Use of transmitted color to calibrate the thickness of silicon samples

In preparing silicon-based semiconductors for transmission electron microscopy (TEM), it has been widely observed that a backlit silicon sample displays a series of colors in the thinnest regions. These colors result from absorption and optical interference of light within the silicon sample and depend upon the type of light source and the silicon sample thickness. These colors can range from deep red for thicknesses greater than or equal to 5 mu m, through orange and yellow in the thinner regions, to essentially colorless at the thinnest regions. In this work we present the first direct measurement of silicon color versus thickness and discuss the factors that influence this relationship. Crown copyright (C) 1997 Published by Elsevier Science Ltd.