Noncontact electrical critical dimensions metrology sensor for chrome photomasks

Abstract

This paper describes a novel non-contact capacitive-sensor metrology tool developed for chrome photomasks. This work further describes suitable types of test structures printed on photomasks appropriate for linewidth metrology. The Critical Dimension (CD) metrology sensor is developed using a Low Temperature Co-Fired Ceramic (LTCC) technology to reduce the effects of parasitic capacitances. The sensor is based on non-contact micro-capacitance measurements of features on chrome-on-glass reticles. The CD-extraction algorithms based on the capacitance measurements are formulated from extensive evaluation with a Maxwell1 simulator. The purpose of the non-contact micro-capacitive sensor is to measure chrome-feature linewidths in the range of 0.4 tm -0.5 jtm. These dimensions correspond to a O.18-jtm process on a 4X mask.

Noncontact Critical Dimension Metrology Sensor for Chrome Photomasks Featuring a Low-Temperature Co-Fired Ceramic Technology

“…Previous articles [8], [9] have shown that this algorithm can be constructed using conformal mapping techniques. These techniques, that map a problem of complex geometry into a problem of simpler geometry for which only a uniform homogeneous field reigns, allowed for determination of an equation linking the measured capacitance to the average width of the features (1) Referring to Figs.…”