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Ultra Short Channel MOSFET Device

IP.com Disclosure Number: IPCOM000078783D
Original Publication Date: 1973-Mar-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Gaensslen, F: AUTHOR

Abstract

As the channel length of a conventional metal-oxide-semiconductor field-effect transistor device is shortened, the depletion layers surrounding source and drain diffusions get closer together. At some point, they merge making it increasingly difficult to turn off the device as is often required for digital applications. This problem may be cured by enhancing the substrate doping in a thin layer next to the oxide/silicon interface. Fig. 1 shows the condition of the depletion layers surrounding source and drain diffusions with voltages, as shown, applied to the diffusions and gate. The enhanced doping of surface region 1 of substrate 2 reduces the depletion width within this layer, as shown in Fig. 1. The boundaries of the depletion layers are shown for an assumed set of doping and voltage levels in a given geometry.

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Ultra Short Channel MOSFET Device

As the channel length of a conventional metal-oxide-semiconductor field-effect transistor device is shortened, the depletion layers surrounding source and drain diffusions get closer together. At some point, they merge making it increasingly difficult to turn off the device as is often required for digital applications. This problem may be cured by enhancing the substrate doping in a thin layer next to the oxide/silicon interface.

Fig. 1 shows the condition of the depletion layers surrounding source and drain diffusions with voltages, as shown, applied to the diffusions and gate. The enhanced doping of surface region 1 of substrate 2 reduces the depletion width within this layer, as shown in Fig. 1. The boundaries of the depletion layers are shown for an assumed set of doping and voltage levels in a given geometry.

Using the approach of Fig. 1, the problem of merging depletion layers has been shifted away from the surface to the lower doped, inner part of substrate 2. It is entirely possible under such circumstances that a subsurface channel can be established beyond control of the gate electrode. The separation between the two depletion layers as shown in Fig. 1 is designated D1. The separation between depletion layers can be greatly enhanced as shown in Fig. 2. A p+ substrate (N(A) = 5 x 10/17/cm/-3/) is used for epitaxially growing a p- layer (N(A) = 5 x 10/15/ cm/-3/) of appropriate thickness thereon. The p+/p- junction concentrates the depletion layers around their respective diffusions, and thereby increases the achievable resolution within the semi...