Manufacturing aspects of an ultra-thin chip technology

Ultra-thin silicon (Si) chips fabricated using the recently developed Chipfilm™ technology feature three distinct manufacturing issues, which are discussed in this paper. In Chipfilm™ technology a thin Si membrane is firmly attached to a conventional bulk Si wafer by vertical Si micro-anchors which, however, in the end are controllably fractured to make the thin chips detachable. The associated mechanical stability window is widened by adjusting the arrangement of the micro-anchors, so that chip detachment yields exceeding 99% are achieved. Another not yet reported issue relates to the process temperature and temperature uniformity within the membrane areas, which are thermally connected to the bulk substrate only by the anchors and at the chip edges during processing. Using rapid thermal oxidation and the local oxide thickness as a temperature monitor an on-chip oxide thickness variation of ±3% is determined. Finally, the inherent deformation (warpage) of free-standing ultra-thin chips due to internal stresses is analyzed and their surface height variation is reduced to only ±4 μm using stress compensation techniques.