A stepper for imaging integrated circuit and flat panel displays uses a
thermoresist instead of photoresist and separates the mask into multiple
masks, each one containing only part of the features which need to be
imaged. The fmal image is generated by combining the images from all the
masks on a single die taking advantage of the fact that thermal resists do
not follow the reciprocity law. For maximum resolution each one of the
multiple masks contains features of only one size.