REACTIVE ION ETCHING OF SILICON-NITRIDE DEPOSITED BY DIFFERENT METHODS IN CF4/H2 PLASMAS

Reactive ion etching in CF4/H-2 of silicon nitride deposited by either plasma-enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD) has been studied. The steady-state etch behavior of the two kinds of silicon nitride is very similar, e.g. the dependence of the nitride etch rate on the H-2 fraction in the gas mixture. However, in situ ellipsometry shows that silicon nitride formed by PECVD exhibits a much greater and longer initial etch transient (almost-equal-to 110 s) than LPCVD Si3N4 (almost-equal-to 20 s) if CF4/H-2 gas mixtures with a high proportion of H-2 are used. The strong etch rate transient seen for PECVD Si3N4 limits the ability to stop abruptly on this material relative to that of LPCVD Si3N4.