The mechanism of instability on device's characteristics due to inter-metal dielectrics with low-k material and the modified process

摘要

In this paper, the effects of backend process on device characteristic shift are explored. It had been found that the transistors with different inter-metal-dielectric (IMD) films (FSG vs. USG) have different performance. Moreover, more of the IMD layers will result in more of the electrical characteristic shifts. The shift is dominated by the interface state reduction. The model of plasma-enhanced hydrogen out-diffusion during IMD film deposition is proposed to explain the BEOL-related device shift. In order to relieve this effect of electrical characteristic shift, another alloy step by pure hydrogen (H_2) anneal is implemented after metal-1 etch and before the Via-1 deposition. It is found the electrical characteristics taken at metal-1 stage are very close to those taken at melal-6 with passivation step. In addition, there is no apparent hot carrier lifetime degradation with or without the pure hydrogen treatment.