Improvement of temperature homogeneity of a silicon wafer heated in a rapid thermal system (RTP: Rapid Thermal Process) by a filtering window

Rapid thermal processes are used in various key stages in the microelectronics industry. In this study, the heat transfer in a rapid thermal system is modelled with the finite volume method. The influence of the radiative properties of the quartz window on the thermal profile of the silicon wafer is first investigated. The obtained temperatures are interpreted by analyzing the radiative properties according to wavelength and temperature. The wafer temperature profile for a non-optimized heating in steady-state is explained by a four-phase scheme where the radiative heat fluxes are depicted. From this scheme, a filter on the underside of the quartz window is envisaged to achieve temperature uniformity for the wafer. Two configurations are tested, one where the filter covers the entire lower surface of the quartz window and another where it is placed in a ring close to the reactor wall to confine the infrared radiations with wavelengths beyond 2.6 μm in order to raise the temperature at the edge of the wafer. Simulations demonstrate that the latter modification enables a more significant improvement of the wafer temperature homogeneity with less than 1% dispersion. The implementation of the filtering window is also discussed.