Removal of dielectric oxides

Details Removal of dielectric oxides Removal of dielectric oxides

1998-08-13

2001-03-13

Zarabian, Amir (Department: 2824)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S625000, C438S637000, C438S743000

Reexamination Certificate

active

06200891

ABSTRACT:

TECHNICAL FIELD
The present invention is concerned with removing silicon oxide from a substrate and particularly selectively removing interlevel dielectric such as silicon oxide without attacking metal also exposed to the composition used for removing the silicon oxide.
BACKGROUND
In the fabrication of microelectronic components, a number of the steps involved, for instance, in preparing integrated circuit chips and the packaging for the chips (articles to which the chips are attached for electrical interfacing and/or protection), are etching processes. Accordingly, over the years, a number of vastly different types of etching processes to remove material, sometimes in selective areas, have been developed and are utilized to varying degrees. Moreover, the steps of etching different layers which constitute, for instance, the finished integrated circuit chip are among the most critical and crucial steps.
Silicon oxide layers such as those formed by reacting tetraethylorthosilicate (TEOS) and oxygen or ozone have been used as insulators especially where gap-filling considerations (i.e. filling gaps between pre-existing structures) are important. Such silicon oxide layers are often used in so-called interlevel dielectric (ILD) between metal interconnects of aluminum/copper or tungsten typically for back end of the line (BEOL) wiring. A general discussion of interlevel dielectrics can be found in “Fundamentals of Semiconductor Processing Technology” by ElKareh, Kluwer Academic Publishers, (1995), pages 565-571, which discussion is incorporated herein by reference. Moreover, silicon oxide layers and other insulators obtained by other processes may likewise be used as interlevel dielectrics. For example, other widely used materials for such purposes are boron and/or phosphorous doped silicate glasses.
In a formation of a conventional ILD oxide structure, a first layer of interlevel dielectric such as silicon oxide may be deposited on a surface having raised metal features (e.g., metal lines) by chemical vapor deposition (CVD) with the silicon oxide filling the gaps between the metal lines. This CVD step typically results in the formation of undesired voids between in the deposited oxide between the metal features. The silicon oxide over the horizontal (top) surfaces of the metal lines may then be removed by an anisotropic etch (e.g., sputter etching) to open the voids. The structure at this point typically has silicon oxide left in spaces between lines and as spacers on the sidewalls of the metal lines. A second layer of an insulator such as silicon oxide can then be deposited to fill the voids and complete the interlevel dielectric structure between different metallic layers.
In some instances, it may be desirable to replace certain components of an interlevel dielectric structure with alternative dielectric materials to modify the dielectric function of the ILD (e.g., by substituting a lower dielectric constant material) and/or to facilitate some other processing step or device construction. For example, the removal of oxide dielectric might be desired in order to form air bridge, air gap or other very low dielectric constant configurations. See for example, the formation of structures discussed in U.S. Pat. Nos. 4,985,990; 4,987,101; 5,308,440; 5,407,860; and 5,461,003, the disclosures of which are incorporated herein by reference.
The ability to economically and reliably form these various dielectric structures often depends on the ability to selectively remove silicon oxides especially where pre-exposed metal features are present or where metal features are to be exposed by the desired oxide removal. Thus, it is desired to obtain improved oxide removal processes which have improved performance capability and reliability. In addition to improving the manufacture of existing device structures, such improved processes would enable the commercial manufacture of structures which may not be practical using known techniques. The need for improved oxide removal processes increases with reduction in size of the metal features in the integrated circuit design.
SUMMARY OF INVENTION
The invention provides improved methods for selective removal of oxides, especially for removal of silicon oxides where pre-exposed metal (or conductive metal-containing) features are present, where metal (or conductive metal-containing) features are to be exposed by the desired oxide removal, or where the silicon oxide otherwise contacts metal (or conductive metal-containing) features. The methods of the present invention are especially useful for removing interlevel dielectric (ILD) oxides, also referred to as BEOL insulator.
In one aspect, the invention encompasses processes for the removal of dielectric oxides wherein the processes comprise contacting an article that contains metal (or conductive metal-containing) features and exposed dielectric oxide with a liquid composition that preferably contains about 0.5 to about 15.0 molar of a fluoride-containing compound and an organic solvent to thereby selectively remove the dielectric oxide.
The organic solvents employed in the present invention preferably have relatively high flash point and provide low viscosity compositions. The more preferred solvents are propylene carbonate, N-methylpyrrolidone and gamma butyrolactone, ethylene glycol and propylene glycol with propylene carbonate being the most preferred. HF is a preferred fluoride-containing compound.
The processes of the invention are especially useful for removing oxides commonly used in the construction of interlevel dielectric structures.
Other objects 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.
BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION
The invention provides improved methods for selective removal of oxides, especially for removal of silicon oxides where pre-exposed metal (or conductive metal-containing) features are present, where metal (or conductive metal-containing) features are to be exposed by the desired oxide removal, or where the silicon oxide otherwise contacts metal (or conductive metal-containing) features (e.g., if partial oxide removal over a covered metal feature is desired).
The methods of invention are especially useful for selectively removing interlevel dielectric oxides without substantial etching of metal or conductive metal-containing features. The dielectric oxide is preferably a silicon oxide (e.g., SiO
2
) and/or a silicate containing one or more elements selected from groups 3A (e.g. boron) and 5A (e.g. phosphorus or arsenic). The interlevel dielectric may be adjacent to metal or metal-containing features formed from various materials such as copper, copper alloy, titanium, titanium nitride, tantalum, tantalum nitride, aluminum and/or aluminum alloy. The methods of the invention may involve contacting both the dielectric oxide and the metal or metal-containing features with the etching composition.
The liquid compositions employed pursuant to the present invention are preferably essentially non-aqueous and contain a fluoride-containing compound and an organic solvent. The amount of the fluoride-containing compound in the composition is preferably about 0.5 to about 15 molar, more preferably about 2 to about 10 molar, most preferably about 5 to about 7 molar. The molarities indicated above are based on the total volume of the liquid composition.
The fluoride-containing compound may be any compound capable of providing fluorine ion activity for removal of the oxide. Preferably, the fluoride-containing compound is

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