Temperature measurement of wafers with varying multilayer structures during rapid thermal annealing

Abstract

Rapid thermal processing for advanced semiconductor production demands improved temperature and uniformity control because the optical properties of the dielectric layers deposited on the wafer front- and backside strongly influence the temperature measurement. The measurement of temperature gets more and more important because the semiconductor fabs do not stay with only one product. In recent years, the diversity in product and technology has increased within many semiconductor fabrication plants. As a result, there can be large differences in substrate film stacks between wafers for any rapid thermal annealing step. This variety in products and consequently the differences in emissivity have to be controlled with a precise, simple temperature measurement. One possible solution is the PinTC/sup TM/ presented here. This is a low-cost, thermocouple-based alternative to classical pyrometric temperature measurement and works in closed-loop control. The PinTC/sup TM/ is in contact with the wafer backside and almost emissivity independent. It was found that the optical properties of the wafer backside influence the temperature slightly. To show the improvement in temperature measurement this technology is compared to open-loop processing on wafers with different layer stacks on the backside. The absorptivity of the coatings dominate the direct contact measurement. For the various backside coatings power absorption by the wafer element per unit time and emissivity calculations are performed to understand and explain the experiments. Nevertheless, this direct contact temperature measurement technology is reliable for wafer production in closed-loop control or as a secondary temperature monitor. Furthermore, the PinTC/sup TM/ offers good repeatability in the production environment.