[CCoE Notice] Dissertation Announcement: Qinzhen Hao

[Apple, Carl]

[Dissertation Defense Announcement at the Cullen College of Engineering]
Plasma-Assisted Atomic Layer Etching of Si in Cl and Br-Containing Plasma

Qinzhen Hao

June 17, 2025; 10:00 AM – 1:00 PM

Location: Mechanical Engineering Conference Room 202
Microsoft Teams Link: https://urldefense.com/v3/__https://teams.microsoft.com/l/meetup-join/19*3ameeting_NDMwYTk3ZDktZDgyZi00YjdjLWFmOTgtYThlZjU0MWJkZTZm*40thread.v2/0?context=*7b*22Tid*22*3a*22170bbabd-a2f0-4c90-ad4b-0e8f0f0c4259*22*2c*22Oid*22*3a*220e3ff7cf-7965-4066-aadb-29ebe11a7c26*22*7d__;JSUlJSUlJSUlJSUlJSUl!!LkSTlj0I!D8c8xfX62RVwwb8r2L4aQbQyU3zv3obIHy1MxeR9c44eBI7UhED6msd3bLkvPvBrqS-40WibhWf5Ju6sKrhezY5X$ 

Committee Chair:
Vincent Donnelly, Ph.D.
Committee Members:
Demetre Economou, Ph.D. | Michael Nikolaou, Ph.D. | Mehmet Orman, Ph.D. |
Qiang Wang, Ph.D.
Abstract
Atomic-scale precision in silicon plasma etching is indispensable for the fabrication of next-generation three-dimensional (3D) semiconductor devices. Yet plasma-assisted atomic layer etching (PA-ALE) continues to be limited by low throughput, poor self-limiting behavior, and an incomplete understanding of surface kinetics. My research tries to address these challenges through a systematic study performed in a modified continuous-wave (CW) inductively coupled plasma (ICP) reactor. Time-resolved, in-situ optical emission spectroscopy (OES) is established as a quantitative tool of surface reactions during ALE cycles employing Cl₂, HBr, and Br₂ chemistries. The measurements show that SiCl₂ and SiCl constitute the primary products in Cl₂-based ALE. Two process sequences—gas dosing and plasma gas dosing—are explored and compared: pseudo-self-limiting behavior emerges in HBr plasma gas dosing cycles, whereas Br₂ have greater Br surface coverage and higher etch rates under gas-dosing conditions compared to HBr. Because HBr have high sticking coefficients, gas residence time experiments reveal a two-stage purge consisting of a volume-limited decay followed by wall retention limited desorption; wall passivation via temperature control, Ar/SF₆/O₂ conditioning, and increased total gas flow rate substantially shortens the wall retention time.
Moreover, fast-pulsed substrate bias with continuous gas flow effectively decouples the dose and etch steps, eliminating mechanical gas-pulsing system and markedly increasing throughput. Simultaneously tracking the ALE percentage and the bias-on integrated intensity of primary products’ OES lines enables evaluation of both self-limiting fidelity and etch rate. Collectively, this work elucidates the primary reaction products and pathways in Si ALE for multiple halogen chemistries, delivers robust, high-throughput recipes that achieve sub-nm precision with cycle times below 2 s, and provides diagnostic and hardware guidelines transferable to other ICP tools. These advances are promising to expedite the transition of PA-ALE from lab to high-volume manufacturing, making a further step to achieve damage-free patterning of sub-10 nm features for future logic and memory devices.

[Engineered For What's Next]


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