Research On Deforming Mechanism Of Nanocrystalline Copper Thin Film Under Contact Deformation

Nanocrystalline metal films have already been widely used in the fields ofmicro-electronics and semi-conductivity as hard coatings on MEMS parts andheat or electronic conduction coatings in electronic components. However,when these parts are on service, they inevitably suffer from the circle stress.Therefore, recent research attaches importance to the mechanical property ofnanocrystalline metal film and the deformation mechanism of films duringworking process plays a significant role on the research of the mechanicalproperty.The microstructure and deformation mechanism of crystalline Cu ultra-thinfilm under contact deformation are studied by film separation. The compositesubstrate of photoresist/SiO2/Si with special patterns is first prepared usingphotoetching technology and then an ultra-thin Cu film,50nm in thickness, isdeposited on the composite substrate by magnetron sputtering technology. Themorphology of nano-indention and transformation of microstructure afternano-indention are studied by scanning electron microscope and transmissionelectron microscope. The micro-deformation mechanism is discussed as well.The results are as follows (1) The shape of indentation area constitutes equilateral triangle which is inaccordance with the shape of indenter. The ’pile-up’ phenomenon is observedaround the indentation area. Comparing with the non-indentation area, thedirection of grains in indentation area changes a lot with the number of grainsdecreasing.(2) The grains in indentation area are equiaxed crystal in high rate state andthe grain size in indentation area is larger than that in intact area. There are alarge number of deformation twins which show an obvious directivity.(3) The migration of grain boundaries, grain rotation and twinning processoccurring under large stress result in the growth of grains by reducing thegrain boundary angles with neighboring grains, or by swallowing smallergrains.(4) The twinning process is another deformation mechanism. Twinning canbe achieved by successive partials emission from grain boundary and at sametime the shape of grains changes. The self-multiplication of partial dislocationin the grain forms the deformation twinning on the twinning plane under localstress. In addition, both ’V-shaped’ twinning and ’parallelogram’ twinning matrixare also observed in this experiment.