Process for selective polishing of metal-filled trenches of...

Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material

Reexamination Certificate

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C438S626000, C438S634000, C438S645000, C438S745000

Reexamination Certificate

active

06503828

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the formation of integrated circuit structures. More particularly this invention relates to the planarizing, by chemical-mechanical polishing, of metal-filled trenches and/or vias of integrated circuit structures.
2. Description of the Related Art
Aluminum and tungsten metals have long been used in integrated circuit structures as filler materials for vias and contact openings as well as for the construction of metal lines or interconnects. However, with ever increasing demands for faster speeds, there has been renewed interest in the use of copper as a filler material for vias and contact openings instead of tungsten, as well as for use in metal lines instead of aluminum because of the well known low electrical resistance of copper, compared to either aluminum or tungsten.
But there are negative aspects to the choice of copper for via filling or in the formation of metal lines. The usual patterning of a blanket-deposited metal layer through a mask to form a pattern of metal lines or interconnects cannot easily be carried out using copper, resulting in the need to first deposit a dielectric layer such as silicon oxide, and then form a series of trenches in the dielectric layer corresponding to the desired pattern of metal lines or interconnects. The trench surfaces are then lined with a diffusion barrier layer or liner (to prevent migration of copper into the dielectric material, as well as to promote adhesion of the filler metal to the trench surfaces), and then filled with copper metal by first forming a copper seed layer over the barrier layer, e.g., by a CVD process, and then filling the remainder of the trench with a blanket deposition of copper, e.g., by a copper plating process.
Finally, the surface portions of both the diffusion barrier layer and the copper layer, formed over the top surface of the dielectric layer during the blanket depositions, are removed using a planarization process such as a chemical-mechanical polishing (CMP), leaving the desired pattern of metal lines or interconnects in the trenches, with the copper metal in the trenches separated from the silicon oxide sidewalls of the trench by the diffusion barrier layer.
While the copper lines or interconnects formed using such procedures provide the desired increased speed of the conductor, and the presence of the diffusion barrier layer between the copper and the silicon oxide dielectric material addresses the problem of diffusion of the copper ions or atoms into the silicon oxide sidewalls, the deposition of copper metal results in a non-planar upper surface of the deposited copper layer, which surface is characterized by depressed regions over the trenches filled by the copper deposition process. Subsequent removal of the surface portions of the copper layer by chemical-mechanical polishing (CMP) can result in dishing of the copper remaining in the trench in such a way that the dishing of the copper filling drops below the upper surface of the dielectric layer which defines the trench.
Turning now to prior art
FIGS. 1-3
, the formation of copper interconnects or lines in a dielectric layer of an integrated circuit structure, in accordance with the prior art, will be illustrated, using the so-called dual damascene process, it being understood that the same planarizing problems are also present when using the single damascene process. As shown in
FIG. 1
, a dielectric layer
20
may be formed over an integrated circuit structure
10
which may comprise active devices previously formed in an underlying silicon substrate and filled vias or contact openings previously formed in an underlying dielectric layer. Such vias or contact openings provide connection, for example, with underlying gate electrodes and source/drain regions of MOS devices of integrated circuit structure
10
formed in the silicon substrate, as is well known to those skilled in the art.
Still referring to
FIG. 1
formed in dielectric layer
20
, are trenches
22
and
24
, and vias
26
and
28
. Trenches
22
and
24
, and vias
26
and
28
, may be formed in dielectric layer
20
, for example, by twice etching dielectric layer
20
through a resist mask, to divide dielectric layer
20
into the illustrated pattern of trenches and vias in dielectric layer
20
as is well known to those skilled in the art. Trenches
22
and
24
, and vias
26
and
28
, represent or illustrate a series of trenches and vias generally formed in dielectric layer
20
in a pattern corresponding to a desired array of metal lines and vias to electrically interconnect, for example, underlying gate electrodes and source/drain regions of MOS devices with other portions of the integrated circuit structure.
Over the surfaces of trenches
22
and
24
, vias
26
and
28
, and the illustrated upper surfaces of dielectric layer
20
, is formed a highly conformal diffusion barrier layer
30
comprising and electrically conductive material, for example, tantalum metal, tantalum nitride, tungsten metal, tungsten nitride, titanium metal, or titanium nitride, or combinations of same. Diffusion barrier layer
30
is blanket deposited over the surfaces of trenches
22
and
24
, vias
26
and
28
, and the upper surface of dielectric layer
20
, by a suitable deposition process such as chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), or any other suitable deposition process to a thickness of, for example, from about 100 Å to about 1000 Å.
Following the formation of barrier layer
30
, a layer of copper metal
40
is blanket deposited over the structure by any suitable deposition process to completely fill the remaining portions of trenches
22
and
24
and vias
26
and
28
, as well as depositing over the portions of barrier layer
30
previously deposited on the top surfaces of silicon oxide dielectric layer
20
, as also shown in FIG.
1
. This copper layer serves as the main metal conductor of trenches
22
and
24
and vias
26
and
28
.
Following the blanket deposition of copper layer
40
, the structure is subject to a chemical-mechanical polishing (CMP) process to remove all of the copper on the portions of diffusion barrier layer
30
on the top surfaces of dielectric layer
20
, as shown in prior art
FIG. 2
, leaving only depressed copper portions
42
and
44
filling respective trenches
22
and
24
and vias
26
and
28
. After removal of all copper from above the top surfaces of layer
20
, the CMP process is continued to remove all portions of diffusion barrier layer
30
over the top surfaces of dielectric layer
20
, leaving only a liner of diffusion barrier material on the walls of the trenches separating the copper metal in trenches
22
and
24
and vias
26
and
28
from the silicon oxide surfaces or walls of the trenches, as shown in prior art FIG.
3
.
During the CMP planarization, copper layer
40
and barrier layer
30
are polished until the portions of copper layer
40
and barrier layer
30
lying above dielectric layer
20
are removed. Since CMP planarization is a conformal process, the depressed portions of layer
40
depicted in
FIG. 1
continue to be depressed throughout the CMP process. The result, as shown in prior art
FIG. 3
, is a dished or depressed upper surface of the copper filler material in trenches
22
and
24
, as shown, respectively, at
52
-and
54
in trenches
22
and
24
. Furthermore, while the problem of surface erosion of the metal trench filler material during CMP planarization has been discussed and illustrated, with respect to its occurrence with copper, the problem also exists when tungsten is used instead of copper, which includes, for example, in vias or contact openings where, tungsten is used more often as the filler material.
It would, therefore, be desirable to control the polishing of metal portions above trenches and vias in forming a pattern of metal interconnects or lines in previously formed trenches and/or vias in a layer of insulation mat

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