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
2001-08-15
2004-06-01
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, C430S905000
Reexamination Certificate
active
06743563
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to photoresist compositions that can exhibit enhanced properties, including enhanced storage stability. In particular, resists of the invention contain an added acidic component which has been found can significantly enhance stability during storage between manufacture and use. Preferred resists of the invention contain an ester-based solvent such as ethyl lactate or propylene glycol methyl ether acetate in addition to the acid component
2. Background
Photoresists are photosensitive films for transfer of images to a substrate. They form negative or positive images. After coating a photoresist on a substrate, the coating is exposed through a patterned photomask to a source of activating energy such as ultraviolet light to form a latent image in the photoresist coating. The photomask has areas opaque and transparent to activating radiation that define an image desired to be transferred to the underlying substrate. A relief image is provided by development of the latent image pattern in the resist coating. The use of photoresists is generally described, for example, by Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York (1975), and by Moreau, Semiconductor Lithography, Principals, Practices and Materials, Plenum Press, New York (1988).
Certain “chemically amplified” photoresist compositions have been employed for higher performance applications. Such photoresists may be negative-acting or positive-acting and rely on multiple crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In other words, the photogenerated acid acts catalytically. In the case of positive chemically amplified resists, certain cationic photoinitiators have been used to induce cleavage of certain “blocking” groups pendant from a photoresist binder, or cleavage of certain groups that comprise a photoresist binder backbone. See, for example, U.S. Pat. Nos. 5,075,199; 4,968,851; 4,883,740; 4,810,613; and 4,491,628, and Canadian Patent Application 2,001,384. Upon selective cleavage of the blocking group through exposure of a coating layer of such a resist, a polar functional group is provided, e.g., carboxyl, phenol or imide, which results in different solubility characteristics in exposed and unexposed areas of the resist coating layer.
An important property of a photoresist is photospeed, which can be defined as the exposure time coupled with the exposure energy required to activate the photoactive component, e.g. to generate a sufficient amount of photoacid to provide the desired solubility differential between exposed and unexposed areas of a photoresist coating layer.
A substantially consistent resist photospeed also can be critical, e.g. so that a device manufacturer can use the same imaging conditions and obtain consistent results despite lot-to-lot differences of a resist product (such as precise amount and/or nature of the photoacid generator, polymer, etc.) that may frequently occur, particularly in large scale resist manufacturing processes. However, many current resists do not exhibit such consistent photospeed, and consequently a device manufacturer may either realize inconsistent results as different lots of a resist formulation are used, or the device manufacture may be forced to carefully test the photospeed of each new lot of resist and then adjust the parameters of the exposure equipment to provide for consistent processing. Clearly, either alternative is undesirable.
Photospeed variations during storage also are indicative of resist degradation. For example, decreased photospeed of a resist upon storage can indicate degradation of the photoactive component or other resist components. Storage stability is typically of high importance for a photoresist Generally, after photoresist manufacture, a resist is stored for several months or more prior to use by a device manufacturer. Any resist degradation during storage typically will only compromise lithographic properties.
It thus would be desirable to have new photoresist compositions. It would be particularly desirable to have new photoresist compositions that can exhibit enhanced storage stability, e.g. as indicated by substantially consistent photospeed over time.
SUMMARY OF THE INVENTION
We have now discovered new photoresist compositions that can provide enhanced storage stability.
Resists of the invention contain an added acid component (stabilizer component), suitably an organic acid. We have surprisingly found that addition of an acid to a resist formulation can provide significantly enhanced stability (e.g. lack of visible particles and/or change in photospeed) over prolonged periods relative to comparable resists that do not contain the added acid. See, for instance, the comparative results set forth in the examples which follow.
Preferred added acids contain carboxylic acid moieties and are suitably relatively weak acids e.g. a pKa (in water at 25° C.) of zero or higher (more positive number), particularly a pKa of about 1, 2 or 3 or greater (i.e. even higher positive number). A pKa of from about 1 to 4 is particularly preferred. The acid also may have other substitution such as hydroxy, halo, cyano, alkoxy such as C
1-12
alkoxy, and the like. The acid may suitably have from 1 to 20 carbon atoms, more typically 2 to about 12 carbons. Acids having from 2 to about 6 carbons are even more preferably. Specifically preferred added acids are lactic acid, acetic acid, propionic acid, and the like.
Preferred photoresists of the invention are positive chemically-amplified resists that contain a resin and a photoactive component. Particularly preferred resists also contain an added base such as an amine, particularly amine salts such as a salt of a tetraalkyl ammonium compound.
Especially preferred resists have a solvent component that comprises an ester-containing solvent such as ethyl lactate, propylene glycol methyl ether acetate (PGMEA), propylene glycol ethyl ether acetate, amyl acetate, or ethyl ether propionate (EEP). Ethyl lactate, amyl acetate and PGMEA are generally preferred. Preferred solvent components suitably contain a significant portion of an ester-based solvent, e.g. at least about 10, 15, 20, 25, 30 40 or 50 volume percent of the total solvent of the resist is one or more ester-based solvents, more preferably, at least about 60, 70, 80, 90 or 95 volume percent of the total solvents of a resist is one or more ester-based solvents such as ethyl lactate, amyl acetate or PGMEA.
Resists of the invention can be prepared by a variety of methods. In one preferred method, the resist formulation is preferred and the acid is added to the formed resist. Alternatively, the acid also may be formulated together with all other resist components, i.e. the resin, photoacid generator, basic component and acid may be added together to solvent carrier.
The invention also provide methods for forming relief images of the photoresists of the invention, including methods for forming highly resolved patterned photoresist images (e.g. a patterned line having essentially vertical sidewalls) of sub-quarter micron dimensions or less, such as sub-0.2 or sub-0.1 micron dimensions. The invention includes photoresists that can be imaged at a wide range of wavelengths, including sub-300 nm and sub-200 nm, such as 248 nm, 193 nm and 157 nm.
The invention further provides articles of manufacture comprising substrates such as a microelectronic wafer or a flat panel display substrate having coated thereon the photoresists and relief images of the invention.
Other aspects of the invention are disclosed infra.
DETAILED DESCRIPTION OF THE INVENTION
As discussed above, we now provide new photoresist compositions that can provide enhanced storage stability.
Resists of the invention contain an added acidic component, preferably an organic acid, more preferably an organic acid that has a pKa (as measured in water at 25° C.) of 0 or higher, particularly a pKa of f
Ablaza Sheri L.
Cameron James F.
Ashton Rosemary
Corless Peter F.
Edwards & Angell LLP
Frickey Darryl P.
Shipley Company L.L.C.
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