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Browse Prior Art Database

Charge Coupled Devices Using Single Level Masking

IP.com Disclosure Number: IPCOM000089391D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Chaudhari, P: AUTHOR

Abstract

A method for fabricating charge-coupled devices (CCDs) using single level masking (no critical alignment) is proposed. Shaped propagating patterns and therefor asymmetric charge transfer are used. Transfer pads are isolated through the use of oxidation, implantation by chemical means. Illustratively, the triangular pads shown above are used.

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Charge Coupled Devices Using Single Level Masking

A method for fabricating charge-coupled devices (CCDs) using single level masking (no critical alignment) is proposed. Shaped propagating patterns and therefor asymmetric charge transfer are used. Transfer pads are isolated through the use of oxidation, implantation by chemical means. Illustratively, the triangular pads shown above are used.

The pads are deposited in one step along with current-carrying conductors C. The pads are subsequently isolated from each other by heating or by chemical means at the encircled regions. The geometry helps to provide insulation quicker than elsewhere.

Once the pads are electrically isolated, a two-phase drive circuit and the asymmetry of the propagating pattern are used to move charge along a given direction. A triangular pad is used here for illustrative reasons only. It may be desirable to shape the pad so that the electrostatic field optimizes asymmetry propagation.

A typical fabrication sequence is as follows: A Si wafer with desired doping level is oxidized to produce a thick oxide layer. Photoresist is placed on the oxide and exposed to produce channels. After removal of photoresist from the channel area, the thickness of the oxide in the channel is reduced to the usual CCD thickness. Alternatively, the oxide can be completely removed and then regrown over the entire wafer.

Once the channels are fabricated, a single mask is used to place the entire propagating pattern wit...