NOVEL ON-AXIS INTERFEROMETRIC ALIGNMENT METHOD WITH SUB-10-NM PRECISION

A novel on-axis interferometric alignment scheme, especially applicabl e to x-ray lithography, is described which combines the position sensi tivity of interferometry and the robustness of imaging. It employs bro adband illumination, and hence should be relatively immune to many of the effects that tend to corrupt alignment signals in conventional int erferometric systems. In its initial demonstration a standard deviatio n (sigma) of 6 nm was achieved in both X and Y. Ultimate limits are ca lculated to be below 1 nm. On an Apple Quadra 800 computer, the spatia l-phase information that measures misalignment is fully analyzed in 20 0 ms.