Monitoring of PVD, PECVD and etching plasmas using Fourier components of RF voltage

Abstract

Fourier components of discharge voltages were measured in two different reactive plasmas and their response to the creation or destruction of a thin film was studied. In reactive magnetron sputtering the effect of transition from the metallic to the compound mode accompanied by the creation of a compound film on the sputtered target was observed. Further, deposition and etching of a diamond-like carbon film and their effects on amplitudes of Fourier components of the discharge voltage were studied. It was shown that the Fourier components, including higher harmonic frequencies, sensitively react to the presence of a film. Therefore, they can be used as a powerful tool for the monitoring of deposition and etching processes. It was demonstrated that the behaviour of the Fourier components was caused in both experiments by the presence of the film. It was not caused by changes in the chemical composition of the gas phase induced by material etched from the film or decrease in gettering rate. Further, the observed behaviour was not affected by the film conductivity. The behaviour of the Fourier components can be explained by the difference between the coefficients of secondary electron emission of the film and its underlying material.

Probe technique for measurement of a plasma potential waveform

“…The fact that the amplitude of higher harmonic frequencies depends on electron concentration is important for an explanation of some monitoring techniques that are used in deposition or etching processes. Higher harmonics are used for end-point detection of etching processes [15][16][17] and for detection of mode transition in reactive magnetron sputtering [17,18]. Both these monitoring techniques rely on the sensitive reaction of higher harmonic frequencies on electron concentration, whether its behaviour is controlled by surface processes or volume ionization [17,19].…”

“…Higher harmonics are used for end-point detection of etching processes [15][16][17] and for detection of mode transition in reactive magnetron sputtering [17,18]. Both these monitoring techniques rely on the sensitive reaction of higher harmonic frequencies on electron concentration, whether its behaviour is controlled by surface processes or volume ionization [17,19].…”

Electric signals measured during plasma thin-film etching and their connection to the electron concentration and the properties of the treated surface

“…Since electric measurements are fast, simple and cheap, the reaction of electric discharge parameters in the presence of various thin films was investigated. It was verified that electric signals can be used for the monitoring of the endpoint detection of thin-film etching [1][2][3], the generation of a thin film during plasma-enhanced chemical vapour deposition (PECVD) [4] and the formation of a compound film on a magnetron target [5]. It was revealed that higher harmonic * Author to whom any correspondence should be addressed.…”

“…It is possible that in the case of SiO 2 etching in CF 4 /Ar plasma, electrons react in the presence of etching products (e.g. CO) in the gas phase [1], but it was shown that the changes of the gas-phase composition play a negligible role in both reactive magnetron sputtering [5] and PECVD/plasma etching of diamond-like carbon (DLC) films [4]. Therefore, it was proposed that the variation in electron concentration in these processes is caused by the change in the electron emission coefficient of the solid surface caused by the formation/destruction of a thin film [4].…”

“…CO) in the gas phase [1], but it was shown that the changes of the gas-phase composition play a negligible role in both reactive magnetron sputtering [5] and PECVD/plasma etching of diamond-like carbon (DLC) films [4]. Therefore, it was proposed that the variation in electron concentration in these processes is caused by the change in the electron emission coefficient of the solid surface caused by the formation/destruction of a thin film [4]. However, a full experimental proof of this theory based on the simultaneous measurement of electric signals and electron concentration complemented with direct measurement of the variations of the electron yield is missing.…”