Diffusion Barriers For Fluorinated Low-k Dielectrics
- PDF / 335,100 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 1 Downloads / 202 Views
ABSTRACT The fluorinated low-k dielectrics SiO:F and Teflon AF were investigated for process integration with aluminum and copper interconnects. To minimize fluorine diffusion, several potential barrier materials were deposited onto the fluorinated dielectrics and characterized after heat treatment at temperatures up to 450 0 C. The barrier layers studied include conventional materials such as Ta, TaN, and TiN, in addition to several novel materials. Barrier layer materials were deposited using evaporation, and sputtering. The materials were characterized using nuclear reaction analysis (NRA) to determine the fluorine concentration profile. A reaction zone was noted at the dielectric-barrier interface on several samples, corresponding to the formation of a fluoride complex. In some instances, this fluoride layer was self-limiting and prevented further fluorine diffusion through the remainder of the barrier layer. INTRODUCTION In previous generations of IC technology, the circuit speed limitation has been the switching speed of the transistor, or intrinsic gate delay. As feature sizes shrink, the intrinsic gate delay improves. However, as the transistor gate length shrinks to less than 0.25 gm, circuit performance becomes limited by the interconnect RC delay, due to increased wiring capacitance. To improve interconnect performance, circuit design techniques can be used such as limiting the wire length and adding repeaters along long interconnect nodes. While these modifications reduce the interconnect delay problem, additional scaling requires new materials to reduce the interconnect resistance and capacitance. Copper interconnections are a promising substitute for aluminum due to coppers lower electrical resistivity, resistance to void formation and electromigration. Among the several interlayer dielectric candidates, there is interest in low dielectric constant fluorinated polymers for this application. To make copper and fluorinated materials suitable for incorporation into ULSI integrated circuits, a suitable interlayer barrier layer (ILBL) to minimize copper and fluorine diffusion must be identified. The ILBL should also promote adhesion between the Cu interconnect and dielectric, and have either a low-k or low resistivity. This last requirement ensures that the composite dielectic or resistivity remains low. In this paper, we present our studies of the interaction of various ILBL materials on the fluorinated dielectrics SiO:F, and Teflon AF. SiO:F was chosen because it was a readily available source of fluorine for our studies. Teflon AF was chosen because its low dielectric constant (k=l.9) will have the greatest impact on improving interconnect speed. The candidate ILBL materials include the ceramics TiN and TaN, and the metals Ag, Ta, Mg, Co, Cr, and Ni. These latter three metals were chosen based on encouraging results using perfluorocyclobutane (PFCB) as the fluorinated dielectric [1].
197
Mat. Res. Soc. Symp. Proc. Vol. 565 c 1999 Materials Research Society
The SiO:F films were deposited in an Applie
Data Loading...
