The Inhibition of Enhanced Cu Oxidation on Ruthenium∕Diffusion Barrier Layers for Cu Interconnects by Carbon Alloying into Ru

Abstract

The inhibition of Cu oxidation by alloying C into the Ru/TaN barrier stack is investigated. By using in-situ XRD measurement, severe copper oxide formation was observed for the Cu/Ru/barrier system during annealing process in He atmosphere. This phenomenon is explained using thermodynamics from the viewpoint of Gibbs free energy of oxide formation. The Cu oxidation can be inhibited by alloying C into the Ru layer, and the more C content in the RuC layer, the more evident the inhibition effect. The RuC/TaN stack also shows better diffusion barrier properties than the Ru/TaN bi-layer. Atomic layer deposition of Cu 2 O on the RuC substrate was carried out and reduction of the Cu 2 O to Cu was observed. The mechanism of inhibition of Cu oxidation on C alloyed Ru was investigated by a first principles calculation based on the density functional theory.As the interconnect line width continually scales down, the reliability problem induced by stress induced voiding (SiV) and electromigration (EM) becomes severe. 1-6 The SiV and EM problem are mainly caused by poor adhesion between Cu and the glue layer or capping layer. 1, 6-11 It is found that the oxidation of Cu or barrier layer will degrade the adhesion between Cu and the glue layer, 1, 12-14 resulting in delamination during chemical mechanical polishing (CMP) and reliability problems. Cu oxidation Cu can also increase the line resistance and thus increase the RC delay and degrade the performance of the devices. During the back end of line (BEOL) manufacturing process, Cu oxidation is easily observed because of many thermal processes and the unavoidable oxygen processes such as electrochemical deposition (ECD) of Cu. In order to inhibit Cu oxidation and improve the reliability of Cu interconnects, many methods have been proposed, such as using Ti instead of Ta as the Cu adhesion layer, 9 or adding an oxygen adsorption layer, such as Al 1 or Ti 15 on the pure ECD-Cu film before annealing.Recently, novel materials such as Ru 16,17,19 and Co 16, 20 etc. with low resistivity have been proposed to replace Ta as Cu adhesion layer because of the ability of direct ECD of Cu on their surface, which is beneficial for conformal ECD Cu gap filling. [16][17][18] Ru is considered as one of the most promising material as Cu adhesion layer in the future technology node. 17,19,21,22 It is reported that the predicted circuitperformance using the Ru based barrier was 10% higher than that with a Ta barrier and the operating-speed distribution was estimated to be less than 5% for the 22 nm-node CMOS generation. 19 However, there are still some concerns such as severe oxidation of copper and galvanic corrosion during the CMP process. 16 In this work, the effect of Ru on enhanced Cu oxidation was studied and by adding C into Ru, the inhibition of Cu oxidation and promotion of Cu 2 O reduction were studied.Experimental P-type Si (100) substrates were loaded into the vacuum chamber through a loadlock after standard chemical cleaning. The base pressure of the vacuum was 2 × 10 −7 mbar. TaCN a...

Spark plasma sintering of sub-micron copper reinforced with ruthenium–carbon nanotube composites for thermal management applications

“…It is possible that a reduction of Cu oxidation takes place due to presence of RuC. This observation is consistence with the inhibition of Cu oxidation by C alloyed Ru reported by Ding et al [40]. The reduction of Cu 2 O was attributed to the effect of RuC layer, as the C doped in Ru capturing the O atom from Cu-O to form CO molecules.…”

“…The high density value obtained in Cu-2 vol%CNT could be attributed to good dispersion of CNTs in Cu matrix. Moreover, this high densification showed that the potential sources of CNTs agglomeration that deteriorate metal-CNT composites density can be avoided by appropriate mixing process and sintering technique [19]. However, a reduction in density was observed in Cu-CNT composites containing 0.5 vol%Ru sintered at 600 C. This reduction could be due to insufficient sintering temperature since Ru has melting point of 2334 C. In addition, the Cu-CNT composites containing 0.5 vol%Ru was found to increase with increasing sintering temperature.…”

“…Owing to the low thermal conductivity of Cu-1 vol%CNT samples Sule et al [27], additional characterization was undertaken to understand the low result. XPS is an analytical technique that has been widely used to identifying the oxidation state of the copper surface [19]. Fig.12(a-f) shows the deconvolutions of the Cu 2p3/2 spectrum of the various samples produced.…”

“…Ruthenium has also been reported to show significantly stronger Ru-C bonds carbon compared to the Pd-C and Ti-C bonds [18]. Ding et al [19] reported that the oxidation of Cu was inhibited to an extent with C alloying into the Ru layer. Furthermore, improved density and hardness results were obtained when increasing the Ru volume fraction in copper matrix by up to 2.5 vol% [8].…”

High Temperature Oxidation Resistance of Ni22Cr11Al Bond Coat Produced by Spark Plasma Sintering as Thermal Barrier Coatings

“…The densification behaviour of the mixed powder was explained through the consideration of the shrinkage displacement and sintering time at different holding temperature during consolidation process [18,19].…”