Mass spectroscopic measurement of time-varying ion composition in a pulse-modulated Ar/C₄F₈/O₂ dual-frequency capacitively coupled plasma

Abstract

The time dependence of the ion composition in pulse-modulated dual-frequency capacitively coupled plasma with Ar/C4F8/O2 was measured using a quadrupole mass spectrometer with an electrostatic energy analyzer. After turning on the pulse, Ar+ ions were preferentially generated, and then, the composition of CxFy + ions, such as C2F4 + and C3F5 + ions, increased. This phenomenon was discussed on the basis of the time variation of electron temperature and the resultant change in the ratio of the C4F8 ionization rate to that of Ar atoms.

Time-varying mechanism of ion composition in a pulse-modulated Ar/C4F8/O2 dual-frequency capacitively coupled plasma

“…Signal time delay due to ion transit time through the QMS was considered. Our previous study 12) has confirmed the proportional relationship between the square root of ion mass number and the ion transit time, from light ions (CF + ) to heavy ions (C 3 F 5 + ). Hereafter, the delay time when the pulse is turned on is determined as T .…”

“…In our previous work, 12) the ion species produced from a pulsed Ar/C 4 F 8 /O 2 plasma were Ar , and C 3 F 5 + were the dominant ions in this study. This is consistent with the calculated ionization rates based on ionization cross sections, 13) and hereafter, we focus on these five ion species.…”

“…The experimental setup used in this study was reported in our previous work 12) and is briefly described here. In this study, a RF electrode (diameter: 10 cm) and an opposing ground electrode (electrode spacing: 3 cm) were installed in a cylindrical vacuum chamber (diameter: 16 cm; height: 18 cm) which was evacuated by a turbomolecular pump at a base pressure less than 10 −4 Pa.…”

“…However, the pulse operation of the plasma induces time-dependent behavior of positive ions, and this behavior might influence the etching performance. In our previous work, 12) the temporal variation of positive-ion (hereinafter simply referred to as "ions") composition was found in a pulse-operated Ar/C 4 F 8 /O 2 DF-CCP which is used to fabricate HAR features in silicon dielectric films. This phenomenon was studied based on the temporal variation of the ion production rates, which depend on gas flow ratio and timevarying electron temperature (T e ).…”

Uniformity enhancement of a microwave surface-wave plasma by a field agitation

“…Furthermore, plasma light intensity is linearly proportional to ion density. [25][26][27] Since the ion density at the SWP near the quartz disk is higher than that of the bulk region by more than 10 times, the light intensity would surpass that from the bulk by at least 10 times, leading to the SWP being the dominant light source for the image. In this sense, it is reasonable to think the measurement results reflect the inhomogeneous distribution of the SWP.…”