Mesoscopic hemisphere arrays for use as resist in solid state structure fabrication

Abstract

The kinetics of formation of disordered arrays of hemispherically shaped islands of cesium chloride on an oxidized silicon wafer, starting from a deposited thin film of CsCl, has been investigated. The essential process step is the exposure of the CsCl thin film to water vapor. Transport of dissolved material in the adsorbed water layer occurs, driven by the size dependent solubility of CsCl. Growth rate is dominated by the kinetics of dissolution and deposition at the solid/solution boundary, rather than by interisland diffusion. The equipment and procedure are arranged so that constant humidity conditions prevail at every moment of hemisphere development. The process variables were: the effective thickness of the CsCl film, the relative humidity and the exposure time. The nature of the solid surface was found to be important and it was monitored using contact angle measurements of the water/solid interface: hydrophilic surfaces were used. The resulting arrays of hemispheres are characterized by a mean diameter, $\mathrm{〈d〉,}$ a standard deviation, and a fractional surface coverage, F. Arrays from $\text{〈d〉=450±145\hspace{0.05em}}\mathrm{\AA }$ at $\text{F=0.4}$ and $\text{2050±330\hspace{0.05em}}\mathrm{\AA }$ at $\text{F=0.09,}$ are reported.