Temporal evolution of plasma parameters in a pulse-modulated capacitively coupled Ar/O2 mixture discharge

Zakia Anjum,N U Rehman

doi:10.1063/5.0019527

Abstract

The time-resolved measurements of the plasma parameters are carried out in a pulse-modulated low pressure capacitively coupled discharge operated in argon and argon–oxygen mixtures. Measurements are performed at a constant radio-frequency (RF) power of 130 W at 13.56 MHz, with the pulse repetition frequency of 1 kHz and 50% duty cycle. A single RF compensated Langmuir probe, synchronized with the modulated signal, is used to investigate the effects of filling gas pressure and O2 content in the discharge on the temporal evolution of electron density ne, electron temperature Te, plasma potential Vp, and electron energy probability function (EEPF). ne shows a rapid increase with time during the start of the pulse-on phase, followed by a gradual increase to attain a steady state value. During the pulse-off phase, ne decreases gradually. ne drops at a higher pressure and with increasing O2 content in the discharge. The temporal variations in Te and Vp, on the other hand, are more abrupt than the temporal variation in ne during the rise and the fall of the pulse. Both Te and Vp show an increase with rising pressure and with increasing O2 content in the discharge. The investigation of the temporal evolution of the EEPF reveals that the discharge is in a highly non-equilibrium state at the start of the pulse and evolves from bi-Maxwellian to Maxwellian distribution with the passage of time. The density of low energy electrons decreases, while the density of high energy electrons increases with increasing pressure and O2 content in the discharge. Moreover, several peaks and broadening in the EEPF profile are also noted with increasing O2 content.

Highlights

A radio-frequency capacitively coupled plasma (RF-CCP) is being extensively used, due to hardware simplicity, in many industrial applications related to material processing such as plasma enhanced chemical vapor deposition, plasma etching, and flat panel display industries.1–4 the growing demand of reducing the device dimensions into the nanometer regime makes it more challenging to achieve the desired processing goals with the conventional RF-CCPs.5 With the given reactor type, its geometrical configuration, and the material, the process outputs such as etching rate, uniformity, anisotropy, etc., can be influenced to some extent by manipulating the operating parameters such as frequency, power, pressure, gas composition, gas flow rate, etc
The temporal evolution of electron density ne measured in the Ar/O2 mixture plasma is shown in Figs. 4(a) and 4(b) as a function of pressure with 0% and 8% O2 in the mixture, respectively
The average pulse-modulated radio-frequency (PM-RF) power, the repetition frequency, and the duty cycle of the modulating signal are kept constant to observe the effects of filling gas pressure and increasing O2 content in the discharge on the temporal evolution of plasma parameters under investigation

Summary

INTRODUCTION

A radio-frequency capacitively coupled plasma (RF-CCP) is being extensively used, due to hardware simplicity, in many industrial applications related to material processing such as plasma enhanced chemical vapor deposition, plasma etching, and flat panel display industries. the growing demand of reducing the device dimensions into the nanometer regime makes it more challenging to achieve the desired processing goals with the conventional RF-CCPs. With the given reactor type, its geometrical configuration, and the material, the process outputs such as etching rate, uniformity, anisotropy, etc., can be influenced to some extent by manipulating the operating parameters such as frequency, power, pressure, gas composition, gas flow rate, etc. Midha and Economou developed a one-dimensional fluid model of a pulsed Cl2 discharge to study the effects of different powers, pressures, duty cycles, and pulsing frequencies on the spatiotemporal evolution of electron temperatures and plasma species They observed a transition from an electron–ion plasma to an ion–ion plasma during the off phase of the pulse.. The O2 containing plasma can be used in numerous applications such as dry etching of polymers, reactive sputtering, oxidation, and resist removal of semiconductors.25 In these discharges, the pulse modulation may affect electron dynamics and, the EEDF, which determines the patterns of feedstock gas dissociation and controls the fluxes of ions and radicals to the substrate during plasma processing..

EXPERIMENTAL DETAILS

RESULTS AND DISCUSSION

CONCLUSIONS