ウェハ保管環境のMOSデバイス特性への影響

抄録

The influence of wafer storage environment on oxidation and organic contamination of Si surfaces has been investigated. And the electronic reliability of thin (2.8 nm) SiO₂ films of metal-oxide-semiconductor (MOS) capacitors and MOS transistors has been measured as a function of the storage method. We found that shielding wafers from visible light is effective to prevent oxidation of silicon. Hydrogen terminated p-Si (100) (8 ∼ 12 Ωcm) wafers were stored in wafer boxes under various brightness levels. The oxidation rate in a dark box (∼ 0 lx) is found to be about one order of magnitude as small as that in a light box (∼ 1,000 lx). The MOS capacitors were fabricated by adding a storage process with various contamination levels before gate oxidation. It was indicated that for samples stored in the polyethersulfone (PES) box with a UV/photoelectron cleaning unit, the organic contamination level was substantially reduced, resulting in an improvement of the time dependent dielectric breakdown characteristics of the gate oxides. Furthermore we fabricated n-channel MOS transistors and investigated the influence of the organic contaminant before and after the gate oxidation on hot-electron degradation of the oxide. The wafer surfaces were contaminated with organic gases during the storage in a front opening unified pod (FOUP) made of polycarbonate for 6 h. In the result, the neutral traps were generated by hot-electron injection. It was shown that the density of the generated traps was larger for the pre-oxidation contamination than for the post-oxidation contamination. The model for the trap generation by the organic contamination was also discussed.