Diffusion Barrier For Metallization Research Articles

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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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.

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

To inhibit rapid Cu diffusion in interconnect structures, 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 . The (AlCrTaTiZr)N film, constructed of mixed crystalline and amorphous nanocomposite structure, was found to remain thermally stable at an extremely high temperature of with low electrical resistance. Neither interdiffusion between Si and Cu through the (AlCrTaTiZr)N layer nor formation of any silicides occurred. Severe lattice distortions caused by the addition 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 as an effective barrier material.

High reflective p-GaN/Ni/Ag/Ti/Au Ohmic contacts for flip-chip light-emitting diode (FCLED) applications

The fabrication of high reflective Ni/Ag/(Ti, Mo)/Au Ohmic contacts for flip-chip light-emitting diode (FCLED) are proposed and considered, Ni/Ag/Au Ohmic contacts are also fabricated to compare their resulting reflectivities. From secondary ion mass spectrometry (SIMS) depth profiles, it indicates that the Au in-diffusion occurs in Ni/Ag/Au contacts after annealing. It is considered that Au in-diffusion, which is intermixed with Ag, Ni and GaN in Ni/Ag/Au contacts after annealing, is responsible for the resulting low reflectance (63% at the wavelength of 465 nm). To avoid Au in-diffusion and enhance the reflectivity, a diffusion barrier metal (Ti or Mo) between Ni/Ag and Au is fabricated and examined. It is demonstrated and found that an insertion of diffusion barrier metal of Ti enables to block Au diffusion effectively and also improve the reflectivity significantly, up to 93%.

Selective Electroless Metallization of Patterned Polymeric Films for Lithography Applications

The fabrication of electrical interconnects to provide power for and communication with computers as their component complementary metal oxide semiconductor (CMOS) devices continue to shrink in size presents significant materials and processing compatibility challenges. We describe here our efforts to address these challenges using top-surface imaging and hybrid photoresist/self-assembled monolayer patterning approaches, in conjunction with selective electroless metal deposition, to develop processes capable of fabricating appropriate submicron and nanoscale metal features useful as electrical interconnects, as well as plasma-etch-resistant masks and metal diffusion barriers. Our efforts focus on the development of cost-effective methods compatible with a manufacturing environment that satisfy materials and process constraints associated with CMOS device production. We demonstrate the fabrication of approximately 50-nm-width features in metal with high fidelity and sufficient control of edge acuity to satisfy current industry design rules using our processes and discuss the challenges and opportunities for fabrication of analogous sub-10-nm metal features.

Diffusion barrier capability of Zr–Si films for copper metallization with different substrate bias voltage

Efficiency of Zr–Si diffusion barriers in Cu metallization has been investigated. Amorphous Zr–Si diffusion barriers were deposited on the Si substrates by reactive magnetron sputtering with different negative substrate bias. The mass density of Zr–Si films increases with substrate bias voltage up to − 150 V. The deposition rate decreased with the negative substrate bias from 5.4 nm/min to 1.8 nm/min. XRD measurements show that the Zr–Si barriers have amorphous structure in the as-deposited state. The FE-SEM images show that the sizes of spherical granules on the Zr–Si film surface increase with increasing the substrate bias. The Cu/Zr–Si/Si structures were prepared and annealed in Ar ambient at temperatures varying from 500 to 650 °C for an hour. It is shown from the comparison study that the Zr–Si film deposited with − 150 V is better at maintaining good performance in Cu/Zr–Si/Si contact system than that of Zr–Si film deposited with − 50 V.

Erratum: Application of Zr-Si Film as Diffusion Barrier in Cu Metallization [Electrochem. Solid-State Lett., 10, H299 (2007)

Erratum: Application of Zr-Si Film as Diffusion Barrier in Cu Metallization [Electrochem. Solid-State Lett., 10, H299 (2007)

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.

Effectiveness of Ta Addition on the Performance of Ru Diffusion Barrier in Cu Metallization

Ru–Ta and Ru thin films ( in thickness) as diffusion barrier for Cu metallization on and Si substrates are studied. Experimental results show that the Ru–Ta film exhibits amorphous structure until annealing at , whereas the Ru film crystallizes in as-deposited and annealed states. Sheet resistances of and stacking layers increase after annealing at 500 and , respectively, regardless of whether the substrate is or Si. Increase in resistance is concurrent with the formation of and when Cu/barrier stacks are deposited on Si substrate. Increase in resistance for Cu/barrier stacks deposited on substrate is related to the diffusion of Cu through the crystallized barrier to the underlayers. Furthermore, current–voltage measurement also reveals that the metallization has a lower leakage current than the system. The failure mechanism and the effectiveness of Ta addition on barrier performance are discussed.

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.

Effect of Si Content on the Barrier Property of Zr–Si as a Diffusion Barrier for Cu Metallization

Barrier properties and failure mechanism of sputtered Zr–Si amorphous thin films of various compositions were studied for the application as a diffusion barrier for Cu metallization. X-ray diffraction (XRD) measurements show that the Zr–Si barriers have amorphous structure in the as-deposited state. The structures were manufactured and annealed in Ar ambient at the temperature up to for . XRD, scanning electron microscopy, and variations of Cu sheet resistance as a function of the annealing temperature were conducted to evaluate the barrier performance of Zr–Si films. The specimen including film is stable up to and that with and film up to . The experimental findings revealed that the failure mechanism of the studied films involved the crystallization of film that occurred at . The grain boundary of the crystalline structure provides paths along which the copper atoms penetrate through the barrier layer to react with the underlying Si substrate to form the phase. The and films remain the amorphous structure even after annealing at . This amorphous structure is beneficial for blocking rapid copper diffusion paths.

Evaluation of the barrier capability of Zr–Si films with different substrate temperature for Cu metallization

Barrier capability of Zr–Si diffusion barriers in Cu metallization has been investigated. Amorphous Zr–Si diffusion barriers were deposited on the Si substrates by RF reactive magnetron sputtering under various substrate temperatures. An increase in substrate temperature results in a slightly decreased deposition rate together with an increase in mass density. An increase in substrate temperature also results in grain growth as deduced from field emission scanning electron microscopy (FE-SEM) micrographs. X-ray diffraction (XRD) spectra and Auger electron spectroscopy (AES) depth profiles for Cu/Zr–Si(RT)/Si and Cu/Zr–Si(300 °C)/Si samples subjected to anneal at various temperatures show that the thermal stability was strongly correlated with the deposition temperature (consequently different density and chemical composition etc.) of the Zr–Si barrier layers. ZrSi(300 °C) with higher mass density make the Cu/Zr–Si(300 °C)/Si sample more stable. The appearance of Cu 3Si in the Cu/Zr–Si/Si sample is attributed to the failure mechanism which may be associated with the diffusion of Cu and Si via the grain boundaries of the Zr–Si barriers.

Study on the amorphous Ta–Zr films as diffusion barrier in Cu metallization

An amorphous Ta–Zr binary alloy diffusion barrier was studied in the Cu metallization. A Cu∕Ta50Zr50∕Si stack with 50nm thick amorphous film was prepared by cosputtering can effectively suppress the penetration of Cu atoms into substrate upon annealing up to 650°C. Examining the thermal stability of the barrier revealed that the crystallization of these amorphous Ta50Zr50 films occurred at 800°C, higher than its failure temperature. The results show that the existence of Cu layer first induced the formation of TaSi2 and ZrSi2 crystalline phases at 650°C, followed by the formation of Cu3Si. A failure mechanism of the diffusion barrier is proposed based on the relation between the thermal stress and the activation energy of barrier/substrate interface reaction.

Nitrogen impurity effects of W–B–C–N quaternary thin film for diffusion barrier for Cu metallization

To investigate the thermal stability of nitrogen stuffing effect of tungsten–boron–carbon–nitrogen (W–B–C–N) thin diffusion barrier, the binding energy shift was studied for various annealing temperature. The X-ray diffraction patterns, the deposition rates and the resistivities of W–B–C–N thin film were measured as a function of nitrogen gas ratios for various annealing temperatures and the binding energy between tungsten and nitrogen was determined by the X-ray photoemission spectroscopy. The interface of Cu/W–B–C–N/Si multilayer was characterized for various nitrogen impurity concentration. Our experimental results indicate that W–B–C–N thin films are effective diffusion barriers to prevent the interdiffusion between Cu and Si interface after annealing up to 850 °C for 30 min.

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.

Effects of Surface Cleaning on Stressvoiding and Electromigration of Cu-Damascene Interconnection

The purpose of this paper is to study the effects of surface-clean process on stressvoiding (SV) and electromigration (EM) of Cu-dual-damascene metallization. Prior to the deposition of copper diffusion-barrier metal, conventional argon bombardment is used to clean Cu surface. Higher preclean bias power and shorter preclean time demonstrate remarkable low via resistance and excellent Cu-reliability performance. In addition, the via-diameter effect to Cu stressmigration is explored. A superior Cu precleaning process condition is developed to improve Cu stress-induced voiding and EM. The preclean bias power of argon plasma should be kept as high as possible but not too high to avoid damaging underlying metal, while the resputtering clean time should keep as short as possible but sufficiently long in order to clean via bottoms. To improve ultralarge-scale integrated-circuit yield and reliability of Cu-damascene metallization, the cleaning process of Cu surface becomes more and more critical as CMOS technology continues shrinking.

Thermally stable amorphous (AlMoNbSiTaTiVZr)50N50 nitride film as diffusion barrier in copper metallization

Results on copper metallization diffusion barriers using high-entropy alloy (HEA) nitride are reported. The HEA nitride (AlMoNbSiTaTiVZr)50N50 is amorphous in the as-deposited state and remains its noncrystallinity up to a high temperature of 850°C. To evaluate its diffusion barrier characteristics, Cu∕(AlMoNbSiTaTiVZr)50N50∕Si test structures were prepared and annealed under 750–900°C for 30min. The results show that the current nitride prevents the reaction between Cu and Si before its failure at 900°C. The outstanding barrier performance and high thermal stability of amorphous structure are suggested to originate from multiprincipal-element effects.

Investigation of Zr–Si–N∕Zr bilayered film as diffusion barrier for Cu ultralarge scale integration metallization

The effectiveness of ZrSiN∕Zr bilayered films to serve as diffusion barriers in Cu∕Si contacts has been investigated. Annealing studies for Cu∕ZrSiN∕Zr∕Si contact systems were carried out in N2∕H2(10%) ambient. X-ray diffraction data suggest that Cu film has preferential (111) crystal orientation and Cu silicide cannot be observed up to 700°C. Scanning electron microscopy micrographs show that the Cu film was integrated and free from agglomeration after annealing at 700°C. Auger electron spectroscopy depth profiles of the Cu∕ZrSiN(10nm)∕Zr(20nm)∕Si samples have no noticeable change except Zr silicide grows with annealing temperature up to 700°C. The results indicate excellent barrier property for ZrSiN(10nm)∕Zr(20nm) bilayer structure for Cu metallization.

Highly Thermal-Stable Amorphous TaSi2Cx Films as Diffusion Barrier

Structural changes at high temperature of amorphous films deposited on Si(100) were evaluated. Increased carbon content remarkably raises crystallization temperature; thus, films ( atom %) sustain amorphous phase at for at least . A preliminary evaluation of such films as a diffusion barrier of Cu metallization in a sandwich scheme showed the stability of ( atom %) or ( atom %) for at least without a sharp increase in sheet resistance nor the formation of . Because Ta, Si, and C are compatible with integrated-circuit processing, these films are readily applicable as diffusion barriers in Cu metallization.