| AVS 60th International Symposium and Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS1-TuM |
| Session: | Plasma Sources |
| Presenter: | Y. Zhang, University of Michigan |
| Authors: | Y. Zhang, University of Michigan M.J. Kushner, University of Michigan |
| Correspondent: | Click to Email |
Dual frequency capacitively coupled plasmas (CCPs) provide the microelectronics fabrication industry with flexible control for high selectivity and uniformity. For a given low frequency (LF) bias, the, magnitude and wavelength of the high frequency (HF) bias will affect the electron density, electron temperature, sheath thickness and so ion transit time through the sheath. These variations ultimately affect the ion energy and angular distributions (IEADs) to the substrate. For example, with higher HF power, the electron density and ion fluxes will increase, which will increase the etch rate. However, the higher HF power will also reduce the sheath thickness and reduce the ion transit time. This will produce more structure in the IEADs. One potential control mechanism for the IEADs is the relative phase of the LF and HF biases. In this paper, results from a two-dimensional computational investigation of Ar and Ar/C4F8/O2 plasma properties in an industrial CCP reactor are discussed. The resulting IEADs are used as inputs to a feature profile model to assess etch profiles. In this reactor, both the LF (2 MHz) and HF (up to 60 MHz) are applied to the lower electrode. The phase between the LF and HF is controlled.
To separately control rates of ionization and the shape of IEADs, the HF should be significantly higher than the LF. Under these conditions, there are many HF cycles per LF cycle. Although there are clear changes in the IEADs when varying the phase between the HF and LF, these changes are modulations to the IEADs whose shape is dominated by the LF. By sweeping the phase difference between the LF and HF, these modulations can be used to smooth and sculpt the IEADs. As the difference between the HF and LF becomes smaller, the IEADs become more sensitive to the phase differences between the HF and LF. These phase differences also affect the dc bias, an affect often call the electrical-asymmetry-effect when the frequencies are equal. Profile simulations are used to demonstrate possible control schemes for over-etch through phase control.
*Work supported by the Semiconductor Research Corp., DOE Office of Fusion Energy Science and the National Science Foundation.