Browse Prior Art Database

Making Charge Coupled Devices

IP.com Disclosure Number: IPCOM000089080D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 120K

Publishing Venue

IBM

Related People

Garbarino, PL: AUTHOR [+2]

Abstract

A polysilicon self-aligned gate structure is obtained without polysilicon etching. This eliminates the bias and tolerance limitations of wet etching, and the FET damage of reactive ion dry etching.

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Making Charge Coupled Devices

A polysilicon self-aligned gate structure is obtained without polysilicon etching. This eliminates the bias and tolerance limitations of wet etching, and the FET damage of reactive ion dry etching.

A two or four phase CCD is fabricated without an ion implant step. The two phase device is of the stepped oxide variety, and results naturally from the complete, localized oxidation of the polysilicon layer.

A semi-recessed silicon dioxide isolation process is used as follows: Layers of thermal oxide 10, silicon nitride 12 and pyrolytic silicon dioxide 14 are grown or deposited. The first level mask opens the isolation pattern. The layer 14 is etched, and the resist is removed. The layer 14 now acts as a mask for the silicon nitride 12 etching, which, in turn, masks the layer 10 etching to produce the Fig. 1 structure. The silicon 16 is now oxidized growing both into and out of the surface to produce layer 18, as shown in Fig. 2.

The gate structure is a silicon dioxide, but a process advantage may exist if a silicon dioxide-silicon nitride gate is used, as will be considered below. The same silicon dioxide used in the recessed silicon dioxide isolation process could be used for the gate oxide, or the silicon dioxide could be stripped and a new layer of thermal silicon dioxide grown, as shown in the Fig. 3 embodiment. Onto the gate regions is deposited polysilicon layer 20, which is, in turn, oxidized very slightly to provide a silicon dioxide adhesion layer 22 for a silicon nitride layer 24 and a pyrosilicon dioxide layer 26. These last three films are etched, as described above, to produce the Fig. 3 structure. The polysilicon layer 20 is now oxidized completely through the silicon nitride mask, resulting in the Fig. 4 structure. The gate can act as an oxidation stop for this process if a silicon dioxide-silicon...