Plasma Technology for Advanced Devices
At room temperature etch anisotropy is always obtained thanks to the formation of a sidewall passivation layer: The sidewall passivation layer can be formed by different mechanisms (slide 1):
Slide 2 illustrates the various passivation mechnisms.
Different etch processes are dominated by different passivation mechanisms (slide 3). This has extremely important consequeces for the response of process results like CD, profile angle and profile microloading to process parameters like pressure, source and biass power. Aluminum etch is dominated by re-deposition of resist etch products on the Al sidewalls generating a carbon-based passivation layer. In dielectric etch, condensation of CFx species from the fluorocarbon gas on the oxide sidewalls and re-deposition of resist etch products both contribute to the CFy passivation layer formation. Re-deposition of silicon etch products from the plasma gas phase and direct line of sight deposition of silicon etch products drive the passivation layer formation during silicon (gate) etch.