Friday, June 5, 2015

Tastes of ALE: New Articles on Atomic Layer Etching (ALE)

Here is a good overview from LAM Research on their ALE developments and recently published materials / Jonas

Interest in atomic layer etching (ALE) is intensifying as it emerges as an enabling technique for advanced etch applications. As features on a chip continue to decrease in size, the ability to precisely remove materials to create those features becomes increasingly difficult and vitally important. ALE can deliver the level of control needed by using cycles of multi-step processes that remove a few atomic layers at a time, making it useful for creating 3D, high aspect ratio, and other challenging structures requiring extreme precision and fidelity.

Two articles by Lam scientists were recently published on this important topic in prestigious technical journals. The first paper discusses the ability for ALE to be both selective (removing only the desired material without removing other materials) and directional (etch rate higher in the z-direction than in lateral directions) and is included in a special edition on ALE and atomic layer clean. The second paper provides an overview of atomic layer etching and includes a survey of existing literature and discussion of the role of power pulsing. Check out the abstracts below or follow the links to access the complete articles.

Highly Selective Directional Atomic Layer Etching of Silicon

Samantha Tan, Wenbing Yang, Keren J. Kanarik, Thorsten Lill, Vahid Vahedi, Jeff Marks, and Richard A. Gottscho, Lam Research Corp.

Following Moore’s Law, feature dimensions will soon reach dimensions on an atomic scale. For the most advanced structures, conventional plasma etch processes are unable to meet the requirement of atomic scale fidelity. The breakthrough that is needed can be found in atomic layer etching or ALE, where greater control can be achieved by separating out the reaction steps. In this paper, we study selective, directional ALE of silicon using plasma assisted chlorine adsorption, specifically selectivities to bulk silicon oxide as well as thin gate oxide. Possible selectivity mechanisms will be discussed.

Read the full article: ECS J. Solid State Sci. Technol. Vol. 4, Issue 6, N5010-N5012 (2015)

Overview of Atomic Layer Etching in the Semiconductor Industry

Keren J. Kanarik, Thorsten Lill, Eric A. Hudson, Saravanapriyan Sriraman, Samantha Tan, Jeffrey Marks, Vahid Vahedi, and Richard A. Gottscho, Lam Research Corp.

Atomic layer etching (ALE) is a technique for removing thin layers of material using sequential reaction steps that are self-limiting. ALE has been studied in the laboratory for more than 25 years. Today, it is being driven by the semiconductor industry as an alternative to continuous etching and is viewed as an essential counterpart to atomic layer deposition. As we enter the era of atomic-scale dimensions, there is need to unify the ALE field through increased effectiveness of collaboration between academia and industry, and to help enable the transition from lab to fab. With this in mind, this article provides defining criteria for ALE, along with clarification of some of the terminology and assumptions of this field. To increase understanding of the process, the mechanistic understanding is described for the silicon ALE case study, including the advantages of plasma assisted processing. A historical overview spanning more than 25 years is provided for silicon, as well as ALE studies on oxides, III–V compounds, and other materials. Together, these processes encompass a variety of implementations, all following the same ALE principles. While the focus is on directional etching, isotropic ALE is also included. As part of this review, the authors also address the role of power pulsing as a predecessor to ALE and examine the outlook of ALE in the manufacturing of advanced semiconductor devices.

Read the full article: J. Vac. Sci. Technol. A Vol. 33, 020802 (2015)

Schematic of ALE concept: first a modification step (Reaction A) forms a reactive layer, then a removal step (Reaction B) takes off only that modified layer. The steps are cycled until the desired etch result is achieved. (Adapted from JVST A)

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