Measurement of thin silicon oxide/nitride/oxide layers using transmission electron microscopy

We present a method of measuring layer thicknesses in silicon oxide/nitride/oxide structures using the Fresnel fringes surrounding each interface when the specimen is out of focus. A simple electron-optical model shows that the interface lies mid-way between bright and dark fringes. If the specimen is thin enough for mass-thickness contrast differences between the materials to be negligible, it is possible to measure average layer thicknesses with an accuracy of about 0.3 nm. Experimental data showing the viability of the approach is presented.