Study on Abnormally Accelerated Oxidation of Tungsten Plugs during Tungsten Chemical Mechanical Polishing in Semiconductor Manufacturing

The root cause of the abnormally accelerated oxidation behavior occurring in tungsten (W) chemical mechanical polishing (CMP) has been performed to provide guidance to those developing practical solutions. Abnormal oxidation behavior refers to the case where the surrounding W contact plugs are normal, but oxidation occurs rapidly and abruptly only at a specific contact, causing device failure. For this study, the failure location was determined through a wafer-level probe test of fully processed DRAM device wafers. With this specific location information, a top-down view inspection was performed on the location immediately after CMP to assess the characteristics, and then a wafer-level probe test was conducted to confirm the failure. In this way, the top-down view plug images immediately after CMP and their potential failure were classified. Based on these results, the CMP process step involving abnormal oxidation was determined, as were the conditions needed to cause abnormal oxidation. Potential solutions to abnormal oxidation are presented based on our results.