Phase transformation and residual stress probed by Raman spectroscopy in diamond-turned single crystal silicon

Abstract

Single-point diamond turning of monocrystalline semiconductors is an important field of research within brittle materials machining. Monocrystalline silicon samples with a (100) orientation have been diamond turned under different cutting conditions (feed rate and depth of cut). Micro-Raman spectroscopy and atomic force microscopy have been used to assess structural alterations and surface finish of the samples diamond turned under ductile and brittle modes. It was found that silicon undergoes a phase transformation when machined in the ductile mode. This phase transformation is evidenced by the creation of an amorphous surface layer after machining which has been probed by Raman scattering. Compressive residual stresses are estimated for the machined surface and it is observed that they decrease with an increase in the feed rate and depth of cut. This behaviour has been attributed to the formation of subsurface cracks when the feed rate is higher than or equal to 2.5 μm/rev. The surface roughness was observed to vary with the feed rate and the depth of cut. An increase in the surface roughness was influenced by microcrack formation when the feed rate reached 5.0 μm/rev. Furthermore, a high-pressure phase transformation induced by the tool/material interaction and responsible for the ductile response of this typical brittle material is discussed based upon the presented Raman spectra. The application of this machining technology finds use for a wide range of high quality components, for example the creation of a micrometre-range channel for microfluidic devices as well as microlenses used in the infrared spectrum range.

Surface and subsurface characterisation in micro-milling of monocrystalline silicon

“…Strain within the silicon lattice shifts the peak, with tensile stresses causing negative peak frequency shifts and compressive stresses causing positive peak frequency shifts. Raman spectra shift shows that the residual stresses are compressive on most of the machined surface, which agrees with those reported in single-point diamond turning of silicon [35] and micro-scratching of silicon [39]. Figures 10 and 11 show the mean values of residual stress under various machining conditions.…”

“…Recently, Raman microspectroscopy method has been used to investigate subsurface layer composition, i.e. phase transformation and residual stress in ultra-precision machining of silicon [34,35]. However, it has yet applied to surface integrity characterisation in micro-milling.…”

Can a carbon nano-coating resist metallic phase transformation in silicon substrate during nanoimpact?

“…Phase transformation of brittle materials is of particular interest to the field of nanometric cutting because it provides the roadmap to obtain the ductile response from brittle materials [9]. An understanding of how high pressure phase transformation can be regulated is necessary to know to control the deviatoric stress conditions in order to drive or suppress ductile response of brittle materials such as during machining of silicon [9][10].…”

Real-Time Identification of Incipient Surface Morphology Variations in Ultraprecision Machining Process

“…(6), the process state can be predicted one step abead; and then using Fq. (8), the weights of the particles of the process state can be updated by using tbe measurement data. By using this sequential Monte Carlo sampling method, Eq.…”

“…Tbese contrasts with conventional machining give rise to distinctly different chip-formation process, magnitude of cutting and thrust forces and their ratio, and surface generation mechanisms [2,7]. These mechanisms can affect the surface properties [8] and functional behavior of a machined component [2]. These factors also make the prediction and control of surface quality and its variations in industrial UPM processes an sensor for process monitoring.…”