Depth profiling of thin surface layers using the amplitude modulation method in radiofrequency-powered glow discharge optical emission spectrometry

A novel technique for accurate in-depth analysis of thin layers is described. Radiofrequency voltages applied to a Grimm-style glow discharge lamp are modulated at a very low frequency, which leads to a reduction in the sputtering rate and variation of the emission signals at the specific modulation frequency. With amplitude modulation associated with phase-sensitive detection, the resultant emission intensities can be measured with better signal-to-noise ratios, although the sputtering rate and the sampling amount are reduced by a factor of ∼10. It is possible to obtain the depth profile of a 13 nm thick Ni-electroplated layer, whereas profiling is difficult for conventional detection.