A low-temperature thin-film electroplated metal vacuum package

This paper presents a packaging technology that employs an electroplated nickel film to vacuum seal a MEMS structure at the wafer level. The package is fabricated in a low-temperature (< 250 degreesC) 3-mask process by electroplating a 40-mum -thick nickel film over an 8-mum sacrificial photoresist that is removed prior to package sealing. A large fluidic access port enables an 800 x 800 mum package to be released in less than three hours. MEMS device release is performed after the formation of the first level package. The maximum fabrication temperature of 250 degreesC represents the lowest temperature ever reported for thin film packages (previous low similar to 400 degreesC). Implementation of electrical feedthroughs in this process requires no planarization. Several mechanisms, based upon localized melting and Pb/Sn solder bumping, for sealing low fluidic resistance feedthroughs have been investigated. This package has been fabricated with an integrated Pirani gauge to further characterize the different sealing technologies. These gauges have been used to establish the hermeticity of the different sealing technologies and have measured a sealing pressure of similar to1.5 torr. Short-term (similar toseveral weeks) reliability data is also presented.