Equipment Condition Monitoring of Multiple Oxide-Nitride Stack Layer Deposition Process

For the 3D NAND memory, the higher oxide/nitride (ON) stacked dielectric is preferred to enhance the storage capacity, and multi-layer dielectric requirements, such as thickness uniformity and interfacial smoothness between films, gathers more interest for the performance of 3D NAND flash memory. Unsatisfactory thickness uniformity between layers is a challenge not only for the device performance but also the following etch process steps. The thickness uniformity can get worse with a little facility degradation. The degradation of the vacuum system, such as the throttle valve position, has the potential to cause process drift. This can have an impact on the thickness repeatability of each layer in a multiple dielectric stack. To reduce the process variation in multi-layer dielectric deposition for 3D NAND fabrication, process monitoring, and equipment diagnostic study is suggested in this paper. Optical emission spectroscopy (OES) is employed for plasma process monitoring and equipment state variable identification (SVID) data are investigated to find the source of the process variation. From the comparison experiments of 5 and 30 paired oxide/nitride stack deposition, we found equipment and/or facility degradation may induce the minute process drift. Among them, we suggest the potential of process drift due to the throttle valve position.