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
2001-06-29
2004-02-24
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, C430S921000
Reexamination Certificate
active
06696216
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to photolithography, and more particularly to thiophene-containing photo acid generators which efficiently generate photo acids when they are exposed to UV light. The present invention is also directed to chemically amplified resist compositions which include the inventive thiophene-containing photo acid generator as one component thereof.
BACKGROUND OF THE INVENTION
In the field of semiconductor manufacturing, optical lithography has been the mainstream approach used in patterning semiconductor devices. In typical prior art lithography processes, UV light is projected onto a silicon wafer coated with a thin layer of photosensitive resist through a mask that defines a particular circuitry pattern. Exposure to UV light, followed by subsequent baking, induces a photochemical reaction which changes the solubility of the exposed regions of the photosensitive resist. Thereafter, an appropriate developer, usually an aqueous base solution, is used to selectively remove resist either in the exposed regions (positive-tone resists) or, in the unexposed regions (negative-tone resists). The pattern thus defined is then imprinted on the silicon wafer by etching away the regions that are not protected by the resist with a dry or wet etch process.
One type of photosensitive resist employed in the prior art is a chemically amplified resist which uses acid catalysis. A typical prior art chemically amplified resist, for example, is formulated by dissolving an acid sensitive polymer and a photo acid generator in a casting solution. A chemically amplified resist is especially useful when relatively short wavelength radiation is employed; including deep UV radiation 150-315 nm wavelengths, and mid-UV radiation, e.g., 350-450 nm wavelengths. The shorter wavelengths are typically desired to increase resolution, and thus, decrease feature size of the semiconductor devices, but fewer photons are radiated for a given energy dose.
Accordingly, higher exposure doses are typically required when using UV radiation to obtain a sufficient photochemical response in the resist unless a chemically amplified resist is employed. In a chemically amplified resist, acid sensitivity of the base polymer exists because acid sensitive side chain groups are bonded to the polymer backbone. When such a resist is exposed to radiation, the photo acid generator produces an acid that, when the resist is heated, causes catalytic cleavage of the acid sensitive side chain groups. A single acid catalyst molecule generated in this manner may be capable of cleaving multiple side chain groups, thus allowing lower exposure doses for the needed photochemical response.
Several acid catalyzed chemically amplified resists have been developed, although their photo acid generators are primarily suited for deep UV radiation, typically at about 248 nm. By comparison, there are very few, if any, photo acid generators which efficiently generate photo acids when they are exposed to a wavelength of light of about 220 nm or less. The challenge for designing photo acid generators for resists exposed at 220 nm involves a balance between absorption, photosensitivity, stability, dissolution and etch resistance.
For 248 nm resists, aryl onium salts (triarylsulfoniums or diaryliodoniums) are typically used as photo acid generators. However, such photo acid generators are generally too absorbing when exposed to wavelengths shorter than 220 nm.
In view of the above-mentioned drawbacks with prior art photo acid generators, there is a need for developing new and improved photo acid generators which can be effectively used with various chemically amplified base polymers at exposure wavelengths of about 220 nm or less.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a new class of photo acid generator that can be employed with various chemically amplified base polymers.
A further object of the present invention is to provide photo acid generators for chemically amplified resists that can used at wavelengths of about 220 nm or less.
Another object of the present invention is to provide a photo acid generator having the proper balance of absorption, photosensitivity, stability, dissolution and etch resistance.
A still further object of the present invention is to provide a photo acid generator that works with 248 nm chemically amplified base polymers, 193 nm chemically amplified base polymers, and 157 nm chemically amplified base polymers.
An even further object of the present invention is to provide a chemically amplified resist composition which has a high resolution at wavelengths of about 220 nm or less.
These and other objects and advantages are achieved in the present invention by using thiophene-containing photo acid generators in place of standard hydrocarbon aromatic ring-containing sulfonium or iodonium photo acid generators. By incorporating thiophene units into sulfonium or iodonium compounds, the absorption of the photo acid generator at low wavelengths (less than about 220 nm) is greatly reduced. Additionally, the thiophene-containing photo acid generators of the present invention still maintain relatively high thermal stability and photosensitivity. Moreover, the chemically amplified resists of the present invention absorb less light at lower wavelengths (220 nm or less) than conventional photo acid generators, which may lead to the inventive chemically amplified resist exhibiting high resolution at these lower wavelengths.
The term “thiophene” as used herein denotes a compound having the following structural formula:
as well as substituted compounds wherein one or more of the ring carbon atoms (not shown) is substituted with a substituent other than hydrogen.
The present invention also provides a chemically amplified resist composition which comprises at least one thiophene-containing photo acid generator having either of the following general formulas:
wherein at least one of R
1
, R
2
or R
3
is thiophene or thiophene that is substituted with alkyl, alkoxy or cycloalkyl, and the remaining R
1
, R
2
or R
3
, not containing a thiophene moiety, are independently selected from the group consisting of alkyl, cycloalkyl and aryl, or at least one of R
1
, R
2
or R
3
are joined together to form a cyclic moiety having from about 4 to about 8 ring carbon atoms; and Y is a counter ion such as a halogen, perfluorinated alkyl sulfonate, perfluorinated aryl sulfonate, perfluorinated alkyl sulfonyl methide, perfluorinated alkyl sulfonyl imide, perfluorinated aryl sulfonyl methide, perfluorinated aryl sulfonyl imide and the like thereof. Preferred counter ions are perfluorinated alkyl compounds.
In addition to thiophene-containing photo acid generators, the inventive chemically amplified resist composition also includes a chemically amplified base polymer and a solvent as essential components. Optional components that may also be present in the inventive chemically amplified resist composition include: a photosensitizer that is capable of absorbing irradiation in the mid-UV, deep-UV, extreme-UV, X-ray or e-beam range; a base; a dissolution modifying agent (DMA) and/or a surfactant.
DETAILED DESCRIPTION OF THE INVENTION
As stated above, the present invention is directed to novel thiophene-containing photo acid generators which efficiently generate photo acids when they are exposed to UV light. The novel photo acid generators of the present invention have a proper balance between absorption, photosensitivity, stability, dissolution and etch resistance thus making them a viable candidate for replacing conventional aryl onium and aryl sulfonium salts. The inventive thiophene-containing photo acid generators of the present invention do not absorb much light, therefore the inventive photo acid generators are especially suitable for use when they are exposed to wavelengths of 220 nm or less, which could, in turn, equate to better resolutions at these wavelengths.
The thiophene-containing photo acid generators of the present invention are formulated with a chemically amplified base
Chen Kuang-Jung
Li Wenjie
Varanasi Pushkara Rao
Ashton Rosemary
Capella, ESq. Steven
Scully Scott Murphy & Presser
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