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3D MERGED MOSFET-BIPOLAR DEVICES

IP.com Disclosure Number: IPCOM000006644D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2002-Jan-18
Document File: 5 page(s) / 193K

Publishing Venue

Motorola

Related People

Carlos Mazure: AUTHOR [+4]

Abstract

A merged MOSFET-Bipolar structure with 3D archi- tecture is proposed. The proposed concept is compati- ble with 16Mb SFL4M and 0.35pm design rules, and it has the potential of further scalability. It could also f&ill on-pitch requirements, which is not possible with the present solutions /l/ due to the area required. In con- trast to the present known solutions /I/ our invention reduces the area required by overlapping the bipolar device with the preformed MOSFET and/or allows the full bipolar formation and modular integration after the MOSFET formation.

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MOTOROLA INC. Technical Developments Volume 17 December 1992

3D MERGED MOSFET-BIPOLAR DEVICES

by Carlos Mazure, Marius Orlowski, Jon Fitch &Jim Hayden

PURPOSE:

  A merged MOSFET-Bipolar structure with 3D archi- tecture is proposed. The proposed concept is compati- ble with 16Mb SFL4M and 0.35pm design rules, and it has the potential of further scalability. It could also f&ill on-pitch requirements, which is not possible with the present solutions /l/ due to the area required. In con- trast to the present known solutions /I/ our invention reduces the area required by overlapping the bipolar device with the preformed MOSFET and/or allows the full bipolar formation and modular integration after the MOSFET formation.

PROPOSAL:

  The idea is to grow the base and the collector of the bipolar device. from the MOSFET's drain area and a diffusion region of opposite doping to the drain area. The drain area is simultaneously the base contact of the bipolar device and the diffusion of opposite doping would correspond to the collector or emitter contact. The base contact could be accessed through the MOSFET or directly through a contact to the drain diffusion. Figure 1 shows a drawing of the fmished merged npn Bipolar- pMOSFET structure with a raised base/collector. The base/collector growth is achieved with selective Si epitaxial growth (SEG). Note that the emitter and base diision contacts are in weUs of opposite doping. It is clear that the idea is applicable to nMOSFET or pMOSFET devices. The doping of the base/collector can be done conventionally with base and collector implants or if available with in-situ doped epitaxy. Fig- ure 2 shows the raised base/emitter. The collector is formed in the substrate. The emitter and base diffusion contacts are formed in the same well region.

PROCESS FLOW:

  The case of a pMOSFET device with an overlapped npn bipolar transistor is presented as an example, but it is clear that a similar procedure holds for the nMOSFET- pnp case. For special applications, it may be desired to

integrate a pMOSFET with a pnp device utilizing the MOSFET's source or drain as the emitter and a well diffusion contact as the base contact. These cases are not shown, but the fabrication procedure requires only very obvious modifications to the presented examples.

  We assume that the MOSFET is already formed. The work by J.D. Cressler /2/ shows that it is possible to form bipolar devices by selectively overgrowing the base electrode. To our understanding, the following steps do not affect the conventional MOSFET formation. We discuss the case of a p-channel MOSFET The basic approach is to deposit a CVD glass followed by a patterning step which defmes the bipolar area. A SEG step follows. Subsequently, the base and collector are implanted. Finally the collector contact is formed.

  The Si epitaxial growth is constrained to the vertical dimension by the predefined (e.g. CVD oxide) pattern which limits the lateral overgrowth component. Th...