Step & Scan technology will be used for the next generation of semiconductor lithography tools. This technology has matured over the last year, and results from several DUV tools have been reported. For economical mass production in sub 0.25 micrometer applications, DUV and i-line lithography have to be combined (mix and match). This paper reports on the performance of a new high throughput, high resolution i-line Step & Scan system. The system has a 0.65 NA, 4X projection lens which, together with the AERIALTM illuminator, provides a resolution of at least 0.28 micrometer. The identical field sizes and the Step & Scan principle, result in a matched machine overlay, which is comparable to matching only DUV Step & Scan systems.
This paper introduces a new wafer stepper on-line calibration sensor, the Image Sensor, which refers directly to the
aerial reticle image at the exposure wavelength. This sensor system is integrated with other stepper metrology
systems by a so-called Image Sensor fiducial plate, which interacts simultaneously with the aerial reticle image, the
Image Sensor, the TTL alignment system and the focus sensor of the stepper. An integrated software package
ensures on-line regular stepper calibration, eliminating dependance on environmental, process and time
parameters. Unique in this concept is the direct measurement of the consequence of wavelength drift in excimer
laser steppers by measuring the aerial image deformation at the exposure wavelength. This information is used as
a direct feedback to the wavelength control of the laser. Initial results of this system are presented for both UV (365
nm) and DUV (248 nm) steppers.
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