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Recently, the production of silicon wafers 450 mm in diameter has begun. However, a precise method for warp measurement of 450 mm wafers has not yet been established. Hence, the authors have developed a four-point-support inverting method to measure the warp shapes of large diameter wafers with high accuracy. The principle of this measurement method is equivalent to that for the three-point-support inverting method developed for warp measurement of 300 mm wafers. In the four-point-support inverting method, surface shape measurement can be performed with decreased deflection due to gravity using an additional central support. In this study, the principle of the proposed measurement method was verified experimentally. It was found that the four-point-support inverting method could measure the warp of a 300 mm wafer with high accuracy, equivalent to that of the three-point-support inverting method. However, in this experiment, a steel ball was used for additional support which caused concern regarding damage to the wafer surface at the point of contact with the support. Hence, a noncontact support method using an air bearing was proposed. It was found that the noncontact support method could measure the warp with accuracy equivalent to the contact support method described previously. Moreover, this study demonstrates the superiority of the four-point-support method to the three-point-support method regarding the repeatability of the warp measurement.

Warp Measurement for Large-Diameter Silicon Wafer Using Four-Point-Support Inverting Method