Chemistry of Plasmas used in the Fabrication of Integrated Circuits
Molecular beam mass spectrometry has been used to study the reactive gas plasmas used in semiconductor integrated circuit manufacture. Details of the design parameters, theory of molecular beam sampling and the fabrication of a molecular beam sampling system are given. The system was built, tested and used to sample various reactive gas plasmas during etching and in the absence of a wafer. Silicon and to a much lesser extent silicon dioxide wafers have been etched in a variety of chlorine containing plasmas such as CCl4, CCl4/02, CCl4/Ar and CFC13. Some other plasmas have also been studied in the absence of a silicon wafer. Polymer formation was found to be a major problem in the present reactor probably due to low gas flow rates. Polymer formation was particularly marked in CCl4/02 plasmas. Aluminium, etched from the r.f. electrodes, was also incorporated into these conductive polymer films. Preliminary results with this system have shown that molecular beam mass spectrometry can be successfully used to sample these plasmas. The results also show that CFCl3 and CCl4/Ar plasmas are suitable etchants for silicon. A detailed survey of the literature on plasma etching and plasma polymer formation is also presented.
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