Measurement of plasma parameters and electron shading effects using patterned and unpatterned SPORT wafers

Electron shading as proposed by Arnold and Sawin (1991) and Hashimoto (1993, 1994, 1996) is recognized as a major mechanism for plasma processing induced damage in commercial plasma etch chambers. During metal etch for high aspect ratio features, charge separation is induced between the resist and the metal. This arises because isotropic electrons are shaded by the resist and prevented from reaching the conductor, unlike the more anisotropic ions. The accumulated positive charge can cause current to be driven through the transistor gate oxide and induce damage. While transistors with comb type antenna structures have been used to quantify this type of damage to transistor gate oxides, others have used SPORT wafers to measure more fundamental plasma phenomena such as charging voltages on bare and patterned pads (Ma and McVittie, 1994, and Patrick et al., 1997). In damage studies, the SPORT probe has an advantage over conventional Langmuir probes in that the plasma parameters are measured at the wafer level where charging takes place. In this paper, SPORT wafers with bare pads are used to measure important plasma parameters such as ion current, plasma potential, electron temperature, and electron energy probability function (EEPF). Furthermore, plasma measurements with patterned pads are compared with the bare pad results to measure electron shading effects