Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2000-08-18
2002-05-21
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Diazo reproduction, process, composition, or product
Composition or product which contains radiation sensitive...
C430S192000, C430S193000, C430S326000
Reexamination Certificate
active
06391514
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for preparing radiation sensitive positive photoresist compositions and particularly such compositions containing film forming resins, such as novolak resins or vinyl phenol resins together with a photosensitizer component, such as a diazonaphthoquinone or a photo-acid generator, such as a diaryliodonium salt or an aryl onium salt. It is well known in the art to produce positive photoresist formulations, such as those described in U.S. Pat. No. 3,666,473, 4,115,128 and 4,173,470. These include alkali soluble phenolformaldehyde novolak resins and vinyl phenol resins, together with light sensitive components (photosensitizers), usually a substituted diazonaphthoquinone compound or a photo-acid generator. The resin and photosensitizer are dissolved in an organic solvent, or mixture of solvents, and are applied as a thin film or coating to a substrate suitable for the particular application desired.
The film forming resin component of these photoresist formulations is normally soluble in an alkaline aqueous solution and insoluble in water, but the photosensitizer, which may be a separate component or be a component of the film forming resin (i.e. the film forming resin may contain both a film forming component and a photosensitive component), acts as a dissolution rate inhibitor with respect to the resin component. Upon exposure of selected areas of the coated substrate to actinic radiation, however, the photosensitizer undergoes a radiation induced structural transformation, and for a positive photoresist, the exposed areas of the coating are rendered more soluble than the unexposed areas. This difference in solubility rates causes the exposed areas of the positive photoresist coating to be dissolved when the substrate is immersed in an alkaline developing solution while the unexposed areas are largely unaffected, thus producing a positive relief pattern on the substrate.
In many instances, the exposed and developed substrate will also be subjected to treatment by a substrate etchant solution or gas plasma. The photoresist coating protects the coated areas of the substrate from the etchant and thus the etchant is only able to etch the uncoated areas of the substrate which, in the case of a positive photoresist, correspond to the areas that were exposed to actinic radiation. Thus, an etched pattern can be created on the substrate that corresponds to the pattern of the mask, stencil, template, etc. that was used to create selective exposure patterns on the coated substrate prior to development.
The relief pattern of photoresist on the substrate produced by the method described above is useful for various applications including, for example, as an exposure mask or a pattern such as is employed in the manufacture of miniaturized integrated electronic components. The properties of a photoresist composition that are important in commercial practice include the photospeed of the photoresist, photoresist resolution and depth of focus.
Good photospeed is important for a photoresist, particularly in applications where a number of exposures are needed, for example, in generating multiple patterns by a repeated process, or where light of reduced intensity is employed, such as in projection exposure techniques where the light is passed through a series of lenses and monochromatic filters. Thus, a fast photospeed is particularly important for a photoresist composition employed in processes where a number of multiple exposures must be made to produce a mask or series of circuit patterns on a substrate. These optimum conditions include a constant development temperature and time in a particular development mode, and a developer system selected to provide complete development of exposed photoresist areas while maintaining a maximum unexposed photoresist film thickness loss not exceeding about 10 percent of initial thickness.
Another important requirement for a photoresist is that the walls of the profiles produced on the substrate should be straight and as close to vertical as possible (i.e. good image edge acuity). Better profiles provide more precise images on the substrate.
Photoresist resolution refers to the capability of a photoresist system to reproduce the smallest equally spaced line pairs and intervening spaces of a mask which is utilized during exposure, with a high degree (greater than 80 degrees) of image edge acuity in the developed exposed spaces. In many industrial applications, particularly in the manufacture of miniaturized electronic components, a photoresist is required to provide a high degree of resolution for very small line and space widths (on the order of 0.5 micron [micrometer] or less). Depth of focus refers to the range of the defocus settings where the given feature size can be replicated.
The ability of a photoresist to reproduce very small dimensions of 0.5 micron (micrometer) or less is extremely important in the production of large-scale integrated circuits on advanced silicon chips and similar components. Circuit density on such a chip can only be increased, assuming photolithographic techniques are utilized, by increasing the resolution capabilities of the photoresist. Although negative photoresists, wherein the exposed areas of photoresist coating become insoluble and the unexposed areas are dissolved away by the developer, have been extensively used for this purpose by the semiconductor industry, positive photoresists have inherently higher resolution and are frequently utilized as replacements for the negative photoresists.
A problem with the use of conventional positive photoresists in the production of miniaturized integrated circuit components is that the positive photoresists generally have slower photospeed than their negative analogs. Various attempts have been made in the prior art to improve the photospeed, resolution and depth of focus of positive photoresist compositions. For example, in U.S. Pat. No. 3,666,473, a mixture of two phenol formaldehyde novolak resins was used together with a typical sensitizer, the novolak resins being defined by their solubility rates in alkaline solutions of a particular pH and by their cloud points. In U.S. Pat. No. 4,115,128, a third component consisting of an organic acid cyclic anhydride was added to the phenolic resin and naphthoquinone diazide sensitizer to provide increased photospeed.
SUMMARY OF THE INVENTION
The present invention provides a process for producing a positive working photoresist composition utilizing a novel solvent system. It has been found that such a photoresist can be formulated when the film forming resin (normally alkali soluble and water insoluble) and the photosensitizer component are blended with a photoresist solvent mixture containing more than 50 weight percent of a C
1
-C
4
alkylene glycol C
1
-C
4
alkyl ether (AGAE), such as propylene glycol methyl ether (PGME) and either a C
1
-C
4
alkyl amyl ketone (MK), such as an MAK (methyl amyl ketone, also known as 2-heptanone), or a C
1
-C
4
alkyl (e.g. ethyl) C
1
-C
4
alkoxy (e.g. ethoxy) propionate (MP), such as an ethyl-3-ethoxy propionate (EEP). Such photoresist compositions provide very good resolution with substantially straight wall profiles.
European Pat. No. 106774 discloses the use of a propylene glycol alkyl ether alone, as a photoresist solvent. U.S. Pat. No. 5,360,696 teaches the use of a C
1
-C
4
alkyl amyl ketone alone as a solvent for positive photoresists. U.S. Pat. No. 5,336,583 discloses a photoresist solvent that is a mixture of a lower alkyl propionate and an alkyl amyl ketone. Japanese Published Pat. Application 10-10711 (Jan. 16, 1998) discloses the use of a photoresist solvent mixture of methyl amyl ketone and PGME, wherein the PGME is from 3 to 28 weight percent of the solvent composition. It is also disclosed that increasing the amount of PGME, e.g. to 30 percent, yields a photoresist composition that is not acceptable. European Pat. No. 211667 discloses the use of C
1
-C
4
alkyl C
1
-C
4
alkyloxy propionates as solvents for
Dioses Alberto D.
Eilbeck J. Neville
Banerjee Krishna G.
Chu John S.
Clariant Finance (BVI) Limited
Sayko, Jr. Andrew F.
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