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
2001-11-07
2004-04-20
Ashton, Rosemary (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
C430S296000, C430S905000
Reexamination Certificate
active
06723488
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a novel photoresist composition that does not undergo photoresist image deterioration in the presence of electrons or ions, particularly when viewed in a scanning electron microscope or exposed to electron beams during curing.
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 to 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. 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 deprotection 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.
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. In many manufacturing applications today, resist resolution on the order of less than one 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 can also be used where subhalfmicron geometries are required. Particularly preferred for exposure below 200 nm are photoresists comprising non-aromatic polymers, a photoacid generator, optionally a solubility 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. Examples of such photoresists are given in the following patents and incorporated herein by reference, U.S. Pat. Nos. 4,491,628, 5,350,660, 5,843,624, GB 2320718, WO 00/17712 and WO 00/67072. Photoresists for 248 nm exposure have typically used substituted polyhydroxystyrene and its copolymers. On the other hand, photoresists for exposure at wavelengths below 200 nm require non-aromatic polymers, since aromatics are opaque at this wavelength. Generally, alicyclic hydrocarbons are incorporated into the polymer to replace the etch resistance of the aromatic functionality. Photoresists that have been designed for use below 200 nm have so far used polymers with the alicyclic compounds (olefins) incorporated in the polymer backbone or acrylate polymers with pendant alicyclic functionalities. Photoresists sensitive at 157 nm may use fluorinated polymers, which are substantially transparent at that wavelength.
It has been found that certain types of photoresists, especially those developed for imaging below 200 nm and lacking aromatic functionality, when viewed in a scanning electron microscope during inspection of the dimension of the imaged photoresist, or exposed to electron or ion beams during curing, undergo undesirable changes in the dimensions of the photoresist image. One aspect of this particular image distortion, generally referred to as linewidth slimming (LWS), is observed as slimming of lines or expansion of holes and trenches. Oftentimes the measurement of the imaged photoresist features takes significant amount of time; during this time the image dimensions can change and result in erroneous measurements. This effect of electrons and ions on changes of the photoresist linewidth has become a critical issue as the printed dimensions have become smaller. Photoresists based on acrylate polymers have been found to be more susceptible to linewidth slimming compared to photoresists derived from cycloolefin based photoresists,.
While the cause of LWS is not clearly understood, and wishing not to be bound by the theory, those skilled in the art believe that several mechanisms are possible when photoresists, especially those designed for imaging below 200 nm, are treated with electrons or ions. Some of the possible mechanisms are crosslinking of the polymer, thermal annealing, decomposition, evaporation of components in the photoresist film, chain scission of the polymer, sputtering, etc. In the past equipment modifications or process changes have helped to improve LWS. The present application has addressed the problem by the incorporation of additives into the photoresist, hence avoiding additional equipment and processing costs. It has been found that additives that inhibit some of the mechanisms discussed previously improve the degradation of the image profile. Monomeric additives that have aromatic functionality, free radical quenchers, and crosslinking agents have found to be especially effective. The object of the present invention is to reduce the effect of electrons and ions on photoresists useful for imaging below 200 nm by the incorporation of monomeric additives into the photoresist.
SUMMARY
The present invention relates to a photoresist composition sensitive to radiation in the deep ultraviolet, where the photoresist composition comprises a) a polymer that is insoluble in an aqueous alkaline solution and comprises at least one acid labile group, and furthermore where the polymer is essentially non-phenolic, b) a compound capable of producing an acid upon radiation
Dammel Ralph R.
Kudo Takanori
Padmanaban Munirathna
Ashton Rosemary
Clariant Finance (BVI) Ltd
Jain Sangya
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