Spectroscopic and Langmuir probe measurements of Ar-N2 mixture plasma in magnetic pole enhanced ICP source

Abstract

Over the last decade, the plasma sources based on electromagnetic power absorption mechanisms have emerged for large scale semiconductor manufacturing. For this purpose inductively coupled plasmas (ICPs), helicons, electron cyclotron resonance (ECR) etc have been widely explored. Recently, new designs of ICPs have been proposed for the improvement of plasma processing reactors including ICPs enhanced by a ferromagnetic core and ICPs with multiple antennas for a uniform spread of plasma over a large processing area. Present paper deals with variation in plasma processing parameters of a low pressure Ar-N2 inductively coupled plasma source with magnetic pole enhancement (MaPE-ICP). Optical emission spectroscopy (OES) and an RF compensated Langmuir probe are employed to examine the trends of parameters including the electron density, electron temperature and electron energy probability functions (EEPFs). Moreover, Ar metastable fractions are also calculated from line ratio method using optical emission intensities of the Ar spectral lines. The variation in emission intensities of the selected lines and in metastable fractions can be related with electron densities in various parts of the EEPFs. Furthermore, at low RF powers the evolution in EEPFs from ‘bi-Maxwellian’ to ‘Maxwellian’ distribution with increasing Ar concentration in the mixture is also observed. The dissociation fraction of N2 determined by ‘advanced actinometry’ technique, based on Trace rare gas-actinometry (TRG-actinometry), is also reported. It is found that dissociation fraction increases with Ar concentration in the discharge as well as RF power and filling gas pressure.