High-Reliability Copper Interconnects through Dry Etching Process

A modified high-temperature dry etching technique, which enables anisotropic patterning with a high etching selectivity and self-aligned passivation of a sidewall of an interconnect simultaneously, has been developed for fabrication of sub-quarter-micron Cu interconnects. Resistivities of the resulting Cu interconnects are in the range of 1.7 to 2.2 µΩ cm for the linewidth of 0.2-3.0 µ m. As a result of electromigration (EM) tests, it has been observed that median time to failure (MTF) of the Cu interconnects depends on their linewidth. This behavior is considered to be caused by their grain structure, such as a bamboo-type structure for linewidths narrower than 0.3 µ m. In comparison with a MTF of a conventional Al-1%Si line, these Cu interconnects have at least 100 times longer lifetime. Activation energy for EM damage of the 0.7-µ m-wide line is 0.88 eV.