Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2001-05-11
2004-05-18
Thornton, Yvette C. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S286100, C430S322000, C430S326000, C430S905000, C430S910000, C526S297000, C526S342000
Reexamination Certificate
active
06737215
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a novel photoresist composition that is particularly useful in the field of microlithography, and especially useful for imaging negative and positive patterns in the production of semiconductor devices. The photoresist composition comprises a novel copolymer and a photoactive component, where the copolymer comprises a unit derived from an ethylenically unsaturated compound containing at least one cyano functionality and a unit derived from an unsaturated cyclic non aromatic compound. The polymer of the novel photoresist has high transparency in the deep ultraviolet (uv) region, and such a composition is especially useful for exposure at 193 nanometers (nm) and 157 nm. The invention further relates to a process for imaging the novel photoresist.
BACKGROUND OF INVENTION
Photoresist compositions are 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, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The photoresist coated on the substrate is next subjected to an image-wise exposure to radiation.
The 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. The trend towards the miniaturization of semiconductor devices has led to the use of new photoresists that are sensitive at lower and lower wavelengths of radiation and has also led to the use of sophisticated multilevel systems to overcome difficulties associated with such miniaturization.
There are two types of photoresist compositions, negative-working and positive-working. The type of photoresist used at a particular point in lithographic processing is determined by the design of the semiconductor device. 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 surface is uncovered.
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. In many leading edge manufacturing applications today, photoresist resolution on the order of less than one-half micron are necessary. In addition, it is almost always desirable that the developed photoresist wall profiles be near vertical relative to the substrate. Such demarcations between developed and undeveloped areas of the resist coating translate into accurate pattern transfer of the mask image onto the substrate. This becomes even more critical as the push toward miniaturization reduces the critical dimensions on the devices.
Photoresists sensitive to short wavelengths, between about 100 nm and about 300 nm are often used where subhalfmicron geometries are required. Particularly preferred are photoresists comprising non-aromatic polymers, a photoacid generator, optionally a dissolution inhibitor, and solvent.
High resolution, chemically amplified, deep ultraviolet (100-300 nm) positive and negative tone photoresists are available for patterning images with less than quarter micron geometries. To date, there are three major deep ultraviolet (uv) exposure technologies that have provided significant advancement in miniaturization, and these use lasers that emit radiation at 248 nm, 193 nm and 157 nm. Photoresists for 248 nm have typically been based on substituted polyhydroxystyrene and its copolymers, such as those described in U.S. Pat. No. 4,491,628 and U.S. Pat. No. 5,350,660. On the other hand, photoresists for 193 nm exposure require non-aromatic polymers, since aromatics are opaque at this wavelength. U.S. Pat. No. 5,843,624 and GB 2320718 disclose photoresists useful for 193 nm exposure. Generally, polymers containing alicyclic hydrocarbons are used for photoresists for exposure below 200 nm. Alicyclic hydrocarbons are incorporated into the polymer for many reasons, primarily since they have relatively high carbon:hydrogen ratios which improve etch resistance, they also provide transparency at low wavelengths and they have relatively high glass transition temperatures. U.S. Pat. No. 5,843,624 discloses polymers for photoresist that are obtained by free radical polymerization of maleic anhydride and unsaturated cyclic monomers, but the presence of maleic anhydride makes these polymers insufficiently transparent at 157 nm. Until now photoresists sensitive at 157 nm have been based on fluorinated polymers, which are known to be substantially transparent at that wavelength. Photoresists derived from polymers containing fluorinated groups are described in WO 00/67072 and WO 00/17712. However, the polymerization of unsaturated fluorinated monomers, such as tetrafluoroethylene, presents severe explosion hazards and a great deal of care needs to be exercised during the polymerization process. Polymerization processes that are environmentally safer are preferred.
The inventors of this application have found that polymers containing cyano groups are transparent at wavelengths below 200 nm. Polymers derived from certain monomers containing cyano functionality are known. U.S. Pat. No. 6,165,674 discloses polymers derived from itaconic anhydride, acrylates with a cyano group and acrylate with a pendant alicyclic group. U.S. Pat. No. 5,399,647 discloses a copolymer of 1-(1′-cyanoethynyl)adamantane and methacrylates or 2-norbornene-2-carbonitrile and methacrylates. The reaction scheme to introduce the cyano group into the unsaturated bond of an alicyclic compound, in order to synthesize 2-norbornene-2-carbonitrile, is difficult and undesirable. Therefore, there is a need for a monomer which can easily copolymerize with cyclic olefins, and yield a polymer which possesses good plasma etch resistance. There is also a need for a monomer that can be made using simple techniques such as Diels Alder reactions of cyclopentadiene and olefins. Polymers based only on unsaturated cyclic monomers that are resistant to plasma etching are also known but they require transition metal catalysts, which are undesirable due to the high likelyhood of metal contamination of the semiconductor device. U.S. Pat. No. 4,812,546 discloses an acrylate rubber (terpolymer) of n-butyl acrylate, methyl cyanoacrylate and ethylidene norbornene, where ethylidene norbornene creates a crosslinkable sites for vulcanization. Such crosslinked copolymers are
Dammel Ralph R.
Sakamuri Raj
Clariant Finance (BVI) Ltd
Jain Sangya
Thornton Yvette C.
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