Atomic layer deposition of AlN using atomic layer annealing—Towards high-quality AlN on vertical sidewalls

Abstract

Atomic layer deposition (ALD) of aluminum nitride (AlN) using in situ atomic layer annealing (ALA) is studied for microelectromechanical systems (MEMS). Effective piezoelectric in-plane actuation and sensing requires deposition of high crystal quality and (0002) oriented AlN on vertical sidewalls of MEMS structures. Previous studies have shown that the crystal quality of ALD AlN can be significantly improved using ALA but have not studied the conformal coverage or crystal quality on metal electrodes, which are required for piezoelectric MEMS devices. In this study, AlN thin films are deposited on Si, Al, Pt, and on vertical sidewalls etched into Si. The AlN microstructure and properties are studied using x-ray diffraction methods, transmission electron microscopy, and Fourier transform infrared spectroscopy. The conformal coverage is evaluated by measuring the film thickness on the vertical sidewalls. The effects of postdeposition annealing are studied as well. This study aims to enable effective piezoelectric actuation and sensing for MEMS sensors. The conformal coverage of the ALA ALD process is excellent and AlN has the best crystal quality and degree of orientation when deposited on Al. The as-deposited films contain oxygen impurities, which might be detrimental to the piezoelectric properties of AlN. Annealing at high temperatures reduced the number of impurities but did not improve the crystal quality.

In‐Plane AlN‐based Actuator: Toward a New Generation of Piezoelectric MEMS

“…[30] However, previously achieved ALD AlN films had quite weak piezoelectric response due to existing of randomly oriented grains in addition to the preferentially [0001] oriented grains. [31][32] Also, a strong relationship between underlying layer and AlN orientation has been reported. [31] In this work, MOCVD was used as a method for AlN deposition because of its superior capability for the growth of highquality textured c-axis oriented AlN on vertical surfaces.…”

“…[31][32] Also, a strong relationship between underlying layer and AlN orientation has been reported. [31] In this work, MOCVD was used as a method for AlN deposition because of its superior capability for the growth of highquality textured c-axis oriented AlN on vertical surfaces.…”

“…[ 31–32 ] Also, a strong relationship between underlying layer and AlN orientation has been reported. [ 31 ]…”

Unlocking the potential of piezoelectric films grown on vertical surfaces for inertial MEMS

“…To overcome this, deposition has been achieved by metalorganic chemical vapor deposition (MOCVD) or atomic layer deposition (ALD) of the piezoelectric AlN and metal electrodes. [11,12]. Fig.…”

Area-Selective Low-Pressure Thermal Atomic Layer Deposition of Aluminum Nitride

“…As native substrates of III-nitrides are hardly available (due to the difficulties with incorporating nitrogen), they are commonly grown on mismatched substrates involving thick buffer layers and high temperatures well above the back-end-of-line (BEOL) limit. , Atomic layer deposition (ALD) is a suitable candidate to investigate thin-film deposition of III-nitrides with a reduced thermal budget. In ALD, high conformality and large area uniformity with thickness control at a sub-monolayer scale are enabled by using sequential self-limiting vapor-solid reactions. ,− It has found use in numerous fabrication processes of devices and circuits with <10 nm feature sizes. − ,, Many authors have reported on ALD of Groups III–V (III–V) compounds since Nishizawa et al’s first paper on GaAs in 1985 (). ,, ALD of AlN commenced in the early 1990s with trimethylaluminum (TMA) as the metal precursor and ammonia (NH 3 ) as the nitrogen precursor. − Currently, a myriad of precursors, precursor combinations, and reactivity-enhancing techniques have been used to alter the ALD temperature window, limit the incorporation of impurities, and improve stoichiometry and crystallinity. Some authors using TMA as metal precursors have resorted to plasma-enhanced deposition to increase the reactivity of NH 3 at reduced temperatures. ,,,,− ,− One author has employed ultraviolet (UV) radiation during TMA injection...…”