density. One problem in fabricating multi layer interconnects is that, as layers are placed one over another the surface becomes uneven and this may lead to stresses and strains in structure. Before a new layer of metal is placed on the chip, the surface must be planarized to avoid this problem. In the past aluminum was used for the metal layers and tungsten was used to implement vias. Due to increase in resistance and electro migration problems copper is introduced to replace aluminum. Unfortunately, copper diffuses rapidly in silicon and typically a thin copper cladding material such as titanium nitrate is used to surround copper to prevent diffusing into SiO₂ .