Methods for fabricating integrated circuit capacitors...

Details Methods for fabricating integrated circuit capacitors... Methods for fabricating integrated circuit capacitors...

1998-12-30

2001-01-30

Whitehead, Jr., Carl (Department: 2822)

Semiconductor device manufacturing: process

Making field effect device having pair of active regions...

Having insulated gate

C438S396000

Reexamination Certificate

active

06180447

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to integrated circuit devices and fabrication methods thereof, and more particularly to integrated circuit capacitors and fabrication methods thereof.
BACKGROUND OF THE INVENTION
Capacitors are widely used in integrated circuit devices, such as Dynamic Random Access Memory (DRAM) devices. As DRAM devices become more highly integrated, various approaches for increasing the capacitance within a defined cell area have been proposed. For example, one approach is to thin the dielectric film. A second approach is to make the capacitor three-dimensional to increase the effective area thereof. A third approach is to use a material having a high dielectric constant. These approaches can also be combined.
Unfortunately, in the first approach, when the thickness of the dielectric film is 100 Å or less, the reliability may deteriorate due to Fowler-Nordheim currents. This may limit the ability to fabricate ultra-thin dielectric films.
In the second approach, complicated processes and high product cost may result when fabricating a three-dimensional capacitor, such as a cylindrical type or a pin type capacitor. This may limit the advantages of three-dimensional capacitors.
For the third approach, various proposals for increasing capacitance using a high dielectric contact material have been made. For the high dielectric constant material, ferroelectric materials such as SrTiO
3
Ba(Sr, Ti)O
3
(BST), Pb(Zr, Ti)O
3
(PZT), Pb(La, Zr)TiO
3
and Ta
2
O
5
may be used.
A metal of the platinum group or an oxide thereof has been used for an electrode material of the high dielectric capacitor. It will be understood that the platinum group metals include the following six metals, all of which are members of Group VIII of the periodic system: ruthenium, rhodium, palladium, osmium, iridium and platinum. The platinum group metals have an excellent oxidation resistance, so they are not oxidized even where they contact the high dielectric layer. Further, platinum has an excellent leakage current characteristic. That is, platinum (Pt) has a work function higher than that of high dielectric material such as BST, SrTiO
3
and PZT, so that a Schottky barrier is formed at an interface with the high dielectric material, which can provide excellent leakage current characteristics.
However, platinum may react with polysilicon at a temperature of 300° C. or higher, to thereby form silicide. Accordingly, it is known to form a barrier layer for preventing silicide formation, at a lower portion of a platinum electrode. Unfortunately, materials commonly used for the barrier layer, for example metal nitrides such as TiN, TaN or WN
1-x
, may be oxidized during a subsequent heat treatment in an oxygen atmosphere.
In particular, the platinum electrode formation generally is performed at a high temperature so that the surface of the electrode is smooth. Subsequently, a high dielectric constant layer is deposited in an oxygen atmosphere at a high temperature. Unfortunately, oxygen may flow into the barrier layer along a grain boundary of the platinum electrode, and then it may additionally diffuse during the subsequent heat treatment. As a result, nitrogen contained in the barrier layer may be replaced with oxygen, which may cause the barrier layer to peel off.
In order to overcome the above problem, it has been proposed to use a conductive oxide layer such as RuO
2
or IrO
2
for the capacitor electrode. In
FIG. 1
, a high dielectric constant capacitor having this structure is shown.
Referring to
FIG. 1
, reference numerals
10
,
11
and
12
indicate an integrated circuit substrate such as a semiconductor substrate, an insulating layer and a conductive plug, respectively. Reference numerals
13
,
14
and
15
indicate an ohmic layer, a barrier layer and a lower electrode, respectively. Reference numerals
17
and
19
indicate a high dielectric constant layer and an upper electrode, respectively.
In
FIG. 1
, the conductive plug
12
is formed of polysilicon, and the barrier layer
14
is formed of a metal nitride such as TiN. Also, the lower electrode
15
is formed of a conductive oxide layer, for example, RuO
2
. The high dielectric constant layer
17
can be formed of a high dielectric constant material such as BST, PZT, PLZT or Ta
2
O
5
, and the upper electrode
19
can be formed of a metal of the platinum group or an oxide thereof.
Unfortunately, although the conductive oxide layer forming the lower electrode
15
can prevent oxygen diffusion more effectively than platinum, it has a work function similar to that of the high dielectric constant layer, which can cause inferior leakage current characteristics. In order to improve the leakage current characteristics, the contact area between the lower electrode
15
and the high dielectric constant layer
17
can be reduced, for example, by reducing the thickness of the lower electrode
15
. However, there may be a limit as to how thin the lower electrode
15
can be made. This is because the lower electrode
15
also functions as an oxygen diffusion barrier layer.
Accordingly, it has also been proposed to thin the lower electrode by forming a sacrificial layer comprising a platinum group metal, between the lower electrode layer and the barrier layer. The sacrificial layer can prevent oxidation as will now be described in connection with FIG.
2
.
FIG. 2
shows a high dielectric constant capacitor including a sacrificial layer. Referring to
FIG. 2
, reference numerals
200
,
201
and
203
indicate an integrated circuit substrate such as a semiconductor substrate, an insulating layer and a conductive plug, respectively. Reference numeral
205
indicates an ohmic layer formed of TiSi
x
, and reference numeral
207
indicates a barrier layer formed of a TiN layer. Also, reference numerals
209
and
211
indicate a sacrificial layer for preventing oxidization and a lower electrode, respectively. Reference numerals
213
and
215
indicate a high dielectric constant layer and an upper electrode, respectively.
The sacrificial layer
209
for preventing oxidization can be formed of a platinum group metal, for example, Ru. Ru reacts with oxygen which flows into the Ru layer during a subsequent processing performed under an oxygen atmosphere at a high temperature, thereby forming RuO
2
. Accordingly, the sacrificial layer
209
for preventing oxidization blocks oxygen from flowing into the barrier layer
207
, which can prevent oxidation of the barrier layer
207
.
However, in the above-described high dielectric constant capacitor, the leakage current characteristics may still be inferior. Specifically, it is difficult to prevent oxygen from flowing from the sidewall of the barrier layer
207
. Accordingly, oxidization of the barrier layer
207
may not be sufficiently prevented.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide improved integrated circuit capacitors and capacitor fabrication methods.
It is another object of the present invention to provide integrated circuit capacitors including high dielectric constant dielectrics, and fabrication methods that can prevent diffusion of oxygen.
It is yet another object of the present invention to provide improved integrated circuit capacitors and fabrication methods that can reduce oxidation of the barrier layer thereof.
These and other objects are provided, according to the present invention, by including a barrier layer in an integrated circuit capacitor, the barrier layer comprising refractory metal and grain boundary filling material. The barrier layer can reduce and preferably prevent diffusion of oxygen therethrough, and thereby can reduce the leakage current and oxidation of the integrated circuit capacitor.
More specifically, integrated circuit capacitors may be fabricated, according to the invention, by forming a conductive plug on an integrated circuit substrate, and forming a barrier layer on the conductive plug. The barrier layer comprises refractory metal and grain boundary filling material. A lower electrode is for

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