Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-10-02
2004-08-24
Nguyen, Cuong (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S302000
Reexamination Certificate
active
06781180
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a trench capacitor for storing an electrical charge and to a method for fabricating such a trench capacitor.
Integrated circuits (ICs) or chips contain capacitors for the purpose of storing electrical charges, such as, for example, in a dynamic random access memory (DRAM). The charge state in the capacitor represents a data bit in this case.
In order to maintain or increase international competitiveness, it is necessary to continually reduce the costs that have to be expended to realize a specific electronic function, and thus to continuously increase productivity. The continuous increase in productivity is achieved by a progressive miniaturization. This necessitates realizing an ever greater number of functions on the same chip area. This is accompanied by a continuous reduction in the size of the individual functions on the chip, so that the dimensions of the capacitors used for charge storage are also reduced.
However, the progressive miniaturization of the capacitors entails a decrease in the capacitance of the capacitors. A series of applications, such as DRAM memories for example, require a minimum storage capacitance of the storage capacitors. Therefore, it is necessary to maintain or even to increase the storage capacitance of the storage capacitors despite reduced structural dimensions. If, as is generally customary nowadays, silicon oxide is used as a capacitor dielectric, then the layer thickness of the storage dielectric would have to be reduced to a few atomic layers in future technologies. However, it is very difficult to fabricate such thin silicon oxide layers reproducibly and with sufficient accuracy, because fluctuation in the layer thickness by one atomic layer means fluctuation by more than 10%. Furthermore, it is very difficult to adequately suppress the leakage currents between two capacitor electrodes which are isolated by a storage dielectric having a thickness of a few atomic layers, since, through the effect of quantum mechanical tunneling, the charge carriers can tunnel through the potential barrier produced by the thin storage dielectric.
The prior art has already disclosed capacitors in which the storage capacitance is increased using materials such as tantalum oxide (TaO
2
) having a dielectric constant &egr;
r
=20, and also barium strontium titanate (BST, (Ba, Sr) TiO
3
) having an &egr;
r
of up to 1000 or lead zirconate titanate (PZT, Pb (Zr, Ti) O
3
). However, complicated and costly deposition methods are necessary for the use of BST, PZT or SBT layers, and barrier layers made of platinum (Pt), ruthenium (Ru) or ruthenium oxide (RuO
2
) that are difficult to process are also necessary.
The increase in the dielectric constant &egr;
r
through the use of TaO
2
(&egr;
r
=20) is relatively small in comparison with NO or ONO layers, which already have a dielectric constant of &egr;
r
=6 to 8. Although the dielectric constant is significantly above that when BST, PZT or SBT is used, the capacitance of the capacitors is nonetheless limited by the required barrier layers with respect to silicon and polysilicon layers which serve as electrodes.
In the case of BST, PZT and SBT, it has been found that these materials belong to the materials which, chemically, cannot be etched or can be etched only with difficulty, in the case of which the etching removal, even given the use of reactive gases, is based predominantly or almost exclusively on the physical component of the etching. Due to the small or absent chemical component of the etching, the etching removal of the layer to be patterned is of the same order of magnitude as the etching removal of the mask or of the support (etching stop). Therefore, the etching selectivity with respect to the etching mask or with respect to the support is generally small, the consequence of which is that, due to the erosion of masks with inclined sidewalls and the unavoidable faceting (beveling, tapering) on the masks, only low dimensional accuracy of the patterning can be ensured. The faceting thus limits the smallest feature sizes that can be attained in the course of patterning, and also the attainable steepness of the profile sidewalls in the layers to be patterned.
Due to a lack of thermal stability, BST layers cannot, moreover, be used for processes which provide high-temperature steps after the formation of the BST layer, as is the case for example in the fabrication of DRAM memories with deep trench capacitors.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a trench capacitor which overcomes the above-mentioned disadvantages of the heretofore-known trench capacitors of this general type and which provides a high storage capacitance in relation to its geometrical dimensions and has sufficient thermal stability for process steps which are carried out after its formation. It is a further object of the invention to provide a method of producing such a trench capacitor.
With the foregoing and other objects in view there is provided, in accordance with the invention, a trench capacitor, including:
a substrate formed with a trench;
the trench having an upper region and a lower region;
an insulation collar formed in the upper region;
a buried well formed in the substrate, the lower region at least partly extending through the buried well;
a dielectric layer of tungsten oxide for lining the lower region, the dielectric layer serving as a capacitor dielectric; and
a conductive trench filling disposed in the trench.
The idea underlying the invention is the use of tungsten oxide (WOx) as a capacitor dielectric. Since tungsten oxide has dielectric constants &egr;
r
of greater than 50 and even greater than 300, the capacitance of the trench capacitor is increased, whilst maintaining the geometrical dimensions, by approximately 2 orders of magnitude (factor 100) if tungsten oxide is used instead of silicon oxide. The trench capacitor according to the invention has the advantage, moreover, that the installations used in semiconductor technology can likewise be used for producing tungsten oxide layers. Specially adapted and thus expensive installations, as are required for fabricating BST, PZT or SBT layers, do not have to be used. The tungsten used for producing tungsten oxide layers diffuses only very slightly into silicon, resulting in a reduced risk of contamination in the case of the trench capacitor according to the invention. The use of tungsten oxide as a capacitor dielectric is not restricted to silicon technology, however, but rather may also be used in connection with other semiconductors such as, for example, gallium arsenide (GaAs). Tungsten oxide can be used as a capacitor dielectric outside the scope of semiconductor technology as well, such as, for example, in discrete components for low-voltage and high-voltage technology. Furthermore, tungsten oxide has markedly good thermal stability up to temperatures in excess of 1100° C. As a result, tungsten oxide can be used as a storage dielectric in memory cells having a trench capacitor, in which a transistor is formed after the trench capacitor has been fabricated, because the processing of a transistor requires, for example, thermal steps for annealing source and drain regions which are above 1000° C.
Progressive miniaturization additionally has the consequence that the sheet resistance of capacitor electrodes continuously increases, due to the decreasing layer thickness. Therefore, in an advantageous embodiment, at least one of the capacitor electrodes is composed of tungsten or a tungsten-containing material. As a result, the resistance of the capacitor electrodes is reduced and the time needed for charging and discharging the trench capacitor is advantageously shortened.
In accordance with another feature of the invention, the conductive trench filling is a tungsten-containing material.
In a further advantageous embodiment of the invention, the tungsten-containing material is composed of tungsten silicide, tungsten nitride or of pure
Drescher Dirk
Karcher Wolfram
Martin Schrems
Wurzer Helmut
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Nguyen Cuong
Stemer Werner H.
LandOfFree
Trench capacitor and method for fabricating the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Trench capacitor and method for fabricating the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Trench capacitor and method for fabricating the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3351744