The purity of fluids exposed to a wafer is critical as the node sizes are approaching low single digit nanometers. The potential impurities could be solid or semi-solid particles, soluble metal cations, anions, organic species, or gases. All these need to be removed for optimum yield and minimal defects. The technical challenge associated with reducing the node sizes also relates to membranes production as membranes with low single digit pore sizes are needed to remove nanometer impurities. The interest in nylon membrane is twofold as it can mechanically remove fine particles as well as by its adsorptive capabilities. In this study, nylon membranes with pore sizes of 2, 5, 10, and 20nm were characterized for microstructure, flow rate versus pressure drop, bubble point, and metal extractables in PGMEA.
The high purity requirements of materials used in semiconductor manufacturing are being pushed to unprecedented levels as demand for reliability in computer processors over increasingly longer lifetimes continues to rise. The production of these high purity chemicals requires new purification methods and technologies. One of the limiting factors in purification process is to bring the metal impurities into close contact with purifying surfaces. Current metal reduction techniques rely on ion exchange technology however, the pathways are large in comparison with the size of the unwanted metal species. A new approach is required to increase the probability of contact between the metal species with the exchange surface. In addition, fluid channels need to be mixed, rotated, and inverted in order to increase the probability of surface contact. The new approach discussed in this paper would present a method for dividing the fluid through micro-channels that form tortuous pathways. These micro-channels allow for further dividing and converging of the fluid thereby presenting the metal species to the purifying surfaces throughout the porous matrix. Several high purity chemicals such as PGMEA used in microelectronic industries were purified using the above approach. The metal concentrations of low parts per billion (ppb) were effectively reduced to low parts per trillion (ppt). The ion exchange capability was a function of the concentration and the presence of the species in the solution. Two ion exchange chemistries of strong acid and chelating were made into these structures and their purification performances were assessed and compared in terms of removal efficiencies. Furthermore, these two chemistries were evaluated in series to demonstrate the overall synergistic purification capabilities.
The trend in microelectronics fabrication is to produce nano-features measuring down to 10 nm and finer. The PPT levels of organic and inorganic contaminants in the photoresist, solvent and cleaning solutions are becoming a major processing variable affecting the process capability and defectivity. The photoresist usually contains gels, metals, and particulates that could interfere with the lithography process and cause microbridging defects. Nano filters of 5 nm polypropylene, 5 nm polyethylene, and 10 nm natural nylon were used to filter propylene glycol methyl ether acetate PGMEA containing 50 ppb of Na, Mg, Al, Ca, Cr, Mn, Fe, Cu, Zn, and Pb. All filters were effective in removing trivalent Al, Cr, and Fe metals indicating the mechanism for their removal as mechanical sieving. However, the nylon was also very effective in removing the divalent metals showing adsorptive properties. Furthermore, the metal removal of the nylon membrane was studied as a function of surface chemistry. Natural and charged 40 nm nylon membranes were tested and found that charged nylon is more effective for metal removal.
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