A Study on the Tip-Based Nanomachining of Silicon Wafer Using Atomic Force Microscopy (AFM)

Abstract

Abstract In this work, the principles of nanoindentation and nanoscratching processes (tip-based nanomachining processes) are applied in the computational study of relevant material behaviors of single crystalline silicon wafer. Molecular dynamics (MD) simulations are carried out to model the tip-based nanomachining process of a silicon substrate by employing LAMMPS, a free MD simulation software. A spherical diamond tool tip with a radius of 8Å is considered. In the MD simulation, a single diamond indenter is treated as a rigid body. The dimensions of the silicon workpiece in the MD simulations are 500Å × 500Å × 350Å, containing 2,207,698 Si atoms. A diamond cubic lattice structure is employed to arrange these Si atoms from the very beginning at 293 K (room temperature) and a lattice constant of 5.43Å is employed. The lowest layer of the Si workpiece model is fixed and this fixed layer is one atom thick i.e. its thickness is 5.43Å. Immediately above the fixed layer is another layer of equal thickness (5.43Å), which is called thermostat layer. This layer serves the purpose of maintaining constant temperature of the system. The force-controlled approach is employed for this study. Essentially, this research evaluates the influence of three parameters: exerted force on indenter, workpiece temperature (room temperature and several higher workpiece temperatures), and indenter size on the depth of indentation, length of scratch, and coordination number of the atoms. Verlet -Velocity algorithm is used to compute the velocities and positions of the atoms. Since we desired to maintain consistency in volume, energy, and the number of particles, the constant-energy ensemble (NVE), also known as microcanonical ensemble is applied in the simulations. Both the Si-Si and C-C interactions are computed using the Tersoff potential throughout the simulations while the Si-C interactions are computed with the Morse potential. The MDS results are visualized and analyzed using OVITO, a free and commonly use visualizing tool. It is found that these parameters (exerted force on indenter, operating temperature of the silicon substrate, and size of the indenter) have substantial influence on the behavior of the silicon substrate.