The Research On Preparation Process, Microstructures And Properties Of AlN Thin Films Deposited By Reactive Magnetron Sputtering

AlN film has wide application potential in piezoelectric devices, optical devicesand microelectronic devices for its high acoustic propagation, excellent piezoelectricproperties, wide direct band gap, favorable thermal and chemical stability. Usuallypreferred orientation is required for these applications. But subject to a high growthtemperature, the film preparation technology does not match with the existingproduction process of electrical and optical devices. In this paper, high quality AlNfilms were deposited by reactive magnetron sputtering. The impact of processparameters on the structure and properties of AlN films under low temperatureconditions were studied. And the preferred orientation and oxygen content of AlNfilms have been controlled by changing sputtering atmosphere.AlN films were deposited without external heating by different sputtering powerof DC, Pulsed-DC and RF. The AlN film deposited by RF power was amorphous. AlNfilms prepared by Pulsed-DC and DC power both exhibited c-axis preferredorientation. Compared to the others, the AlN films fabricated by the Pulsed-DC powerhad a better crystallization property, a larger grain size and a higher transmittance.In the temperature range of75℃~521℃, AlN films showed a preferredorientation along the c axis and a high crystallization. In order to improve the qualityof AlN thin films deposited at low temperature, systematic study of the sputteringpower, pulse frequency, duty cycle and sputtering pressure on structures andproperties of AlN films was conducted. And the optimization process of preparingc-axis oriented AlN thin film is as follows: substrate temperature of75℃; sputteringpower of150W; pulse frequency of28kHz; duty cycle of40%and sputtering pressureof0.5Pa. High nucleation density and high energy particle bombardment during filmdeposition are good for low temperature crystallization of AlN thin films.Sputtering atmosphere plays a role in the control of AlN film preferredorientation. When the working gas was N2or the mixture of N2and Ar, the AlN filmsshowed c-axis preferred orientation. After H2was added to the mixture gases, the AlNfilm transited from c-axis to a-axis with the reduction of oxygen in the film. And thesurface morphology changed from pebble-like structure to worm-like structure.What’s more, the transmittance and adhesive strength were also enhanced by theintroduction of H2. But when the hydrogen content was above15%, AlN films cracked. Hydrogen realizes the control of the preferred orientation of AlN films by changingthe energy of deposited particles, chemical adsorption and physical adsorption on filmsurface.