Modeling of radial uniformity at a wafer interface in a 2f-CCP for Si O₂ etching

Two-frequency capacitively coupled plasmas (2f-CCP) are commonly used as a powerful tool for etching of metallic and dielectric materials. Functional separation between two sources, by which independent control of high-density plasma production and high-energy ion injection onto a wafer surface can be realized, will be strongly required for a precise control of the plasma etcher. When increasing the size of the wafer and aiming at high productivity, radial uniformity in the characteristics of Si O2 etching will become a more essential issue to be addressed. The predicted radial uniformity at the wafer interface and the functional separation have been examined numerically by using VicAddress [in Advances in Low Temperature RF plasmas, edited by T. Makabe (Elsevier, Amsterdam, 2002)] in a 2f-CCP etcher in C F4 (5%) Ar at 50 mTorr. This etcher was driven at very high frequency (100 MHz) for the production of high-density plasma and at low frequency (1 MHz) for the bias source. The plasma structure and ion velocity distribution at a wafer interface, which have a direct influence on the property of etching, are mainly discussed. Close to the wafer edge, the distortion of the potential intrinsic to the etcher has a greater effect on the ion angular distribution rather than on the ion energy distribution, resulting in a reduction of the radial uniformity of etching.