Analysis and modeling of wafer thermal transfer in a PECVD reactor

The temperature distribution in the reactor, especially on the surface of the wafer, is the important factors influencing the chemical reaction in CVD and PECVD process. This paper focused on a typical cylindrical PECVD reactor carrying with a wafer, and established the combination calculation model, which divided the chamber system into two calculation domains according to the rarefied degree of the gases. A one-dimensional thermal model was developed to calculate the temperature profiles in the narrow gap between the wafer and the heater, considering the heat conduction, radiation and thermal accommodation phenomenon between the gas and the surfaces in low pressure conditions; a two-dimensional axisymmetric model was applied to calculate the temperature profiles in the chamber above the wafer, considering the heat conduction, radiation and mass transfer. We verified the validity of the model through the experimental measurement in different pressure with the aluminum matrix pedestal and the one without. The experiment and numerical calculation both pointed out that there are 15~30K temperature drop in the narrow gap between the wafer and heater with the pressure of 1~10Torr at the outlet of the chamber, the mass flow of 5000sccm at the inlet, and the fixed temperature of 673K within the heater. The lower the pressure was, the greater the differences were, and it presented a negative exponential relation. In addition, this paper predicted the response of the wafer surface temperature to the change of the narrow gap height and chamber pressure via numerical calculation model. The results showed a negative linear relationship between the wafer top surface temperature and the narrow gap height. When the narrow gap height was changed in the range of 0.15~2mm and chamber pressure of 1~10Torr, the temperature of wafer will drop 0.5~5.5K.