Patent Application
20050118796
The present invention relates to a process for forming an electrically conductive metallic interconnect in a via in a dielectric. More particularly, the present relates to reducing field induced metal contamination of the dielectric and/or leakage failure of the metallic interconnect. The present invention is of especial significance when the dielectric is a low-k dielectric.
Copper is presently the preferred material choice for forming interconnects in integrated circuits. Copper replaced aluminum and AlCu alloys due to lower resistance and better resilience to electromigration. The advantage of copper metallization has been recognized by the entire semiconductor industry. Copper metallization has been the subject of extensive research documented by two entire issues of the Materials Research Society (MRS) Bulletin. One dedicated to academic research on the subject is MRS Bulletin, Vol. XVIII, No. 6 (June 1993) and the other dedicated to industrial research in MRS Bulletin, Vol. XIX, No. 8 (August 1994). A 1993 paper by Luther et al, “Planar Copper-Polyamide Back End of the Line Interconnection for ULSI Devices:, in Proc. IEEE VLSI Multitevel Interconnection Conference, Santa Clara, Calif., June 8-9, 1993, p. 15, describes the fabrication of copper chip interconnections with four levels of metallization.
However, since copper has a tendency when used in interconnect metallurgy to diffuse into surrounding dielectric materials such as silicon dioxide, encapsulation of the copper is essential. The encapsulation inhibits hiss diffusion. One widely suggested method of lining includes employing a conductive barrier layer along the sidewalls and bottom surface of a copper interconnect. Typical of such barrier layers are tantalurn, titanium, tungsten, and nitrides thereof. In many devices, multiple layers of different barrier materials are employed such as a combination of tantalum and tantalum nitride as described in U.S. Pat. No. 6,291,885 to Cabral et al, disclosure of which is incorporated herein by reference. Capping of the upper surface of a copper interconnect usually employs silicon nitride.
The tantalum employed is typically an alpha-phase tantalum layer, which besides acting as a barrier, also acts as a redundant current carrier layer to assist the main conductor copper in current distribution.
One technique employed to provide these structures involves a sacrificial liner process. This sacrificial liner process comprises first etching the via/trench and liner patterns in a low-k dielectric material into which a Cu dual damascene structure will be processed to connect to the previous line in the layer below. Next an adhesive liner layer such as TaN is deposited, followed by an etch such as an argon sputter etch to remove, for instance, the TaN at the bottom of the via and the top layer of the metal line in the metallization layer such as a copper line to form a clean contact. This is typically followed by a barrier layer such as tantalum layer being deposited, for instance, in an HCM magnetron sputter system. The barrier layer, e.g.-tantalum, is then subsequently sputter etched from the bottom of the via to leave the barrier layer remaining on the sidewalls of the trench/via or lines.
However, at the same time the Ar etch removes the TaN from the bottom of the line, or trench, it tends to pattern into the dielectric. When the Ta is subsequently deposited and sputter etched the bottom of the trenches are poorly covered such that the Cu that is later deposited is able to escape through the defected liner into the dielectric causing failure.
The present invention relates to a process that makes it possible to reduce field induced metal contamination of dielectric by metallic interconnect in a via and/or leakage failure of the metallic interconnect. The present invention relates to a process for forming an electrically conductive metallic interconnect in a via in a dielectric.
The process comprises:
Another aspect of the present invention relates an electrically conductive metallic interconnect structure obtained by the above disclosed process.
A still further aspect of the present invention relates to an electrically conductive metallic interconnect in a via or trench in a via or trench in a dielectric which comprises:
Other objectives and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.
In order to facilitate an understanding of the present invention, reference is made to the figures.
According to the present invention dielectric layers 10 and 16 are provided on a semiconductive substrate 8 such as silicon, silicon-germanium alloys, and silicon carbide or gallium arsenide. The dielectric layer 10 contains electrically conductive lines 12 and can contain a barrier or liner 14 on the bottom and sidewalls the conductive lines 12. Also, typically a capping layer 30 such as silicon nitride is provided on the conductive lines 12. See
Typical conductive lines 12 are Cu, Al, and alloys thereof, and more typically Cu and Cu alloys. Liner materials 14 typically are Ta, W, Ti and nitrides thereof. A plurality of layers of different liner materials 14 can be employed, if desired.
A trench or via 18 is formed in dielectric 16 such as by etching, an example of which being reactive ion etching. The electrically conductive line 12 is also exposed by the etching. See
Next an adhesion liner layer 20 can optionally be deposited on the walls and bottom of the trench or via 18. See
The layer 20 can be etched back in order to thicken the sidewalls of the trench 18. See
Residual contamination is removed from the bottom of the trench or via 18 by sputter etching such as employing argon sputter etching. See
A liner layer 22 is deposited such as by employing an HCM(Hollow Cathode Magnetron) magnetron sputter system, such as available from Applied Materials under the trade designation “Endura”. See
Typically, the sputter apparatus use a DC magnetron source configuration and use as the source of tantalum, tantalum having a purity of about 99.9% or greater. In carrying out the process, an inert gas such as argon at a flow rate of about 50 to about 130 standard cubic centimeters per minute (sccm) is injected into the process cavity which contains the target along with the wafer upon which the tantalum is to be deposited. The process cavity prior to injection of the inert gas was previously evacuated to a vacuum level of at least 1.0.×10 E6 torr using for example a cryogenic pump. Simultaneous to flowing the inert sputter gas, an additional gas flow of nitrogen is also begun at a flow rate of 20 to about 60 standard cubic centimeters per minute. The process cavity is filled with both gases to achieve an effective pressure of about 1 to about 10 million. The power typically employed to create a plasma for the purposes of the present invention is between about 0.4 and about 4.8 watts/square cm, and preferably about 1.6 to about 2.4 watts/square cm. Any combination of target voltage and current to achieve this power level can be employed. The material deposited is the highly oriented alpha-phase tantalum material of the present innovation. The deposition rate is typically about 1000 to about 2000 Å per minute and more typically about 1200 to about 1500 Å per minute.
Residual contamination is next removed from the bottom of the trench or via 18 by sputter etching such as employing argon sputter etching. See
This sputter cleaning also results in removing liner 22 from the bottom of the via or trench 18 and sputtering of conductive material from conductive line 12.
According to the present invention, a second liner layer 24 is deposited on the walls and bottom of the trench or via 18. See
The process of the present invention makes it possible to provide a pure metal contact at the bottom of the via/trench or a Ta/Cu contact which is mechanically robust and tenaciously bonded. The process of the present invention also provides for a good diffusion barrier between the electrically conductive lives such as copper and the dielectric. In addition, the present invention makes it possible to have a liner on the sidewalls that differs from the liner at the bottom of the trench or via.
A comparison of
The structure can then be completed following processing known in the art. For instance, a copper seed layer can be deposited, followed by depositing copper to file the trench or via and then planarizing such as using chemical-mechanical processing (CMP).
All publications and patent applications cited in this specification are herein incorporated by reference, and for any and all purposes, as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference.
The foregoing description of the invention illustrates and describes the present invention. Additionally, the disclosure shows and describes only the preferred embodiments of the invention but, as mentioned above, it is to be understood that the invention is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the invention concept as expressed herein, commensurate with the above teachings and/or e skill or knowledge of the relevant art. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with the various modifications required by the particular applications or uses of the invention. Accordingly, the description is not intended to limit the invention to the form disclosed herein. Also, it is intended tat the appended claims be construed to include alternative embodiments.
