J. S. Reid

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.

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>>

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.

Reactively sputtered Ti-Si-N films. II. Diffusion barriers for Al and Cu metallizations on Si

Ti-Si-N films synthesized by reactively sputtering a TiSi2, a Ti5Si3, or a Ti3Si target in Ar/N2 gas mixture were tested as diffusion barriers between planar (100) Si substrates and shallow n+p Si diodes, and Al or Cu overlayers. The stability of the Ti-Si-N barriers generally improves with increasing nitrogen concentration in the films, with the drawback of an increase in the film’s resistivity. Ti34Si23N43 sputtered from the Ti5Si3 target is the most effective diffusion barrier among all the Ti-Si-N films studied. It works as an excellent barrier between Si and Cu. A film about 100 nm thick, with a resistivity of around 700 μΩ cm, maintains the stability of Si n+p shallow junction diodes with a 400 nm Cu overlayer up to 850 °C for 30 min vacuum annealing. When it is used between Al and Si, the highest temperature of stability achievable with a 100-nm-thick film is 550 °C. A thermal treatment at 600 °C causes a severe intermixing of the layers. The microstructure, atomic density, and electrical resistivi...

Amorphous Ta-Si-N diffusion barriers in Si/Al and Si/Cu metallizations

Abstract Thin films of amorphous Ta-Si-N alloys were deposited by reactive RF sputtering of a Ta5Si3 target in an Ar/N2 ambient. These alloy films were tested as diffusion barriers between Al and Si, as well as between Cu and Si. Electrical measurements on Schottky diodes and on shallow n+p junction diodes were used to evaluate the thermal stability of the 〈Si〉 /W48Si20N32(20 nm)/Ta36Si14N50(80 nm)/Al(1000 nm) metallization. The amorphous W48Si20N32 contacting layer was added to raise the Schottky barrier height of the metallization on n-type Si. Both the shallow junctions and the Schottky diodes are stable up to 700°C for 20 min (above the Al melting point of 660°C) which makes this material the best thin-film diffusion barrier on record. Furthermore, the same Ta36Si14N50 amorphous film maintains the integrity of the I–V characteristics of the shallow n+p junctions with the 〈Si〉 /TiSi2(30 nm)/Ta36Si34N50(80 nm)/Cu(500 nm) metallization up to 900°C for 30 min annealing in vacuum. The TiSi2 contacting layer was added to assure an ohmic characteristic of the contact. For comparison, the same shallow junctions with 〈Si〉 /Cu metallizations were shorted after annealing at 300°C.

W-B-N diffusion barriers for Si/Cu metallizations

Reactively sputtered from a W2B target, amorphous W-B-N thin films are investigated. The physical properties of the films, namely density, resistivity, crystallization behavior and reaction temperature with silicon, are given as functions of composition. Additionally, the films are assessed as diffusion barriers between silicon substrates and copper overlays. By I(V) measurements of shallow-junction diodes, a 100 nm W64B20N16 barrier prevents copper from reaching the silicon during an 800 °C, 30 min heat treatment in vacuum. W79B21 films are able to prevent diffusion into the diodes only up to 500 °C. High resolution transmission electron microscopy shows that W64B20N16 and W79B21 films are both marginally amorphous with local ordering of less than 1.5 nm.