Characteristics of Palladium Thin Films Deposited by the Ionized Cluster Beam Technique
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CHARACTERISTICS OF PALLADIUM THIN FILMS DEPOSITED BY THE IONIZED CLUSTER BEAM TECHNIQUE MARIA HUFFMAN*, T.S. KALKUR**, L. KAMMERDINER*, R. KWOR**, L.L. LEVENSON-**, AND M. REEDER* *Ramtron Corparation, 1850 Ramtron Drive, Colorado Springs, CO 80921 "**Departmentof Electrical and Computer Engineering, University of Colorado, Colorado Springs, CO 80833-7150 ***Department of Physics and Energy Science, University of Colorado, Colorado Springs, CO 80933-7150 ABSTRACT An ionized cluster beam (ICB) source was used to deposit Pd onto oxidized silicon substrates. The ICB source was operated in both the neutral mode (no ionization and no acceleration) and in the ICB mode with ionization and acceleration voltages at 3 kV and 6 kV. Also, substrate temperatures were varied between 100*C and 400'C. The Pd film thicknesses were generally between 1,200A and 1,800A, with one film thickness about 500A. The films were examined by transmission electron microscopy (TEM), transmission electron diffraction (TED), and x-ray diffraction (XRD). Grain size measurements by TEM and XRD showed that ionization and acceleration of Pd resulted in a slight increase in grain size compared to films deposited without ionization or acceleration at any substrate temperature. However, the grain size increased significantly as the substrate temperature rose. XRD showed that all ICB deposited Pd films have significant (111) texturing as determined by comparison to XRD data for Pd powder. For Pd films deposited at 400'C, almost all grains were oriented with the (111) planes parallel to the substrate surface. The electrical conductivity of all Pd films was comparable to that of bulk Pd.
INTRODUCTION The microstructure of thin films is known, both theoretically and experimentally, to depend on deposition conditions [1-5]. Two main parameters influence film structure. One of these parameters is the ratio T/Tm, where T is the substrate temperature and Tm is the melting point of the film material. The other important parameter is the kinetic energy of the impinging atoms. T/Tm is related to the surface mobility of surface atoms and grain boundaries during film growth. The kinetic energy of impinging atoms can increase the surface mobility of surface atoms [6] as well as produce dense films of high crystal quality [7-9]. Here, we report on the influence of these parameters on the structure of Pd films deposited on oxidized silicon substrates by ICB.
EXPERIMENTAL The ionized cluster beam (ICB) technique has been described by Takagi [10,111. A commercial ICB apparatus manufactured by Mitsubishi Electric Corporation was used for the8 deposition of Pd. This apparatus was cryopumped and had a base pressure of about 3x10Torr. During Pd deposition the ambient pressure was about lxl0-7 Torr. A carbon crucible with a 2 mm diameter cylindrical nozzle and 2 mm long was used as the Pd source. The crucible inside diameter was 15 mm and the crucible cavity below the nozzle was 19.3 mm deep. The crucible was heated to approximately 2,000'C by electron bombardment. The Pd vap
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