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

我们开发了一种降低通过二氧化硅（SiO_2）层的泄漏电流密度的新方法。该方法在SiO_2层上沉积厚度为~ 3nm的铂（Pt）层，在氧气中~ 300℃热处理，去除Pt层后沉积铝电极，得到<Al/SiO_2/Si(100)> MOS结构。将解离氧离子(O)注入到SiO_2层中，并与SiO_2中的亚氧化物态和Si/SiO_2界面中的Si悬空键态等缺陷态发生反应。反应的结果是消除作为电流路径的缺陷状态。由于高电场增强了O离子在SiO_2层薄层的迁移，在SiO_2层薄层选择性氧化，提高了SiO_2的厚度均匀性，从而降低了泄漏电流密度。当Si相对于Pt层施加正偏置电压时，界面态密度降低。我们发现，将Si浸入硝酸共沸溶液中形成的~ 1.4 nm厚度的SiO_2层的漏电流密度低于或略低于高温下生长的热SiO_2层的漏电流密度。因此，我们首次成功地观察到超薄化学SiO_2层的电容-电压曲线。在氢气中加热200℃后，泄漏电流密度大大降低，仅为相同厚度的热SiO_2层的1/20 ~ 1/4。结果表明，泄漏电流密度的减小是由于1)界面态的消除，2)SiO_2隙态的消除，3)SiO_2层带隙能量的扩大。

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.