Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
1999-04-19
2001-02-13
Lee, Eddie C. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S750000, C257S758000, C257S760000, C257S761000, C257S762000, C257S774000, C257S775000
Reexamination Certificate
active
06188135
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to the general field of integrated circuits, more particularly to the design and use of copper interconnections therein.
(2) Description of the Prior Art
As wire widths in integrated circuits continue to shrink, the electrical conductivity of the wiring material itself becomes increasingly more important. Thus, in this regard, aluminum, which has been the material of choice since the integrated circuit art began, is becoming less attractive than other better conductors such as copper, gold, and silver. These materials, in addition to their superior electrical conductivity, are also more resistant than aluminum to electromigration, a quality that grows in importance as wire widths decrease.
The metals in question have not been widely used for wiring as yet because they also suffer from a number of disadvantages, including formation of undesirable intermetallic alloys and/or recombination centers in other parts of the integrated circuit and they often have high diffusion rates. Copper has the additional disadvantage of being readily oxidized at relatively low temperatures. Nevertheless, copper is seen as an attractive replacement for aluminum because of its low cost and ease of processing so that the prior and current art has tended to concentrate on finding ways to overcome these limitations.
A particular problem related to copper's high susceptibility to oxidation is that conventional photoresist processing cannot be used when the copper is to be patterned into various wire shapes because the photoresist needs to be removed at the end of the process by heating it in a highly oxidizing environment, such as an oxygen plasma, thereby converting it to an easily removed ash.
Several solutions to the above problems associated with copper processing have been proposed in the prior art. Hoshino (U.S. Pat. No. 4,910,169 March 1990) teaches the use of low temperature deposition techniques, such as RF sputtering, for coating copper layers with materials such as silicon oxide, silicon nitride, and phosphosilicate glass. It should be noted that the materials mentioned were for the purpose of forming inter-metal dielectric layers rather than for use as barrier layers, implying that they were relatively thick.
Li et al. (U.S. Pat. No. 5,447,599 September 1995) use TiN(O) as a barrier layer material for copper. The copper is initially coated with a layer of titanium and a copper-titanium alloy is formed by heating at 3-400° C. Unreacted titanium is then removed and the alloy is transformed to TiN(O) by means of a rapid thermal anneal in ammonia and oxygen.
Nakasaki (U.S. Pat. No. 5,084,412 January 1992) underlays the copper layer with a metallic nitride and then heats the combination in nitrogen to bring about grain boundary diffusion of the nitrogen into the copper. This results in a material having relatively low electrical resistivity together with good resistance to electromigration.
Tokunaga et al. (U.S. Pat. No. 4,931,410 June 1990) use photoresist for shaping their copper but first protect it with an anti-oxidizing layer. Etching is then performed in two steps—first the anti-oxidizing layer is etched in conventional fashion, including photoresist removal, following which said anti-oxidizing layer is used as the mask for the etching of the copper.
Filipiak et al. (U.S. Pat. No. 5,447,887 September 1995) use an intermediate layer of copper silicide to improve the adhesion between a copper layer and a silicon nitride layer.
It should be noted that none of the above-cited examples of the prior art is based on a damascene process nor do they incorporate more than a single barrier layer in their structures or processes. The term ‘damascene’ is derived from a form of inlaid metal jewelery first seen in the city of Damascus. In the context of integrated circuits it implies a patterned layer imbedded on and in another layer such that the top surfaces of the two layers are coplanar.
SUMMARY OF THE INVENTION
It has been an object of the present invention to provide a copper connector in an integrated circuit.
A further object of the present invention has been to provide means for preventing the outdiffusion of copper from said connector into adjoining layers.
Yet another object of the present invention has been to provide a method for manufacturing said copper connector that does not expose the copper to the possibility of being oxidized during processing.
A still further object of the present invention has been to provide a method for manufacturing said copper connector without having a layer of photoresist in contact with the copper at any time.
These objects have been achieved by providing a damascene copper connector whose upper surface is coplanar with the upper surface of the insulating layer in which it is embedded. Out-diffusion of copper from the connector is prevented by two barrier layers. One is located at the interface between the connector and the insulating layer while the second barrier is an insulating layer which covers the upper surface of the connector. The damascene process involves filling a trench in the surface of the insulator with copper and then removing the excess by chem.-mech. polishing. Since photoresist is never in direct contact with the copper the problem of copper oxidation during resist ashing has been effectively eliminated.
REFERENCES:
patent: 4910169 (1990-03-01), Hoshino
patent: 4931410 (1990-06-01), Tokunago et al.
patent: 5084412 (1992-01-01), Nakasaki
patent: 5447599 (1995-09-01), Li et al.
patent: 5447887 (1995-09-01), Filipiak et al.
patent: 5612254 (1997-03-01), Mu et al.
patent: 5900672 (1999-05-01), Chan et al.
Chan Lap
Zheng Jia Zhen
Chartered Semiconductor Manufacturing Company
Clark Jhihan B.
Jones II Graham S.
Lee Eddie C.
Pike Rosemary L. S.
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