Vm. Donnelly et al., Oxidation of Si beneath thin SiO2 layers during exposure to HBr/O-2 plasmas, investigated by vacuum transfer x-ray photoelectron spectroscopy, APPL PHYS L, 74(9), 1999, pp. 1260-1262
Thin SiO2 layers were exposed to an HBr/O-2 plasma for a variety of short p
eriods, reproducing the over-etching process after polycrystalline Si gate
electrodes have been etched and the gate oxide layer is exposed. Samples we
re transferred under vacuum to an x-ray photoelectron spectrometer for anal
ysis. After relatively thick (> 60 Angstrom) films were exposed to a 10% O-
2/HBr plasma at an average ion energy of similar to 150 eV, the near-surfac
e region becomes brominated, and the thickness of the film decreases, indic
ating an etching rate of similar to 1 - 2 Angstrom/s. When the starting fil
m thickness is between 10 and 20 Angstrom, however, exposure to the plasma
results in an increases in the thickness of the film, and is enhanced with
the increasing addition of oxygen to the feed gas. At mean ion energies of
40 or 150 eV, the transition from etching to deposition occurs at oxygen ad
ditions of similar to 1% or similar to 8%, respectively. The increase in Si
O2 thickness is ascribed mainly to oxidation of the Si at the oxide-substra
te interface, and not to deposition resulting from sputtering of reactor ma
terials. Consumption of crystalline Si beneath a 12 Angstrom thick SiO2 gat
e oxide, adjacent to a 600 Angstrom linewidth, polycrystalline gate electro
de was also observed after etching of this transistor structure, as confirm
ed by transmission electron microscopy. (C) 1999 American Institute of Phys
ics. [S0003-6951(99)01509-0].