Effect of beam voltage on the properties of aluminium nitride prepared by ion beam assisted deposition

Abstract

The effects of nitrogen-beam voltage on the structure, stress, energy band gap and hardness of AIN thin films deposited on Si (1 1 1), Si (1 00) and sapphire (0001) by ion beam assisted deposition (IBAD) are reported. As the nitrogen-beam voltage was increased from 50 to 200 V, the stress and disorder in the AIN films increased as determined by X-ray diffraction, FTIR and Raman spectroscopy. The preferred orientation of the film's c-axis changed from completely normal to the film at 100 V, to a mixture of normal and in the plane of the film at 200V. For AIN films deposited under the same conditions, the films were more highly oriented on sapphire (000 1) than in Si (1 1 1). The hardness of the films increased from 18.2 to 23.7 GPa with the nitrogen-beam voltage, and possible reasons for this change in hardness are considered. IntroductionAluminium nitride a wurtzite structure, wide energy band gap (6.2 eV) semiconductor -has many valuable physical properties for electronic, optoelectronic and acoustoelectronic devices, including high thermal conductivity (theoretically as high as 3.2 W m t K-t [1]), high electrical resistivity [2], high ultrasonic velocity and negative electron affinity [3]. Device applications using these properties remain largely undeveloped due to the difficulty in producing high quality A1N thin films with smooth morphologies over large areas. Two obstacles to improving AlN thin film quality are the high susceptibility of AIN to impurity incorporation (particularly oxygen), and the difficulty of depositing stoichiometric, crystalline A1N at a low substrate temperature. Aluminium nitride thin films have been prepared by many methods, including chemical vapour deposition [4 6], gas-source molecular beam epitaxy [7,8], magnetron sputtering [9, 10], and ion beam assisted deposition (IBAD) [11,12].The present IBAD study of A1N was undertaken to determine how the properties of A1N are affected by the energy of the ion beam (in this case nitrogen) and to examine the capabilities of IBAD in producing electronic grade thin films. This work focuses on the

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