Investigation of molybdenum contamination in 11B+ and 31P+ implants

Ion implantation ion source equipment employing Mo or W arc chambers, W filaments and Al₂O₃ insulators allow F from BF₃ source gasses to chemically react, forming metallic fluorides and oxides that are volatile species at common operating temperatures. These gases get ionized and extracted together with the desired ions. There is evidence that all MoF_x molecules (1<x<6) and probably some clusters exist in the plasma and get dissociated after extraction. It can be speculated that some oxides MoO _y with 1<y<3 also exist. Experiments showed that for ¹¹B⁺ and ³¹P⁺ implantations Mo can be co-implanted energetically. This paper shows three different transport mechanisms that allow Mo to pass the mass separation. The first two transport mechanisms below contribute in case of ¹¹B⁺ tuning and the third dominates the contamination in ³¹P⁺ tuned beams: 1^st, a molecular dissociation of Mo-halogenides with subsequent transport of ^98...100Mo⁺⁺⁺, 2^nd, a straight electron stripping reaction (⁹⁸Mo⁺→⁹⁸Mo⁺⁺⁺) and 3 ^rd, straight ^92...94Mo⁺⁺⁺ extraction. It turned out that the metallic contamination can act as nucleation sites for extended defects or interfered with those. The paper also describes ways to avoid this contamination that is reported to have measurable effects on bipolar devices