METAL REMOVAL FROM SILICON SURFACES IN WET CHEMICAL-SYSTEMS

The steady decrease in the minimum feature size of silicon ICs has tig htened the wafer cleanliness standards needed to achieve satisfactory device yields. While wet cleaning cycles continue to be used because o f their excellent ability to remove particles and native oxides, the d eposition of trace amounts of metals from contaminated solutions is a growing concern. A quantitative description of metal removal and depos ition 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 mixtu re 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.