Examples of a method of forming an integrated circuit device with an interfacial layer disposed between a channel region and a gate dielectric are provided herein. In some examples, the method includes receiving a workpiece having a substrate and a fin having a channel region disposed on the substrate. An interfacial layer is formed on the channel region of the fin, and a gate dielectric layer is formed on the interfacial layer. A first capping layer is formed on the gate dielectric layer, and a second capping layer is formed on the first capping layer. An annealing process is performed on the workpiece configured to cause a first material to diffuse from the first capping layer into the gate dielectric layer. The forming of the first and second capping layers and the annealing process may be performed in the same chamber of a fabrication tool.