Molecular Dynamics Simulation Of Structural Change In Heterogenous Interface Induced By Nanoindentation

Over the past few decades, production of IC keeps the strategy of high speed,high integration, high density and high performance. The surface of VLSI iscomposed by copper and dielectric thin film material. The elastic modulus and otherphysical properties of these two materials are inconsistent, which lead to somequestions in the process of heterogeneous surface planarization manufacture, such asthe material interfacial debonding, the injury of interconnect wires, the roughness ofthe surface and some other questions. The damage of interface is the core question.Therefore, we studied the changing regularity of the atomic structure from theinterface and the damage mechanism of the Si/Cu heterogenous under nano-scale,which have very important academic significance.To solve this problem，the structures of the Si/Cu heterogenous interfaceimpacted by the nanoindentations with different incident angles and depths wereinvestigated in detail at nano-scale using the molecular dynamics simulation. We willreveal the reason of the atomic migration and reconfiguration, and the damage ofnano-scale material at the interface under nanoindentation with different incidentangles. Firstly, we set up the Si/Cu heterogenous interface using the moleculardynamics calculation software of LAMMPS at nano-scale. We should take account ofthe difference of lattice between Si and Cu, and study the rule of the molecularinteraction, as well as stress distribution at the interface. Secondly, we study the Si/Cuheterogenous interface structure at nano-scale, and we also explore the micro-damagemechanism at the interface. Finally, the micro-damage mechanism at the interface will be revealed. To propose the control of the damage at the interface will provide thetheoretical basis and support for the planarization technology of the very large scaleintegration circuits (VLSI) manufacture.In the present work, the results indicate that the indentation depth, the incidentangle of the nanoindenter, and the size of abrasive particles play important roles in thestructural deformation of the heterogenous interface. The simulation results suggestthat the increase depth of the nanoindenter with certain incident angle could firstlyincrease the stress of each atom at the interface, and then introduce more seriousstructural deformation of the heterogenous interface of Si/Cu. Simultaneously, theextended length of Si or Cu is not only related to the incident angle of nanoindenter,but also related the radius size of the nanoindenter. When wiring on the IC board, thedistance of neighbor copper wires cannot be too intensive. The most appropriateradius of each abrasive particle should be smaller than the distance of neighbor copperwires on IC board, to avoid the overlapping of the neighbor copper wires. Especially,when the incident angle is80°, the extended length of Cu atom layer is about38.38,which is larger than the radius of the nanoindenter. In other words, the smaller size ofthe abrasive particles than the distance of neighbor copper wire is a better choice forpolishing. In the mechanical polishing process, the best choose of the incident angleof nanoindenter is from-45°to45°. At this case, these atoms under thenanoindentation get enough energy from the nanoindentation to overcome thepotential barrier, and reach the stable state. Then the stress of these atoms is released.Adding spoiler in the CMP equipment will increase the numbers of the abrasiveparticles with the grinding angle distribution from-45°to45°, and reducing thenumbers of the abrasive particles with the grinding angle less than-45°or more than45°. It can improve the stability of heterogenous interface structure, and it also canimprove the quality of IC board.