Isolation enhancement in integrated circuits using dummy metal fill

Metal fill patterning in modern IC processes is often viewed as parasitics to be minimized. Here, we use metal fills to improve isolation. The improved isolation comes at the cost of increased capacitive loading. This isolation-loading tradeoff is analyzed for various grounding strategies. It is found to be best to ground first inner metal-fill. The effect of finite ground impedance is analyzed. An assumed worst-case ground impedance path of 50Omega is shown to give sufficient grounding up to 10 GHz.