The barrier layer in Cu technology is essential to prevent Cu from diffusing into the dielectric layer at high temperatures; therefore, it must have a high stability and good adhesion to both Cu and the dielectric layer. In the past three decades, tantalum/tantalum nitride (Ta/TaN) has been widely used as an inter-layer to separate the dielectric layer and the Cu. However, to fulfill the demand for continuous down-scaling of the Cu technology node, traditional materials and technical processes are being challenged. Direct electrochemical deposition of Cu on top of Ta/TaN is not realistic, due to its high resistivity. Therefore, pre-deposition of a Cu seed layer by physical vapor deposition (PVD) or chemical vapor deposition (CVD) is necessary, but the non-uniformity of the Cu seed layer has a devastating effect on the defect-free fill of modern sub-20 or even sub-10 nm Cu technology nodes. New Cu diffusion barrier materials having ultra-thin size, high resistivity and stability are needed for the successful super-fill of trenches at the nanometer scale. In this review, we briefly summarize recent advances in the development of Cu diffusion-proof materials, including metals, metal alloys, self-assembled molecular layers (SAMs), two-dimensional (2D) materials and high-entropy alloys (HEAs). Also, challenges are highlighted and future research directions are suggested.

Recent Advances in Barrier Layer of Cu Interconnects

Laser‐assisted chemical vapor deposition of tungsten microstructures (dots, stripes, or films) has been accomplished via the H2 reduction of WF6 on polycrystalline silicon‐coated quartz substrates irradiated with a focused cw argon‐ion laser beam. Tungsten dots were grown on the substrates via a pyrolytic process occurring within the laser‐heated zone of about 200 μm in diameter. The morphology and height of these dots were determined as functions of deposition parameters by profilometer measurements. The effects of WF6 and H2 partial pressures on the morphology and deposition rate of W dots were investigated at a laser‐induced surface temperature ranging from 340 to 950 °C. The deposition rate of flat‐topped dots was independent of the deposition temperature and proportional to the WF6 partial pressure. The deposition rate of W dots with a Gaussian profile was independent of the WF6 partial pressure. At low temperatures (340–670 °C) and high H2 partial pressures (50–700 Torr), the deposition rate of Gaussian W dots was proportional to the square root of the H2 partial pressure. At high temperatures (750–950 °C) and reduced H2 partial pressures (20–80 Torr), the deposition rate of these dots was proportional to the H2 partial pressure. This reaction order equal to 1 was interpreted on the basis of the Rideal model involving a direct reaction between H2 molecules and fluorinated adspecies on the W surface. The nature of the fluorinated adsorbed phase on the metal surface was discussed in terms of coordination number of W and F atoms. A new reaction mechanism for the H2 reduction of WF6 promoted by laser irradiation of the deposition zone or accomplished in a conventional furnace‐type reactor is discussed and proposed.

Growth kinetics of tungsten microstructures produced via the hydrogen reduction of tungsten hexafluoride on laser‐heated substrates

Low-temperature (575 degrees C), low-pressure chemical vapor deposition (LPCVD) of thick (250-800-nm) TiN films was investigated. Submicron contact holes could be filled completely with TiN. The influence of the LPCVD chemistry on the materials properties and conformality of the deposit was addressed. The compatibility of LPCVD TiN contact filling with a TiSi/sub 2/ salicide process was demonstrated with electrical measurements of junction leakage and contact resistance. >

Contact hole fill with low temperature LPCVD TiN

Chemical vapour deposition of tungsten by H2 reduction of WC16

Comparison of the diffusion barrier properties of tungsten films prepared by hydrogen and silicon reduction of tungsten hexafluoride

Tungsten films were deposited on Si substrates by the H2 or Si reduction of WF6 under various experimental conditions. The composition and structure of as-deposited samples as well as the interfacial reactions and interdiffusion of elements in annealed samples were characterized by nuclear reaction analyses, sheet resistance measurements, x-ray diffraction technique, and Rutherford backscattering spectroscopy. The amount of oxygen at W–Si interfaces was found to be dependent on the cleaning treatment of the Si surface used before WF6–Si interaction. The interfacial oxygen concentration was less than 1 ⊠ 1014 at./cm2 (detection limit of the nuclear reaction analysis) and (2–7) ⊠ 1016 at./cm2 using an HF cleaning and the RCA treatment, respectively. For W/Si samples, the formation temperature of WSi2 was dependent on the dopant level in the Si substrates and the oxygen concentration at W–Si interfaces. The silicidation reaction occurred at 625 °C in “oxygen free” W/Si structures while for structures containing interfacial oxygen atoms, this reaction occurred above 800 °C. In Al/W/Si structures, the intermetallic compound, WAl12, was formed by annealing at 450 °C for 90 min. Furthermore, the formation of WSi2 was observed in structures annealed at a temperature in the range of 550 °C–600 °C regardless of the oxygen concentration at the W–Si interface. A model to explain the effect of interfacial oxygen atoms on the silicidation reaction and the influence of the Al overlayer on the thermal stability of Al/W/Si structures is proposed and discussed in this paper.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400004143

Silicide formation in metal/Si structures and diffusion barrier properties of CVD tungsten films

The interactions of tungsten films with silicon and aluminum during annealing treatments of W/Si and Al/W/Si structures have been investigated using sheet resistance measurements, nuclear reaction analyses, x‐ray diffraction techniques, Rutherford backscattering, and Auger electron spectroscopy. W(H) and W(Si) films, 100–200 nm thick, were deposited via the H2 reduction of WF6 on undoped single‐crystal Si wafers and the Si reduction of WF6 on As implanted Si wafers, respectively. Prior to the metal deposition, As implanted Si wafers were cleaned by dipping in NH4OH:H2O2 followed by HCl:H2O2 at 80 °C for 20 min (RCA cleaning treatment). The oxygen content at the metal–Si interface in W(Si)/As implanted Si structures can reach 3 at. % whereas in W(H) /mono‐Si structures, the metal–Si interface is oxygen free. In W/Si samples, the formation temperature of WSi2 was found to be dependent on the interfacial oxygen concentration. For oxygen‐free W/Si structures, the silicidation reaction occurred at 625 °C while...

The influence of an aluminum overlayer on the interaction of tungsten films with silicon substrates

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Silicide formation in metal/Si structures and diffusion barrier properties of CVD tungsten films

The influence of an aluminum overlayer on the interaction of tungsten films with silicon substrates