Method and apparatus are provided for accurately placing first and second semiconductor wafers onto a first and a second platforms, respectively, in a single processing chamber despite changes in the exact positions of the platforms caused by variations in temperature within the chamber. A computer controls a mechanism having a pair of wafer-supporting blades to insert the wafers into the chamber. The computer determines from position sensors when the first wafer is centered over the first platform, then actuates lift pins associated with the first platform to lift the first wafer off of its respective blade. Then the computer in the same way in response to other position sensors moves the second wafer into alignment with the second platform, and raises by lift pins the second wafer off of its respective blade. Thereafter the computer removes the blades from the chamber, and lowers the wafers in precise positions onto their respective platforms.