Effect of mechanical vibration on patterning characteristics in synchrotron radiation lithography

In order to improve pattern precision and overlay accuracy in synchrotron radiation (SR) X-ray lithography, it is required that a stepper be very stable mechanically and have a high positioning accuracy with regard to both the mask-to-wafer gap and the stage. It is important to clarify the effect of mechanical vibrations on patterning characteristics. We investigated the effect of mechanical vibrations on line-and-space patterns with dimensions of less than 0.2 µ m by carrying out exposure experiments and patterning simulations. Strong vibrations generally increase the line width, thereby reducing the dose margin. The amplitude of the vibrations should be kept at less than a quarter of the minimum feature size in order to prevent reduction of the dose margin. Furthermore, we developed a simple method of calculating resist pattern profiles from the intensity profile, the thickness of the remaining resist, and the electron scattering depth. The change in line width obtained in this way was almost the same as the measured change.