Understanding Thinfilm radiation mechanics

HDP chambers has been extensively use in the area of dielectric deposition. Among its known advantage compared to the PECVD chambers is that it offers better gap filling capability by providing an insitu dep and sputter cycle during the whole deposition process. By having this cycle the process is able to ensure that the oxide valley or trench remains open by sputter and removing a portion of the film before the two opposing edges remain open throughout the whole process. By having this insitu sputtering on the wafers causes the wafer to heat up and again monitoring the temperature of the wafers are critical to ensure we do not exceed the stipulated thermal budget.

Then comes the radiometry which uses the radiation from the wafers as it gets heated up transmitting radiation through the process chamber. The radiation emitted from this heating process can be use to establish the actual temperature reading of the wafers. In the NTM (Non Contact Temperature Measurement) system that we used, it actually utilizes two distinct signal in order to decouple the two information required to obtain an accurate reading of the wafer temperature. One of it is the wafer emission and another one is the emissivity of the wafers itself. The emissivity is determined by emitting a signal of photons which actually bounces or reflected back by the wafer surface and hence derived the information of the wafer emissivity.

Since the emissivity is a function and direct correlation of the reflectivity of the wafers itself then, the number of the photon reflected back by the signal shows how reflective the wafer surfaces are and hence the emissivity of the said wafers. The emissivity calibration is done by moving wafers and heating the wafers up with polished surface to indicate an emissivity value of 0 while when the wafers are transferred out this situation is considered as a blackbody condition or an emissivity value close to 1. But the thing that bothers me is running the wafer at an elevated temperature will surely induce a different emissivity compared to when the plasma is turn off. How are we able to plot a straight line based on this two condition for the emissivity calibration. This is something that I need to ponder through in order to understand further the mechanics of how does this radiometry actually works