A Study on Elementary Process of Self-limited Surface Adsorption and Reaction Si Atomic Layr Etching

本研究的目的是阐明硅原子层腐蚀的基本过程，即，反应物原子在Si表面的自限性吸附和低能离子辐照引起的表面刻蚀反应。本年度作为该两年计划的最后一个研究年度，研究内容从Si的自限原子层刻蚀扩展到Ge的自限原子层刻蚀，以及低能ECR氯等离子体在超小型MOS栅制造中的应用。和（211）的超净ECR实验研究表明，氯离子吸附和低能Ar^+离子辐照交替进行，能有效地降低样品中的氯离子浓度。结果表明，当供给氯自由基时，饱和状态下的每周期腐蚀速率是仅供给分子时的两倍。此外，它是由一个良好的调节分数的原子层厚度为每个基板取向表示。此外，饱和蚀刻速率是在一个简单的关系，表面键结构和吸附位置的每个基板取向。XPS测试结果表明，在原子层刻蚀过程中，无论是在分子氯吸附表面还是在氯自由基吸附表面，都没有Si^<2+>和Si^<3+>的存在，只有氯的-1原子层吸附。在Si的这些原子层蚀刻中，蚀刻深度取决于氯吸附的量。在Ge的情况下，蚀刻特性显示出对低能Ar^+离子照射量的依赖性。这一显著的结果说明吸附和反应的动力学常数不同。同时，利用低能ECR氯等离子体实现了0.1 μ m特征尺寸的超小型MOSFET的高选择性定向栅刻蚀，该项目的成功为深入理解原子层刻蚀工艺提供了一把钥匙，并对该项目进行了总结。

The purpose of this study is to clarify the basic process of atomic layr etching of Si, ie., self-limited adsorption of reactant atoms on the Si surface and etching reaction of the surface induced by the low energy ion irradiation. In this fiscal year, as the last research year of this 2 year project, research has been extended from self-limited atomic-layr-etching of Si to that of Ge and to application of low energy ECR chlorine plasma to ultrasmall MOS gate fabrication.Atomic layr etching of Si (100), (111), (110), and(211)has been investigated by alternated chlorine adsorption and low energy Ar^+ ion irradiation using an ultraclean ECR apparatus. It is found that the etch rate per cycle in saturation when chlorine radicals are supplied is twice as high as that when only molecules are supplied. Also it is expressed by a well-regulated fractional number of the atomic layr thickness for each substrate orientation. Moreover, the saturated etch rate is in a simple relation to the surface bond structure and the adsorption site of each substrate orientation. Not only on the molecular chlorine adsorbed surface but also on the chlorine radical adsorbed surface during atomic-layr-etching, XPS measurements showed the absence of Si^<2+> and Si^<3+>and the -1 atomic layr adsorption of chlorine. In these atomic-layr etching of Si, etching depth depends on the amount of the chlorine adsorption. In the case of Ge, etching characteristics showed dependence on the amount of the low energy Ar^+ ion irradiation. This remarkable result demonstrates difference of kinetic constant of adsorption and reaction. Also, highly selective directional gate etching of ultrasmall MOSFET's with a 0.1 micron feature size have been fabricated by low energy ECR chlorine plasmas.The success of this project supplies a key to understand more deeply the atomic layr etching process and we summarized this project.