Nitride etching with hydrofluorocarbons III: Comparison of C₄H₉F and CH₃F for low-k′ nitride spacer etch processes

The performance of low-k nitride spacer etch processes for fin-field effect transistor device fabrication was investigated using C4H9F based and CH3F based plasma gas chemistries. C4H9F showed a larger process window of O2 gas flow rate to obtain infinite etch selectivities of blanket SiN/SiO and SiN/poly-Si than CH3F. The etch selectivity increased in both gases with the reduction of duty cycle in synchronously pulsed plasmas. Low-k spacer formation using a 60-nm gate pitch testsite was demonstrated resulting in the minimized fin recess of 4.7 nm using C4H9F-O2-He plasma at a duty cycle of 30%. This was 2.2 times smaller than that by the CH3F-He plasma. Fifty percent extended etch time resulted in a fin recess of 5.1 nm, suggesting self-limiting behavior using C4H9F-O2-He plasma chemistry. Gap structure analysis on the blanket films suggested that the selective deposition of fluorocarbon, which enhances the selectivity, is driven by plasma assisted deposition in case of the C4H9F-O2-He plasma. These unique characteristics of C4H9F can facilitate innovative plasma etch processes for nitride-based materials patterning in a wide range of applications.