Atomic Layer Etching of Metal with Anisotropy, Specificity and Selectivity

Expanding the support for Internet of Things (IoT) to Internet of Everything (IoE), including smart home, autonomous cars, wearable health and wellness devices, and point-of-use manufacturing, the backbone of the infrastructure is the ever-progressing evolution of integrated circuits that includes transistors and memory devices at nanometer scales. Amongst the dozens of steps involved in the manufacturing process, chemical etching plays a crucial role since it determines the quality of pattern transfer and feature registration. To sustain the functional device performance requirement with continuous transistor miniaturization, novel architectures have been developed and implemented. The need for complex topographies and materials integration in next-generation logic and memory devices imposes stringent requirements on processing uniformity and consistency. For example, the state-of-the-art 5-nm CMOS technology offers nearly twice the logic density and a 15% speed gain or 30% power reduction over the 7-nm technology node, once again pushing the limit of device performance. Amongst many challenges in developing such processes, two related to metal patterning should be noted: (1) an anisotropic patterning process to shape the thin metal absorbers on the extreme ultra-violet (EUV) mask so it can be used to replace multiple immersion photomasks and produce better features with greater pattern transfer fidelity and (2) an anisotropic patterning process to etch magnetic multi-layers so that their integration in spintronics can be more effective, where the non-volatile nature of magnetization switching can be used to significantly reduce the power requirement.

In this talk, current work addressing the era of metals, referring to the introduction of complex metal stacks in enabling technologies, will be presented. This is a real challenge in materials integration since many of these metals are chemically inert. Metals offer superior physical properties such as high electrical and thermal conductivities – traits desirable for microelectronics integration. However, in contrast to the rapid increase in application needs, metal patterning at the nanometer scale remains largely unsolved, as many of these metals are etch-resistant. This work highlights the importance of tailoring the energy and distribution of low energy reactive ions to enable atomic layer etching, the potential of which can be fully explored to tailor the surface reactions and selectivity. This atomic layer etching process is comprised of low energy ions introducing well controlled and directional reaction front in creating the chemical contrast that is needed in the subsequent self-limiting and thermally driven reactions to achieve an anisotropic profile. The experimental results, combined with first-principle calculations, demonstrate how surface reactivity and selectivity, instead of etch rate, is the focus of realizing nanometer-level patterning on etch-resistant materials. This novel process is generalizable to realize atomic precision in removing etch-resistant materials with complex compositions or structures.