Abstract:
Devices with lightly-doped semiconductor channels (e.g., FinFETs) need mid-gap (˜4.6-4.7 eV) work-function layers, preferably with low resistivity and a wide process window, in the gate stack. Tantalum carbide (TaC) has a mid-gap work function that is insensitive to thickness. TaC can be deposited with good adhesion on high-k materials or on optional metal-nitride cap layers. TaC can also serve as the fill metal, or it can be used with other fills such as tungsten (W) or aluminum (Al). The TaC may be sputtered from a TaC target, deposited by ALD or CVD using TaCl4 and TMA, or produced by methane treatment of deposited Ta. Al may be added to tune the threshold voltage.
Abstract:
Tungsten silicide layers can be used in CMOS transistors in which the work function of the tungsten silicide layers can be tuned for use in PMOS and NMOS devices. A co-sputtering approach can be used in which silicon and tungsten are deposited on a high dielectric constant gate dielectric layer. The tungsten silicide layer can be annealed at or above a critical temperature to optimize the resistivity of the tungsten silicide layer. In some embodiments, the concentration of as-deposited tungsten silicide can be between 50 at % silicon to 80 at % silicon. The critical temperatures can be lower at higher silicon concentration, such as 700 C. at 63 at % silicon to 600 C. at 74 at % silicon.