Reflectometry-based wavelength scanning interferometry for thickness measurements of very thin wafers.

With the development of microelectronics, the demand for silicon wafers is greatly increased for various purposes, especially the use of thin wafers for smart cards, cellular phones and stacked packages. In this paper, we describe an innovative scheme of combining wavelength scanning interferometry (4 nm tuning range centered at 1550 nm) with spectroscopic reflectometry that enables us to measure the thickness profile of thin wafers below 100 microm with high thickness resolution. The performance of this method is compared with that of an existing technique and verified by measuring several thin wafers.