Metal removal from silicon surfaces in wet chemical systems

Abstract

The steady decrease in the minimum feature size of silicon ICs has tightened the wafer cleanliness standards needed to achieve satisfactory device yields. While wet cleaning cycles continue to be used because of their excellent ability to remove particles and native oxides, the deposition of trace amounts of metals from contaminated solutions is a growing concern. A quantitative description of metal removal and deposition phenomena is possible using E-pH diagrams. These diagrams define a thermodynamic driving force for deposition, which is the difference between the chemical potential of the metal ion in the cleaning mixture and the metal or metal oxide on the silicon surface. A mechanistic model, which combines the thermodynamic driving force with etching and mass transport effects, is presented for metal removal and deposition in oxidizing cleaning solutions.