Optical and electrical diagnostics of fluorocarbon plasma etching processes

Abstract

This article reviews recent work concerning the role of CF and CF 2 radicals in etching and polymerization processes occurring in capacitively coupled radio-frequency plasmas in fluorocarbon gases used for the selective etching of SiO 2 layers in microelectronic device fabrication. Laser-induced fluorescence (LIF) was used to determine time-resolved axial concentration profiles of these species in continuous and pulse-modulated CF 4 and C 2 F 6 plasmas. Calibration techniques, including broad-band UV absorption spectroscopy, were developed to put the LIF measurements on an absolute scale. A novel technique was used to determine the ion flux to the reactor walls in these polymerizing environments. The mass distribution of the ions arriving at the reactor walls was determined using a quadrupole mass spectrometer.It was found that CF x radicals are produced predominantly by the reflection of neutralized and dissociated CF +x ions at the powered electrode surface. When the fluorine atom concentration is high, the CF x radicals are destroyed effectively by recombination catalysed by the reactor walls. When the fluorine atom concentration is lowered, the CF 2 concentration rises markedly, and it participates in gas-phase oligomerization processes, forming large C x F y molecules and, after ionization, large C x F + y ions. These species appear to be the true polymer precursors. This mechanism explains the well known correlation between high CF 2 concentrations, polymer deposition and SiO 2 over Si etch selectivity.

Radial structure of low pressure rf capacitive discharges

“…The radio frequency (rf) capacitive gas discharge is widely used in various technological processes: plasma etching and modification of different materials [1][2][3][4], depositing nitride, oxide, diamond-like and other thin films [4][5][6], plasma cleaning of technological gas-discharge chambers [7], plasma chemistry [8], pumping gas lasers [9], sterilizing medical tools [10,11] etc. On performing, e.g., etching semiconductor plates and depositing films it is important to possess a uniform distribution of plasma parameters across the electrode (plate) area.…”

Deep germanium etching using time multiplexed plasma etching

“…27 Booth mentioned that neutral and charged heavy C x F y species are responsible for the deposition. 28 Most probably, ions and neutrals participate in species deposition, one or the other being dominant depending on the plasma conditions. In our plasma conditions, neutrals' deposition seems to dominate.…”

Modelling of anomalous Doppler broadened lines, thermalization of electrons and the role of radicals in discharges at high E/N

“…CF 4 belongs to the Freon group of gases that unfortunately significantly contribute to the global warming of our planet with a lifetime of 50 000 years. In industrial applications a large number of radicals are produced in plasmas, and in etching reactors the densities of radicals may reach several percent [9]. In CCP (capacitively coupled plasma) [10] and ICP (inductively coupled plasma) [11] etching reactors in fluorine-poor gas mixtures the dominant reactive radical is CF 2 .…”

“…Of all the CFx radicals the CF 2 molecule may be present at the level of several percent [9,15] in industrially relevant plasmas. As a result it could play a significant role even at the level of electron transport that determines the electron energy distribution function (EEDF) and the basic kinetics.…”