Using Deionized Water to Remove Polystyrene Latex Particles from Oxide Layer by Single-Wafer Spin Processing

Abstract

Residual particles significantly degrade the performance of large-scale integrated circuits; hence, the methods and efficiencies of particle-removal technologies for semiconductor wafer-cleaning processes are continuously being improved. This paper reports a deionized water (DIW)-based approach that significantly improves the particle removal efficiency (PRE) of polystyrene latex (PSL) particles from oxide surfaces. PSL particles are generally very difficult to remove from silicon oxide surfaces using DIW alone. We previously attempted to improve the PSL removal rate with DIW by increasing the wafer rotation speed and the medium flow rate in single-wafer spin processing. However, the maximum PRE was below 50% (PSL, 500 nm spheres). This study reports on the improvement of the PRE to >98.0% by combining a DIW clean with a very low wafer rotation speed (10 rpm) and a very low DIW flow rate (200 ml/min). The spatial distribution of the PRE matches that of the calculated capillary numbers across the wafer. We propose that the low wafer rotation speed and DIW flow rate impact the capillary number, allowing the DIW to percolate between the PSL particles and the oxide surface. Particles uplifted by this process become suspended in or on top of the liquid layer covering the wafer, and are removed when the rotation speed of the wafer is increased during the final drying process.