Impact of annealing temperature on the mechanical and electrical properties of sputtered aluminum nitride thin films

Abstract

Aluminium nitride (AlN) is a promising material for challenging sensor applications such as process monitoring in harsh environments (e.g., turbine exhaust), due to its piezoelectric properties, its high temperature stability and good thermal match to silicon. Basically, the operational temperature of piezoelectric materials is limited by the increase of the leakage current as well as by enhanced diffusion effects in the material at elevated temperatures. This work focuses on the characterization of aluminum nitride thin films after post deposition annealings up to temperatures of 1000 °C in harsh environments. For this purpose, thin film samples were temperature loaded for 2 h in pure nitrogen and oxygen gas atmospheres and characterized with respect to the film stress and the leakage current behaviour. The X-ray diffraction results show that AlN thin films are chemically stable in oxygen atmospheres for 2 h at annealing temperatures of up to 900 °C. At 1000 °C, a 100 nm thick AlN layer oxidizes completely. For nitrogen, the layer is stable up to 1000 °C. The activation energy of the samples was determined from leakage current measurements at different sample temperatures, in the range between 25 and 300 °C. Up to an annealing temperature of 700 °C, the leakage current in the thin film is dominated by Poole-Frenkel behavior, while at higher annealing temperatures, a mixture of different leakage current mechanisms is observed.

Review—Investigation and Review of the Thermal, Mechanical, Electrical, Optical, and Structural Properties of Atomic Layer Deposited High-kDielectrics: Beryllium Oxide, Aluminum Oxide, Hafnium Oxide, and Aluminum Nitride

“…[201][202][203][204] Interestingly, recent investigations of the electrical properties of sputter deposited and PEALD AlN have also reported electrical leakage to occur predominantly by the PF mechanism. [205][206][207] More recent electrically detected magnetic resonance (EDMR) measurements by Mutch et al have conclusively shown that electron transport in PECVD SiN:H specifically occurs through silicon dangling bond defect states located in the mid-upper portion of the SiN bandgap. 208,209 Owing to the similar IV characteristics, deduced leakage mechanism, and band structure, 210 it seems plausible that electron transport in amorphous AlN (independent of deposition method) may also occur through Al dangling bond defect states.…”

Reduction of dislocation density of aluminium nitride buffer layer grown on sapphire substrate

“…This is evidence that annealing releases the stress in the film and decreases the stress effect on the crystal lattice [14]. AlN annealed at 700°C showed improved electrical properties, whereby the flatband voltages (VFB) value was positive and the peak intensity increased [15]. Post-deposition rapid thermal annealing between 900°C and 1300°C showed a reduction of defects in the AlN thin films' crystallization process and was identified by the increase of grain size of the original crystallites as well as the growth of new small grains exhibiting tensile strain [16].…”

Harsh Environmental Surface Acoustic Wave Temperature Sensor Based on Pure and Scandium doped Aluminum Nitride on Sapphire

“…The distance between target and substrate is fixed at 65 mm. The parameters were chosen based on pre-investigations for good caxis orientation [7,11]. The total film thickness h is 2 µm.…”

“…AlN promises operation up to 700°C even in pure oxygen atmosphere for two hours without measureable film degeneration [7]. Whereas, AlScN has a higher d33 and therefore the electromechanical coupling factor is increased by a factor of ~3, compared to pure AlN [8][9][10].…”