High resolution lithography using synchrotron radiation

This paper reviews the current state of X-ray lithography (XRL) with special emphasis on the exposure equipment, the resolution limitations and on the expected overlay accuracy. Recent developments in mask technology will also be considered concisely. In order to take full advantage of XRL (high throughput, ultimate resolution), one has to use the parallel high-intensity synchrotron radiation. The compact storage ring 'COSY' being built at BESSY presently shows all the features concerning cost and physical dimensions required for a semiconductor fabrication environment. The same holds for the low-cost beam line equipped with an X-ray mirror for the illumination of large areas on the wafer. The wobbling of the electron beam within the storage ring has also been investigated for the enlargement of the exposure area. The first X-ray stepper suitable for synchrotron sources being operated in the lithography laboratory in Berlin shows an alignment accuracy which meets the requirements of a sub-half micron lithography. Experimental and theoretical results show that a structure resolution down to 0.2 mu m is achievable and that an exposure field of several cm2 can probably be used even at a feature size well below 0.5 mu m.