Beneficial influence of continuous ion bombardment during reactive sputter deposition of chromium nitride films

When spatial objects are coated by plasma vapor deposition (PVD) or reactive PVD the objects perform a planetary motion in front of one or more targets. Sputtering from the target is achieved by an intense ion bombardment from a plasma in front of the target. This plasma is concentrated in front of the target by a magnet assembly behind the target. Usually a bias voltage is applied to the substrate in order to obtain an ion bombardment during the deposition. The function of this ion bombardment is to supply energy to the growing film in order to arrive at dense films under compressive stress. In the present article it is shown that for high quality coatings on spatial objects it is mandatory to guarantee not only a bias voltage, but also a bias current during all times of the deposition. For the coating of spatial objects this is realized by using a second plasma source to fill all of the deposition chamber with plasma.