A New Fabrication and Assembly Process for Ultrathin Chips

A new ultrathin chip fabrication and assembly process, consisting of a preprocess module Chipfilm and a postprocess module Pick, Crack, and Place, is presented. In contrast to the established wafer thinning technique, the preprocessed wafer substrates are prepared with extremely narrow buried cavities beneath the chip areas at a well-defined distance from the wafer surface, thus precisely defining the chip thickness a priori. After CMOS integration on those dedicated wafer substrates, chips are detached from the wafer surface by etching trenches at the chip edges into the buried cavities and breaking of residual anchors by mechanical force in the postprocess. The feasibility of the new process is demonstrated through a mixed-signal circuit having 38 000 digital and 2700 analog transistors, showing full functionality within specifications for 20-mum-thin chips even under a bending stress of up to 110 MPa.