Advanced Ultrathin Spray Coating Process Technology for Heterogeneous Integration Applications

In this work the spray coating deposition of thin and ultrathin homogeneous layers of Divinylsiloxane-bis-benzocyclobutene (DVS-BCB or BCB) is presented. Film thicknesses from 200 nm down to 5 nm are achieved. The layer thickness is assessed using Variable Angle Spectroscopy Ellipsometry (VASE), which allows for nondestructive high precision thickness measurement. Multiple positions mapping provides information about thickness distribution across the substrate. This spray coating process study reveals that the layer deposition for thicker films (> 75 nm) is mainly driven by hardware parameters. For thinner layers, additional material solution adjustment (dilution) is necessary. For each studied layer thickness (200 nm, 35 nm and 5 nm), batches of 25 wafers are prepared aiming to study the wafer-to-wafer process stability necessary for successful industrial application. Finally, the thin and ultrathin BCB layers are used for different bonding technologies, i.e. die-to-wafer permanent adhesive bonding as well as micro transfer printing (μ Tp). Multiple electronic integrated circuits (EICs) and quantum dot lasers (QDLs) devices are heterogeneously integrated to Si/SiO₂/BCB wafers using the layers with thicknesses of 35 nm and 5 nm. For all devices a 100 % process yield is obtained.