Plasma Atomic Layer Etching Process of Silicon/Aluminum Oxide

SUN Bowen; FENG Yuqun; YANG Fan; CAO Kun; CHEN Rong

doi:10.16490/j.cnki.issn.1001-3660.2025.23.004

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Surface Technology ›› 2025, Vol. 54 ›› Issue (23) : 68-77. DOI: 10.16490/j.cnki.issn.1001-3660.2025.23.004

Special Topic—Atomic-level manufacturing

Plasma Atomic Layer Etching Process of Silicon/Aluminum Oxide

SUN Bowen, FENG Yuqun, YANG Fan, CAO Kun, CHEN Rong^*

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Abstract

The work aims to present a comprehensive investigation into atomic layer etching (ALE) processes for aluminum oxide (Al₂O₃) and silicon dioxide (SiO₂), focusing on the effect of process parameters on etching precision, surface morphology, and material selectivity. As the scaling of semiconductor devices continues to push the limits of conventional fabrication techniques, ALE has emerged as a critical process technology capable of delivering sub-nanometer precision, excellent anisotropy, and enhanced control over material interfaces. By combining advanced experimental techniques with plasma simulation, the mechanisms underlying self-limiting etching behavior were analyzed systematically and the optimized ALE conditions were established for both dielectric materials. Special attention was paid to the role of surface modification agents and ion energy control in achieving high selectivity and minimizing physical damage to the etched surfaces. The results demonstrated that Al₂O₃ and SiO₂ each exhibited distinct but well-defined ALE windows under specific bias voltage ranges- 96-120 V for Al₂O₃ and 59-74 V for SiO₂-where the etching per cycle stabilized at approximately 0.12 nm/cycle and 0.11 nm/cycle, respectively. Within these windows, the etching reactions proceeded in a highly controlled, layer-by-layer manner, and the self-limiting nature of the chemical reactions ensured excellent reproducibility and precision. Notably, the use of BCl₃ as a surface modification precursor for Al₂O₃, and CHF₃ for SiO₂, significantly reduced the threshold energy required for initiating etching reactions. These gases facilitated the formation of volatile byproducts and reactive surface intermediates, which enhanced both the efficiency and the selectivity of the ALE process. Comparative control experiments confirmed that in the absence of these passivation gases, the films either did not etch or exhibited non-uniform sputtering behavior, highlighting the indispensable role of chemical pre-modification in achieving atomic-scale precision. High-resolution transmission electron microscopy (TEM) and atomic force microscopy (AFM) were employed to evaluate film morphology before and after etching. The results revealed that both Al₂O₃ and SiO₂ films maintained excellent structural integrity and surface smoothness after multiple etching cycles, with no significant increase in surface roughness. The ALE process effectively removed nanoscale surface defects and prevented the roughening often associated with conventional plasma etching techniques. The ALE process was further found to effectively remove nanoscale surface defects introduced during prior deposition steps, such as atomic layer deposition (ALD), thereby improving the overall material quality. In addition to process control and surface preservation, ALE also improved material selectivity in patterned structures. Auger electron spectroscopy (AES) analysis showed that ALE treatment could eliminate unwanted deposition in non-growth regions following area-selective deposition (ASD), particularly in Cu/Si test structures. This capability was essential for the fabrication of advanced multi-material semiconductor architectures where nanoscale precision was critical. The findings confirm that plasma-assisted ALE provides a reliable and controllable platform for the precision etching of high-k dielectrics such as Al₂O₃ and widely used insulators like SiO₂. The ability to achieve angstrom-level thickness control, excellent surface uniformity, and improved material selectivity makes ALE a promising candidate for next-generation semiconductor device fabrication. This work lays a solid foundation for further development and integration of ALE into mainstream micro- and nano-fabrication processes.

Key words

atomic layer etching / etching window / self-limitation / selectivity / roughness

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SUN Bowen, FENG Yuqun, YANG Fan, CAO Kun, CHEN Rong. Plasma Atomic Layer Etching Process of Silicon/Aluminum Oxide[J]. Surface Technology. 2025, 54(23): 68-77 https://doi.org/10.16490/j.cnki.issn.1001-3660.2025.23.004

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