Hydrogenated and Fluorinated Diamondlike Carbon as the Interconnect Dielectric for VLSI Chips

The signal delay along the back end of the line (BEOL) interconnect structure of a VLSI circuit is
controlled by the RC of the structure which, at a certain metallization level, is given by: RC=2rk(4L 2 /P 2 +L 2 /T 2 ) where R is the resistance of the metal line, C the line capacitance, L the line length, P the metal pitch, T the metal line thickness, r metal resistivity and k the dielectric constant of the insulator
between the lines. The continuous shrinking of the dimensions of the electrical devices in the VLSI circuits results in reduced P and T and increased RC delays of the electrical signals. The switching performances of the circuit can be improved by replacing the insulators with materials having lower dielectric constants than the historically used SiO2 (k=4). The reduced capacitance will also reduce the power consumption of the device which is given by: Power=CV 2 f where V and f are the operating voltage and frequency of the circuits. Diamondlike carbon (DLC) has found a variety of applications based on its attractive mechanical, tribological, optical and chemical resistance properties [1,2]. The materials are also dielectrics whose electrical resistivities can reach values of 10 16 W.cm at low fields. The DLC type materials are attractive dielectrics because of their isotropic properties and the ability to deposit them by plasma enhanced CVD (PECVD) techniques. The integration of a new low-k dielectric material in a VLSI device imposes a significant number of requirements that such a material has to satisfy, among which are: low-k, low leakage current, and low dissipation factor, thermal stability at 400 o C, low stresses, minimal Young's modulus and minimal hardness, adhesion and compatibility with other materials, patternability, chemomechanical polishing (CMP) capability [3]. Hydrogenated diamondlike carbon (DLC) films, typically prepared as a wear and corrosion resistant coating, can be modified by the adjustment of the PECVD deposition conditions to obtain materials with lower dielectric constants than SiO2 Incorporation of fluorine in DLC (FDLC) films further reduces their dielectric constant. The properties of low-k DLC and FDLC films and the ability to integrate them in VLSI devices will be discussed next.