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

: Lüthje, H.; Mackens, U.; Mescheder, U.; Matthießen, B.


Microelectronic engineering 5 (1986), No.1-4, pp.39
ISSN: 0167-9317
Journal Article
Fraunhofer IST ()

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 (4.6×1011 N/m2) 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.