Cleaning and liquid contact with solids – Processes – Oils – grease – tar – or wax removal – by dissolving
Reexamination Certificate
1998-07-10
2002-04-09
Markoff, Alexander (Department: 1746)
Cleaning and liquid contact with solids
Processes
Oils, grease, tar, or wax removal, by dissolving
C134S038000, C134S039000, C510S175000, C510S176000, C510S365000
Reexamination Certificate
active
06368421
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to the field of microelectronics, such as integrated circuits, and more particularly to compositions and methods of removing photoresists or other organic materials from the surfaces of substrates used in the fabrication of integrated circuits. In particular the present invention relates to amine-free stripping compositions comprising solvent and surfactant that can effectively remove photoresist layers or organic materials without corroding the underlying substrate, and methods for removing these materials layers with the novel stripping composition.
Photoresist compositions ate used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of film of a photoresist composition is first applied to a substrate material used for making integrated circuits, where the substrate may be silicon wafers, or silicon wafers with a silicon oxide or a metallic coating. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to radiation.
This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist. Subsequent processing then can be carried out on the substrate, which may include metal deposition, etching of the substrate, doping of the substrate or other processes known in the art. Once this processing is complete the photoresist is removed from the substrate. Traditionally, the photoresist layer is removed by wet chemical processing that attacks the photoresist and strips it from the substrate without corroding or destroying the integrity of the substrate surface.
There are two types of photoresist compositions, negative-working and positive-working. When negative-working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to such a solution. Thus, treatment of an exposed negative-working resist with a developer causes removal of the non-exposed areas, of the photoresist coating and the creation of a negative image in the coating, thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited.
On the other hand, when positive-working photoresist compositions are exposed image-wise to radiation, those areas of the photoresist composition exposed to the radiation become more soluble to the developer solution (e.g. a rearrangement reaction occurs) while those areas not exposed remain relatively insoluble to the developer solution. Thus, treatment of an exposed positive-working photoresist with the developer causes removal of the exposed areas of the coating and the creation of a positive image in the photoresist coating. Again, a desired portion of the underlying substrate surface is uncovered.
Positive working photoresist compositions are currently favored over negative working resists because the former generally have better resolution capabilities and pattern transfer characteristics. Photoresist resolution is defined as the smallest feature which the resist composition can transfer from the photomask to the substrate with a high degree of image edge acuity after exposure and development.
Positive photoresists comprising alkali-soluble resins and photoactive compounds that are well-known in the art may be used, for example, as discussed in the following patents and incorporated herein by reference, U.S. Pat. No. 4,944,893, U.S. Pat. No. 4,853,315, U.S. Pat. No. 5,501,936, U.S. Pat. No. 5,532,107 and U.S. Pat. No. 5,541,033.
Stripping compositions known in the prior art contain compounds that make the composition difficult and expensive to handle in view of their toxicity, disposal, attack on the substrate, limited bath life, contamination of the processing environment, etc. Traditionally acidic strippers such as those disclosed in U.S. Pat. No. 4,944,893 were used to remove photoresists from silicon or silicon oxide surfaces, but these strippers cannot be used for substrates with metallic coating since acids attack these coatings. Organic strippers containing phenolics and hydrocarbon solvents are described in JP 6,167,813, and can be used for metal substrates but are not desirable due to the high toxicity and disposable cost of the hydrocarbon solvent. Strippers containing chromium trioxide and sulfuric acid also present a disposal difficulty associated with chromium. Stripping compositions containing basic compounds such as amines, alkanolamines, amides or tetramethyl ammonium hydroxide are known and are incorporated herein by reference, U.S. Pat. No. 4,770,713, U.S. Pat. No. 4,824,763, U.S. Pat. No. 4,904,571, U.S. Pat. No. 5,185,235, U.S. Pat. No. 5,279,791, and U.S. Pat. No. 5,545,353. Strippers containing only solvent to remove hard-baked photoresist are known, where the solvent is acetone or N methyl pyrollidone (NMP). Acetone presents a fire hazard and its use is discouraged. NMP strippers or those strippers containing basic compounds, such as amines, ethanolamines, amides or tetramethyl ammonium hydroxide were believed to be essential to effectively remove baked photoresists. However basic components are undesirable in environments where the photoresist is sensitive to environmental contamination, causing neutralization of the acid generated during photolysis and thereby effecting the characteristics of the photoresist. The contamination issue is made worse by the fact that most of these strippers need to be heated to temperatures of around 90° C. for effective stripping of the photoresist, leading to increased evaporation of the stripper components. Chemically amplified photoresists, for example, such as those developed for deep uv exposure are particularly sensitive to basic contamination as disclosed in the publication “Influence of polymer properties in airborne chemical contamination of chemically amplified resists,” W. D. Hinsberg et al, SPIE Vol. 1925, 43-52. Thus there is a demand for effective strippers that are free of acidic and basic components or where such components can be generated.
Therefore a great need has developed for stripper compositions for photoresists, where the stripper compositions are non-corrosive to metallic substrates, are easily disposed of, are of low toxicity, contain no volatile components that are lost on heating and thus reducing the bath life of the stripper, can work with minimal or no heating, are cost effective and preferably contain no basic compounds that can lead to contamination of the photoresists being processed in the fabrication laboratories.
The objective of the present invention is to provide stripper compositions that exhibits substantially little human or environmental toxicity, are water miscible and are biodegradable. It is also the objective of the present invention to provide a stripping composition that is essentially, non-flammable, non-corrosive to metals, has low or no loss of the components during evaporation, and is effective with minimal or no heating. Another object of the present invention is to provide stripper compositions that are free of basic components, such as amines, ammonium hydroxide and hydroxylamines. Yet another objective of the present invention is to provide a stripper that can remove crosslinked photoresist or hardened photoresist without causing corrosion of the metallic substrate.
SUMMARY OF TH
Durham Dana L.
Khanna Dinesh N.
Oberlander Joseph E.
Slezak Mark S.
Spinicelli Lawrence F.
Clariant Finance (BVI) Limited
Jain Sangya
Markoff Alexander
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