Structural and electroacoustic studies of AlN thin films during low temperature radio frequency sputter deposition

AIN is a material used in a wide variety of applications such as electroacoustic devices, blue diodes, IR windows, thermal conductors, metal-insulator-semiconductor structures, integrated circuit packaging, etc. In this work thin piezoelectric AIN polycrystalline films have been grown on Si and SiO2 using rf magnetron sputter deposition in an Ar/N-2 gas mixture. The structural properties of the film have been optimized by varying the deposition parameters, such as process pressure, gas mixture, substrate temperature, discharge power, etc. [K. Tominaga et al., Jpn. J. Appl. Phys., Part 1 35, 4972 (1996); H. Okana et al., ibid. 31, 3446 (1992); K. Kazuya, T. Hanabusa, and K. Tominaga, Thin Solid Films 281-282, 340 (1996)]. It was found that the best film texture was obtained for a particular set of parameters, namely process pressure of 4 mTorr, substrate temperature 350 degreesC, discharge power 350 W, and a gas mixture of 25% Ar and 75% N-2. The films as examined by x-ray diffraction exhibited a columnar structure with a strong (001) texture, and a fall width at half maximum (FWHM) rocking curve of 1.6 degrees. Atomic force microscopy measurements indicated a surface roughness with a rms value of 8 Angstrom. Classical nonapodized transversal surface acoustic wave filters operating at a frequency of 534 MHz were fabricated to characterize the electroacoustic properties of the films. The measurements indicated a coupling coefficient of 0.37% and a phase velocity of 4900 m/s. Further, thin epitaxial films were grown on (001)alpha -Al2O3 (sapphire) under the same deposition conditions except the substrate temperature. The films exhibited a (001)AlN//(001)alpha -Al2O3 plane orientation with a (002) rocking curve FWHM value of about 0.4 degrees, showing a relatively good alignment of the c axis. The in-plane orientation was [110]AlN//[120]alpha -Al2O3 corresponding to a rotation of the AIN film of 30 degrees with respect to the (001)alpha -Al2O3 surface. Cross-sectional transmission electron microscopy studies indicated a population of both thread and edge dislocations with decreasing concentrations with film thickness. (C) 2001 American Vacuum Society.

[1]  H. Ahn,et al.  Effect of the substrate bias voltage on the crystallographic orientation of reactively sputtered AlN thin films , 1994 .

[2]  H. Okano,et al.  Preparation of c-Axis Oriented AlN Thin Films by Low-Temperature Reactive Sputtering , 1992 .

[3]  T. Hirai,et al.  Synthesis and Surface Acoustic Wave Properties of AlN Thin Films Fabricated on (001) and (110) Sapphire Substrates Using Chemical Vapor Deposition of AlCl3–NH3 System , 1997 .

[4]  H. M. Liaw,et al.  The characterization of sputtered polycrystalline aluminum nitride on silicon by surface acoustic wave measurements , 1995, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[5]  H. Morkoç,et al.  Progress and prospects for GaN and the III–V nitride semiconductors , 1993 .

[6]  Y. Ide,et al.  Control of preferential orientation of AlN films prepared by the reactive sputtering method , 1998 .

[7]  H. Okano,et al.  GHz-Band Surface Acoustic Wave Devices Using Aluminum Nitride Thin Films Deposited by Electron Cyclotron Resonance Dual Ion-Beam Sputtering , 1993 .

[8]  Toshio Hirai,et al.  Synthesis of AlN Thin Films on Sapphire Substrates by Chemical Vapor Deposition of AlCl3–NH3 System and Surface Acoustic Wave Properties , 1996 .

[9]  M. Niigaki,et al.  Growth of AlN films by magnetron sputtering , 1998 .

[10]  K. Kusaka,et al.  Effect of nitrogen gas pressure on residual stress in A1N films deposited by the planar magnetron sputtering system , 1996 .

[11]  Charles G. Sodini,et al.  Low‐Temperature Deposition of Highly Textured Aluminum Nitride by Direct Current Magnetron Sputtering for Applications in Thin‐Film Resonators , 1999 .

[12]  A. Hårsta,et al.  Synthesis of highly oriented piezoelectric AlN films by reactive sputter deposition , 2000 .

[13]  Akira Kawabata,et al.  Low‐temperature growth of piezoelectric AlN film by rf reactive planar magnetron sputtering , 1980 .

[14]  I. Mori,et al.  Gas Pressure Dependence of AlN Film Properties in Alternating Sputtering System , 1996 .

[15]  W. Tsai,et al.  Growth of ZnO thin films on interdigital transducer/Corning 7059 glass substrates by two-step fabrication methods for surface acoustic wave applications , 1998 .

[16]  T. Shiosaki,et al.  Piezoelectric thin films for saw applications , 1982 .