| abstract |
The etch rate in a plasma etching system has been monitored in-situ by using optical emission spectroscopy to measure the intensities of two or more peaks in the radiation spectrum and then using the ratio of two such peaks as a direct measure of etch rate. Examples of such peaks occur at 338.5 and 443.7 nm and at 440.6 and 437.6 nm for the fluoride/SOG system. Alternately, the intensities of at least four such peaks may be measured and the product of two ratios may be used. Examples of peaks used in this manner occurred at 440.5, 497.2 and 502.3 nm, also for the fluoride/SOG system. The method is believed to be general and not limited to fluoride/SOG. |