Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-02-13
2003-05-27
Whitehead, Jr., Carl (Department: 2813)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S625000, C438S627000, C438S630000, C438S648000, C438S655000
Reexamination Certificate
active
06569759
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a semiconductor device and, more particularly, to a semiconductor device having interconnections and a process for fabricating it.
DESCRIPTION OF THE RELATED ART
Semiconductor manufacturers have progressively increased component elements integrated on a semiconductor substrate. Manufacturers are fabricating the component elements on the semiconductor element. Various patterns are transferred during the fabrication process to semiconductor/insulating layers forming a multiple-layered structure on the semiconductor substrate, and contact holes in the inter-layered insulating layers. These contact holes are miniaturized together with the component elements and, accordingly, have a large aspect ratio, i.e., the ratio of the depth to the diameter. The contact holes are filled with conductive material during the deposition for upper wirings, and the upper conductive lines are electrically connected to the lower conductive lines through the conductive material in the contact holes. Thus, the conductive lines are connected between the component elements on the different levels, and the component elements form an integrated circuit.
Aluminum is popular with semiconductor manufacturers as the conductive material. The aluminum is deposited through sputtering, and the aluminum layer is patterned to the conductive lines through photo-lithography and etching. However, the aluminum is poor in step coverage, and the poor step coverage is the cause of disconnection due to its large resistance. Even if the aluminum layer is patterned to the conductive lines without disconnection, the conductive lines are less durable. Namely, the conductive lines are exposed to the electro-migration, where the step coverage is poor, and are liable to be disconnected.
One of the approaches against the poor step coverage is the formation of contact plugs in the contact holes. A typical example of the material used for a contact plug is tungsten. The tungsten plugs are formed as follows. First, contact holes are formed in an inter-layered insulating layer, and barrier metal layers are formed on the inner surfaces of the contact holes. A titanium layer and a titanium nitride layer are formed in combination with the barrier metal layer, and the titanium and the titanium nitride are deposited by using sputtering techniques. The titanium layer lowers the contact resistance seen by a lower semiconductor layer. On the other hand, the titanium nitride layer enhances the adhesion between the titanium layer and a tungsten plug, and prevents the lower semiconductor layer from diffusing the tungsten. The barrier metal layer defines a recess in the contact hole, and tungsten is deposited by using a chemical vapor deposition, which provides good step coverage. The tungsten fills the recess, and swells into a tungsten layer over the inter-layered insulating layer. The tungsten layer is uniformly etched without any mask, and a tungsten plug is left in the recess.
Although the tungsten plug fairly improves the step coverage, the titanium layer and the titanium nitride layer deposited to target thickness in miniature contact holes required for an ultra large-scale integration. If the titanium/titanium nitride layers do not have the target thickness, the contact resistance is increased, and/or the tungsten damages the component elements in the lower semiconductor layer.
In order to exactly control the titanium layer and the titanium nitride layer, a chemical vapor deposition is desirable. A chemical vapor deposition using a thermal reaction is the most appropriate especially for the titanium nitride layer from the view point of the step coverage, and is widely used for the barrier metal layer. Thus, the titanium, the titanium nitride and the tungsten are respectively deposited by using the three chemical vapor deposition techniques. However, the prior art process' sequence is complicated, and the tungsten is costly. This results in increase of the production cost.
It is proposed to fill the recess with the titanium nitride deposited through the chemical vapor deposition technique. The tungsten plug is eliminated from the interconnection, because the titanium nitride forms fairly good step coverage.
FIGS. 1A
to
1
D show the prior art process. The prior art process starts with preparation of a silicon substrate
501
where a field oxide layer (not shown) is selectively grown. Silicon oxide or boro-phosphosilicate glass is deposited to 1.5 microns thick by using a chemical vapor deposition, and forms an inter-layered insulating layer
502
. A photo-resist etching mask (not shown) is formed on the inter-layered insulating layer
502
by using the photo-lithography, and the inter-layered insulating layer
502
is selectively etched by using a dry etching. Then, a contact hole
503
is formed in the inter-layered insulating layer
502
as shown in
FIG. 1A
, and is 0.4 micron in diameter.
Subsequently, titanium is deposited over the entire surface of the resultant structure to thickness between 5 and 20 nanometers by using a plasma-assisted chemical vapor deposition. This forms a titanium layer
504
. The titanium layer
504
conformably extends, and defines a recess in the contact hole
503
. Titanium nitride is deposited over the entire surface of the resultant structure by using a thermal chemical vapor deposition. The titanium nitride fills the recess, and swells into a titanium nitride layer
505
of 0.4 micron thick. Thus, the contact hole
503
is perfectly filled with the titanium and the titanium nitride as shown in FIG.
1
B.
Subsequently, the titanium nitride layer
505
and the titanium layer
504
are etched without any mask until the inter-layered insulating layer
502
is exposed again. Chlorine-containing etching gas is used in the dry etching. As a result, a titanium layer
504
a
and a piece of titanium nitride are left in the contact hole
503
as shown in FIG. IC, and serve as a conductive plug.
Aluminum alloy is deposited over the entire surface of the resultant structure by using sputtering, and forms an aluminum alloy layer. A photo-resist etching mask (not shown) is formed through the photo-lithography, and the aluminum alloy layer is selectively etched away by using a dry etching technique. An aluminum alloy strip
506
is formed on the inter-layered insulating layer
502
as shown in FIG.
1
D.
Thus, the conductive plug is formed from the titanium layer
504
and the titanium nitride layer
505
, and no tungsten is used for the conductive plug. This results in reduction in production cost. However, the above-described prior art process results in low production yield.
The present inventor investigated the defective products fabricated through the prior art process. The defective products were grouped into three classes. The first class had been rejected due to damage of the inter-layered insulating layer
502
. The second class had been rejected due to contaminant, and the third class had been rejected due to leakage current flowing into the silicon substrate
501
or impurity regions formed in the silicon substrate
501
.
In the defective products grouped in the first class, the inter-layered insulating layers
502
were violently etched during the dry etching for patterning the titanium layer
504
. The present inventor observed the titanium nitride layer
505
, and found many cracks therein and separation between the titanium nitride layer
505
and the titanium layer
504
. The present inventor assumed that the inter-layered insulating layer
502
had been attacked by the etchant penetrating through the cracks and the gap between the titanium layer
504
and the titanium nitride layer
505
.
In the defective products grouped into the second class, the contaminant was pieces of titanium nitride. The pieces of titanium nitride were assumed to be produced from the titanium nitride layer
505
due to the cracks and the separation.
In the defective products grouped into the third class, the silicon substrate
501
and the impurity regions were damaged by th
Hayes & Soloway P.C.
Jr. Carl Whitehead
NEC Electronics Corporation
Pham Thanhha S.
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