Height measurement of solder bumps using two-wavelength parallel four-step phase shifting digital holography

Digital holography (DH) with two wavelengths (TW) that are close to each other was applied to height measurement of solder bumps having spherical specular surfaces with diameters of ∼ 20 µ m and heights of ∼ 20 µ m . We employed the parallel phase shifting method for instantaneous image capturing, and we improved the spatial resolution of our TW-DH system having two beams with different wavelengths that traveled in opposite directions in the interferometer. It gave 74-times higher repetition and 2.4-times higher spatial resolution than those in our previous DH system based on the Fourier transform method.