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
1999-06-21
2001-07-31
Baxter, Janet (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
Reexamination Certificate
active
06268106
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a chemical amplification positive photoresist composition. More particularly, the present invention relates to a chemical amplification positive photoresist composition, which makes it possible to perform a sub-micro lithography process using a deep UV such as a KrF excimer laser or an ArF excimer laser, an X ray such as synchrotron radiation, or charged particle beams such as electron beams.
2. Description of the Prior Art
The high integration of semiconductor devices has been partly, but critically based on a significant advance in lithography. For example, ultra-fine patterns as small as sub-microns, e.g. 0.2 microns or less, in size, are required for the fabrication of ultra-LSI. Now, the light sources used to form the fine patterns become increasingly shorter in wavelength, for example, from g-line or I-line, to deep UV light, including KrF excimer lasers and ArF excimer lasers, further to X-rays, and finally to electron beams.
With near UV light, such as g-line or I-line, which is used in conventional lithography, micro patterns as small as quarter microns (0.25 microns) are virtually impossible to realize. Such a micro pattern requires shorter wavelengths which belong to deep UV excimer lasers, X rays, and electron beams. Of them, KrF and ArF excimer lasers occupied the attention of the researchers in expressing such exquisiteness, and were developed as a light source, requiring novel photoresists. Now, chemical amplification photoresists are prevalently used for deep UV light.
A chemical amplification photoresist composition suitable for deep UV light fundamentally comprises a polymer with an acid-dissociable functional group, a compound which generates an acid (hereinafter referred to as “photoacid generator”), and a solvent, and avails itself of chemical amplification effect in lithography.
Most of the chemical amplification photoresists used for KrF excimer lasers are based on phenolic resins which, however, are found to be unsuitable for utilizing an ArF excimer laser because their aromatic rings absorb the light.
As an alternative, polyacrylate derivatives appeared to avoid such absorption. Polyacrylate derivatives show little absorbance at 193 nm, but suffer from a great disadvantage in that they are far inferior in dry etch resistance. Recently, much effort has been made to overcome the disadvantage, including the introduction of alicyclic derivatives into polyacrylate (Proc. SPIE, 1996, 2724, 365). The introduction of alicyclic derivatives certainly brings about an improvement in dry etch resistance, but causes a significant problem in a developing process because their hydrophobicity has a negative influence on the affinity for developing solutions.
It is known that copolymers of maleic anhydride and olefin can be used as matrix resins which show not only hydrophilicity, but also etch resistance. In the copolymers, maleic anhydride, responsible for hydrophilicity, serves as a promoter which enables the copolymerization with olefinic monomers to be accomplished at low temperatures at low pressures.
SUMMARY OF THE INVENTION
The present invention was developed during the processing of developing a base resin for photoresist, and resulted in the finding that carboxylic acid acts to increase the adherence of base polymer to substrate while hydrophobic groups play a role in restraining the solubility increase in basic solutions attributed to the carboxylic group and that the coexistence of the carboxyl group and hydrophobic group in a polymer brings about an improvement in adherence to substrate as well as controls the solubility in developing solutions.
Therefore, it is an object of the present invention to provide a copolymer which allows a photoresist superior in adherence to substrate and developability as well as in transparency to deep UV light, and dry etch resistance, photosensitivity and resolution.
It is another object of the present invention to provide a copolymer as a base resin for photoresist, with which there can be obtained patterns as fine as 0.2 &mgr;m.
It is a further object of the present invention to provide a chemical amplification positive photoresist composition containing the resin.
DETAILED DESCRIPTION OF THE INVENTION
In order to obtain patterns as fine as 0.2 microns by use of light as short in wavelength as ArF excimer laser, new chemical amplification photoresists have been being actively developed because previous ones did not give desirable patterns. For example, polyhydroxystyrene-based photoresists show a large absorbance at the wavelength of the light source (193 nm).
In forming 0.2 micron or less patterns, the adherence of a resist composition to a substrate plays an important role. Carboxylic acid was introduced into the side chains of matrix polymers for the purpose of increasing the adherence. Carboxylic acid-grafted matrix polymers, however, require a change in the basicity of developing solutions because the existence of carboxylic acid alters the solubility of the matrix polymers in the aqueous alkaline solutions.
In the polymer according to the present invention, a hydrophobic group-containing norbornene derivative is introduced into its main chain with the aim of controlling the adherence to substrates and the solubility in aqueous alkaline solutions while a cyclic group exists as a member of its main cain to enhance dry etch resistance.
Accordingly, the present invention provides a polymer for chemical amplification photoresist, having a repeating unit which comprises a norbornene moiety and a maleic anhydride moiety, and a chemical amplification photoresist composition based on the polymer.
More details are given of the present invention, below.
POLYMER
The polymer useful in the present invention has a repeat unit consisting of a norbornene, norbornene derivatives and a maleic anhydride. The polymer itself is insoluble or hard-soluble in aqueous alkaline solutions and contains at least one protecting group which can be dissociated by acid.
The alkali solubility of the polymer is primarily determined by the content of the acid functional groups which are dissociable by acid. Accordingly, the photoresist properties of the polymer, including adherence to substrate, photo-sensitivity, resolution and the like, can be controlled by the kind and quantity of the norbornene derivatives used in the polymer.
The polymer of the present invention is a multi-membered copolymer represented by the following general formula I:
wherein,
R
1
and R
2
are independently selected from the group consisting of straight or branched alkyl groups, cyclic alkyl groups, polycyclic (bi, tri) alkyl groups, and alkoxyalkyl groups, all containing 1-10 carbon atoms, which are exemplified by methyl, ethyl, t-butyl, iso-propyl, cyclohexyl, adamantyl, bicyclo[2,2,1]heptane methyl and the like; and
l, m, n and o each are a repeating number not more than 0.5, satisfying the condition that l+m+n+o=1 and 0.4≦o≦0.5. The photoresist properties, such as adherence to substrate, photosensitivity and resolution, are taken into account in determining the repeating numbers, l, m and n.
The repeating unit of the Formula I can be prepared by polymerizing a maleic anhydride of the following structural formula II, a norbornene of the following structural formula III, and norbornene derivatives represented by the following general formulas IV and V:
wherein R
1
and R
2
are independently selected from the group consisting of straight or branched alkyl groups, cyclic alkyl groups, polycyclic (bi, tri) alkyl groups, and alkoxyalkyl groups, all containing 1-10 carbon atoms, which are exemplified by methyl, ethyl, t-butyl, iso-propyl, cyclohexyl, adamantyl, bicyclo[2,2,1]heptane methyl and the like.
The photoresist polymer according to the present invention may be a quar-polymer or ter-polymer. As far as quar-polymer, the monomers represented by the formulas II, III, IV and V all participate in copolymerization. For the terpolymer, the mon
Kim Seong-Ju
Park Joo-Hyeon
Park Sun-Yi
Seo Dong-Chul
Ashton Rosemary
Baxter Janet
Harrison & Egbert
Korea Kumho Petrochemical Co. Ltd.
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