Materials Science and Engineering Program and ‡Department of Chemistry and Biochemistry, University of California-San Diego , La Jolla, California 92093, United States.
ACS Appl Mater Interfaces. 2017 Jun 21;9(24):20947-20954. doi: 10.1021/acsami.7b02060. Epub 2017 Jun 7.
The selective etching characteristics of silicon, germanium, and SiGe subjected to a downstream H/CF/Ar plasma have been studied using a pair of in situ quartz crystal microbalances (QCMs) and X-ray photoelectron spectroscopy (XPS). At 50 °C and 760 mTorr, Si can be etched in preference to Ge and SiGe, with an essentially infinite Si/Ge etch-rate ratio (ERR), whereas for Si/SiGe, the ERR is infinite at 22 °C and 760 mTorr. XPS data showed that the selectivity is due to the differential suppression of etching by a ∼2 ML thick CHF layer formed by the H/CF/Ar plasma on Si, Ge, and SiGe. The data are consistent with the less exothermic reaction of fluorine radicals with Ge or SiGe being strongly suppressed by the CHF layer, whereas, on Si, the CHF layer is not sufficient to completely suppress etching. Replacing H with D in the feed gas resulted in an inverse kinetic isotope effect (IKIE) where the Si and SiGe etch rates were increased by ∼30 times with retention of significant etch selectivity. The use of D/CF/Ar instead of H/CF/Ar resulted in less total carbon deposition on Si and SiGe and gave less Ge enrichment of SiGe. These results are consistent with the selectivity being due to the differential suppression of etching by an angstrom-scale carbon layer.
采用一对原位石英晶体微天平（QCM）和 X 射线光电子能谱（XPS）研究了硅、锗和 SiGe 在下游 H/CF/Ar 等离子体作用下的选择性刻蚀特性。在 50°C 和 760 mTorr 下，Si 可以优先于 Ge 和 SiGe 被刻蚀，其 Si/Ge 刻蚀速率比（ERR）基本为无穷大，而对于 Si/SiGe，在 22°C 和 760 mTorr 时 ERR 为无穷大。XPS 数据表明，选择性是由于 H/CF/Ar 等离子体在 Si、Ge 和 SiGe 上形成的约 2 ML 厚的 CHF 层对刻蚀的不同抑制作用所致。数据与氟原子与 Ge 或 SiGe 的反应放热性较低一致，强烈抑制了 CHF 层，而在 Si 上，CHF 层不足以完全抑制刻蚀。在进料气体中用 D 代替 H 导致了反动力学同位素效应（IKIE），其中 Si 和 SiGe 的刻蚀速率增加了约 30 倍，同时保持了显著的刻蚀选择性。使用 D/CF/Ar 代替 H/CF/Ar 导致 Si 和 SiGe 上的总碳沉积减少，并且 SiGe 中的 Ge 富集减少。这些结果与选择性归因于碳层对刻蚀的不同抑制作用一致。
