with a view to increasing the packing density of elements and improving the performance of lsi's drastically, great efforts are now being made to develop the fundamental technologies for three-dimensional ics. to realize these vertically stacked devices, planarization technology is indispensable because the surface steps seriously affect device formation process. the authors have developed a new planarization technology utilizing a dummy pattern method to solve the problem, and were successful in planarizing the whole surface of a wafer. in this method, organic materials are coated over the whole surface where a dummy pattern has been previously formed. subsequently by etching the above superficial layers and the underlying layer with steps at the same etch rate, a final flat surface can be obtained. the authors have applied this method to the fabrication of a three-layer stacked image sensor device and for the first time the coordinated operation of these three layers in optical sensing