Dose performance characterization of extreme ultraviolet exposure system using enhanced energy sensitivity by resist contrast method

Characterization of the systematic and random dose errors of an extreme ultraviolet (EUV) exposure system is performed using an EUV resist as an energy sensor for fast and repeatable measurements. Dose error measurement is enabled by a critical phenomenon that occurs when the photoresist is exposed to a dose in the region between the onset dose of E 1 and the clearing dose of E 0 on the photoresist contrast curve, which results in enhanced sensitivity to the applied dose relative to the resist thickness. At doses near the enhanced sensitivity point, changes in the thickness of the photoresist can be detected based on the change in the reflected light intensity, and any intensity variations in a captured image of an exposed wafer can be reverse translated into the dose error of the exposure system. With a dose sensitivity that is capable of resolving approximately 0.25% of the nominal dose, it is possible to decompose the measured systematic in-band EUV dose error of the exposure system into the intrafield slit and scan uniformity, the field-to-field variation within a wafer, the scan-up to scan-down difference, and the chuck-to-chuck difference. Even a random dose error, such as the intermittent pulse energy drop-out error that occurs in laser-produced plasma EUV sources, can be detected.