Atomic layer etching (ALE) has emerged as an innovative technique for precisely removing materials in nanoscale devices. It offers high material selectivity, etch uniformity, and atomic-scale resolution, making it a popular choice. This article provides valuable insights into the role of plasma in ALE, focusing on thermal ALE for nanometer-scale device manufacturing. In addition to discussing the advantages and challenges of ALE compared to classic reactive ion etching, it also lists various plasma-based ALE processes and explores novel thermal ALE processes based on the ligand addition mechanism.
The article highlights the potential of using plasma in a manufacturing environment to increase wafer throughput, tune anisotropy, enable a wider range of pre-cursors in thermal ALE, and enhance thermal ALE of crystalline materials. It discusses the benefits and challenges of different plasma sources in ALE, providing an outlook for future development. Furthermore, it outlines the applications of plasma for productivity reasons such as particle avoidance and process stability.
As chip feature sizes continue to shrink and new device architectures emerge, new wafer processing regimes are required to meet these demands. Traditionally, this required the development of new processing equipment. However, ALE offers a solution by allowing for precise addition and removal of materials on an atomic scale. It is particularly useful for fabricating complex 3D nanostructures in high-performance microelectronic devices.
ALE can be classified into two principal implementations: thermal or isotropic ALE, and plasma-based or directional ALE. The former relies on chemical reactions between the device surface and a gas to achieve uniform etching in all directions, while the latter uses a flux of accelerated ions or radicals to etch in a specific direction. Plasma-based ALE typically removes more material per cycle, but it is less precise and can cause unintentional damage.
ALE is characterized by alternating self-limited process steps that enable the processing of wafer substrates with atomic scale precision. This allows for superior etch selectivity and simplifies uniformity control across a wafer. The first industrial implementation of ALE utilized ions in the removal step, resulting in directional ALE.
In conclusion, ALE offers numerous advantages for nanometer-scale device manufacturing, including high selectivity, uniformity, and resolution. However, it also faces challenges that need to be addressed for its widespread adoption. Plasma-based ALE processes play a crucial role in achieving ALE, and their potential benefits and limitations are discussed. The article provides valuable insights into the future of ALE and its applications in device manufacturing.
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