Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-11-28
2004-03-16
La Villa, Michael (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S674000, C428S673000, C428S627000, C428S336000, C427S437000, C427S438000, C174S126400
Reexamination Certificate
active
06706422
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electroless Ni—B plating liquid, an electronic device and a method for manufacturing the same. More particularly, this invention relates to an electroless Ni—B plating liquid useful for forming a protective film for protecting the surface of the interconnects of an electronic device which has such an embedded interconnect structure that an electric conductor, such as silver or copper, is embedded in fine recesses for interconnects formed in the surface of a substrate such as a semiconductor substrate, and to an electronic device having the interconnects-protecting film formed by using the plating liquid, and a method for manufacturing the same.
2. Description of the Related Art
As a process for forming interconnects in an electronic device, the so-called “damascene process” which comprises filling trenches for interconnects and contact holes with a metal (electric conductor), is coming into practical use. According to this process, aluminum or, more recently a metal such as silver or copper, is filled into trenches for interconnects and contact holes previously formed in the interlevel dielectric of a semiconductor substrate. Thereafter, an extra metal is removed by chemical mechanical polishing (CMP) so as to flatten the surface of the substrate.
In the case of interconnects formed by such a process, the embedded interconnects have an exposed surface after the flattening processing. When an additional embedded interconnect structure is formed on such an exposed surface of the interconnects of a semiconductor substrate, the following problems may be encountered. For example, during the formation of a new SiO
2
in the next interlevel dielectric forming process, the exposed surface of the pre-formed interconnects is likely to be oxidized. Further, upon etching of the SiO
2
film for formation of via holes, the pre-formed interconnects exposed on the bottoms of the via holes can be contaminated with an etchant, a peeled resist, etc.
In order to avoid such problems, it has conventionally been performed to form a protective film of SiN or the like not only on the interconnect region of a semiconductor substrate where the interconnects are exposed, but on the whole surface of the substrate, thereby preventing the contamination of the exposed interconnects with an etchant, etc.
However, the provision of a protective film of SiN or the like on the whole surface of a semiconductor substrate, in an electronic device having an embedded interconnect structure, increases the dielectric constant of the interlevel dielectric, thus inducing delayed interconnection even when a low-resistance material such as silver or copper is employed as an interconnect material, whereby the performance of the electronic device may be impaired.
In views of this, it may be considered to selectively cover the surface of the exposed interconnects with a Ni—B alloy film having a good adhesion to an interconnect material such as silver or copper and having a low resistivity (&rgr;). A plated Ni—B film, obtained by electroless Ni—B plating, is either a crystalline or an amorphous plated film depending on the boron content of the film. In this regard, a crystalline plated film is obtained when the boron content of the film is less than 10 at % (atomic %), and an amorphous plated film is obtained when the boron content of the film is 10 at % or more, generally.
When a plated Ni—B film is used for the purpose of protecting the interconnects of an electronic device having an embedded interconnect structure, the plated film is required to be thermally stable. From this point of view, it is necessary to use a crystalline plated film having a boron content of less than 10 at %. This is because a crystalline plated Ni—B film maintains its crystallinity after a heat treatment, whereas an amorphous Ni—B plated film forms a Ni—B compound upon the heat treatment and thus becomes an unstable film.
However, when an intended crystalline Ni—B film, for the purpose of protecting the interconnects of an electronic device having an embedded interconnect structure, is formed by electroless plating by using a plating liquid that is formulated to provide a plated film having a lowered boron content, the plating rate is likely to become too high to make a proper control of the process.
In this regard, in electroless plating, the reaction time is equal to the solid-liquid contact time between the plating liquid and an object to be plated. Further, a plated Ni—B film to be used for protecting the interconnects of an electronic device must be as thin as several tens to several hundreds nm. Accordingly, an enhanced plating rate makes the process control more difficult.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above situation in the related art. It is therefore an object of the present invention to provide an electroless Ni—B plating liquid which can lower the boron content of the resulting plated film without increasing the plating rate and form a Ni—B alloy film having an FCC (face centered cubic) crystalline structure, and also to provide an electronic device in which the interconnects are protected with the plated film formed by electroless plating carried out by using the plating liquid, and a method for manufacturing the same.
In order to achieve the above object, the present invention provides an electroless Ni—B plating liquid for forming a Ni—B alloy film on at least part of interconnects of an electronic device having an embedded interconnect structure, the electroless Ni—B plating liquid comprising nickel ions, a complexing agent for the nickel ions, a reducing agent for the nickel ions, and ammoniums (NH
4
+
).
The inclusion of ammonums (NH
4
+
) in the plating liquid can lower the boron content of the plated film to provide a Ni—B alloy film having an FCC crystalline structure, and can also lower the plating rate by ammoniums (NH
4
+
) so as to thereby facilitate the process control. It is considered, in this regard, that an ammonia ion, due to its generally high chelating force, may form a complex with a nickel ion to thereby lower the plating rate.
The reducing agent may be, for example, an alkylamine borane or a hydrogen boride compound. Specific examples of the alkylamine borane include dimethylamine borane, diethylamine borane and trimethylamine borane. NaBH
4
may be mentioned as a specific example of the hydrogen boride compound.
The ammonums may be prepared from e.g. ammonia water.
The pH of the electroless Ni—B plating liquid may be adjusted within the range from 8 to 12. By thus increasing the pH of the plating liquid to 8-12, it becomes possible to lower the boron content of the plated film and form a Ni—B alloy film having an FCC crystalline structure. The pH of the plating liquid is preferably 9-12, more preferably 10-12.
The temperature of the electroless Ni—B plating liquid may be adjusted within the range from 50° C. to 90° C. To raise the liquid temperature to 50° C. or higher promotes the plating reaction, whereas to control the liquid temperature to 90° C. or lower prevents an increase in the boron content of the plated film. The temperature of the plating liquid is preferably adjusted to 55-75° C.
The present invention also provides an electronic device having an embedded interconnect structure of silver, silver alloy, copper or copper alloy, wherein a surface of an interconnect is selectively covered with a protective layer of a Ni—B alloy film.
By thus selectively covering the surface of the interconnects and protecting the interconnects with the protective film of a Ni—B alloy film that has a high adhesion to silver or copper and has a low resistivity (&rgr;), an increase in the dielectric constant of the interlevel dielectric of an electronic device having an embedded interconnect structure can be suppressed. Further, the use as an interconnect material of a low-resistance material, such as a silver or copper, can attain speedup and densification of the electronic device.
Ezawa Hirokazu
Inoue Hiroaki
Matsumoto Moriji
Miyata Masahiro
Nakamura Kenji
Ebara Corporation
La Villa Michael
Wenderoth , Lind & Ponack, L.L.P.
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