Progress of a CVD-based photoresist 193-nm lithography process

Abstract

ABSTRACT Plasma polymerized organosilane resist films have been shown to exhibit high sensitivity to DUV radiation 15 We havepreviously demonstrated a 193nm CVD photoresist process in which plasma polymerized methylsilane (PPMS) is patternedvia photo-oxidation, dry-developed, converted into silicon dioxide, and then transferred into an underlying Si layer with highselectivity. The PPMS resist exhibits linearity down to a resolution of l3Onm US for a 1 : 1 pitch. We have demonstrated 100nm Iso-lines at 28 mi/cm2 dose with 1 1 % dose latitude and 600nm focus latitude. Depths of focus (DOF) greater than 500nmhave been demonstrated for l6Onm nested US.However, there is a general tradeoff between photospeed, line-edge-roughness (LER), and x-wafer CD uniformity. Therefore,it is difficult to achieve optimized performance for all lithographic parameters simultaneously in the PPMS process. Wepresent experimental results to support that the tradeoff is in part due to: (a) a high content of weak Si-H bonds which causesthe surface of a PPMS film to non-selectively oxidize in ambient air (b) a rigid inhomogeneous Si-Si bond structure in thePPMS film which influences the minimum level of LER observed for all printed featuresand (c) the impact of the dry developselectivity upon the develop contrast.As a result of our studies, we have turned to studying alternative CVD dry-resist precursor materials with chemical micro-structural properties appropriate for reducing the photospeed-LER-uniformity tradeoff. We show results for a CVD dry-resistprocess which utilizes an alternative precursor that still contains a high (50% atomic concentration, excluding H) Si content tomaintain good etch resistance during pattern transfer. We also tune the develop etch process to yield improved performance.The new process is shown to print lOOnm Iso features with the following simultaneous lithographic performances using a0.6ONA 193nm stepper: 20 mJ/cm2 dose, 550nm DOF, 18% dose latitude, 6nm 3-sigma LER, and a x-wafer CD uniformitysignificantly improved compared to an equivalent PPMS process. The new process also prints l6Onm nested US with 22mJ/cm2 dose, 560nm DOF, 15% dose latitude, and 7nm 3-sigma LER.Keywords: Top surface imaging, top layer imaging, thin layer imaging, 193nm, dry-resist, photoresist, lithography