Deposition of Thin Alumina Films from Supercritical Water Jets
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DEPOSITION OF THIN ALUMINA FILMS FROM SUPERCRITICAL WATER JETS
J. I. Brand and D. R. Miller Dept. of Applied Mechanics and Engineering Sciences, B-010 University of California, San Diego , La Jolla, Ca. 92093
ABSTRACT films are grown on a silicon substrate, in Thin alumina and at substrate vacuum, at a rate of about 10 1 per second, 1500C. Alumina is dissolved in supercritical temperatures below in a supersonic free water and the resulting solution expanded The films are is directed at the substrate. jet, which characterized by ESCA and FTIR
INTRODUCTION water to We recently reported on the use of supercritical jet expansion of this followed by a free dissolve alumina, solution to deposit thin films[l]. This is a technique developed [2), who grew particles and fibers of by Smith and colleagues Water above its critical point will polymers and silicas. dissolve sparingly soluble materials such as quartz and alumina. the solution pressure free jet expansion lowers The subsequent of the solute. Free jet causing precipitation rapidly, and commonly used for molecular expansions are well understood used to date for these beam studies [3]. At the pressures a strong normal supercritical expansions, the free jet forms through which the clustered species must pass before shock wave striking a surface or equilibrating with the ambient background. is not precipitation or clustering The kinetics of the understood, and certainly involves a non-equilibrium process. We model of the nozzle flow and completed a supersonic gas-dynamic solubilities as a first free jet expansion using equilibrium This model showed that, under proper conditions, approximation. such precipitation is thermodynamically prohibited from occurring before the exit of the nozzle and must occur within the free jet Further, our calculations showed that expansion or beyond [1). either a short capillary tube or a simple orifice in a plate could serve equally well as the nozzle. We have consistently grown thin films of alumina which hexagonal alpha phase. In this appear to be in the anhydrous, report, we discuss the vacuum facility we have recently completed expansions. We also report on to investigate the supercritical vacuum, instead the characterization of an alumina film grown in we have grown conditions. This film is the first of atmospheric tube nozzle. We using an orifice nozzle rather than a capillary of the jet source also present operating characteristics calculated using our gas-dynamic model.
Mat. Res. Soc. Symp. Proc. Vol. 131. '-1989Materials Research Society
618
IFS
DC
P
J
H 0__.-
._0 _
to mass specromter
C
SH
-760 torr10tn
10
f IlIter
Roots
3
pump
diffusion
H20pump 2
1. Schematic of Ceramic Beam and Film Growth Apparatus. HPSP = high pressure solvent pump; DC = dissolving cell; N = nozzle; FJ = free jet; SH = substrate holder; S = skimmer; C = chopper.
EQUIPMENT AND OPERATING CHARACTERISTICS Figure 1 shows the vacuum facility used for the present study. The first chamber is pumped by a 330 CFM Roots pump and can be operated at
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