The improvement of photolithographic fidelity of two-dimensional structures through double exposure method

Abstract

With the semiconductor fabrication groundrule approaching the 32 nm node, double exposure or patterning method with 1.35 NA immersion seems to be the primary candidate due to its relative easiness to implement when compared to the other two competitors, the high refractive index immersion and the 13.4 nm extremely ultraviolet (EUV) lithography. However, the splitting of one mask into two is not a trivial task. In this paper, we would like to discuss about the best splitting method for several typical 2D structures, such as the isolated opposing line (or space) end shortening, T-like structures with narrow gaps, etc. From our recent experimental studies, we have found that, for line and space photolithography, the optimized illumination condition has a sigma value very close to 0.5. When compared to the single exposure processes, which will typically use more annular condition, a sigma of 0.5 can generate worse process windows for isolated features. This will put more pressure on the precision of the already challenging optical proximity correction (OPC) because the doubly exposed patterns and singly exposed patterns follow two different models. In our study, we find that the extra degrees of freedom in the double exposure method can be utilized to repair some intrinsic printing deficiency, such as, line end shortening. In this paper, we will analyze each typical 2D structure and, for each splitting method of the typical 2D features we study, we will discuss its capabilities in realizing good process windows, the MEF, and OPC correction easiness.