Etching of Silicon, Silicon Nitride, and Atomic Layer Etching of Silicon Dioxide using Inductively Coupled Plasma Beams



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Selective, anisotropic etching of silicon nitride (SiN) over Si or SiO2 is vital for fin field-effect transistor (FinFET) fabrication. Anisotropic etching with high selectivity of SiN over Si, and moderate selectivity over SiO2, can be achieved by ion-assisted etching using hydrofluorocarbon gases, such as CH3F, often with addition of O2. Despite the importance of this process, studies of the basic plasma chemistry and plasma-surface interactions when using these gases are largely lacking. Furthermore, fabrication of devices with feature sizes below 10 nm requires manufacturing with atomic level precision, making Atomic Layer Etching (ALE) indispensable for nano-device fabrication.
Silicon nitride (SiN) film (300 nm-thick) on Si substrate (wafer), Si film (10 nm) on Ge film (1000 nm) on Si-substrate (wafer) stack, and p-type Si substrates, were exposed to plasma beams emanating from CH3F/O2 or CH3F/CO2 inductively coupled plasmas (ICPs). Conditions within the plasma beam source were maintained at power of 300 W, pressure of 10 mTorr and total flow rate of 10 sccm. X-ray photoelectron spectroscopy (XPS) was used to determine the near surface chemical composition as well as the thickness of Si on Ge in addition to the thickness of hydrofluorocarbon polymer films formed on p-Si and SiN at low %O2 or %CO2 additions. Faster etching rates were measured in CH3F/CO2 than CH3F/O2 plasmas above 70% O2 or CO2 addition. The removal of the top Si film in the Si/Ge/Si-substrate stack stopped after a loss of ~ 3 nm, regardless of plasma beam exposure time and %O2 or %CO2 addition. Atomic layer etching (ALE) of SiO2 was studied by alternating exposure of a 5 nm-thick SiO2 film on a Si substrate to (1) a plasma beam emanating from a c-C4F8 inductively coupled plasma (ICP), to grow a fluorocarbon (FC) film composed mainly of CF2, and (2) an energetic (130 eV) Ar+ ion beam extracted from a separate Ar ICP. A very thin (3-6 Å), near self-limiting thickness CF2-rich FC film was found to deposit on the SiO2 surface. Exposure of the thin film to the Ar+ beam led to removal of 1.9 Å SiO2/cycle over multiple ALE cycles.



Atomic Layer Etching, Fluorocarbon Plasmas, Etching, X-ray Photoelectron Spectroscopy, Silicon, Silicon Nitride, Silicon Dioxide, Hydro-fluorocarbon plasmas


Portions of this document appear in: Kaler, Sanbir S., Qiaowei Lou, Vincent M. Donnelly, and Demetre J. Economou. "Silicon nitride and silicon etching by CH3F/O2 and CH3F/CO2 plasma beams." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 34, no. 4 (2016): 041301. And in: Kaler, Sanbir S., Qiaowei Lou, Vincent M. Donnelly, and Demetre J. Economou. "Atomic layer etching of silicon dioxide using alternating C4F8 and energetic Ar+ plasma beams." Journal of Physics D: Applied Physics 50, no. 23 (2017): 234001.