Polyphenol oxidase and peroxidase were puri®ed from white yam (Dioscorea rotundata) using DEAE-cellulose ionexchange chromatography. Thermoinactivation curves for polyphenol oxidase showed monophasic kinetics, while those for peroxidase were biphasic. Urea partially stabilised peroxidase against irreversible thermoinactivation, but did not do so in the case of polyphenol oxidase. Only peroxidase was capable of regenerating activity after thermoinactivation. The results showed that thermoinactivation of peroxidase was mainly due to conformational changes, while that of polyphenol oxidase was probably due to covalent damage. Peroxidase reactivation might play an important role in the browning of processed yam. INTRODUCTIONDespite the importance of yam as a major food crop in West Africa, its postharvest biochemistry has been poorly studied. 1 As a consequence, postharvest losses due to sprouting, physical damage, pests and pathogens have remained relatively high. 2 One relatively successful procedure for improving the postharvest storage of white yam (Dioscorea rotundata) tubers involves processing into¯our. This consists of (1) peeling off the outer covering, (2) cubing, (3) boiling in distilled water for 10±15 min, (4) drying and (5) milling into¯our. Unfortunately, consumer acceptability and the shelf-life of the¯our are adversely affected by the inability of the¯our to retain the typical white colour of yam which is highly desired by consumers. 3,4 Colour changes in freshly damaged plant materials have been attributed to the activity of polyphenol oxidase (PPO; o-diphenol:O 2 oxidoreductase, EC 1.10.3.2), which catalyses the oxidation of polyphenols to o-quinones. 5,6 Peroxidase (Px; donor: hydrogen peroxide oxidoreductase, EC 1.11.1.7) catalyses the oxidation of a number of aromatic compounds and has been associated with darkening in fresh and processed vegetables and fruits. 7 Both PPO and Px are known to be highly heat-resistant but each displays a different capability for reactivation after thermoinactivation. 5,8±11In D rotundata, which contains PPO, 3,4,12 correlating PPO activity with tissue browning was shown to be contraindicative. 13 The purpose of the present study was to relate the thermoinactivation processes of PPO and Px to the discolouration of processed yam.
Trilayer stacks with alternating etch selectivity were developed and extensively investigated for high NA immersion lithography at 32nm node and beyond. The conveyance of pattern transfer function from photoresist to Si-containing bottom anti-reflective coating (Si-BARC) and carbonrich underlayer hard-mask (UL) elegantly solved the small etch budget issue for ultra-thin photoresists in immersion lithography. However, due to the hybrid nature of Si-BARC, many different behaviors were observed in comparison to conventional BARC. Lithographic performance, stability, and reworkability were among the most challenging issues for trilayer scheme.Despite of the rapid improvement in lithographic performance and stability of trilayer materials reported by several papers, the rework and cleaning of trilayer materials by wet chemistry remained a challenging problem for manufacturability. The dual function requirement of reflection control and pattern transfer (i.e. hard-masking) for spin-on Si-BARC mandates hybrid materials. Si-BARC containing both organic moiety and inorganic backbone were extensively studied and demonstrated excellent performance. However, the hybrid nature of Si-BARC necessitates the revisit of different wet chemistries and process adjustment is essential to achieve desirable results. In addition, the similarity in chemical structures between Si-BARC and low-κ dielectrics demands subtle rework differentiation by wet chemistry from a chemistry point of view.In our development, we strived to identify rework solutions for trilayer materials in both front-end-of-line (FEOL) and back-end-of-line (BEOL) applications. Rework solutions including diluted HF, Piranha, and low-κ compatible strippers were extensively investigated. The optimization of solution mixture ratios and processing conditions was systematically studied. Thorough defect inspection after rework was performed to ensure the readiness for manufacturability. Extensive Piranha rework study on stack wafers and monitor wafers were carried out and excellent results are reported.
Improvement of line edge roughness (LER) and line width roughness (LWR) is required for integration of semiconductor devices. This paper describes various process factors affecting LER/LWR of 193 nm resists such as mask layout (bright field/dark field), pitches, optical settings, substrates, film thickness, baking temperature and development condition. The origins of line roughness are discussed in view of aerial image contrast, transmittance of resists and pattern profiles. Bright field mask exhibited lower LER/LWR values than dark field mask, LER/LWR deteriorated as larger pitches and illumination condition affected roughness and these results are explained using normalized image log-slope (NILS). BARC dependence of line roughness is explained by pattern profile difference due to interactions between resist and BARC and in some cases BARC reflectivity. Contributions of film thickness, SB & PEB temperature and development condition to line roughness are also reported.
We will give an account of our investigation on structure property relationships of amines with regards to line width roughness (LWR) and line edge roughness (LER) of a 193 nm alicyclic-acrylate resist. Specifically, we have looked at basicity, molar volume and logD as factors which may have an influence of roughness of 80 nm 1:1 L/S features. For relatively hydrophobic amines (Log D > -1), the lower the hydrophilicity at acidic pH the greater the LER and LWR becomes. Specifically, in this range of Log D, more hydrophobic larger amines, with higher basicity, tend to give worse L/S feature roughness. For amines which are more hydrophilic, the relationship becomes more complex with some amines giving a lower LER while others do not. This appears to be predicated on a delicate balance between basicity, hydrophilicy and size.
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