Enhanced etching of ion-implanted silicon nitride in buffered hydrofluoric acid

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Abstract
The preferential etching of ion‐implanted pyrolytic silicon nitride (Si3N4) and plasma‐deposited silicon nitride in buffered hydrofluoric acid has been studied as a function of ion mass, energy, and dose. The dose dependence of etching enhancement produced by light ions (H and He) shows that the relevant concentration parameter is the density of displaced atoms rather than the concentration of the implanted impurity. In addition to the atomic displacement mechanism, a species‐dependent contribution is seen. For Si3N4 the enhancement produced by most ions is 7, whereas P gives 15. For plasma‐deposited nitride, the average enhancement is 3, with values of 8 observed for P and 1.5 for B. These enhancement values can be reduced by i n s i t uannealing due to localized ion beam heating. This annealing occurs at bulk sample temperatures which are several hundred degrees Centrigrade lower than the temperatures required to produce the same result in a furnaceanneal.

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