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Spin-On Dielectrics: Good News and Bad News!

Published online by Cambridge University Press:  21 February 2011

G. Smolinsky ,
N. Lifshitz  and
V. Ryan
G. Smolinsky
Affiliation:
AT&T Bell Laboratories, Murray Hill, NJ 07974–2070
N. Lifshitz
Affiliation:
AT&T Bell Laboratories, Murray Hill, NJ 07974–2070
V. Ryan
Affiliation:
AT&T Bell Laboratories, Murray Hill, NJ 07974–2070
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Abstract

Five classes of spin-on dielectrics are discussed: polysilicates, polysiloxanes, polysilsesquioxanes, polyhydrocarbons, and polyimides. The emphasis is on the first three materials because very few polyhydrocarbon spin-on materials are available for study while spin-on polyimides sorb significant amounts of water. The polymer chemistry of the silicates, siloxanes, and silsesquioxanes is linkage through Si-O-Si-O bonds. Polyhydrocarbons are primarily linked through C-C bonds. As the name implies, polyimides are linked through (usually aromatic) imide groups. Because of their polar nature, polyimides, polysilicates, and polysiloxanes have dielectric constants >3, while the large hydrocarbon content of the remaining materials results in a dielectric constant of <3. Films of polysilicates are relatively brittle and thus are limited to a thickness <1 μm. On the other hand, films of polysilsesquioxanes, polyimides, and polyhydrocarbons can be readily deposited to a thickness >1 μm. Polysilicates have high temperature (>900°C) stability and do not react with O2; most polyhydrocarbons decompose above ˜350°C and oxidize readily; some polyimides are stable to 500°C; polysiloxanes and polysilsesquioxanes readily survive 425°C in N2. (Films of the latter two materials are converted to silicates upon heating at high temperatures in O2 or steam.) The infrared spectrum of a 425°C-cured silicate film shows the presense of Si-OH bonds and water, but after a 900°C anneal, the spectrum is almost identical to that of thermal oxide. The spectra of films of polysiloxanes or polysilsesquioxanes do not exhibit Si-OH absorption. Water retention in films is deleterious to the electrical and mechanical (swelling) properties of the dielectric and to making good aluminum-to-aluminum electrical contact through submicron vias. The water leads to a mobile charge (H+) phenomenon that is readily detected by a Triangular Voltage Sweep technique. Except for polysilicates, solutions of the other spin-on materials have reasonably long (weeks-to-months) shelf-lives. Polysilicate solutions are sols and tend to gel; the time to gelling is a function of solids content and solvent. Even though they exhibit shortcomings, polysiloxanes appear to be best suited as interlevel dielectrics in multilevel metalization schemes.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 154: Symposium K – Electronic Packaging Materials Science IV , 1989 , 173
Copyright
Copyright © Materials Research Society 1989

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