A 45° dual dipole decomposition scheme to improve image fidelity

Abstract

Dipole exposure techniques are currently being explored as alternatives to the low k1 problem that hinders the manufacture of sub 100 nm logic technology. Recently, there has been a great deal of interest in using a combination of vertical and horizontal dipole exposures capable of producing manufacturing-robust image results for Manhattan features. In this technique, a design is split into two complementary masks that have enhanced contrast at a given dipole imaging condition. The dipole is a strong case of off-axis illumination, and significant resolution enhancement can be achieved, but only for one pattern direction. Complementary dipole exposures are required when dense pitches in horizontal and vertical direction are present. Dipole decomposition approaches that separate vertical and horizontal features in a layout are based on the fact that horizontal features form an improved aerial image with a vertical dipole illumination, and vertical features show the same aerial image improvement with a horizontal dipole illumination. This technique, though conceptually simple, requires a computer algorithm to decompose a design layout into two patterns consisting of features oriented mainly in the horizontal and vertical directions. Some layout features, landing pads or angled lines for example, cannot easily be assigned to a particular mask based on this simple orientation logic. In this work a new approach has been presented in which 45° decomposition of the pattern is used to improve image contrast, pattern fidelity and focus behavior. The results will be analyzed in terms of contrast, pattern fidelity and focus dependence in order to determine the feasibility of printing manhattan and angled features using a dual dipole approach for sub 100 nm processes.