Interface integration defect of copper and low-K materials beyond nano-scale copper damascene process

This paper discusses the first evidence about the low pattern density causing abnormally high VIA resistance, which is at least more than two times the normal level. The low pattern density also induces the exposure-like shape formed in VIA bottom, where high concentration of sulfur element is detected in the copper film after electric- and thermal-torture testing. These effects, due to the low pattern density, are significantly important for nano-scale feature filling and the quality of VIA superfilling. This paper also proposes a mechanism to explain the observed results by inferring from the local resistance and chemical polarity difference with different numbers of VIA serially connected. The experiment with high accelerator concentration also supports the proposed mechanism by locating abnormal voids in the region with low VIA pattern density.