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
2001-08-29
2004-04-06
Hamilton, Cynthia (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
C430S325000, C430S330000, C430S311000, C430S272100, C430S275100
Reexamination Certificate
active
06716568
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photoimageable epoxy compositions useful as photoresists for applications requiring thick films. In particular, this invention relates to specific compositions useful for that purpose that include at least one solvent, at least one epoxidized bisphenol A formaldehyde novolak resin, at least one polyol reactive diluent and at least one photoacid generator.
2. Brief Description of Art
Photoimageable coatings are currently used in a wide variety of semiconductor and micromachining applications, where photoimaging is accomplished by exposure to patterned radiation of a coating on a substrate, where the radiation induces a solubility change of the coating in a developer, such that the exposed or unexposed regions can be selectively developed away. The photoimageable coating (photoresist) may be either of the positive or negative type, where exposure to radiation increases or decreases the developer solubility, respectively. Advanced packaging applications requiring solder bumps having a high aspect ratio (defined as the height to width ratio of the imaged feature), or applications involving the fabrication of micro electromechanical devices (MEMS) require photoresists which are capable of producing uniform spin-coated films and high aspect ratio images of greater than one hundred microns thickness. Conventional positive resists based on diazonaphthoquinone-novolak chemistry are not suitable for applications for which the thickness is required to be greater than about 50 microns. This thickness limitation is caused by the relatively high optical absorption of the diazonaphthoquinone-type (DNQ) photoactive compound in the near-ultraviolet region of the optical spectrum (350-450 nm) which is typically used to expose the resist. Also, DNQ-type of photoresist possesses limited contrast, or differential solubility, of the exposed vs. unexposed resist in a developer solution. Optical absorption necessarily reduces the radiation intensity as it traverses from the top to the bottom of the film, such that if the optical absorption is too high the bottom of the film will be underexposed relative to the top, causing a tapered or otherwise distorted profile of the developed image.
A negative, spin-coated, thick-film photoresist of the chemically amplified type, which has a very low optical absorbance at wavelengths in the 350-450 nm range has been described in the literature (N. LaBianca and J. D. Gelorme, “High Aspect Ratio Resist for Thick Film Applications”, Proc. SPIE, vol. 2438, p. 846 (1995)). High aspect ratio (>10:1) photoimaging was demonstrated in 200 micron thick films. This resist comprises a solution in a casting solvent of a highly branched eight functional epoxy novolak resin, EPON® SU-8 from Shell Chemical Company, and a photoacid generator (PAG) such as CYRACURE® UVI 6974 from Union Carbide which consists of a triarylsulfonium hexafluoroantimonate salt. Suitable photoacid generators based on sulfonium salts are well-known and have been extensively discussed in the literature (see for ex. Crivello et al., “Photoinitiated Cationic Polymerization with Triarylsulfonium Salts”, Journal of Polymer Science: Polymer Chemistry Edition, vol. 17, pp. 977-999 (1979).) The photoacid generator is added at concentrations of less than 10% by weight of the total solids in order to keep the optical transparency sufficiently high to maintain nearly uniform radiation intensity through the film thickness. The resulting photoresist formulation may be spin-coated onto a wide variety of substrates, pre-baked to evaporate solvent, leaving a solid photoresist coating of one hundred microns or greater thickness which may be photoimaged by exposure to near-ultraviolet radiation through a patterned photomask by contact, proximity, or projection exposure. Subsequent immersion in a developer solution dissolves away the unexposed regions, leaving behind a high resolution, three dimensional, negative image of the photomask.
EPON® SU-8 is a low molecular weight epoxy-functional polymer that has several characteristics making it advantageous for high aspect ratio photoimaging: (1) it has a high average epoxide functionality (eight), (2) a high degree of branching, (3) high transparency from 350-450 run, and (4) the molecular weight is sufficiently low to allow high solids formulation, assisting in the application of defect-free thick films. The high functionality and branching result in efficient crosslinking under the influence of strong acid catalysts, while the high transparency allows uniform irradiation through thick films, making the resist capable of forming images with aspect ratio of greater than 10:1 at film thicknesses of greater than 100 microns. Photoresist formulations based on EPON® SU-8 are currently commercially available from MicroChem Corp. (Newton, Mass., USA) under the general name SU-8.
U.S. Pat. Nos. 4,882,245 and 4,940,651 assigned to International Business Machines Corp. disclose a photoimageable cationically polymerizable composition for use in printed circuit boards which consists of a mixture of up to 88% epoxidized bisphenol A formaldehyde novolak resin with average epoxide functionality of eight and a reactive diluent which serves as a plasticizer, and a cationic photoinitiator. Reactive diluents disclosed were difunctional or trifunctional epoxide compounds, preferably at 10-35% by weight solids. However, no polyol reactive diluents were disclosed.
U.S. Pat. Nos. 5,026,624, 5,278,010, and 5,304,457 assigned to International Business Machines Corp. disclose a photoimageable cationically polymerizable composition suitable for use as a solder mask, which consists of a mixture of the 10-80% condensation product of bisphenol A and epichlorohydrin, 20-90% of epoxidized bisphenol A formaldehyde novolak resin, and 35-50% by weight of epoxidized glycidyl ether of tetrabromobisphenol A, with 0.1-15 parts per hundred by weight of a cationic photoinitiator. No polyol reactive diluents were disclosed. Curtain coating, roll coating, and wound wire rod coating were used.
U.S. Pat. No. 5,102,772 assigned to International Business Machines Corp. discloses photocurable epoxy compositions consisting of a mixture of the epoxidized bisphenol A formaldehyde novolak and a difunctional cycloaliphatic epoxy compound and/or trifunctional aromatic epoxy compound, and a sulfonium hexafluoroantimonate salt photoinitiator. No polyol reactive diluents were disclosed.
U.S. Pat. No. 4,256,828 assigned to Minnesota Mining and Manufacturing Co. discloses a photopolymerizable composition based on an epoxy resin of functionality greater than 1.5, a hydroxyl-containing additive, and a photoacid generator. The hydroxyl-containing additive is reported to increase flexibility and decrease shrinkage for coatings of up to 100 microns thickness. However, the intended application was for UV-curable coatings. Furthermore, use of a highly branched, eight functional epoxy novolak resin for the purpose of high aspect ratio photoimaging was not disclosed.
U.S. Pat. No. 5,043,221 assigned to Union Carbide discloses a photopolymerizable conformal coating for printed circuit boards based on an cycloaliphatic epoxy resin, a polyether polyol additive, and a photoinitiator. However, use of a highly branched, eight functional epoxy novolak resin for the purpose of high aspect ratio photoimaging was not disclosed.
While the EPON® SU-8 resin based compositions disclosed previously are capable of very high resolution and aspect ratio, the cured material has a tendency to be brittle, and may undergo stress-induced cracking and delamination of the coating from the substrate. Both the cracking and delamination is exacerbated by the shrinkage-induced stress that occurs when the material undergoes polymerization, which is manifested in substrate bowing, where shrinkage of the coating induces bending (bowing) of the substrate. The present disclosure describes a composition containing polyol reactive diluents which reduces the stress, cracking, and delaminat
Alemy Eric L.
Minsek David W.
Geschke Elizabeth A.
Hamilton Cynthia
Microchem Corp.
Simons William A.
Wiggin & Dana LLP
LandOfFree
Epoxy photoresist composition with improved cracking resistance does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Epoxy photoresist composition with improved cracking resistance, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Epoxy photoresist composition with improved cracking resistance will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3198032