Ultrahigh efficiency EUV contact-hole printing with chromeless phase shift mask

Contact-hole layer patterning is expected to be one of the first applications for EUV lithography. Conventional darkfield absorber masks, however, are extremely inefficient for these layers, placing even more burden on the already challenging source power demands. To address this concern, a checkerboard phase shift mask configuration has been proposed yielding theoretical throughput gains of 5x assuming a thin-mask modeling. In this manuscript we describe the fabrication of such a mask and demonstrate its imaging performance using the SHARP EUV microscope and MET exposure tool at Lawrence Berkeley National Laboratory. For 25-nm dense features, the phase shift mask was shown to provide a throughput gain of 8x based on SHARP and 7x based on the Berkeley MET. The higher then predicted gain is expected to be due to the fact that the thin mask modeling used in the initial prediction misses shadowing effects.