Using Raman Microscopy to Detect Leaks in Micromechanical Silicon Structures

Abstract

We demonstrate the use of Raman microscopy for leak detection in hermetically sealed micromachined accelerometers. Leaks were indicated by the presence of a foreign gas, in this case oxygen, in the 70-μm-deep cavity enclosing the accelerometer between a silicon cap and a Pyrex® window. Confocal, nondiffraction-limited operation of the Raman microscope utilized the available pathlength in the sample while still rejecting most of the fluorescence from the Pyrex®. Raman peak intensities were accurately determined in the presence of noise by fitting the spectra to a function that modeled the unresolved Q-branch line shapes of oxygen and nitrogen.