Semiconductor device with capping layer and method for fabricating the same

A method for fabricating a semiconductor device, comprising:

• providing a substrate;
• forming a capping mask layer on the substrate;
• forming a first trench along the capping mask layer and extending to the substrate;
• conformally forming a layer of first insulating material into the first trench;
• forming a first work function layer on the layer of first insulating material and in the first trench;
• forming a first conductive layer on the first work function layer and in the first trench;
• and
• forming a first capping layer on the first conductive layer;
• wherein the first capping layer comprises germanium oxide;
• wherein the first conductive layer comprises germanium;
• wherein the first work function layer comprises silicon and/or germanium with substantially no oxygen and nitrogen;
• wherein the first gate insulating layer comprises silicon oxide, silicon nitride, silicon oxynitride, silicon nitride oxide, a high-k material, or a combination thereof;
• wherein the capping mask layer comprises silicon oxide, silicon oxycarbide, silicon oxycarbonitride, silicon oxynitride, silicon nitride oxide, or a combination thereof;
• wherein forming the first capping layer on the first conductive layer comprises:
• alternately and sequentially introducing a germanium precursor and an oxygen source to form a layer of first capping material filling the first trench;
• and
• performing a planarization process until a top surface of the capping mask layer is exposed to turn the layer of first capping material into the first capping layer.