Dielectric targets have been used for direct sputtering of the
dielectric. These materials are, for the most part, relatively porous, with
target density sometimes only 50% of bulk[7.1]. This porosity leads to
entrapped gases which are released slowly as the target ablates, in essence,
a virtual leak. These gases, mostly water and air, contaminate the films,
usually degrading them. Often, to insure stoichiometry, reactive
sputtering is used to insure the total conversion of the target material to
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its oxide or nitride. RF sputtering is used to deposit metals as well as
dielectrics. Thus it is possible in a single pump down to deposit both
conductive and dielectric films.