4. New Directions in the Application of Surface Wave Plasmas for Environmental Technology
Current and past Support: Environmental Protection Agency,
ERP TAMU, NSF-REU

Objectives
As mentioned previously, our group has been responsible for the first successful beta testing of non-thermal plasmas for the successful reduction of such global warming emissions from a number of 200 mm semiconductor manufacturing processes {4-8, references in bibliography}. These investigations were, however, limited to a small number of manufacturing process [2]. Semiconductor manufacturing is a very competitive and rapidly developing industry. Recently, there have been important semiconductor process developments that have not been tested using our point-of-use surface wave plasma abatement technology. Furthermore, we would like to find new applications for this versatile technology. Such applications will require first laboratory and subsequently on-site beta testing. This project is primarily concerned with the former to assess the most promising directions for future application of this technology. Specifically: 
Laboratory investigation of surface wave plasma abatement of 300 mm etch processes.
300 mm etch processes introduce new etch feedstock process mixtures that are quite different from current 200 mm manufacturing recipes. Many of these processes operate at higher throughputs so the potential global warming emissions will be greater. However, optimization of feedstock composition is more critical from a quality control perspective, thus giving less flexibility for minimization of global warming emissions. A recipe that promises to be widely used for example will be 100 sccms CO, 440 sccms of Ar, 10 sccms O2 and 20 sccms CF4, very different from those currently used. Laboratory tests will be necessary to quantitate factors such as applied power, gas mixture ratios, additive gases and other factors necessary to optimize the effective DREs of PFCs emitted from such 300 mm technologies.  
Plasma Abatement of Alternative PFC feedstock for Etch Processes in 200 mm tools.
 Each of these new approaches has different nuances as far as reduction of global warming emissions is concerned. For example, it has recently been proposed that a feedstock mixture of NF3 and acetylene can be used for this purpose [5]. We have recently carried out preliminary investigations on such processes and demonstrated that HCN is generated under certain circumstances. We would like to optimize the surface wave plasma abatement technology to see how effective it is in treating HCN and the other undesirable byproducts in such processing. Another alternative PFC stream that is currently being tested by the semiconductor industry involves 10 sccms CF4 + 6 C4F8 sccms + 35 sccms CHF3 and we would like to ensure that our technology is capable of treating such emissions efficiently. Another alternate PFC being considered for commercial application is hexafluoro 1,3 hexadiene. The global warming process emissions using this feedstock have also not been investigated, and quantitative DREs and mass balance studies need measurement.
Prevention of Global Warming Emissions from Resist Stripping.
 The stripping of resist and post-etch residue in structures containing low-k polymer materials provides the opportunity of new applications of surface wave plasmas. Low dielectric constant materials such as benzocyclo-butene are being introduced as organic interlayer dielectric (ILD) to replace conventional oxides and nitrides as they have advantages of allowing higher performance in integrated circuits [6,7]. However, conventional resist stripping involving high temperature with plasma oxygen is unsuitable as it attacks the low-k polymer layer [8]. New fluorine containing technologies have been developed to overcome this problem but involve CF4 and NF3 which contribute to global warming emissions unless treated. As such low-k polymer materials such as benzocyclo-butene are very sensitive to the composition of the fluorine/oxygen mixture, it is difficult to optimize the effectiveness of such mixtures while maintaining quality control standards and minimizing global warming emissions. We shall thus simulate emissions for typical CF4 flow rates characteristic of oxygen/fluorine mixtures(O2/CF4/N2/H2) and investigate application of our point-of-use surface wave plasma abatement technology for this purpose. 
Expected Results

The current studies represent new research directions for a technology that has been demonstrated to set new benchmarks(>99.998% DREs) for control of global warming emissions from semiconductor manufacture associated with specific low flow CH3F and CF4 etch processes and for C2F6 chamber clean processes. We are now proposing to explore applications of this technology in three new areas. The intention is to establish the wider applicability of the technology, thus further enhancing the probability that it will find semiconductor industry-wide acceptance for control of global warming emissions. The proposed studies will initially involve laboratory investigation of the applicability of the technology to plasma treatment of 300 mm etch processes that are now coming commercially on line. We know of no abatement studies of PFC emissions for such recipes. Plasma abatement studies of recently introduced alternative PFCs(C4F8, hexafluoro 1,3 hexadiene) process streams for 200 mm etch technologies that have not been previously investigated and will enhance applications in the retrofit industry. Application of plasma abatement technology to low-k photoresist emissions has not been previously undertaken so this would test the capabilities of the technology for a new industrial application . Finally, our previous research has not addressed the modeling of non-thermal plasma abatement processing for general optimization of emissions control. This latter project is very involved, so we propose to concentrate on studies of electron-molecule collisions critical initiators of the plasma control processes which are discussed below.

We are developing environmentally compatible non-thermal plasma-based technologies for their efficient disposal.

     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 and CF4 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).