A HIGHLY ACCURATE STRESS MEASUREMENT SYSTEM FOR PRODUCING PRECISE X-RAY MASKS

A new system that measures stress in film deposited on Si wafers has b een developed to produce highly accurate X-ray masks. The system consi sts of very rigid air sliders, an electrostatic sensor, and a soft-han dling wafer chuck. With the system, wafer warp is precisely measured b efore and after film deposition, and the stress distribution is calcul ated from those measurements. Wafer warps can be measured with a repea tability of a few nanometers by this system. The stress distribution o f absorber film on 2-mm-thick Si wafers can be determined with an accu racy of +/- 5 MPa. The stress distribution agrees well with the patter n position shifts in the membrane.