The impact of damage etching on fracture strength of diamond wire sawn monocrystalline silicon wafers for photovoltaics use

Abstract

To reduce silicon kerf loss, we have cut silicon bricks into wafers using a thin diamond wire (the diameter of core wire: 80 µm, the average size of abrasives: 10 µm). Damages caused by diamond wire sawing are responsible to have an asymmetry in fracture strength, a lower strength in parallel bending and a higher strength in perpendicular bending to the saw marks. To elucidate the asymmetry to the depth of subsurface damage, front and backside surfaces of wafers are etched in 3, 5, and 10 µm depth by 24% KOH aqueous solution. By etching 3 and 5 µm, the strength are enhanced by a factor of 1.96 and 2.9 times in parallel bending and by 1.03 and 1.31 times in perpendicular bending compared to bare wafers. Etching more than 5 µm removes the asymmetry, showing the equal strength in the bending in both directions. We cystallographically consider several fracture mechanisms of bare and etched wafers through the observation of each fracture surface.

Adapting M2 silicon half-wafers processing on industrial-scale equipment dedicated to 4″ solar technology

“…Thereafter, the half wafers will be referred simply to as "wafers." It is useful to specify before starting work, whether the silicon wafers to be used were cut by multi-wire slurry sawing (MWSS) or by more recent diamond wire sawing process (Sekhar et al, 2018;Kumar and Melkote, 2018). Because of surface morphological differences between the two types of cut, the chemical solutions should be adapted.…”

Photovoltaic integration in curved parts: Mechanical limits and key parameters from a theoretical point of view

“…These defaults are mainly located near cells surfaces and take the form of micro‐grooves of a few tens of microns, which come as a consequence of the sawing process 2–5 . The characteristics and impacts of these defaults are therefore strongly influenced by the surface treatments performed afterwards 6,7 . Regarding crack propagation, the local orientation of the crystalline structure has a noticeable influence on its fracture toughness 6,8 .…”

“…4,9 These effects explain the wide scattering of characteristic fracture stress values (80-300 MPa) assessed and reported in the literature. 4,6,7,[9][10][11][12] Furthermore, these experiments are expected to be scattered themselves since failure depends on a statistical event (the interaction between a stress field and the pre-existing cracks). Therefore, the characteristic fracture stress of a type of PV cell is not specific to every single cell of this type.…”

Two-dimensional detection of subsurface damage in silicon wafers with polarized laser scattering

“…Currently, there are two types of the methods for detecting SSD, namely, destructive and nondestructive methods. In terms of the destructive methods, Gao et al (2010) used the angle J o u r n a l P r e -p r o o f polishing method to obtain depth of SSD; Yin et al (2018b) used the cross-sectioning technique to study the configuration of subsurface cracks; Zhou et al (2016) revealed the microstructure in the wafers with the transmission electron microscopy; and Sekhar et al (2018) carried out the chemical etching to elucidate the asymmetry to the depth of SSD induced in the wire sawing.…”

“…They are promising for in-process detection and can greatly increase the overall production efficiency. Sun et al (2016) proposed a model of grinding force in the self-rotating grinding of silicon. Based on the grinding force model, the distribution of subsurface damage depth in the whole wafer could be revealed.…”