Improvement of leakage current characteristics of MOS devices by use of catalytic of platinum

本文提出了一种降低流过SiO_2层的漏电流密度的新方法。该方法在SiO_2层上淀积约3 nm厚的铂（Pt）层，然后在约300 ℃的氧气中热处理，去除Pt层后淀积铝电极，得到<Al/SiO_2/Si（100）> MOS结构。在SiO_2层中注入氧离子，氧离子与SiO_2层中的缺陷态如低价氧物种和Si/SiO_2界面处的Si悬空键界面态发生反应。由于在SiO_2层的较薄部分，高电场增强了O离子的迁移，氧化选择性地发生在较薄部分，从而改善了SiO_2层的厚度均匀性，降低了漏电流密度。当Si相对于Pt层加正偏压时，界面态密度变低，我们发现用Si在硝酸共沸溶液中浸渍形成的厚度为1.4nm的SiO_2层的漏电流密度与高温下热生长的SiO_2层的漏电流密度一样低或略低。因此，我们首次成功地观察到了化学修饰SiO_2膜的电容-电压曲线。在200℃氢气氛中加热，淀积Al层后，漏电流密度仅为相同厚度热SiO_2层的1/20 ~ 1/4。结果表明，漏电流密度的降低是由于界面态的消除，SiO_2带隙态的消除和SiO_2层带隙能的加宽。

We have developed a new method of decreasing a leakage current density flowing through silicon dioxide (SiO_2) layers. In this method, a platinum (Pt) layer of 〜 3 nm thickness is deposited on a SiO_2 layer, followed by heat treatment at 〜 300 ℃ in oxygen, and after the removal of the Pt layer, an alminum electrode is deposited, resulting in the <Al/SiO_2/Si(100)> MOS structure. Dissociated oxygen ions (O) are injected into the SiO_2 layer, and the ions react with defect states such as suboxide species in SiO_2 and Si dangling bond interface states at the Si/SiO_2 interface. The reaction results in the elimination of the defect states which work as a current path. Since the migration of O ions is enhanced in thin parts of the SiO_2 layer because of a high electrical field, oxidation selectively occurs in the thin part, leading to the improvement of the SiO_2 thickness uniformity and hence decreasing the leakage current density. When a positive bias voltage is applied to Si with respect to the Pt layer, the interface state density becomes lower.We have found that SiO_2 layers of 〜 1.4 nm thickness formed by immersion of Si in an azeotropic solution of nitric acid possess a leakage current density as low as or slightly lower than those for thermal SiO_2 layers grown at high temperatures. Consequently, we have succeeded in the observation of a capacitance-voltage curve for ultrathin chemical SiO_2 layers for the first time. When an Al layers deposited and the specimen is heated at 200℃ in hydrogen, the leakage current density is greatly decreased to 1/20 〜 1/4 of those for thermal SiO_2 layers of the same thickness. It is concluded that the decrease in the leakage current density results from 1) elimination of interface states, 2) elimination of SiO_2 gap-states, and 3) widening of the band-gap energy of the SiO_2 layer.