Optical emission spectroscopy has been established as a powerful and versatile method for in-situ diagnostics in ion beam etching. In broad argon and oxygen beams particle energies could be determined by the detection of Doppler shifted emission lines. The line widths correspond to the beam divergence. The Doppler resolved emission spectra also provide information on collision phenomena. Moreover etch products could be detected during ion beam etching of silicon, silicondioxide, and an organic photoresist. A new method is introduced for in-situ etch rate determination and endpoint detection applicable to reactive ion beam etching and reactive ion etching as well. Interference of light reflected at the surfaces of a thin layer and at the underlying substrate is used for this purpose. In contrast to the conventional interferometric procedures no additional light source is required. The plasma or beam itself serves as a light source. As an advantage compared to He-Ne laser interferometry, the method presented here offers the opportunity of better resolved determination of the film thickness variation because shorter wavelengths are available in general. A sharp endpoint signal is, additionally, obtained in many cases if emission lines of an etch product or an etchant (loading effect) are used.
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