Influence of bias voltage on the Ar/CH₂F₂/O₂ plasma etching of Si₃N₄ films

Abstract The etching mechanism of silicon nitride (Si 3 N 4 ) films depending on peak-to-peak bias voltage ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">pp</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) in an Ar/CH 2 F 2 /O 2 gas-mixture plasmas for high-aspect-ratio etching process was investigated. It was observed that the Si 3 N 4 film etch rate initially decreased with an increase in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">pp</mml:mi> </mml:mrow> </mml:msub> </mml:math> up to 3630 V, but then increased beyond this threshold. This unusual etching behavior can be attributed to the formation of a modified layer on the surface of the Si 3 N 4 film. The characteristics of the modified layer, such as thickness and atomic composition, were found to be strongly influenced by the ion energy and gas chemistry of the process conditions.