Importance

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Abstract

A non-contact pneumatic-electric dimensional measurement system comprises a stable base on which a semiconductor wafer or workpiece to be measured is placed. A measurement head is held aloft over the wafer or workpiece and base by a rigid support bracket attached to the base. The tip of an air nozzle in the measurement head is directed at the wafer or workpiece and automatically extended to near contact. The nozzle is servo-positioned by an air sensor and motor combination that maintains an air gap between the tip and wafer of about 150 microns with an overall precision of about 3-4 microns. A Heidenhaim linear displacement gauge is attached to the air nozzle and is used to determine the nozzle position to within 0.5 micron. The dimension of the wafer or workpiece is determined to within 0.5 micron by combining the linear displacement gauge reading with an estimate of the air gap derived from a reading of the air nozzle backpressure that has an accuracy of about 0.1 micron. A calibration method is used while the air sensor and motor servo combination is temporarily disabled. The nozzle is stepped in ten micron increments of air gap from a reference starting at zero using readings from the linear displacement gauge. The specific back pressure in the air sensor is read into a linearization table for 0-300 microns in ten micron steps.

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First Claim