Resins used in photoresist manufacturing are often relatively expensive once processing steps (fractionation e.g.) and yield losses are factored into the net cost. We have previously reported on the merits of using an economically more attractive fractionation process using a liquid/liquid centrifuge. Further refinements of this method indicate that waste streams could be reduced by recycling the extractant phase and that lower molecular weight fractions removed from the starting resin might be used in making other resist ingredients [speed enhancers, photoactive compound (PAC) backbones e.g.]. Both of these improvements would reduce the overall manufacturing costs of making resist raw materials and the final products made with them.
The need to make well characterized resins consistently is paramount to the preparation of high performance photoresists. Solid resins fractionated by selective precipitation have been separated by ultracentrifugation at varying temperatures. At sufficiently high revolutions per minute, solvents and oligomers are efficiently squeezed out leaving behind polymer with higher average molecular weight and lower dispersity than resins obtained by more common isolation techniques. By controlling isolation conditions, resins with desired dissolution rates could be produced. Lithographic test confirmed that resists properties could effectively be controlled by manipulation of process conditions to isolate resins used in the formulations.
Novolak resins fractionated using a unique method, were compared to resins fractionated with conventional methods. The potential for improving the fractionation/separation process and for making improved or more consistent resist with the resins was identified. Several experimental designs were run to determine optimum conditions needed to achieve better separation. Isolated resins were used to make experimental i-line photoresists which were tested against resists made with the conventional processes.
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