Enhancement of XeF2-assisted gallium ion beam etching of silicon layer and endpoint detection from backside in circuit editing

Abstract

Within the semiconductor industry, backside circuit editing is the process of modifying individual nanometer-scale devices after they have been fabricated by conventional mass production techniques. The technique includes the removal of bulk silicon, to reach the devices, followed by the removal of small and precisely defined volumes of silicon and other materials. It also includes the ability to deposit precise patterns of conductors or insulators to modify the devices in question. Essential to the circuit edit processes are the focused ion beam (FIB) instruments, usually providing a gallium ion beam, to sputter away the volumes which need to be removed. When used in conjunction with specific “precursor” gases, the FIB instrument can deposit metals and insulators in arbitrary patterns to achieve the desired circuit repair or modification. Other gases, such as xenon difluoride (XeF2), can work in conjunction with the FIB to improve the effectiveness and the rate of material removal. Our experimental investigation found that the removal rate of backside silicon by a gallium FIB could be enhanced by 100 times when used in conjunction with the XeF2 gas. The XeF2 also reduced the redeposition of the removed silicon material, making the removal more effective. And importantly, the production of secondary electrons was found to offer a viable endpoint signal to indicate the transition to a new material.