Abstract
Use of atomic layer deposition (ALD) in microelectromechanical systems (MEMS) has increased as ALD enables conformal growth on 3-dimensional structures at relatively low temperatures. For MEMS device design and fabrication, the understanding of stress and mechanical properties such as elastic modulus, hardness and adhesion of thin film is crucial. In this work a comprehensive characterization of the stress, elastic modulus, hardness and adhesion of ALD aluminum oxide (Al2O3) films grown at 110-300 C from trimethylaluminum and water is presented. Film stress was analyzed by wafer curvature measurements, elastic modulus by nanoindentation and surface-acoustic wave measurements, hardness by nanoindentation and adhesion by microscratch test and scanning nanowear. The films were also analyzed by ellipsometry, optical reflectometry, X-ray reflectivity and time-of-flight elastic recoil detection for refractive index, thickness, density and impurities. The ALD Al 2O3 films were under tensile stress in the scale of hundreds of MPa. The magnitude of the stress decreased strongly with increasing ALD temperature. The stress was stable during storage in air. Elastic modulus and hardness of ALD Al2O3 saturated to a fairly constant value for growth at 150 to 300 C, while ALD at 110 C gave softer films with lower modulus. ALD Al2O3 films adhered strongly on cleaned silicon with SiOx termination.
Original language | English |
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Pages (from-to) | 124-135 |
Journal | Thin Solid Films |
Volume | 552 |
Early online date | 6 Dec 2013 |
DOIs | |
Publication status | Published - 2014 |
MoE publication type | A1 Journal article-refereed |
Funding
OMEY thanks Leif Grönberg and Antti Tolkki for guidance given in profilometer measurements. RLP thanks Prof. Steven George for discussion on the Al 2 O 3 ALD growth mechanism. Tatu Muukkonen is thanked for initiating the microscratch measurements. This work has been carried out within the MECHALD project funded by Tekes and is linked to the Finnish Centers of Excellence in Atomic Layer Deposition (ref. 251220) and Nuclear and Accelerator Based Physics (refs. 213503 and 251353) of the Academy of Finland. Parts of these results were presented in posters at the 12th AVS-ALD 2012 conference, June 17–20th, 2012, Dresden, Germany.
Keywords
- Adhesion
- Aluminum oxide
- Atomic layer deposition
- Elastic modulus
- Hardness
- Residual stress