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刻的基本过程，即反应物原子在硅表面的自限吸附和低能离子辐照引起的表面刻蚀反应。在本财政年度，作为这两年项目的最后一年，研究已经从对硅的自限原子层蚀扩展到对锗的研究，以及低能ECR氯等离子体在超小型MOS栅制作中的应用。利用超薄ECR装置，采用交替氯吸附和低能Ar~(++)离子辐照的方法研究了Si(100)、(111)、(110)和(211)的原子层蚀。结果表明，在饱和状态下，当提供氯自由基时，每一循环的刻蚀速率是只提供分子时的两倍。此外，它由每个衬底取向的原子层厚度的调节良好的分数来表示。此外，饱和刻蚀速率与表面键结构和各衬底取向的吸附位置有很好的关系。XPS测试表明，无论是在分子氯的吸附表面，还是在原子层蚀过程中的氯自由基吸附面上，都没有Si^&lt；2+&gt；和Si^&lt；3+&gt；以及氯的-1原子层吸附。在这些对硅的原子层刻蚀中，刻蚀深度取决于氯的吸附量。对于Ge，刻蚀特性与低能Ar~(++)离子辐照的量有关。这一显著结果表明，吸附和反应的动力学常数不同。同时，利用低能ECR氯等离子体实现了特征尺寸为0.1微米的超小型MOSFET的高选择性定向栅刻蚀，为深入理解原子层刻蚀工艺提供了一把钥匙，并对本课题进行了总结。

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.