Compositions – Etching or brightening compositions – Inorganic acid containing
Patent
1994-12-19
1996-03-05
Dang, Thi
Compositions
Etching or brightening compositions
Inorganic acid containing
252 794, C09K 1300
Patent
active
054964857
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with etching compositions useful in the fabrication of semiconductor devices. More particularly, this invention concerns etching compositions containing an amine surfactant.
Historically, compositions comprising ammonium fluoride, hydrofluoric acid and de-ionised water have been used for etching and cleaning substrates at various process stages during the fabrication of semiconductor devices. As device geometries have decreased, making them more sensitive to process deviation and contamination, it has become essential for etch uniformity to be enhanced and contamination reduced.
It is difficult to define structures below five microns in size using the above wet etching compositions due to their nonuniform etching properties. This problem is related to the physical wetting of the low surface energy substrates used, e.g. photoresists. Mixtures of ammonium fluoride and hydrofluoric acid typically exhibit relatively high surface tension properties of approximately 80-90 dynes/cm at 25.degree. C. (higher concentration ammonium fluoride mixtures exhibit even higher surface tensions). The result of this property is the inability of the mixture to penetrate small geometries and uniformly etch the substrate. For ammonium fluoride and hydrofluoric acid mixtures to be useful for etching small geometries, it is necessary to modify their surface wetting properties.
Semiconductor manufacturers presently utilise two methods to improve surface wetting and etch uniformity. The first involves the use of an acid pre-dip solution comprising a surfactant in de-ionised water. The second involves the direct addition of a surfactant into the acid etch bath.
The pre-dip process, however, results in regular changes of the acid etchant due to carry-over of the pre-dip solution into the etch bath which subsequently causes dilution, resulting in etch variation.
The addition of a surfactant directly to the etch bath also suffers problems related to the solubility of the surfactant in the highly ionic environment exhibited by the ammonium fluoride/hydrofluoric acid mixtures. This is detected as a visual clouding of the etch tank solution caused by the surfactant remaining in suspension. This problem becomes more apparent as the industry moves from stagnant to recirculating-filtration tanks in an effort to reduce particle contamination. The surfactants which are not entirely soluble in the mixtures tend to be removed by the filtering system, resulting in a detrimental increase in the surface tension of the mixtures.
Many attempts to provide stable aqueous solutions of ammonium fluoride, hydrofluoric acid and surfactant have been made. For example, it is disclosed in U.S. Pat. No. 4,517,106 to add a fluoroalkylsulfonate to improve the wetting properties of the acid solutions. U.S. Pat. No. 4,761,245 discloses addition of a nonionic alkylphenol polyglycidol for the same purpose. There are many other examples.
In U.S. Pat. No. 4,795,582, it is disclosed that surfactants selected from the group consisting of aliphatic carboxylic acids and salts thereof, aliphatic amines and aliphatic alcohols may be added to aqueous mixtures of ammonium fluoride and hydrofluoric acid to improve surface wetting. Whilst a number of different compounds, including octylamine, are exemplified in the U.S. patent as being suitable surfactants, no preference is expressed. In a recirculation-filtration tank comprising an aqueous solution of ammonium fluoride, hydrofluoric acid and octylamine surfactant it was noted that a significant build-up of foam occurred, which could have detrimental effects such as staining of the substrate or inhibition of the etch process.
It is an object of the present invention to provide etchant compositions which do not suffer significant foam problems. It is a further object of the present invention to provide etchant compositions which are stable solutions.
In accordance with the present invention, there is provided an aqueous composition for etching and cleaning semiconductor devices comprising at least one
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patent: 3935118 (1976-01-01), Czirr et al.
patent: 4795582 (1989-01-01), Ohmi et al.
patent: 4826565 (1989-05-01), Suzuki et al.
patent: 5277835 (1994-01-01), Ohmi et al.
patent: 5387361 (1995-02-01), Kohara et al.
Dang Thi
Micro-Image Technology Limited
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