Multi-Wavelength Position Sensor for Buried Mark Metrology

The patent changes the wavelength parameter of measurement radiation from single-wavelength infrared to multi-wavelength radiation. By selecting specific wavelengths from the swing-curve model, the system optimizes penetration through opaque layers while minimizing scattering effects. The swing-curve model identifies wavelength combinations where position errors cancel each other, resolving the contradiction between detection capability and measurement accuracy.

The patent uses composite measurement radiation comprising multiple wavelengths instead of single-wavelength radiation. This composite approach combines the advantages of different wavelengths: some wavelengths penetrate opaque material layers effectively while others minimize scattering from substrate surface roughness. The combined effect achieves accurate mark position detection that neither single wavelength could accomplish alone.

The patent implements a wavelength selection system that chooses specific wavelengths based on the swing-curve model. This model calculates position errors for different wavelengths and identifies combinations where errors cancel. The system complexity is justified by the significant improvement in measurement precision, as the multi-wavelength approach actively compensates for substrate topography effects that would otherwise cause unacceptable errors.

The patent incorporates a feedback mechanism where the swing-curve model continuously evaluates wavelength selections based on measured or known substrate properties. The system adjusts wavelength choices to optimize error compensation, creating a closed-loop system that adapts to different substrate conditions and maintains high measurement precision across varying topography.