A Development of Atomic Layr Etching Technology of Si with Self-limited Mechanism for Directional Ultrafine Pattern Fabrication

本研究旨在建立具有自限吸附和反应机制的硅原子层刻蚀技术，并对Ge原子层刻蚀以及低能量ECR氯等离子体在超小型MOS器件栅图形制作中的应用进行了研究。在硅的自限幅原子层蚀中，发现每一晶体取向的每一周期饱和刻蚀速率与原子层厚度的有序分数很好地吻合，并且当提供氯自由基时比只提供分子时的刻蚀数高一倍。此外，各饱和速率由表面键结构和各取向的吸附位置组成的简单关系来表示。在这样的结果中，硅的刻蚀量取决于氯的吸附量。反之，对于Ge，在饱和氯吸附条件下，在低Ar~(++)离子辐照下，每周的刻蚀速率为1/4原子层厚度，随着Ar~(++)离子辐照的增加而增加，并饱和到单原子层厚度。此外，在高Ar~(++)离子辐照下，刻蚀特性可用基于简单等概率Ar~(++)离子诱导反应的指数逼近方程来表示。从测量的入射Ar~(++)离子通量与能量的关系可以看出，Ge的原子层状刻蚀主要是能量高于-13 eV的Ar~+离子。此外，利用低能量的ECR氯等离子体实现了特征尺寸小于0.1微米的超小型MOSFET的高选择性定向栅刻蚀。原子层状刻蚀可以被认为是一种最终的选择性刻蚀过程，它对吸附原子的存在或不存在非常敏感。该项目的成功为在第四族半导体上制造超小型器件的基础技术提供了关键。

In this study, we have aimed at establishing the atomic layr etching technology of Si with a self-limited adsorption and reaction mechanism, and extended the research onto the Ge atomic layr etching as well as application of the low energy ECR chlorine plasma to the gate pattern fabrication in ultrasmall MOS devices.In self-limited atomic-layr-etching of Si, the etch rate per cycle in saturation for each crystal orientation has been found to agree well with the well-regulated fractional number of the atomic layr thickness, and the number when chlorine radicals are supplied is twice as high as that when only molecules are supplied. Moreover, the each rate in saturation is expressed by a simple relation consisting of the surface bond structure and the adsorption site of each orientation. In such the results, the Si etching amount depends on the amount of the chlorine adsorption. On the contrary, in the case of Ge, under the condition of saturated chlorine adsorption, it has been found that the etch rate per cycle at the low Ar^+ ion irradiation is 1/4 atomic layr thickness, and increases with the Ar^+ ion irradiation and saturates to the single atomic layr thickness. Furthermore, at the high Ar^+ ion irradiation, the etching characteristics have been expressed by an exponentially approaching equation which is based on a simple equi-probability Ar^+ ion induced reaction. From the measured energy dependence of the incident Ar^+ ion flux, atomic layr etching of Ge has been found to be dominated by Ar^+ ions with energy higher than -13eV.Also, highly selective directional gate etching for ultrasmall MOSFET's with a sub-0.1 micron feature size have been achieved by low energy ECR chlorine plasmas.Atomic layr etching can be considered as a final-selective-process, which is sensitive to the presence or the absence of adsorbed atoms. The success of this project supplies a key to the basic technology for ultrasmall device fabrication on group IV semiconductors.