MEMBRANE PROCESSES IN THE PURIFICATION OF ELECTRONIC GRADE CHEMICALS
Advancing the chemical engineering fundamentals
Membranes and Membrane Science (T2-8P)
Keywords: MEMBRANES, PURIFICATION, ELECTRONIC GRADE CHEMICALS
The quality requeriments for wet processing chemicals have been increasing during the last 30 years in line with the increasing complexity of the semiconductor devices. In addition, the overall product portfolio of wet processing chemicals expands due to the introduction of new technologies, which also leads to a change in volume consumption of chemicals. Specifically, the big volume products of the past, sulphuric acid and hydrogen peroxide are hit by new cleaning technologies. Among the main products still used for cleaning purposes during the manufacturing process are sulphuric acid, hydrogen peroxide, 2-propanol, and ammonium hydroxide, whereas the group of chemicals used for structuring the silicon or silicon oxide surfaces includes hydrofluoric acid as the key chemical of semiconductor technology [1].
According to the complexity of the manufacturing process and the sensitivity of highly integrated devices, specific quality requirements have been developed and established by the industry, with the SEMI base standards for wet chemicals. It is important to notice that the development of more and more stringent specifications was related to the introduction of the multielement atomic absorption (AAS), inductive coupled plasma-optical emission spectroscopy (ICP-OES), inductive coupled plasma-mass spectroscopy (ICP-MS), and the high resolution-inductive coupled plasma-mass spectroscopy (HR-ICP-MS).
The manufacturing of high purity wet chemicals (with different specifications of metallic impurities such as EG/MOS, 10-500 ppb ; VLSI, 10-100 ppb; ULSI, < 10ppb ; SLSI, < 1ppb ; XLSI, < 100ppt) require (i) the selection of materials, (ii) the filtration to remove the particles, and (iii) the purification to the specifications of the determined grades by the introduction of some advanced separation technologies based on distillation, ion-exchange, and membranes [1].
Taking into account that the aqueous hydrofluoric acid (HF) is the only cleaning and etching material that exposes the base silicon surface in the production process of the integrated circuits, the ultrapurity of the HF is an important concern both in the virgin and the processed product. The etching rate of silicon dioxide generally increases with the increase of the concentration of HF but delamination problems may arise, so wafer oxide removal operations generally tend toward the use of lover concentrations of HF, around 0.1 to 5 % [2].
Under these considerations, this work is focused to the use of membranes to the purification of hydrofluoric acid, being analysed the behaviour of reverse osmosis and nanofiltration membranes in order to advance the chemical process fundamentals.
Acknowledgements
This research is financially supported by the Spanish Ministry of Science and Technology (Project CTM2006-00317).
References
[1] W.J. Sievert, Setting standards- the development of standards in the field of electronic chemicals, Semiconductor Fabtech, 13th ed. 175-179, 2003. [2] D. Mukherjee, A. Kulkarni, W.N. Gill, Membrane based system for ultrapure hydrofluoric acid etching solutions, J. Membr. Sci. 109, 205-217, 1996.
Presented Tuesday 18, 13:30 to 15:00, in session Membranes and Membrane Science (T2-8P).
