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13 May 1994 Reactive-ion etching of tungsten for high-resolution x-ray masks
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A process for etching fine features in tungsten (100 nm linewidth or less) to produce patterned absorbers has been developed. The pattern is first defined in a chrome etch mask on the tungsten absorber layer using e-beam lithography and s then transferred into the tungsten by reactive-ion-etching. H2 is mixed with SF6 to passivate the sidewalls of the tungsten features because SF6 alone causes severe undercutting of the features. Control of undercutting is the key challenge in reactive ion etching of tungsten. With an optimum mixture of 20% H2 and 80% SF6, plus substrate cooling to -25 degree(s)C, undercutting can be controlled for 250 nm geometries. Increased undercutting has been observed at the endpoint of the etching process, the chromium etch stop layer. This is demonstrated through a computer model. The endpoint can be controlled through laser endpoint detection. For sub 250 nm geometries, additional sidewall passivation is accomplished with an intermittent etch process, thereby allowing the etching of high aspect ratio 100 nm features in 650 nm thick tungsten layers.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Loretta M. Shirey, Kelly W. Foster, William P. Chu, John Kosakowski, Kee Woo Rhee, Elizabeth A. Dobisz, Charles R. Eddy Jr., D. W. Park, I. Peter Isaacson, Daniel McCarthy, Christie R. Marrian, and Martin C. Peckerar "Reactive-ion etching of tungsten for high-resolution x-ray masks", Proc. SPIE 2194, Electron-Beam, X-Ray, and Ion-Beam Submicrometer Lithographies for Manufacturing IV, (13 May 1994);

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