Thermally stable high effective work function TaCN thin films for metal gate electrode applications

Abstract

TaCN layers were deposited using metal-organic chemical-vapor deposition for applications as metal gate electrodes in p-type metal-oxide-semiconductor (pMOS) devices. The films were formed by thermal decomposition of tertiary-amylimido-tris(dimethylamido)tantalum (TAIMATA®) between 400 and 600 °C. The composition was dependent on the growth temperature with increasing C and decreasing N content at higher temperature. Films grown below 500 °C were nearly amorphous and became weakly polycrystalline with a cubic structure at higher growth temperature. The layer density was ∼8.1 g/cm3, about half of the TaCN bulk density. Grazing-incidence x-ray diffraction and transmission electron microscopy showed that the films consist of small polycrystalline grains in an amorphous matrix. The resistivity was found to decrease with increasing growth temperature. Lowest resistivity values were around 1 mΩ cm for films grown at 600 °C. The films formed an ∼4 nm thick insulating surface oxide, which leads to a thickness dependence of the film resistivity. Oxygen was also found to diffuse slowly into the bulk metal, which leads to a resistivity aging effect. The effective work function of the TaCN films was found to be 4.8 eV on HfSiO4 and HfSiON and to shift weakly by high thermal budget annealing toward the Si valence band, reaching 4.9 eV on HfSiO4.

Plasma-Enhanced Atomic Layer Deposition of TaCx Films Using Tris(neopentyl) Tantalum Dichloride and H2 Plasma

“…Ta nitride ALD was also reported using a range of metal-organic precursors, such as Ta-based alkylamides and alkylimides such as pentakis (dimethylamido) tantalum [PDMAT, Ta(NMe 2 ) 5 ], 12 6,23 Basically, the use of metalorganic precursors has benefits in producing halogen-free films.…”

“…[1][2][3][4][5][6] Although the main applications of these materials are as a diffusion barrier for copper metallization, [1][2][3][4][5] they are also considered to be a metal gate with high-permittivity gate dielectrics. 6 For these applications, they need to be deposited uniformly at high aspect ratio (AR) structures with a conformal thickness as the demand for shrinking dimensions is increased. In addition, a deposition technique with high process controllability and large-area uniformity is needed.…”

“…13,16,17,19,22 Although N 2 plasma 12 or NH 3 plasma 15 was used to reduce PDMAT, the resulting film was Ta 3 N 5 , whose resistivity was too high to be measured. Only when the H 2 -based plasma such as H 2 or methane/H 2 or Ar/H 2 plasma 6,12,17,20,22,23 was used as a reactant, highly conductive Ta-based nitride film, actually TaC x N y could be deposited, where the C or N content in the film could be controlled by the deposition conditions, such as growth temperature, plasma condition, and type of reactant. Although these plasma-enhanced ALD (PEALD)-TaC x N y films could be successfully used as a diffusion barrier against Cu, 12,14,20 they have some limitations as metal gate material in n-MOSFET (ntype metal-oxide-semiconductor field effect transistor) because the existence of nitrogen in metal carbide gates tends to increase the work function.…”

Thermal stability of hafnium and hafnium nitride gates on HfO2 gate dielectrics

“…However, it has been shown that as the nitrogen content increases, an optically transparent and electrically insulating phase appears to form [31]. The work function of Hf films is around 4.1 eV [11], whereas that of HfN x films is between 4.55 and 4.9 eV [11,24,32]. The work function of HfN x appears to be dependent on the nitrogen content and the interface properties of HfN x /gate dielectrics.…”

“…The three key points for selection of gate electrode materials are work function, thermal stability, and lower resistivity. So far, many types of materials have been investigated to replace poly-silicon, such as pure metals [2][3][4][5][6], binary alloys [7][8][9][10], metal nitrides [11][12][13][14][15], metal carbides [16], and fully silicided Si (FUSI) [17][18][19][20]. Of these, the refractory transition metal nitrides are of interest owing to their good thermal stability, good oxygen diffusion barrier characteristics, and tunable work function.…”