Interconnection structure and fabrication process therefor

Details Interconnection structure and fabrication process therefor Interconnection structure and fabrication process therefor

1999-11-08

2002-04-30

Everhart, Caridad (Department: 2825)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S639000, C438S643000, C438S688000, C438S715000

Reexamination Certificate

active

06380065

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an interconnection structure and a fabrication process therefor and more particularly to an interconnection structure that improves a filling performance of an interconnect material in itself and a fabrication process for the interconnection structure.
2. Description of the Related Art
Aluminum alloy has widely been adopted as an interconnect material for LSI. As a demand for miniaturization of LSI and its fast operating speed has been piled up, however, ensuring sufficient performances such as high reliability and low resistivity has increasingly become difficult with aluminum alloy interconnection. To cope with such a situation, a copper interconnection technique, because copper is excellent in electromigration resistance as compared with aluminum alloy, draws attention and is on the move toward practical use.
In formation of copper interconnects, since dry etching of copper generally is not easy, a fabrication process by means of trench interconnection is regarded as prospective. The trench interconnects are formed in a procedure such that predetermined trenches are in advance formed in an interlayer insulating film made of silicon oxide or the like, an interconnect material is filled into the trenches and thereafter, unnecessary portion of the interconnect material is removed by a chemical, mechanical polishing (hereinafter referred to as CMP, which is an abbreviation of Chemical Mechanical Polishing) or the like.
In the above described trench interconnect technique, various processes or methods for filling an interconnect material into the interior of contact holes and trenches have been studied, such as an electrolytic plating process, a chemical vapor deposition (hereinafter referred to as CVD, which is an abbreviation of Chemical Vapor Deposition) method, a reflow method and a high pressure reflow method, the latter two of which are effected after sputtering. Among them, an electrolytic plating process for copper which process has a high filling ability into the interiors of fine contact holes or trenches is regarded as an especially important technique.
An example of a process in which copper is filled into trenches and contact holes by means of the electrolytic plating method will be described with reference to FIG.
4
.
As shown in FIG.
4
(
1
), after a predetermined element (not shown) is formed on a semiconductor substrate (not shown), an interlayer insulating film
111
is formed thereon and an lower layer interconnect
112
constituted of trench interconnection is further formed in the inter layer insulating film
111
. An interlayer insulating film
113
, between upper and lower layer interconnection, which covers the lower layer interconnect
112
, is formed on the interlayer insulating film
111
with an oxide silicon film
114
and a silicon nitride film
115
. Then, part of a contact hole
116
is formed in the silicon oxide film
114
and thereafter, an interlayer insulating film
117
is further formed. A trench
118
, in which a trench interconnect is formed, is formed in the interlayer insulating film
117
and thereafter, the contact hole
116
is completed in the interlayer insulating film
113
so as to reach the lower layer interconnect
112
. Subsequently, titanium nitride is deposited on inner walls of the trench
118
and a contact hole
116
to form a barrier metal layer
119
of 70 nm in thickness. The barrier metal layer
119
has a blocking function against diffusion of copper into the interlayer insulating films made of silicon oxide or the like.
Then, as shown in FIG.
4
(
2
), a seed layer
120
made of copper is deposited on the barrier layer
119
to a thickness of 100 nm by sputtering. The seed layer
120
functions as a seed in electrolytic plating conducted in a later step. Then, as shown in FIG.
4
(
3
), copper
121
is filled into the interiors of the contact hole
116
and the trench
118
by means of an electrolytic plating process.
In the above described process, in order to realize good filling of copper
121
, it is important to form the seed layer
120
in the respective interiors of the trench
118
and contact hole
116
, so to speak, in a conformal manner. Furthermore, it is also significant to constantly supply a fresh plating solution into the respective interiors of the trench
118
and the contact hole
116
.
However, decrease in interconnect line dimensions has progressed and a high aspect ratio, as a whole, of a trench and a contact hole combined has been a reality in a filling process in which the trench and the contact hole are simultaneously filled, by which a sputtering method has been hard to achieve a sufficient step coverage performance of a copper seed layer. In such circumstances, it is also difficult to constantly supply a fresh plating solution into respective interiors of a trench and a contact hole. In cases where step coverage of a copper seed layer is insufficient, or a fresh plating solution cannot sufficiently be supplied into the respective interiors of a trench and a contact hole in a continuous manner, voids or the like are produced in the respective interiors of a trench and a contact hole, thereby leading to poor filling. As a result, defective connection is provoked between a plug made of copper filled in the though-hole and a lower layer interconnect.
To cope with such inconvenience, methods have been studied of improving step coverage of copper in sputtering through improvement of an apparatus, For example, a long-distance sputtering in which a distance between a target and a substrate is increased and an ionization sputtering in which sputtered atoms are ionized to increase a fraction of vertical directionality in movement. A low-melting point metal material such as copper, however, is essentially poor in step coverage performance as compared with a high-melting point metal material such as tantalum nitride or titanium nitride and therefore, improvement of step coverage by the above described methods is not necessarily attained with ease. In a plating solution, on the other hand, while a process has been adopted in which wettability of the plating solution is increased by mixing an additive such as a surfactant into the plating solution, there is a limitation on improvement by increase in the wettability and a sufficient improvement of the filling characteristic of copper cannot be expected only by use of an additive.
Besides, in a structure in which a barrier metal layer is formed, since the barrier metal layer is formed between a lower layer interconnect and a copper plug formed in a contact hole, a contact resistance between the copper plug formed in the contact hole and the lower layer interconnect is increased.
SUMMARY OF THE INVENTION
The present invention is directed to an interconnection structure developed in order to solve the above described problem and a fabrication process therefor and the interconnection structure comprises: a recess, which is connected onto a conductive material mass formed in an insulating film, and which is formed in the insulating film, including a contact hole, or a trench, or a trench and a contact hole formed at a bottom of the trench; a barrier metal layer formed on side walls of the recess; and a metal material mass filled in the interior of the recess. The metal material mass is made of a metal that is repeatedly filled into the interior of the recess a plurality of times and the metal material mass is directly connected with the conductive material mass.
In the above described interconnection structure, a barrier metal layer is formed only on side walls of a recess and a lower portion of the metal material mass is directly connected to the conductive material mass at a bottom of the recess without a barrier layer interposed therebetween. Hence, a contact resistance between the conductive material mass and the lower portion of the metal material mass is low. Besides, the metal material mass is made of a metal that is repeatedly filled into the interior of the rece

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