Current 90nm Flash memory design introduces imaging critical points in several devices levels: active, poly, contacts, and first metallization. Among standard Resolution Enhancement Techniques (RET), Off-axis illuminations play a fundamental role, because they are capable of providing better imaging contrast and improved process latitude in low K1 regime with very dense structures. Starting from the simulation study of real device layer geometries, object of this work is to propose a solution in terms of illumination schemes and mask choice (binary or halftone) for each critical layer, considering K1 around 0.35 in ArF lithography. Dedicated off-axis illuminations will be compared to standard illumination modes, underlining the benefits in terms of ultimate resolution, process window and line edge roughness improvement. Experimental data confirmed the predicted gain in process robustness and, as expected, showed great line edge roughness improvement and less marginality to pattern collapse.
According to sizes dictated by ITRS road map, contact holes are one of the most challenging features to be printed in the semiconductor manufacturing process. The development of 90[nm] technology FLASH memories requires a robust solution for printing contact holes down to 100[nm] on 200[nm] pitch. The delay of NGL development as well as open issues related to 157[nm] scanner introduction pushes the industry to find a solution for printing such tight features using existing ArF scanner. IDEALSmile technology from Canon was proven to be a good candidate for achieving such high resolution with sufficiently large through pitch process window using a binary mask, relatively simple to be manufactured, with a modified illumination and single exposure, with no impact on throughput and without any increase of cost of ownership. This paper analyses main issues related to the introduction of this new resolution enhancement technology on a real FLASH memory device, highlighting advantages as well as known problems still under investigation.