Origin of electrical signals for plasma etching endpoint detection

Abstract

To investigate the electrical changes observed at plasma etching endpoints, experiments were performed in an inductively coupled, rf-biased reactor, during CF 4 /Ar plasma etches of silicon dioxide films on silicon substrates. The rf bias current, voltage, and impedance were measured vs. time during etching. Simultaneously, a Langmuir probe measured the electron and ion densities, ion current density, and electron energy distribution function (EEDF). At endpoint, we detected changes in the Langmuir probe parameters caused by changes in the flux and density of oxygencontaining etch products. Measured changes in ion current density, EEDF, and voltage, when input into a numerical model of the plasma and sheaths, fully explain the change in discharge impedance measured at endpoint. Changes in the yield of electrons emitted from the wafer surface were not significant. The understanding provided by this work should enable electrical endpoint detection to be used with greater reliability and confidence.

Effect of surface derived hydrocarbon impurities on Ar plasma properties

“…can also tell the state of surfaces, walls, and gaseous species flowing into the plasma. [10][11][12] Ar plasma interaction with hydrocarbon films is of interest for multiple applications. Hydrocarbon gas (CH 4 , C 2 H 2 , etc.)…”

Probe technique for measurement of a plasma potential waveform

“…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].…”