Asymmetric alignment signal is a major problem in optical lithography. Perhaps the most unavoidable source of such asymmetry is the resist profile covering the alignment marks. Such asymmetry can arise from the spin coating process. We describe a new technique of using TM polarized light and Brewster angle illumination to minimize the reflection from the top resist surface and hence minimize alignment error induced by asymmetric resist coating. A basic model is developed to describe the optical effect of the resist coating and to calculate the alignment signals. The results show that the Brewster angle illumination technique can reduce the alignment error more than tenfold when using standard marks such as 16 mu m period gratings. Nearly error-free alignment can be achieved even on wafer marks that are covered by asymmetric resist, if the alignment marks are suitably designed.