Abstract: Methods of forming integrated circuit devices include patterning an electrically insulating layer to support dual-damascene interconnect structures therein. The steps of patterning the electrically insulating layer include using multiple planarization layers having different porosity characteristics. Forming an interconnect structure within an integrated circuit device may include forming an electrically insulating layer on a substrate and forming at least one via hole extending at least partially through the electrically insulating layer. The at least one via hole is filled with a first electrically insulating material having a first porosity. The filled at least one via hole is then covered with a second electrically insulating material layer having a second porosity lower than the first porosity. The second electrically insulating material layer is selectively etched back to expose a first portion of the first electrically insulating material in the at least one via hole.