Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Utility Patent
1998-02-17
2001-01-02
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Diazo reproduction, process, composition, or product
Composition or product which contains radiation sensitive...
C430S280100, C430S278100, C430S272100, C430S275100, C430S277100, C430S271100, C430S162000, C522S031000, C522S032000, C522S129000
Utility Patent
active
06168898
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to microdevice manufacture by photolithography. More particularly, the invention relates to a photosensitive composition that can be used as a permanent dielectric in electronic circuits.
2. Description of the Prior Art
It is known to the skilled artisan to produce positive photoresist compositions such as those described in U.S. Pat. Nos. 3,666,473; 4,115,128 and 4,173,470. These include water insoluble, aqueous alkali-soluble resins together with light-sensitive materials. Upon imagewise exposure of portions of the coated substrate to actinic radiation, the sensitizer is rendered alkali soluble and the exposed areas of the coating therefore become more soluble than the unexposed areas. This difference in solubility rates causes the exposed areas of the 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. The exposed and developed substrate is usually thereafter subjected to an etching process. 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 correspond to the areas that were exposed to actinic radiation. Thus, an etched pattern can be created on the substrate which corresponds to the pattern of the mask that was used to create selective exposure patterns on the coated substrate prior to development. The relief pattern of photoresist on a substrate produced by this method is useful for various applications including the manufacture of miniaturized integrated circuits.
As the ability to wire-bond integrated circuits reaches the limits of technology, the density of a chip places increasing demands on utilization of the board area. This drives the need for a high density package with a significant amount of interconnections on the outer surface of a multilayer board as well as for increasing use of blind microvias. Resin coated copper has been used to fabricate high density buildup multilayer printed circuit boards. Currently microvias in such circuit boards are produced by two methods including plasma etching and laser drilling. As such, only fabricators with access to plasma or laser via hole fabrication can provide these advanced, blind-via boards. The high cost of the plasma and laser equipment hinders wide adoption of resin coated copper technology. Furthermore, the technical disadvantages associated with the plasma etching and laser drilling techniques such as undercutting due to isotropic etching of plasma and low throughput due to sequential drilling by laser also limit large scale commercialization of resin coated copper based high density multilayer circuit boards. Photodefinable resin coated copper, which allows for mass production of microvias by photolithography, has been developed to address the issues related to the plasma and laser microvia technologies. This invention provides for an aqueous developable, positive acting photodielectric composition, which can be used to mass produce microvias via photo resin coated copper technology. The composition is also useful for producing solder masks.
Photo resin coated copper allows for mass production of microvias by photolithography. Circuit board fabricators have photolithography capability and can thus easily adopt the new technology. Moreover, photodefinition of microvias avoids the undercut and low throughput problems associated with plasma and laser methods, respectively. This invention provides an aqueous developable, positive acting photodefinable resin, which enables photo resin coated copper technology.
Image forming photoresists useful for photolithography are well known in the art as exemplified by U.S. Pat. No. 4,968,581 and U.S. Pat. No. 5,081,001. However, most commercial positive photoresists are not designed as permanent dielectrics, but are removed during microdevice manufacture. Commercial photoresist compositions suffer from poor thermal and photo stability, high moisture uptake and inadequate dielectric properties and hence are not suitable for permanent applications. This invention provides a photodielectric composition for a permanent photoresist that can be used as a permanent dielectric in electronic circuits. This photodielectric is epoxy based and is similar to the common epoxy dielectrics that are currently used in the electronics industry. After final cure, this photodielectric provides for excellent thermal and photo stability and good dielectric performance.
The composition includes a mixture of epoxy resins, anhydride polymers such as styrene maleic anhydride (SMA) copolymers, an amine catalyst, a photo acid, and optionally phenol containing polymers such as phenolic resins. The amine catalyst catalyzes the curing reaction between SMA and epoxy and/or between phenol and epoxy. Upon photo exposure, an acid is generated from the photo acid. The acid neutralizes the amine catalyst and decreases its catalytic activity. Therefore, the exposed resin cures much slower than the non-exposed resin during thermal baking. The differentiation in curing speed leads to differentiation of solubility in a developer solution between the exposed and non-exposed resins. When a film of the resin is exposed to light through a photomask, the mask features can be reproduced in the film after developing. Since the photoexposure inhibits thermal curing and makes the exposed part more soluble than the non-exposed part a positive image is obtained.
The photodielectric composition can be coated on a variety of substrates. Desired structures can be obtained by photolithographic techniques. Because of its thermal and photostability and good dielectric properties as well as its excellent photo resolution, this photodielectric can be used as a permanent dielectric in printed wiring boards and high density packaging interconnection substrates where fine features such as nicrovias are required.
SUMMARY OF THE INVENTION
The invention provides a positive acting, photoimageable composition which comprises at least one a photoacid generator capable of generating an acid upon exposure to actinic radiation, at least one organic acid anhydride monomer or polymer, at least one epoxy, at least one nitrogen-containing curing catalyst, and an optional aromatic hydroxyl containing monomer, polymer or mixture thereof.
The invention also provides a photographic element which comprises a substrate and a dried positive acting, photoimageable composition on the substrate, which composition comprises at least one a photoacid generator capable of generating an acid upon exposure to actinic radiation, at least one organic acid anhydride monomer or polymer, at least one epoxy, at least one nitrogen-containing curing catalyst, and an optional aromatic hydroxyl containing monomer, polymer or mixture thereof.
The invention further provides a process for producing a positive image which comprises
a) providing a photographic element which comprises a substrate and a dried positive acting, photoimageable composition on the substrate, which composition comprises at least one a photoacid generator capable of generating an acid upon exposure to actinic radiation, at least one organic acid anhydride monomer or polymer, at least one epoxy, at least one nitrogen-containing curing catalyst, and an optional aromatic hydroxyl containing monomer, polymer or mixture thereof,
b) imagewise exposing the composition to sufficient actinic radiation to thereby provide imagewise exposed and imagewise nonexposed portions of the composition; and
c) removing the imagewise exposed portions of the composition with a liquid developer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the practice of the present invention, a positive acting, photoimageable composition is produced by admixing a photoacid generator capable of generating an acid upon exposure to actinic radiation, an organic acid anhydride monomer or p
Huang Ming Mei
Leyrer Laura M.
Xu Chengzeng
Hamilton Cynthia
Isola Laminate Systems Corp.
McDonnell & Boehnen Hulbert & Berghoff
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