450 mm dual frequency capacitively coupled plasma sources: Conventional, graded, and segmented electrodes

Wafer diameters for microelectronics fabrication will soon transition from 300 to 450 mm at a time when excitation frequencies for capacitively coupled plasmas (CCPs) are increasing to 200 MHz or higher. Already for 300 mm tools, there is evidence that wave behavior (i.e., propagation, constructive, and destructive interference) affects the uniformity of processing. The increase in diameter to 450 mm is likely to exacerbate these effects, perhaps requiring nontraditional tool designs. This is particularly important in dual frequency (DF) CCP tools in which there are potential interactions between frequencies. In this paper, results from a two-dimensional computational investigation of Ar plasma properties in a 450 mm DF-CCP reactor, incorporating a full-wave solution of Maxwell’s equations, are discussed. As in 300 mm DF-CCP reactors, the electron density collapses toward the center of the reactor with increasing high frequency $(HF)$⁠, however, with more pronounced finite wavelength effects. Graded conductivity electrodes with multilayer of dielectrics are computationally demonstrated as a possible means to suppress wave effects thereby increasing plasma uniformity. Segmentation of the $HF$ electrode also improves the plasma uniformity by making the electrical distance between the feeds and the sheath edges as uniform as possible.