Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Electron beam imaging
Reexamination Certificate
2002-03-04
2004-06-22
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Electron beam imaging
C430S311000, C430S328000, C430S329000, C430S942000
Reexamination Certificate
active
06753129
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method and apparatus for increasing the etch resistance of photoresists which are suitable for use in the production of electronic devices such as integrated circuits. More particularly, the invention provides an improved process for increasing the etch resistance of positive working chemically amplified photoresists such as 193 nm, 157 nm, deep-UV 248 nm and x-ray wavelength sensitive, and electron beam sensitive photoresists while improving and maintaining fidelity of lithographic features and critical dimensions.
2. Description of the Related Art
The production of positive photoresists is well known in the art as exemplified by U.S. Pat. Nos. 3,666,473; 4,115,128 and 4,173,470. These contain aqueous alkali soluble polyvinyl phenol or phenol formaldehyde novolak resins together with light sensitive materials, usually a substituted naphthoquinone diazide compound. The resins and sensitizers are dissolved in an organic solvent and are applied as a thin film coating to a substrate suitable for the particular application desired. The resin component of photoresist formulations is soluble in an aqueous alkaline solution, but the photosensitizer is not. Upon imagewise exposure of the coated substrate to actinic radiation, the exposed areas of the coating are rendered more soluble than the unexposed areas. This difference in solubility rates causes the exposed areas of the photoresist coating to be dissolved when the substrate is immersed in an alkaline developing solution, while the unexposed areas are substantially unaffected, thus producing a positive image on the substrate. The uncovered substrate is thereafter subjected to an etching process. Frequently, this involves a plasma etching against which the resist coating must be sufficiently stable. The photoresist coating protects the covered areas of the substrate from the etchant and thus the etchant is only able to etch the uncovered areas of the substrate. Thus, a pattern can be created on the substrate which corresponds to the pattern of the mask or template that was used to create selective exposure patterns on the coated substrate prior to development.
Photoresists are either positive working or negative working. In a negative working resist composition, the imagewise light struck areas harden and form the image areas of the resist after removal of the unexposed areas with a developer. In a positive working resist the exposed areas are the non-image areas. The light struck parts are rendered soluble in aqueous alkali developers. The ability to reproduce very small dimensions, is extremely important in the production of large scale integrated circuits on silicon chips and similar components. As the integration degree of semiconductor devices becomes higher, finer photoresist film patterns are required. One way to increase circuit density on a semiconductor chip is by increasing the resolution capabilities of the resist. Positive photoresists have been found to be capable of much higher resolution and have almost universally replaced negative resists for this purpose.
The optimally obtainable microlithographic resolution is essentially determined by the radiation wavelengths used for the selective irradiation. However the resolution capacity that can be obtained with conventional deep UV microlithography has its limits. In order to be able to sufficiently resolve optically small structural elements, wavelengths shorter than deep UV radiation must be utilized. The use of UV radiation has been employed for many applications, particularly radiation with a wavelength of 157 nm, 193 nm and 248 nm. In particular, the radiation of lasers is useful for this purpose. The deep UV photoresist materials that are used today, however, are not suitable for 157 nm, 193 nm and 248 nm exposure. Materials based on phenolic resins as a binding agent, particularly novolak resins or polyhydroxystyrene derivatives have too high an absorption at wavelengths and one cannot image through films of the necessary thickness. This high absorption results in side walls of the developed resist structures which do not form the desired vertical profiles. Rather they have an oblique angle with the substrate which causes poor optical resolution characteristics at these short wavelengths. Polyhydroxystyrene based resists can be used in top surface imaging applications in which a very thin (~500 Å) layer of resist is required to be transparent at ArF laser exposure wavelengths.
Chemical amplification photoresists have been developed, which have been found to have superior resolution. 157 nm, 193 nm and 248 nm photoresists are based on chemically amplified deprotection. With this mechanism, a molecule of photogenerated acid catalyzes the breaking of bonds in a protecting group of a polymer. During the deprotecting process, another molecule of the same acid is created as a byproduct, and continues the acid-catalytic deprotection cycle. The chemistry of a 157 nm, 193 nm and 248 nm photoresist is based on polymers such as, but not limited to, acrylates, cyclic olefins with alicyclic groups, and hybrids of the aforementioned polymers which lack aromatic rings. However, chemically amplified resist films have not played a significant role in the fine pattern process using deep UV because they lack sufficient etch resistance, thermal stability, post exposure delay stability and processing latitude. While such photoresists are sufficiently transparent for deep uv radiation, they do not have the etching stability customary for resists based on phenolic resins for plasma etching. A typical chemical amplification photoresist film comprises a polymer, a photoacid generator, and other optional additives. The polymer is required to be soluble in the chosen developer solution, and have high thermal stability and low absorbance to the exposure wavelength in addition to having excellent etch resistance. It would be desirable to overcome the above mentioned problems and to provide a photoresist film superior in etch resistance, as well as transmittance to deep UV.
There have been several attempts to solve this problem. One attempt to improve the etching stability of photoresists based on meth(acrylate) polymers introduced cycloaliphatic groups into the meth(acrylate) polymers. This leads to an improvement in etching stability, but not to the desired extent. Another proposal aims at producing sufficient etching stability only after irradiation in the resist coating. It has also been proposed to treat the substrate with the finished, developed, image-structured photoresist coating with specific alkyl compounds of magnesium or aluminum, in order to introduce the given metals in the resist material as etching barriers (See U.S. Pat. No. 4,690,838). The use of metal-containing reagents, however, is generally not desired in microlithography process, due to the danger associated with contamination of the substrate with metal ions.
U.S. Pat. No. 6,319,655, which is incorporated herein by reference, describes a process for improving the etch resistance of chemically amplified resists, in particular 193 nm sensitive photoresists, using a large area electron beam exposure. Electron beam exposure of chemically amplified photoresists, in particular 193 nm sensitive photoresists has been shown to improve the etch resistance and thermal stability of these photoresists. Many different formulations of chemically amplified photoresist utilized for 193 nm exposure have been developed. Some examples of materials used for 193 nm lithography are given in U.S. Pat. No. 6,319,655. For the next generation of lithography, new resist materials sensitive to 157 nm irradiation will be utilized for this application. Some of these materials (incorporated herein by reference) are listed in “Organic Imaging Materials, A View of the Future” by Michael Stewart et al., Journal of Physical Organic Chemistry,
J. Phys. Org. Chem.
2000; 13: 767-774, “157 nm Resist Materials: Progress Report” by Colin Brodsky et al.,
J. Vac. Sci
Livesay William R.
Ross Matthew F.
Ross Richard L.
Applied Materials Inc.
Roberts & Mercanti
Young Christopher G.
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