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Spalling of a Single Crystalline Silicon Layer By Electroless/Electrodeposit-Assisted Stripping(EAS) Process for Flexible Silicon Devices
The EAS process is consisted of three steps: 1) forming a Ni seed layer with nano-rod using anelectroless deposition to enhance the adhesion of seed layer on Si substrate, and 2) forming a low stress layer as a buffer layer to prevent cracks on a seed layer and then finally 3) forming a high stress layer using electrodeposit at room temperature. A high quality Si film could be obtained by the precise control of two parameters: 1) adhesion between a metal seed layer and Si, 2) critical stress applied to Si substrate.
Concerning control of the adhesion of the Ni seed layer-Si interface, a Ni seed layer has to be satisfied with both high adhesion on Si and high resistance of crack by a high stress-inducing layer. We investigated a high adhesive electroless seed layer on Si in place of a conventional high cost PVD(physical vapor deposition) process. Firstly, nano-holes were formed with control of a critical spacing on Si surface by MACE(metal assisted chemical etching) and then both holes and Si surface were covered with Ni using autocatalytic electroless deposition. The effect of the nano-hole in silicon, such as a pretreatment for enhance adhesion, is also investigated using different MACE parameters – control of metal distribution, depth in Si, the size of the nano-hole, various etched structure.
Concerning control of a critical stress applied to Si substrate, a stress layer has to be satisfied with a certain stress value high enough to propagate a crack within Si during electrodeposition. We investigated both internal stress value of the Ni deposit and the spalling behavior under different conditions of composition, current density, pH, temperature etc.