High aspect ratio SiO2 etching with high resist selectivity improved by addition of organosilane to tetrafluoroethyl trifluoromethyl ether

Measurements of the ion species generated in the planar type neutral loop discharge of tetrafluoroethyl trifluoromethyl ether (CF3–O–CHF–CF3;HFE 227) demonstrate the presence of CFx+ species and CFx radicals, in a comparable manner to plasmas of more established gases such as C4F8, C2F6 or CHF3. However, as the etch selectivity of boron phosphorus silica glass (BPSG) to resist is quite poor in HFE 227 plasmas, organosilane Si(CH3)xH4−x additive gases are investigated as a source of Si to improve the BPSG/resist selectivity. The addition of 10% trimethylsilane to HFE 227 is capable of providing selectivity close to 5, which is desirable for the fabrication of deep holes. It is shown that the HFE 227/trimethylsilane plasma chemistry also preserves the resist hole pattern and does not cause hole expansion during the etching process. These latter observations are attributed to the deposition of polymer precursors induced by the trimethylsilane addition which reduces the top resist surface etch rate and balanc...