A semiconductor device and methods of forming a semiconductor device are disclosed. In the methods, a layer, such as an insulating interlayer, is formed on a substrate. A first trench is formed in the layer, and a mask layer is formed in the first trench. The mask layer has a first thickness from a bottom surface of the first trench to the top of the mask layer. The mask layer is patterned to form a mask that at least partially exposes a sidewall of the first trench. A portion of the mask adjacent to the exposed sidewall of the first trench has a second thickness smaller than the first thickness. The layer is etched to form a second trench using the mask as an etching mask. The second trench is in fluid communication with the first trench. A conductive pattern is formed in the first trench and the second trench.