The residual stress and structural properties of tungsten thin films prepared by magnetron sputtering as a function of sputtering-gas pressure are reported. The films were analyzed in situ by a cantilever beam technique, and ex situ by x-ray diffraction, cross-sectional transmission electron microscopy (TEM), x-ray photoelectron spectroscopy, electron energy-loss spectrometry, and energy-filtered electron diffraction. It is found that the residual stress, microstructure, and surface morphology are clearly correlated. The film stresses, determined in real time during the film formation, depend strongly on the argon pressure and change from highly compressive to highly tensile in a relatively narrow pressure range of 12–26 mTorr. For pressures exceeding ∼60 mTorr, the stress in the film is nearly zero. It is also found that the nonequilibrium A15 W structure is responsible for the observed tensile stress, whereas the stable bcc W or a mixture of bcc W and A15 W are in compression. Cross-sectional TEM eviden...

Residual stress, microstructure, and structure of tungsten thin films deposited by magnetron sputtering

Publisher Summary There exists a multitude of chemical vapor deposition (CVD) processes. In thermally activated CVD (TACVD), the deposition is initiated and maintained by heat. This chapter introduces the underlying principles of thermally activated chemical vapor deposition (TACVD). In addition, large-area deposition and selective CVD on patterned substrates are discussed. CVD is a process where a solid material is deposited from a vapor by a chemical reaction occurring on or in the vicinity of a normally heated substrate surface. The resulting solid material is in the form of a thin film, powder, or single crystal. By varying experimental conditions, including substrate material, substrate temperature, and composition of the reaction gas mixture, total pressure gas flows, etc., materials with a wide range of physical, tribological, and chemical properties can be grown. A characteristic feature of the CVD technique is its excellent throwing power, enabling the production of coatings of uniform thickness and properties with a low porosity even on substrates of complicated shape. Another important feature is the capability of localized, or selective deposition, on patterned substrates. CVD and related processes are employed in many thin film applications, including dielectrics, conductors, passivation layers, oxidation barriers, conductive oxides, tribological and corrosion-resistant coatings, heat-resistant coatings, and epitaxial layers for microelectronics. Other CVD applications are the preparation of high-temperature materials (tungsten, ceramics, etc.) and the production of solar cells, high-temperature fiber composites and particles of well-defined sizes.

Chemical Vapor Deposition

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

Thin tungsten films were produced by magnetron sputtering at room temperature in Ar and O 2 gas mixture. The influences of oxygen impurities by varying oxygen partial pressures on the formation and stability of the A15 β-W phase were investigated. The films were analyzed by X-ray photoelectron spectroscopy (XPS), electron energy-loss spectrometry (EELS), X-ray diffraction (XRD), and energy-filtered electron diffraction (EFED). It was found that the formation of the body-centered-cubic (bcc) α-W structure was favored when the oxygen content in the films was less than 3 at.%, while the A15 β-W phase was formed between 6 and 15 at.% oxygen. At higher oxygen partial pressures, the films deposited in this manner were found to be essentially amorphous. Phase transformation from A15 W to bcc W by higher temperature annealing (∼900 K) was accompanied by reduction of oxygen in the films. The driving force for the irreversible phase transition process, A15 β-W→bcc α-W by anneal, is discussed.

Influences of oxygen on the formation and stability of A15 β-W thin films

The deposition of ultra-thin tungsten films and their related 2D chalcogen compounds on large area dielectric substrates by gas phase reactions is challenging. The lack of nucleation sites complicates the adsorption of W-related precursors and subsequent sulfurization usually requires high temperatures. We propose here a technique in which a thin solid amorphous silicon film is used as reductant for the gas phase precursor WF6 leading to the conversion to metallic W. The selectivity of the W conversion towards the underlying dielectric surfaces is demonstrated. The role of the Si surface preparation, the conversion temperature, and Si thickness on the formation process is investigated. Further, the in situ conversion of the metallic tungsten into thin stoichiometric WS2 is achieved by a cyclic approach based on WF6 and H2S pulses at the moderate temperature of 450 °C, which is much lower than usual oxide sulfurization processes.

/pdf/the-conversion-mechanism-of-amorphous-silicon-to-38wdaxu57f.pdf

The conversion mechanism of amorphous silicon to stoichiometric WS2

Tungsten films produced by selective deposition onto silicon wafers

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

Selective deposition of tungsten by chemical vapour deposition from SiH4 reduction of WF6

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Tungsten films produced by selective deposition onto silicon wafers

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

Selective deposition of tungsten by chemical vapour deposition from SiH4 reduction of WF6