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This article describes a method for fabricating metal-semiconductor field effect transistors (MESFETs) employing a self-aligning technique to reduce the separation between the source and drain electrodes.
English (United States)
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Fabrication Method For High Performance MESFET
This article describes a method for fabricating metal-semiconductor field
effect transistors (MESFETs) employing a self-aligning technique to reduce the
separation between the source and drain electrodes.
Figs. 1A through 1D illustrate the self-aligning MESFET process which uses
the technique of undercut resist lift-off in a new manner, wherein a nitride
oxidation mask is defined under the lift-off resist. For the purposes of explanation
a silicon MESFET is illustrated because the process is most obviously workable
with the silicon technology, but the process steps can be adapted to GaAs as
As shown in Fig. 1A, in the first process step a conventional semiROX
isolation 14 is formed with a P+ channel stopper 15. Part of the oxide pad 10
and nitride layer 12 from the ROX formation 14 may be retained with the next
mask, or new layers of oxide and nitride may be deposited. The former is
assumed for the sake of illustration. Next, an undercut or "lift-off" resist pattern
11 is defined for the metal Schottky gates and lines, and a shallow N+ source
and drain ion implant is performed. The undercut resist wings 15 provide a
spacing 13 between the source and drain edges and the boundaries of the future
Next, as shown in Fig. 1B, a conductive layer 16 (e.g., WSi(2)) is deposited
to provide electrical contact to the shallow source any drain regions. Returning
to Fig. 1A, however, it is attractive to use the undercut resist as a nitride-defining
layer, implant mask, and silicide lift-off material. After lifting off the silicide, the
structure is thermally oxidized to provide insulating layers 18. Then the nitride
12 and oxide 10 pads are dissolved. This leaves the structure shown in Fig. 1C.
Note that now the spacings 13 are filled by oxide regions 18. The third masking
pattern (not shown) is used to open contact holes 20 in the insulation oxi...