A Selective SiO₂ Film-Formation Technology Using Liquid-Phase Deposition for Fully Planarized Multilevel Interconnections

A selective SiO₂ film-formation technology using liquid-phase deposition (LPD) around room temperature for fully planarized multilevel interconnections is developed. The LPD technique utilizes supersaturated hydrofluosilicic acid (H₂SiF₆) aqueous solution as a source liquid. The LPD-SiO₂ films can be selectively formed on chemical vapor deposition (CVD) SiO₂ underlayers in the trenches between photoresist patterns or tungsten wiring with photoresist as mask. For polysilicon patterns with photoresist masks, the LPD-SiO₂ films creep along the polysilicon and photoresist sidewalls. The selective deposition mechanism can be explained as siloxane oligomers, which are formed in the supersaturated H₂SiF₆ aqueous solution, have different chemical reactivity between the photoresist and substrate surface. Global planarization of trenches between tungsten wiring is achieved using the selective LPD-SiO₂ deposition technique. A fully planarized double-level tungsten interconnection is realized using both selective LPD-SiO₂ film deposition and selective tungsten CVD via filling. Low contact resistance of ca. 0.3Ω/unit is achieved for via holes 0.8 μm in diam.