Development of preferred orientation in polycrystalline AlN thin films deposited by rf sputtering system at low temperat
- PDF / 329,931 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 46 Downloads / 186 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Development of preferred orientation in polycrystalline AlN thin films deposited by rf sputtering system at low temperature A. Rodr´ıguez-Navarroa) Instituto Andaluz de Ciencias de la Tierra-CSIC, Campus de Fuentenueva, 18002 Granada, Spain
W. Ota˜no-Rivera Materials Research Lab., The Pennsylvania State University, University Park, Pennsylvania 16802
J. M. Garc´ıa-Ruiz Instituto Andaluz de Ciencias de la Tierra-CSIC, Campus de Fuentenueva, 18002 Granada, Spain
R. Messier and L. J. Pilione Materials Research Lab., The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 14 August 1996; accepted 23 December 1996)
The development of preferred orientation in AlN thin films deposited on silica glass substrates by rf sputtering at low substrate temperature (,150 ±C) has been studied. The main factors controlling the preferential orientation of the AlN thin films are the ion-bombardment energies, incidence angle of the arriving particles, and deposition rate. At low pressure, a perpendicular and highly directional energetic ion-bombardment induces an orientation of the crystallites with their c-axis perpendicular to the substrate surface. At higher pressure (.15 mTorr), a spreading in the incidence angle of the arriving particles, due to gas phase collisions, favors the formation of AlN crystal ° ¢ twinning. A change in the preferred orientation of the films from (0001) to 1011 for ˚ is observed. deposition rates above 1.8 Ays
I. INTRODUCTION
There has been considerable interest in the growth of aluminum nitride (AlN) thin films for fabrication of surface acoustic wave devices,1 photonic detectors,2 as well as other applications3 due to its high ultrasonic velocity and piezoelectricity, chemical inertness, and wide band gap (6.2 eV). AlN crystallizes with a hexagonal compact structure (wurtzite-type). For many of these applications, an adequate control of the crystallographic orientation and microstructure is desirable, since the final properties of the films are strongly dependent on the orientation of the crystal grains and texture. In this paper we study some mechanisms that control the development of a preferred orientation in AlN thin films. II. EXPERIMENTAL PROCEDURE
AlN polycrystalline thin films were deposited on silica glass substrates using a rf (13.56 MHz) reactive diode sputtering system at low substrate temperature (,150 ±C). Using a cryogenic high vacuum pump, the system routinely achieved a base pressure below 2 3 1027 Torr. Water-cooled 3-inch 99.999% pure Al target and argon/nitrogen gas mixtures were used. In order to clean the Al target, a presputtering process was carried
out before each set of experiments. Typical sputtering conditions are shown in Table I. To study the ion-bombardment processes, a planar electrostatic probe4 in the configuration of our substrate5 was used to measure the substrate bias potential sVsb d, with respect to the ground. Deposition rates were obtained by measuring the thickness of the films with a
Data Loading...
