Two-dimensional numerical simulation of non-uniform plasma immersion ion implantation

One of the biggest advantages of plasma immersion ion implantation (PIII) is the capability of treating objects with irregular geometries without complex manipulation of target holder or beam rastering. The effectiveness of this approach depends on the uniformity of the incident ion dose. However, it is known that the lateral dose variation (non-uniformity) is less than optimal in some applications. Ion dose non-uniformity may lead to large variations in the biocompatibility for biomaterial implants. Therefore, ion dose uniformity is an issue frequently investigated since the inception of PIII. Unfortunately, perfect dose uniformity is usually difficult to achieve when treating samples with a complex shape. The problem arises from the non-uniformity of the plasma density and self-consistent expansion of the plasma sheath. Concave surfaces frequently receive a smaller ion dose compared to convex surfaces since ions in a limited volume are competing for more surfaces and are depleted more readily. An effective solution is to produce non-uniform plasmas. For example, at the concave site, a higher plasma density may be helpful to weaken the ion competition and delay the depletion time. Consequently, the ion dose uniformity can be improved. In the work described here, we conduct two-dimensional numerical simulation of PIII into a trench target with the novel notion of non-uniform plasma.