Modeling the copper microstructure and elastic anisotropy and studying its impact on reliability in nanoscale interconnects

BackgroundCopper is the primary metal used in integrated circuit manufacturing of today. Even though copper is face centered cubic it has significant mechanical anisotropy depending on the crystallographic orientations. Copper metal lines in integrated circuits are polycrystalline and typically have lognormal grain size distribution. The polycrystalline microstructure is known to impact the reliability and must be considered in modeling for better understanding of the failure mechanisms.MethodsIn this work, we used Voronoi tessellation to model the polycrystalline microstructure with lognormal grainsize distribution for the copper metal lines in test structures. Each of the grains is then assigned an orientation with distinct probabilistic texture and corresponding anisotropic elastic constants based on the assigned orientation. The test structure is then subjected to a thermal stress.ResultsA significant variation in hydrostatic stresses at the grain boundaries is observed by subjecting the test structure to thermal stress due to the elastic anisotropy of copper. This introduces new weak points within the metal interconnects leading to failure.ConclusionsInclusion of microstructures and corresponding anisotropic properties for copper grains is crucial to conduct a realistic study of stress voiding, hillock formation, delamination, and electromigration phenomena, especially at smaller nodes where the anisotropic effects are significant.

[1]  K. Weide-Zaage.  The Finite Element Analysis of Weak Spots in Interconnects and Packages , 2012 .

[2]  Branching mechanism of intergranular crack propagation in three dimensions. , 2005, Physical review. E, Statistical, nonlinear, and soft matter physics.

[3]  C. Thompson.  Structure Evolution During Processing of Polycrystalline Films , 2000 .

[4]  F. Hauser,et al.  Deformation and Fracture Mechanics of Engineering Materials , 1976 .

[5]  Robert E. Rudd,et al.  Void nucleation and associated plasticity in dynamic fracture of polycrystalline copper: an atomistic simulation , 2002 .

[6]  R. Kistler,et al.  X-Ray Strain Measurements in Fine-Line Patterned AL-CU Films , 1994 .

[7]  P. Ho,et al.  Scaling effects on microstructure and electromigration reliability for Cu and Cu(Mn) interconnects , 2014, 2014 IEEE International Reliability Physics Symposium.

[8]  G.B. Alers,et al.  Stress migration and the mechanical properties of copper , 2005, 2005 IEEE International Reliability Physics Symposium, 2005. Proceedings. 43rd Annual..

[9]  Carl V. Thompson,et al.  Effects of microstructure on the formation, shape, and motion of voids during electromigration in passivated copper interconnects , 2008 .

[10]  Alvin Leng Sun Loke,et al.  Microstructure and reliability of copper interconnects , 1998 .

[11]  Frank Werner,et al.  Tessellation Methods for Modeling the Material Structure , 2015 .

[12]  Carl V. Thompson,et al.  Electromigration in Cu interconnects with very different grain structures , 2001 .

[13]  Oliver Aubel,et al.  Grain structure analysis and effect on electromigration reliability in nanoscale Cu interconnects , 2013 .

[14]  G. Cailletaud,et al.  Three-dimensional finite element simulation of a polycrystalline copper specimen , 2007 .

[15]  Young-Chang Joo,et al.  Effect of low- k dielectric on stress and stress-induced damage in Cu interconnects , 2004 .

[16]  Paul S. Ho,et al.  Electromigration reliability issues in dual-damascene Cu interconnections , 2002, IEEE Trans. Reliab..

[17]  Oliver Aubel,et al.  Stress-induced phenomena in nanosized copper interconnect structures studied by x-ray and electron microscopy , 2009 .

[18]  Christian Witt,et al.  Stress control during thermal annealing of copper interconnects , 2011 .

[19]  Brigitte Bacroix,et al.  Generalized vertex model of recrystallization – Application to polycrystalline copper , 2008 .

[20]  Ehrenfried Zschech,et al.  Advanced Interconnects for ULSI Technology , 2012 .

[21]  T. Lu,et al.  Effects of free surface and heterogeneous residual internal stress on stress-driven grain growth in nanocrystalline metals , 2013 .

[22]  Yintang Yang,et al.  Structure-dependent behavior of stress-induced voiding in Cu interconnects , 2010 .

[23]  K. Barmak,et al.  Simulation of electrical conduction in thin polycrystalline metallic films: Impact of microstructure , 2013 .

[24]  Texture and strain in narrow copper damascene interconnect lines: An X-ray diffraction analysis , 2008 .

[25]  Yun-Jiang Wang,et al.  Studying the elastic properties of nanocrystalline copper using a model of randomly packed uniform grains , 2013, 1303.2421.

[26]  Ehrenfried Zschech,et al.  Electron Backscatter Diffraction: Application to Cu Interconnects in Top-View and Cross Section , 2005 .

[27]  K. Barmak,et al.  Effect of downscaling nano-copper interconnects on the microstructure revealed by high resolution TEM-orientation-mapping , 2012, Nanotechnology.

[28]  S. N. Kosolobov,et al.  Long term operation of high quantum efficiency GaAs(Cs,O) photocathodes using multiple recleaning by atomic hydrogen , 2009 .

[29]  D. Field,et al.  Barrier layer, geometry and alloying effects on the microstructure and texture of electroplated copper thin films and damascene lines , 2005 .

[30]  James R. Lloyd,et al.  Electromigration in integrated circuit conductors , 1999 .

[31]  Z. Suo,et al.  Reliabilityof Interconnect Structures , 2003 .

[32]  Chee Lip Gan,et al.  The effect of stress migration on electromigration in dual damascene copper interconnects , 2011 .

[33]  A. von Glasow,et al.  Experimental data and statistical models for bimodal EM failures , 2000, 2000 IEEE International Reliability Physics Symposium Proceedings. 38th Annual (Cat. No.00CH37059).

[34]  I. Avci,et al.  A numerical model using the phase field method for stress induced voiding in a metal line during thermal bake , 2013, 2013 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD).

[35]  Eric Beyne,et al.  Microstructure simulation of grain growth in Cu Through Silicon Via using phase-field modeling , 2014, 2014 15th International Conference on Thermal, Mechanical and Mulit-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE).

[36]  J. Weertman,et al.  Rapid stress-driven grain coarsening in nanocrystalline Cu at ambient and cryogenic temperatures , 2005 .

[37]  S.S. Wong,et al.  Effect of texture on the electromigration of CVD copper , 1997, 1997 IEEE International Reliability Physics Symposium Proceedings. 35th Annual.

[38]  U. F. Kocks,et al.  Texture and Anisotropy: Preferred Orientations in Polycrystals and their Effect on Materials Properties , 1998 .

[39]  K. Ganesh,et al.  Texture and stress analysis of 120 nm copper interconnects , 2010 .

[40]  J. J. Clement,et al.  Electromigration in copper conductors , 1995 .

[41]  Marc Legros,et al.  Stress-assisted discontinuous grain growth and its effect on the deformation behavior of nanocrystalline aluminum thin films , 2006 .

[42]  M. Liang,et al.  A full Cu damascene metallization process for sub-0.18 /spl mu/m RF CMOS SoC high Q inductor and MIM capacitor application at 2.4 GHz and 5.3 GHz , 2001, Proceedings of the IEEE 2001 International Interconnect Technology Conference (Cat. No.01EX461).

[43]  W. Nix,et al.  Microstructure Effect on EM-Induced Degradations in Dual Inlaid Copper Interconnects , 2009, IEEE Transactions on Device and Materials Reliability.

[44]  Robert R. Keller,et al.  Grain boundary misorientation angles and stress-induced voiding in oxide passivated copper interconnects , 1997 .

[45]  J. Bravman,et al.  The influence of strain energy on abnormal grain growth in copper thin films , 1995 .

[46]  Carl V. Thompson,et al.  Dependence of the electromigration flux on the crystallographic orientations of different grains in polycrystalline copper interconnects , 2007 .

[47]  A. Fischer,et al.  Stress-induced voiding in aluminum and copper interconnects , 2002 .

[48]  Xiaopeng Xu,et al.  Elastic anisotropy of Cu and its impact on stress management for 3D IC: Nanoindentation and TCAD simulation study , 2012 .

[49]  Chih-Chao Yang,et al.  Electromigration challenges for advanced on-chip Cu interconnects , 2014, Microelectron. Reliab..

[50]  A. H. Fischer,et al.  Modeling bimodal electromigration failure distributions , 2001, Microelectron. Reliab..

[51]  E. Lifshin,et al.  Sidewall Texture and Microstructure of iPVD Copper Seed in Narrow Damascene Trenches , 2013 .

[52]  Paul S. Ho,et al.  Thermal stress characteristics of Cu/oxide and Cu/low-k submicron interconnect structures , 2003 .

[53]  Valeriy Sukharev,et al.  A model for electromigration-induced degradation mechanisms in dual-inlaid copper interconnects: Effect of interface bonding strength , 2004 .

[54]  Zhixin Chen,et al.  The effects of size and orientation on magnetic properties and exchange bias in Co3O4 mesoporous nanowires , 2011 .

[55]  Theory for Electromigration Failure in Cu Conductors , 2006 .

[56]  Siegfried Selberherr,et al.  Electromigration in submicron interconnect features of integrated circuits , 2011 .

[57]  L. Chen.  Impact of aspect ratio and line spacing on microstructure in damascene Cu interconnects , 2015, 2015 IEEE 22nd International Symposium on the Physical and Failure Analysis of Integrated Circuits.

[58]  Xiaopeng Xu,et al.  Copper Anisotropy Effects in Three-Dimensional Integrated Circuits Using Through-Silicon Vias , 2012, IEEE Transactions on Device and Materials Reliability.

[59]  J. Li,et al.  Mechanical grain growth in nanocrystalline copper. , 2006, Physical review letters.

[60]  J. Bravman,et al.  Thermal Stresses in Passivated Copper Interconnects Determined by X-Ray Analysis and Finite Element Modeling , 1994 .