Toyokazu Fujii

Effect of Thin Tungsten Oxide on Resistance Increase in Annealed Aluminum/Chemical Vapor Deposited Tungsten Interconnects

Aluminum/chemical vapor deposited tungsten (Al/CVD-W) interconnects shows an undesirable large increase in sheet resistance due to Al-W reaction during annealing at 450°C. The effect of native oxides on W surfaces on the resistance increase has been studied. When there is no native oxides on W surfaces, the narrower interconnects show a larger increase in sheet resistance after annealing due to the nonuniform formation of WAl 12 . On the other hand, the interconnects with the native oxide at the Al/W interface show a large increase in sheet resistance, which has little dependence on linewidth. This is because WAl 12 formation is suppressed by Al 2 (WO 3 ) 4 and WAl 5 formation.

Suppression of Resistance Increase in Annealed Al/W Interconnects by Capacitively Coupled Plasma Nitridation on W Surface.

The suppression of the resistance increase in annealed Al/chemical vapor deposition (CVD)-W interconnects has been achieved by exposing the W surface to N2 plasma before Al deposition. The N2 plasma was generated in a capacitively coupled parallel-plate reactor. This process forms a thin WN x layer at the interface between the Al and the W layer. The WN x layer prevents Al-W alloy formation during annealing at 450°C. With this N2 plasma treatment, the resistance increase after annealing at 450°C is suppressed to only 10% compared to 140-180% in samples without the N2 plasma treatment. The N/W ratio and the thickness of the WN x layer are about 1.1 and 4 nm, respectively. The WN x layer formed in our experiment is found to be thicker and have a higher N concentration than the WN x layer formed by electron cyclotron resonance (ECR) plasma nitridation. This is probably due to the large self-bias voltage of the N 2 plasma generated in a capacitively coupled parallel-plate reactor.

A Novel Al/TiN/CVD-W Structure to Eliminate Resistance Anomaly in Deep Submicron Al/CVD-W Interconnects

The sheet resistance increase of Al/chemical vapor deposition (CVD)-W interconnects after low-temperature annealing has been investigated. Anomalous sheet resistance increase depending on the linewidth in sub-half-micron Al-Si-Cu/CVD-W lines after 450°C annealing is found for the first time. The sheet resistance increase of the Al/CVD-W lines becomes larger for narrower linewidth after annealing. It is considered that this anomalous sheet resistance increase is due to more nonuniform high-resistivity WAl 12 formation in the narrower lines. Using a TiN interlayer to eliminate WAl 12 formation, sub-half-micron lines of a new Al-Si-Cu/TiN/CVD-W structure have demonstrated sufficiently low line resistance even after 450°C annealing for 300 min and exhibited 6 times longer electromigration (EM) lifetime compared with the previous Al-Si-Cu/CVD-W structure. This longer EM lifetime is also attributed to the suppression of WAl 12 formation. This structure is one of the most promising interconnect structures for realising sub-half-micron interconnects in future ULSIs

Leakage Degradation in n+ Si Contact Filled with Selective Chemical Vapor Deposition Tungsten Plug due to Aluminum Diffusion along the Plug Sidewall

In this paper, the thermal stability of the leakage of the n + -p diodes with AlSi/W/n + Si contacts has been investigated. A serious degradation of leakage characteristics occurred after annealing at 500 o C. Such a degradation is considered to be a severe drawback to the diodes with AlSi/W/n + Si contacts. In contrast, the diodes with WSi x /n + Si contacts did not fail even after 550 o C annealing. In order to investigate the role of the Al, the AlSi/W interface reaction was examined