Digital holography with a set of two close wavelengths for height measurement of solder bumps

Abstract

Digital holography with two wavelengths that are close to each other is applied to the height measurement of solder bumps having a spherical specular surface and a height of several tens of micrometers. To meet industrial requirements, the error should be less than about 1 μm, and therefore the two wavelengths should have a difference of just a few nanometers for digital holographic measurement. In this research, an optical system in which two beams with wavelengths that are close to each other travel in opposite directions when they enter and exit the interferometer was developed for the first time. The main feature of the optical system is that it requires no special optical element for separating the two wavelengths. In this paper, we describe the position calibration of two cameras that support two-wavelength measurement, the accuracy evaluation of the digital holography, and the height measurement of the solder bumps. © 2020 The Japan Society of Applied Physics 2.2. Digital holography with two-wavelength method Digital holography using the two-wavelength method is reviewed here. First, interference fringes are captured with two wavelengths λ 1 and λ 2 , respectively. Two