Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having schottky gate
Reexamination Certificate
2003-01-15
2004-08-31
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having schottky gate
C438S285000, C438S590000, C438S199000, C438S153000, C438S752000, C257S019000, C257S192000, C257S194000, C257S369000, C257S351000, C257S616000, C257S020000
Reexamination Certificate
active
06784035
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to devices for regulating the flow of electric current, and has specific application to the fabrication of these devices in the context of an integrated circuit (“IC”). More particularly, it relates to a transistor for regulating the flow of electric current having a Schottky-barrier source and/or drain.
One type of field effect transistor (“FET”) known in the art, a metal oxide semiconductor field effect transistor (“MOSFET”), is shown in FIG.
1
. As shown, the MOSFET device
100
, typically includes a silicon substrate
110
, an impurity doped source
120
, and an impurity doped drain
130
, separated by a channel region
140
. Atop the channel region
140
is a gate insulating layer
150
, which typically consists of silicon dioxide. A gate electrode
160
, made from electrically conductive material, is located on top of the insulating layer
150
. An insulating layer
170
typically surrounds the gate electrode
160
. A field oxide
180
electrically isolates devices
100
from one another. When an appropriate voltage V
g
is applied to the gate electrode
160
, current flows between the source
120
and drain
130
through the channel region
140
. This current is referred to as the drive current, or I
d
.
One consideration in the design of current regulating devices is the charge carrier mobility or ease with which charge carriers (i.e., electrons or holes) travel through the substrate lattice in the channel region
140
. From conventional MOSFET theory, drive current scales linearly with carrier mobility. Channel regions
140
that have higher charge carrier mobilities allow charge carriers to travel in less time between the source
120
and the drain
130
, and also to dissipate less power in the carrier transport process. This directly results in devices operating at higher speeds and consuming less power. One known technique for increasing the charge carrier mobility of the channel region
140
is to employ a strained substrate. For example, the mobilities of electrons and holes in strained silicon can be enhanced by factors of approximately two and ten respectively, compared to unstrained silicon. (M. V. Fischetti, S. E. Laux, Journal of Applied Physics, vol. 80 no. 4, 15 Aug. 1996, pp. 2234-52.) As a result, MOSFET devices with strained silicon channel regions
140
are expected to demonstrate power and speed performance characteristics superior to conventional, unstrained silicon devices.
Another known substrate used to fabricate MOSFET devices is a silicon-on-insulator (“SOI”) substrate. This semiconductor substrate includes a buried oxide layer to reduce source-to-drain leakage currents and parasitic capacitances. The prior art includes fabrication of MOSFET devices on a semiconductor substrate having a strained SOI layer. (B. Metzger, “Silicon Takes the Strain for RF Applications,” Compound Semiconductor, vol. 7, no. 7, August 2001; T. Mizuno, “Design for Scaled Thin Film Strained-SOI CMOS Devices with Higher Carrier Mobility,” IEDM Proceedings, December 2002, p. 31.)
Experimental results, however, for MOSFETs having impurity doped sources and drains and strained silicon channels, show that the devices do not fully benefit from the improvement in carrier mobility. For example, in one study, a 70% improvement in electron mobility led to only a 35% improvement in drive current. (K. Rim, S. Koester, M. Hargrove, J. Chu, P. M. Mooney, J. Ott, T. Kanarsky, P. Ronsheim, M. Ieong, A. Grill, H.-S. P. Wong, Proceedings of the 2001 IEEE VLSI Symposium, Kyoto, Japan (2001).) Because drive current scales linearly with mobility, the net improvement of 35% in drive current implies that the effective mobility for electrons only improved 35% for this example.
There is a need in the art for a FET having a strained substrate, demonstrating an improvement in effective mobility, and therefore improvement in drive current closer to that of the improvement in carrier mobility.
BRIEF SUMMARY OF THE INVENTION
The present invention, in one embodiment, is a FET having a Schottky-barrier source and/or drain and a strained semiconductor substrate. In this embodiment, the device includes a strained semiconductor substrate. A source electrode and a drain electrode are in contact with the strained substrate, and at least one of the electrodes forms a Schottky or Schottky-like contact with the substrate. The source and drain electrodes are separated by a channel. An insulating layer is disposed on the strained substrate above the channel. A gate electrode is disposed on the insulating layer.
The present invention, in another embodiment, is a method of fabricating a Schottky-barrier FET on a strained semiconductor substrate. In this embodiment, the method includes providing a strained semiconductor substrate. It further includes providing an electrically insulating layer in contact with the strained substrate. The method further includes providing a gate electrode on the insulating layer such that the substrate on one or more areas proximal to the gate electrode is exposed. The method further includes depositing a thin film of metal and reacting the metal with the exposed strained substrate, such that Schottky or Schottky-like source and drain electrodes are formed on the substrate.
While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.
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Larson John M.
Snyder John P.
Dorsey & Whitney LLP
Smith Matthew
Spinnaker Semiconductor, Inc.
Yevsikov Victor V
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