 2 MV/cm to obtain a current of 9.6×10−4 A/cm2, on as‐fabricated samples was larger than 90% for all samples with Si‐rich oxide. The samples were not destroyed by the passage of a relatively high current density (1.21×10−2 A/cm2) through the oxide and subsequent measurements resulted in approximately the same field to produce the specified current as for the first measurement. The yield was found to have a maximum at R0=1–10 depending on the thickness of Si‐rich oxides and SiO2. Current‐voltage reproducibility was also found to be improved by the deposition of Si‐rich oxide.