Surface mechanisms in O2 and SF6 microwave plasma etching of polymers

Abstract

Photoresist etching mechanisms in O2 abd SF6 microwave plasmas are investigated using x-ray photoelectron spectroscopy (XPS) and etch rate measurements. Experiments are performed in a microwave multipolar plasma using an electron cyclotron resonance at 2.45 GHz and independent rf biasing at 13.56 MHz. The photoresist etch rates are studied as a function of the parameters of the plasma polymer interaction. As in an O2 plasma, the etch rate in SF6 exhibits a two-step evolution with ion energy as well as a monolayerlike adsorption of atomic fluorine on photoresist. The relationship between the surface mechanisms deduced from the etch kinetics and the surface compositions analyzed by XPS is explored. The effect of reactive species concentration, intensity of ion bombardment, and surface temperature on etching and/or degradation of the photoresist is investigated. In particular, the phenomenon of resist damage, described as a graphitization of the polymer layer, is shown to appear when the mechanical effects of ion bombardment become significant with respect to the chemical effects.

Analyses of the chemical topography of silicon dioxide contact holes etched in a high density plasma source

“…The resist was etched in a distributed electron cyclotron resonance ͑DECR͒ etcher using O 2 , SF 6 , and Ar plasmas. 13,14 In contrast to polyimide, the degradation was not confined to the surface but extended into the bulk.…”

“…In oxygen or fluorine based plasmas, the degradation phenomenon has also been observed. 13,14 On the other hand, in reactive plasmas, the degradation results from the competition between the formation ͑due to ion bombardment͒ and etching of the graphitized film ͑by reactive species͒. The surface degradation of the resist and its thermal extension into the bulk can be avoided if the carbonaceous graphitized layer, induced by ion bombardment, is stripped by the chemically active species in the plasma as it forms.…”

“…15 The degradation mechanism has been proposed as follows: the mechanical effects of ion bombardment induce a surface degradation of the photoresist, and self-diffusion of the chains induced by thermal effects allow renewal of the chains subjected to ion bombardment, allowing the extension of the degradation to the resist volume. 13 The chemical nature of the plasma also has a strong influence on the degradation phenomenon. In argon plasmas, ions have purely mechanical effects which induce the bulk graphitization of the resist if the substrate temperature goes above the Tg of the resist.…”

The SF5Ox Radicals, x=0–3

“…Detailed mechanisms to describe their formation remain unclear. [13,14] The observation of the even stronger greenhouse gas SF 5 CF 3 , chemically related to SF 6 , in stratospheric air samples has further raised questions of the atmospheric consequence of these species. [15] At present the molar ratio of SF 5 CF 3 relative to SF 6 amounts to about 4 %.…”

Sulfur hexafluoride plasma surface modification of Gly-Ala and Ala-Gly as Bombyx mori silk model compounds: Mechanism investigations

“…The main species of such plasmas have been delineated by Picard, who indicated three kinds of energetic species reacting on the polymer surface: neutral molecules, ions, and an electron density [23]. The studies of Joubert and Frank suggested that the reaction mechanism at the material surface in a plasma system was a two-step process for energetic species of fluorine reacting with the polymer surface [24,25].…”