Browse Prior Art Database

Contacts to Isolation Region

IP.com Disclosure Number: IPCOM000093647D
Original Publication Date: 1967-Nov-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 79K

Publishing Venue

IBM

Related People

Rideout, AJ: AUTHOR

Abstract

The isolation region of a junction-isolated monolithic integrated circuit is usually electrically contacted. Low-resistance contacts to this isolation region are difficult to achieve using the usual technique of making an opening in the silicon dioxide isolation, coating over the isolation region during the base silicon dioxide etching step, and then reopening it during the contact hole etching step. Very often this contact region is heavily stained. The staining results because the silicon dioxide over the isolation region is thinner than that of the silicon dioxide over the remainder of the wafer. The isolation contact thus opens first during the base silicon dioxide etching step. The stain results from the continued exposure of the heavily doped silicon surface to the buffered hydrofluoric acid etch used.

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Contacts to Isolation Region

The isolation region of a junction-isolated monolithic integrated circuit is usually electrically contacted. Low-resistance contacts to this isolation region are difficult to achieve using the usual technique of making an opening in the silicon dioxide isolation, coating over the isolation region during the base silicon dioxide etching step, and then reopening it during the contact hole etching step. Very often this contact region is heavily stained. The staining results because the silicon dioxide over the isolation region is thinner than that of the silicon dioxide over the remainder of the wafer. The isolation contact thus opens first during the base silicon dioxide etching step. The stain results from the continued exposure of the heavily doped silicon surface to the buffered hydrofluoric acid etch used. The stain is composed of either pure silicon or silicon hydrides. Attempts to remove the stain chemically have not been very successful.

Drawings A, B, C, and D show a process which utilizes an opening large enough to overlap the isolation region during the base silicon dioxide etching step and then is reopened prior to the contact metal deposition. This process provides a low-resistance path around the stained region. Drawing A shows silicon dioxide layer 1 covering monolithic device 2 which includes junction- isolation region 3. The silicon dioxide is removed over region 3 and a portion of an adjoining region 4 to produce the dr...