Silicon etching in NF3/O-2 remote microwave plasmas

The etching of silicon in remote microwave discharges fed with NF3/O-2 has been investigated. In situ ellipsometry and x-ray photoelectron spectroscop y (XPS) were used to monitor surface effects, while mass spectrometry was u sed to monitor the gas phase dynamics. Varying the microwave power from 600 to 1400 W has little effect, due to the near complete dissociation of the NF3, even at lower powers. For discharges containing pure NF3, the poly-Si etch rate increases linearly with NF3 flow. When a low proportion of O-2 (O -2/NF3=0.1) is added to the discharge, the etch. rate increases quickly to its maximum of similar to 700 nm/min. With further O-2 addition, this etch rate decreases below that observed for pure NF3 processing. The fluorine co ncentration in the processing region decreases for all O-2 additions by a d ilution effect. For pure NF3 discharges, XPS measurements reveal 1-2 nm thi ck, highly fluorinated reaction layers with a gradual loss of fluorine cont ent as the NF3 flow is increased. Specimens processed with both NF3 and O-2 show much less surface fluorination that decreases with increasing O-2 con tent in the feed gas. At the etch rate maximum, the observed N (1s) signal is also:maximized. The reaction layer thickness increases with added O-2 an d continues to more than 10 nm at O-2:NF3 ratios greater than unity. We dis cuss the enhanced reactivity of the modified Si surface and compare our res ults with the role of-admired Nz into the CF4/O-2 system. We also injected NO directly into the effluent of NF3 and CF4/O-2 discharges. For fluorine r ich discharges, NO removes the modified surface layer on Si and provides fo r an enhanced etch rate. In the oxygen rich regime, NO injection can increa se both the etch rate and the reaction layer thickness. We will present a m echanism for the enhanced etching of Si in the presence bf fluorine, oxygen and the NO molecule. (C) 1999 American Vacuum Society. [S0734-2101(99)1020 5-7].