Interactions of WF(6) with TiN/Ti barriers during W chemical vapor deposition.

摘要

Delamination of sputter-deposited TiN/Ti bilayers on SiO{dollar}sb2{dollar} is a serious problem during W chemical vapor deposition (CVD) using WF{dollar}sb6{dollar} gas to form vertical interconnects in integrated circuits. In order to obtain insight into the delamination mechanism, the microchemical changes occurring in the bilayers during WF{dollar}sb6{dollar} exposure have been studied in detail using a variety of spectroscopic and microscopic techniques. For the first time, the chemical reactions occurring at the buried surfaces of the bilayer have been studied quantitatively. The primary cause of delamination has been identified, and long-term solutions have been proposed.; The depth-distributions of W and F in sputter-deposited TiN/Ti bilayers on SiO{dollar}sb2{dollar} have been determined as a function of WF{dollar}sb6{dollar} exposure time t{dollar}rmsb{lcub}WFsb6{rcub}{dollar} at 445{dollar}spcirc{dollar}C. Even for short exposures {dollar}rm(tsb{lcub}WFsb6{rcub}<6{dollar} s), significant concentrations of both W ({dollar}approx{dollar}3.5 at%) and F ({dollar}approx{dollar}2 at%) penetrate through the 106-nm-thick TiN film. W piles up at the TiN/Ti interface, while F rapidly saturates the TiN layer and accumulates in the Ti underlayer at concentrations up to {dollar}approx{dollar}10 at% for t{dollar}rmsb{lcub}WFsb6{rcub}=60{dollar} s.; It is demonstrated that nanometer-scale intercolumnar voids (nanopipes) surrounding the TiN grains and spanning the entire film thickness act as fast diffusion paths allowing the gas-phase transport of WF{dollar}sb6{dollar} molecules. WF{dollar}sb6{dollar} dissociates and reacts with the top as well as the buried TiN surfaces provided by the nanopipes, depositing a few monolayers of W. The nanopipes are etched due to the evolution of TiF{dollar}sb4{dollar} as a byproduct. WF{dollar}sb6{dollar} molecules reaching the TiN/Ti interface react with the exposed surface of the Ti underlayer at the bottom of the nanopipes. As a result {dollar}approx{dollar}1 ML excess W is deposited at the interface and large quantities of F enter the Ti layer. F rejected from TiN by surface diffusion along the nanopipes and F{dollar}sb2{dollar} evolution also contribute to the fluorination of the Ti underlayer.; The sequence and mechanism of phase formation, and morphological changes occurring during the reaction of WF{dollar}sb6{dollar} with Ti have been elucidated for the first time. Ti reduction of WF{dollar}sb6{dollar} is a rapid process leading to W deposition at rates greater than that observed when SiH{dollar}sb4{dollar} or H{dollar}sb2{dollar} are used as reductants. At low WF{dollar}sb6{dollar} doses, Fluorine permeates hcp Ti lattice, forming a Ti-F solid solution. When the F concentration exceeds {dollar}approx{dollar}10 at%, which is shown to be the solubility limit of F in Ti, a non-volatile TiF{dollar}sb3{dollar} compound is formed. The large volume change occurring during TiF{dollar}sb3{dollar} formation results in the formation of microcracks in the W film. WF{dollar}sb6{dollar} enters through the microcracks and attacks the underlying Ti both laterally and vertically. The entire Ti film is etched away due to the evolution of gaseous TiF{dollar}sb4,{dollar} leaving behind a poor quality W film on the SiO{dollar}sb2{dollar} substrate.; F buildup in the Ti underlayer of TiN/Ti bilayers is suggested to be the major cause of delamination. High F concentration causes phase formation and alters the chemistry of the Ti/SiO{dollar}sb2{dollar} interface. Large stresses generated due to TiF{dollar}sb3{dollar} formation, and destruction of the Ti glue layer due to TiF{dollar}sb4{dollar} evolution jeopardize the adhesion of the TiN/Ti bilayer at the Ti/SiO{dollar}sb2{dollar} interface. The delamination problem can be alleviated by improving the TiN microstructure and/or by hastening the W nucleation process to minimize the interaction of WF{dollar}sb6{dollar} with