Level Set Simulation on Single Wafer Wet Processing Improvement

To improve the single wafer process for wafer edge yield performance, the liquid film thickness is the key indicator to be investigated. The traditional measurement of liquid film thickness is difficult to execute, due to wafer spinning. The numerical method becomes essential to simulate the process. This paper uses the multiple flow level set method to simulate single wafer spin process. An inlet hydraulic jump is approximated by a two-dimensional axisymmetric approach with a collar inlet. Various spin rotation speeds, variable flow rates, different liquid types and contact angles are simulated. The results indicate liquid film discontinuity at a certain radius and a lower shear rate at the wafer edge. After modifying the process recipe based on the level set simulation result, the wafer edge yield shows improvement. This level set simulation model provides useful information for single wafer wet process control. The level set simulation results can estimate the liquid distribution on the wafer surface before the real process and can avoid experiments on production wafers and hence lead to a lower cost.