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Lateral Nonuniform Doping of Semiconductor Structures by Ion Implantation

IP.com Disclosure Number: IPCOM000080990D
Original Publication Date: 1974-Mar-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Brack, K: AUTHOR [+3]

Abstract

Controlled lateral nonuniform doping of a great number of semiconductor devices, e.g., on a wafer, can be effected concurrently with the ion implantation step by varying the beam's angle of incidence, and by using the shadowing effects of the mask window edges.

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Lateral Nonuniform Doping of Semiconductor Structures by Ion Implantation

Controlled lateral nonuniform doping of a great number of semiconductor devices, e.g., on a wafer, can be effected concurrently with the ion implantation step by varying the beam's angle of incidence, and by using the shadowing effects of the mask window edges.

Lateral nonuniform doping profiles of this kind are used to increase the device performance of the semiconductor elements. For example, in unipolar and lateral bipolar transistor structures, a doping gradient from source-to-drain and emitter-to-collector (drift transistor), respectively, is frequently required. The method proposed also permits doping only a partial area, e.g., the gate zone of a field-effect transistor (FET) in the direction of the channel length or the channel width.

A lateral NPN transistor is shown schematically in the figure. Wafer 1 is covered by an oxide mask 2 having a thickness H (approx. 10 000 Angstroms), but any other mask material such as photoresist would be equally suitable. Windows (having a width W) are opened for base implantation, using B+ ions with an energy of < 150 keV for NPN structures or, e.g., P+ ions for PNP transistors. If the ion beam impinges on the surface at an angle of Phi(< 90 degrees), the shadowing of window edge 3 prevents the implantation of the base area between B and C. Only the area between A and B is doped by ion implantation.

If the angle Phi is changed (continuously or in st...