Semiconductor wafer metrology apparatus and method
A semiconductor wafer metrology technique which corrects for the effect of electrostatic forces on an atmospheric buoyancy compensated weight force measurement of a semiconductor wafer. In one aspect a wafer is weighed in a faraday cage whose is measured independently. A change in the measured weight of the faraday cage can be used to correct the measure weight the wafer. In another aspect a direct electrostatic measurement can be converted into a weight correction using a predetermined correlation between an electrostatic charge measured by the charge meter and a weight error force. In another aspect the electrostatic measurement may be indirect, e.g. derived from varying the distance between the wafer and a grounded plate parallel to the wafer to effect a change in an electrostatic force between the grounded plate and the wafer.
1. A method of measuring the mass of a semiconductor wafer, the method including:
placing the wafer on a weighing instrument;
measuring an electrostatic charge in or on the wafer; and
using a predetermined correlation between measured electrostatic charge and weight error force experienced by the weighing instrument to correct the weight of the wafer measured by the weighing instrument.
2. A method according to claim 1 , wherein the electrostatic charge is measured by a charge meter that is operable to measure the electric field strength created by the wafer's charge.
3. Apparatus for measuring the mass of a semiconductor wafer, the apparatus having:
a weighing instrument for measuring the weight of the wafer;
a charge meter for measuring the electrostatic charge in and/or on the wafer; and
a processor arranged to correct the weight of the wafer measured by the weighing instrument by using a predetermined correlation between an electrostatic charge measured by the charge meter and a weight error force experienced by the weighing instrument.