The invention relates in general to copper interconnect structure, and more particularly to a copper recess formed in a damascene structure.
Chip manufacturers continually attempt to improve manufacturing processes to achieve higher chip operating speed. As semiconductor process technologies evolve, operating speed has been hindered by an RC delay of a multilevel interconnect. The RC delay is a multiplication of resistance and capacitance of the multilevel interconnect. Copper is among the best choices for use in multilevel interconnect due to its low resistance.
In a conventional copper interconnect process, a dielectric stop layer, such as nitride layer, is deposited after copper CMP (chemical mechanical polishing). The poor interface between copper and the stop layer is a major obstacle to reliability. To improve the interface between copper and the stop layer, metal capping such as W, Co, CoWP and CoWB have been proposed. Such metal capping is often formed by selective growth, thus, it is not easy to control and results in lateral growth of metal capping. The leakage current due to lateral growth of metal capping is of great concern.
Embodiments of the invention provide an interconnect structure. The interconnect structure comprises a damascene structure and a copper conductor in the damascene structure. The damascene structure comprises a via and/or a trench in a dielectric layer. A top surface of the conductor is lower than a top surface of the dielectric layer and a conductor recess is thus formed.
Embodiments of the invention additionally provide another interconnect structure. The interconnect structure comprises a conductor recess in a damascene structure and a conductive cap on the conductor recess without overfilling the conductor recess.
Embodiments of the invention further provide a method for fabricating an interconnect structure. A via/trench is formed in a dielectric layer. The via/trench is subsequently overfilled with copper conductor. Thereafter, a copper removal process is performed to make a top surface of the copper conductor lower than a top surface of the dielectric layer. Thus, a copper recess is formed.
Since the interconnect structure comprises a copper recess, the selective growth of a metal cap in the copper recess can be well controlled. No lateral growth of the metal cap results and thus no short or leakage issues occur.
Embodiments of the invention will become more fully understood from the detailed description given herein below and the accompanying drawings, given by way of illustration only and thus not intended to be limitative of the present invention.
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Subsequently, a chemical mechanical polishing (CMP) process is performed to remove part of copper conductor 50 and smooth the top surface so that the remainder of the copper conductor 50′ is substantially coplanar with the surface of the conductive barrier layer 42 (or the seed layer 44 if one exists) on the dielectric layer 30, as shown in
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The conductor recess 52 can also be formed by a clean process performed after removal of the conductive barrier layer on the dielectric layer 30. The clean process is performed in an acid environment, wherein the acid comprises nitric acid, hypochlorous acid, chromic acid or the like.
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Another embodiment of the invention provides an interconnect structure. As shown in
Furthermore, another embodiment of an interconnect structure according to the invention, as shown in
Since the structure of copper connection comprises a copper recess, the selective growth of a conductive cap on the copper recess can be well controlled. No lateral growth of the conductive cap results and thus no short or leakage issues occur. In a preferred embodiment, an etch stop layer 56 can be formed covering the conductive cap 54 and the dielectric layer 30, as shown in
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.