Effects of hydrogen content in films on the etching of LPCVD and PECVD SiN films using CF4/H-2 plasma at different substrate temperatures

The dependences of etching characteristics on substrate temperature (T-s, from -20 to 50 degrees C) of the plasma-enhanced chemical vapor deposition (PECVD) SiN films (PE-SiN) and low-pressure chemical vapor deposition (LPCVD) SiN films (LP-SiN) with CF4/H-2 plasma were investigated. The Fourier-transform infrared spectroscopy shows that both film types were N-H bond-rich films, but in different hydrogen contents (PE-SiN 22.7 at% and LP-SiN 3.8 at%) from the Rutherford backscattering spectroscopy analyses. A higher hydrogen content led to a thinner fluorocarbon thickness because of the reaction between hydrogen outflux and C and N to form an HCN byproduct. The etch rates (ER) for the PE-SiN were higher than that of the LP-SiN at all T-s, due to the different FC thickness and etching mechanisms proposed. The formation of the N-H-x layer on PE-SiN at low temperature caused the decrease in ER. For the LP-SiN, the weak dependences of T-s on surface structure and ER were observed.