Improving Nikon XY-2i performance

Due to the need for better repeatability in mask registration measurement, Intel Corporation instigated a joint project with Nikon Precision Inc attempting to improve the performance of their new XY-2I to +/- 0.05μ over lOOmn. The empirical experimentation focused on controlling and/or more accurately monitoring the errors associated with interferometer compensation for air and mask temperature, temperature differences between the X and Y portions of the interferometer, plate temperature non-uniformity, and incorrect plate climatization. Flouroptic temperature probes monitoring plate and X/Y interferometer temperatures showed that installation of curtains and precisely-placed fans, better placement of Nikon air and mask temperature sensors, and proper plate climatization eliminated X/Y interferometer temperature differences, improved plate temperature stability and uniformity, and greatly reduced the air and plate temperature measurement errors. Long-term repeatability and residual-orthogonality measurements both showed large improvements with the range of orthogonality fluctuations ^ +/- 0.14” of arc and long-term repeatability ^ +/- 0.06μ over 100mm. These results indicate that with a few simple and inexpensive modifications, XY-2I performance improvement is possible.