Shau-Lin Shue

Diffusion of Copper in Titanium Zirconium Nitride Thin Films

Honeywell Electronic Materials Star Center, Sunnyvale, California, USAThe diffusion coefficient of Cu in~Ti, Zr!N was measured by X-ray diffraction~XRD! and four-point probe~FPP! analyses afterannealing Cu/~Ti, Zr!N/Si multilayered samples in the temperature range of 500-900°C. Cu diffusion in~Ti, Zr!N had componentsfrom both the grain boundaries and the lattice based on diffusional analysis. This study suggests that for the measurement of thediffusion coefficient of Cu, FPP analysis is more precise and sensitive than XRD analysis. Additionally,~Ti, Zr!N has better Cudiffusion barrier properties than those of TaN and TiN.© 2004 The Electrochemical Society. @DOI: 10.1149/1.1644355# All rights reserved.Manuscript received May 1, 2003. Available electronically January 22, 2004.

Reliability of dual damascene Cu metallization

The electromigration (EM) and bias temperature stress (BTS) performances of Cu metallization in dual damascene structure were examined. The experimental results show that Cu has more than one order of magnitude EM lifetime relative to Al alloy. The activation energy of electromigration of Cu trench is 0.9 eV. The failure sites of Cu dual damascene process after EM stress testing are mainly in the bottom of cathode sites vias. Via electromigration can be improved up to one order magnitude by optimizing several processes such as PR stripping, pad structure, etc. BTS study results indicate that the activation energy of Cu ion drift leakage is around 1.1 to 1.4 eV. The interface of capping SiN and SiO/sub 2/ was found to be the major copper diffusion path. Lifetime extrapolated from the empirical data indicates that the device can sustain longer than 1000 years under normal operation condition.

Growth of (Ti,Zr)N Films on Si by DC Reactive Sputtering of TiZr in N 2 / Ar Gas Mixtures Effect of Flow Ratio

Titanium zirconium nitride [(Ti,Zr)N] films were prepared on Si substrates by dc reactive magnetron sputtering from a Ti-5 atom % Zr alloy target in N 2 /Ar gas mixtures. Material characteristics of the (Ti,Zr)N films were investigated by X-ray photoelectron spectroscopy, four-point probe, X-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. According to those results, the deposition rate, chemical composition, crystalline structure, and film resistivity of the deposited films correlate with the N 2 /Ar flow ratio. The microstructure of the (Ti,Zr)N films was an assembly of very small columnar crystallites with a rock-salt (NaCI) structure and an enlarged lattice constant (over pure TiN). A minimum film resistivity of 59.3 μΩ cm was obtained at an N 2 /Ar flow ratio of 2.75, corresponding to near stoichiometric film composition [N/(Ti,Zr) = 0.96] and crystalline structure.

Characteristics of DC Reactively Sputtered (Ti,Zr)N Thin Films as Diffusion Barriers for Cu Metallization

(Ti,Zr)N films were prepared by dc reactive magnetron sputtering from a Ti-5 atom % Zr alloy target in N 2 /Ar gas mixtures and then employed as diffusion barriers between Cu thin films and Si substrates. Material characteristics of the (Ti,Zr)N film were investigated by X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy (XTEM). The (Ti,Zr)N film microstructure was an assembly of Very small columnar crystallites with a rock-salt (NaCI) structure. Metallurgical reactions of Cu/(Ti,Zr)N 0 . 9 5 /Si, Cu/(Ti,Zr)N 0 . 7 6 /Si, and Cu/TaN 0 . 7 1 /Si were studied by X-ray diffraction and sheet resistance measurements. The variation percentage of sheet resistance for all Cu/barrier/Si systems stayed at a constant value after annealing up to 500°C for 30 min. However, the sheet resistance increased dramatically after annealing above 750°C for Cu/(Ti,Zr)N 0 . 9 5 /Si, and 500°C for both Cu/(Ti,Zr)N 0 . 7 6 /Si and Cu/TaN 0 . 7 1 /Si. For these samples, the interface deteriorated seriously and formationof Cu 3 Si was observed by XTEM. Our results suggest thai the refractory binary metal nitride film, (Ti,Zr)N, can be used as a diffusion barrier for Cu metallization as compared to the well-known TaN film.

Electrochemical Investigation of Pd-Free Electroless Co-Based Capping Layers on Cu Surfaces

Electroless Co-based capping layers with dimethylamine borane (DMAB) and hypophosphite as reductants on Cu lines were achieved without Pd activation. The oxidation process of electroless Co-based deposition was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The oxidation of DMAB was greatly suppressed with the addition of hypophosphite during electroless CoBP deposition. At low [OH - ], an obvious oxidation peak of hypophosphite was attained due to insufficient formation of BH 3 OH - , which showed slow charge transfer on the Cu surface; at high [OH - ], distinct competition between hypophosphite and OH - and sufficient BH 3 OH - formed enhanced the oxidation of DMAB, indicating fast charge transfer. The selectivity of electroless Co-based deposition was also strongly influenced by [DMAB], [hypophosphite], and [OH - ].

The evaluation of the diffusion barrier performance of reactively sputtered TaN/sub x/ layers for copper metallization

Ta-based Cu diffusion barrier properties were widely studied. This work demonstrates that grain boundary diffusivity of Cu diffusion in various TaN/sub x/ (x=0/spl sim/0.62) thin films can be extracted from the copper concentration profile, based on the Whipple analysis of grain boundary diffusion, after annealing the samples at fixed temperatures between 200 and 500/spl deg/C. We used the grain boundary diffusivity to predict the penetration depth (2/spl radic/Dt) of Cu in Ta and TaN/sub x/ films at fixed temperatures 250 and 400/spl deg/C. Cu/TaN/sub x/(45 A)/N/sup +/P junction diode leakage, SIMS and XSEM analysis results indicated that the Whipple model correlates well with experimental results.

Low damage etch approach for next generation Cu interconnect

This research focus on low radical plasma etch (LRPE) process and its impact on highly porous dielectric material (extreme-low-k, ELK, k=2.4). We demonstrate a dual damascene (DD) process flow without k degration by low radical and pore sealing plasma etch. Comparing to tranditional DD etching process, 12% resistance-capacitance (RC) improvement, 15% via resistance reduction and a factor of 3 inter-metal-dielectric (IMD) time dependent dielectic breakdown (TDDB) improvement can be achieved by the proposed approach.

Low capacitance approaches for 22nm generation Cu interconnect

Various integration approaches, including homogeneous porous Low-k and air gaps, for low-capacitance solution were investigated for 22nm Cu interconnect technology and beyond. For homogeneous Low-k approach, K=2.0 Low-k material is successfully integrated with Cu. Up to 15% line to line capacitance reduction compared with LK-1 (K= 2.5) was demonstrated by a damage-less etching and CMP process. For air gap approach, a cost-effective and Selective air gaps formation process was developed. Air gaps are selectively formed only at narrow spacing between conduction lines without additional processes.

Advanced patterning approaches for Cu/Low-k interconnects

The RC delay, electro migration (EM) and TDDB performance become more challenges to meet device requirement as continuous geometry shrink on BEOL dual damascene interconnects. To overcome these challenges from interconnect patterning point of view, we proposed Cu subtractive RIE as a potential solution for next generation Cu/Low-k interconnects.

Ultra-thin ALD-MnN barrier for low resistance advanced interconnect technology

As dimension shrinks the volume percent occupied by conventional barrier and liner increases and line resistance (Rs) and via resistance (Rc) increases dramatically. An ultrathin ALD MnN barrier is being evaluated as a single layer barrier for resistance reduction in small structures. >20% and >80% Rs and Rc reduction was demonstrated, while 4× better mean time to failure (MTTF) on the time dependent dielectric breakdown (TDDB) was achieved comparing to conventional barrier/liner. ALD MnN is a potential barrier candidate for future interconnects technology.