Monocrystalline silicon enjoys a prominent role as the foundational material in the manufacture of microelectronic semiconductor components due to their favourable physical and chemical properties, comparatively cheap price and nearly limitless availability.
Silicon crystallises in the diamond lattice, which can be described with two interpenetrating face-centered cubic elementary cells that are shifted in each direction by the distance of a quarter of edge length.
The mechanical properties of silicon are informed by the anisotropic bonding forces prevalent in the monocrystalline corpus. For the elastic modulus for instance, values of E<100> = 130.2 GPa, E<110> = 168.9 GPa and E<111> = 187.5 GPa result for the crystal directions [100], [010] und [111].
The covalent bond of silicon in the diamond lattice is highly stable because of a strict localisation of the valence electrons. From this we obtain a material that is very strong and brittle. The deformation characteristic values reached in a tensile test at room temperature show that silicon behaves in an ideal/elastic manner to a large extent, i. e. there is only a small amount of total expansion. Considered mac — roscopically, fracture stress without previous mentionable plastic deformation leads without interruption to breakage of the atomic bonds and destruction of the latticework (brittle fracture) [HOLZ94, TOEN90].
Investigations with higher temperatures have shown that temperatures exist in which silicon exhibits plastic material behaviour. Data on the transition temperature between brittle and ductile behaviour waver between 400 and 1000 °C. The transition from brittle to ductile material behaviour shifts to lower temperatures in the case of higher dislocation densities [HADA90, HOLZ94]. However, under intensive stress, deformation can be observed in crystal areas near the surface at room temperature as well [HOLZ94].
Silicon is primarily used as wafer material. The wafers are separated from a silicon monocrystal (ingot) and undergo chip removal on planar surfaces. Established praxis when grinding the isolated wafers dictates a two-step process comprising a pre-processing and a post-processing stage. First there is a rough grinding process, which is required to remove the wafer surface, which is quite faulty after separation, as well as to smooth out the grooves. For this process, a relatively coarse grain is often selected (D46 in a synthetic resin or ceramic bond) in order to realise a high material removal rate (Qw = 100 bis 200 mm3/s). In this case, brittle machining mechanisms are acceptable if the damage depth of the external zone is less than the depths of cut of the subsequent fine-grinding process. The state of the art for fine grinding are D6 grits bonded in synthetic resin. Synthetic resin bonds are preferred to vitrified bonds. In fine grinding, low material removal rates of Qw = 5 to 15 mm3/s tend to be chosen. Using a ductile machining mechanism in this way, a surface quality of Ra < 10 nm and external zone damages smaller than 3 pm [KLOC00] can be realised, lessening post-processing costs.