Sample tilting technique for preventing electrostatic discharge during high-current FIB gas-assisted etching with XeF2

FIB-induced electrostatic discharge (ESD) is a major limiting factor for achieving successful and efficient circuit modifications of LSI. We have discovered a novel antistatic technique applicable to high-current (nanoampere-order) FIB gas-assisted etching with XeF2. The method simply utilizes inclined incidence of FIB by sample tilting. The effect of the sample tilting technique on preventing ESD was investigated using a logic LSI device fabricated by 0.13 μm technology and eight-layer copper metallization. The result demonstrated that inclined incidence of 60° prevents ESD even for high-current (12.5 nA) FIB gas-assisted etching with XeF2. The mechanism of ESD suppression by the sample tilting technique was proposed by taking account of the presence of processing gas molecules and the tilting-angle dependences of ion range, back-scattering yield, secondary-electron yield and etching rate. In the case of FIB irradiation at inclined incidence with XeF2 gas flow, more secondary-electrons and sputtered particles are ejected with higher energies than those for the case of normal incidence. This leads the ionization probabilities of neutral gases and the sputtered particles to be increased, and results in producing increased low-energy electrons around the FIB processing area. These low-energy electrons suppress the FIB-induced positive charging.