Metrology of lithographic features: balanced illumination eliminating diffractive bias.

Optical microscope metrology of shallow relief patterns is shown to be capable of greater accuracy, to smaller dimensions, when phase features are imaged rather than intensity ones. This comes from the inherent symmetry in diffraction from pure phase discontinuities. Thus when intensity variations are suppressed, as by appropriate illumination or filtering, the diffractive bias can be eliminated. The approach is analyzed and demonstrated. When it can be used, greater accuracy is available than with traditional approaches. In ideal conditions the approach has the potential for absolute accuracy within 0.1lambda, down to dimensions of

Aligning lithography on opposite surfaces of a substrate.

Equipment has been developed for aligning lithographic features between opposite surfaces of substrates to within 1 microm. It will work with opaque substrates and allows registration to existing features on the other surface.

Long-range holography.

Long-range holography is investigated for improving telescope resolution through a distorting atmosphere. Theoretical concepts are developed and operational parameters are discussed. A scaled simulation is made in the laboratory of a scene subtending an angle of 1 min of arc, illuminated by a laser and viewed holographically with a 40-cm telescope through fixed and moving atmospheres.