Broadband alignment scheme for a stepper system using combinations of diffractive and refractive lenses

Area of Science:

• Optics and Photonics
• Semiconductor Manufacturing Technology

Background:

• Stepper alignment systems utilize broadband illumination for enhanced accuracy.
• Projection lenses in these systems are susceptible to chromatic aberrations due to the wide spectral range.

Purpose of the Study:

• To develop and implement a chromatic aberration correction system for broadband stepper alignment.
• To mitigate image plane spread and magnification differences caused by chromatic aberrations.

Main Methods:

• A Schupmann optical system was designed and employed.
• The system integrates a projection lens, an achromat lens, and a refractive-diffractive hybrid lens.
• Optical performance was evaluated across the 550–650 nm spectral range.

Main Results:

• The proposed Schupmann system reduced image plane spread from 11.28 mm to 50 µm.
• Magnification difference was decreased from 1.18% to 0.05% within the 550–650 nm spectrum.
• Significant improvements in optical performance were achieved compared to systems without aberration correction.

Conclusions:

• The developed Schupmann system effectively corrects chromatic aberrations in broadband stepper alignment.
• This correction enhances lithography accuracy and process yield.
• The integration of achromat and hybrid lenses offers a viable solution for advanced semiconductor manufacturing.