The impact of surface finish conditions of silicon bricks on the mechanical strength of diamond-wire-sawn thin wafers (120 µm)

Abstract

Present study mainly focuses on to cut silicon bricks into thin (120 µm) wafers in multi-wire saw with higher cutting yields using thin diamond wires. The diamond wire quality and silicon brick surface conditions are the deciding factors on its production yields and wafer fracture strengths. The improvements in diamond wire (DW) quality allows us to cut thin (120 µm) Si wafers with a slicing yields of above 90%. The DW quality is improved by considering diamond particles are small in size and uniformly coated with a high dispersion (or with low agglomeration) on the wire. We have developed a diamond wire by matching above qualities and the wire labelled as 100d-M6/12, where 100d represents steel wire diameter (100 µm) and M6/12 the size range of diamond abrasives (6 to 12 µm). To address the impact of surface finish of silicon bricks on its slicing yields and wafer fracture strengths, we prepared two bricks, mirror-polished one and ground the other one. After sawing wafers are separated as fresh and worn-out wire sides. The wafers sawn from ground brick are labeled as g-wafers and mirror polished brick are labeled as p-wafers. The improvements in silicon bricks surface condition (mirror-polish) allows to improve slicing yields above 96%. In three-line bending test, mechanical loads are applied perpendicular to wire saw marks on the middle of the wafer surface. We observed two fundamental differences in fracture strengths of p- and g-wafers. The g-wafers have lower strength compared to p-wafers. In both wafers, fresh wire side wafers have lower strength compared to worn-out wire side wafers. From fractographical studies, cracks of low-strength wafers tend to propagates through short distance paths and break the materials at lower loads. The wafers having higher fracture strength, cracks tend to propagates through longer and complex paths and break the materials at higher loads.