REAL-TIME DETERMINATION OF THE DIRECTION OF WAFER TEMPERATURE-CHANGE BY SPATIALLY-RESOLVED INFRARED-LASER INTERFEROMETRIC THERMOMETRY

Interferometric thermometry is a noncontact method of directly measuri ng the temperature of a semiconductor wafer. Periodic modulation in th e intensity of reflected laser light is detected as the temperature-de pendent change in the optical pathlength causes transitions from const ructive to destructive interference between the front and back surface s of the wafer. In its simplest implementation, only a temperature cha nge is detected; heating and cooling are indistinguishable. In this ar ticle, a simple method for determining the direction of temperature ch ange is described and demonstrated, based on sensing phase differences in periodic signal intensity detected from two regions of slightly di fferent thickness. A statistical analysis reveals that this method wil l have an extremely high probability of correctly determining the dire ction of temperature change in almost all instances.