Pattern Related Non-Uniformities During Rapid Thermal Processing

Abstract

AbstractState of the art rapid thermal processing is able to produce a lateral thermal homogeneity which is within the inherent resolution limits of current meterology. For the most commonly used direct or indirect control methods such as multiple thermocouple measurements, rapid thermal oxidation (RTO), or rapid thermal annealing (RTA) of plain semiconductor wafers this limit is ± 2°C. As homogeneity requirements approach those limits, pattern induced non-uniformities are getting more important.In order to achieve rapid heating and high substrate temperatures in RTP, heater and substrate are not in equilibrium and their emission spectra differ considerably. Under such circumstances laterally varying optical characteristics on the substrate itself imply thermal non-uniformities. The influence of patterns on a silicon wafer surface on the temperature uniformity is studied. Passive patterns showing interference effects were formed out of thermal oxide and Si3N4. RTO and RTA, as well as embedded thermocouples were used for temperature measurement. The data presented show that major non-uniformities due to interference effects can be reduced by restricting the energy transfer through the patterned side of the wafer. It is shown that independent top and bottom heater bank control and controlled thermal kinetics are suitable methods to reduce the pattern related process non-uniformities.