Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-03-25
2003-09-09
Thompson, Craig (Department: 2813)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
Reexamination Certificate
active
06617245
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an etching mask, a process for forming contact holes using the same etching mask, and a semiconductor device which is manufactured by the same process.
BACKGROUND OF THE INVENTION
With an recent advance in high integration density and smaller size of semiconductor devices, the area of each element has been remarkably reduced. However, the thickness of the films therefor should be increased if the same materials are used since it is necessary to provide an electric resistance which is equal to or less than that of the conventional semiconductor devices. Thus, the thickness of the inter layer films will increase, so that a case where contact holes in the second and subsequent films require a depth which is 3 &mgr;m or more is not rare. Since the diameter of the contact holes has become smaller and smaller, the technique to fabricate contact holes having a higher aspect ratio at a high precision has been demanded.
A process for forming contact holes in the course of manufacturing conventional general DRAM (Dynamic Random Access Memory) process will now be described with reference to the drawings.
FIGS. 10 through 12
are sectional views schematically showing a conventional process for manufacturing a DRAM. For convenience of drawing, these drawings are separated with an alphabetical sequence.
After an element isolation oxide film
2
is formed in a given region of a silicon substrate
1
by a trench isolation method as shown in FIG.
10
(
a
), memory regions and peripheral circuit regions are formed. Well-regions
8
are formed by implanting ions of phosphorous, boron, etc. into respective regions. A gate oxide film
3
, gate electrode film
4
and silicon nitride film
5
are successively deposited on the silicon substrate
1
, and gate electrodes are formed by etching process, source/drain regions
7
are formed by the implantation of ions of phosphorus and the like.
Subsequently, after a silicon oxide film is deposited to cover the gate electrodes as shown in FIG.
10
(
b
), side walls
6
are formed by applying an anisotropic etching and n
+
/p
+
layers are formed by protecting given regions with a resist and implanting ions of phosphorus and boron, etc.
Then, a first interlayer film
9
is deposited over an entire surface of the silicon substrate
1
as shown in FIG.
10
(
c
) and a resist pattern
22
is formed in such a manner that regions to be connected to bit lines are exposed. Contact holes are formed in the first interlayer film
9
by plasma etching using the resist pattern
22
as an etching mask and using a carbon fluoride (CF system) gas.
In order to enhance the precision of the size of openings of the resist pattern
22
by eliminating the influence of the reactivity with the underlying layer (or substrate) and the reflected light from the underlying layer (or substrate) on formation of the resist pattern
22
, an antireflection coating (hereinafter referred to as ARC)
28
may be formed between the first interlayer film
9
and the resist
22
. In this case, hole is first formed in the ARC using oxygen gas by plasma etching with the aid of the resist pattern
22
as a mask. Thereafter, the first interlayer film
9
is formed leaving a contact hole
10
by the plasma etching using CF gas. The ARC
28
will be removed together with the resist pattern
22
after formation of the first contact hole
10
.
Then, a bit line (first film wiring
11
) which is to be connected to polysilicon is formed after polysilicon (and the like) is buried in the first contact hole
10
as shown in FIG.
10
(
d
).
Subsequently, after a silicon oxide film
12
is deposited over an entire surface of the silicon substrate
1
and the resist pattern
22
is formed so that a region which is to be connected to storage nodes will be exposed as shown in
FIG. 11
(
e
), (second) contact holes which extends through the silicon oxide film
9
are formed by a plasma etching using the resist pattern
22
as an etching mask and using an CF gas. An ARC
28
may also be formed on the silicon oxide film
12
in order to prevent the influence of underlying substrate in the course of the resist pattern forming process. In this case, the ARC is firstly subjected to boring (hole-opening) by the plasma etching with oxygen gas. Thereafter, the (second) contact holes are formed in the silicon oxide film
12
and the first interlayer film
9
by using CF gas.
After polysilicon, etc. is buried in second contact holes
13
as shown in FIG.
11
(
f
), a metal film (second layer wiring
14
) which will be connected to polysilicon is formed, and a high dielectric thin film and a metal film are subsequently formed thereon, so that a capacitor
15
comprising a dielectric thin film which is sandwiched between the metal films is formed.
Subsequently, a second interlayer film
16
is deposited over the entire surface of the silicon substrate
11
and a resist pattern
22
is formed in such a manner that regions which are connected to the source/drain regions
7
and the capacitor
15
are exposed as shown in FIG.
11
(
g
). Third contact holes extending through the second inter layer film
16
, silicon oxide film
12
and first interlayer film
9
and a fourth contact hole extending through the second interlayer film
16
are formed by the plasma etching using the resist pattern
22
as an etching mask and using CF gas. In this process, the ARC may also be similarly formed for canceling the influence of an underlying layer (or layers)
Then, after titanium and titanium nitride is buried in a fourth contact hole
18
which is connected with the capacitor
18
and titanium nitride is buried in the third contact holes
17
which are connected to the source/drain regions
7
as shown in FIG.
12
(
h
), titanium silicide is formed in the source/drain regions
7
by conducting heat treatment.
After a third layer wiring
19
is formed by depositing a film of a metal such as Al as shown in FIG.
12
(
i
), a DRAM is formed by depositing an interlayer insulating film and a passivation film (not shown) thereon.
SUMMARY OF THE DISCLOSURE
In the above-mentioned process for manufacturing DRAM, there is a tendency that the contact holes shown in FIGS.
11
(
e
) and
11
(
g
) will have an increased aspect ratio in association with the reduction in the size of the device and the enhanced performance thereof. It is of great importance in the manufacturing of DRAM how the contact holes can be opened at high precision.
The resist patterns have heretofore been used as an etching mask when such contact holes are opened. However, there are problems in that the openings (i.e., hole edges) of the resist will gradually increase, so that the opening diameter of the contact holes will also increase since the resist per se is also etched on dry etching for forming the contact holes and in that the thickness of the resist may be reduced. On the other hand, the thickness of the resist tends to decrease in association with the reduction in the size of the devices. The resist is not endurable against the dry etching for an extended period of time.
The last problem will be explained with reference to
FIGS. 13 and 14
in more detail.
FIGS. 13 and 14
are sectional views schematically showing a process for forming contact holes by using a conventional resist pattern as an etching mask. In
FIG. 14
, an antireflection film
28
of an organic material is formed on a silicon oxide film
20
for canceling the activity with the underlying layer(s) and the influence of the underlying layer(s).
In the conventional process for forming contact holes, the resist pattern having a film thickness of about 700 nm has been formed on an inorganic interlayer film
20
such as silicon oxide film having a thickness of 3 &mgr;m as shown in FIG.
13
and the contact holes have been formed by the plasma etching using a fluorocarbon mixture gas (termed herein “CF gas”). Since the film thickness of the resist is gradually reduced and the diameter of the opening becomes gradually larger, the opening diameter
McGinn & Gibb PLLC
NEC Electronics Corporation
Thompson Craig
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