Study of the SiO2-to-Si3N4 etch selectivity mechanism in inductively coupled fluorocarbon plasmas and a comparison with the SiO2-to-Si mechanism

The mechanisms underlying selective etching of a SiO2 layer over a Si or Si 3N4 underlayer, a process of vital importance to modern integrated circuit fabrication technology, has been studied: Selective etching of SiO2-to-Si3N 4 in various inductively coupled fluorocarbon plasmas (CHF3, C2F6/C3F6, and C3F6/H-2) was performed, and the results compared to selective SiO2-to-Si etching. A fluorocarbon film is present on the surfaces of all investigated substrate materials during steady state etching conditions. A general tren d is that the substrate etch rate is inversely proportional to the thicknes s of this fluorocarbon film. Oxide substrates are covered with a thin fluor ocarbon film (<1.5 nm) during steady-state etching and at sufficiently high self-bias voltages, the oxide etch rates are found to be roughly independe nt of the feedgas chemistry. The fluorocarbon film thicknesses on silicon, on the other hand, are strongly dependent on the feedgas chemistry and rang e from similar to 2 to similar to 7 nm in the investigated process regime. The fluorocarbon him thickness on nitride is found to be intermediate betwe en the oxide and silicon cases. The fluorocarbon film thicknesses on nitrid e range from similar to 1 to similar to 4 nm and the etch rates appear to b e dependent on the feedgas chemistry only for specific conditions. The diff erences in etching behavior of SiO2, Si3N4, and Si are suggested to be rela ted to a substrate-specific ability to consume carbon during etching reacti ons. Carbon consumption affects the balance between fluorocarbon deposition and fluorocarbon etching, which controls the fluorocarbon steady-state thi ckness and ultimately the substrate etching. (C) 1999 American Vacuum Socie ty. [S0734-2101(99)03201-7].