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 d ischarge of tetrafluoroethyl trifluoromethyl ether (CF3-O-CHF-CF3;HFE 227) demonstrate the presence of CFx+ species and CF, radicals, in a comparable manner to plasmas of more established gases such as C4F8, C2F6 Or CHF3. How ever, as the etch selectivity of boron phosphorus silica glass (BPSG) to re sist is quite poor in HFE 227 plasmas, organosilane Si(CH3)(x)H4-x additive gases are investigated as a source of Si to improve the BPSG/resist select ivity. The addition of 10% trimethylsilane to HFE 227 is capable of providi ng selectivity close to 5, which is desirable for the fabrication of deep h oles. It is shown that the HFE 227/trimethylsilane plasma chemistry also pr eserves the resist hole pattern and does not cause hole expansion Juring th e etching process. These latter observations are attributed to the depositi on of polymer precursors induced by the trimethylsilane addition which redu ces the top resist surface etch rate and balances the removal rate of the r esist sidewalls. As a result, 0.15 mu m diam holes with an aspect ratio of 15 are successfully fabricated. Mass spectrometry measurements of fluorocar bon radicals and ionic species imply that the high aspect ratio feature can be fabricated by having mostly CF: ions and lower density of fluorocarbon radicals. Furthermore, the microloading-free etching of contact holes is ac hieved at a bias voltage of -500 V for diameters down to 0.15 mu m holes. T he limit of the etching performance of the HFE 227/10% trimethylsilane plas ma etch chemistry is investigated using very fine patterns defined by elect ron beam lithography. Trenches of 20 nm in width and mesh holes of 70 nm ca n be fabricated. (C) 2000 American Vacuum Society. [S0734-2101(00)02301-0].