Inverse lithography OPC correction with multiple patterning and etch awareness

In advanced nodes, the extension of DUV lithography deep into the sub-wavelength dimensions has led to exploration of many new Resolution Enhancement Techniques (RET). Generally speaking, these RET have enabled higher resolution capabilities using the same exposure wavelength, but at the cost of increasingly complex mask optimization process. One such technique applied to perform Optical Proximity Correction (OPC) is called Inverse Lithography Technique (ILT). It promises the best possible theoretical mask design by solving the inverse problem, where the optical transform from mask to wafer image is solved in reverse using a rigorous mathematical approach [1]. Although the benefits and potentials of ILT in producing a single exposure mask are well documented [2], its implementation in multiple patterning OPC (MP-OPC) is less explored. In this paper, an ILT mask optimization is applied on a metal layer, consisting of 3 exposures in a litho-etch x 3 (LELELE) process flow. It demonstrates the application of both multi-exposure and etch awareness within the ILT mask correction scheme. This is accomplished by including inter-layer constraints for the resist and the post-etch contours in the objective function of the ILT optimization. The ability to reduce potential interexposure failure modes as well as the associated increase in computational resources will be assessed. Additionally, the results will be compared against a conventional model-based OPC with similar multi-exposure and etch awareness.