CD measurements of IPL stencil masks with optical microscopes

Arne Bentfeldt; Albrecht Ehrmann; Thomas Schaetz; Thomas Struck

doi:10.1117/12.373377

30 December 1999 CD measurements of IPL stencil masks with optical microscopes

Arne Bentfeldt, Albrecht Ehrmann, Thomas Schaetz, Thomas Struck

Proceedings Volume 3873, 19th Annual Symposium on Photomask Technology; (1999) https://doi.org/10.1117/12.373377
Event: Photomask Technology and Management, 1999, Monterey, CA, United States

Abstract

CD measurement of photomasks is currently mostly done with microscopes using white light. In the development phase of ion projection lithography, it is useful to evaluate the limitations of this approach. Here, the focus is on measurements with a Muetec2010/Leica LWM200 optical microscope which operates with white light. Stencil masks for ion projection lithography consist of a 3 micrometer thick silicon membrane with a top carbonic protection layer of about 0.5 micrometer. For a feature size of 0.4 micrometer, which corresponds to a wafer technology of 0.10 micrometer (IPL uses a 4:1 reduction), an aspect ratio of about 10:1 results. So, it is questionable if transmissive measurements are appropriate. Effects of reflections on the sidewalls and diffraction effects influence the repeatability. The absolute intensity of the transmitted light is reduced compared to thin mask layers. Results of transmissive measurements are presented and compared to reflective measurements on the same tools. But as the stencil openings are retrograde, the CD which is critical for the use in the ion exposure tool is defined on the top of the Si layer. This can be measured by a reflective method. For stencil openings, it resulted a repeatability of less than 16 nm 3s for a whole range of structure sizes down to 0.5 micrometer (smaller sizes were not evaluated for this purpose yet). This is comparable to the repeatability of chromium-on-glass masks, so a good perspective for future use results assuming an evolutive development of optical CD microscopes.

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Arne Bentfeldt, Albrecht Ehrmann, Thomas Schaetz, and Thomas Struck "CD measurements of IPL stencil masks with optical microscopes", Proc. SPIE 3873, 19th Annual Symposium on Photomask Technology, (30 December 1999); https://doi.org/10.1117/12.373377

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KEYWORDS

Photomasks

Critical dimension metrology

Reflectivity

Ions

Microscopes

Projection lithography

Silicon

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