Abstract
In this paper, a comprehensive analysis methodology for gate oxide integrity (GOI) failure using combined FA techniques is proposed. The current method integrates the failure analysis flow we previously reported with a new flow proposed in this paper. The method is applicable to a wide range of GOI failure cases and has been used in analyzing many product wafers with GOI failure. In particular, there is one wafer with GOI failure that results from known failed process machines. This wafer could be readily analyzed with this new method to identify the root causes. The newly proposed flow is based on our previous report on GOI failure analysis, but the detection limit of contamination elements was significantly improved. The enhancement of detection limit is mainly attributable to the utilization of Vapor Phase Decomposition and Inductively Coupled Plasma Mass Spectrometry (VPD ICP-MS). The ICP-MS technique is highly sensitive and capable of simultaneously measuring a large number of elements at very low concentration level in the range of ppb (part per billion) to ppt (part to trillion). This enhanced sensitivity enables effective investigation of contamination caused by specific machines. A case study of GOI failure investigated by the proposed new method will be discussed in detail. In the study, Al, Fe, Mo and Sn contamination from a suspected tool were detected by ICPMS, followed by confirmation by Secondary Ion Mass Spectrometry (SIMS) on the affected product wafers. Failurepart isolation investigations of the affected diffusion furnace revealed that the root cause of the failure is due to a defective gas flow valve.
