Fabrication of high-resolution, self-aligned palladium electrodes

Here, a fabrication approach is presented, which allows for the patterning of vertically displaced, high density and high resolution palladium electrodes in a single processing step. A top down method, namely ion milling, was used to transfer the e-beam lithography pattern into the palladium. Hereby hydrogen silsesquioxane (HSQ) was employed as a hard mask. Other than the conventionally used lift-off based approach, this method does not restrict the line height to spacing ratio and therefore permits the fabrication of very densely spaced electrodes. Specifically, electrodes with as little as 25 nm spacing were obtained, although only lines with spacings of 80 nm or more were electrically isolated without any further processing. By adjusting the tilting angle and the HSQ to Pd thickness the cross-sectional profile can be controlled and varied from triangular (30 degrees side-wall slope at 10 degrees tilt) to rectangular (30 degrees tilt). This can be used to its advantage in order to reduce the parasitic capacitance of adjacent lines for a given pitch. Additionally, a proximity effect was observed as the decrease of spacing of electrodes was correlated with an increase in side-wall verticality. In summary, we have demonstrated a robust process to pattern perfectly aligned electrodes on complex topographical substrates. The here presented method is characterized by a high degree of scalability and also high flexibility in terms of materials selection. (C) 2016 Elsevier B.V. All rights reserved.