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
1999-12-07
2002-04-02
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
C430S326000, C430S914000, C430S921000
Reexamination Certificate
active
06365322
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photoresist composition sensitive to radiation in the deep ultraviolet, particularly a positive working photoresist sensitive in the range of 100-300 nanometers(nm).
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 lead 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 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.
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 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 are 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 and GB 2320718. Photoresists for 248 nm have typically been based on substituted polyhydroxystyrene and its copolymers. On the other hand, photoresists for 193 nm exposure require non-aromatic polymers, since aromatics are opaque at this wavelength. Generally, alicyclic hydrocarbons are incorporated into the polymer to replace the etch resistance lost by not having aromatics present. Photoresists sensitive at 157 nm may use fluorinated polymers, which are substantially transparent at that wavelength.
Chemically amplified resists, in which a single photo generated proton catalytically cleaves several acid labile groups, are used in photolithography applicable to sub quarter-micron design rules. As a result of the catalytic reaction, the sensitivity of the resulting resist is quite high compared to the conventional novolak-diazonaphthoquinone resists. But chemically amplified resists suffer from the so-called delay time effects. Photoresists based on a chemically amplified system comprise a polymer and a photoactive compound. The photoactive compound on exposure decomposes to form an acid. However, it is well known that the acid generated can diffuse from the exposed area to the unexposed area, hence causing a loss in image quality and resolution. Acid diffusion can result in changes in the dimensions of the imaged photoresist and in poor process latitude. Another issue is the loss of photogenerated acid on the surface of the latent image either due to evaporation of the acid or due to the reaction with the clean room amine contaminants. Acid loss on the surface leads to the formation of a severe surface insoluble layer in the exposed regions when there is a time delay between exposure and baking after exposure. Such problems of chemically amplified materials are well documented by several authors, including S. A. MacDonald et al. “Airborne Chemical Contamination of a Chemically Amplified Resist”, in Advances in Resist Technology and Processing, Proceedings of SPIE 1466, 2-12 (1991) and H. Ito, “Deep-UV Resists: Evolution and Status”, Solid State Technology pp164-173, July 1996. For instance, the resist left after exposure in a clean room environment with an ammonia concentration of as low as 10 ppb, develops T-tops (an insoluble resist layer on the surface of the exposed areas) as well as changes in the critical dimension occur. The reasons for such shortcomings of chemically amplified resists are: (1) loss of acid or neutralization of the acid at the surface of the exposed areas of the resist by the base contaminants in the clean room atmosphere, and (2) diffusion of acid from the exposed areas to the non-exposed areas between exposure and development steps.
Several methods to control the problems associated with chemically amplified resists are proposed and used in production. An in-line production process, in which the resist is continuously processed without allowing any delays between exposure-post exposure bake and development steps and often enclosed from the clean room environment is one such method. This involves investment in the lithography tools as well as a preplanned production schedules with no interruptions. Another approach is the use of topcoats, often a polymeric film of few tens of nanometers coated upon the resist film. The film acts as a barrier layer between the resist and the clean room atmosphere, as discussed by O. Nalamasu et al. J. Photopolym. Sci. Technol. Vol. 4, p.299, (1991).
Dammel Ralph R.
Padmanaban Munirathna
Ashton Rosemary
Clariant Finance (BVI) Limited
Jain Sangya
LandOfFree
Photoresist composition for deep UV radiation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photoresist composition for deep UV radiation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photoresist composition for deep UV radiation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2840898