Shift-Free Optical Coatings(Staff of Vacuum Innovations LLC)
The deposition of optical interference coatings requires precise control of layer thicknesses and refractive indices in order to yield predictable, reliable performance. One of the challenges in the use of evaporated coatings is the porous lm structure and the associated sensitivity to relative humidity and temperature which results from the low energy of the deposited molecules
Broad-Beam Industrial Ion Sources (Staff of Kaufman & Robinson, Inc.)
A broad ion beam is typically several centimeters or more in diameter. The beam diameter is also much larger than the Debye length, which is the typical distance an electric field can penetrate into a plasma. If a broad beam is to be kept near ground potential, it must be neutralized (see Tech. Note KRI-02). For neutralization, there must be approximately equal numbers of electrons and positively charged ions in each volume of the ion beam. For a dielectric target, the electrons and ions must arrive in equal numbers. The target can be either a sputter target or a substrate. The ion energy in a broad ion beam is 2000 eV or less. (A singly charged ion “falling” through a potential difference of 2000 V acquires an energy of 2000 eV.) To minimize damage, the energy is usually 1000 eV or less. High energy implanting-type applications are not consider-ed here. Concern about damage to processed surfaces has led to decreased ion energies. There are two general categories of broad-beam ion sources: gridded and gridless.
As described in Technical Note KRI-01, an ion beam from a broad-beam industrial source must be neutralized. This is done by emitting electrons from a neutralizer. A hot-filament, plasma-bridge, or hollow-cathode type of neutralizer may be used. The ion source in Fig. 1 could be either gridded or gridless. For a gridless source, the neutralizer is a called a cathode-neutralizer. The target can be a sputter target or a substrate being etched. Connected to a voltmeter in Fig. 1, it serves as a neutralization probe.
Gas cleanliness is important to some vacuum-process equipment and processes. For example, contamination can decrease the lifetime of hollow cathodes and plasma-bridge neutralizers by a factor of ten or more. The techniques required to assure gas cleanliness are reviewed herein.
In-Situ Cleaning for Thin-Film Deposition
Thin films are deposited on substrates in a variety of vacuum deposition processes. The properties of such a deposited film depends on the cleanliness of the substrate surface on which the film is deposited. Contamination on this surface can result in reduced adhesion of the film to the substrate, more rapid degradation of the film after deposition, greater contact resistance for electrically conducting films, and poor optical qualities for optical films.