Dependence of E-H transition in argon ICP discharges for treatment of organic molecules

Carlos Eduardo Farias,Euclides Alexandre Bernardelli,Paulo César Borges,Márcio Mafra

doi:10.1590/s1517-707620170005.0256

Carlos Eduardo Farias, Euclides Alexandre Bernardelli + Show 2 more

Open Access

https://doi.org/10.1590/s1517-707620170005.0256

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Abstract

ABSTRACT Plasma surface cleaning is an alternative process that aims at the fully removal of organic contaminants on several kinds of materials. Despite its advantages, there are still lacks on the comprehension of the complex relations between plasma-generated species and organic molecules during plasma cleaning. In the present work, a linear alkane (hexatriacontane - C36H74), used as a contaminant model, was exposed to an Argon radiofrequency (RF) inductively coupled plasma (ICP). The by-products from degradation were monitored by optical emission spectroscopy (OES) and residual gas analysis (RGA), to identify the influence of sample positioning on E and H discharge modes regions. The exposition to H-mode discharge resulted in more intense and profuse emissions of C-H and C2 systems. RGA results show similar byproducts from degradation in both modes; however, the intensity from treatment in H-mode is largely greater. It was also observed that plasma etching in H-mode is enough to melt the sample, while E-type discharge leaves the surface of the sample apparently unchanged.

Highlights

There are several ways to treat the surface of materials to modify its properties [1]
Several studies already evaluated the changes that occur in plasma properties during this transition and some of the most relevant results are as follows: E-mode has an electron density generally close to 109 cm-3, while H-mode ranges from 1010 to 1011 cm-3 at the same applied power [8, 10, 11]; the plasma potential is reduced at the H-mode even with the increase of applied power [12, 13]; the energy distribution function (EEDF) changes to a more Maxwellian electron distribution at the Hmode [9, 10, 14]; electron temperature is reduced at H-mode, while gas temperature is increased [13,14,15]; electron-electron collision frequency is greatly increased [12]; after the H-mode is initiated, it can be sustained even at lower powers [12, 16]; both E and H modes can coexist inside the reactor [9]
The treatments were performed in 99,999% pure Argon, flowing at 300 sccm, at pressure of 1 Torr. In this configuration and settings, H-mode is centered close to the last turn of the coil, with a size of about 10 cm of tube length. In this setup the H-mode plasma can be changed by moving the coil, while the sample was at a fixed position in relation to the optical system

Summary

INTRODUCTION

There are several ways to treat the surface of materials to modify its properties [1]. The treatments were performed in 99,999% pure Argon, flowing at 300 sccm, at pressure of 1 Torr In this configuration and settings, H-mode is centered close to the last turn of the coil, with a size of about 10 cm of tube length. In this setup the H-mode plasma can be changed by moving the coil, while the sample was at a fixed position in relation to the optical system. RGA analysis used a Residual Gas Analyser Accu-quad RF-2910 model with range from 1 to 100 m/Z with precision of 1 m/Z with internal pressure of 8,5E-4 Torr When organic materials are present, as seen in the picture with sample, it visually changes discharge appearance to a blue color, even in small amounts as contaminations from reactor walls

RESULTS

CONCLUSIONS