Radical flux control in reactive ion beam etching (RIBE) by dual exhaust system

Radicals generated during reactive ion etching (RIE) cannot be electrically controlled, causing isotropic etching and chemical damage to the sidewall of the etched feature during the etching process. In this study, using a reactive ion beam etcher (RIBE) installed with a dual exhaust system, where an additional exhaust valve was introduced to pump out radicals from the inductively coupled plasma (ICP) source chamber in addition to the conventional main gate valve in the process chamber, the radical flux relative to ion flux during the RIE process has been controlled and the effect of additional exhausting through the ICP source chamber for the control of radical flux relative to ion flux on the properties of etching has been investigated using CF4 gas. The results showed that the additional exhausting of the radicals through the ICP source chamber not only decreased the ICP source chamber pressure but also decreased the ratio of radical flux to ion flux to the substrate. The lower ICP source chamber pressure could be also obtained without additional exhausting through the ICP source chamber by decreasing the CF4 gas flow rate to the ICP source chamber, however, the lower ratio of radical flux to ion flux was observed for the dual exhaust system. It is believed that, for the next generation RIBE, multiple exhausting is beneficial for anisotropic etching of nanoscale features by controlling the radical flux to the sidewall and ion flux to the bottom of a nanoscale feature during the etching.