| Popis: |
Until now, the determination of the herm eticity of microelectronic packages is related to the MIL-STD-883 method 1014 which is based on the He leak detection method. But this method is no more suited for small packages due to the resolution limit of the apparatus used conventionally. Indeed the minimum detectable leak rate is of the order of 5.10 -11 atm.cm 3 .s -1 . Leaks induced by non hermetic MEMS packages are often one order of magnitude smaller. So, the sensitivity of the He leak detector method is too low and th is method can not be applied anymore. , the MEMS packages produced with wafer level encapsulation techniques, require new methodologies to measure hermeticity appropriately and accurately. The purpose of this paper is to present the development of alternative methods for testing the hermeticity of MEMS micro-cavities. Two methods will be investigated in the context of this study: The membrane deflection measurement 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 (FT-IR). The calculated leak rates are compared for samples where standard fine leak test gave no results. The values obtained for the leak rates within optical test and FT-IR test for the same sample are identical, showing the relevance of these two methods. Keywords: Hermeticity, MEMS, wafer-level packaging, helium leak test, reliability |
