Ultra clean processing of silicon surfaces v vol:92 pages:139-142
In this paper we investigate the deposition of sub micrometer sized particles - initially present in a carryover layer - onto a wafer that is being rinsed. Due to the significant difference in diffusion constant between H+ ions and particles, the concentration of H(+)ions (and hence the pH) in the carryover layer will rapidly change in comparison with the particle concentration. Because the pH influences particle/substrate interactions, particle deposition will change with time during the rinsing step. Theoretical models are derived for a system where: (i) interactions are repulsive during the entire rinse process, (ii) interactions are initially attractive, but become repulsive after a certain time, (iii) interactions are initially repulsive, but become attractive after a certain time. Analytical expressions are obtained for the case of stagnant liquids. A comparison with experimental data shows satisfactory agreement for all three cases. In the case of flowing systems viscous forces will result in the presence of a static boundary layer close to the surface. It is therefore expected that the models can also be used qualitatively to describe flowing systems. This is confirmed by experimental results.