Electrical instability of low-dielectric constant diffusion barrier film (a-SiC:H) for copper interconnect

An a-SiC:H deposited by CVD system is the most promising dielectric diffusion barrier to replace silicon nitride in the Cu-interconnect structure due to its low dielectric constant, good Cu barrier ability, and low moisture uptake. In this paper, electrical instabilities of a-SiC:H film under electric field were reported for the first time. At electric field higher than 1.8 MV/cm and independent of the polarity, charges will be built up in the SiC film even at room temperature. A dielectric polarization model was proposed to explain this high field instability. The formation of molecular dipole is attributed to the incorporated nitrogen atoms, which distort the symmetric tetrahedral SiC molecule. The dielectric polarization is further verified by the increase of dielectric constant at high temperature and low frequency. At elevated temperature, film instability can be observed at electric field as low as 0.4 MV/cm. A carrier injection model combined with the polarization was proposed to explain the low-field instability. It is assumed that slight polarization occurs at such a low electric field because of high temperature. The dominant mechanism is electron injection from metal gate into SiC film via the Schottky emission process. It is thus recommended that the incorporation of nitrogen must be minimized and the film stability must be carefully evaluated at real circuit level.