The progress of integration in semiconductor (LSI) is remarkable. We expect that the mass-production of 256M DRAM shall start in the next few years. The design rules for this level of integration will require even more accurately in a system to measure a reticle pattern's position. To meet the measurement requirements for future IC designs, Nikon Corporation has developed to XY-5i. During development, we introduced some new technologies to improve the systems' measurement performance. In this paper, we will explain the new flexure compensation concept and the reduction of measurement error caused by temperature drift. These are the key technologies used to attain the improved performance. This performance will be demonstrated with actual measurement data from the XY-5i.