A method of distinguishing a set of highly doped regions from a set of lightly doped regions on a silicon substrate is disclosed. The method includes providing the silicon substrate, the silicon substrate configured with the set of lightly doped regions and the set of highly doped regions. The method further includes illuminating the silicon substrate with an electromagnetic radiation source, the electromagnetic radiation source transmitting a wavelength of light above about 1100 nm. The method also includes measuring a wavelength absorption of the set of lightly doped regions and the set of heavily doped regions with a sensor, wherein for any wavelength above about 1100 nm, the percentage absorption of the wavelength in the lightly doped regions is substantially less than the percentage absorption of the wavelength in the heavily doped regions.