| AVS 56th International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS2-ThA |
| Session: | Plasma Diagnostics, Sensors, and Control II |
| Presenter: | Z.Y. Chen, University of Houston |
| Authors: | Z.Y. Chen, University of Houston V.M. Donnelly, University of Houston D.J. Economou, University of Houston L. Chen, Tokyo Electron America M. Funk, Tokyo Electron America R. Sundararajan, Tokyo Electron America |
| Correspondent: | Click to Email |
Dual-frequency capacitively coupled plasmas (2f-CCP) used in the fabrication of modern integrated circuits may provide quasi-independent control of ion flux and energy. The accurate determinations of the electron temperature (Te) and the electron energy distribution function (EEDF) are important for understanding plasma behavior and optimizing plasma processes in 2f-CCPs. In this study, measurements of Tes and EEDFs in CF4/O2 plasmas generated in a 2f-CCP etcher were performed as a function of pressure, applied RF power, and O2 feed gas content by using trace rare gases-optical emission spectroscopy (TRG-OES). The parallel plate etcher was powered by a high frequency (60 MHz) “source” top electrode, and a low frequency (13.56 MHz) “substrate” bottom electrode. 80%CF4+20%O2 or 90%CF4+10%O2 plasmas were ignited at pressures ranging from 4 to 200 mTorr, top RF powers of 500 and 1000 W, four different bottom RF powers (0, 100, 300 and 500 W), and three different wafers (Si, Al and anodized Al). Te was measured across the plasma at a height of 5 mm above the lower electrode. For Si substrates, Te increased with increasing pressure between 4 and 20 mTorr (typically from 5 to 6.5 eV). The dependence of plasma electronegativity on pressure may be responsible for this behavior. Te decreased rapidly with increasing pressure in the 20-60 mTorr range, and then slowly decreased with further increases in pressure to 200 mTorr, where Te = 2.4 to 2.7 eV. Increasing the applied bottom RF power resulted in higher Te, caused by enhanced stochastic heating of electrons with increasing low frequency voltage. Over the entire pressure range investigated, Tes in 90%CF4+10%O2 plasmas were similar to those in 80%CF4+20%O2 plasmas. The EEDFs exhibited bi-Maxwellian characteristics with an enhanced high energy tail, especially at pressures >20 mTorr. Different dependences of Te on pressure and applied top and bottom RF powers were observed for Al and anodized Al wafers.