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
2001-04-17
2003-05-27
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, C430S906000, C525S420000, C528S324000, C528S332000, C528S335000
Reexamination Certificate
active
06569598
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to positive photoresist compositions. The invention is more particularly related to photoactive poly(N-alkyl-o-nitroamides), which may be used to prepare photosensitive compositions that yield en dry photoresist films that are resistant to a broad range of organic solvents.
BACKGROUND OF THE INVENTION
Receptor-ligand interactions are critical components of many fundamental biological processes. Such interactions involve specific binding of a macromolecule receptor (e.g., enzyme, cell-surface protein, antibody or oligonucleotide) to a particular ligand molecule. Receptor-ligand binding may affect any of a variety of intercellular and intracellular processes in an organism, such as signal transduction, gene expression, immune responses or cell adhesion. An improved understanding of receptor-ligand interactions is necessary for many areas of research in the life sciences, as well as for the development of agents that modulate such interactions for therapeutic and other applications.
Miniaturized ligand-arrays, formed using microfabrication and solid-phase chemical synthesis on substantially planar supports, have been used to facilitate the study of receptor-ligand interactions (for representative examples, see Fodor et al., Science (1991) 251:767; Pease et al.,
Proc. Natl. Acad. Sci. USA
91:5022, 1994; Pirrung et al., U.S. Pat. No. 5,405,783; Fodor et al., U.S. Pat. No. 5,445,934; Pirrung et al., U.S. Pat. No. 5,143,854; Fodor et al., U.S. Pat. No. 5,424,186 and Fodor et al., U.S. Pat. No. 5,510,270; Chee et al., Science (1996) 274:610 and Brennan, U.S. Pat. No. 5,474,796). Contacting a ligand array with labeled receptor allows many ligands to be simultaneously screened for receptor binding. The location of bound receptor on the array is determined by detecting photons or radioactivity. However, the surface density of ligand is often low, resulting in the need for costly imaging equipment and long image acquisition times. Drug discovery efforts have been further hampered by low ligand surface density, since many functional assays require higher ligand concentrations to identify drug leads.
One approach to increasing surface density of ligands involves immobilizing ligands on an array of polyacrylamide pads using microfabrication techniques (see Guschin et al.,
Anal. Biochem
. 250:203, 1997 and Yershov et al.,
Proc. Natl. Acad. Sci. USA
93:4913, 1996). Such an approach increases the surface density of the ligands, but places a size restriction on diffusion into the polymer that many receptors exceed. Furthermore, such polymeric supports may not be compatible with solid-phase chemical synthesis, which requires adequate swelling and solvation of a polymeric matrix in order to achieve efficient mass transfer of reagents. Further, although this polymer can be photopatterned (i.e., multiple discrete pads may be generated by a process involving exposure to irradiation), the photosensitivity is severely limited, requiring 30 minutes of illumination. Such a low throughput is inadequate for mass production.
Photopattemed barriers with improved photosensitivity and other properties could potentially permit the preparation of higher density arrays, using solid-phase synthesis and a series of photopatterned barrier layers. Such barrier layers could allow applied reagents to react with surface-attached molecules only in predefined regions. Within such a procedure, however, a barrier layer must meet several criteria. First, the barrier layer should maintain integrity and impermeability while in contact with reagents solubilized in a wide variety of solvents. Second, irradiated regions of the barrier layer must undergo a photochemical reaction that is substantially inert with respect to the surface-attached molecules in contact with the layer. Third, removal of the barrier layer must be accomplished with a stripping solution that does not react with the surface-attached molecules. Finally, the barrier layer must be photopatterned with light having a wavelength larger than about 300 nm in order to avoid direct photodegradation of the surface-attached molecules.
Although numerous negative and positive photoresist compositions have been described, compositions that meet the above criteria are not currently available. For example, negative photoresists containing cinnamate, chalcone, coumarin, diphenylcyclopropene, bis-azide, and other such similar groups function by light-induced cross-link formation [see
Desk Reference of Functional Polymers: Synthesis and Applications
, edited by Reza Arshady, (1997), American Chemical Society, Washington, DC., Chapters 2.1 and 2.3]. Although the irradiated films are insoluble in numerous solvents, the photoreactions leading to cross-linking also react non-specifically with other molecules in contact with the photoresist. Similarly, harsh stripping agents required to remove the cross-linked photoresist film will degrade other molecules indiscriminately. Such cross-linking and stripping reactions are incompatible with photoresist directed solid-phase synthesis.
A further problem encountered with cross-linked photoresists relates to swelling of irradiated regions in a variety of solvents. In order to generate an image, the unexposed regions of a negative photoresist must be removed by solubilization with a suitable solvent. Any solvent that will dissolve the uncross-linked material will also interact with the cross-linked regions to produce a solvated and swollen-state. Though the irradiated regions maintain their overall integrity, swelling results in image distortion, reduced resolution, and permeability of reagents such that the photoresist fails to provide a barrier. Such difficulties are avoided in photoresists that employ a radiation-induced solubility differential resulting from changes in chemical (e.g., a polarity change) rather than physical (e.g., cross-linking) properties.
Positive photoresists containing a phenolic polymer and a diazoquinone are well known in the art, and have been used extensively in microelectronic manufacturing [see U.S. Pat. Nos. Steinhoff et al., U.S. Pat. No. 3,402,044; Moore, U.S. Pat. No. 2,797,213; Endermann et al., U.S. Pat. No. 3,148,983; Schmidt, U.S. Pat. No. 3,046,118; Neugebauer et al., U.S. Pat. No. 3,201,239; Sus, U.S. Pat. No. 3,046,120; Fritz et al., U.S. Pat. No. 3,184,310; Borden, U.S. Pat. No. 3,567,453; and Pampaione, U.S. Pat. No. 4,550,069]. Such positive photoresists employ a radiation-induced polarity change that transforms the diazoquinone from a hydrophobic molecule to a carboxylic acid. Selective dissolution of irradiated regions ensues upon contact with an aqueous alkaline developer. Although swelling by the developer is avoided, diazoquinone photoresists are unsuitable as barrier layers for reagents during solid-phase synthesis since they are soluble in a variety of organic solvents.
Other positive photoresists have been developed for the microelectronic industry based on polyamides, polyimides, and polyamic acids. In all cases, the art teaches that it is desirable to prepare such compositions so they are soluble in conventional process solvents. For example, polyamide photoresists and polyimides have been described with modifications that intentionally provide a broad solubility profile to these polymers [see Mueller and Khanna, U.S. Pat. No. 4,927,736; Kwong et al., U.S. Pat. No. 5,114,826 and Flaim et al., U.S. Pat. No. 5,281,690]. In contrast, photoresist directed solid-phase synthesis requires a broad insolubility profile so as to provide a film that maintains integrity and impermeability while in contact with a myriad of solvents.
Efforts to develop both positive and negative photoresists for microelectronics have also been directed toward compositions that are reactive to very short wavelengths of light or electron beams [see
Desk Reference of Functional Polymers: Synthesis and Applications
, edited by Reza Arshady, (1997), American Chemical Society, Washington, DC., Chapters 2.3 and 2.4]. The w
Ashton Rosemary
Haymond Charles R.
Lee Sin J.
Syntrix Biochip, Inc.
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