E. Kolawa

Tantalum‐based diffusion barriers in Si/Cu VLSI metallizations

We have studied sputter-deposited Ta, Ta36Si14, and Ta36Si14N50 thin films as diffusion barriers between Cu overlayers and Si substrates. Electrical measurements on Si n + p shallow junction diodes demonstrate that a 180-nm-thick Ta film is not an effective diffusion barrier. For the standard test of 30-min annealing in vacuum applied in the present study, the Ta barrier fails after annealing at 500 °C. An amorphous Ta74Si26 thin film improves the performance by raising the failure temperature of a /Ta74Si26(100 nm)/Cu(500 nm) metallization to 650 °C. Unparalled results are obtained with an amorphous ternary Ta36Si14N50 thin film in the Si/Ta36Si14N50 (120 nm)/Cu(500 nm) and in the Si/TiSi2(30 nm)/Ta36SiN50 (80 nm)/Cu(500 nm) metallization that break down only after annealing at 900 °C. The failure is induced by a premature crystallization of the Ta36Si14N50 alloy (whose crystallization temperature exceeds 1000 °C) when in contact with copper.

Evaluation of amorphous (Mo, Ta, W)SiN diffusion barriers for 〈Si〉|Cu metallizations

Abstract Amorphous binary M(= Mo, Ta or W)-Si and ternary MSiN, r.f.-sputtered from M 5 Si 3 and WSi 2 targets, are assessed as diffusion barriers between silicon substrates and copper overlayers. By I ( V ) tests of the metallizations on n + p shallow junction diodes, the ternary MSiN barriers prevent copper from reaching the silicon at 800 °C or higher during a 30 min heat treatment in vacuum. Failure of the metallizations correlates with the crystallization temperature of the barrier, which is presumably a prelude to fast grain-boundary diffusion. Metal-rich MoSiN and WSiN barriers liberate nitrogen during annealing, which poses a limitation to their crystallization temperatures. No reaction products of copper with metal-rich MSi or MSiN barriers are observed, which is in agreement with our recent thermodynamic modelling of the MSiCu ternary systems.

REACTIVELY SPUTTERED TI-SI-N FILMS. I. PHYSICAL PROPERTIES

Films of Ti-Si-N were synthesized by reactively sputtering TiSi2, Ti5Si3, or Ti3Si targets in an Ar/N2 gas mixture. They were characterized in terms of their composition by MeV 4He backscattering spectrometry, their atomic density by thickness measurements combined with backscattering data, their microstructure by x-ray diffraction and high-resolution transmission electron microscopy, and their electrical resistivity by four-point-probe measurements. All films have a metal–to–silicon ratio close to that of their respective targets. The as-deposited films are either entirely amorphous or contain inclusions of TiN-like nanometer-sized grains when the overall atomic composition of the films approaches the TiN phase in the ternary Ti-Si-N diagram. A correlation between the resistivity of the as-deposited films and their position in the ternary phase diagram is evident, indicating that at the atomic scale, the spatial arrangement of atoms in the amorphous phase and their bonding character can approximate those...

Properties of reactively sputter-deposited TaN thin films

Abstract We deposited TaN films by reactive r.f. sputtering from a Ta target with an N 2 Ar gas mixture. Alloys over a composition range 0–60 at.% N have been synthesized. We report on their composition, structure and electrical resistivity before and after vacuum annealing in the temperature range 500–800 °C. We found that the film growth rate decreases with increasing ratio of the nitrogen flow rate to the total flow rate, while the nitrogen content in the films first increases with the N 2 partial flow rate and then saturates at about 60 at.%. B.c.c.-Ta, Ta 2 N, TaN and Ta 5 N 6 appear in succession as the nitrogen content rises, with Ta 2 N being the only single-phase film obtained. The atomic density of the films generally increases with the nitrogen content in the film. Transmission electron micrographs show that the grain size decreases from about 25 to 4 nm as the nitrogen concentration increases from 20 to 50 at.%. The Ta 2 N phase can exist over a wide range of nitrogen concentration from about 25 to 45 at.%. For as-deposited films an amorphous phase exists along with polycrystalline Ta 2 N in the center portion of that range. This phase crystallizes after vacuum annealing at 600 °C for 65 min. A diagram of stable and metastable phases for TaN films based on X-ray diffraction and transmission electron microscopy results is constructed. The resistivity is below 0.3 m ohms cm for films with 0–50 at.% N and changes little upon vacuum annealing at 800 °C.

Full field measurements of curvature using coherent gradient sensing : application to thin film characterization

This paper introduces coherent gradient sensing (CGS) as an optical, full-field, real-time, non-intrusive and non-contact technique for measurement of curvature and curvature changes in thin film and micro-mechanical structures. The technique is applied to determine components of the curvature tensor field in multilayered thin films deposited on silicon wafers. Curvature field measurements using CGS are compared with average curvatures obtained using high-resolution X-ray diffraction. Finally, examples are presented to demonstrate the capability of CGS in measuring curvature in a variety of thin film and micro-mechanical structures.

Ti-Si-N diffusion barriers between silicon and copper

Thin films of Ti-Si-N, reactively spattered from a Ti/sub 5/Si/sub 3/ target, are assessed as diffusion barriers between silicon substrates and copper overlayers. By tests on shallow-junction diodes, a 100 nm Ti/sub 34/Si/sub 23/N/sub 43/ barrier is able to prevent copper from reaching the silicon substrate during a 850/spl deg/C/30 min anneal in vacuum. A 10 nm film prevents diffusion up to 650/spl deg/C/30 min. By high-resolution transmission electron microscopy, Ti/sub 34/Si/sub 23/N/sub 43/ predominantly consists of nanophase TiN grains roughly 2 nm in size.<<ETX>>

Amorphous Ta-Si-N thin-film alloys as diffusion barrier in Al/Si metallizations

Amorphous Ta–Si–N thin films of a wide range of compositions were prepared by rf reactive sputtering of a Ta5Si3 target in a N2/Ar plasma. The relationship between films’ composition and resistivity is reported. All obtained films were tested as diffusion barriers between Al and Si. Backscattering spectrometry combined with cross‐sectional transmission electron microscopy were used to determine the barrier effectiveness. It was found that aluminum can be melted on top of the Si/Ta–Si–N structure (675 °C for 30 min) without any evidence of metallurgical interactions between the layers.

Sputtered Ta-Si-N diffusion barriers in Cu metallizations for Si

Electrical measurements on shallow Si n/sup +/-p junction diodes with a 30-nm TiSi/sub 2/ contacting layer demonstrate that an 80-nm-thick amorphous Ta/sub 36/Si/sub 14/N/sub 50/ film prepared by reactive RF sputtering of a Ta/sub 5/Si/sub 3/ target in an Ar N/sub 2/ plasma very effectively prevents the interaction between the Si substrate with the TiSi/sub 2/ contacting layer and a 500-nm Cu overlayer. The Ta/sub 36/Si/sub 14/N/sub 50/ diffusion barrier maintains the integrity of the I-V characteristics up to 900 C for 30-min annealing in vacuum. It is concluded that the amorphous Ta/sub 36/Si/sub 14/N/sub 50/ alloy is not only a material with a very low reactivity for copper, titanium, and silicon, but must have a small diffusivity for copper as well.<<ETX>>

Amorphous (Mo, Ta, or W)-Si-N diffusion barriers for Al metallizations

M–Si–N and M–Si (M=Mo, Ta, or W) thin films, reactively sputtered from M5Si3 and WSi2 targets, are examined as diffusion barriers for aluminum metallizations of silicon. Methods of analysis include electrical tests of shallow-junction diodes, 4He + + backscattering spectrometry, x-ray diffraction, transmission electron microscopy, scanning electron microscopy, and secondary-ion-mass spectrometry. At the proper compositions, the M–Si–N films prevent Al overlayers from electrically degrading shallow-junction diodes after 10 min anneals above the melting point of aluminum. Secondary-ion-mass spectrometry indicates virtually no diffusivity of Al into the M–Si–N films during a 700 °C/10 h treatment. The stability can be partially attributed to a self-sealing 3-nm-thick AlN layer that grows at the M–Si–N/Al interface, as seen by transmission electron microscopy.

Performance of W100−xNx diffusion barriers between 〈Si〉 and Cu

Abstract The performance of reactively RF sputtered tungsten nitride diffusion barriers in both amorphous (W 76 N 24 ) and polycrystalline (W 46 N 54 ) forms is studied in the 〈Si〉/W 100- x N x /Cu contact metallization by electrical measurements on shallow n + p jun ction diodes, backscattering spectrometry, and X-ray diffraction analyses. The DC characteristics of the diodes measured before and after vacuum annealings for 30 min reveal that about 120 nm thick, initially X-ray amorphous W 76 N 24 film between 〈Si〉 and Cu preserves the integrity of the metallization up to 750° C. The stability is confirmed also both by 2 MeV 4 He 2+ backscattering and X-ray diffraction analyses. Annealing at 800°C for 30 min results in overall intermixing of the layers, causing a shorting of the shallow junction diodes and forming a mixture of Cu, β-W 2 N, α-W, (Cu, Si)′, and W 5 Si 3 phases in the structure observed by X-rays. Analysis by electrical measurements on shallow junction diodes and X-ray diffraction reveals that the initially polycrystalline form of the W 100- x N x alloy is an inferior barrier. After annealing at 750°C for 30 min the DC characteristics of the diodes show a significant increase of the leakage current, and a mixture of Cu, β-W 2 N, and (Cu, Si)-ϵ phases are found by X-ray diffraction analysis.