Annealing of copper electrodeposits

The properties of electroplated copper film have been investigated as a fun ction of annealing temperatures together with the diffusion barrier perform ance. Electroplated copper films on copper and tungsten seed materials were annealed from 300 to 700 degrees C in N-2 atmosphere for grain growth stud y. The average grain size of the as-deposited copper films was found to be different; larger copper grains (0.6 mu m) were formed on the W seed layer compared to those formed on Cu (0.2 mu m). The copper films also started to recrystallize at 300 degrees C and grain growth occurred from 400 degrees C onward. Regardless of the initial grain size of the electroplated copper films, the final grain size was found to be similar on both seed materials. After 600 and 700 degrees C annealing, the average grain sizes became 1.00 and 1.20 mu m, respectively. The driving force for grain growth is from th e elimination of grain boundaries where the surface energy is being release d to achieve the equilibrium state. The annealed films produced a layered m icrostructure, together with the presence of pinholes and cavities. The ave rage grain size of the electroplated copper increased in proportion to the square root of the annealing time and increasing temperature. The activatio n energies of grain growth were 0.31 eV from 400 to 700 degrees C on the W seed material and 0.62 eV from 400 to 500 degrees C and 0.28 eV from 500 to 700 degrees C on the Cu seed material. With annealing, the tensile stress decreased from 202 to 105-149 MPa while the strain at break increased from 7.6% to 17.7%-20.7%. The resistivity of the electroplated copper films was reduced from 2.25 to 1.87 mu Omega cm after high temperature annealing. X-r ay diffraction results show that only the ionized metal plasma (IMP) TaN su rvived as the diffusion barrier between copper and silicon up to 700 degree s C while chemically vapor deposited TiN, physically vapor deposited TiN an d IMP Ta failed at lower temperature. (C) 1999 American Vacuum Society. [S0 734-2101(99)04604-7].