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Home > 6.ISSUES > Effect Of Grounded VS. Floating Fill Metal On Parasitic Capacitance

Effect Of Grounded VS. Floating Fill Metal On Parasitic Capacitance

In oxide chemical-mechanical polishing (CMP) processes, variations in dielectric thickness can reduce yield and affect performance. Metal fill patterns are commonly used to reduce layout dependent thickness variation, but they become more important especially at 130 nm and below. Metal-fill patterning can be performed in First Encounter. It fills large open areas on each metal layer with a metal pattern, which is either grounded or left floating, to compensate for pattern-driven variations. Fill metal algorithms add metal to achieve a certain metal density per “window” area, since dielectric thickness variation is proportional to fill pattern density. Put another way, if through fill metal you reduce the range in pattern density by 50%, then the resulting dielectric thickness variation should be reduced by half as well. The goal of metal-fill patterning is to meet the dielectric thickness variation spec for your foundry’s lithography requirements, while minimizing added interconnect capacitance. This paper will examine how fill metal affects parasitics, and whether grounded fill has any advantage over floating fill, if all else is held equal…

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