Mechanical characteristics of thin dies/wafers in three-dimensional large-scale integrated systems

Ultra-thin silicon dies/wafers with thickness less than 30 μm are profoundly used in the 3D-integration (vertical stacking of functional chips) and in the optoelectronics, in order to reduce the interconnect length and the resistive-capacitive delay. However, to improve the quality and fabrication yield of the three-dimensional large-scale integration (3D-LSI) process, it is important to have very good mechanical properties of such ultra-thin dies. Mechanical properties of the ultra-thin dies such as Young modulus (using nano-indenter), residual stress (by laser micro-Raman spectroscopy), and also the crystal orientation (by using electron back-scatter diffraction) were investigated with respect to different die thinning processes (chemical mechanical polishing, plasma etching, dry polishing, kai-dry polishing, poly grinding, ultra-poly grinding, #2000, etc), for various wafer thicknesses (10 μm, 30 μm, 50 μm, 100 μm, 200 μm) and for the different kinds of the wafer (P/P+, P/P-, and wafer with internal gettering (IG) layer). The chemically-mechanically polished ultra-thin dies/wafers were found to be extraordinarily good in terms of mechanical strength as well as residual stress as compared to the ultra-thin dies/wafers fabricated by all other die thinning procedures.