S. C. Sun

Comparison of the diffusion barrier properties of chemical‐vapor‐deposited TaN and sputtered TaN between Cu and Si

This work investigated the barrier properties of metalorganic chemical‐vapor‐deposited (CVD) tantalum nitride (TaN) and physical‐vapor‐deposited (PVD) TaN between Cu and Si. The CVD TaN film had a preferred orientation (200) with a grain size of around 60 nm, while the PVD TaN had a (111) preferred orientation with a grain size of around 20 nm, as determined by transmission electron microscopy (TEM) and x‐ray diffraction (XRD) analyses. Degradation study of the Cu/TaN/Si contact system was also performed by sheet resistance measurement, scanning electron microscopy (SEM), XRD, secondary ion mass spectroscopy (SIMS), and shallow junction diodes. These results indicated that the PVD TaN film can act as a better diffusion barrier than the CVD TaN film. The higher thermal stability of PVD TaN than CVD TaN can be accounted by their difference in microstructures. The failure mechanisms of both CVD TaN and PVD TaN films as diffusion barriers between Cu and Si were also discussed.

Effect of oxygen to argon ratio on properties of (Ba,Sr)TiO3 thin films prepared by radio-frequency magnetron sputtering

Thin films of (Ba,Sr)TiO3 on Pt/SiO2/Si substrates were deposited using rf magnetron sputtering at various substrate temperatures and O2/(Ar+O2) mixing ratios (OMR). The crystallinity of the films improved significantly as the OMR increased. The dielectric constant increased with increasing OMR and reached a maximum value at 50% OMR. The leakage current density decreased with increasing oxygen flow, but had a minimum value at 40% OMR. The results for the dielectric constant and the leakage current were interpreted in terms of polarization effect and loss theory. The film deposited at 450 °C and 50% OMR exhibited good surface morphology and had a dielectric constant of 375, a tangent loss of 0.074 at 100 kHz, a leakage current density of 7.35×10−9 A/cm2 at an electric field of 100 kV/cm with a delay time of 30 s, and a charge storage density of 49 fC/μm2 at an applied field of 150 kV/cm. The 10 yr lifetime of time-dependent dielectric breakdown studies indicate that a 50% OMR sample has a longer lifetime t...

Metalorganic chemical vapor deposition of tantalum nitride by tertbutylimidotris(diethylamido)tantalum for advanced metallization

We deposited tantalum nitride (TaN) films by low‐pressure metalorganic chemical vapor deposition (LP‐MOCVD) using a new precursor tertbutylimidotris(diethylamido)tantalum (TBTDET). Strong Ta–N double bond in the precursor preserved the ‘‘TaN’’ portion during the pyrolysis process. This method has yielded low‐resistivity films. It changed from 10 mΩ cm (deposited at 500 °C) to 920 μΩ cm (obtained at 650 °C). The carbon and oxygen concentrations were low in the films deposited at 600 °C, as determined by x‐ray photoelectron spectroscopy. Transmission electron microscopy and x‐ray diffraction analysis indicated that the as‐deposited films exhibited polycrystalline structures with the lattice constants close to the bulk TaN value. The TaN barrier layer was successfully applied as a glue layer for CVD tungsten (W) metallization schemes.

Metalorganic chemical vapor deposition of tungsten nitride for advanced metallization

In this study, the physical and electrical properties of tungsten nitride thin films deposited by thermal decomposition of bis(tertbutylimido)bis(tertbutylamido)tungsten have been investigated. The films have an excellent step coverage over high aspect‐ratio contact holes as well as a low carbon concentration. Strong W–N double bonds in the precursor preserved the nitrogen atoms during the pyrolysis process. This method subsequently yielded low‐resistivity films. A decrease in film resistivity from 4300 to 620 μΩ cm corresponded to an increase in the deposition temperature from 500 to 650 °C. X‐ray diffraction (XRD) and wavelength dispersive spectroscopy (WDS) results indicated that the as‐deposited films have face centered cubic (fcc) phase polycrystalline structures with excessive nitrogen atoms.

Metal-organic chemical vapor deposition of tantalum nitride barrier layers for ULSI applications

Abstract Low-resistivity tantalum nitride (TaN) films were deposited by low-pressure metal-organic chemical vapor deposition (MOCVD) using a new precursor tertbutylimidotrisdiethylamidotantalum. The surface morphology and the step coverage of TaN films were characterized by scanning electron microscopy. The film deposited at 450 °C had nearly 100% step coverage and the step coverage decreased to 25% for the films deposited at 650 °C. The carbon and oxygen concentrations are about 10 at.% in the CVD TaN films, as determined by Auger electron spectroscopy. From Rutherford backscattering spectroscopy and secondary ion mass spectroscopy analysis, TaN films were found to be effective diffusion barriers between aluminum and silicon up to 550 °C. The electrical measurements of diode-leakage current indicate that the Al/TaN Si structure remained stable up to 500 °C, after which Al started to diffuse through the TaN layer and resulted in a higher leakage current.

Thermal Stability of Sputtered Tungsten Carbide as Diffusion Barrier for Copper Metallization

This work investigated the thermal stability of tungsten carbide (WC x ) films deposited by a sputtering process with a WC target as diffusion barrier layer between Cu and Si. The as-deposited WC x film has a nanocrystalline structure and a low electrical resistivity of around 227 μΩ cm. Film characterization reveals that the WC x film was able to preserve the integrity of the Cu (2000 A)/WC x (500 A)/n-Si structure without formation of Cu 3 Si, up to a 600°C annealing for 30 min. In addition, diode leakage current measurements on the same contact structure, but with a p + n-Si substrate did not show deterioration of electrical characteristics up to a 550°C annealing. As the thickness of the WC x barrier was reduced to 150 A, the WC x film retained the integrity of diodes up to 500°C without increasing the diode leakage current, The failure of WC x film after high temperature annealing is attributed to the Cu diffusion into the Si substrate through grain boundaries or local defects of the WC x barrier layer, in which some local defects may arise from the formation of W 5 Si 3 .

Characterization of Sputtered Tantalum Carbide Barrier Layer for Copper Metallization

In this study, tantalum carbide (TaC x ) films deposited by a sputtering process with a TaC target as diffusion barriers for Cu metallization were investigated for the first time. The thermal stability of Cu/TaC x /n-Si and Cu/TaC x /p + n systems as a function of annealing temperature are reported and analyzed. The deposited TaC x , having an amorphous structure and a low resistance of around 385 μΩ cm, were characterized by sheet resistance measurement, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), secondary ion mass spectroscopy, and diode leakage current measurement. From XRD and SEM analysis, it was found that 600 A TaC X in Cu/TaC X /Si structure can effectively prevent Cu penetration up to 600°C for 30 min, while more sensitive diode leakage measurement of Cu/TaC X /p + n indicates that the failure temperature is around 500°C. The failure of the TaC x layer was found to be mainly due to the diffusion of Cu along the localized defects of the TaC x barrier layer into underlying silicon. This has caused the formation of copper silicides and high junction leakage currents.

A comparative study of sputtered TaCx and WCx films as diffusion barriers between Cu and Si

Abstract The barrier properties of sputter-deposited tantalum carbide (TaC x ) and tungsten carbide (WC x ) for Cu metallization were investigated and compared. The incorporation of the C atom is shown to be effective in decorating local defects of the barrier layer and improving the thermal stability of the Cu/barrier/Si contact system. Owing to a higher melting point and better chemical inertness, with respect to Si substrate, the TaC x (600 A) film shows a better thermal stability (up to 650°C) than that of WC x (∼600°C) film based on material analyses, while the highest stable temperature as evaluated by the n + p-diode leakage measurement is found to be approximately 550°C for the TaC x and 500°C for the WC x barrier layer. The failure of the TaC x and WC x barriers is found to be mainly due to Cu diffusion through the localized defects of the barrier layers into the Si substrate. The interfacial reaction between the WC x layer and the Si substrate is found to play an additional role in the failure of the WC x film.

Performance of MOCVD tantalum nitride diffusion barrier for copper metallization

A low-resistivity and low carbon concentration CVD TaN film has been realized by using a new precursor terbutylimido-tris-diethylamido tantalum (TBTDET). Results show that CVD TaN as a diffusion barrier for Cu has higher thermal stability up to 500/spl deg/C than CVD TiN of 450/spl deg/C.

Influence of Nitrogen Doping on the Barrier Properties of Sputtered Tantalum Carbide Films for Copper Metallization

The effect of nitrogen doping on the barrier properties of sputter-deposited tantalum carbide (Ta–C) films was investigated for the first time. With increasing nitrogen concentration, it was found that the resistivity of the barrier layer increases, while the growth rate decreases. In addition, the use of an optimum N2/Ar flow rate ratio of 2/24 during sputtering allows one to achieve tantalum carbon nitride (Ta–C–N) films with the highest thermal stability. According to I–V measurements on reverse-biased Cu/barrier/p+n diodes, the 600-A-thick Ta–C–N barrier layer appeared to be effective in preventing Cu from reaching the Si substrate after 600°C annealing in N2 for 30 min, which is about 100°C higher than that in the case without nitrogen incorporation. The failure of the thermally annealed Ta–C–N film was attributed to the Cu diffusion through the local defects or grain boundaries of the layer into the Si substrate, which results in a significant increase in the diode leakage current.