DEVELOPMENT OF ANISOTROPIC ETCHING TECHNOLOGY WITH PERFECT SELECTIVITY USING LANGMUIR'S ADSORPTION LAYER

本研究的目的是利用Langmuir吸附层开发具有完全选择性的各向异性刻蚀技术，重点是选择性等离子体加工。研究结果总结如下：(1)在ECR等离子体刻蚀中，在去除脱氧污染和抑制离子入射损伤的超净条件下，氮加氯显著增强了各向异性。对n^+-多晶硅侧壁表面的直接ESCA分析表明，n原子的化学吸附形成Si-N键，导致各向异性增强。将n -化学吸附的n^+-多晶硅表面暴露在洁净室空气中会导致表面氧化。(2)加入氮对蚀刻速率的依赖性表现为langmuir型吸附和与氮、氯的竞争反应。此外，利用水平过蚀刻速率，在添加和不添加氮的情况下，对氯自由基和氮自由基的迁移和失活进行了评估。(3)在相同的超净ECR等离子体系统中，通过加入H_2的Ar等离子体分解SiH_4，实现了硅的低温选择性外延，并在不加热衬底的情况下实现了仅在SiO_2上选择性沉积多晶硅。ESCA分析表明，在硅选择性外延中，SiO_2表面的Si^0吸附来源于SiH_4，抑制了SiO_2的蚀刻。此外，选择性的反转是由氢自由基的化学腐蚀和离子诱导SiH_4分解的竞争性贡献造成的。

The object of this research is to develop an anisotropic etching technology with perfect selectivity using Langmuir's adsorption layer, with focusing on selective plasma processing. Research results are summarized as follows.(1) In ECR plasma etching, under an ultraclean condition with eliminating deoxidizing contamination onto the wafer and suppressing damages caused by ion incidence, nitrogen to addition to chlorine drastically enhances anisotropy. Direct ESCA analysis of the side wall surface of n^+-polysilicon reveals chemisorption of the N-atom forming Si-N bonds, which results in anisotropy enhancement. Exposure of the N-chemisorbed n^+-polysilicon surface to clean room air results in oxidation of the surface.(2) The added nitrogen dependence of the etch rate is well characterized by a Langmuir-type adsorption and reaction scheme as a competitive reaction with nitrogen and chlorine. Furthermore, using the horizontal over-etch rates with and without nitrogen addition, transport and deactivation of chlorine and nitrogen radicals are evaluated.(3) Using the same ultraclean ECR plasma system, low temperature Si selective epitaxy and inversion to selective polysilicon deposition only on SiO_2 without substrate heating was achieved by SiH_4 decomposition with a H_2 added Ar plasma. ESCA analysis shows the Si^0 adsorption on the masking SiO_2 surface, which originates from SiH_4 and suppresses SiO_2 etching, in Si selective epitaxy. Moreover, the inversion in selectivity results from the competitive contributions of chemical etching with hydrogen radicals and ion induced decomposition of SiH_4.