Dual-layer low-k dielectrics, FLARE at AlliedSignal conference
08/01/1997
Dual-layer low-k dielectrics, FLARE at AlliedSignal conference
Challenges in integrating low-k dielectric spin-on polymers (SOPs) into IC production were explored at Planar `97, in Santa Clara, CA, a dielectrics conference sponsored by AlliedSignal Inc.
The first use of low-k films is in dual dielectric layered structures (what TI calls the "embedded" process). Since there are two layers (one SiO2 or SiOF glass, and one low-k polymer), an interface exists between the two. While traditional spin-on glass (SOG)/ SiO2 processes also have an interface, the new low-k SOP processes have different materials properties that are decidedly nonoptimal in integration.
Chuanbin Pan, of Intel Corp., presented data on the thermal stability of fluorinated polyarylene ether films (AlliedSignal`s FLARE family). He showed that new FLARE-2 films without fluorine lose only 1 wt % at 450? C over 2 hrs, compared to over 4 wt % loss for the FLARE-1 materials with fluorine. He also determined that typical spin-on adhesion promoters, such as SiOxCnH2n+1Ny (organosilane), are very thermally unstable. This instability may explain improvements in leakage current observed after bake steps.
Jeff Wetzel, of Motorola`s Materials Research & Strategic Technologies group, presented data showing that the leakage current through the interface between the two layers of an SiO2/polyimide sandwich was three orders of magnitude higher than through the bulk for as-deposited test structures. Baking for 25 hrs at 150?C lowered both the interfacial and the bulk leakage, due to water outgassing. However, the interfacial leakage was more significantly reduced by the bake, ending at only one to two orders of magnitude over the bulk. Adhesion promotion coatings, stabilized and/or partially driven off by the bake, may participate in the as-deposited interface leakage path. Other combinations of materials and adhesion promoters were not investigated, so it is too early to determine if this mechanism influences other low-k dielectric sandwiches.
- E.K.