Mediated Patterning of Sol -Gel Thin Layers: Shrinkage, Decohesion, and Lift-Off

Abstract

The shrinkage and densification of sol-gel layers were determined by in-situ and ex-situ measurements, where a &sim;30% decrease in thickness (t) was typical during drying of sol-gel layers (T < 300&deg;C). Constrained shrinkage, resulting from adhesion to the supporting silicon substrate, led to a coherent (crack-free) film with biaxial stresses of &sim;200 MPa (t &sim; 50 nm). For ODTS-mediated sol-gel films, however, precise in-situ wafer curvature measurements determined that film stresses never exceeded 75 MPa. Additionally, interfacial adhesive strength between the substrate and the sol-gel film were evaluated for the first time using a unique pulsed-laser stress-wave technique. An adhesive strength threshold of 15 MPa was determined for sol-gel films on ODTS-functionalized silicon, whereas, the threshold strength of films deposited on unmodified silicon was determined as >25 MPa and greater than the fracture strength of silicon. In this work, hydrophobic surface regions, facilitated by directed mu-CP of a molecular film, affected adhesion so as to reduce the substrate constraint and promote de-cohesion of the sol-gel film on the sub-micron scale. That is, selective de-cohesion and lift-off were enabled by the control of local mechanical interfacial constraints.