Multimillion-atom molecular dynamics simulation of atomic level stresses in Si(111)/Si3N4(0001) nanopixels

Abstract

Ten million atom multiresolution molecular-dynamics simulations are performed on parallel computers to determine atomic-level stress distributions in a 54 nm nanopixel on a 0.1 m silicon substrate. Effects of surfaces, edges, and lattice mismatch at the Si͑111͒/Si 3 N 4 ͑0001͒ interface on the stress distributions are investigated. Stresses are found to be highly inhomogeneous in the nanopixel. The top surface of silicon nitride has a compressive stress of ϩ3 GPa and the stress is tensile, Ϫ1 GPa, in silicon below the interface. © 1998 American Institute of Physics. ͓S0003-6951͑98͒00116-8͔Sub-100 nm pixel sizes pose special challenges in Si electronics. In this regime, the significance of spatial inhomogeneities in the dopant distribution to the device characteristics is being increasingly appreciated.1 Spatially nonuniform stresses induced by such nanoscale pixellation may have profound impact 2 -rapidly varying stresses at and near edges may lead to defect formation or even initiate a crack. Understanding the stress distribution is therefore essential in the design of nanoscale devices.On larger (Ͼ1 m) length scales, edge stresses in Si/SiO 2 and Si/Si 3 N 4 have been examined utilizing the framework of linear elasticity and finite-element ͑FE͒ simulations. 3,4 In nanoscale devices, however, the surface-tovolume ratio is so large that the influence of surfaces, edges, and corners on elastic properties become significant. In addition, chemical bonding at the Si/Si 3 N 4 interface introduces types of stresses not present in silicon or silicon nitride materials. These effects have to be included in constitutive relations to achieve realistic description of nanoscale devices in the FE approach. An alternative approach is to use molecular-dynamics ͑MD͒ simulations where surface and interface bonding effects are explicitly included at the atomistic level. With recent progress in parallel computer architectures, it has now become possible to carry out direct atomistic simulations for submicron structures with realistic descriptions of the materials involved. In particular, largescale MD simulations have proven to be useful in the study of dynamic fracture.5 MD simulations provide spatially resolved stress distributions on the length scales not accessible to experimental techniques, such as MicroRaman spectroscopy.6 Such numerical experiments can be used to establish the validity of constitutive relations used in FE simulations, in particular the treatment of surface/interface/ edge effects.In this letter, the results of a ten million atom moleculardynamics study of atomic stress distribution in a Si/Si/Si 3 N 4 nanopixel are reported. The simulations were performed on 128 processors of the 256-processor HP Exemplar at Caltech requiring a total of 180 h of computational time. We have considered a crystalline Si 3 N 4 film forming a coherent Si͑111͒/Si 3 N 4 ͑0001͒ interface 7 with the Si mesa. An interatomic potential model for the Si/Si 3 N 4 interface has been developed using the charge transfer values computed from...

Atomistic damage mechanisms during hypervelocity projectile impact on AlN: A large-scale parallel molecular dynamics simulation study

“…The stresses averaged in each of these voxels will provide a grid with the local stress distribution in the total system. This approach was used successfully in large-scale MD simulations of stress relaxation at materials interface (Bachlechner et al, 1998;Omeltchenko et al, 2000). Although this choice of voxel is convenient for problems of stress relaxation in stable solids, it is not a good choice for the description of strong shock waves with large gradients of stress and flux of atoms.…”

Coupling of Length Scales: Hybrid Molecular Dynamics and Finite Element Approach for Multiscale Nanodevice Simulations

“…The system we chose for this study is a realistic application of the interface problem between dissimilar materials: a 25×25×1 nm Si(111) mesa covered with a 25×25×5 nm Si 3 N 4 (0001) film, on a 50×50×15 Si(111) substrate [11] (see Fig. 3).…”

“…Atomistic simulations utilizing the molecular dynamics (MD) method through use of suitable interatomic potentials can provide the necessary atomic level information [11], but cannot reach the desired length scales due to high computational cost. A multiscale scheme, that will efficiently combine atomistic and continuum simulations, is thus needed.…”

Local stress calculation in simulations of multicomponent systems

“…In atomistic simulations, the local stress field can be used to locate individual defects and characterize their structure and dynamics under arbitrary loading conditions. In molecular dynamics (MD) simulations, local stresses have been useful in the analysis of a wide range of phenomena such as film growth [1], shock loading [2][3][4], dislocation dynamics [5,6], and semiconductor nanopixel relaxation [7,8].…”