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Method of Fabricating Fully Overlapped, Lightly Doped Drain FET

IP.com Disclosure Number: IPCOM000107681D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 96K

Publishing Venue

IBM

Related People

Subbanna, S: AUTHOR [+2]

Abstract

Disclosed is a new process for fabricating a fully overlapped, lightly doped drain (FOLD) field-effect transistor (FET). This structure (1) has been proposed to reduce series resistance in sub half-micron gate- length FETs, while still maintaining hot-electron reliability.

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Method of Fabricating Fully Overlapped, Lightly Doped Drain FET

       Disclosed is a new process for fabricating a fully
overlapped, lightly doped drain (FOLD) field-effect transistor (FET).
This structure (1) has been proposed to reduce series resistance in
sub half-micron gate- length FETs, while still maintaining
hot-electron reliability.

      In prior art, formation of polysilicon sidewall directly on the
etched gate oxide (2) has been proposed. However, this suffers from
problems such as non-vertical sidewalls and reliability of gate on
etched gate oxide.

      In the present process, after formation of the n- and p-wells,
channel stops, and field oxide isolation (ROX), a thin (5-20 nm) gate
oxide is grown.  This is followed by a single-step, two-layer
polysilicon deposition.  This dual layer consists of 50 nm intrinsic
poly, followed by 250 nm of N++ in-situ doped polysilicon.  Because
of the single-step deposition, there is no interfacial (native) oxide
layer.  A CVD low-temperature oxide cap is then deposited (Fig. A).

      The gates are then lithographically defined.  This is followed
by reactive ion etching, using an etch that etches N++ polysilicon
selectively to i-polysilicon.  Using a chlorine-based chemistry, a
selectivity of 20:1 or better can be obtained.  This etch stops on
the i-polysilicon, leaving about 40 nm of polysilicon.  In this way,
damage to the gate oxide under the drain-overlapped gate is avoided.
In recent prior a...