Particle Removal in Wet Wafer Cleaning Processes

Abstract

Defects in semiconductor manufacturing that originate from add-on particles can contribute to device yield loss. One possible avenue in removing these particles is a wet wafer cleaning process. Single wafer wet cleaning systems are the current industry standard for defect removal due to their superior ability to control particle re-deposition, especially near wafer edge, as compared to batch cleaning systems. However, our experiments have shown that large micron-sized particles re-deposit during a typical single wafer cleaning process in a model system. These particles were moved and re-deposited primarily during the initial wetting stage. A mechanistic model has been developed to estimate the forces acting on the particles at the three-phase contact line during the wetting stage. The model results show that the forces acting on a particle in the wetting stage are orders of magnitude higher than those in the steady state condition (Fig. 1). Thus, particles are more likely to be moved during the initial wetting step. However, if these moved particles were not transported out of the flow boundary, they could re-deposit and stress produced in steady state flow condition is insufficient to remove them. To further remove smaller particles from wafer surface, a novel particle removal technology based on a polymer solution is reported in this paper. Physical cleaning methods, such as cryogenic aerosol spray, two-phase fluid aerosol spray and megasonic cleaning, have been used in both front-end- and back-end-of-line cleaning processes for a long time. However, all these methods have the risk of damaging fine features on the wafer in today’s advanced process nodes. Thus, there is a need for a damage-free high efficiency particle removal technology. Polymer solutions have long been used in paper making and water treatment industries to aggregate particles either to deposit them on papers or for their removal from water. The same particle aggregation property of polymer solution has been successfully applied to particle removal. High particle removal and no pattern damage have been demonstrated. The particle removal effect is also highly synergistic with SC1 chemistry. By combining these two approaches, particles 25 nm and above can be removed with >90% efficiency. Fig. 1 Schematic of forces acting on defects during wetting stage. FM is motion induced interfacial force, Fdis the hydrodynamic drag force. Figure 1