Diffusion Barrier For Cu Metallization Research Articles

Diffusion Barrier Characteristics of WSiN Films

WSiN films were produced through hybrid pulse direct current/radio frequency magnetron co-sputtering and evaluated as diffusion barriers for Cu metallization. The Cu/WSiN/Si assemblies were annealed for 1 h in a vacuum at 500–900 °C. The structural stability and diffusion barrier performance of the WSiN films were explored through X-ray diffraction, Auger electron spectroscopy, and sheet resistance measurement. The results indicated that the Si content of WSiN films increased from 0 to 9 at.% as the power applied to the Si target was increased from 0 to 150 W. The as-deposited W76N24, W68Si0N32, and W63Si4N33 films formed a face-centered cubic W2N phase, whereas the as-deposited W59Si9N32 film was near-amorphous. The lattice constants of crystalline WSiN films decreased after annealing. The sheet resistance of crystalline WSiN films exhibited a sharp increase as they were annealed at 800 °C, accompanied by the formation of a Cu3Si compound. The failure of the near-amorphous W59Si9N32 barrier against Cu diffusion was observed when annealed at 900 °C.

Organosiloxane nanolayer as diffusion barrier for Cu metallization on Si

Development of emerging technologies such as artificial intelligence, big data, and smart vehicles brings increasing demands on high-performance integrated circuits (ICs). To achieve this goal, ultra-miniaturization of Cu interconnects as well as diffusion barrier layer to increase the integration density is imperative. In this study, we demonstrate that an ultrathin organosiloxane nanolayer exhibits excellent barrier efficacy against the active diffusion of Cu towards Si. The organosiloxane nanolayer is constructed on the SiO2 surface using dehydration to covalently tether the hydrolyzed organosilane molecules. The amine termini of organosilanes are used to adsorb catalytic Pd nanocluster to accomplish the Cu metallization on Si. Rapid thermal annealing is performed with respect to the Si/SiO2/organosiloxane/Cu junctions to evaluate the efficacy of diffusion barrier. Based on microstructural and crystallographic examinations, the organosiloxane nanolayer with a shorter alkyl chain performs better with a higher breakdown temperature of 923 K at which the Cu diffusion and the Cu silicide formation at the junctions occur. The grafting conformations of organosilane molecules with various alkyl chain lengths on the SiO2 surface are constructed based on energy minimization calculations to rationalize the diffusion barrier efficacy.

Thermal stability of AlCrTaTiZrMo-nitride high entropy film as a diffusion barrier for Cu metallization

In this study, an amorphous (AlCrTaTiZrMo)N senary nitride film was prepared by DC reactive magnetron sputtering as a single-layer barrier material for Cu interconnection. To evaluate its thermal stability, Cu/(AlCrTaTiZrMo)N/Si structure was annealed at 600 °C for different amounts of time in high vacuum to simulate the actual working environment. The layer maintained a suitable thermal stability after annealing for 7 h. No large holes or cracks were observed on the surface, and the layer remained amorphous without any grain boundaries and maintained excellent interface adhesion with the Cu and Si. The minimal amount of Cu that diffused into the layer suggested that inter-diffusion between the Cu and Si atoms was effectively suppressed. The excellent diffusion barrier performance and high temperature long-term thermal stability is attributed to the stable amorphous structure with no rapid diffusion path, and its structural and chemical stability. Thus, the amorphous (AlCrTaTiZrMo)N thin film can be used for Cu interconnections as a reliable and effective material.

Nano-grained ZrB2 thin films as a high-performance diffusion barrier in Cu metallization

Nano-grained ZrB2 thin films are prepared by radio-frequency (rf) magnetron sputtering and, the thermal stability and the diffusion barrier performance are evaluated at elevated temperatures.

(Invited) Ru-Based Binary or Ternary Thin Films By Atomic Layer Deposition for a Seedless Cu Interconnects

Ru has been suggested as a diffusion barrier that is compatible with the direct plating of Cu. However, previous studies showed that Ru itself is not a suitable diffusion barrier for Cu metallization due mainly to its poor microstructure with polycrystalline columnar grains. This study developed several Ru-based multi-component thin films, RuMn, RuSiN, and RuAlO using atomic layer deposition (ALD) process, which are compatible with the direct plating of Cu as well as show better diffusion barrier performance against Cu than Ru. Mn, SiNx, AlOx were incorporated into the Ru by combining the Ru and corresponding ALD cycles, and Ru-based binary alloy, RuMn, ternary thin films, RuSiN and RuAlO, were fabricated at 225 oC. As a typical example, the results on ALD-RuAlO were shortly described. The step coverage of ALD-RuAlO was perfect at contact holes with an aspect ratio of ~ 25 (top-opening diameter: ~ 85 nm). XRD and TEM results indicate that ALD-Ru film prepared without AlOx ALD cycle forms a polycrystalline structure with columnar grains. But, with incorporating the AlOx cycles, RuAlO films were formed with non-columnar grains and nano-crystalline microstructure consisting of Ru nano-crystals separated by amorphous AlOx matrix. XRD analysis showed that the structure of Cu/ALD-RuAlO (8 nm)/Si was stable after annealing at 600 oC for 30 minute while Cu/Ru (15 nm)/Si structure was failed after annealing at 450 oC. It was also shown that the electroplating of Cu was directly achieved on a very thin (~8-nm-thick) RuAlO film at blanket and pattern wafer. In the case of binary ALD-RuMn film, it should be noted that after annealing ALD-RuMn film at 500 oC, the self-formation of Mn silicate barrier between Ru(Mn) film and SiO2 was confirmed based on XRD and TEM analysis, which was due to the diffusion of Mn into underlying SiO2, resulting in better diffusion barrier performance than Ru counterpart. Acknowledgements This work was supported by the Technology Innovation Program (Industrial Strategic technology development program, 10035430, Development of reliable fine-pitch metallization technologies) funded by the Ministry of Knowledge Economy (MKE, Korea) and also partially supported by Tanaka Precious Metals, Japan.

Properties of plasma-enhanced atomic layer deposited TiCx films as a diffusion barrier for Cu metallization

TiCx films were grown on thermally grown SiO2 substrate by atomic layer deposition (ALD) using tetrakis–neopentyl–titanium [Ti(CH2C(CH3)3)4, TiNp4, Np=neopentyl, CH2C(CH3)3] and direct plasma of H2 as a reactant at the substrate temperature ranging from 200 to 400°C. A narrow ALD temperature window from 275 to 300°C was shown and a growth rate of 0.054nm/cycle at the ALD temperature window was obtained. The ALD-TiCx films formed nanocrystalline structure with rock-salt phase that was confirmed by X-ray diffractometry and transmission electronic microscopy (TEM) analysis. Its resistivity was dependent on the microstructure features characterized by grain size and crystallinity as well as its density, which could be controlled by varying the deposition temperature. Resistivity of ~600μΩcm was obtained at the deposition temperature 300°C where is in the ALD temperature window, by optimizing deposition condition. In this study, a performance of very thin ALD-TiCx (6nm) as a diffusion barrier for Cu interconnects was evaluated. The results showed that the structure of Cu (80nm)/ALD-TiCx (6nm)/Si was stable after annealing at 600°C for 30min. Cross-sectional view TEM analysis combined with energy-dispersive spectroscopy revealed that ALD-TiCx diffusion barrier failed by the diffusion of Cu through the thin barrier layer into Si at 650°C without interfacial reactions between the layers.

Highly Conformal Amorphous W–Si–N Thin Films by Plasma-Enhanced Atomic Layer Deposition as a Diffusion Barrier for Cu Metallization

Ternary and amorphous tungsten silicon nitride (W–Si–N) thin films were grown by atomic layer deposition (ALD) using a sequential supply of a new fluorine-free, silylamide-based W metallorganic precursor, bis(tert-butylimido)bis(bis(trimethylsilylamido))tungsten(VI) [W(NtBu)2{N(SiMe3)2}2], and H2 plasma at a substrate temperature of 300 °C. Here, W(NtBu)2{N(SiMe3)2}2 was prepared through a metathesis reaction of W(NtBu)2Cl2(py)2 (py = pyridine) with 2 equiv of LiN(SiMe3)2 [Li(btsa)]. The newly proposed ALD system exhibited typical ALD characteristics, such as self-limited film growth and linear dependency of the film growth on the number of ALD cycles, and showed a high growth rate of 0.072 nm/cycle on a thermally grown SiO2 substrate with a nearly zero incubation cycle. Such ideal ALD growth characteristics enabled excellent step coverage of ALD-grown W–Si–N film, ∼100%, onto nanotrenches with a width of 25 nm and an aspect ratio ∼4.5. Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy analysis confirmed that the incorporated Si and W were mostly bonded to N, as in Si–N and W–N chemical bonds. The film kept its amorphous nature until annealing at 800 °C, and crystallization happened at local areas after annealing at a very high temperature of 900 °C. An ultrathin (only ∼4 nm thick) ALD-grown W–Si–N film effectively prevented diffusion of Cu into Si after annealing at a temperature up to 600 °C.

Stability of TaRhx as a potential diffusion barrier for Cu metallization: capacitance–voltage tests after bias temperature stress

Amorphous TaRhx was integrated in metal oxide semiconductor (MOS) capacitors with Cu gate metallization (Al/Si/25 nm SiO2/10 nm TaRhx/Cu). The stability of TaRhx diffusion barriers was investigated under bias temperature stress testing using capacitance–voltage (C–V) measurements. The stability of these capacitors was compared with similar capacitors with TaNx as the diffusion barrier layer or with capacitors with no diffusion barrier. The electrical measurements were compared with compositional information obtained by backside secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). Comparison of C–V measurements on capacitors with TaRhx/Cu and TaRhx/Al gate metallizations revealed that both mobile alkali ions and Cu+ contribute to the flatband voltage shift of the MOS capacitors. C–V measurements of capacitors with various barriers showed that the mobile ion concentration (Cu+) in the capacitors with TaRhx diffusion barriers is reduced to 32 % of the value for capacitors with no diffusion barrier. In contrast, capacitors with TaNx barriers showed the lowest mobile ion concentration among all the barrier types. Based on flatband voltage shift values, TaNx barriers outperform TaRhx barriers. However, if the percentage of deformed C–V curves is used as the reliability criterion, both barriers perform quite similarly. Compositional analysis data suggests that the concentrations of the diffused species are below the detection limits of SIMS and TEM. This work demonstrated the importance of employing electrical reliability tests for evaluation of potential diffusion barrier materials.

Thermal stability of RuZr alloy thin films as the diffusion barrier in Cu metallization

Thin films of RuZr/Cu stacking were deposited on Si substrates by magnetron sputtering technology. The as-deposited RuZr thin films were amorphous, while Cu thin films were polycrystalline with (111) preferred orientation. The films were then annealed at given temperatures to evaluate the thermal stability. It was demonstrated that the amorphous state could be maintained up to 450°C and, the inter-diffusion between Cu and Si atoms was effectively suppressed. However, the atom diffusion became significant at higher temperatures and resulted in the formation of high-resistance Cu3Si phase. So RuZr amorphous alloy thin films can be readily used for Cu metallization, but the working temperature should be not higher than 450°C.

Characteristics of reactively sputtered niobium nitride thin films as diffusion barriers for Cu metallization

NbN films were prepared by radio frequency reactive magnetron sputtering and then employed as diffusion barriers between Cu and Si. The microstructure of the NbN films was an assembly of very small columnar crystallites with a cubic structure. To investigate the properties as diffusion barriers, we performed metallurgical reactions of Cu/NbN0.8/Si, Cu/Nb/Si and Cu/TaN0.7/Si for comparisons. The sheet resistance increased dramatically after annealing above 750°C for Cu/NbN0.80/Si, and above 500°C for both Cu/Nb/Si and Cu/TaN0.7/Si. The interfaces were deteriorated seriously and formation of Cu3Si was observed when the sheet resistance was significantly increased. The diffusion coefficient of Cu in NbN barrier films was estimated by using the change of resistance (ΔR s /R s %). Compared with TaN0.7, NbN0.8 films possess larger grain size and lower Cu diffusion coefficient. Our results suggest that the NbN film can be used as a diffusion barrier for Cu metallization as compared to the well-known TaN film.

Stability of Glassy Ta-Rh Diffusion Barriers for Cu Metallization

Amorphous Ta-Rh thin films were studied as diffusion barriers for Cu metallization. Thermodynamic calculations were performed to predict the glass forming ability of the Ta-Rh system. Various compositions were deposited by co-sputtering from two targets and the theoretically predicted amorphization range was confirmed by structural characterization using XRD and TEM observations. These calculations provide a useful guide for selecting a glass forming composition suitable for diffusion barrier applications for Cu metallization. The selected composition was studied as a diffusion barrier in contact with Cu and Si. A 13 nm-thick Ta0.45Rh0.55 film is effective at temperatures up to 550°C, whereupon it dissociates into its constituents followed by formation of RhSi.

Growth, Thermal Stability and Cu Diffusivity of Reactively Sputtered NbN Thin Films as Diffusion Barriers between Cu and Si

NbNx films were prepared by RF reactive magnetron sputtering from a Nb target in N2/ Ar gas mixtures and then used as diffusion barriers between Cu and Si substrates. Material characteristics of the NbNx, films were investigated and were correlated with the N2/Ar flow ratio. The variations in film resistivity is correlated with the change of phases and chemical compositions from α-Nb, β-Nb2N, γ-Nb4N3, δ-NbN + δ′-NbN as the N2/Ar ratio is increased. The thermal stability of Cu (60 nm)/NbNx (25 nm)/Si multilayers were investigated and our results indicated that the barrier performances were significantly affected by the chemical composition of NbNx films. The diffusion coefficient of Cu in NbNx was measured by four-point probe analysis after annealing Cu/NbNx/Si multilayered samples in the temperature range of 600-850°C. Cu diffusion in NbNx had components from the grain boundaries and the lattice. In addition, our results suggest that the NbNx can be used as a potential diffusion barrier for Cu metallization as compared to the conventional TaN.

Performance Improved by Incorporating of Ru Atoms into Zr-Si Diffusion Barrier for Cu Metallization

Thin Ru21Zr64Si15 films deposited on Si substrates by radio frequency reactive magnetron sputtering are studied and evaluated as diffusion barriers for Cu metallization. Cu/Ru21Zr64Si15/Si and Cu/Zr67Si33/Si structure samples are prepared under the same procedures for comparison. The thermal stability, phase formation, surface morphology and atomic depth profile of the Cu/Ru21Zr64Si15/Si and Cu/Zr67Si33/Si structures before and after annealing at different temperatures are investigated. In conjunction with these analyses, the Cu/Ru21Zr64Si15/Si contact system shows high thermal stability at least up to 650°C. The results obtained reveal that the incorporation of Ru atoms into the Zr67Si33 barrier layer is shown to be beneficial for improving the thermal stability of the Cu/barrier/Si contact system.

Impurity-controlled Mo films as diffusion barriers for Cu metallization

Effects of vacuum conditions on the oxygen content and microstructure of Mo layers used with Cu gate lines as thin-film transistor-liquid crystal display diffusion barriers were investigated. Mo was deposited using ion-beam sputtering at 1.0 × 10−5 and 7.0 × 10−7 Torr. The Mo layer oxygen content and the microstructure and changes in chemical composition of the Cu/Mo/SiO2/Si layer during annealing were examined. The Mo layer microstructure was influenced by oxygen; increasing concentration increased the energy required for secondary grain growth. Growth was suppressed at high oxygen levels. Therefore, diffusion barrier performance is enhanced by finer Mo layer grain sizes.

Amorphous Ta-N as a Diffusion Barrier for Cu Metallization

ABSTRACTAmorphous Ta-N thin films (14 and 62 nm thick) are deposited on Si substrates by reactive magnetron sputtering followed by Cu film deposition. The interlayer reaction and failure mechanism of the annealed metallization stacks are investigated by resistance measurements, xray diffraction (XRD) and detailed electron microscopy analysis accompanied with electron energy-loss spectroscopy (EELS). Amorphous Ta-N crystallizes at 600°C by a polymorphous transformation to Ta2N. The crystallized Ta2N barrier prevents Cu-Si interaction and intermixing up to 700-800°C, depending on the barrier thickness. Copper appears to be the main diffusing species and reacts with Si at the Ta-N/Si interface to form η˝-Cu3Si. Local Cu-Si reaction enhances the formation of TaSi2 precipitates. Silicon also diffuses, though at a much slower rate, to the surface and reacts with Cu. Local oxidation of Cu3Si occurs upon exposure to air, accompanied by SiO2 formation.

Thermal Stability and Performance of NbSiTaTiZr High-Entropy Alloy Barrier for Copper Metallization

Development of better diffusion barriers for Cu metallization is one of the key issues for the microelectronics industry. Although metallic diffusion barriers offer many advantages, their application is hindered due to their inferior thermal stability relative to ceramic barriers. Here we report on a metallic diffusion barrier, NbSiTaTiZr, which shows thermal stability comparable to ceramic barriers. The outstanding performance of NbSiTaTiZr is due to its better structural and chemical stability at high temperatures.

Ultrathin Mo/MoN bilayer nanostructure for diffusion barrier application of advanced Cu metallization

Ultrathin Mo (5 nm)/MoN (5 nm) bilayer nanostructure has been studied as a diffusion barrier for Cu metallization. The Mo/MoN bilayer was prepared by magnetron sputtering and the thermal stability of this barrier is investigated after annealing the Cu/barrier/Si film stack at different temperatures in vacuum for 10 min. The failure of barrier structure is indicated by the abrupt increase in sheet resistance and the formation of Cu 3Si phase proved by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). High resolution transmission electron microscopy (HRTEM) examination suggested that the ultrathin Mo/MoN barrier is stable and can prevent the diffusion of Cu at least up to 600 °C.

Barrier capability of Zr–N films with titanium addition against copper diffusion

Zr–Ti–N film prepared by sputtering deposition has been employed as a potential diffusion barrier for Cu metallization. It is thought that the existing states of Ti and Zr in the films are Ti–N and Zr–N phase in Zr–Ti–N films. Material analysis by XRD, XPS and sheet resistance measurement reveal that the failure of Zr–N film is mainly due to the formation of Cu 3Si precipitates at the Zr–N/Si interface by Cu diffusion through the grain boundaries or local defects of the Zr–N barrier layer into Si substrate. In conjunction with sheet resistance measurement, XRD and XPS analyses, the Cu/Zr–Ti–N/Si contact system has high thermal stability at least up to 700 °C. The incorporation of Ti atoms into Zr–N barrier layer was shown to be beneficial in improving the thermal stability of the Cu/barrier/Si contact system.

Multiprincipal-Element AlCrTaTiZr-Nitride Nanocomposite Film of Extremely High Thermal Stability as Diffusion Barrier for Cu Metallization

To inhibit Cu diffusion in interconnects, an effective diffusion barrier of high thermal stability is strongly demanded. Thus in this study, a nitride nanocomposite film of equimolar five-element high-entropy alloy, (AlCrTaTiZr)N, was developed and deposited by reactive sputtering. Thermal stability of the (AlCrTaTiZr)N film and its barrier performance to the interdiffusion of Si and Cu were investigated under thermal annealing at 700 to 900oC. The (AlCrTaTiZr)N, constructed of mixed crystalline and amorphous nanocomposite structure, was found to remain thermally stable at an extremely high temperature of 900oC. Neither interdiffusion between Si and Cu through the (AlCrTaTiZr)N layer nor formation of any silicides occurred. Severe lattice distortions caused by the incorporation of multiprincipal elements and the nanocomposite structure of nanocrystallites surrounded by an amorphous matrix without the existence of grain boundaries were expected as the dominant factors for the high thermal stability and superior diffusion resistance of the (AlCrTaTiZr)N film.

Multiprincipal-Element AlCrTaTiZr-Nitride Nanocomposite Film of Extremely High Thermal Stability as Diffusion Barrier for Cu Metallization

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