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Roughness Effects During Focused Ion Beam Repair of X-Ray Masks with Polycrystalline Tungsten Absorbers

Published online by Cambridge University Press:  25 February 2011

R. R. Kola ,
G. K. Celler  and
L R. Harriott
R. R. Kola
Affiliation:
AT&T Bell Laboratories, Murray Hill, NJ 07974
G. K. Celler
Affiliation:
AT&T Bell Laboratories, Murray Hill, NJ 07974
L R. Harriott
Affiliation:
AT&T Bell Laboratories, Murray Hill, NJ 07974
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Abstract

Tungsten is emerging as the absorber material of choice for x-ray masks due to recent advances in the deposition of low stress films. For a practical technology, the masks must be free from defects. These defects may be in the form of excess or missing absorber. Finely focused ion beams have been used for defect repair on x-ray masks, both for removal of excess absorber material by physical sputtering and for addition of absorber material by ion-induced deposition. The eifect of ion channeling in polycrystalline tungsten films is spatially nonuniform material removal during sputtering. Different grains will have significantly different sputtering yields, depending on their orientation with respect to the direction of the ion beam. The repaired features then suffer from roughness on the bottoms and sidewalls of the sputter craters. We have investigated the use of XeF2 assisted sputtering with a 20 keV Ga+ focused ion beam to reduce this roughness. The chemical etching component of the material removal lessens the directional dependence and therefore the roughness during defect repair. It was also found that chromium etch rate was reduced in the presence of XeF2 gas while the etch rate of W was enhanced so that the removal rate of Cr is much less than that of W. We can take advantage of this etch selectivity by using a thin Cr layer under the W absorber as an etch stop layer to eliminate the roughness at the bottom of the features and a thin layer of Cr on top of the W as an etch mask for reducing the sidewall roughness.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 279: Symposium A – Beam-Solid Interactions–Fundamentals and Applications , 1992 , 593
Copyright
Copyright © Materials Research Society 1993

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