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5 Mechanical Properties
Reasons for wafer breakage is the mechanical handling (pick, place, transport) [447], stress loads
due to processing (dielectrics, metals, asymmetric structures) and stress during processing for example
due to thermal loads in annealing or deposition steps and cutting/dicing. The problem is less important
in microelectronics but especially severe in photovoltaics (PV) industry, handling large total areas;
on the other hand the profit loss per broken wafer is much higher in the microelectronics industry.
An additional problem poses the grain structure of multicrystalline silicon wafers used for PV [448]
and the effect of surface cracks and irregularities at wafer edges and corners. Just going from a wafer
thickness of 270 µm to 250 µm can more than double the breakage rate at certain process steps [449].
The minimum strength of a wafer with surface cracks is about 100 MPa, while the strength of wafers
with cracks at the edge can reach rather low values around 20 MPa. Also the careful shaping of the
wafer edge is important to avoid breakage [450].
5 Mechanical Properties
Reasons for wafer breakage is the mechanical handling (pick, place, transport) [447], stress loads
due to processing (dielectrics, metals, asymmetric structures) and stress during processing for example
due to thermal loads in annealing or deposition steps and cutting/dicing. The problem is less important
in microelectronics but especially severe in photovoltaics (PV) industry, handling large total areas;
on the other hand the profit loss per broken wafer is much higher in the microelectronics industry.
An additional problem poses the grain structure of multicrystalline silicon wafers used for PV [448]
and the effect of surface cracks and irregularities at wafer edges and corners. Just going from a wafer
thickness of 270 µm to 250 µm can more than double the breakage rate at certain process steps [449].
The minimum strength of a wafer with surface cracks is about 100 MPa, while the strength of wafers
with cracks at the edge can reach rather low values around 20 MPa. Also the careful shaping of the
wafer edge is important to avoid breakage [450].