Etching mechanisms of Si and SiO₂in fluorocarbon ICP plasmas: analysis of the plasma by mass spectrometry, Langmuir probe and optical emission spectroscopy

Abstract

In this paper, we analyse, by the use of different plasma diagnostics, appearance potential mass spectrometry (APMS), optical emission spectroscopy (OES) and Langmuir probe measurements, a commercialized ICP source devoted to the etching of SiO2 using a Si mask. First, the influence of the gas composition (C2F6 mixed with H2 or CH4) and the residence time (varying gas flow rate) on the etching rates and selectivity is studied to optimize the process. Second, in order to improve the understanding of the etching mechanisms, the plasma is characterized according to the previous discharge conditions. We point out the presence of plasma instability due to the electronegative character of the fluorocarbon gas used. To determine the ion flux (ϕi) which is an essential parameter for oxide etching, Langmuir probe measurements have been associated with a plot of the bias power versus bias voltage (Pbias(Ei)). Absolute concentrations of CFx (x = 1–3), CH3 and CHF2 radicals have been determined by APMS and the atomic fluorine concentration has been sampled by OES using argon actinometry. The techniques employed for concentration determinations are largely discussed. Finally, we compare the evolutions of the etch rates and the evolutions of the different plasma species with experimental conditions.

Porous SiOCH, SiCH and SiO2 Etching in High Density Fluorocarbon Plasma with a Pulsed Bias

“…A lot of studies have dealt with SiO 2 etch mechanisms in fluorocarbon‐based plasmas 16, 26–34. Briefly, depending on ion energy, SiO 2 etching presents two behaviours.…”

“…With higher ion energy, the fluorocarbon layer is thin (<1 nm), and rather mixed with the SiO 2 material (sputtering regime). In this case, CF x species on the surface do not inhibit the etching and etch mechanisms are strongly dependent on ion composition 32, 33…”

From Carbon Nanostructures to New Photoluminescence Sources: An Overview of New Perspectives and Emerging Applications of Low‐Pressure PECVD

“…[50,52] Other aspects of the behavior of CF x radicals in fluorocarbon plasmas are presently being studied by various groups. [53,54] and CN were found to be "sticky" with high surface reactivity, whereas NH and SiCl 2 do not tend to stick to the surface of growing films. The authors of these studies indicate a possible correlation between surface reactivity and electronic structure of the radicals; species with a doublet electron configuration are found to have a high reactivity whereas those with a singlet configuration tend to be generated at the surface during film deposition.…”

Spectroscopy diagnostic of dual-frequency capacitively coupled CHF3/Ar plasma

“…22,37 When the dissociative excitation and quenching processes could be neglected, the observed optical emission intensities for selected transitions are expressed as 38…”