Synchrotron X-ray Lithography Research Articles

Stability of SiC-masks for high resolution synchrotron X-ray lithography

Synchrotron X-ray lithography is a promising technique for high volume production of Ultra-LSI devices with latteral resolution down to 0.2 μm. Besides the powerful source, the X-ray stepper, and the high sensitive resist, mask technology is one of the main features in the development of X-ray lithography. For X-ray masks with high contrast a relatively thick absorbing pattern (0.8 μm) on a thin membrane (2.0 μm) is necessary. The achievable overlay accuracy depends mainly on the alignment accuracy of the X-ray stepper and of the stability of the masks. For a given stress in the absorping layer we will discuss the stability of X-ray masks which is mainly determined by the Young's modulus of the membrane material if we compare identical membrane geometries. SiC-membranes deposited by a high temperature CVD process can be fabricated with a Young's modulus as high as the bulk value (4.6×10 11 N/m 2) which is roughly a factor of 3 higher than for other relevant membrane materials. Membranes of 2 μm in thickness have been prepared with excellent transparency for synchrotron and optical radiation. A description of the preparation of the rigid SiC-membrane, as well as results of the transparency and the stability of these membranes against strong X-ray exposure will be given. For a high X-ray absorption a tungsten layer has been selected. Because of the thermal expansion coefficient which is comparable to SiC and the high Young's modulus tungsten is a promising material for sub-half micrometre pattern in a stress compensated absorber system. In view of X-ray masks with minimum distortion a description of the etch performance of the tungsten absorber system on SiC-masks will be given.

High contrast synchrotron x-ray lithography by means of silicon based masks and magnesium beam windows

This paper deals with the investigation of novel beam line windows based on magnesium in combination with silicon X-ray masks. Mg enables, because of the distinct absorption edge at 10Å, an effective contrast enhancement in synchrotron lithography. In regard to BESSY radiation and PMMA resist the contrast of Si-masks can be increased more than sixfold by use of Mg-beam windows instead of silicon/kapton windows. In comparison to Be-beam windows the contrast can be threefold enhanced. The prospects of a one-to-one submicron mask technology based on a thin absorbing layer are being discussed in view of exposure experiments with only 0.3 μm thick Au patterns on Si-masks. It turned out that also by adjusting a reliable proximity distance of 30 μm between mask and wafer 0.1 μm features can be replicated in 1 μm thick resist. This offers the important possibility of copying Si master masks having very thin absorbing layers by means of synchrotron lithography after inspection and elimination of faults.