1. Field of the Invention
The present invention relates to a dual damascene process. It is particularly related to a method of fabricating a pattern of a via and an interconnective trench with a via-first method, namely by first forming the via so as to connect upper and lower layers with interconnect.
2. Description of the Prior Art
Recently, improvements in performance and function of semiconductor integrated circuits used for electronic information technology devices including mobile phones are well known. The fact that such semiconductor integrated circuit is manufactured with a high-precision semiconductor manufacturing process is also well known. In addition, attention is given to an interconnection structure manufactured with the dual damascene process within the above high-precision semiconductor manufacturing process.
Such dual damascene process is an approach to forming multi-layered interconnection by forming both an interconnective trench, which becomes an upper layer interconnect formed and embedded in an interlayer insulating film, and a via hole, which is used to connect an upper layer interconnect with a lower layer interconnect, and then embedding a metal film in the upper layer interconnect and the lower layer interconnect, simultaneously. There are advantages where semiconductor manufacturing steps may be reduced and manufacturing costs thereof may be greatly reduced in comparison to the process that individually forms a via hole and interconnective trench. Particularly, the via-first method is one dual damascene process that first forms the via hole within the interlayer insulating film, subsequently forming the interconnective trench.
FIG. 1A through FIG. 1D and FIG. 2A through FIG. 2C depict a conventional via-first method. To begin with, as illustrated in FIG. 1A, an interlayer insulating film 117 is formed by successively layering a silicon dioxide film 113, an etch stop film 114, a low-permittivity film 115 and a silicon dioxide film 116 upon a lower layer interconnect 112 formed on an insulating film 111 that is upon a silicon substrate not shown in the drawings with the conventional via-first method.
A via hole 118, which reaches the lower layer interconnect 112, is then opened in the interlayer insulating film 117 with photolithography techniques utilizing a photoresist not shown in the drawings. Next, as illustrated in FIG. 1B, an anti-reflective coating 119 is applied across the entire interlayer insulating film 117 and baked to harden, whereby the anti-reflective coating 119 is embedded in the via hole 118 up to nearly half its depth with the conventional via-first method. Subsequently, as illustrated in FIG. 1C, a chemically amplified positive type resist 121 for patterning is applied. Next, as illustrated in FIG. 1D, the positive type resist 121 is exposed into a predetermined pattern and developed so as to form an interconnective trench resist pattern 121a. Following as in FIG. 2A, an interconnective trench 122 is formed by etching the low-permittivity film 115 and silicon dioxide film 116 upon the etch stop film 114 using the interconnective trench resist pattern 121a. 
Thereafter, upon removal of the anti-reflective coating 119 within the via hole 118 and on the interlayer insulating film 117 as illustrated in FIG. 2B, the silicon dioxide film 116 is etched and removed as in FIG. 2C. Subsequently, a metallic material 123 is embedded in the interconnective trench 122 and via hole 118, and only the metallic material 123 is left therein using chemical mechanical polishing (CMP). The dual damascene structure that is configured from a via 124 and a trench interconnect (upper layer interconnect) 125 is then completed.
However, the following problems arise with the conventional via-first method. Namely, when forming the interconnective trench resist pattern 121a by subjecting the positive type resist 121 to an exposure and a development process as indicated in the procedure of FIG. 1D, development using a developing fluid for the positive type resist 121 that is applied in the deep via hole 118 is not adequately performed, whereby a portion of the resist 121 remains in the via hole 118.
Consequently, forming the interconnective trench 122 by etching the low-permittivity film 115 and silicon dioxide film 116 under these conditions causes etch residue X that is called a crown to generate in the interconnective trench 122 along the remaining resist 121 as in FIG. 2A. This etch residue X cannot be easily eliminated by an organic stripping solution.
Consequently, as in FIG. 2B and FIG. 2C, the metallic material 123 is embedded in the interconnective trench 122 and via hole 118 thereafter, and moreover, the etch residue X remains until the via 124 and trench interconnect 125 are formed. As a result, electrically discontinuous portions or highly electrical highly resistant portions generate between the via 124 and trench interconnect 125, and decline in interconnect yield and reliability occurs.
As causes for such crown generation, the following two points can be given. First, since the vial hole is considerably deep, the resist that has penetrated into the via hole is exposed in a nearly 1 mm defocused state when forming the resist pattern of the interconnect trench through exposure. Accordingly, optical power in this area is extremely low, and a high rate of solution can no longer be obtained during development. As a result, resist remains within the via hole.
Second, density of the low-permittivity interlayer insulating film that is used in multilayered interconnections is typically low, and large amounts of moisture and basic impurities are included in the inner portions thereof. Since they diffuse from the via hole into the resist, a chemically amplified reaction is inhibited. Accordingly, the rate of solution of the resist within the via hole further decreases, and residual resist called poisoning and/or poor resolution occur.
Consequently, according to examination by the inventor, with the dual damascene process of the via-first method, the resist left in the via hole must be eliminated. The via-first method in such light is disclosed in Japanese Patent Application Laid-Open No. 2000-195955 (Reference 1).
In Reference 1, material including a thermally cross-linked compound is proposed as the embedding material for filling in the via hole, whereat the given example uses an alkali soluble resin and positive type resist composite as comparative examples. Since these are embedded in a different procedure than that of the resist used for forming the resist pattern for the interconnect trench, a portion of that resist penetrating into the via hole and remaining therein due to development when forming that resist pattern is unavoidable.
The object of the present invention is to inhibit residual resist in the via hole; and to provide a pattern formation method, which can manufacture a highly reliable dual damascene structure.
A method of fabricating patterns with a dual damascene process of the present invention, including the steps of: opening a via hole in an interlayer insulating film, which covers a lower conductive layer, so as to expose part of the lower conductive layer; embedding a protective film on the base portion of the via hole; embedding a soluble resin, which dissolves in a resist developing fluid under unexposed conditions upon the protective film in the via hole; forming a resist pattern, which has an aperture window in a region including the via hole, by applying a photoresist upon the interlayer insulating film, and subjecting this photoresist to an exposure and a development process; forming an interconnective trench in the surface of the interlayer insulating film utilizing the resist pattern; removing the protective film; and forming a dual damascene structure by embedding a metallic material into the vial hole and interconnective trench.
According to the present invention, by pre-embedding the soluble resin into the via hole, the interconnect trench photoresist will not be filled into the via hole, nor will the resist be left within the via hole when developing the photoresist; furthermore, since the soluble resin within the via hole is dissolved and removed by being subjected to a development process easier than the resist, the resist and resin remaining in the via hole can ultimately be avoided. Accordingly, a highly reliable dual damascene structure may be realized without generation of a crown, which is caused by resist remaining in the via hole.
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