1. A method for manufacturing an integrated circuit, comprising the steps of: forming first transistors on a first semiconductor layer; depositing a first insulating layer above the first semiconductor layer and the first transistors, and leveling the first insulating layer; depositing a conductive layer above the first insulating layer, and covering the conductive layer with a second insulating layer; bonding a semiconductor wafer to the second insulating layer; thinning the semiconductor wafer to obtain a second semiconductor layer; and forming second transistors on the second semiconductor layer.