APPARATUS AND METHOD FOR SURFACE PREPARATION USING ENERGETIC AND REACTIVE CLUSTER BEAMS

摘要

An apparatus and method for surface preparation of substrates, for example, semiconductor wafers, micropackages, disk media, disk heads, and medical devices, using energetic cluster beams is disclosed. In this system, charged beams consisting of microdroplets or clusters having a prescribed composition, velocity, energy and size are generated using electrohydrodynamic (EHD) principles, then directed onto a target substrate in order to modify the surface. Cleaning, drying, deposition, and texturing are typical surface modifications that can be performed on the substrate. Charged cluster beams are formed by electrostatically atomizing a conductive fluid fed pneumatically to the tip of one or more capillary-like emitters. The extraction field necessary for atomization and formation of charged clusters is provided by applying a potential difference between the emitters and a counterelectrode. Depending upon mode of operation, the charged clusters are typically 0.01 to 2.0 microns in diameter, and are multiply charged. For some applications, acceleration through 10 IcV or more results in large substrate impact energies greater than 0.5 million electronvolts (eV). Because beam clusters are massive compared to ion beams, they can expend their energy over an extended area of the target causing the simultaneous liftoff and removal of micron and submicron particulates, organic films, metallic contaminants, and surface moisture. Although individual cluster impact energies may be high, the energy is shared by the large number of cluster nucleons. This results in specific energies at impact less than 1 eV/nucleon, well below material sputtering thresholds. To prevent substrate charging, cluster beam neutralization can be included. The shape and other characteristics of the cone exiting the nozzle orifice depend on the charge density of the microdroplets. For example, the cone of Photo #1 results from a relatively small charge density and the cone of Photo #2 results from a larger charge density.