Disclosed herein are integrated circuit (IC) package substrates formed with a dielectric bi-layer, and related devices and methods. In some embodiments, an IC package substrate is fabricated by: forming a raised feature on a conductive layer; forming a dielectric bi-layer on the conductive layer, where the dielectric bi-layer includes a first sub-layer having a first material property and a second sub-layer having a second material property, and where the top surface of the second sub-layer is substantially planar with the top surface of the raised feature; and removing the first sub-layer until the second material property is detected to reveal the conductive feature. In some embodiments, an IC package substrate is fabricated by: forming a dielectric bi-layer on a patterned conductive layer, where the first sub-layer is less susceptible to removal than the second sub-layer; forming an opening in the dielectric bi-layer; etching; and forming a via having vertical sidewalls.