Argon plasma characteristics in a dual-frequency, capacitively coupled, 300 mm-wafer plasma processing system were investigated for rf drive frequencies between 10 and 190 MHz. We report spatial and frequency dependent changes in plasma parameters such as line-integrated electron density, ion saturation current, optical emission and argon metastable density. For the conditions investigated, the line-integrated electron density was a nonlinear function of drive frequency at constant rf power. In addition, the spatial distribution of the positive ions changed from uniform to peaked in the centre as the frequency was increased. Spatially resolved optical emission increased with frequency and the relative optical emission at several spectral lines depended on frequency. Argon metastable density and spatial distribution were not a strong function of drive frequency. Metastable temperature was approximately 400 K.

Inductively coupled plasma ͑ICP͒ etching reactors are rapidly becoming the tool of choice for low gas pressure, high plasma density etching of semiconductor materials. Due to their symmetry of excitation, these devices tend to have quite uniform etch rates across the wafer. However, side to side and azimuthal variations in these rates have been observed, and have been attributed to various asymmetries in pumping, reactor structure and coil properties. In this article, a three-dimensional computer model for an ICP etching reactor is reported whose purposes is to investigate these asymmetries. The model system is an ICP reactor powered at 13.56 MHz having flat coils of nested annuli powering Ar/N 2 and Cl 2 plasmas over a 20-cm diam wafer. For demonstration purposes, asymmetries were built into the reactor geometry which include a wafer-load lock bay, wafer clamps, electrical feeds to the coil, and specifics of the coil design. Comparisons are made between computed and experimentally measured ion densities and poly-silicon etch rates in Cl 2 plasmas. We find that the electrical transmission line properties of the coil have a large influence on the uniformity of plasma generation and ion fluxes to the wafer.

There is much interest in scaling rf-excited capacitively coupled plasma reactors to larger sizes and to higher frequencies. As the size approaches operating wavelength, concerns arise about non-uniformity across the work piece, particularly in light of the well-documented slow-surface-wave phenomenon. We present measurements and calculations of spatial and frequency dependence of rf magnetic fields inside argon plasma in an industrially relevant, 300 mm plasma-processing chamber. The results show distinct differences in the spatial distributions and harmonic content of rf fields in the plasma at the three frequencies studied (13.56, 60 and 176 MHz). Evidence of a slow-wave structure was not apparent. The results suggest that interaction between the plasma and the rf excitation circuit may strongly influence the structures of these magnetic fields and that this interaction is frequency dependent. At the higher frequencies, wave propagation becomes extremely complex; it is controlled by the strong electrical nonlinearity of the sheath and is not explained simply by previous models.

Articles you may be interested inAnalysis of the chemical composition and deposition mechanism of the SiO x -Cl y layer on the plasma chamber walls during silicon gate etching Environmentally benign etching process of amorphous silicon and tungsten using species evaporated from polytetrafluoroethylene and fluorinated ethylene propylene J. Vac. Sci. Technol. A 21, 302 (2003); 10.1116/1.1531131Etch characteristics of optical waveguides using inductively coupled plasmas with multidipole magnets Process variation with chamber surface condition in high density plasma reactors can seriously affect the process performance and productivity of device manufacturing. In this work, the impact of chamber surface coating on polycrystalline-silicon ͑polysilicon͒ gate etching with Cl 2 -and HBr-based plasma has been studied. The dependence of process sensitivity to surface coating on various processing conditions has been characterized and the mechanism of process shift has been analyzed. Based on the experimental results, the root cause of process sensitivity has been attributed to the change of surface recombination rate of free radicals on different chamber surfaces which leads to a variation in reactive neutral density. Under a certain discharge condition, the Cl and Br densities in a clean chamber with anodized aluminum and alumina surfaces are Ͼ60% lower than those in a seasoned chamber with silicon oxide deposition, resulting in lower polysilicon and oxide etch rate in the former case. In general, the process sensitivity to chamber surface condition depends on process regime and is higher for those processes where etching is more chemical in nature, such as processes at higher pressure and with Cl 2 -based chemistry. Processes with higher oxygen concentration and higher source power are also more sensitive due to the accelerating surface oxidation of polysilicon surface in a clean chamber. Approaches to reduce the effect of process sensitivity have been discussed.

No abstract