A variety of source technologies are currently being proposed for x‐ray lithography. Some are broadband sources, producing a continuum spectrum or a broad distribution of wavelengths. The performance of a system using a broadband source is strongly affected by the vacuum window, mask substrate, and resist composition because of the wavelength‐selective transmission and absorption of these layers. A desired ‘‘optimum’’ spectrum of energy deposited in the resist can be obtained by proper choice of source parameters, vacuum window, and mask substrate. The calculated performances of different source technologies are compared, using source parameters appropriate to each technology. The effect of vacuum window and mask substrate on performance is shown for a representative broadband source spectrum. The feasibility of x‐ray lithography sources for manufacturing use should be viewed in terms of theoretical 0.25‐μm patterning capability, which is found to depend principally on three factors: power, geometry (isotropic or collimated), and whether a vacuum window is required.