3. Surface Wave Plasma Abatement of Semiconductor Global Warming Compounds
Current and past Support: Environmental Protection Agency,,
National Science Foundation, ATP Texas Higher Education Coordinating
Board, SEMATECH, Motorola, Rf Environmental Systems Inc., ERP TAMU

Background

Political pressures to reduce emissions of greenhouse gases continue to build following the Third Conference of Parties held in Kyoto [1]. Whereas forced global warming due to CH4, N2O and especially CO2 have received most attention, it is now recognized that there could be significant climate impact in the near future [2] due to emissions of hydroflurocarbons (HFCs), perflurocompounds (PFCs) and SF6. The latter are vital to the semiconductor manufacturing industry and consequently US semiconductor chip manufacturers are working intensely to develop technologies to cost effectively treat such emissions [3]. Although global warming by these chemicals is currently relatively small compared to CO2, this situation could change radically in the near future due to the almost exponential increase predicted in chip production [2] over the next few years, and because of high infrared absorption cross-sections of PFCs and their particularly long lifetimes in the atmosphere. As typically only 30-40% of PFC feedstocks are consumed in chip manufacture, the remainder are essentially emitted into the atmosphere where they accumulate and will continue to influence global climate for tens of thousands of years. Seven years ago, our group recognized [4] the potential application of surface wave plasmas as a technology for effective abatement of such PFC emissions and initiated investigations of a specific CF4 /CHF3/Ar semiconductor manufacturing etch process. These studies subsequently involved both alpha and beta testing with destruction and removal efficiencies (DREs) of >99.998%. CF4 is one of the most potent global warming compounds of the PFCs with a lifetime of 50,000 years in the atmosphere and GWP100 of 6500. The technology exploits pre- and post- additive gases to optimize the DREs of PFCs and also to produce the most desirable final product distributions with minimum intrusiveness in production processes. Although the DREs for this specific manufacturing recipe has been remarkably effective more investigations are needed. The plasmas involved are cold plasmas and consequently non-equilibrium processes, which cannot be accounted for by currently available theory, drive the kinetics. Such information is critical for generalization of this technology to other different types of semiconductor manufacturing processing and for prototype optimization.
     
    Methods
The methods that we use to experimentally quantitate the final plasma emissions have been described previously {4-9}. Such EPA protocol techniques were used to establish DREs >99.998 % for PFCs in specific etch processes under conditions commonly found in semiconductor manufacture (i.e. flow rates, pressures, compositions etc) c.f. Figure 1(SiF4 is efficiently removed by post-scrubbing). Following initial tests in the laboratory, this surface wave based microwave plasma prototype was then installed downstream of an Applied Materials Centura 5200 MxP+ contact via etcher in Motorola,s Advanced Products Research and Development Laboratory at Austin, Texas. Processes run in the chamber included recipes using CHF3, CF4, and argon on blanket TEOS oxide, PECVD nitride, I-line resist, and patterned TEOS oxide wafers. The test plan included: (1) the evaluation of the DRE for PFCs and the identification and quantitation of plasma byproducts using FTIR and QMS and (2) the evaluation of possible impact on etch process performance, whether through the backstreaming of low molecular weight species such as H2, or the generation of particulates. Abatement performance tests called for evaluating DRE as a function of input gas composition, etch process parameters, and applied microwave power to the abatement device. A two-level design, 17 point experimental matrix was run at a high and low applied microwave power to the abatement unit.The surface wave plasma abatement device achieved a DRE of 99.998% for CF4 with 1923 W of applied microwave power [6] with no effect on quality control. The decrease in global warming potential obtained from application of this technology at Motorola was 11,700:1 for CHF3, 6500:1 for CF4, and 9200:1 for C2F6 [6,9]. We shall use these and other techniques to investigate the generalization of surface wave techniques to all semiconductor manufacturing processes currently used as they have different global warming impact.
     Bibliography

[1] COP 3 Report Document FCCC/CP/1997/7/Add.1, Kyoto December 1-10, 1997.

[2] Proceedings of the Global Semiconductor Industry Conference on PFC Emissions Control US EPA, Monterey, CA, April 7 and 8, 1998.

[3] W. Worth, "Recent Advances in the PFC Emission Reduction Technologies," IESH Conference, Milan, Italy, June 23-26 (1997).

[4] C. Hartz, B.A. Wofford, M. Jackson, and J.W. Bevan, "Surface Wave Plasma Abatement of CHF3 CF4 and Containing Semiconductor Emissions," Environ. Science and Technology, 34, 1892-1897, (1999).

[5] B.A. Wofford and J.W. Bevan, "Current Status of Surface Wave Plasma abatement of Semiconductor Global Warming Emissions," Fut. Fab. International 11, 89-96 (2001).

[6] S. Karecki et al. ,PTB Meeting, Sematech, Feb. 15, 2000.

[7] W.W.Lee, P.S.Ho, MRS Bulletin, 22, 19 (1997).

[8] N.P.Hacker, MRS Bulletin, 22, 19 (1997).

[9] M.Boumerzoug, H.Xu, R.L.Bersin, Mat. Res. Soc. Symp. Proc. 495, 345 (1998).





Affect of power on surface-wave abatement of low flow etch process at Motorolla.





Infrared on-line surface-wave abatement of low flow etch process at Motorolla. i) no applied rf or microwave ii) normal tool operation iii) application of surface-wave abatement.