Diamondlike Carbon Materials as Low-k Dielectrics

Hydrogenated diamondlike carbon (DLC) and fluorinated DLC (FDLC) films have been investigated as potential candidates for low-k materials for the back end of the line (BEOL) dielectric in ULSI circuits. The films have been characterized as deposited and after annealing in He for 4 hours at 400 C. It was found that, by changing the deoposition conditions, the dielectric constant (k) of the DLC film can be changed from >3.3 to 2.7. The stresses in the films have been found to decrease with decreasing dielectric constant, from 700 MPa to about 250 MPa. However, the thermal stability of the films was found to be correlated to the values of the dielectric constant, decreasing with decreasing k. While DLC films having dielectric constants >3.3 appear to be stable at 400 C, a film having a dielectric constant of 2.7 lost more than half of its thickness upon exposure at the same temperature for 4 hours in He. FDLC films characterized by a dielectric constant of about 2.8 were found to have similar thermal stability as DLC films with k>3.3. The thermally stable FDLC films have internal stresses <200 MPa and are promising cadidates as a BEOL dielectric.