As overlay budgets quickly approach a total allowed variation of around 30 nanometers serious consideration must be given to the technique used to measure overlay between successive layers. This problem becomes particularly acute if different machines are used to expose alternating layers, or if different illumination settings are used between successive layers. As a result of overlay degradation observed between two production layers, a comprehensive study was initiated to evaluate the accuracy of conventional 'frame in frame' and 'box in box' alignment schemes. The insufficient accuracy of these structures is demonstrated using experimental techniques and through the use of photolithographic simulations. Using these simulations, new overlay markers were developed to minimize the sensitivity to Zernike fringe polynomial lens aberrations in both steppers and scanners. The improved accuracy of these overlay markers is finally demonstrated by experimental techniques. Despite significant improvements in the measurement accuracy of these new overlay markers, the accuracy of present techniques may not be sufficiently accurate to measure overlay as budgets approach 30 nanometers, and new techniques may have to be developed.