In today's rapidly advancing field of semiconductor device manufacturing and technology, smaller and faster transistors are being produced enabling the evolution of semiconductor devices that are more complicated and more highly integrated. CMOS, complementary metal oxide semiconductor, semiconductor devices and other semiconductor devices include both NMOS (n-type metal oxide semiconductor) and PMOS (p-type metal oxide semiconductor) gate structures. The NMOS and PMOS gate structures operate most efficiently under different operating conditions and each benefits from being formed of dedicated materials particularly suited to the device requirements of the respective NMOS or PMOS transistor. NMOS and PMOS transistors are desirably formed of gate electrode materials that have different work functions so that the respective transistors may perform at the highest operational efficiencies. Since the NMOS and PMOS transistors are formed in and on the same semiconductor substrate, it is critical to form the NMOS and PMOS transistors using materials formed over the semiconductor substrate that have the appropriate material characteristics. One such characteristic is the stress of the material, i.e. compressive or tensile. Both the NMOS and PMOS transistors work most efficiently with a gate structure formed of a particular film or films having particular stress characteristics which are associated with particular work functions.
The processing operations used to deposit films such as may be used for transistor gate electrodes, have inherent characteristics as do the films formed using the deposition processes. While it may be possible to tune the deposition process itself by varying process parameters such as power, gas constituents, gas flow rates, temperatures and pressures, and while the process tuning efforts may advantageously alter some film characteristics such as changing an inherently compressive stress to be a tensile stress as deposited, such process tuning typically brings about undesirable film characteristics such as poor uniformity across the semiconductor substrate, poor step coverage of the deposited film and other undesirable film qualities.
It would therefore be desirable to tune the transistors and semiconductor devices by providing transistor gates formed of materials with desired material characteristics such as stress, without causing other undesirable aspects.