| 摘要 |
<p>The position of a product is measured using an alignment mark on the product. Radiation is transmitted towards the alignment mark and diffracted by a pattern in the alignment mark. Position information is determined from phase relations of the diffracted radiation. The alignment mark comprises a set of mutually parallel conductor tracks from which the diffracted radiation is collected, the pattern being defined by a pattern of variation of the pitch between successive tracks a function of position along the surface of the product. Thus, for example the pattern comprises alternating first and second areas wherein the pitch has a first and second value respectively. Because the tracks in the different parts of the pattern, such as the first and second areas, are parallel to each other improved measurements are possible.</p> |
