Hermetic wafer-level glass sealing enabling reliable low cost sensor packaging

A batch compatible glass deposition process is presented, that enables the use of molded packages for optical sensors even in the field of high quality devices. The deposition technology discussed allows to form compact and dense borosilicate glass layers at very low temperatures. The glass material employed is a highly robust and long-term stable material with high chemical and hydrolytic resistance. Being a glass, it is highly transparent in the visible range, making it the material of choice for optical sensors. One further main advantage of borosilicate glass is its well matched coefficient of thermal expansion (CTE), avoiding additional influences on stress sensitive silicon-based sensors by temperature change in application. The glass films are applied by an e-beam evaporation deposition assisted by a simultaneous plasma compaction. The borosilicate glass deposition technology and its capabilities are described in depth as well as the experiments performed to verify its usability in the addressed packaging application including extensive reliability testing. Example packaging applications are presented and it is shown, that the glass sealing is performed at wafer-level making it a cost-efficient process. However, the main cost benefits are achieved in simplifying the subsequent packaging steps. Therefore this unique deposition process can provide a significant cost advantage especially in high quality sensor applications, while at the same time helping to further miniaturize the overall package.