Aging Effects in Test Silicon Wafers Prepared for Wafer Cleaning Process Evaluation

This paper presents an experimental study of the aging of contaminated test wafers prepared for particle removal (cleaning) process evaluation in semiconductor wafer processing. Two wafer preparation techniques were compared: a conventional wet technique in which bare silicon wafers were dipped in a particle-laden solution and then dried, and a dry technique in which particles were deposited from a dry particle-aerosol stream. The extent of wafer aging was quantified through cleaning tests. Wafers contaminated with silicon nitride and tungsten particles were cleaned on different days following particle deposition, and the variation in the cleaning efficiency with wafer storage time was monitored. The tests showed that the dry-deposited wafers aged very little compared to the wet-dipped wafers, particularly for tungsten particles. The low-aging characteristic of the dry-deposition process has positive implications for the repeatability and consistency of tests involving new particle materials of interest such as copper and low-k dielectrics.