Method of fast surface particle and scratch detection for euv mask backside

A method of scanning a substrate, comprising:

• directing a collimated light beam to impinge on a surface of the substrate, wherein the collimated light beam comprises a plurality of wavelengths each comprising a respective wavelength-dependent focal length;
• receiving reflected light from a first point on the surface of the substrate;
• directing the reflected light to pass through a pinhole;
• detecting the reflected light from the first point after passing the pinhole;
• determining a spectrum of the reflected light;
• determining a peak wavelength at a peak intensity of the spectrum;
• and
• determining a height or depth of the first point on the surface of the substrate based on the peak wavelength.

A system for scanning a substrate, comprising:

• a light source configured to generate multi-wavelength light;
• a chromatic lens configured to receive the multi-wavelength light and to generate a collimated light beam comprising a plurality of wavelengths each comprising a respective wavelength-dependent focal length;
• an optical system configured to direct the collimated light beam to impinge on a surface of the substrate and to receive S904 reflected light from the surface;
• a spectrometer configured to receive reflected light and to determine a peak wavelength of the reflected light;
• and
• a processor configured to determine a local height or depth of the surface based on the peak wavelength.