Atomic Layer Etching of Nanowires Using Conventional RIE Tool

Innovative material and processing concepts are needed to further enhance the performance of complementary metal-oxide-semiconductor (CMOS) transistors-based circuits as the scaling limits are being reached. To achieve that, we report on the development of an atomic layer etching (ALE) [1] process to fabricate smooth and thin nanowires using a conventional dry etching tool. Firstly, a negative tone resist (hydrogen silsesquioxane) is spin-coated on SiGe-on-insulator (SiGeOI) samples and electron beam lithography performed to create nano-patterns. These patterns act as an etch mask and are transferred into the SiGeOI layer using an inductively-coupled plasma reactive ion etching (ICP-RIE) process. Subsequently, an SF6 and Ar+ based ALE process is employed to smoothen the nanowires and reduce their widths. SF6 modifies the surface of the samples, while in the next step Ar+ removes the modified surface. The ALE cycle sequence is surface modification with 60 sccm SF6 for 20 s, 60 sccm Ar purge for 15 s, removal of the layer with 60 sccm Ar for 10 s at 25 W platen power, and 40 sccm Ar purge for 10 s.
To investigate the effect of ALE on the nanowire roughness and width, several ALE cycles are performed. The surface of the etched features is studied using scanning electron microscopy and atomic force microscopy. With the increasing number of ALE cycles, a reduction in the width of the nanowires, as well as surface roughness, is observed. The roughness reduced from ca. 6 nm to 1 nm (the resolution of the AFM tip) as the number of ALE cycles is increased from 78 to 102.
An etch per cycle of 1.1 Å is obtained. Sub-12 nm nanowires with smooth sidewalls were achieved after performing 63 ALE cycles. This process, developed on a conventional ICP-RIE tool, can be used to further down-scale semiconductor nanowires.

1. Kanarik, Keren J., et al. "Overview of atomic layer etching in the semiconductor industry." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 33.2 (2015): 020802.