A wide variety of lithography enhancement techniques have been introduced in recent years. Each method has certain virtues, such as improving the resolution of tightly packed features or increasing the depth of focus for isolated ones. Normally, these schemes are analyzed for areas in which they work best. However, it is desirable to have a phase-shift method and illumination system which improves the depth of focus for a large variety of patterns. To satisfy both requirements, promising techniques must be biased to obtain the best process improvement. These issues are particularly relevant for masks with random logic. To address the two problems, we have developed an E-D tree based computer aided design system which analyzes phase-shift masks and illumination methods for one-dimensional features and calculates the proper bias for them. Our simulations concentrate on analyzing constant width lines and spaces of varying duty cycle. The results from analyzing the features illustrate that both phase-shifting masks and off-axis illumination have regions of reduced performance, or dead zones, in which the depth of focus is degraded. Examples of dead zones are evident with many types of phase-shift masks, such as attenuating, alternate aperture, and rim, and with illumination systems, such as annular illumination. Combinations of enhancement techniques, however, can reduce the effect.