Diamond machining of silicon: A review of advances in molecular dynamics simulation

Abstract

Molecular Dynamics (MD) simulation has enhanced our understanding about ductile-regime machining of brittle materials such as silicon and germanium. In particular, MD simulation has helped understand the occurrence of brittle-ductile transition due to the high-pressure phase transformation (HPPT), which induces Herzfeld-Mott transition. In this paper, relevant MD simulation studies in conjunction with experimental studies are reviewed with a focus on (i) The importance of machining variables: undeformed chip thickness, feed rate, depth of cut, geometry of the cutting tool in influencing the state of the deviatoric stresses to cause HPPT in silicon, (ii) The influence of material properties: role of fracture toughness and hardness, crystal structure and anisotropy of the material, and (iii) Phenomenological understanding of the wear of diamond cutting tools, which are all non-trivial for cost-effective manufacturing of silicon. The ongoing developmental work on potential energy functions is reviewed to identify opportunities for overcoming the current limitations of MD simulations. Potential research areas relating to how MD simulation might help improve existing manufacturing technologies are identified whichmay be of particular interest to early stage researchers.

A review on ductile mode cutting of brittle materials

“…MD simulation demonstrated that the amorphous phase transformation in cutting of silicon is a key mechanism for inelastic deformation, and crack propagation can be avoided by stable shearing under a compressive stress [90]. MD simulations show that the high-pressure phase transformation (HPPT) of silicon results in a metallization to form a metastable phase, which persists only when the cutting tool is able to retain sufficient stress [91]. However, currently MD simulations suffer from the spurious effects of high cutting speeds and the accuracy of the simulation results has yet to be fully explored [91].…”

Influence of microstructure on the cutting behaviour of silicon

“…Silicon has been used extensively in both single crystal as well as in polycrystalline form for a wide range of microelectronic applications including solar cells and conducting gates for CMOS and MOSFET processing devices [1]. Recent technological trends have also led to the synthesis of nanospheres and nanowires of silicon, which would potentially provide an even broader range of applications.…”

“…In this regard, the existing research details several aspects of silicon, but this material is so versatile that many new phenomena are still being explored to bridge the missing gaps in our existing understanding. Across a number of those research studies, ductility in silicon by large has been attributed either to the occurrence of high pressure phase transformation (HPPT) [1], crystal twinning [2] or surface nucleation of dislocations [3,4]. It is understood that the nucleation of dislocations is more prevalent than HPPT in the presence of free surfaces, for examples in, nanoparticles of silicon [5] while no evidence of crystal twinning during contact loading of silicon has been reported in the literature other than the work of Mylvaganam et al [2].…”

“…Reports of HPPT of silicon on the other hand have a richer history [6], and in the past, several phases of silicon were identified [7] by post-experimentation analysis, which are summarised in Table I along with the typical stress levels at which these phases persist. Figure 1: High pressure phase transformation of silicon during its contact loading [1] -Blue line signifies high pressure phase transformation of silicon to cause metallisation while the red line signifies back transformation after HPPT to an atmospheric phase depending on the rate of release of load.…”

“…Molecular dynamics (MD) simulation has played a key role in developing our understanding of such processes, and an overview of insights gained from atomic-scale modelling of diamond machining of silicon has recently been given by the authors [1]. Typically, three-body potentials of the Tersoff [12,13] or the analytical bond order potential (ABOP) [14] type have been used in the past to model the interaction between Si and C atoms.…”