Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2001-09-17
2003-10-28
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S629000, C438S653000, C438S656000, C438S643000, C438S648000, C257S758000
Reexamination Certificate
active
06638852
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to metalization, and more particularly to a structure and method for preventing a phenomena called “tungsten volcano”.
BACKGROUND OF THE INVENTION
Metalization is an integrated circuit structure that connects individual devices by metal wires to form circuits. Pressure to decrease die area affects all circuits and circuit-related processes, including metalization. Specifically, in current chips, metal wires now carry electrical currents in the milliampere range, thereby resulting in extremely high current density. Therefore, defects in these metal wires can significantly impact the performance of the individual devices, the resulting circuits, and the chip itself. Thus, the goal of any metalization or associated process is to minimize both the number and size of such defects.
One of the most difficult problems in metalization is ensuring appropriate metal continuity at contact windows and vias.
FIG. 1
illustrates a cross section
100
of a semiconductor device including two contact windows
101
. To form the plugs within windows
101
, three layers are typically provided: a titanium layer
102
, a titanium-nitride (TiN) layer
103
, and a tungsten layer
104
. Titanium layer
102
acts as a glue layer between the underlying structures and TiN layer
103
. As known to those skilled in the art, titanium-nitride is used as a nucleation layer to facilitate formation of tungsten layer
104
. Tungsten, a refractory metal, provides a plug with low resistance to underlying layers and to subsequent metal layers, typically including aluminum (not shown). Tungsten layer
104
is typically formed through silane reduction of WF
6
.
Unfortunately, titanium reacts readily with WF
6
. Those skilled in the art have surmised that defects in TiN layer
103
allow WF
6
to penetrate TiN layer
103
and to react with titanium layer
102
to form a defect known as “tungsten volcano”. TiN layer
103
, which is generally formed by sputter-deposition, has a high stress point at the edge of a “step”
105
(i.e. the edge of a contact window). This stress may affect other areas of TiN layer
103
, thereby resulting in numerous pin holes and cracks throughout TiN layer
103
. TiN layer
103
tends to be porous at such steps, cracks, and pin holes and thus more vulnerable to WF
6
penetration at these locations.
FIG. 2A
illustrates the resulting peel back of TiN layer
103
after the fluorine reacts with titanium layer
102
. During this reaction, the tungsten continues to be deposited irrespective of the peeling of TiN layer
103
. Thus, tungsten forms on both sides of the peeling portion and eventually forms tungsten volcano
106
, usually greater than 1 micron in size. For additional details regarding this phenomena, see ULSI Technology, by C. Y. Chang and S. M. Sze, pages 371-471, published by McGraw-Hill in 1996. A subsequent RIE etch cannot remove these volcanoes, thereby resulting in intra- or interlevel metal shorts.
SUMMARY OF THE INVENTION
A structure and method to prevent barrier failure is provided. The present invention replaces the standard titanium-nitride (TiN) barrier metal layer with two separately-formed TiN layers. The two TiN layers provide smaller and mismatched grain boundaries. During subsequent tungsten deposition using WF
6
, the WF
6
finds it difficult to penetrate through these mismatched grain boundaries, thereby significantly minimizing the possibility of reacting with the underlying layer and forming a tungsten volcano. One embodiment includes a native or a grown oxide formed between the two TiN layers, thereby providing yet another diffusion barrier to the WF
6
and acting as a glue layer between the two TiN layers. The present invention provides a thin and strong barrier metal layer with minimal barrier failures.
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“ULSI Technology” edited by C. Y. Chang and S. M. Sze, Chapter 8, “Metallization”, published by the McGraw-Hill Companies, Inc. 1996, pp. 371-471.
Kubodera John
Lee Calvin
Smith Matthew
Xilinx , Inc.
Young Edel M.
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