MicroChem Corp. and Nippon Kayaku Co., Ltd. have jointly developed a new, photoimageable coating composition for use in fabricating a wide variety of micro-electromechanical systems (MEMS) and optical MEMS. This chemically amplified thick-film photoresist, known as KMPR, has many of the same high-aspect ratio photo imaging properties as solvent developable SU-8, but can be developed in a conventional aqueous alkaline developer (TMAH) and readily stripped from the wafer.
Single-factor experimental methods rarely find the optimum performance of a photoimageable coating efficiently and often fail to detect the interactions so common in complicated photochemical systems. By combining the settings of several factors simultaneously in an array (experimental design), it is possible to separate out the main effects and their interactions.¹
This paper presents the optimization of KMPR for contact alignment and near diffraction-limited, thick film reduction stepper applications. A Sequence of Taguchi style, half-factorial experimental designs was used to evaluate the process parameters for a 5 and 50 Μm thick film exposed on a contact aligner followed by a third half-factorial design for a 10 Μm thick film of KMPR photoresist exposed on a 365 nm, 0.40 N.A. stepper. Independent factors, such as: soft bake time, focus, exposure dose, initiator activation time (post-exposure bake time), developer time and delay time were evaluated

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In order to work out indispensable criteria for a promising process of innovation, a historical review is given for two paths of innovation, which the author was involved in as an chemist in electrical industry from the initial idea up to commercialization and application in the field of microelectronics and electronics. The examples concern the approach to thermally stable organic patterns via photosensitive precursors of polyimides (negative mode) and of poly(benzoxazoles) (positive mode). After direct photolithographic patterning the precursor layers can be thermally converted into polyimide and poly(benzoxazole), respectively. The photoresists have been commercialized by licensed chemical companies. They have been and still are mainly applied to memory and logic devices as protective and buffer coatings to reduce the stress caused by an encapsulating resin, and to thin film multichip modules as planarizing interlayer dielectrics.

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Photopolymerization kinetics of thick aqeous-developable negative photoresist film was studied using photo-DSC in order to correct the background properly. We compared the heat fraction from ingredients in photopolymer. Thus, we confirmed that the typically used second scan method will derive overestimation of photochemical conversion, using the photobleachable aminobenzophenone photosensitizer. In the case of benzildimethylketal formulation, the second scan method will derive underestimation due to photocoloring. In order to solve this problem, we devised a background correction method using a dummy formulation and demonstrated that this method will improve the quantitative analyses using photo-DSC.

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Polymeric materials with photoinduced-thermally cleavable property were prepared. A blended system of poly(methacrylic acid-co-ethyl methacrylate) (MAA-EMA), photoacid generator (PAG), and diepoxides having tertiary ester linkages became insoluble in methanol when baked above 120 oC for 10 min without irradiation. On UV irradiation and subsequent post-exposure-bake (PEB) treatment, the blended film dissolved in methanol. The dissolution profile of the films was strongly dependent on the type of PAG used, structure of diepoxides, fraction of methacrylic acid in MAA-EMA, and MAA-EMA/diepoxide ratio. A mechanism for the dissolution of the crosslinked films was studied by FT-IR spectroscopy. A resist pattern simulation revealed the possibility of sub-micron feature size by using this system.

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Crosslinking using pendant basic groups generated on irradiation at 366 nm and thermally generated isocyanato groups from oligomers bearing carbamoyloxyimino (COI) groups was demonstrated. Acetophenone O-methacryloyloxyethylcarbamoyloxime (AMCO) and 2-butanone O-methacryloyloxyethylcarbamoyloxime (BMCO) were used as monomers bearing COI groups. Benzophenone and anthracene showed little effect on the photolysis of COI groups in AMCO and BMCO in oligomers, and isopropylthioxanthone (iPTX) sensitized for COI groups in AMCO efficiently. On irradiation of an oligomer of AMCO, BMCO, and methyl methacrylate (MMA) at 366 nm in the presence of iPTX, only COI groups in AMCO were photolyzed. These oligomer films became insoluble on irradiation, and the insolubilization was much enhanced by post-exposure bake (PEB) at 150 °C due to crosslinking between photo-generated basic groups and thermally generated isocyanato groups. Furthermore, we succeeded in the preparation of an oligomer consisting of AMCO, BMCO, and 2-(acryloyloxy)thioxanthone, which showed similar photoreactivity and solubility behavior to AMCO-BMCO-MMA containing iPTX.

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Elastic property of polymer aggregates in a resist pattern is characterized by using atomic force microscope (AFM). In order to determine Young's modulus of polymer aggregates based on Hertz theory, a separation force between polymer aggregates is measured by using the AFM. Young's modulus of polymer aggregates composing resist pattern can be determined to be 10-25MPa. The results of our experiment clearly show that the polymer aggregates indicates relatively low cohesion property.

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We designed diphenyliodonium salts with diazoxide group for a photo-acid generator (PAG) in chemically amplified resists. The absorption coefficients at 365 nm for the new PAGs were 103 -104 orders, originating in diazoxide structure. The quantum yield for acid generation irradiating 365 nm wavelength light of diphenyliodonium 1-diazo-2-hydroxynaphthalene-4-sulfonate (AZO-DPI) and diphenyliodonium 1-diazo-2-hydroxy-6-nitronaphthalene-4-sulfonate (NO2-AZO-DPI) was 0.21 and 0.14, respectively. The thermal stability of AZO-DPI and NO2-AZO-DPI were 144.2 and 153.2°C, respectively. The photosensitivity of AZO-DPI and NO₂-AZO-DPI irradiating 365 nm wavelength light in polymer bearing ethoxyethyl protecting group were 120 and 98 mJ/cm², respectively. The diphenyliodonium salt is the promising PAG sensitizing for 365 nm chemically amplified resists.

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Pyridines are known to have different pKa* in the excited state from pKa in the ground state. They are easily protonated in their photo-excited states. In previous studies, we reported the luminescence properties of thin films of a pyridine-containing polymer, poly(4-vinylpyridine)(P4VPy). In this study, the changes in emission spectra of bulk solid and thin films of P4VPy with UV-irradiation are reported, and the influence of the film thickness of P4VPy is re-examined taking the effect of surface protonation into consideration. Though protonation of P4VPy has been reported many times, and the proton source are inside of the polymer, the surface protonation of P4VPy in this study are caused by the extrinsic, outer proton sources.

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