Sputter coating
This process produces thin metallic or ceramic coatings on to a wide range of substrates, which can themselves, be either metallic or non-metallic. The films are generally in the 1-10µm thickness range but these limits are not rigid. Film adherence is generally better than that from vacuum evaporation or electroplating.
The process involves the use of two electrodes, one being the target which is deposited on to the other electrode, or substrate. The electrodes are in a dynamic vacuum of approximately 10 millibars, produced by bleeding an inert gas, usually high purity argon, into a continuously pumped chamber. The potential difference across the electrodes may be DC or RF (usually 13.6MHz) and is in the order of 1000V, with the target being negative with respect to the substrate. The argon gas forms a plasma of positive ions which bombard the target material and literally knock out (i.e. sputter) atoms of the target. The sputtered atoms have a high energy and when they impinge on any surface, they form an adherent coating. The substrate is arranged to receive the maximum flux of sputter material.
One advantage of the system is that the targets do not have to be homogeneous and can be produced by powder metallurgical methods or they can be cast or simply cut from bar or sheet. The composition of the coating may be varied by making composite targets from blocks, etc taking advantage of the mixing that occurs in the plasma.
Substrates up to 100mm diameter may be coated to a reasonable degree of uniformity.
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