A low-damage copper removal process by femtosecond laser for integrated circuits

To develop a low-damage, low-cost, high-precision copper (Cu) removal process is conducive to promoting the development of integrated circuits in the direction of three-dimensional integration. In this study, a Cu film removal process without damage to the underlying substrate for integrated circuits by femtosecond (fs) laser was proposed. Theoretically, the feasibility of removing Cu film without damaging the substrate by fs-laser was demonstrated by studying the laser energy absorption and coupling, and temperature transient response of Cu/SiC bilayer material under fs-laser irradiation. Experimentally, fs-lasers were used to remove Cu films on SiC, SiO2, and Si3N4 substrates commonly used in integrated circuits. The experimental results show that the fs-laser with suitable fluence can effectively remove the Cu film without damaging the substrate, which is due to the nonlinear absorption of laser fluence by Cu film and the thermal resistance at the metal-nonmetal interface. Moreover, compared with the high-fluence fs-laser, the low-fluence multi-pulse fs-laser is more suitable for the effective removal of Cu film without damage to the substrate. Finally, the application of fs-laser in the preparation of an on-chip filter demonstrates the great potential of fs-laser in the fields of ICs and electronic device processing.