Process optimization and characterization of deep metaljunction contact
In this paper, we elaborate a process optimization of deep metal contact in 0.25 ?m embedded DRAM technology and investigate its electrical characteristic. The contact size is 0.32 ?m and its height is varied between 2.1 and 3.8 ?m which give aspect ratio from 6.7 to 11.9. It appears that both Ti thickness and aspect ratio play important role on contact resistance. Especially, P+ contact resistance is more sensitive to these parameters. P+ contact resistance in contact array is increased from 1 to 4 K? per contact when Ti thickness decreases from 900 to 500 , while N+ contact resistance is just increased from 300 to 400 ?. TEM image reveals that the degree of Ti silicidation depends on the Ti thickness. The boundary between silicon and TiSi2 is non-uniform with Ti thickness of 500 , however, it becomes uniform and flat with Ti thickness of 900 . To characterize the behavior of current flow in various contacts, both contact array and Kelvin resistor patterns are used. It appears that Schottky barrier plays major role at low voltage region, while the spreading resistance dominates at high voltage region and thus contact resistance approaches to 220 ? at high voltage region regardless of process condition. The Schottky barrier evaluated by thermionic emission model increases with decreasing Ti thickness and increasing aspect ratio. It appears that a relationship between Schottky barrier and process parameters is given by Schottky barrier energy=(Ti thickness)?0.26(aspect ratio) 0.53.
aspect ratio ti thickness contact resistance schottky barrier thermionic emission model