Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2001-10-11
2003-11-11
Nguyen, Tuan H. (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S309000, C257S310000, C257S532000
Reexamination Certificate
active
06646298
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to capacitors, and more particularly to capacitors made with high dielectric constant dielectric materials having reduced leakage current, and to methods of making such capacitors and their incorporation into DRAM cells.
The increase in memory cell density in DRAMs presents semiconductor chip designers and manufacturers with the challenge of maintaining sufficient storage capacity while decreasing cell area. One way of increasing cell capacitance is through cell structure techniques, including three dimensional cell capacitors. The continuing drive to decrease size has also led to consideration of materials with higher dielectric constants for use in capacitors. Dielectric constant is a value characteristic of a material and is proportional to the amount of charge that can be stored in a material when the material is interposed between two electrodes. Promising dielectric materials include Ba
x
Sr
(1-x)
TiO
3
(“BST”), BaTiO
3
, SrTiO
3
, PbTiO
3
, Pb(Zr,Ti)O
3
(“PZT”), (Pb,La)(Zr,Ti)O
3
(“PLZT”), (Pb,La)TiO
3
(“PLT”), KNO
3
, Nb
2
O
5
, Ta
2
O
5
, and LiNbO
3
, all of which have high dielectric constants making them particularly desirable for use in capacitors. However, the use of these materials has been hampered by their incompatability with current processing techniques and their leakage current characteristics. For example, present RuO
x
/Ta
2
O
5
/TiN capacitor structures show several orders of magnitude leakage degradation after subsequent rapid thermal processing (RTP) at 650° C. in a nitrogen atmosphere.
Producing a metal/insulator/metal structure that does not degrade under subsequent high temperature processing remains an unsolved problem for incorporating high dielectric constant (high K) materials into advanced DRAM cells. A concern with using metal electrodes in the capacitor structure is that there is vacancy diffusion during subsequent high temperature treatments. At the electrode interface boundary, it would be advantageous to have an electrode that could supply oxygen to fill oxygen vacancies.
The use of oxygen-doped, sputter deposited platinum (PVD Pt) electrodes have been proposed in the literature. Y. Tsunemine, et al., “A manufacturable integration technology of sputter-BST capacitor with a newly proposed thick Pt electrode,” 1998 IEDM 30.3.1. However, PVD Pt electrodes cannot be used in capacitor container structures. As shown in
FIG. 1
, when a layer of Pt 12 is sputter deposited in a container structure
10
, the deposition produces uneven layer thicknesses. Because conformal coverage is required for capacitor container structures, sputter deposition cannot be used.
Therefore, there remains a need in this art for improved processes for incorporating high dielectric constant dielectric materials into capacitor constructions and for capacitors containing these materials.
SUMMARY OF THE INVENTION
The present invention meets these needs by providing a stabilized capacitor having improved leakage current characteristics using high dielectric constant oxide dielectric materials, and methods of making such capacitors. By “high dielectric constant oxide dielectric” materials we mean oxides of barium, titanium, strontium, lead, zirconium, lanthanum, and niobium, including, but not limited to Ba
x
Sr
(1-x)
TiO
3
(“BST”), BaTiO
3
, SrTiO
3
, Ta
2
O
5
, Nb
2
O
5
, PbTiO
3
, Pb(Zr,Ti)O
3
(“PZT”), (Pb,La)(Zr,Ti)O
3
(“PLZT”), (Pb,La)TiO
3
(“PLT”), KNO
3
, and LiNbO
3
and having a dielectric constant of at least about 20.
In accordance with one aspect of the present invention, the method includes depositing a metal electrode on a semiconductor substrate, oxygen doping the metal electrode, oxidizing an upper surface of the oxygen-doped metal electrode, depositing a high dielectric constant oxide dielectric material on the oxidized oxygen-doped metal electrode, and depositing an upper layer electrode on the high dielectric constant oxide dielectric material. The metal electrode is preferably selected from the group consisting of TiN, Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof. The upper layer electrode is preferably selected from the group consisting of TiN, W, Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof. The high dielectric constant oxide dielectric material is preferably selected from the group consisting of Ta
2
O
5
and Ba
x
Sr
(1-x)
TiO
3
.
The oxygen doping is preferably obtained by chemical vapor depositing the metal electrode in an oxygen-containing environment. By “oxygen containing environment,” it is meant an atmosphere which contains gaseous oxygen. The upper layer electrode is also preferably chemical vapor deposited in an oxygen-containing environment. In a preferred form, the method deposits the metal electrode layer and/or the upper layer electrode using chemical vapor deposition (CVD) techniques.
Another aspect of the invention provides a capacitor including an oxygen-doped metal electrode having an oxidized surface, a high dielectric constant oxide dielectric material adjacent to the oxidized surface of the oxygen-doped metal electrode, and an upper layer electrode adjacent to the high dielectric constant oxide dielectric material. The metal electrode is preferably selected from the group consisting of TiN, Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof. The upper layer electrode is preferably selected from the group consisting of TiN, W, Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof. The high dielectric constant oxide dielectric material is preferably selected from the group consisting of Ta
2
O
5
and Ba
x
Sr
(1-x)
TiO
3
.
Both the metal electrode and the upper layer electrode are preferably deposited using chemical vapor deposition (CVD) techniques. Also, preferably, both the metal electrode and the upper layer electrode are doped with oxygen.
The capacitor may also include a first layer of a chemical vapor deposited metal electrode beneath the oxygen-doped layer of the metal electrode, and a second layer of a chemical vapor deposited upper layer electrode adjacent to the first layer of the upper layer electrode.
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Won et al., Conformal CVD-Ruthenium Process for MIM Capacitor in Giga-bit DRAMs, Electron Devices Meeting, 2000, IEDM Technical Digest. International, pp. 789-792.*
Tsunemine et al., A manufacturable integration technology of sputter-BST capacitor with a newly proposed thick Pt electrode, IEEE, 1998, pgs. 30.3.1-30.3.4.
Dinsmore & Shohl LLP
Nguyen Tuan H.
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