Interfacial adhesion of spin-coated thin adhesive film on silicon substrate for the fabrication of polymer optical waveguide

An investigation was carried out to study the interfacial adhesion of spin-coated polymeric adhesive thin film on a silicon substrate for fabrication of a polymeric optical waveguide. An adhesive shear button was made on a silicon substrate by using a photolithography process, and interfacial adhesion was measured with a Dage D2400 shear tester. Different adhesion strengths were found at different portions of the same sample. Higher adhesion strength was observed at the center of the substrate than at other locations of spin-coated adhesive films. Adhesion strength was also measured after heat exposure of the deposited and cured adhesive layer to evaluate the heat resistance of the adhesive film. After heat exposure, adhesion strength decreased substantially from all locations of the substrate due to the thermal degradation. Again, the adhesion was measured for different plasma-treated substrate conditions. The surface morphology of plasma-treated and untreated silicon substrates before deposition were characterized by atomic force microscopy. Lower adhesion strength was unexpectedly observed for all plasma-treated substrates, even for higher surface roughness. The fracture surfaces after shear testing were also characterized by optical microscopy. The complete study provides important indications for the fabrication of better-performing polymeric optical waveguides for photonic devices.