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
2001-10-23
2004-02-17
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
C430S914000, C430S919000, C430S921000, C430S925000, C430S326000, C430S327000, C430S328000, C430S330000, C430S331000, C568S028000, C568S030000, C568S034000, C568S035000, C568S036000
Reexamination Certificate
active
06692893
ABSTRACT:
This invention relates to novel onium salts, photoacid generators for resist compositions, resist compositions comprising the photoacid generators, and a patterning process using the same. The resist compositions, especially chemical amplification type resist compositions are sensitive to such radiation as UV, deep UV, electron beams, x-rays, excimer laser beams, &ggr;-rays, and synchrotron radiation and suitable for the microfabrication of integrated circuits.
BACKGROUND OF THE INVENTION
While a number of efforts are currently being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology.
One technology that has attracted a good deal of attention recently utilizes as the deep UV light source a high-intensity KrF excimer laser, especially an ArF excimer laser featuring a shorter wavelength. There is a desire to have a microfabrication technique of finer definition by combining exposure light of shorter wavelength with a resist material having a higher resolution.
In this regard, the recently developed, acid-catalyzed, chemical amplification type resist materials are expected to comply with the deep UV lithography because of their many advantages including high sensitivity, resolution and dry etching resistance. The chemical amplification type resist materials include positive working materials that leave the unexposed areas with the exposed areas removed and negative working materials that leave the exposed areas with the unexposed areas removed.
In chemical amplification type, positive working, resist compositions to be developed with alkaline developers, an alkali-soluble phenol or a resin and/or compound in which carboxylic acid is partially or entirely protected with acid-labile protective groups (acid labile groups) is catalytically decomposed by an acid which is generated upon exposure, to thereby generate the phenol or carboxylic acid in the exposed area which is removed by an alkaline developer. Also, in similar negative working resist compositions, an alkali-soluble phenol or a resin and/or compound having carboxylic acid and a compound (crosslinking agent) capable of bonding or crosslinking the resin or compound under the action of an acid are crosslinked with an acid which is generated upon exposure whereby the exposed area is converted to be insoluble in an alkaline developer and the unexposed area is removed by the alkaline developer.
On use of the chemical amplification type, positive working, resist compositions, a resist film is formed by dissolving a resin having acid labile groups as a binder and a compound capable of generating an acid upon exposure to radiation (to be referred to as photoacid generator) in a solvent, applying the resist solution onto a substrate by a variety of methods, and evaporating off the solvent optionally by heating. The resist film is then exposed to radiation, for example, deep UV through a mask of a predetermined pattern. This is optionally followed by post-exposure baking (PEB) for promoting acid-catalyzed reaction. The exposed resist film is developed with an aqueous alkaline developer for removing the exposed area of the resist film, obtaining a positive pattern profile. The substrate is then etched by any desired technique. Finally the remaining resist film is removed by dissolution in a remover solution or ashing, leaving the substrate having the desired pattern profile.
The chemical amplification type, positive working, resist compositions adapted for KrF excimer lasers generally use a phenolic resin, for example, polyhydroxystyrene in which some or all of the hydrogen atoms of phenolic hydroxyl groups are protected with acid labile protective groups. Onium salts such as iodonium salts and sulfonium salts, bissulfonyldiazomethane compounds, and N-sulfonyloxyimide compounds are typically used as the photoacid generator. If necessary, there are added additives, for example, a dissolution inhibiting or promoting compound in the form of a carboxylic acid and/or phenol derivative having a molecular weight of up to 3,000 in which some or all of the hydrogen atoms of carboxylic acid and/or phenolic hydroxyl groups are protected with acid labile groups, a carboxylic acid compound for improving dissolution characteristics, a basic compound for improving contrast, and a surfactant for improving coating characteristics.
Onium salts as shown below are advantageously used as the photoacid generator in chemical amplification type resist compositions, especially chemical amplification type, positive working, resist compositions adapted for KrF excimer lasers because they provide a high sensitivity and resolution and are free from storage instability as found with the N-sulfonyloxyimide photoacid generators.
Since a finer pattern size is required, even the use of such photoacid generators gives rise to many problems including low resolution, low environmental stability, and the formation of insoluble or difficultly soluble foreign matter upon development with an alkaline developer or removal of the resist with a solvent.
Of these problems, improvements in resolution are made by introducing into a resin acid labile groups which are more prone to scission by an acid, or adding a basic compound, or modifying processing conditions.
It is known from JP-A 8-123032 to use two or more photoacid generators in a resist material. JP-A 11-72921 discloses the use of a radiation-sensitive acid generator comprising in admixture a compound which generates a sulfonic acid having at least three fluorine atoms upon exposure to radiation and a compound which generates a fluorine atom-free sulfonic acid upon exposure to radiation, thereby improving resolution without inviting nano-edge roughness and film surface roughening. However, we empirically found that these resist compositions are unsatisfactory in resolution and in the effect of eliminating the foreign matter on the pattern upon development.
For the purpose of improving the resolution upon microfabrication, JP-A 6-148889 discloses a positive photosensitive composition comprising a polyfunctional enol ether compound and an alkali-soluble resin as typified by polyhydroxystyrene, which are thermally crosslinked on a substrate, followed by exposure to radiation and PEB to provide a desired pattern. JP-A 6-266112 discloses a photosensitive resist composition comprising a photosensitive acid generator and a polymer composed of hydroxystyrene and an acrylate and/or methacrylate. These compositions are unsatisfactory in resolution and pattern profile. Substantial sliming upon post-exposure delay (PED) is also a problem.
The environmental stability is generally divided into two categories. One environmental stability is related to the deactivation of a photo-generated acid by an air-borne base above the resist film or a base beneath the resist film and on the substrate. This phenomenon is often seen when a photoacid generator capable of generating an acid having a high acid strength is used. It is expected that this problem is solved by introducing into the resin acid labile groups which are more prone to scission by acid or by lowering or weakening the acid strength of the photo-generated acid. The other environmental stability is that when the period from exposure to post-exposure baking (PEB) is prolonged, which is known as post-exposure delay (PED), the photo-generated acid diffuses in the resist film so that acid deactivation may occur when the acid labile groups are less susceptible to scission and acid decomposition may take place when the acid labile groups are susceptible to scission, often inviting a change of the pattern profile in either case. For example, this invites a sliming of the line width in the unexposed area in the case of chemical amplification type, positive working, resist compositions having acid labile groups, typically acetal groups.
As mentioned above, for achieving a high resolution, the resin should have int
Hatakeyama Jun
Nagata Takeshi
Ohsawa Youichi
Watanabe Jun
Lee Sin J.
Millen White Zelano & Branigan P.C.
Shin-Etsu Chemical Co. , Ltd.
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