Numerical optimization of a chamber structure design for the wet etching

In order to determine the optimal Gap between the wafer and showerhead, a flow field simulation analysis was employed to investigate the mass transport distribution of the chambers with different Gap, and the physical and chemical evolution of HF acid when etching SiO₂ in the ethanol environment was explored, then an empirical etch-rate formula was established to analyze the etch rate and uniformity of the chambers. Finally, a Gap with the best process performance was found. Analysis result shows that much wider Gap will cause high etching rate at the center of the wafer and much narrower Gap will high etching rate on the edge. With the increase of the Gap, the average etch rate gradually reduces while the etch non-uniformity decreases at first and then increases, therefore the etch uniformity is the most optimal when the Gap is 70 mm, and the etch rate is relative higher.