Probing local adhesion: A miniaturized multi-photon lithography design demonstrated on silanized vs. untreated surfaces

As multi-photon lithography technology matures, advanced integrated device design concepts become possible, positioned onto small surfaces, such as an optical fibre face. Only local adhesion anchors the printed object on the surface and ensure proper print-development without structure loss and long-term usability. Although surface treatments such as silanization are well known to considerably increase adhesion strength, quantification of adhesion is not straightforward and commonly assessed indirectly by surface characteristics and technological methods. The present work aims to quantify adhesion on a micrometer scale through SEM in situ tension experiments, that utilize a newly developed specimen geometry. Multiple specimens, with various footprints, were manufactured on both silanized and untreated fused silica substrates, allowing the quantification to be compared between the adhesions stresses of different surface conditions. Specimens on an untreated substrate failed with a high scatter in detaching force, whereas specimens on a silanized substrate tend to fail within the photoresist, either at the gauge section or just above the substrate, rather than at the interface. Thus, the adhesion stress was increased at least by a factor of 1.4 by the salinization treatment. Generally, a novel approach was developed, that can quantify local adhesions properties in realistic packaging or integrated circuits.