Improvements in wafer temperature measurements

Abstract

Accurate and repeatable wafer temperature measurement and control is critical in many semiconductor processing applications. Many of these applications are done at moderate pressures (0.5–2 Torr) where thermal contact resistance between the wafer and a contact temperature probe is high, and could vary wafer to wafer. The result is an unpredictable difference between the actual wafer temperature and contact measurement probe due to heat transfer across this interface from exothermic reactions, hot plasma gases, or radiant heating. In some applications, this temperature difference is so great that backside helium cooled electrostatic chucks are used to minimize this effect. In many applications, the use of this type of solution is not practical but accurate and repeatable wafer temperature measurement is still required. A new temperature sensor has been developed that utilizes gas injection through a pinhole in a thermocouple pad that creates a “microenvironment” between the pad and the wafer. This results in reduced thermal contact resistance, and more accurate and repeatable temperature measurement. Temperature data on the operation of this probe will be presented, verifying the robustness of this probe. Additionally, diffuse reflectance spectroscopy will be used as a noncontact temperature measurement technique to corroborate data from the new gas-cushion thermocouple.