Testing new chemistries for mask repair with focused ion beam gas assisted etchingCritical dimension ͑CD͒ control during silicon gate etching has been investigated with state-of-the-art chemistries. In particular, we have compared the etched profile of both isolated and dense gates obtained after the main etch step of a gate etch process using HBr/Cl 2 /O 2 and HBr/Cl 2 /O 2 /CF 4 gas mixtures, and study the influence of the CF 4 /O 2 ratio in this mixture. We demonstrate that the gate etch profile is mainly driven by the passivation layer deposited on the gate and mask sidewalls during the etching. Due to aspect ratio dependant etching effect the passivation layer formation is thinner in dense than in isolated structures resulting in significant profile microloading. However, CF 4 addition to HBr/Cl 2 /O 2 strongly minimizes the difference in passivation layer thickness between dense and isolated lines thus potentially improving the critical dimension control. These results will be discussed in terms of chemical composition of the passivation layer and deposition mechanisms, based on previous studies by x-ray photoelectron spectroscopy and mass spectrometry studies. Finally, we will discuss the influence of the soft-landing and overetch steps on the final profile of the gates, and show that aspect ratio dependant etch rate during the main etch step of the process can become an additional source of CD microloading.

We have used x-ray photoelectron spectroscopy (XPS) to analyze resist patterned silicon surfaces etched in a commercial 200 mm high density plasma etcher. After anisotropic etching using gate etching chemistries based on HBr/Cl2/O2 gas mixtures with or without CF4 addition, wafers are transferred under vacuum to perform chemical topography analysis using XPS in order to measure the element concentration on the silicon surfaces at the bottom of the trenches as well as the silicon sidewalls. Composition of the layers formed on the silicon sidewalls as a function of the plasma operating conditions is reported and discussed. The sidewall layer formation is mainly attributed to the oxidation of silicon etching by-products and the deposition of fluorocarbon species. Depending on the O2 and CF4 amount during a silicon gate main etch step, composition of the layer can be either SiOx-like or fluorocarbon rich. In all cases, the sidewall layer is transformed into a SiOx material during the subsequent fluorine free soft-landing step, as a result of the direct oxidation of silicon combined with the fluorocarbon species removal by oxygen in the plasma.