Choices of metallization is an important parameter that affects the performance of chip interconnects. Ag is one of the potential interconnect materials and has excellent electromigration resistance. However, Ag tends to agglomerate at higher temperatures, and does not adhere too well to dielectrics due to its inert nature when in contact with most materials.
Both applications are incorporated herein by reference. Like the provisional application, the PCT application mainly deals with the thermal stability of Ag Al alloy thin films on SiO 2 in terms of prevention of agglomeration and improvement of adhesion between the metallization and the substrate. The present invention, however, deals with a cladded Ag metallization structure. In accordance with the present invention interconnects for integrated circuits, components and devices of substantially pure Ag are clad in an Ag Al alloy.
Preferably, in an exemplary embodiment, an Ag Al alloy is deposited on a semiconductor oxide layer to a thickness of from about 6 nm to 12 nm, and preferably from about 8 nm to about 10 nm.
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A layer of substantially pure Ag is then deposited on the thin alloy film. A further thin film of the Ag Al is then deposited over the Ag to a thickness of preferably from about 3 nm to about 10 nm and more preferably from about 4 nm to about 6 nm. The alloy in accordance with the preferred exemplary embodiment has Al content in a range from about 0. Put another way, in the preferred embodiment, the layer of alloy deposited on the oxide layer is of a thickness sufficient to create a continuous film separating the Ag from the underlying oxide.
This prevents agglomeration and the alloy film on the oxide is also of a thickness so as to prevent diffusion of the silver into the oxide. The further alloy film deposited over the Ag is of a thickness so as to be a continuous film capable of passivating the Ag upper surface. In the preferred exemplary embodiment the oxide is SiO 2 grown on a Si wafer. The clad structure is intended to alleviate problems of adhesion and agglomeration observed in pure Ag films and is put forth as a replacement for Al and Cu interconnect metallization in the microelectronics industry because of the reasons listed below:.
This invention solves the problems of electromigration and Joule heating-induced early failure of interconnect metallization. It also alleviates problems, viz. For conventional electronics, microelectronics fabrication industries can use this invention. Also fabrication companies which are still using Al as interconnect metallization can switch to the Ag and Ag alloy clad structure proposed here and forgo the difficulties of Cu processing etching, step coverage, CMP. For high temperature electronics, automotive companies are interested in electronics for under the hood applications.
The invention is useful for flexible OLED displays and flexible electronics also. This invention will be useful for interconnect metallization used for conventional microelectronics as well as high temperature applications.
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The Alford group at Arizona State University previously developed a reactive ion etch process for Ag metallization. Nguyen, Y. Zeng, and T. Alford, J. B 19, , incorporated herein by reference.
Mayer, James W. 1930-
The conjunction with these two technologies will also enable smaller fabrication facilities to use current Al etch processes and extend their usefulness by not encumbering the cost of chemical mechanical polishing toolsets associated with copper metallization and the accompanying diffusion barrier technology. Moreover, the low resistivity and good adhesion properties makes this metallization compatible with the Ag contacts used in organic light emitting diodes.
A cross-section of such a structure is shown in FIG. Silver does not adhere well to SiO 2. Kim, and T.
Mayer, James W. [WorldCat Identities]
The alloy thin film on the top of the oxide acts as a cladding layer for the pure Ag and thus reduces surface diffusion and enhances the electromigration resistance of the stack structure. The electromigration behavior of the entire structure is further improved because the Ag alloy encapsulation, being harder due to solution hardening effect, produces compression stress between the Ag alloy-Ag interface thus leading to reduced hillock formation and also since most of the current flows through the Ag layer due to its comparatively lower resistivity.
Thus the Joule heating effect in the clad structure is lower. The present structure, then, is based on the proposition that the use of the Ag Al alloy layers in such a clad structure offsets the need for extra diffusion barrier layers and also improves the overall electromigration behavior of the structure.
The Ag Al alloy should contain Al from about 0. Preferably the percentage of aluminum in the alloy is between greater than about 0. The thickness of the thin alloy film in contact with the SiO2 can range between about 6 nm to about 12 nm, more preferably from about 8 nm to about 10 nm.
A benefit of this construction is that the Ag layer thickness has no criticality and may be of any of a wide range of thicknesses. The final Ag Al alloy layer can have a thickness in the range from about 3 nm to about 10 nm, and more preferably is from about 4 nm to 6 nm thick. Single-line test structures of 3. At this point in the formation of an integrated circuit, the SiO 2 layer would be patterned as is conventional, as indicated at This then was followed by deposition of metal contacts as at The pure Ag and Ag Al alloy metal depositions were also done by known e-beam evaporation technique.
The deposition environment pressure should be as near to null as possible. The failure time of the fabricated single line test structures was determined using a Tektronics Semiconductor Workbench. In order to accelerate the failure of the structures the testing was done at elevated temperatures by placing the samples on a resistance heated hot stage. The test structures were all subjected to a constant current 0. The failure criterion for the test lines was set to be complete open circuit. In case of the clad structure the failure time is nearly 38 times better than pure Ag and almost 7 times better than that of the alloy structure because of the reasons cited in the previous section.
Thus it has been experimentally proven that the cladded Ag and Ag alloy structure shows better adhesion and electromigration resistance compared to pure Ag and can be thus proposed to be used as high temperature interconnect metallization. While one or more specific preferred embodiments have been described application, those skilled in the art will readily recognize modifications, variations and equivalents that do not depart from the spirit and scope of the subject invention, as herein claimed.
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In semiconductor integrated circuit and device fabrication interconnect metallization is accomplished by a clad Ag deposited on a SiO2 level on a Si surface. The alloy improves adhesion to the SiO2, avoids agglomeration of the Ag, reduces or eliminates diffusion at the SiO2 surface, reduces electromigration and presents a passive exterior surface. The clad structure is intended to alleviate problems of adhesion and agglomeration observed in pure Ag films and is put forth as a replacement for Al and Cu interconnect metallization in the microelectronics industry because of the reasons listed below: a Less processing steps in comparison to Cu metallization.
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