X‐ray resist line edge profiles are explored as a function of exposure, mask, and resist properties. The study is based on an exposure‐scission and development‐etching model of positive resists. Development rate curves for two actual and three hypothetical resists are used. The simulation is implemented by using a string of points to follow the contour of the developer–resist interface as a function of development time. Control of the resist profile suitable for liftoff of 0.4‐μm lines is explored in the context of low flux levels for a high throughput production environment. High aspect ratio lines (3:1) and profiles degradation due to mask edge effects for Al k α and Cu L exposures are considered.