Influence of polymer formation on the angular dependence of reactive ion beam etching

The decreasing dimensions and increasing complexity of very large scale integrated circuits will also result in a more complex topography. There will be an increasing demand for simulation programs in order to accurately predict the topography during, e.g., dry etching. Such simulation programs need information about the angular dependence of the etch rate of the used etch process. The angular dependence can be measured for every specific etch process and the results can be used as input data for the simulation program. A general knowledge of the angular dependence may contribute substantially to the development of future simulation programs. The angular dependence of the etch rate has been studied for Si3N4 using a Kaufman type ion beam source and CHF3+O2 as processing gas mixture. The experimental results confirm that the formation of a polymer layer plays an important role for the angular dependence of the etch rate in the case of Si3N4. We have found that it is possible to change the angular dependence to a large extent by varying the O2 content in the gas mixture. This is the case because the oxygen will strongly affect the formation of the polymer layer on the etched surface. The angular dependence of physical sputtering with Ar and a more chemical etch with CF4 of such a polymer, deposited from CHF3, has also been studied.