Mechanisms for the Deposition of Thin Metallic Films by Laser Driven Gas Phase Reactions
- PDF / 1,417,158 Bytes
- 5 Pages / 417.6 x 639 pts Page_size
- 38 Downloads / 155 Views
MECHANISMS FOR THE DEPOSITION OF THIN METALLIC FILMS BYLASER DRIVEN GAS PHASE REACTIONS T. R. JEkVIS, S. K. MENON*, E. L. JOYCE, and D. W. CARROLL Materials Science and Technology Division, Mailstop E549, Los Alamos National Labordtory, Los Alamos, NM87545 *Present Address: Naval Chemical & Metallurgical Laboratory, Naval Dockyard, Tiger Gate, Bombay 400023, India.
ABSTRALI
6as phase processing rakes laser deposition over large areas possible but homogeneous nucleation of large atomic clusters must be avoided if films are to be proauced. Clusters can be highly variable in size from a few atoms to significant fractions of a micrometer. If conditions do not allow for coriplete quenching of the clusters produced in the gas phase, these clusters can arrive at the substrate with sufficient energy to self sinter into horoenecus films which are substantially different from metallic films grown by thermal techniques. Using transmission electron microscopy (TEM), we have characterized the microstructure of thin metallic films deposited by laser breakdown chemical vapor deposition and identified a range of ueposition conditions which can lead from powders to homogeneous polycrystalline films and mixed phase materials. Gas phase nucleation is aeperaent on reactant partial pressures and the gas phase quench rate which car be varied in part by adjusting the H2 content of the source gas. Manipulation of these parameters can vary powder size from about one inicioraeter to less than 2 nanometers. Variation of the quench rate durino the aeposition of polycrystalline films varies the grain size in the films. heating the substrate drastically changes the conditions under which the film is formed and as a consequence, can radically alter the microstructure oi the filrai itself.
I NTRODUCTION
The use of gas phase laser chemical vapor deposition (CVD) techniques holds substantial promise for large area, low temperature depositions in the sem.iconouctor and energy fields. However, films with suitable electrical and structural properties must be produced. In these techniques, a laser L-eam activates chemical precursors in the gas phase, resulting in chemical reactions which lead to the deposition of a thin film. The substrate is held at a temperature below that necessary for thermal deposition from the precursors. Because the overall gas and substrate temperatures are low, the possibility of homogeneous gas phase nucleation and growth exists. Indeed, deposition results through a competing combination of gas phase and surface processes. The control of gas phase nucleation is a key factor in the applicability of these techniques to production processes. We have studied the effect of gas phase nucleation on the microstucture of thin films deposited by laser breakdown chemical vapor deposition[l], but trhegeneral conclusions of this study are applicable to other gas phase laser techniques as well[2,3j. The microstructure of laser deposited films is substantially different from that of thermally deposited films, which is largely determined
Data Loading...
