X-Ray Mask Fabrication Process Using Cr Mask and ITO Stopper in the Dry Etching of W Absorber

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Abstract
An X-ray mask fabrication technology using a tungsten (W) absorber with a chromium (Cr) mask and indium titanium oxide (ITO) stopper was developed. When SF6 was used as the dry etching gas, substantial side etching occurred because the F radical reacts with W on the sidewall. In order to prevent side etching, a SF6 and CHF3 gas mixture was applied; however, the ratio of dry etching rate of W to that of resist is low. Furthermore, the underlying layer such as that of silicon dioxide (SiO2), which was used as the etching stopper, was easily damaged. Instead of a resist mask and SiO2 stopper, a Cr layer as the etching mask and ITO layer as the stopper layer were applied. By the use of these structures and etching procedures, high aspect ratio W patterns with vertical sidewalls have been successfully fabricated.

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