Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2001-02-28
2003-12-30
Fahmy, Wael (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S295000
Reexamination Certificate
active
06670668
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a microelectronic structure having a semiconductor structure, a barrier structure, an electrode structure and a dielectric structure made of a high-epsilon material. Structures of this type are used, in particular, as part of a capacitor.
With increasing miniaturization of semiconductor circuit configurations, in particular memory cell configurations, high-epsilon materials are used as a dielectric for capacitor structures. Capacitors of this type are used, in particular, as a storage capacitor or as part of a sensor element. High-epsilon material is a term used to denote dielectric materials having a dielectric constant ∈>10. In particular, the high-epsilon materials include paraelectric and ferroelectric materials. In particular, barium strontium titanate (BST) and strontium bismuth tantilate (SBT) are being investigated with regard to their use as a storage dielectric in a storage capacitor.
High-epsilon materials are usually deposited by metal organic deposition in MOCVD (metal organic chemical vapor deposition) or MOD (metal organic deposition) processes which are carried out at high temperatures in an oxygen-containing atmosphere. In order to obtain the leakage currents of less than 10
−8
A/cm
2
which are desired for memory applications, a subsequent heat treatment in oxygen is furthermore necessary, which is carried out at 550° C. in the case of BST.
It has been proposed (see U.S. Pat. No. 5,005,102), in the context of the fabrication of capacitors in integrated circuits, to use a barrier layer made of titanium/titanium nitride in order to protect semiconductor structures configured underneath the high-epsilon material.
Investigations (see, for example, J. O. Olowolafe et al., J. Appl. Phys. Vol. 73, No. 4, 1993, pages 1764 to 1772) show that when a barrier made of titanium/titanium nitride is used, during the deposition process of the high-epsilon material, the barrier is easily oxidized and TiO
2
is formed, which is an insulator and adversely affects the conductivity of the electrode structure. Moreover, titanium nitride separates at high temperatures, which can lead to the destruction of the storage capacitors.
Therefore, it has been proposed (see T. Hara et al., Jpn. J. Appl. Phys. Vol. 36 (1997), pages L893 to L895) to use as the barrier a material including three components, for example TaSiN. However, additional equipment with expensive targets is required for depositing these materials.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a microelectronic structure that can form part of a storage capacitor and a method for producing the microelectronic structure which overcomes the above-mentioned disadvantageous of the prior art apparatus and methods of this general type. In particular, it is an object of the invention to provide a microelectronic structure having a semiconductor structure, a barrier structure, an electrode structure and a dielectric structure made of a high-epsilon material that can be used in producing a storage capacitor and can be fabricated without costly equipment.
With the foregoing and other objects in view there is provided, in accordance with the invention a microelectronic structure for a capacitor, which includes: a semiconductor structure; a barrier structure including a titanium layer and a titanium nitride layer; an electrode structure having a tensile mechanical layer stress; and a dielectric structure made of a high-epsilon material. The electrode structure is disposed on the barrier structure, and the dielectric structure is disposed on the electrode structure. The barrier structure, the electrode structure, and the dielectric structure form a layer stack disposed on the semiconductor structure.
The microelectronic structure has an electrode structure having a tensile mechanical layer stress. Experts also commonly use the term stress for the mechanical layer stress. The invention makes use of the insight that high-epsilon materials deposited at high temperatures have a tensile layer stress. Furthermore, the invention makes use of the insight that the layer stress of the electrode structure determines the total layer stress of electrode structure and barrier structure. By virtue of the fact that, in the structure according to the invention, the electrode structure has a tensile layer stress, that is to say the layer stress is greater than 0 Pa, and the structure curves away from the substrate at the edge of the structure, the dielectric structure and the substrate on which it is produced have a similar layer stress. This prevents a change in the layer stress as a result of the application of the dielectric structure. Such a change in the layer stress is held responsible for the separation of the electrode structure from the barrier structure in the known method and the oxidation of the barrier structure in the known method.
The dielectric structure can be formed from any desired high-epsilon material. In particular, the dielectric structure has barium strontium titanate (BST), strontium bismuth tantalate (SBT), lead zirconium titanate (PZT) or the like.
In accordance with an added feature of the invention, the electrode structure contains platinum, which is often used as an electrode material in connection with high-epsilon materials because of its reaction behavior.
In accordance with an additional feature of the invention, the electrode structure made of platinum preferably has a resistivity in the range between 10.5 and 13 &mgr;&OHgr;cm. It has been shown that platinum with a resistivity in this range additionally has a diffusion barrier effect for oxygen. This effect is presumably attributable to the higher density of the platinum. As a result of this diffusion barrier effect, the underlying barrier structure is additionally protected against oxidation during the deposition of the dielectric layer.
In accordance with another feature of the invention, the platinum in the electrode structure preferably has an average grain size of between 60 and 100 nm. With an average grain size in this range, platinum has a distinct [111] texture, which has proved to be advantageous for the quality of the dielectric structure deposited thereon.
In accordance with a further feature of the invention, the barrier structure is provided in such a way that it contains a titanium layer and a titanium nitride layer, since these materials are customary and have been well investigated as barrier materials in semiconductor technology. The titanium nitride layer preferably has a resistivity in the range between 70 and 200 &mgr;&OHgr;cm. This reduces the sheet resistance of barrier structure and electrode structure.
In accordance with a further added feature of the invention, it is particularly advantageous to provide the titanium nitride layer having a stoichiometry N:Ti>1, since the oxidizability of the barrier structure is thereby reduced.
In accordance with a further additional feature of the invention, the barrier structure preferably has a layer stress >−200 MPa resulting in that the combination of barrier structure and electrode structure has a tensile layer stress. It is particularly advantageous if the layer stress of the barrier structure is >200 MPa, since the barrier structure then also has a tensile layer stress.
In accordance with yet an added feature of the invention, the semiconductor structure preferably contains silicon and the barrier structure contains titanium nitride and titanium. The titanium layer has a thickness of between 10 and 40 nm and the titanium nitride layer has a thickness of between 80 and 200 nm. The electrode structure contains platinum and has a thickness of between 50 and 200 nm. The dielectric structure has BST and a thickness of between 8 and 50 nm.
As an alternative, the dielectric structure contains a different high-epsilon material, in particular lead zirconium titanate or strontium bismuth tantalate. In this case, the materials of the barrier structure and of the
Fahmy Wael
Mayback Gregory L.
Weiss Howard
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