Note serious overshoots and slow flow-settling times. Figure 5 shows traces from a particle monitor and a gas valve. Therefore, before proceeding to fancy data analysis techniques, try gleaning the story within the trace-data record. Doing so takes time, and the effort will sorely test your computer literacy skills, but you will find it interesting and illuminating. Opening of half-gate valve has caused a particle event.
Many processes routinely change over time.
Pads on chemical-mechanical polishing tools wear out, vacuum systems deteriorate as they accumulate reaction products, and the thermal properties of furnace elements change as they age. Accounting for that kind of variability can be tricky, but the key is to understand that even variation can be consistent. As long as things happen as they have happened in the past, it is safe to assume that all is right with the world. Your challenge is to sort out the truly anomalous wafer-killing behavior from the gray haze of normal process variation. Trace data analysis is a little like archaeology.