Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-02-01
2001-06-12
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S637000, C438S638000, C438S639000, C438S648000, C438S673000
Reexamination Certificate
active
06245671
ABSTRACT:
TECHNICAL FIELD
This invention relates to semiconductor processing methods of forming an electrically conductive contact plug relative to a wafer.
BACKGROUND OF THE INVENTION
This invention arose out of problems associated with tungsten plug formation in contacts formed through silicon dioxide insulating layers. The problem is best understood with reference to the accompanying
FIGS. 1 and 2
. There illustrated is a semiconductor wafer fragment
10
comprised of a bulk substrate
12
and an overlying silicon dioxide layer
14
, such as borophosphosilicate glass (BPSG). Bulk substrate
12
includes a dopant diffusion/active region
16
to which electrical connection is to be made. A contact opening
18
is provided through BPSG layer
14
to active area
16
.
A thin layer
20
of titanium is deposited atop the wafer to within contact opening
18
. Titanium layer
20
is provided to function as a silicide formation layer at the base of contact
18
for reducing resistance. An undesired oxide layer (not shown) also typically forms atop diffusion region
16
. The deposited elemental titanium also functions to break-up this undesired oxide and thereafter form a titanium silicide with the silicon of substrate
12
to reduce contact resistance between active area
16
and subsequently deposited plug filling tungsten. Additionally, titanium layer
20
functions as an adhesion
ucleation layer for the subsequently deposited tungsten. Tungsten does not readily deposit over silicon dioxide and exposed silicon substrate, and the intervening titanium layer
20
facilitates deposition and adhesion of tungsten thereto.
Titanium layer
20
is typically deposited by sputter deposition, and undesirably results in formation of contact projecting cusps
22
. This results in a back or re-entrant angle
24
being formed relative to contact opening
18
. A layer
26
of tungsten is subsequently deposited with the intent being to completely fill the remaining volume of contact opening
18
. Unfortunately, an undesired keyhole
28
typically forms, leaving a void within contact
18
.
Referring to
FIG. 2
, layers
26
and
20
are subsequently etched back by dry etch of chemical-mechanical polishing to form a contact-filling plug
30
. Undesirably, this typically opens-up the upper end of keyhole
28
. In processing, this undesirably creates a thin void which is difficult to clean and rinse during processing. Also in the final construction, the outer surface area of plug
30
is reduced due to the void created by keyhole
28
. This counters the desired goal of maximizing electrical contact with plug
30
with a subsequent layer for ultimately making electrical connection with active area
16
. Further, the etch back typically conducted to produce plug
30
undesirably over-etches titanium layer
20
, forming edge “fangs”
32
.
One prior art solution for overcoming this problem is described with reference to FIG.
3
. Like numerals are utilized where appropriate, such that only differences are described and numbered with a suffix “a”. Here, BPSG layer
14
is angle-etched from its outer surface downwardly to active area
16
. Subsequently deposited titanium layer
20
therefore does not form cusps, which will result in elimination of a keyhole by the subsequently deposited tungsten layer. This method is, however, highly undesirable as contact opening
18
a
has the added drawback of being narrower at its base than the illustrated
FIGS. 1 and 2
embodiment, and also significantly wider at its outermost portion. This undesirably consumes precious wafer area and thereby counters the a continuing semiconductor processing goals of making device components smaller and smaller.
It would be desirable to overcome these and other problems associated with formation of electrically conductive contact plugs. Although the invention principally arose out of concern specific to tungsten plug formation, the artisan will appreciate that the invention has applicability with other materials and constructions. The invention is intended to only be limited by the accompanying claims appropriately interpreted in accordance with the Doctrine of Equivalents.
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Fazan Pierre C.
Jeng Nanseng
Mathews Viju K.
Micro)n Technology, Inc.
Nguyen Ha Tran
Niebling John F.
Wells, St. John, Roberts Gregory & Matkin P.S.
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