Thin film oxides as probe for homogeneity measurements of 3-dimensional objects treated by plasma immersion ion implantation

Results on an optical method are presented for investigation of the lateral homogeneity of treatment of 3-dimensional objects by plasma immersion ion implantation (PIII). It is based on interference colours of thin oxide films of transition metals such as titanium, niobium or tantalum. The thickness of the oxides and hence their colour changes when they are sputter etched by the plasma immersion ion bombardment. With the example of cube-shaped samples which are treated by argon PIII, it is demonstrated how this method works. Cube-shaped samples with slots with both inner and outer surfaces are a particularly interesting and illustrative example both for homogeneity effects of PIII and its measurement. It turns out that large differences in ion irradiation intensity between the outer parts and the inner parts of such samples develop. For the outer sides, a gradient in irradiation intensity is found. In contrast, the inner walls are hardly changed. However, by far most the inner bottom side of the samples is affected; it is considerably sputter etched. These unexpected results are explained by the shape of the cathode sheath from which the ions are accelerated and by the resulting ion trajectories