1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device.
2. Related Art
In order to microfabricate a semiconductor device, there has been developed a technique using a high dielectric film, such as HfSiON, as a gate dielectric film and using metal as a gate electrode on the gate dielectric film.
A gate electrode made of metal is difficult to be processed, unlike a gate electrode made of polysilicon, and has poor thermal stability. In order to solve these problems, a method of forming a gate electrode using a damascene process has been proposed. According to this process, a dummy gate is formed first, and an extension layer is formed using this dummy gate electrode as a mask. Thereafter, this dummy gate electrode is removed to form a trench. A gate dielectric film and a metal gate electrode are embedded into this trench.
However, at the time of depositing the gate dielectric film in the trench, a high dielectric material that becomes the gate dielectric film is deposited on the side surface of the trench as well as the bottom surface of the trench. When a gate dielectric film is formed on the side surface of the trench, a length or a width of the gate electrode becomes small. As a result, a distance between a source/drain diffusion layer (an extension layer) and the gate electrode becomes long. Consequently, an on-current decreases. Furthermore, because a distribution of an electric flux line changes at the end of the gate electrode, a MOSFET does not operate easily due to a short-channel effect.
A MISFET (metal insulator semiconductor field effect transistor) requires various leak characteristics, various threshold voltages, and various operation powers, depending on specifications. In order to form a MISFET having various characteristics on the same semiconductor substrate, it is necessary to form gate dielectric films having different film thickness of gate dielectric films and different concentrations of high-dielectric materials (such as hafnium) in the gate dielectric films.
According to a conventional method of manufacturing a semiconductor device, it has been necessary to repeat processes such as film forming, patterning, and etching many times in order to form gate dielectric films having various film thicknesses and various concentrations of high-dielectric materials. Because the number of processes of manufacturing a semiconductor device increases, the cost of the semiconductor device increases, and it becomes difficult to maintain stable characteristics of the semiconductor device.