When high temperature processes are being carried out in a diffusion furnace, temperature control is accomplished in a straight forward manner. By using thermocouples and a proportional controller, sufficient accuracy and control are available to the process engineer.
But with the current shift toward the more rapid annealing schemes, better control is a necessity. In order to achieve this accuracy, especially when the heat source is a 100 kilowatt arc lamp, more sophisticated control methods must be employed. By using an optical pyrometer tuned to operate at a wavelength where external interferences are minimized, wafer temperature may be monitored to a high degree of accuracy and with the fast response times needed.
Coupling the output of the pyrometer to a microprocessor based controller allows the engineer to create and use multi stepped time/temperature profiles which are highly repeatable.
This paper will describe such a system and how it is used in a production oriented rapid optical annealing system.