Uniformity Control of 3-D Stacked ICs: Optical Metrology and Statistical Analysis

This paper evaluates various optical metrology techniques for in-line control of the uniformity of 3-D stacked structures. Key process steps during 3-D integration flow were identified and characterized in order to quantify their specific intra-wafer dispersion signature. The cross correlation between the various intra-wafer process step signatures was then analyzed to verify the data set consistency. The analysis indicated that the measurement data are consistent over the process integration flow, and that a simple model quantitatively explains the intra-wafer signatures observed. The results highlight the importance of controlling those specific steps and provide a new alternative for advanced process control implementation.