On the ductile response dependence upon phase transformation in diamond turning of semiconductors

Abstract

It is well established that during machining, materials with lower hardness presents higher ductility. However, in the machining of semiconductor crystals the brittle to ductile transition may not strictly follow this rule. This paper intends to show that the extent of the ductile response of monocrystalline semiconductors can not be related to its microhardness value, since the plastic behavior of semiconductor crystals is related to a phase transformation induced by pressure/stress. This was investigated by carrying out microindentation and single point diamond turning tests in three different semiconductors, InSb, GaAs and Si[001]-oriented single crystals. Based upon tests results it is observed that the onset of brittle behavior is brought forward to semiconductors with higher transition pressure value.

Dependence of brittle-to-ductile transition on crystallographic direction in diamond turning of single-crystal silicon

“…Moreover, to date, little work has been carried out to investigate the relationship between anisotropy of silicon crystal and phase transformation during micromachining. In addition, as mentioned earlier, the indentation and diamond-turning studies suggested different ductile responses when a difference between microhardness and transition pressure value is present [8,23]. It has been shown that when the values of indentation hardness and the critical transition pressure are close, as in the case of silicon, the ordinary diamond-cubic silicon transforms to the denser b-tin structure under hydrostatic pressure at room temperature, and the ductile mode is the main material removal mechanism during machining.…”

“…The phase transition for GaAs is estimated to occur at a pressure around 17 GPa, and the accepted hardness is considerably lower than this value. Jasinevicius and Pizani have shown [23] that semiconductors may present a totally different response to machining based upon the difference between indentation hardness of the pristine crystal and the transition pressure value. According to the authors, InSb (Hv ; 2.3 GPa) presents a larger plasticity than GaAs (Hv ; 6.9 GPa) and Si (Hv ; 11-12.5 GPa).…”

Diamond turning of small Fresnel lens array in single crystal InSb

“…Besides the geometrical aspects described above, another parameter which affects the brittle-to-ductile transition is the rake angle, together with the material's pressure-induced phase transformation. The use of highly negative rake angles for ductile machining has proved its efficiency in ductile mode diamond turning tests of silicon wafers and other II-VI semiconductors crystals [21][22][23]. This is relevant once Fresnel lenses' fabrication demands the prevention of brittle damage to the edges of the zone steps [25].…”

“…It has been proposed that the critical thickness of cut for these materials varies with the transition pressure value of each crystal [22]. The higher the value of the transition pressure, the lower the critical thickness of cut [23]. The application of a deterministic material removal process to generate rotational diffraction optical elements in semiconductor crystals has recently been tried [24][25][26].…”