| AVS 60th International Symposium and Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS-TuP |
| Session: | Plasma Science and Technology Poster Session |
| Presenter: | S. Wang, University of Wisconsin-Madison |
| Authors: | S. Wang, University of Wisconsin-Madison J.B. Boffard, University of Wisconsin-Madison C.C. Lin, University of Wisconsin-Madison A.E. Wendt, University of Wisconsin-Madison S.B. Radovanov, Varian Semiconductor Equipment, Silicon Systems Group, Applied Materials Inc. H.M. Persing, Varian Semiconductor Equipment, Silicon Systems Group, Applied Materials Inc. |
| Correspondent: | Click to Email |
Plasma process control applications require acquisition of diagnostic data at a rate faster than the characteristic time scale of perturbations to the plasma. Diagnostics based on optical emission spectroscopy (OES) of intense emission lines permit rapid noninvasive measurements with low-resolution (~1nm), fiber-coupled spectrographs, which are included on many plasma process tools for semiconductor processing. The use of OES is an established practice to determine when a process is completed, i.e., the process “endpoint,” by detecting changes in intensity in optical emissions of key gas-phase chemical species, and OES can also be used to detect the presence of impurities and monitor changing reactor wall conditions. More detailed real-time information about the plasma state is increasingly desirable for process monitoring, however, due to progression in the semiconductor industry toward plasma processes with both tighter tolerances and multiple steps, i.e., where operating parameters are varied over the course of the process. In this work,* we examine the utility of plasma optical emissions from argon measured with a low-resolution spectrograph (Verity 1024 SH) as a real-time monitor of plasma parameters during the course of a plasma process, based on a rapid method to monitor and analyze the intensities of a select group of Ar emission lines to dynamically determine the following plasma parameters. Electron temperature and density are relevant parameters for characterization of the dynamic behavior of processing plasmas, because gas phase reactions are driven by collisions involving energetic plasma electrons. Metastable and resonance level concentrations are also relevant as these species play significant roles in plasma processing, through energy released when they de-excite upon reaching substrate surfaces, and through the emission of VUV photons which enhance surface reactions. These parameters are unambiguous indicators of the instantaneous plasma state and as such may play a valuable role as monitors for closed- loop process control. Results will be presented for argon and argon/mixed-gas (Ar/N2, Ar/O2, Ar/H2) inductively coupled plasmas. Accuracy of the results (which are compared to measurements under static conditions made by Langmuir probe and white-light absorption spectroscopy) are typically better than ±15%. The system time resolution is ~0.1 s, which is more than sufficient to capture the transient behavior of many processes, limited only by the time response of the spectrograph used.
Support by NSF grant PHY-1068670 and Applied Materials Inc. is gratefully acknowledged.
* J. Vac. Sci. Technol. A 31(2), 021303 (2013).