Development of high-repetition-rate ArF excimer lasers is vital requirement for achieving high throughput and high energy-dose stability in a scanner system. ArF excimer laser, with increasing light pulse duration, can reduce the peak power without the energy-dose change. Then, the spectral bandwidth ⌬ FWHM becomes narrower by increasing the number of light round trips in a cavity, and optical damage is reduced from high-peak power. Laser operation exceeding 4 kHz is needed for next-generation technologies that can enable high numerical aperture and development of high-throughput scanners. In the present work, we examined the possibilities of achieving a repetition rate to 6 kHz from 4 kHz in the ArF laser the authors developed, taking the following innovations. The spatial width of discharge region was reduced by about 30%. The uniform gas flow condition between the electrodes was obtained by improving gas flow guides. As a result, we have obtained an average power of 42 W, a standard deviation for pulse-to-pulse energy of 3.5%, and an integral-square pulse width T is of 44 ns at 6 kHz for ⌬ FWHM Ͻ 0.40 pm. Finally, it was concluded that developing a 6 kHz ArF excimer laser for the next-generation sub-65 nm lithography is feasible.

Reliability of Ti–Pt–Au and Ti–Mo–Au systems has been investigated for GaAs integrated circuit first-level metallizations on semi-insulating GaAs substrates and second-level metallizations on interlayer SiO2 films using Auger depth profile analysis, residual resistance examination and temperature storage step-stress testing. Auger analysis and residual resistance examination showed significant reaction between first-level Ti–Pt–Au and GaAs substrates during metallization processes, while Ti–Mo–Au system with the electron-beam evaporated Mo film showed higher thermal stability because the Mo film acted as a good diffusion barrier between GaAs and Au. The second-level Ti–Pt–Au on SiO2 was found to be free from the reaction with GaAs substrates, and its degradation was ascribed to interdiffusion of composite metals. The resistance increase in step-stress testing for the second Ti–Pt–Au was analyzed on the basis of a new diffusion-controlled model, and long-term reliability was estimated. A mean time to failure value of 3×105 h at 150 °C was obtained for a failure defined as 10% increase in resistance. Much higher reliability was estimated for Ti–Mo–Au, because the resistance continued to decrease as long as 3000 h at 250 °C. The decrease in resistance clearly indicates defect annealing with reduced defect scattering in Au layers. This also shows that foreign metal diffusion into Au, acting as impurity scattering centers, is perfectly eliminated by Mo diffusion barriers.

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