Advances in trace element analysis of silicon wafer surfaces by vapor phase decomposition (VPD) and inductively coupled plasma mass spectrometry (ICP-MS)

The vapor phase decomposition (VPD) technique is used to dissolve the silic on oxide layer on a Si wafer surface by exposing the wafer to HF vapor. Aft er VPD, the hydrophobic Si wafer surface is scanned with an acidic droplet of solution to extract the surface trace metals. ICP-MS is applied for the determination of metals in the droplet of solution. Matrix effects resultin g from the formation of polyatomic species are investigated. The molecular interferences from the presence of different levels of Si concentration lef t after VPD are investigated. The interference of F on Co-59 is found to be negligible and controllable. They are also insignificant for the isotopes of Ga, Cu, Ge and Ni. However, for Ti-47, Zn-68 and Ca-44, pronounced matri x effects are observed. A procedure for reducing Si concentration resulting from thick oxide films is carried out and optimum ICP-MS parameters are ch osen for the measurement of these samples. Instrumental and method detectio n limits for 35 elements of interest are determined and provided in this st udy. Spike recovery for these 35 elements is also performed and the accurac y of the method is confirmed for 34 elements. Silver recovery is poor due t o the reduction of this element on the silicon surface. An alternative extr action solution containing HNO3 and HCl is used to collect Ag from the Si w afer surface.