Characterization of silicon oxide films deposited using tetraethylorthosilicate

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Abstract
Silicon dioxide films prepared by plasma enhanced chemical vapour deposition (PECVD) from tetraethylorthosilicate (TEOS) are known to exhibit better step coverage than films prepared from silane chemistry. We have prepared TEOS oxide films under various processing conditions to investigate their electrical properties in view of their applicability to the fabrication of silicon devices. Films deposited using TEOS only and in the presence of an oxidant such as O2 or N2O were prepared. In each case we have submitted some of the samples to a rapid thermal densification cycle in N2. Metal oxide semiconductor (MOS) capacitors with oxide thickness of 50 nm were prepared for the measurements of dielectric strength, leakage current, flat-band voltage, and interface charge density. Several devices were measured to obtain significant statistical data regarding dielectric strength and uniformity of the film properties over the wafer. Thermal SiO2 films of the same thickness were used for comparison. Thicker films (~500 nm) were also prepared for FTIR (Fourier transform infrared) spectroscopy and ERD (elastic recoil detection), for the characterization of the material properties of the films. We have found that rapid thermal annealing (RTA) does not modify the electrical properties of films deposited with O2 or N2O. For the films deposited without oxidant that did not receive RTA, the flat-band voltage is less than −10 V and the interface charge density cannot be calculated reliably. Films deposited in the absence of oxidant that received RTA and films deposited with N2O with and without RTA have Vfb around −5 V and Qf/q of the order of 2E12 cm−2. Films deposited with O2 have Vfb near −0.6 V and Qf/q near 1E11 cm−2; this compares favorably with thermal oxides that have Vfb of −0.3 V and Qf/q near 1E10 cm−2. These oxides can withstand up to 5 MV/cm of electric field. The material analysis reveals that the oxide films prepared in the presence of either oxygen or nitrous oxide have a more ordered structure and contain fewer impurities that the oxide film prepared with TEOS in a nitrogen only ambient.

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