REDUCTION OF MECHANICAL-STRESS IN MICROMACHINED COMPONENTS CAUSED BY HUMIDITY-INDUCED VOLUME EXPANSION OF POLYMER LAYERS

Polymer layers frequently used in microsystem technology tend to absor b water from ambient humid air which typically results in swelling of the polymer layers. Depending on the specific component design, this v olume expansion may cause changes in the mechanical stress, or even di splacement of device structures. In most applications, these effects l imit performance and reliability, and should therefore be minimized. T he present paper describes an approach for the investigation of swelli ng phenomena in thin polymer layers. Polyimide PI2540 was chosen as a model polymer. After extensive characterization of the polymer layer p roperties, static and dynamic sorption behavior was investigated by di fferent means. Based on our experimental results, we have developed li nearized models to accurately describe the swelling behavior. Several polymers were characterized. Although the micro-physical mechanisms re sponsible for the humidity-induced swelling are still poorly understoo d, we are - based on our data - able to effectively reduce humidity in duced stress by selecting suitable polymers and optimizing processing procedures.