A new isolation technique is proposed by adding a thin polysilicon layer between pad oxide and nitride layer in the LOCOS process. To optimize the new structure, the thicknesses of the pad oxide, polysilicon and nitride layers are varied. The bird's beak length and silicon edge defects are monitored. It is observed that for an 8000A field oxide thickness the bird's beak could be reduced to a significant amount by the new isolation technique using 1500A Si_3N_4/550A Polysilicon/200A pad oxide combination. Monitoring of silicon defects is done by measuring diode leakage and MOS capacitor breakdown.
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