Voltage waveform tailoring for high aspect ratio plasma etching of SiO₂ using Ar/CF₄/O₂ mixtures: Consequences of ion and electron distributions on etch profiles

Journal Article · Fri Dec 30 00:00:00 EST 2022 · Journal of Vacuum Science and Technology A

DOI:https://doi.org/10.1116/6.0002290· OSTI ID:2331488

Krüger, Florian ^[1]; Lee, Hyunjae ^[2]; Nam, Sang Ki ^[2]; Kushner, Mark J. ^[3]

---

1. Univ. of Michigan, Ann Arbor, MI (United States); University of Michigan
2. Samsung Electronics Corporation, Ltd., Hwaseong-si (Korea, Republic of). Mechatronics R&D Center
3. Univ. of Michigan, Ann Arbor, MI (United States)

The quality of high aspect ratio (HAR) features etched into dielectrics for microelectronics fabrication using halogen containing low temperature plasmas strongly depends on the energy and angular distribution of the incident ions (IEAD) onto the wafer, as well as potentially that of the electrons (EEAD). Positive ions, accelerated to high energies by the sheath electric field, have narrow angular spreads and can penetrate deeply into HAR features. Electrons typically arrive at the wafer with nearly thermal energy and isotropic angular distributions and so do not directly penetrate deeply into features. These differences can lead to positive charging of the insides of the features that can slow etching rates and produce geometric defects such as twisting. In this work, we computationally investigated the plasma etching of HAR features into SiO₂ using tailored voltage waveforms in a geometrically asymmetric capacitively coupled plasma sustained in an Ar/CF₄/O₂ mixture at 40 mTorr. The tailored waveform consisted of a sinusoidal wave and its higher harmonics with a fundamental frequency of 1 MHz. We found that some degree of control of the IEADs and EEADs is possible by adjusting the phase of higher harmonics φ through the resulting generation of electrical asymmetry and electric field reversal. However, the IEADs and EEADs cannot easily be separately controlled. The control of IEADs and EEADs is inherently linked. The highest quality feature was obtained with a phase angle φ = 0° as this value generated the largest (most negative) DC self-bias and largest electric field reversal for accelerating electrons into the feature. That said, the consequences of voltage waveform tailoring (VWT) on etched features are dominated by the change in the IEADs. Although VWT does produce EEADs with higher energy and narrower angular spread, the effect of these electrons on the feature compared to thermal electrons is not large. Finally, this smaller impact of VWT produced EEADs is attributed to thermal electrons being accelerated into the feature by electric fields produced by the positive in-feature charging.

• Research Organization: Univ. of Michigan, Ann Arbor, MI (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: SC0020232
• OSTI ID: 2331488
• Journal Information: Journal of Vacuum Science and Technology A, Journal Name: Journal of Vacuum Science and Technology A Journal Issue: 1 Vol. 41; ISSN 0734-2101
• Publisher: American Vacuum Society / AIP
• Country of Publication: United States
• Language: English

Related Subjects

47 OTHER INSTRUMENTATION
Monte Carlo methods
electric field reversal
etching
etching simulator
high aspect ratio etching
microelectronics
plasma etching
plasma processing
plasma properties and parameters
plasma sheath
plasma simulation
plasma sources
voltage waveform tailoring