Extension of infrared-laser interferometric thermometry to silicon wafers polished on only one side

Interferometric thermometry, a noncontact method of measuring the temperature of semiconductor substrates, has been extended to standard Si wafers that are polished on only one side. These substrates make up the majority of wafers used in manufacturing. This is the first application of this technique to substrates that are not polished to an optical finish on both sides. Contrasts between constructive and destructive interference were typically 19% and as high as 39% when the 1.5 μm laser beam was incident on the rough surface and the reflected beam was monitored. While considerably lower than the near-100% contrast with Si wafers that are polished on both sides, this level of contrast is nonetheless sufficient for correctly counting interference cycles and therefore determining temperature in real time. Temperature measurements were successfully made on both bare substrates and processed Si wafers covered with transparent films and photoresist patterns.