Failure Mechanism of Metal-Polysilicon-Doped Silicon Butting Contacts

The metal-polysilicon-doped silicon butting contact is presently widely used in MOS silicon gate integrated circuits because it occupies minimum area on the chip and does not require additional photolithography. A possible failure mechanism of this contact with self-aligned, ion-implanted sources and drains has been observed. Recent data obtained on processes used to fabricate two-phase, two-level polysilicon CCDs are presented. Results show that oxide etching under the edges of the polysilicon gate during contact window definition can lead to excessive leakage due to metal-to-substrate shorts at the metal-polysilicon-doped silicon butting contact.