Have you considered dry etching?  It is possible to achieve high aspect
ratio holes using RIE or ICP techniques.  Your sputtered chrome would be a
suitable mask.  How deep do you want to go?

Martin Walker
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Plasma Technology, Oxford Instruments
North End, Yatton
Bristol, BS49 4AP, England
Tel: +44 (0)1934 833851 Fax: +44 (0)1934 834918
URL http://www.oxfordplasma.com/
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