A total overlay accuracy of less than 35 nm was obtained with two synchrotron radiation (SR) x-ray steppers developed by NTT and ASET. This value includes the pattern placement errors of two masks, errors due to the wafer etching process, and errors of two steppers that arise in exposure. The error factors affecting the overlay compatibility among SR x-ray steppers were analyzed using double-exposure experiments. The results show that the overlay error induced by the difference in runout between the two steppers was negligibly small and that the magnification change from shot. to shot was caused by gap setting variations between the two steppers. These results demonstrate that a SR x-ray stepper can provide sufficient overlay compatibility for the 100 nm technical node and beyond.