A new method for the hermeticity testing of wafer-level packaging

Until now, the determination of microelectronic packages hermeticity has been related to the MIL-STD-883 method 1014 which is based on the helium leak detection method. But this method is no longer suited for small packages due to the resolution limit of the apparatus. Indeed, leaks induced by nonhermetic MEMS packages are often one order of magnitude smaller than the resolution of the helium leak tester. Consequently, characterization of MEMS packages requires new methodologies to measure hermeticity accurately. Two methods will be investigated in the context of this study: the membrane deflection measurement, when exposed to different pressures, using optical profilometry, and the measurement of the variation of gas concentration in a sealed silicon cavity by Fourier transform infrared spectroscopy (FTIR). The calculated leak rates are compared for samples where the standard fine leak test gave no results. The values obtained for the leak rates with the optical test and FTIR test for the same sample are identical, showing the relevance of these two methods. FTIR spectroscopy is a promising method which enhances standard detection limits. It can be used as a reliable process quality control tool.