Diffusion Barrier Materials Research Articles

First-principles simulations of copper diffusion in tantalum and tantalum nitride

To explore potential applications of tantalum and tantalum nitrides (TaN) as diffusion barrier materials in integrated circuits with Cu interconnects, we carry out detailed first-principles simulations of Cu/Ta and Cu/TaN systems. Various interfacial structures between Cu- and Ta-based compounds are examined by considering different surface orientations, in-plane arrangements, surface terminations, and chemical compositions. The coexistence of strong Cu-N ionic bonding and Ta-Cu covalent/metallic bonding dictates the stable interfacial structures. Using nudged elastic band method, we calculate the diffusion energy barriers of Cu to the pre-existing vacancies across Cu/Ta, Cu/TaN interfaces, and in bulk TaN compounds. As a comparison, Cu diffusion in Si is also studied. It was found that Cu can easily diffuse into Si either spontaneously or with small energy barriers. On the other hand, although the Cu/Ta interfacial diffusion barrier is low, the high vacancy formation energy in Ta renders Cu diffusion difficult. We find that fcc TaN is an excellent candidate for diffusion barrier material owing to its extremely high interfacial diffusion energy barrier. The bulk diffusion barrier of Cu in fcc TaN is also very high.

Performance of FCCI barrier foils for U–Zr–X metallic fuel

Diffusion couple tests of U–Zr or U–Zr–Ce alloys vs. ferritic martensitic steels such as HT9 or T91 were carried out in order to evaluate the performance of the diffusion barrier candidates. Elemental metal foils of Zr, Nb, Ti, Mo, Ta, V and Cr were very effective in inhibiting interdiffusion between these fuels and steels. Eutectic melting between the fuels and steels was not observed in any of the diffusion couples using these diffusion barrier foils at annealing temperatures up to 800 °C. Among the metallic foils evaluated in this study, V and Cr exhibited the most promising performances as a diffusion barrier material for eliminating the fuel cladding chemical interaction problem. However, Zr, Nb and Ti showed an active interaction with the fuel mainly due to the large U solubility.

Improvement of Adhesion Performances of CVD-W Films Deposited on B[sub 2]H[sub 6]-Based ALD-W Nucleation Layer

The resistivity of chemical-vapor-deposited (CVD)-W film was reported to be significantly reduced using a B 2 H 6 -based atomic layer deposited (ALD)-W nucleation layer for continuously shrinking memory devices. But, we found that the adhesion performances of CVD-W films growing on the B 2 H 6 -based ALD-W nucleation layer were poor compared to those on the SiH 4 -based W nucleation layer. Scanning electron microscopy and secondary ion mass spectrometry analysis clearly suggest that the boron penetration into the interface between underlying TiN and SiO 2 during the deposition of W nucleation layer is a possible reason to degrade the adhesion performances of CVD-W films with B 2 H 6 -based W nucleation layers. By rigorous selection of both the deposition conditions for W nucleation layer and diffusion barrier materials, we can demonstrate the successful deposition of CVD-W film with a very low resistivity of ∼12 μΩ cm (50 nm in thickness) without an adhesion failure. Noticeably, the application of 5 nm thick sputter-deposited WN x film as a glue layer was found to present an excellent adhesion performance, which was due to its excellent diffusion barrier performance with amorphous structure.

Properties of reactively sputtered W–B–N thin film as a diffusion barrier for Cu metallization on Si

Thin films of W–B–N (10 nm) have been evaluated as diffusion barriers for Cu interconnects. The amorphous W–B–N thin films were prepared at room temperature via reactive magnetron sputtering using a W2B target at various N2/(Ar + N2) flow ratios. Cu diffusion tests were performed after in-situ deposition of 200 nm Cu. Thermal annealing of the barrier stacks was carried out in vacuum at elevated temperatures for one hour. X-ray diffraction patterns, sheet resistance measurement, cross-section transmission electron microscopy images, and energy-dispersive spectrometer scans on the samples annealed at 500°C revealed no Cu diffusion through the barrier. The results indicate that amorphous W–B–N is a promising low resistivity diffusion barrier material for copper interconnects.

Improvement of Copper Diffusion Barrier Properties of Tantalum Nitride Films by Incorporating Ruthenium Using PEALD

Ru-incorporated TaN (Ru–TaN) films were investigated as a Cu diffusion barrier material. Ru–TaN films were prepared by sequential deposition of Ru and TaN using plasma-enhanced atomic layer deposition (PEALD). The film composition was controlled by the number of Ru unit cycles. While the resistivity of Ru–TaN films was increased abruptly at low Ru composition , the resistivity of Ru–TaN films was decreased gradually as the Ru composition increased after that composition. The crystal structures of Ru–TaN films were amorphous at the Ru composition range from 0.19 to 0.52 due to disturbance of grain growth. However, the Ru–TaN films had TaN-like structure below this range and Ru-like structure above this range. The amorphous Ru–TaN films had nanocrystallite embedded structure in an amorphous matrix. This amorphous Ru–TaN barrier showed a better Cu diffusion barrier property than the TaN barrier because the Cu diffusion through the grain boundary was suppressed by the amorphization. In addition, the Ru–TaN barrier exhibited good adhesion to both Cu and .

Ion beam sputter deposited TiAlN films for metal–insulator–metal (Ba,Sr)TiO 3 capacitor application

The present study evaluated the feasibility of TiAlN films deposited using the ion beam sputter deposition (IBSD) method for metal–insulator–metal (MIM) (Ba,Sr)TiO 3 (BST) capacitors. The BST films were crystallized at temperatures above 650 °C. TiAlN films deposited using the IBSD method were found having smooth surface and low electrical resistivity at high temperature conditions. TiAlN films showed a good diffusion barrier property against BST components. The J– E (current density–electric field) characteristics of Al/BST/TiAlN capacitors were good, with a high break down electric field of ± 2.5 MV/cm and a leakage current density of about 1 × 10 − 5 A/cm 2 at an applied field of ± 0.5 MV/cm. Thermal stress and lateral oxidation that occurred at the interface damaged the capacitor stacking structure. Macro holes that dispersed on the films resulted in higher leakage current and inconsistent J– E characteristics. Vacuum annealing with lower heating rate and furnace cooling, and a Ti–Al adhesion layer between TiAlN and the SiO 2/Si substrate can effectively minimize the stress effect. TiAlN film deposited using IBSD can be considered as a potential electrode and diffusion barrier material for MIM BST capacitors.

Diffusion of nickel and tin in p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3 thermoelectric materials

The diffusion and spatial distribution of tin from solder, and nickel from diffusion barrier in p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3 thermoelectric materials were investigated using electron microscopy. The results indicate that nickel is a suitable diffusion-barrier material for tin in both (Bi,Sb)2Te3 and Bi2(Te,Se)3. However, even though it is not an issue in the (Bi,Sb)2Te3, the nickel diffuses several microns into the Bi2(Te,Se)3 during the soldering processing and degrades its performance. Diffusion coefficients of nickel in p-type (Bi,Sb)2Te3 and in n-type Bi2(Te,Se)3 were also quantitatively studied.

Application of Zr-Si Film as Diffusion Barrier in Cu Metallization

The diffusion barrier's performance of Zr-Si film in Cu/Si contacts has been investigated. Cu/Zr-Si/Si contact system was deposited by using radio frequency reactive sputtering technique. Annealing studies for Cu/Zr-Si/Si were then carried out in nitrogen to investigate Cu diffusion and barrier film crystallization. The contact system was characterized by using four-point probe sheet resistance measurements, X-ray diffraction, scanning electron microscope, and Auger electron spectroscopy (AES), respectively. It is observed that the sheet resistance of Cu/Zr-Si/Si contact system is lower than that of as-deposited specimens even after annealing at 700°C. The Cu/Zr-Si/Si contacts tolerated annealing at 800°C for an hour without structural change of the barrier. AES depth profiles of the annealed Cu/Zr-Si/Si samples are similar to each other and have no intermixing evidence. Zr-Si was found to be a promising diffusion barrier material for Cu metallization.

Cu/barrier CMP on porous low- k based interconnect schemes

Dielectric stacks containing porous low- k materials were investigated regarding their ability to pass CMP processes as used in Cu interconnect technology. Beside the low- k material itself, the impact of layout, cap layer materials and different diffusion barrier materials has been proven. Advanced consumables, partly specially designed for future technology nodes, have been tested within these experiments. Compatibility of the slurries with the low- k stacks, dishing and erosion, impact of polishing parameters like down force and platen speed on low- k stack integrity were examined. Low- k stacks based on a porous MSQ material capped with PECVD-SiC or with a MSQ-hard mask were found to be promising candidates. Low- k stacks based on porous SiO 2-aerogel could not meet the stability requirements at present and need additional efforts for adhesion enhancement between cap layer and porous material. Consumables used within the experiments enable an efficient processing with low dishing and erosion as well as an excellent surface quality.

Adsorption and thermal chemistry of 1,1,1,5,5,5,-hexafluoro-2,4-pentanedione ( hfacH) and (hexafluoroacetylacetonate)Cu(vinyltrimethylsilane) (( hfac)Cu(VTMS)) on TiCN-covered Si(1 0 0) surface

The chemistry of a common copper deposition precursor, (hexafluoroacetylacetonate)Cu(vinyltrimethylsilane) (( hfac)Cu(VTMS)), and the chemistry of a hydrogenated form of one of its ligands, 1,1,1,5,5,5,-hexafluoro-2,4-pentanedione ( hfacH) were examined by a combination of experimental surface analytical techniques and by computational analysis on a surface of TiCN diffusion barrier material deposited on a Si(1 0 0) single crystal. This surface proves to be very reactive. Although ( hfac)Cu(VTMS) can be condensed at a submonolayer coverage in its molecular form at cryogenic temperatures of 100–130 K, hfacH reacts with the surface of the TiCN film even at these conditions. At room temperature, both ( hfac)Cu(VTMS) and hfacH chemisorb on this substrate. VTMS is released by ( hfac)Cu(VTMS) immediately upon adsorption. At this point, the hfac ligand is bound to the copper atom; it decomposes upon thermal annealing and is the primary source of fluorine, oxygen, and carbon contamination at the Cu/TiCN interface.

Investigation of W-Ge-N deposited on Ge as a diffusion barrier for Cu metallization

The properties of W-Ge-Nthin films were investigated as a diffusion barrier material for Cu metallization. The W-Ge-Nfilms were grown by reactive sputtering on a single crystal Ge substrate. This was followed by in-situ deposition of Cu. Diffusion barrier test was performed by annealing the film stack under Ar atmosphere. Phase identification and film crystallization were determined by X-ray diffraction. The deposited W-Ge-Nfilms remained amorphous even after high temperature annealing. The Cu diffusion profile in the film was assessed by Auger electron spectroscopy and energy dispersive spectroscopy. The results indicate that Cu diffusion was minimal in W-Ge-Nfilms even at high annealing temperatures. Interface reactions and properties were analyzed by cross-section transmission electron microscopy. The results suggest that W-Ge-Nmay be a superior diffusion barrier as compared to WNx for Cu metallization.

Electrografting, A Unique Wet Technology for Seed and Direct Plating in Copper Metallization

This paper introduces a novel electrochemical technology called electrografting (eG{trade mark, serif}). After describing electrografting the main characteristics, it will be shown that this technology can be successfully applied to the formation of thin, conformal, and uniform seed layers for IC copper interconnects. Seed layer thicknesses down to 10nm thick are deposited on various copper diffusion barrier materials and characterized in terms of sheet resistance, morphology, conformality, adhesion, and gapfilling capability. Initial results pointed out that the technology can be extended to seedless direct filling of interconnect structures.

Microstructure evolution of gold-tin eutectic solder on Cu and Ni substrates

The microstructures of the eutectic Au20Sn (wt.%) solder that developed on the Cu and Ni substrates were studied. The Sn/Au/Ni sandwich structure (2.5/3.75/2 µm) and the Sn/Au/Ni sandwich structure (1.83/2.74/5.8 µm) were deposited on Si wafers first. The overall composition of the Au and the Sn layers in these sandwich structures corresponded to the Au20Sn binary eutectic. The microstructures of the Au20Sn solder on the Cu and Ni substrates could be controlled by using different bonding conditions. When the bonding condition was 290°C for 2 min, the microstructure of Au20Sn/Cu and Au20Sn/Ni was a two-phase (Au5Sn and AuSn) eutectic microstructure. When the bonding condition was 240°C for 2 min, the AuSn/Au5Sn/Cu and AuSn/Au5Sn/Ni diffusion couples were subjected to aging at 240°C. The thermal stability of Au20Sn/Ni was better than that of Au20Sn/Cu. Moreover, less Ni was consumed compared to that of Cu. This indicates that Ni is a more effective diffusion barrier material for the Au20Sn solder.

Reliability studies of barrier layers for Cu/PAE low- k interconnects

Electromigration and electrical breakdown are two of the most important concerns in the reliability of modern electronic devices. The electromigration lifetimes and electrical breakdown field ( E BD) in single damascene copper lines/porous polyarylene ether (PAE) dielectric with different diffusion barrier materials (i.e., amorphous-SiC:H and TaN/Ta) were studied. The results showed a “wafer edge effect” in both groups of samples. The electromigration lifetime of samples taken from the center of the wafer is five to nine times longer of those taken from the wafer edge in the accelerated test. The samples from wafer edge showed a bi-modal failure characteristic. It was also found that electromigration resistance of the structure with new diffusion barrier a-SiC:H/Ta was comparable to that with the conventional TaN/Ta. On the other hand, the electrical testing showed that E BD of the a-SiC:H/Ta structure is about twice of that with TaN/Ta barrier, indicating a significant improvement of the electrical performance.

Influence of tungsten sputtering target density on physical vapor deposition thin film properties

Tungsten (W) is commonly used for diffusion barrier, via, and gate material in semiconductor devices. In order to achieve the desired properties and minimize particle generation, control of the sputter target properties, which include density, purity, grain size, and orientation, are essential. This study focused on the effect of sputtering target density on the thin-film properties and defect generation. By controlling the powder sintering process, three sputtering targets from 82.5% to 99.5% of theoretical density were prepared. By physical vapor deposition (PVD), about 1600 A thin films were deposited onto the silicon wafers. The deposited films were then evaluated by four-point probe, x-ray diffraction (XRD), and scanning electron microscope (SEM) to determine the influence of target density on the deposited film properties. In addition to film properties, the erosion morphology on the sputtered surface was also investigated by SEM. The voids are known to be the potential particle sources from the target. By monitoring the generation of voids, the correlation between target density and potential particle sources was established.

Formation of Ti–Si–N film using low frequency, high density inductively coupled plasma process

Titanium silicon nitride (Ti–Si–N) has emerged as a strong candidate for next generation diffusion barrier material in copper/low-k dielectric back-end-of-line device fabrication. Low frequency, high density inductively coupled plasma process has been developed for the growth of Ti–Si–N film. This work employs the reaction between TixSiy and the nitrogen plasma. Ti–Si–N films have been successfully grown over different process conditions. Film properties were characterized by Rutherford backscattering spectrometry (RBS), x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy, x-ray diffraction (XRD), and four-point resistivity probe. RBS reveals that 2–67at.% of nitrogen can be achieved through the implantation of nitrogen in TixSiy film. XPS and XRD results show that TiN and Si3N4 are successfully formed. As the external bias increases from 100to300V, there is an 80% increase in sheet resistance. Other process conditions investigated do not show a significant effect on film sheet resistance. Increasing argon plasma activation time can significantly increase the implantation depth of nitrogen into TixSiy substrate.

Properties of W–Ge–N as a diffusion barrier material for Cu

The properties of W–Ge–N thin films are reported, focusing on issues relevant to their use as diffusion barriers for Cu metallization on silicon. The amorphous W–Ge–N thin films were deposited on thermally grown SiO2∕Si using reactive sputter deposition. This was followed by in situ deposition of Cu films. Annealing studies for W–Ge–N were then carried out in a vacuum to investigate Cu diffusion and barrier film crystallization. X-ray diffraction was used to assess the crystallinity of the films upon annealing. The results show that W–Ge–N has a recrystallization temperature that is higher that that for WNx. Auger electron spectroscopy was used to measure the depth profile of Cu diffusion through the barrier layer. Little or no Cu diffusion was detected for a relatively high annealing temperature. The W–Ge–N films were conductive, although the resistivity is somewhat higher than that for WNx. The results suggest that W–Ge–N may be an attractive diffusion barrier material for Si or SiGe devices.

The Texture Effect on Diffusion Barrier Property on TiN Films between Copper and Si Wafer

TiN thin films are widely used as a coating material due to their good mechanical and conductivity properties, high thermal properties, strong erosion and corrosion resistance. Also TiN has been used in Si devices as a diffusion barrier material for Al and Cu-based metallization. The uniform and dense structure of thin films is influenced by the texture of films. It was good to have uniform and dense structure and bad to have an open columnar structure in TiN thin films. Therefore, the property of diffusion barrier of the TiN films in semiconductor also is related to the texture and microstructure of TiN coated layer. In this study, the relationship between the texture and microstructure and the best diffusion barrier propertiy of TiN coated films (by PVD and MOCVD) on semiconductor devices (Cu/TiN/SiO2/Si layer) were investigated under different processing conditions and textures. The property of diffusion barrier for Cu of physical vapor deposited TiN thin films is better than that of metal organic chemical vapor deposited TiN thin films. Also the property of diffusion barrier for Cu of (111) textured TiN thin films is better than that of (200) textured TiN thin films.

Potential of Cat-CVD deposited a-SiC:H as diffusion barrier layer on low- k HSQ films for ULSI

Cu diffusion in the spin-on hydrogen silsesquioxane (HSQ) is a major obstacle in the low- k plus Cu technology for future ULSI devices. We have optimized the process conditions for the spin-on HSQ low- k films. Subsequent metallization with Al and Cu shows a higher leakage current for Cu contact. We have employed Cat-CVD to deposit a-SiC:H films of different thickness on HSQ and studied their effect on the leakage current with both Al and Cu electrodes. The films were deposited using silane (SiH 4) and acetylene (C 2H 2) gases. Also, an independent determination of the dielectric constant of the Cat-CVD a-SiC:H layer has been carried out from the C– V measurements on Al/c-Si/a-SiC:H/Al structure. The electrical characteristics of the Al/c-Si/HSQ + a-SiC:H/Cu structures show almost two orders of magnitude lower leakage current compared with Al/c-Si/HSQ/Cu, indicating very good barrier properties of the a-SiC:H material. Moreover, the low dielectric value observed for a-SiC:H compares favorably to other diffusion barrier materials.

Atomic Layer Deposition of Molybdenum Nitride Thin Films for Cu Metallizations

Molybdenum nitride thin films were deposited by the atomic layer deposition technique within a temperature range of 350-500°C from molybdenum pentachloride and ammonia. The films were characterized by time-of-flight elastic recoil detection analysis, X-ray diffraction (XRD), and standard four-point probe method. films deposited at 400°C and above had a resistivity below 500 μΩ cm and the chlorine content was below 0.3 atom %. The diffusion barrier properties were studied from approximately 10 nm thick films deposited at 350, 400, and 500°C. Additionally, the barrier tests were performed with Mo(Ta)N and Mo(Ti)N films deposited at 400°C. The stability of the barrier layer was studied from the annealed Cu/barrier/Si structures by measuring the sheet resistance values, XRD data, and by performing etch-pit tests. Molybdenum nitride showed to be a promising diffusion barrier material. The barriers deposited at 400 and 500°C were observed to fail only after the annealing at 650°C.