From DLC to DLC-SiO₂ hybrid low-k dielectrics for ulsi interconnects

Alfred Grill

IBM – T.J.Watson Research Center, Yorktown Heights, NY, USA

Abstract

Low dielectric constant (k) insulators, with k significantly lower than that of presently used SiO₂, are needed for reducing the interconnect capacitances of the continuously shrinking ULSI chips. The reduced capacitance will improve the switching performances of future ULSI circuits and reduce their power consumption.

Diamondlike carbon (DLC), which has found a variety of applications based on its attractive mechanical, tribological, and optical properties, is also a dielectric material whose electrical resistivity can reach values of 10¹⁶ W.cm. However, the amorphous carbon materials with diamondlike properties are characterized by dielectric constants similar, or even higher than that of SiO₂ (k=4). It has been found that, by adjusting the PECVD deposition conditions of hydrogenated diamondlike carbon, its dielectric constant can be reduced to values ranging from 3.3 to 2.7. Incorporation of F in the DLC further reduces the dielectric constants to values as low as 2.4. While these are attractive values, the integration of the materials in the ULSI chips imposes a significant number of requirements that are not easily achieved by the new dielectrics. The integration of DLC has been demonstrated for up to two levels in a Cu based damascene structure, however FDLC could not be integrated at the processing temperature of 400 ^oC, typically used in the processing of the interconnect structures.

The integrability and reliability of the low-k carbon based materials have been improved by developing a hybrid composition of DLC and SiO₂. These hybrids, which are deposited by PECVD techniques and comprise Si, C, O and H, are referred to as SiCOH, or carbon doped oxides (CDO) films, and have achieved dielectric constant values lower than 2.8. The dielectric constants of the CDO films can be further lowered by depositing multiphase films, containing at least one thermally unstable phase, and annealing the films to remove the unstable phase from the material. Dual phase films have been prepared by PECVD from mixtures of SiCOH precursors with hydrocarbons. By proper choice of the precursors and deposition conditions, the dielectric constant of the stabilized films reach values significantly lower than previously reported.

The talk will discuss the preparation of the low-k materials, their properties, and the potential of their integration in the interconnect structures of the ULSI chips.

Keywords: low-k dielectrics, DLC, SiCOH, carbon doped oxides

Corresponding author

Alfred Grill

IBM – T.J.Watson Research Center

Yorktown Heights, NY 10598, USA

Tel: (914) 945-1492

Fax: (914) 945-2141

e-mail: grilla@us.ibm.com