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
2000-07-21
2002-08-13
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
C430S919000, C522S065000
Reexamination Certificate
active
06432609
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel photoacid generator, a method of changing a structure of a resin with said photoacid generator, particularly a photoresist containing said photoacid generator, and a method of cross-linking a resin using such a photoacid generator.
BACKGROUND OF THE INVENTION
In recent years, industries of Taiwan develop rapidly along with the rise of the information industry, wherein the semiconductor industry bears the brunt of this impact. Along with the rapid development of the semiconductor fabricating processes, the versatility of functions and miniaturization of the products have become the research objectives of the industry. With no doubt, the lithographic techniques are crucial in a semiconductor fabricating process. In brief, the basic steps of the lithography comprise (1) coating a photoresist, (2) exposing, and (3) developing. Firstly, a photoresist is coated on a surface of a chip. Next, a specific light source is irradiated on the photoresist coating through a photomask thereby imagewise exposing the photosensitive material of the photoresist. This step is called “Exposure”. Next, a suitable developer is used to remove the exposed or unexposed photoresist. This step is called “Developing”. The change of a structure of a polymer contained in the photoresist prior to and after the exposure causes a change in the solubility of the polymer in the developer, creating a soluble region and an insoluble region according the pattern of the photomask, and thus the pattern transfer is achieved.
In general, according to the change of the solubility of the polymer in the developer, photoresists can be classified into positive tone photoresists and negative tone photoresists according to the following:
Positive tone: After exposure, the exposed region has a higher solubility in the developer than the unexposed region.
Negative tone: After exposure, the exposed region has a lower solubility in the developer than the unexposed region.
After decades of R & D, numerous positive tone or negative tone photoresists have been proposed, which includes the free radical polymerization photoresists of diazo and azide types in the early days and the chemical amplication photoresists predominant in the recent market. The reaction mechanisms of the chemical amplication photoresists have diversified from the initial two mechanisms:
(1) photoacid-catalyzed, epoxide-ring-opening cross-linking reaction; and
(2) photoacid-catalyzed, t-butoxycarbonyl (t-BOC) deprotection; to the following reaction mechanisms:
(3) photoacid-catalyzed dehydration;
(4) photoacid-catalyzed rearrangement;
(5) photoacid-catalyzed condensation;
(6) photoacid-catalyzed ionic polymerization;
(7) photoacid-catalyzed depolymerization.
The fundamental principle of a chemical amplication photoresist is utilizing a photoacid generator (PAG), after irridation, to react with a H-donor (usually a solvent or other material) thereby generating a proton acid. In a post-exposure bake (PEB) process following the irridiation, the proton acid initiates a series of chain-breaking, cross-linking or other chemical reactions of a polymer in the photoresist as an acid catalyst, causing a structural change and a difference in solubility to the developer between the exposed region and the unexposed region of the polymer, so that a positive tone or negative tone pattern are obtained. The use of a chemical amplication photoresist, in addition to greatly increasing the sensitivity of the photoresist, also improves the contrast and resolution of the photoresist pattern.
Generally speaking, chemical amplication photoresists, according to the difference in the quantity of the major components, can be classified into binary photoacid photoresists and ternary photoacid photoresists. A binary photoacid photoresist mainly comprises a photoacid generator and a polymeric resin; while a ternary photoacid photoresist mainly comprises a photoacid generator, a dissolution inhibitor or a cross-linking agent, and a polymeric resin. Take the famous t-BOC deprotection photoresist proposed by H. Ito, et al. In U.S. Pat. No. 4,491,628 as an example. This photoresist belongs to a binary photoacid photoresist containing triphenylsulfonium hexafluoroantimonate as the photoacid generator and poly(4-t-butoxycarbonyloxystyrene) (PBOCST) as the polymeric matrix, the reaction mechanism of which is shown in the following Scheme 1:
In Scheme 1, triphenylsulfonium hexafluoroantimonate, upon subjected to UR irradiation, releases a proton acid. The PBOCST, which has a weaker polarity, releases t-butoxycarbonyl (abbreviated as t-BOC) in the presence of an acid catalyst, and forms poly(4-hydroxystyrene) (abbreviated as PHOST) having a higher polarity. In other word, there is a conspicuous difference in solubility between the exposed region and the unexposed region. By selecting an appropriate developer, e.g. a non-polar organic solvent, a negative tone photoresist pattern can be obtained. Alternatively, by using a polar aqueous base as the developer, a positive tone photoresist pattern can be obtained. Since PBOCST and PHOST do not have a high absorbency to UV light at 250 nm, this photoresist is suitable for deep UV lithography. Furthermore, PHOST can be dissolved in an aqueous base. Undoubtedly, this photoacid amplication t-BOC deprotection photoresist is a turning point in the development of photoresists.
Other typical photoresists that contain a photoacid generator are disclosed in U.S. Pat. Nos. 5,585,223; 5,532,106; 5,391,465; 5,296,332; and 5,055,439.
Photoresists not only can be applied in the semiconductor industry, but also have unique applications in other fields. For example, in a photoacid-catalyzed epoxide ring-opening reaction (as shown in Scheme 2) or in a photoacid-catalyzed ionic polymerization reaction, a photoresist can greatly increase the molecular weight of the polymer and receives wide applications in the manufacture of microelectromechanical devices (MEMs). A high level of cross-linking is necessary for forming a pattern with a high aspect ratio in a thick film (>50 micron) by lithography, wherein said aspect ratio is a ratio between the film thickness and the resolution.
The photoacid-catalyzed dehydration reaction, generally speaking, can be classified into the intermolecular dehydration and the intramolecular dehydration. The reaction mechanism of the intermolecular dehydration is shown in Scheme 3, wherein the photoacid-catalyzed dehydration will cause cross-linking of the polymeric resin of a negative tone photoresist. The intramolecular dehydration reaction (as shown in Scheme 4) is similar to a photoacid-catalyzed reforming reaction (as shown in Scheme 5), both of which will alter the polarity of the polymeric resin. As a result, a polar solvent or a nonpolar solvent can be selected as a developer to obtain a positive tone or a negative tone photoresist pattern.
SUMMARY OF THE INVENTION
One objective of the present invention is to provide a novel photoacid generator.
Another objective of the present invention is to provide a photoresist.
Still another objective of the present invention is to provide a method of carrying out a photoacid-catalyzed reaction in a resin system.
Still another objective of the present invention is to provide a method of photo-cross-linking a resin system.
In order to achieve the above-mentioned objectives, a photoacid generator synthesized according to the present invention has the following structure of formula (I):
wherein R′ and R are radicals which enable the photoacid generator (I) forming
and RH under an irradiation, wherein R′ is defined as above, and RH is a proton acid.
Preferably, R in the formula (I) is a halogen,
Preferably, R′ in the formula (I) is hydrogen, methyl or chloromethyl.
Preferably, R′ is hydrogen, when R in the formula (I) is not a halogen.
Preferably, R′ is not hydrogen, when R in the formula (I) is halogen.
Preferably, the photocaid generator (I) is 1,4-dichloromethyl-2-nitrobenzene, 2-nitrobenzyl ester of for
Ashton Rosemary
Fish & Richardson P.C.
National Science Council
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