The Estimation and Improvement of TTL Alignment Error Budgets for an Excimer Laser Aligner.

This paper describes studies on the alignment error budgets caused by a TTL (through the lens) alignment optical system (SMART : separated mark TTL alignment) for an excimer laser aligner. Alignment error factors, such as the optical phase fluctuation of the alignment beam, the inclination variation of the alignment incident beam, the tilt of the wafer and the reticle, and the defocus of the reticle, have been analyzed and estimated. It was demonstrated that the total error of the alignment optical system was required to be better than 0.02 μm in order to satisfy the positioning strategy of the excimer laser aligner with a 0.05 μm (3σ) overlay accuracy. Several compensation methods have been developed and adopted to SMART. As a result, it was obtained experimentally that the total error of the alignment optical system became better than 0.02 μm. It has met the development goal. The new SMART optical system which was adopted to the KrF excimer laser aligner showed an excellent performance with a better than 0.05 μm (3σ) overlay accuracy.