USING RAMAN MICROSCOPY TO DETECT LEAKS IN MICROMECHANICAL SILICON STRUCTURES

We demonstrate the use of Raman microscopy for leak detection in herme tically sealed micromachined accelerometers. Leaks were indicated by t he presence of a foreign gas, in this case oxygen, in the 70-mu m-deep cavity enclosing the accelerometer between a silicon cap and a Pyrex( R) window. Confocal, nondiffraction-limited operation of the Raman mic roscope utilized the available pathlength in the sample while still re jecting most of the fluorescence from the Pyrex(R), Raman peak intensi ties were accurately determined in the presence of noise by fitting th e spectra to a function that modeled the unresolved Q-branch line shap es of oxygen and nitrogen.