Use of TiN(O)/Ti as an effective intermediate stress buffer and diffusion barrier for Cu/parylene-n interconnects

Copper and parylene-n (Pa-n) are studied for ultralarge scale integration c ircuits because of their low electrical resistivity, resistance to electrom igration and low dielectric constant, chemical inertness, and compatibility with current integrated circuit manufacturing, respectively. Copper diffus ion observed at and above 300 degreesC in Pa-n correlates to an increase in the crystallinity of the alpha phase and subsequent transformation to the more open structure of beta parylene. Titanium nitride (oxygen) [TiN(O)]/ti tanium (Ti) bilayers are successfully implemented as a diffusion barrier. T iN is proven to be a very good diffusion barrier up to 500 degreesC for cop per due to its large negative heat of formation and hence its thermal stabi lity. Incorporation of an intermediate titanium layer reduced the residual stress and thermal mismatch between Pa-n and TiN. Without the Ti layer ther mal cracking of TiN occurred. The presence of the buffer layer had no detri mental effects on the overall resistivity. The effectiveness of the barrier is attributed to stuffing of the grain boundaries with oxygen and nitrogen . This results in the elimination of rapid diffusion paths. This work provi des the foundation for future implementation of Cu/Pa-n for higher temperat ure microelectronics. (C) 2001 American Institute of Physics.