Selectivity inversion in plasma processing at low temperatures

随着用于硅LST的超细图案器件制造技术的进步，低温等离子体处理变得越来越重要。为了实现理想的材料与等离子体之间的本征反应，沿着离子能量的精确控制，目前的研究者已经发展出超净加工技术，在本项目中，我们研究了低温等离子体加工技术，重点研究了表面吸附和反应的选择性，发现了沉积和刻蚀之间的选择性反转。我们还澄清，这是由于离子辐照诱导的沉积和自由基蚀刻化学的竞争性贡献。研究了在高选择性条件下的各向异性控制和超细间距内等离子体输运，阐明了在有效离子刻蚀产率小于1的条件下获得各向异性刻蚀特性的基本工艺，多晶硅的横向刻蚀速率与载流子浓度呈线性关系，纵向刻蚀速率与载流子浓度呈平方根关系，在分子流状态下，自由基的输运可用流动方程描述。此外，我们还通过吸附反应性气体原子而不受污染气体干扰，以及通过低能离子的交替辐照，实现了自限原子层刻蚀。这可以被看作是一个最终的选择性处理，因为反应只发生在吸附位点，而不是在非吸附位点。这个项目的成功提供了一个关键的千兆规模集成过程技术，我们继续研究相关的主题。

Plasma processing at low temperatures becomes more and more important with advancement in ultrafine pattern device fabrication technology for silicon LSTs. The present investigators have developed ultraclean processing along with precise control of ion energy in order to realize ideal intrinsic reactions between materials and plasmas.In this project, we studied on plasma processing at low temperatures without substrate heating, focusing on selectivity in surface adsorption and reaction, and found a selectivity inversion between deposition and etching. We also clarified that this is due to a competitive contribution of ion irradiation induced deposition and radical etching chemistry. Also, we studied on anisotropy control and plasma transport within an ultrafine spacing under highly selective condition, and clarified basic process such that anisotropic etching features are obtained at an effective ion etching yield less than 1, that the lateral etch rate of polysilicon increases linearly with carrier concentration and the vertical one shows square root dependence, and that the radical transport in overetching is described by a flow equation in the molecular flow regime. Futhermore, we achieved self-limited atomic layr etching by adsorption of reactive gas atoms without disturbance by contaminant gases as well as by alternate irradiation of low energy ions. This can be regarded as a final selective processing, because the reaction occurs only at the adsorbed site and not at the non-adsorbed site.The success of this project supplies a key to giga-scale integration process technologies, and we continue to study the related subjects.