Future trends for interlayer dielectric films and their formation technologies in ULSI multilevel interconnections

Abstract

In the future quarter-micron multilevel interconnections, the interlayer dielectric film properties and their formation techniques will have to meet three requirements: (1) a high surface planarization capability, (2) a low dielectric constant, and (3) a low deposition temperature. In order to achieve these requirements, many technologies have been investigated. Selective deposition of SiO 2 films is the best way to achieve full planarization of the interlayer dielectric film surface. Two selective SiO 2 film deposition techniques have been developed. One is a liquid phase deposition (LPD) technique at room temperature, using a supersaturated hydrofluosilicic acid (H 2SiF 6) aqueous solution. The other is a semiselective SiO 2 film deposition technique at 390 °C, using tetraethylorthosilicate (TEOS, Si(OC 2H 5) 3) and ozone (O 3) as gas sources, with the assistance of tetrafluorocarbon (CF 4) plasma pretreatment for TiW or TiN surfaces of wiring top layers. The dielectric constant of SiO 2 films can be reduced from 3.9–4.3 to 3.7 at 1 MHz, by the LPD technique or a room temperature chemical vapor deposition (RTCVD) technique using the fluorotrialkoxysilane (FTAS) group and pure water as gas sources. Room temperature film formation can be achieved by the following three techniques: (i) LPD, (ii) RTCVD, and (iii) fluoroalkoxysilane vapor treatment (FAST) for spin-on-glass (SOG).