Fluorocarbon high density plasmas. VII. Investigation of selective SiO2-to-Si3N4 high density plasma etch processes

Abstract

A comparison of the plasma etching characteristics of SiO2 and Si3N4 in high-density fluorocarbon discharges with the goal of identifying an etching chemistry with a very high SiO2-to-Si3N4 etch selectivity has been initiated. High-density plasmas were excited in an electron cyclotron resonance apparatus equipped with a cooled rf powered electrostatic chuck. Gas mixtures of either CF4/H2, CHF3/H2 (low carbon/fluorine ratio fluorocarbon gases), or C2F4/H2, C2F6/H2, and C3F6/H2 (high C/F ratio) were used in this work. We will show that a carbon-rich fluorocarbon gas like C2F4 and a modest amount of H2 are useful in achieving high SiO2/Si3N4 etch selectivity (≳28). On the other hand, hydrogen-rich fluorocarbon gas mixtures which contain less carbon, e.g., CHF3/H2, are not useful for achieving SiO2 over Si3N4 etch selectivity although they will enable SiO2/Si etch selectivity. The gas phase and surface chemical aspects of the different gas mixtures were studied by optical emission spectrometry and line of sight mass spectrometry and by post plasma x-ray photoelectron spectroscopy. The results of these measurements can explain the etch rate data by selective deposition of fluorocarbon films on Si3N4 and Si surfaces.

Simulation of Si and SiO2etching in CF4+ H2plasma

“…The thickness of the fluorocarbon layer on SiO 2 is much smaller than on Si for comparable discharge conditions [4,5]. During Si etching in CF 4 + H 2 plasma the adsorption of CF 2 radicals on the Si surface is enhanced by ion bombardment, i. e. the sticking coefficient of CF 2 radicals on the Si surface is increased in the presence of ion bombardment [6].…”

Challenges of Tailoring Surface Chemistry and Plasma/Surface Interactions to Advance Atomic Layer Etching

“…2 (compare to Ref. 44). Initial results for other materials show great promise for future ALE processes, but have yet to achieve the desired self-limited atomic scale precision.…”

“…Additionally fluoro(hydro)carbon plasmas have been used quite extensively in manufacturing for many years. Much understanding to the mechanism for etching silicon oxide was discussed by Zhang, 44 Standaert, 41 and others. 45 Typically, oxide exhibits a lower etching threshold than silicon nitride or silicon due to the thickness differences of a fluorocarbon reaction layer, leading to desired selectivites for back-end-of-line (BEOL) processing.…”

“…1c. While the approach varies in detail, in general, species 'R' (this could be ions, 3,28 energetic neutrals 44,46 or others 4,29 ) interact with the adsorbed monolayer and the top layer of the substrate to form volatile species. Neutral species not participating in the reaction (purple) may be present in case of plasma exposure.…”

Fast Etching of Molding Compound by an Ar/O2/CF4Plasma and Process Improvements for Semiconductor Package Decapsulation

“…4f). Although optimization of recipes helps to reduce damage in both deprocessing methods, etching of Si 3 N 4 passivation by plasma decapsulation [16][17][18] and etching of copper wires by acid decapsulation seems inevitable.…”