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.
CMOS devices with submicrometer minimum features have been fabricated using X-ray/photo hybrid lithography. The device fabrication process utilized thirteen lithography steps, including four X-ray lithography levels, such as local oxidation of silicon (LOCOS) [l], gate, contact, and wiring, that required the most critical dimension control and alignment accuracy. A step and repeat exposure system and a SIN, membrane mask were used for the X-ray lithography process. The SiN, membrane mask was improved in its flatness and effective contrast by employing a stress compensating structure and a secondary electron trapping film. As a result, CMOS devices with 0.4-pm effective channel length were fabricated using a single-layer resist process.
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