Effect of bulk trap density on HfO/sub 2/ reliability and yield

The trap density in an ALD SiO/sub 2//HfO/sub 2/ stack is measured with charge pumping. A critical trap density at breakdown is found and a percolation model is proposed to explain HfO/sub 2/ breakdown. On this particular stack, a direct link between the bulk trap density and the HfO/sub 2/ yield and reliability is demonstrated. A low initial HfO/sub 2/ bulk trap density is essential in order to guarantee the reliability of these stacks.