Vertical and Lateral Etch Survey of Ferroelectric AlN/Al1-xScxN in Aqueous KOH Solutions

Tang, Zichen; Esteves, Giovanni; Zheng, Jeffrey; Olsson III, Roy H.

doi:10.3390/mi13071066

Vertical and Lateral Etch Survey of Ferroelectric AlN/Al_1-xSc_xN in Aqueous KOH Solutions

Journal Article · Sat Jul 02 00:00:00 EDT 2022 · Micromachines

DOI:https://doi.org/10.3390/mi13071066· OSTI ID:2469905

Tang, Zichen ^[1]; Esteves, Giovanni ^[2]; Zheng, Jeffrey ^[1]; ^[1]

University of Pennsylvania, Philadelphia, PA (United States)
Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States). Microsystems Engineering, Science and Applications (MESA)

Due to their favorable electromechanical properties, such as high sound velocity, low dielectric permittivity and high electromechanical coupling, Aluminum Nitride (AlN) and Aluminum Scandium Nitride (Al_1-xSc_xN) thin films have achieved widespread application in radio frequency (RF) acoustic devices. The resistance to etching at high scandium alloying, however, has inhibited the realization of devices able to exploit the highest electromechanical coupling coefficients. In this work, we investigated the vertical and lateral etch rates of sputtered AlN and Al_1-xSc_xN with Sc concentration x ranging from 0 to 0.42 in aqueous potassium hydroxide (KOH). Etch rates and the sidewall angles were reported at different temperatures and KOH concentrations. We found that the trends of the etch rate were unanimous: while the vertical etch rate decreases with increasing Sc alloying, the lateral etch rate exhibits a V-shaped transition with a minimum etch rate at x = 0.125. By performing an etch on an 800 nm thick Al_0.875Sc_0.125N film with 10 wt% KOH at 65 °C for 20 min, a vertical sidewall was formed by exploiting the ratio of the {$$10\overline{11}$$ planes and {$$1\overline{1}00$$ planes etch rates. This method does not require preliminary processing and is potentially beneficial for the fabrication of lamb wave resonators (LWRs) or other microelectromechanical systems (MEMS) structures, laser mirrors and Ultraviolet Light-Emitting Diodes (UV-LEDs). It was demonstrated that the sidewall angle tracks the trajectory that follows the {$$\overline{1}2\overline{12}$$ of the hexagonal crystal structure when different c/a ratios were considered for elevated Sc alloying levels, which may be used as a convenient tool for structure/composition analysis.

View Accepted Manuscript (DOE)

Research Organization:: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF)

Grant/Contract Number:: NA0003525

OSTI ID:: 2469905

Journal Information:: Micromachines, Journal Name: Micromachines Journal Issue: 7 Vol. 13; ISSN 2072-666X

Publisher:: MDPICopyright Statement

Country of Publication:: United States

Language:: English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Chemistry
Instruments & Instrumentation
Physics
Science & Technology - Other Topics
aluminum nitride (AlN)
aluminum scandium nitride (AlScN)
ferroelectric
potassium hydroxide (KOH)
wet etch

Vertical and Lateral Etch Survey of Ferroelectric AlN/Al1-xScxN in Aqueous KOH Solutions

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Vertical and Lateral Etch Survey of Ferroelectric AlN/Al_1-xSc_xN in Aqueous KOH Solutions