Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2002-10-15
2004-11-23
Hail, III, Joseph J. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S041000, C451S056000, C451S057000, C438S691000
Reexamination Certificate
active
06821187
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is directed to a method for chemical-mechanical polishing of layers composed of metals from the group of platinum metals, particularly iridium. The invention is also directed to a method for planarizing and/or structuring a metal layer composed of a metal from the platinum group, particularly iridium.
In order to be able to reproducibly read out the charge stored in a storage capacitor of a memory cell, the capacitance of the storage capacitor should have a value of at least approximately 30 fF. At the same time, the lateral expanse of the capacitor must be constantly reduced for the development of DRAM memory cells in order to be able to achieve further enhancements of the storage densities. These inherently contradictory demands made on the capacitor of the memory cell lead to more and more complex structuring of the capacitor (“trench capacitors”, “stack capacitors”, “crown capacitors”). Accordingly, the manufacture of the capacitor becomes more involved and, thus, more and more expensive.
Another way of assuring adequate capacitances of the storage capacitors is by employing materials having an extremely high dielectric constant between the capacitor electrodes. Recently, new materials, particularly high-&egr; para-electrics and ferro-electrics, are therefore being employed as a dielectric instead of the traditional silicon oxide/silicon nitride, and these have a clearly higher, relative dielectric constant (>20) than the traditional silicon oxide/silicon nitride (<8). Given the same capacitance, the capacitor area and, thus, the required complexity of the structuring of the capacitor can thus be clearly diminished. Significant representatives of these materials are barium strontium titanate (BST), which has a formula of (Ba, Sr)TiO
3
, lead zirconate titanate (PZT), which has a formula of Pb(Zr,Ti)O
3
or, respectively, lanthanum-doped lead zirconate titanate or strontium bismuth tantalate (SBT), which has the formula SrBi
2
Ta
2
O
9
.
In addition to traditional DRAM memory modules, ferro-electric memory arrangements, what are referred to as FRAMs, will also play an important art in the future. Compared to traditional memory arrangements such as, for example, DRAMs and SRAMs, ferro-electric memory arrangements have the advantage that the stored information is not lost but remains stored even given an interruption of the voltage supply or, respectively, the power supply. This non-volatility of the ferro-electric memory arrangements is based on the fact that the polarization impressed by an external electrical field in the ferro-electric materials is also essentially retained even after the external electrical field is shutoff. The new materials such as lead zirconate titanate (PZT), (Pb (Zr, Ti)O
3
) or, respectively, lanthanum-doped lead zirconate titanate or strontium bismuth tantalate (SBT), (SrBi
2
Ta
2
O
9
) are also utilized for the ferro-electric memory arrangements.
Unfortunately, the employment of the new para-electrics or, respectively, the ferro-electrics requires the employment of new electrode materials and barrier materials. The new para-electrics or, respectively, ferro-electrics are usually deposited on electrodes (lower electrode) that are already present. The processing ensues under high temperatures at which the materials which normally make up the capacitor electrodes, thus, for example, doped polysilicon, are easily oxidized and lose their electrically conductive properties, which would lead to the failure of the memory cell.
Due to their good oxidation resistance and/or the formation of electrically conductive oxides, 4d and 5d transition metals, particularly platinum metals such as Ru, Rh, Pd, Os, Pt and, particularly, Ir or, respectively, IrO
2
, are considered promising candidates that could replace the doped silicon/polysilicon as electrode material and barrier material.
Unfortunately, the aforementioned electrode and barrier materials, which are newly utilized in integrated circuits belong to a class of materials that are extremely difficult to structure. Due to their chemically inert nature, they are very difficult to etch, so that the etching erosion, even given the employment of “reactive” gases, is based mainly or almost exclusively on the physical part of the etching. For example, iridium was previously usually structured with a dry-etching process. A significant disadvantage of this process is the lack of selectivity of the method which is caused by the high physical part of the etching. This results therein that only a slight trueness to dimension of the structures can be assured due to the erosion of the masks, which have unavoidably inclined sidewalls. Over and above this, undesired re-depositions on the substrate, on the mask or in the unit employed will occur.
Over and above this, these materials also prove extremely resistant given the employment of what are referred to as CMP processes (chemical mechanical polishing).
In typical CMP processes, a semiconductor wafer whose surface is to be polished is applied on a wafer carrier and is pressed by this onto an elastic, perforated support (polishing pad) that is attached on a polishing table. The semiconductor wafer and the polishing table and, thus, the polishing support thereby rotate in opposite direction. The polishing support contains a polishing agent (slurry) that also contains active chemical additives in addition to polishing bodies.
CMP standard methods for planarization and structuring of metal surfaces exist, for example, for tungsten and copper as well as for the materials employed as barrier layer such as Ti, TiN, Ta and TaN. The CMP processes for planarization of polysilicon, silicon oxide and silicon nitride are also in the prior art.
Such methods are disclosed, for example, in U.S. Pat. Nos. 5,527,423, 5,976,928 and 5,863,838. 5,783,489 discloses a method for eroding layers of titanium, titanium nitride and aluminum alloys. In this method, polishing agents are utilized that, in addition to containing water, contain an abrasive, for example aluminum oxide, two different oxidation agents, including, among other things, peroxide disulfate (ammonium per sulfate) and hydrogen peroxide, and a stabilizer such as, for example, various phosphone acid derivatives.
The polishing fluids employed in these methods, however, are not considered suitable for the erosion of precious metal layers due to the chemical inertness and difficult oxidizability of the precious metals and their oxides such as Pt, Ir or IrO
2
. Methods for chemical-mechanical polishing of layers composed of metals from the group of the platinum metals, particularly iridium, have thus not yet been disclosed.
SUMMARY OF THE INVENTION
The present invention is therefore based on the object of offering a method for chemical-mechanical polishing with which layers of metals from the group of platinum metals, particularly iridium, can be polished or, respectively, eroded and/or structured and that assures an adequately high erosion rate.
This object is achieved by a method for chemical-mechanical polishing of layers composed of metals from the platinum metals, particularly iridium with a polishing fluid. Further, a method for planarizing and/or structuring layers composed of metals from the platinum metals, particularly iridium is also disclosed. Further advantageous embodiments, developments and aspects of the present invention will be apparent from the claims, from the specification and from the attached drawings.
Inventively, a method is offered for chemical-mechanical polishing of layers composed of metals from the group of platinum metals, particularly iridium, that comprises the following steps: preparing a layer of a metal of the platinum group; preparing a polishing fluid that contains 1 through 6% by weight abrasive particles; contains 2 through 20% by weight of at least one oxidation agent that is selected from the group consisting of Ce(IV) salts, salts of chloric acid, salts of peroxodisulfuric acid and hydrogen peroxide as well as the salts of hydrogen peroxide;
Beitel Gerhard
Mainka Gerd
Saenger Annette
Schnabel Rainer Florian
Hail III Joseph J.
Infineon - Technologies AG
Ojini Anthony
Schiff & Hardin LLP
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