A Technological Study of Lithographical Structuring of Aluminum on Select Low-Temperature-Cofired-Ceramic Surfaces

Today, the reliability of electronic circuits plays a central role in many challenging applications. Due to the ever-increasing demand for integration density, high-frequency properties, and temperature stability, low-temperature-cofired-ceramic (LTCC) technology offers solutions for new integration methods for microsystems. Currently, the most commonly used processing technology for LTCC circuit carriers is thick-film processing. However, the implementation of thin-film technologies promises higher resolution and better integration density, although a key issue is the compatibility of the LTCC substrates with thin-film technologies, which is required in order to achieve high-resolution metallization on multilayer substrates, thus combining advantages of both multilayer technology and thin-film technology. To achieve this new integration step, it is first necessary to comprehensively characterize the LTCC substrates and identify limiting parameters in regard to the realization of high-resolution structures. This article seeks to narrow this knowledge gap. To verify and correlate the achievable structural resolution with the given substrate properties, thin-film processes were applied to several types of substrate with varying geometrical properties utilizing photolithographic processing via mask-alignment, with feature sizes as small as $2~\mu $ m being achieved.