Influences of laser energy density and annealing on structure properties of AIN films prepared by pulsed laser deposition

Abstract

Aluminum nitride (AlN) films with h<100> crystalline orientation are fabricated on p-Si (100) substrates at room temperature by pulsed laser deposition. The effects of laser energy density and annealing on the quality of the films are studied byx-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The crystalline quality of AlN films is improved considerably by increasing the laser energy density while there is increased number of farraginous particles on the surface. The annealing treatment at 600ºC produces a recrystallization process in the film, characterized by the improvement of the original crystallinity, the appearance of new crystalline orientations, and the increase of the crystallites.The surface becomes rougher due to the increase of the grain size during annealing.Due to their unique properties of wide band gap (6.2eV), high resistivity (10 13 cm), high thermal conductivity (320W/mK), high hardness and chemical inertness, aluminum nitride (AlN) films have been widely used for applications in micro-electronic and optoelectronic devices such as high power and high temperature devices, short wavelength emitters, dielectric layers in integrated circuits and surface acoustic wave (SAW) devices [1][2][3][4][5][6] . In addition, AlN films can also be good buffer layers for the epitaxial growths of GaAs and GaN [7,8] . The preparation of AlN films with high quality is indispensable to enhance the performances of these devices. Such techniques as chemical vapor deposition (CVD) [9] , metal-organic chemical vapor deposition (MOCVD) [10,11] , molecular beam epitaxy (MBE) [12,13] , and pulsed laser deposition (PLD) [2,[14][15][16] are used to prepare AlN films. Among these, PLD has been one of the most frequently used techniques to obtain AlN thin films with required properties because it is easy to control the parameters accurately with computers. The ablated species arrive at the substrate surface with high kinetic energies which are enough to induce migration and crystallization even at low temperature. Additionally, a post-annealing process can enhance some properties of polycrystalline AlN films by reducing the residual stress [17] . There are few reports about the effects of laser energy density and post-annealing treatment on the structure of AlN films.In this paper, we carry out research on the crystal and surface morphological characters of AlN films prepared by PLD. Efforts have been made to investigate the differences of the structural properties with different laser energy density and the changes as a result of annealing. The influence of pulse repetition rate on the films is also investigated.The deposition of AlN films was performed at room temperature under 5 Pa N 2 (99.999%) in a vacuum chamber with a residual pressure of 5×10 -6 Pa. A KrF excimer laser (TuiLaser, ThinFilmStar20, =248 nm, =20 ns) ablated a hot sintered AlN ceramic target at an incidence angle of 45°w ith various energy density and the pulse repetition rate of 5 Hz. The target was parallel to...