Ion-Implantation Effects on Spin-on-Glass (Sol-Gel) SiO 2 Films
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ION-IMPLANTATION EFFECTS ON SPIN-ON-GLASS (SOL-GEL) SiO 2 FILMS Y. SHACILAM-DIAMAND', N. MORJYA** and R. KALISH" *214 Phillips Hall, Cornell University, Ithaca, NY 14853 "4 Solid State Institute, Technion - I.I.T., Haifa 32000, Israel
ABSTRACT Silicon and phosphorus ions were implanted into Spin-On-Glass (Sol-Gel) SiO 2 films and were found to modify the material properties. Two SOG types, polysiloxane and silicate, were ion-implanted with doses in the 5 x 1014 - 1.65 x 1016 crmrange and energies of 40keV - 190keV. The implanted SOG on silicon samples were characterized by ellipsometry, infra-red spectroscopy, etching and capacitance measurement of aluminum/SOG/silicon devices. The results indicate that the polysiloxane type SOG shrinks due to the implant and its effective refractive index increases. The ion-implant of the polysiloxane SOG also changed its structure and composition as seen by the variations of the infra-red transmission spectrum, etching characteristics, and dielectric constant. Silicate SOG exhibits less shrinkage due to the implant but its other characteristics show dependence on the dose similar to that of the polysiloxane SOG. INTRODUCTION Spin-On-Glass (SOG), or Sol-Gel, layers have become part of the Very-LargeScale-Integration (VLSI) technology for Integrated-Circuits (IC) production. The final properties of the fully annealed SOG are comparable to those of ChemicalVapour-Deposited (CVD) SiO 2 , which is widely used in VLSI technology [1]. The CVD oxide is commonly used as a part of the dielectric insulation between the first metal level and the substrate or between metal levels on the chip. As the chip dimensions shrink, the vertical topography dimensions become the same size as the lateral dimensions. CVD oxide may fail to reliably cover steep steps and narrow trenches in such topographies. In this case, SOG offers better step-coverage due to the self-planarizing properties of its liquid state. The fluid SOG coats even harsh topographies and results in a more moderate topography which can be used as a base for the subsequent steps (e.g. CVD oxide, sputtered metal). SOG is typically combined with CVD oxide in multi-layer metal-interconnect structures realized in VLSI technology. For example, in a layered CVD oxide/SOG/CVD oxide structure one takes advantage of the planarizing properties of SOG with the qualified integrity of the CVD oxide. Spin-on-glass is often called sol-gel, a term which aptly describes the two states of the material. Initially, it is a silicon compound dissolved in organic solvents. The liquid is spin-cast on the silicon wafer at a typical spin-speed of 3000-7000 RPM for 20-30 seconds. After a thermal stabilization step at relatively low temperatures (900C-120"C) the film is processed at a sequence of increasing temperatures in the 1800C-450 0 C temperature range. At elevated temperatures, the material polymerizes and forms a silicon-oxygen backbone chain with an organic group attached to it. Two types of SOG materials are discussed here [2]: polysiloxane and silicate.
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