Diffusion Barrier For Copper Metallization Research Articles

Enhanced Thermal Stability of Sputtered TiN Thin Films for Their Applications as Diffusion Barriers against Copper Interconnect

In this work, the deposition of titanium nitride (TiN) thin film using direct current (DC) sputtering technique and its application as diffusion barriers against copper interconnect was presented. The deposited film was analyzed by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS) techniques. XRD patterns showed the face-centered cubic (FCC) structure for the TiN/SiO2/Si film, having (111) and (200) peaks and TiN (111), Cu(111), and Cu(200) peaks for Cu/TiN/SiO2/Si film. FESEM images revealed that the grains were homogeneously dispersed on the surface of the TiN film, having a finite size. XPS study showed that Ti2p doublet with peaks centered at 455.1 eV and 461.0 eV for TiN film was observed. Furthermore, the stoichiometry of the deposited TiN film was found to be 0.98. The sheet resistance of the TiN film was analyzed by using a four-point probe method, and the resistivity was calculated to be 11 μΩ cm. For the utilization, TiN film were tested for diffusion barrier performance against Cu interconnect. The results exhibited that TiN film has excellent performance in diffusion barrier for copper metallization up to a temperature of 700 °C. However, at a higher annealing temperature of 800 °C, the formation of Cu3Si and TiSi2 compounds were evident. Thus, stoichiometric TiN film with high thermal stability and low resistivity produced in this study could be applied for the fabrication of microelectronic devices.

Effectiveness of tungsten addition on the performance of electroplated nickel diffusion barriers for copper metallization on textured silicon

In this work, the nickel-tungsten alloy is used as the diffusion barrier for copper metallization on textured silicon. Nickel silicides formed as the seed layer for the nickel-tungsten alloy. Then, copper metallization was performed by an electroplating method to create the Cu/NiW/NiSiy/Si structure. The Cu/NiW/NiSiy/Si samples were annealed at various temperatures for 10 minutes in an annealing furnace under Ar/H2 atmospheres. The annealed Cu/NiW/NiSiy/Si samples were characterized by X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy. For the Cu/NiW/NiSiy/Si samples with NiW thicknesses of 300 nm and 350 nm, the Cu3Si phase developed at annealing temperatures of 500 °C and 600 °C, respectively. The NiW layer is a better diffusion barrier against copper than the Ni layer.

Preparation of NiO Monolayer by Langmuir–Blodgett Technique and Its Characterization as Diffusion Barrier for Copper Metallization

Langmuir–Blodgett (LB) technique was used to prepare monolayers of NiO over SiO2/Si substrate. Diffusion barrier capability of NiO layer against the diffusion of copper into the dielectric was evaluated. Deposition and structure of the NiO layer were analyzed using X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and atomic force microscopy (AFM) techniques. Thermal stability of Cu/SiO2/Si and Cu/NiO/SiO2/Si test structures was compared using X-ray diffraction (XRD), scanning electron microscope (SEM), and four probe techniques. The samples were annealed at different temperatures starting from 473 K up to 873 K (200 °C up to 600 °C) in vacuum for 30 minutes each. XRD and SEM results indicated that combination of NiO/SiO2 worked as diffusion barrier up to 773 K (500 °C), whereas SiO2 alone could work as barrier only up to 573 K (300 °C). Sheet resistance of these samples was measured as a function of annealing temperature which also supports XRD results. Capacitance–voltage (C–V) curves of these structures under the influence of biased thermal stress (BTS) were analyzed. BTS was applied at 2.5 MV cm−1 at 423 K (150 °C). Results showed that in the presence of NiO barrier layer, there was no shift in the C–V curve even after 45 minutes of BTS. Little shift was observed after 60 minutes of BTS while in the absence of barrier there was a significant shift in the C–V curve even after 30 minutes of BTS. For the structure with NiO barrier, the threshold voltage (V t) was almost unchanged up to 60 minutes under BTS while Vt of structure without barrier changed significantly even after 15 minutes of stress. Further, these test structures were examined for leakage current density (j L) at same BTS conditions. It was found that the Cu/NiO/SiO2/Si test structure could survive about one and half time more than the Cu/SiO2/Si test structure.

Deposition and Characterization of 3-Aminopropyltrimethoxysilane Monolayer Diffusion Barrier for Copper Metallization

Diffusion barrier capability of 3-aminopropyltrimethoxysilane (APTMS) against the diffusion of copper into the dielectric is studied. A self-assembled monolayer (SAM) of APTMS was deposited on SiO2/Si substrate. Cu/SiO2/Si and Cu/SAM/SiO2/Si test structures were compared for their thermal stability using X-ray diffraction (XRD) characterization, sheet resistance variation, and Capacitance-Volatage (C-V) characterization. The samples were annealed at different temperatures starting from 473 K (200 °C) up to 973 K (700 °C) in vacuum for 30 minutes each. XRD results indicated that combination of SiO2/SAM worked as diffusion barrier up to 873 K (600 °C), whereas SiO2 alone could work as a barrier only up to 673 K (400 °C). Sheet resistance of these samples was measured as a function of annealing temperature, which also supports XRD results. C-V curves of these structures under the influence of biased thermal stress (BTS) were analyzed. BTS was applied with different parameters, i.e., 1.25 MV cm−1 at 323 K (50 °C), 1.25 MV cm−1 at 373 K (100 °C), and 2.5 MV cm−1 at 423 K (150 °C). A change in threshold voltage (∆V t) was observed for each BTS. Results showed that in the case of higher electric field, i.e., 2.5 MV cm−1 at 423 K (150 °C), V t of the Cu/SiO2/Si/Al structure was changed significantly even after 15 minutes of stress, while V t of the Cu/APTMS/SiO2/Si/Al structure was almost unchanged for up to 60 minutes.

The role of oxygen in the deposition of copper–calcium thin film as diffusion barrier for copper metallization

The properties of copper (Cu) metallization based on copper–calcium (CuCa) diffusion barrier as a function of oxygen flux in the CuCa film deposition were investigated in view of adhesion, diffusion and electronic properties. The CuCa film as the diffusion barrier of Cu film improves the adhesion of Cu film, however, and increases the resistance of Cu film. The introduction of oxygen into the deposition of CuCa film induces the improvement of adhesion and crystallinity of Cu film, but produces a slight increase of resistance. The increased resistance results from the partial oxidation of Cu film. The annealing process in vacuum further improves the adhesion, crystallinity and conductivity of Cu film. X-ray diffraction (XRD) and Auger electron spectroscopy (AES) show that the CuCa alloy barrier layer deposited at oxygen atmosphere has perfect anti-diffusion between Cu film and substrate due to the formation of Ca oxide in the interface of CuCa/substrate.

Characteristics of Plasma-Treated Amorphous Ta-Si-C Film as a Diffusion Barrier for Copper Metallization

Ta-Si-C film was prepared by magnetron sputtering, and the thermal stability of the plasma-treated film as a copper diffusion barrier was evaluated. The barrier properties and failure behaviors of the studied films were elucidated using a four-point probe, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The as-deposited Ta-Si-C film had an amorphous structure, and the structure remained stable at an elevated temperature, allowing the film to be adopted as a barrier to inhibit Cu diffusion. The Cu/Ta26Si41C32/Si stacked structure had a failure temperature of 750°C/1 min when the 5-nm-thick Ta26Si41C32 film was treated by exposure to Ar/H2 plasma mixture, while the stacked film failed at 800°C/1 min when treated by exposure to Ar/N2 plasma mixture. Using the Ar/N2 plasma treatment favorably enhanced the thermal stability of the Ta26Si41C32 thin film as a barrier for Cu interconnections. When the Ta-Si-C film thickness was further reduced to 2 nm, the film retained the barrier effect at 650°C, 700°C, and 750°C for Ta34Si47C18, Ta30Si44C25, and Ta26Si41C32 compositions, respectively.

Ultrathin amorphous Ti–Al film used as a diffusion barrier for copper metallization

The viability of ultrathin amorphous Ti–Al film (∼4 nm) as a diffusion barrier layer between Cu and Si for the application in Si-based ultra-large scale integration (ULSI) has been investigated. The Cu/Ti–Al/Si heterostructures are annealed in a high vacuum at various temperatures. There is no impurity peaks in the X-ray diffraction patterns for the samples up to annealing temperature of 800 ∘C, although the island-like grains were observed on the surface of the 800 ∘C annealed sample due to dewetting and agglomeration of the Cu film. No inter-reactions can be found from the images of transmission electron microscopy and Ti–Al is still amorphous after high-temperature annealing. These results indicate that Ti–Al film can effectively separate Cu from Si at high temperatures, and that the amorphous ultrathin Ti–Al film can be a very good barrier layer for Cu metallization.

Effect of composition on electroless deposited Ni–Co–P alloy thin films as a diffusion barrier for copper metallization

Ni–Co–P alloy films were deposited on silicon substrate by electroless technique for diffusion barrier application in copper interconnects technology. The composition of films was varied by varying the concentration of contents in electroless deposition baths. The thermal stability of the films was evaluated by the annealing of samples at elevated temperature and the samples were characterised by using X-ray diffractometer (XRD), four probe method and field-emission scanning electron microscope (FE-SEM). Results indicated that barrier properties degraded with increasing the concentration of Co i.e. decreasing the P. The lower Co and higher P contents alloy film act as a good diffusion barrier up to the 500°C.

Thermally Stable TiVCrZrHf Nitride Films as Diffusion Barriers in Copper Metallization

In the present study, 10 nm-thick TiVCrZrHf nitride films were developed as diffusion barrier materials for Cu interconnects. The TiVCrZrHf nitride films were prepared at room temperature via reactive magnetron sputtering using a TiVCrZrHf target. Barrier properties were examined by annealing in vacuum at elevated temperatures for 60 min. The results show that the (TiVCrZrHf)N0.4 and (TiVCrZrHf)N films prevent the reaction between Cu and Si before failure at 600 and 800°C, respectively. The excellent thermal and structural stabilities of nitride for preventing silicide formation are assumed to originate from the incorporation of different-sized elements.

Characteristics of a 10 nm-thick (TiVCr)N multi-component diffusion barrier layer with high diffusion resistance for Cu interconnects

To fulfill the strict demands for Cu interconnects below 65 nm, a 10 nm-thick (TiVCr)N film with ternary metallic elements was developed in this study as a candidate diffusion barrier by reactive sputtering in an N 2/Ar mixed atmosphere. Barrier properties were examined by annealing over a temperature range of 700–900 °C for 30 min. From the analyses of diffusion behaviors after thermal annealing at 700 °C, the electrical resistance of the Si/(TiVCr)N/Cu film stack remained as low as the as-deposited value. No interdiffusion between the Si substrate and the Cu metallization was found through the (TiVCr)N film at temperatures as high as 700 °C. After annealing at 800 °C, the penetration of a partial number of Cu atoms through the (TiVCr)N barrier occurred and thus some Cu silicides were formed. With temperature further increased to 900 °C, severe interdiffusion of Si and Cu through the layer occurred and induced the formation of a large amount of Cu silicides. This demonstrates that TiVCr ternary refractory metal nitrides have potential use as effective diffusion barriers for copper metallization.

Chemical Mechanical Polishing of a Ti-Si-N Nanocomposite and AFM Study on Its Nanostructure

Ti-Si-N films were characterized as a nanocomposite consisting of cubic titanium nitride (TiN) nanocrystallites embedded in an amorphous matrix of silicon nitride (Si3N4). Ti-Si-N films have been used as anti-wear coatings due to their mechanical properties and diffusion barriers for copper metallization in semiconductor processing. The surface of Ti-Si-N is so rough that it is hard to characterize its nanostructure with an atomic force microscope (AFM). Therefore, the Ti-Si-N surface should be polished and smoothened to reduce its roughness before an AFM study. In this study, we investigated a chemical mechanical polishing (CMP) process for preparing Ti-Si-N surfaces for an AFM study on the Ti-Si-N nanostructure by using two different types of CMP slurries. Then a characterization of TiN embedded in a Si3N4 matrix was conducted by using a tapping mode AFM and phase shift imaging.

Ultrathin Diffusion Barrier for Copper Metallization: A Thermally Stable Amorphous Rare-Earth Scandate

Highly stable with different thicknesses as the Cu diffusion barrier on Si is prepared and characterized. The ultrathin (3 nm) barrier scheme is stable after 50 h annealing at , while its electrical resistivity shows no noticeable increase after annealing at for 1 h. Both the 5 and 10 nm thick barrier schemes are stable up to according to the resistivity result. Transmission electron microscopy and Auger electron spectroscopy reveal that the ultrathin amorphous barrier is uniformly present at the interface after annealing at high temperatures. The results indicate that the 3 nm thick is an effective diffusion barrier for copper metallization.

HIGHLY IONIZED SPUTTERING FOR TSV-LINING

The barrier and seed layers for electroplating of copper play a critical role in the realization of through silicon vias (TSV) in 3D IC packaging. Physical vapour deposition (PVD) is still the preferred method for depositing these films, but must meet the technical challenges presented by the need to line high aspect ratio vias of 10:1 or more that often have rough sidewalls, and the market demand of low cost. A bilayer of TaNx/ α-Ta is the preferred diffusion barrier for copper metallization in CMOS multilevel damascene structures, providing a good adhesion and wetting layer for the PVD copper seed layer. A new method called Highly Ionized Sputtering (HIS) has been developed using power pulses of 50 to 200μsec length with a low duty cycle but very high peak current of several hundred amps. The high pulse current generates a very high ionization fraction of the sputtered material giving – with an appropriate bias voltage applied to the wafer – a high directionality of metal ions and providing very dense films as needed for the diffusion barrier. HIS uses regular sputtering equipment, planar targets and works at low target-to-substrate distances thus providing excellent transfer factors of the ionized PVD material, resulting in high target utilization and a low cost of ownership. HIS hardware and processes with competitive deposition rates, good uniformities and low stress have been developed on the Oerlikon 200mm and 300mm PVD cluster tools for TaNx, Ta, Ti and Cu. The applicability has been verified experimentally in TSVs with different sidewall qualities and supported by simulations.

High thermal stability of AlCrTaTiZr nitride film as diffusion barrier for copper metallization

To inhibit rapid Cu diffusion in interconnect structures, an effective diffusion barrier layer with high thermal stability, low electrical resistivity and good interface adhesion is strongly demanded. Thus in this study, an amorphous nitride film of equimolar AlCrTaTiZr alloy with an N content of about 41 at.% was deposited by reactive radio-frequency magnetron sputtering. Thermal stability of the AlCrTaTiZr nitride film and its barrier property to Cu diffusion were investigated under thermal annealing at 700–900 °C. The AlCrTaTiZr nitride film remained an amorphous structure after thermal annealing at 700 °C and then crystallized at 800 °C. However, no interdiffusion between Si substrate and Cu metallization through the AlCrTaTiZr nitride film occurred. The electrical resistivity of the film remained at the low level of as-deposited value, indicating its good thermal stability as an effective diffusion barrier layer. With temperature further increasing to 900 °C, severe interdiffusion occurred, along with the formation of silicides and large pores. The electrical resistivity then significantly increased, implying the failure of the AlCrTaTiZr nitride film.

Atom beam sputtered Mo2C films as a diffusion barrier for copper metallization

The saddle field fast atom beam sputtered (ABS) 50nm thick molybdenum carbide (Mo2C) films as a diffusion barrier for copper metallization were investigated. To study the diffusion barrier properties of Mo2C films, the as-deposited and annealed samples were characterized using four probes, X-ray diffraction, field enhanced scanning electron microscopy, energy dispersive X-ray analysis, atomic force microscopy and Rutherford back scattering techniques. The amorphous structure of the barrier films along with presence of carbon atoms at the molybdenum carbide–silicon interface is understood to reduce effective grain boundaries and responsible for increased thermal stability of Cu/Mo2C/Si structure. The lowest resistivity of the as-deposited molybdenum carbide barrier films was ∼29μΩcm. The low carbon containing molybdenum carbide was found thermally stable up to 700°C, therefore can potentially be used as a diffusion barrier for copper metallization.

Reactively Sputtered Mo–V Nitride Thin Films as Ternary Diffusion Barriers for Copper Metallization

The effectiveness and performance of Mo-based ternary nitride films as copper diffusion barriers were investigated. Thermally stable Mo–V nitride thin diffusion barrier layers were deposited using radio frequency reactive magnetron sputtering and their barrier capability was evaluated and studied. Cu/Mo–V nitride/Si structures were fabricated and annealed at different temperatures. The agglomeration of Cu and the formation of due to high-temperature annealing were probed using scanning electron microscopy/energy-dispersive X-ray spectroscopy. The drastic increase in sheet resistance after annealing at was found to take place due to the formation of highly resistive , also evident from X-ray diffraction patterns. The formation of inverted pyramidal structure of at the interface penetrated into the Si substrate corroborated the breakdown of the barrier layer at . Our results suggest that an 8 nm thick Mo–V nitride barrier can effectively prevent the formation of up to high annealing temperatures.

Ir ∕ Ta N as a bilayer diffusion barrier for advanced Cu interconnects

The properties of an Ir (5nm)∕TaN (5nm) stacked layer as a copper diffusion barrier on Si have been investigated. Ir∕TaN bilayer barriers were prepared at room temperature by magnetron sputtering followed by in situ Cu deposition for diffusion tests. Thermal annealing of the barrier stacks was carried out in vacuum at high temperatures for 1h. X-ray diffraction patterns, cross sectional transmission electron microscopy images, and energy-dispersive spectrometer line scans on the samples annealed at 600°C revealed no Cu diffusion through the barrier. The results indicate that the Ir∕TaN bilayer is an effective diffusion barrier for copper metallization.

5 - nm -thick TaSiC amorphous films stable up to 750°C as a diffusion barrier for copper metallization

Ultrathin TaSiC amorphous films prepared by magnetron cosputtering using TaSi2 and C targets on Si(100), in a sandwiched scheme Si(100)∕TaSiC(5nm)∕Cu, were evaluated for barrier performance in copper metallization. Optimizing carbon content maximizes thermal stability of the films as depicted by sheet-resistance, x-ray diffraction, and transmission electron microscopy examination. The stability temperatures of 700°C (24at.% C) and 750°C (34at.% C) have been systematically verified and discussed. Since Ta, Si, and C are compatible with integrated circuit (IC) processing, the TaSiC films are readily applicable for sub-65-nm IC production.

Effect of film thickness on the breakdown temperature of atomic layer deposited ultrathin HfO 2 and Al 2O 3 diffusion barriers in copper metallization

We investigate the effect of thickness of HfO 2 and Al 2O 3 barrier films on the breakdown temperature of Cu/barrier film/Si structures. The HfO 2 and Al 2O 3 films are deposited using tetrakis-diethylamino hafnium and tris-diethylamino aluminum, respectively, as the metal precursors and ozone as the oxidizer at 250 °C. Interactions between the layers of Cu/barrier film (1 or 2 nm-thick)/Si structures due to high-temperature annealing in N 2 are probed using sheet resistance measurements. The crystallinity of the multilayer structure and the possible formation of any anneal-induced reaction products are investigated with X-ray diffraction (XRD). The formation of Cu-silicide phase(s) due to diffusion of Cu atoms through the barrier layer indicates the failure of the corresponding diffusion barrier. The surface morphology of Cu is examined using scanning electron microscopy (SEM) and elemental mapping is done with energy dispersive X-ray spectroscopy (EDS). Our results show that both 1 and 2 nm-thick HfO 2 and Al 2O 3 barrier films are capable of restricting the diffusion of Cu at high annealing temperatures; therefore, they could be used as effective diffusion barriers between Cu and Si.

Diffusion barrier properties of AlMoNbSiTaTiVZr high-entropy alloy layer between copper and silicon

The application of an AlMoNbSiTaTiVZr high-entropy alloy film as diffusion barrier for copper metallization has been investigated. The AlMoNbSiTaTiVZr and copper layers are deposited sequentially, without breaking vacuum, onto silicon substrates by DC magnetron sputtering. The AlMoNbSiTaTiVZr films are found to possess a stable amorphous structure due to their high-entropy and limited diffusion kinetics. The AlMoNbSiTaTiVZr high entropy alloy film is determined to prevent copper–silicide formation up to 700 °C for 30 min. Thus, HEAs appear to have potential use as effective diffusion barriers for copper metallization.