Particle control for advanced wet process
Researchers from Mykrolis and STMicroelectronic present results of a recent study on particle filtration in recirculation HF and SC1 baths that was completed at ST Crolles 1 in France
Particle reduction in the Front-End-Of-the-Line (FEOL) cleaning processes, such as dilute Hydrofluoric Acid (HF), Standard Clean One (SC1), and Standard Clean Two (SC2) for wet etch and cleaning of wafer surfaces, is critical to achieving high yields in the semiconductor manufacturing process. Point-of-use (POU) membrane filters are used for the removal of sub-micron size particles from these aggressive cleaning chemicals in recirculation cleaning baths. As wafers are processed in the bath, particles generated must be removed rapidly to keep the bath clean and reduce the processing time between batches.
The POU filters for this application therefore should have high particle retention and high flow rate to allow rapid turnover of the bath liquid through the filters. These conflicting requirements are often not met by the traditional membrane filters that remove particles by sieving mechanism, based on size, as high particle retention calls for a tighter filter with attendant lower permeability. Recently filters have been developed that rely on surface adsorption, rather than sieving alone, as the principal particle capture mechanism, by creating a surface that is electrostatically neutral in the fluid of interest. Retention by an adsorptive means, such as attractive particle-filter surface interactions, allows the use of membrane with more open pore structures that provide high flow rates and high retention.[1-5] Key applications of such filters are in POU recirculation etch baths using HF and Buffered oxide etch chemistries.
For particle removal from SC1 and SC2 baths, Teflon membrane filters of high chemical resistance (low ionic and organic extractables even at elevated temperatures) are exclusively used. To provide a stable system performance in these outgassing type processes at elevated temperatures, we have developed the Teflon filters with a modified surface to make it non-dewetting. The filter comes pre-wet in DI and is ready for installation for a fast start up of the aqueous chemical based processes.
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ST Engineers using Mykrolis Intercept(R) filtration technology on a wet clean tool (photo used with permission of ST Microelectronics) |
References:
[1] D. C. Grant and B. Y. H. Liu, Sieving capture of liquid borne particles by microporous membrane filtration media, Part. Part. Syst. Charact. 8(1991) 142-150
[2] J.-K. Lee, B. Y. H. Liu and K. Rubow, Latex sphere retention by microporous membranes in liquid filtration, J. Inst. Env. Sci. (January/February) (1993) 26-36
[3] W. P. Kelly and D. C. Grant, Optimisation of filter properties for recirculating etch baths, Journal of the IEST 44(2000) 30-40
[4] W. P. Kelly, D. C. Grant, J. Zahka, W. Huang and S. Raghavan, Effect of surface charge and fluid properties on particle removal characteristics of a surface-optimized REB filter, Diffusion and Defect Data - Solid State Data, Part B: Solid State Phenomena 76-77(2000) 271-274
[5] Communication with Dr. Chase Duclose-Orsello
