Semiconductor devices and methods of forming semiconductor devices are provided. A method includes forming a first mask layer over an underlying layer, patterning the first mask layer to form a first opening, forming a non-conformal film over the first mask layer, wherein a first thickness of the non-conformal film formed on the top surface of the first mask layer is greater than a second thickness of the non-conformal film formed on a sidewall surface of the first mask layer, performing a descum process, wherein the descum process removes a portion of the non-conformal film within the first opening, and etching the underlying layer using the patterned first mask layer and remaining portions of the non-conformal film as an etching mask.