We developed a heterodyne interferometry system cancelling the noise caused by floor vibration and mechanical vibration using accelerometers. The interferometry is one of the powerful tools to precisely measure the flatness of a polished semiconductor wafer. Generally, the noise caused by vibration affects the displacement measured by the interferometers, and it is difficult to completely avoid the noise even if we use a vibration isolation table or perform motor tuning of the driving parts. The noise cancelling has been conducted by compensating the distance between a pair of interferometers using the signals obtained by accelerometers mounted on near the interferometers. Here, we propose and demonstrate a noise cancelling method. Utilizing the system, we successfully reduced the influence of floor vibration and mechanical vibration, and the precision of the measurement of the wafer flatness has been improved 38% by the technique in this experiment.
