The demand for miniaturization and high integration of semiconductor devices has ever been increasing. In order to achieve the requirements of the semiconductor industry, plasma etching processes using fluorocarbon-based gases are being designed to have higher selectivity and ion energy. Generally, to have a higher selectivity to the mask material, a more polymerizing gas (i.e. low F/C ratio gas) is used [1, 2], and therefore the removal of etching residues formed inside the pattern after the etching process has a crucial effect on the performance of the semiconductor devices. As the pattern size becomes smaller, there is an area that cannot be cleaned by the conventional wet cleaning method. Recently, various dry-cleaning techniques using plasma radicals and ions have been proposed [3, 4]. However, for precise control and understanding of residue removal, a detailed compositional analysis of the etching residue must be performed. These studies are also very important in evaluating the effectiveness of dry-cleaning. However, little research has been done to investigate the characteristics of etching residues formed inside the nano-scale patterns (i.e. sidewall and bottom) in much detail.

In this work, we conducted a study on the characteristics of the etching residues formed inside the nano-scale patterns. A C₄F₈/CH₂F₂/O₂/Ar mixture gas plasma was used to form a high-aspect-ratio silicon dioxide contacts (HARCs) on a silicon wafer. The chemical compositions and binding states of etching residues inside the patterns were examined by an x-ray photoelectron spectroscopy (XPS) with angle changes in detail. To investigate the formation of etching residues, the plasma characteristics (i.e. radicals, ions and electrons) were examined in parallel using an optical emission spectroscopy (OES) and a Langmuir probe (LP) system.

As a result of the analysis, it was observed that the etching residues formed on the sidewalls of the line and hole patterns changed to the same tendency. At the same time, it was confirmed that depending the etched depth, the composition of the residue on the sidewall of holes and lines changed.

[1] Takahashi, Kunimasa, Masaru Hori, and Toshio Goto. "Fluorocarbon radicals and surface reactions in fluorocarbon high density etching plasma. I. O2 addition to electron cyclotron resonance plasma employing CHF3." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 14.4 (1996): 2004-2010.

[2] Kwon, B. S., et al. "Ultrahigh selective etching of SiO2 using an amorphous carbon mask in dual-frequency capacitively coupled C4F8/CH2F2/O2/Ar plasmas." Journal of The Electrochemical Society 157.3 (2010): D135-D141.

[3] Koh, Kyongbeom, et al. "Quasi atomic layer etching of SiO2 using plasma fluorination for surface cleaning." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 36.1 (2018): 01B106.

[4] Cagomoc, Charisse Marie D., et al. "RF plasma cleaning of silicon substrates with high-density polyethylene contamination." Japanese Journal of Applied Physics 57.1S (2017): 01AB04.