A comparison of pulsed-laser-deposited and ion-beam-enhanced-deposited AlN thin films for SOI application

Aluminum nitride (AlN) thin films have attracted interests as the buried dielectric layer in silicon-on-insulator (SOI) substrates. The precondition for this application is that AlN films have smooth surfaces for wafer bonding and excellent insulation properties. In this work, AlN films synthesized by pulsed-laser deposition (PLD) and ion-beam-enhanced deposition (IBED) techniques are compared under the concern of their suitability for SOI application. Both PLD-deposited and IBED-deposited AlN films exhibit smooth surface morphologies. However, AlN films show quite different electrical properties due to different microstructures: microcrystalline wurtzite by PLD but amorphous by IBED. PLD AlN films have high leakage current and high dynamic charge densities. In contrast, IBED films have low leakage current and the breakdown field is about 2.1 MV/cm. Moreover, after postannealing at 800-1100 deg. C, the breakdown field exceeds 4 MV/cm and the leakage current is reduced nearly two orders in magnitude. We conclude that IBED is more suitable technique to fabricate AlN films as buried insulators in SOI substrates