Browse Prior Art Database

Application of Reactive Ion Etch in Fabrication of High Performance Charge Coupled Shift Registers

IP.com Disclosure Number: IPCOM000088420D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Garbarino, PL: AUTHOR [+3]

Abstract

Charge-coupled devices (CCD) depend on closely spaced clock lines for acceptable operation. The larger the gap between adjacent clock lines the lower the maximum operating frequency will be. Equivalently, the larger the gap, the lower will be the charge transfer efficiency at a given frequency.

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Application of Reactive Ion Etch in Fabrication of High Performance Charge Coupled Shift Registers

Charge-coupled devices (CCD) depend on closely spaced clock lines for acceptable operation. The larger the gap between adjacent clock lines the lower the maximum operating frequency will be. Equivalently, the larger the gap, the lower will be the charge transfer efficiency at a given frequency.

Attainment of maximum charge transfer efficiency at high frequencies is the objective of CCD design. A method has been described of making the clock line gap controllably narrow, thereby attaining the objective [*]. The polysilicon process theredescribed has difficulties in producing delineated polysilicon clock lines. This is because photoresist will float off the polysilicon surface during a conventional wet chemical etch. Employment of an oxide etch mask to etch the polysilicon leads to oxide overhangs of dimension equal to the polysilicon etch bias. These overhangs shadow the deposition of aluminum, yielding uncontrollably wide gaps between clock lines.

This problem is overcome by using reactive ion etching of the polysilicon layer rather than wet etching. In this case, the photoresist can be employed directly on the polysilicon surface with impurity. There is no shadowing effect of the photoresist because it is stripped before metal evaporation. After the photoresist strip, the polysilicon is oxidized as in the reference and the gap between aluminum and polysilicon clock...