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Oxidized Porous Silicon Moisture Sensors for Evaluation of Microelectronic Packaging
Published online by Cambridge University Press: 15 February 2011
Abstract
Accurate moisture measurements in microelectronic assemblies are crucial in assessing reliability of integrated circuits (ICs). We describe the fabrication and use of a silicon-based device for evaluation of moisture barrier coatings. The capacitive moisture sensors use oxidized porous silicon (OPS) as the sensing element. Porous silicon (PS) is formed by anodization of Si in hydrofluoric acid (HF). Oxidation of PS in oxygen produces OPS, which is also porous if an appropriate starting microstructure and oxidation treatment are selected. Metallization layers on the OPS and the wafer back complete the capacitor structure. The capacitance of OPS sensors is functionally related to the moisture content of the surrounding atmosphere. For example, the capacitance of one sensor changed from 4 nF/cm2 when exposed to a moisture level of 300 ppm by volume (ppmv) to 36 nF/cm2 at 10,000 ppmv. In addition to this excellent sensitivity, capacitor response to step changes in moisture is rapid and reversible. The sensors are also rugged, as demonstrated by their consistent performance during accelerated testing at 85% relative humidity and 140°C. A silicon nitride IC moisture barrier coating was deposited on sensors of this type after normal ceramic dual in-line packaging. Sensor operability after coating deposition was confirmed following intentional introduction of a pinhole into the moisture barrier coating.
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- Copyright © Materials Research Society 1991
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