Wet chemical etching of AlN and Sc0.2Al0.8N thin films

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Title: Wet chemical etching of AlN and Sc0.2Al0.8N thin films
Alternative title: AlN ja Sc0.2Al0.8N ohutkalvojen märkäkemiallinen etsaus
Author: Airola, KonstaPetteri
Other contributor: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta
University of Helsinki, Faculty of Science
Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten
Publisher: Helsingin yliopisto
Date: 2022
Language: eng
URI: http://urn.fi/URN:NBN:fi:hulib-202206282967
Thesis level: master's thesis
Degree program: Materiaalitutkimuksen maisteriohjelma (Materials Research)
Master 's Programme in Materials Research
Magisterprogrammet i materialforskning
Specialisation: Epäorgaaninen materiaalikemia
Inorganic Materials Chemistry
Oorganisk materialkemi
Abstract: Aluminium nitride is a piezoelectric material commonly used in piezoelectric microelectromechanical systems (MEMS) in the form of thin films deposited by sputtering. AlN-based devices are found in wireless electronics in the form of acoustic filters, but they also have prospective applications in a wide variety of sensor systems. To enhance the piezoelectric properties of AlN, some of the Al can be replaced with scandium, which is required for next-generation devices. However, addition of Sc makes both the deposition and patterning of the film more difficult. This work focuses on patterning of AlN and Sc0.2Al0.8N thin films with wet etching. Both materials are etched anisotropically, which in theory enables etching the materials with little deviation from the mask dimensions. However, in practise, undercutting at the mask edges occurs easily making the structures narrower compared to the etch mask. This work investigates and compares the mechanisms and etch rates of AlN and Sc0.2Al0.8N. Tetramethyl ammonium hydroxide was mostly used for etching, but also H3PO4 and H2SO4 were tested. Addition of 20 atom-% Sc lowered the etch rate of the material and resulted in more undercutting. The causes behind mask undercutting were examined by using 11 differently deposited etch masks, and the undercutting was minimized by optimizing the mask deposition, using thermal annealing, and optimizing the etching temperature. Finally, the work identifies and discusses the relevant factors in depositing and patterning the AlN, ScxAl1-xN and mask films.
Subject: AlN
thin film
wet etching

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