Capacitor for semiconductor devices

Details Capacitor for semiconductor devices Capacitor for semiconductor devices

2000-03-16

2002-08-20

Loke, Steven (Department: 2811)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S532000

Reexamination Certificate

active

06437391

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a capacitor for semiconductor devices which prevents resistance between a lower electrode and a plug therein from increasing.
2. Discussion of Related Art
There has been a variety of research directed toward increasing the capacitance density of a semiconductor device in order to allow the capacitor to have a specific amount of capacitance even if the cell area becomes smaller as the device is more highly integrated. To obtain a large amount of capacitance, the lower electrode of a capacitor is configured as a three-dimensional structure such as a stacked or trench structure, enlarging the surface area of the dielectric of the capacitor. However, the stacked or trench structured capacitor is fabricated through a complicated process. Thus, there are limitations in increasing the surface area of the dielectric.
To solve this problem, there has been developed a method of enlarging the capacitance in which the dielectric is made of a substance of a high dielectric constant such as Ta2O5, PZT(Pb(ZrTi)O3), PLZT((PbLa)(ZrTi)O3), PNZT(Pb(NbZrTi)O3), PMN(Pb(MgNb)O3), BST((BaSr)TiO3) and the like.
FIG. 1
shows a cross-sectional view of a capacitor according to a related art.
Referring to
FIG. 1
, an N type impurity region
13
is formed in a semiconductor substrate
11
, which serves as source and drain regions of a transistor including a gate (not shown in the drawing). An insulating interlayer
15
is formed on the semiconductor substrate
11
to cover the transistor. And a contact hole
17
(see
FIG. 2A
) exposing the impurity region
13
is patterned in the insulating interlayer
15
.
The contact hole
17
is filled with impurity doped polysilicon to form a plug
19
which is electrically connected with an impurity region
13
. Specifically, the plug
19
is formed by depositing the doped polysilicon by chemical vapor deposition (hereinafter abbreviated CVD) and by etching back the doped polysilicon to expose the insulating interlayer by reactive ion etching (hereinafter abbreviated RIE).
A barrier layer
21
and a lower electrode
23
are successively deposited on the insulating interlayer
15
including the plug
19
. The barrier layer
21
, which is in contact with the plug
19
, is made of TiN, TaN or the like. The lower electrode
23
is formed by depositing oxidation-resistant metal such as Pt, Mo, Au or another metal of which the oxide is electrically-conductive such as Ir, Ru and the like on the barrier layer
21
. The barrier layer
21
prevents silicide from being formed by the reaction between the metal of the lower electrode
23
and the silicon of the plug
19
. This is because silicide is easily oxidized into an insulator.
A dielectric layer
25
is formed on the insulating interlayer
15
to cover the lower electrode
23
. The dielectric layer
25
is made of a substance, of which the dielectric constant is high, such as Ta2O5, BST((BaSr)TiO3), PZT(Pb(ZrTi)O3), PLZT((PbLa)(ZrTi)O3), PNZT(Pb(NbZrTi)O3), PMN(Pb(MgNb)O3), etc. An upper electrode
27
is made of the same metal as the lower electrode
23
on the dielectric layer
25
. When the lower and upper electrodes
23
and
27
are formed with oxidation-resistant metal, they are prevented from being oxidized even if they come into contact with the dielectric layer
25
. Moreover, when they are made of metal of which the oxide is conductive, resistance stops increasing.
FIG. 2A
to
FIG. 2D
show cross-sectional views of fabricating a capacitor according to the related art of FIG.
1
.
Referring to
FIG. 2A
, an insulating interlayer
15
is formed on a P-type semiconductor substrate
11
including an N-type impurity region
13
which serves as source and drain regions of a transistor having a gate (not shown in the drawing). A contact hole
17
exposing the impurity region
13
by patterning the insulating interlayer
15
by photolothography.
Referring to
FIG. 2B
, impurity doped polysilicon is deposited on the insulating interlayer
15
to fill up the contact hole
17
by CVD. In this case, polysilicon is contacted with the exposed impurity region
13
through the contact hole
17
. A plug
19
is formed by etching back the polysilicon to expose the insulating interlayer
15
by RIE. In this case, polysilicon remains only in the contact hole
17
.
Referring to
FIG. 2C
, a barrier layer
21
contacted with the plug
19
is formed by depositing TiN or TaN on the insulating interlayer
15
. A lower electrode
23
is formed by depositing oxidation resistant metal such as Pt, Mo, Au, etc. or another metal of which the oxide is electrically conductive such as Ir, Ru or the like on the barrier layer
21
. In this case, the barrier layer
21
prevents the lower electrode
21
from being reacted with the plug
19
, thereby eliminating the formation of silicide between the barrier layer
21
and the plug
19
.
The lower electrode
23
and barrier layer
21
are patterned to remain at the part corresponding to the contact hole
17
by photolithography. In this case, the lower electrode
23
and barrier layer
21
are paterned to have the barrier layer
21
come into contact with the plug
19
.
Referring to
FIG. 2D
, a dielectric layer
25
is formed by depositing a substance, of which dielectric constant is high, such as Ta2O5, BST((BaSr)TiO3), PZT(Pb(ZrTi)O3), PLZT((PbLa)(ZrTi)O3), PNZT(Pb(NbZrTi)O3), PMN(Pb(MgNb)O3) or the like on the insulating interlayer
15
to cover the lower electrode
23
. Oxidation of the lower electrode
23
made of an oxidation-resistant substance such as Pt, Mo, Au and the like is prohibited even though the lower electrode
23
is contacted with the dielectric layer
25
which includes oxygen atoms. Moreover, when the lower electrode
23
is made of metal of which the oxide is electrically conductive, resistance stops increasing because of the electric conductivity of metal oxide.
An upper electrode
27
is formed by depositing the same substance of the lower electrode
23
on the dielectric layer
25
. In this case, oxidation of the upper electrode
27
made of an oxidation-resistant substance such as Pt, Mo, Au and the like is prohibited even though the upper electrode
27
is contacted with the dielectric layer
25
which includes oxygen atoms, too. Moreover, when the upper electrode
27
is made of metal of which the oxide is electrically conductive, resistance stops increasing because of the electric conductivity of metal oxide as well.
Then, the upper electrode
27
and dielectric layer
25
are patterned to remain on the corresponding part to the lower electrode
23
. In this case, a portion of the dielectric layer
25
inserted between the upper and lower electrodes
27
and
23
is used as a charge-storing dielectric.
Thus, electric capacitance of a capacitor according to the related art may be increased by forming the dielectric layer with a substance of a high dielectric constant.
Unfortunately, oxygen contained in the dielectric substance having a high dielectric constant diffuses through the sides of a barrier layer to oxidize the barrier layer, thereby increasing contact resistance between the plug and the lower electrode.
Moreover, it is hard to increase electric capacitance of the capacitor due to the limited surface area of the dielectric layer between the upper and lower electrodes.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a capacitor for semiconductor devices and a fabricating method thereof that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
The present invention provides, in part, a capacitor of which electric capacitance is increased by increasing the surface area of a dielectric layer between upper and lower electrodes.
The present invention also provides, in part, a method of fabricating a capacitor which prevents the contact resistance between a plug and a lower electrode from increasing by prohibiting the oxidation of a barrier layer which occurs because of exposure to oxygen through the side

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