Abstract

In this paper a method is presented to remove the silicon substrate from the back of a CMOS chip altogether, whilst leaving gate oxide and silicide intact. This is achieved by grinding the chip until it becomes transparent and then selectively etching the remaining silicon away. The procedure developed is very fast: A 50 mm2 die can be prepared in under an hour, with the gate and silicide of every transistor intact. The method is especially valuable when front-end process features need to be examined over a large sample area. Information can thus be gained with less effort than by using front side deprocessing or cross sections. Several case studies are used to illustrate the effectiveness of the technique and its benefits over deprocessing from the front. These include accurate measurements of gate length (+/- 2 nm) over the entire chip in a 0.18 µm CMOS technology, and applications to investigation of silicide formation.

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