Improvement of the Information Depth in In-depth Analysis by Radio-frequency-powered Glow Discharge Optical Emission Spectrometry

Abstract

Two novel measuring methods in radio-frequency-powered glow discharge optical emission spectrometry: an amplitude modulation technique and a bias-current conduction technique, are reviewed. They are both effective for the in-depth analysis of relatively thin films. In the amplitude modulation technique, radio-frequency voltages supplied to the glow discharge lamp are modulated at a very low frequency, which leads to a reduction in the sputtering rate as well as a cyclic variation in the emission signal. With a lock-in amplifier, the emission intensities can be selectively detected with a better signal-to-noise ratio, although the sampling amount is reduced and thus the emission intensities decrease. In the bias-current conduction technique, a d.c. bias current is conducted by connecting an electric circuit consisting of a low-pass filter and a load resistor to the glow discharge lamp. The bias current can introduce a large number of electrons into the plasma, thus leading to an enhancement in the emission intensities from the plasma, whereas the sputtering rate is reduced due to the deceased d.c. bias voltage. Both of the techniques can contribute to an improvement in the information depth in glow discharge optical emission spectrometry.