Active solid-state devices (e.g. – transistors – solid-state diode – With means to control surface effects
Reexamination Certificate
2003-03-18
2004-05-11
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
With means to control surface effects
C257S629000, C257S277000
Reexamination Certificate
active
06734531
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods for conditioning or reoxidizing dielectric layers of semiconductor device structures without substantially oxidizing conductive or semiconductive structures adjacent thereto. Particularly, the present invention relates to methods for conditioning or reoxidizing capacitor dielectric layers without substantially oxidizing the materials of adjacent capacitor electrodes.
2. State of the Art
In state of the art semiconductor devices, capacitors typically include a bottom electrode having a relatively large surface area, a dielectric layer formed over the bottom electrode, and an upper electrode formed over the dielectric layer.
FIG. 1
illustrates an exemplary semiconductor device capacitor
10
, formed over and in contact with an active device region
14
of a semiconductor substrate
12
. Capacitor
10
includes a bottom electrode
16
formed over and in contact with the active device region
14
, a dielectric layer
18
positioned over the bottom electrode
16
, and an upper electrode
20
positioned over the dielectric layer
18
.
After the bottom electrode
16
and dielectric layers
18
of the capacitor
10
have been formed, these layers and various other structures may be patterned in accordance with a particular integrated circuit design. Among the processes that are employed to effect such patterning, dry etch processes, including plasma etches, may be used. Nonetheless, plasma etches tend to cause considerable damage to the dielectric layer
18
. Such damage may result regardless of efforts to optimize etch selectivity and optical end point measurement techniques. Aside from physical thinning and possibly creating voids or other defects in the dielectric layer
18
, plasma etching may damage oxide bonds, creating charge trap sites, such as dangling silicon bonds when polysilicon is employed as the bottom electrode
16
. The presence of voids, other defects, and charge trap sites in the dielectric layer
18
may diminish the desired dielectric properties of the dielectric layer
18
and, thus, the capacitance of the finished capacitor
10
. Accordingly, this damage should be repaired to improve the quality and life expectancy of the dielectric layer
18
and of the capacitor
10
. An oxidation or reoxidation step is commonly used to repair the dielectric layers.
As the dimensions of semiconductor device structures, including the thicknesses of capacitor dielectric layers, are ever decreasing, materials with greater dielectric constants are being used with increased frequency. These dielectric materials, like tantalum pentoxide (Ta
2
O
5
) and barium strontium titanate (BST), are typically deposited and annealed at temperatures near 600° C. and in the presence of high oxygen partial pressure. Nonetheless, voids, defects, and charge trap sites may be present in the extremely thin capacitor dielectric layers formed with such materials. Thus, conditioning by oxidizing or reoxidizing of dielectric layers formed with these materials may be necessary to fabricate a capacitor with the desired electrical properties. Conditioning can involve wet oxidation at temperatures above 900° C. for a relatively long period of time (e.g., up to about 30 minutes). During oxidation at such high temperatures, the dielectric layer
18
is typically thickened.
Unfortunately, conditions during oxidation also result in oxidation of the underlying materials, including portions of the bottom electrode
16
. The longer the oxidation process and the higher the temperature, the more metal, metal nitride and/or silicide are consumed. Such oxidation of the bottom electrode
16
further effectively thickens the dielectric layer
18
, often undesirably changing the capacitance of the capacitor
10
. In addition, some metals, such as tungsten, are so readily oxidized in such processes that these metals are effectively rendered impractical for use as the bottom electrodes in capacitors.
One commonly utilized solution to the problem of oxidizing a bottom electrode of a capacitor structure during conditioning of an overlying dielectric layer is to provide an oxidation barrier layer between the bottom electrode and the overlying dielectric layer. However, there are a limited number of oxidation barrier materials which are conductive.
Processes are also known for oxidizing silicon with selectivity over adjacent structures formed from tungsten or tungsten nitride.
The inventors are not aware of any art that teaches conditioning of a dielectric layer of a capacitor structure by selective oxidization of the dielectric layer without substantially oxidizing an adjacent, underlying bottom electrode layer.
BRIEF SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a method is provided for selectively oxidizing a dielectric layer of a structure without substantially oxidizing an adjacent conductive or semiconductive layer or structure. The inventive method includes exposing at least a portion of the dielectric oxidizing the electronic device by exposing the layer or structure to a selective oxidation atmosphere. The selective oxidation growth ambient selectively oxidizes or reoxidizes the dielectric layer or structure without the bottom electrode.
Another embodiment of the method of the present invention provides a method for conditioning a dielectric layer or structure by repairing voids or other defects in the dielectric layer or structure. Such a method includes forming a dielectric layer above a bottom electrode of a capacitor structure, exposing the bottom electrode to hydrogen species, and oxidizing the dielectric layer. The adsorption of the hydrogen species to a surface of the bottom electrode, substantially prevents oxidation of the bottom electrode, making the oxidation process selective for the dielectric layer.
A further embodiment of the method of the present invention includes forming a capacitor structure, which method includes a bottom electrode, forming at least one dielectric layer above the bottom electrode, adsorbing a hydrogen species on a surface of the bottom electrode, and oxidizing said at least one dielectric layer. Again, the adsorption of hydrogen species to a surface of the bottom electrode makes oxidation of the dielectric layer selective for the dielectric layer.
The present invention also includes a semiconductor device structure with a conductive or semiconductive structure adjacent to the dielectric structure. A hydrogen species is at least adsorbed to a portion of a surface of the conductive or semiconductive structure in contact with the dielectric structure. In an intermediate state, the dielectric structure may include voids, other defects, or charge traps. In a subsequently formed intermediate structure, the dielectric structure of the semiconductor device structure may be substantially free of voids, other defects, and charge traps while the hydrogen species remain present at least at an interface between the dielectric structure and the adjacent conductive or semiconductive structure.
Other features and advantages of the present invention will become apparent to those of skill in the art through a consideration of the ensuing description, the accompanying drawings, and the appended claims.
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Powell Don Carl
Weimer Ronald A.
Nelms David
Nguyen Thinh T.
TraskBritt
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