Journal of Vacuum Science & Technology B, Vol.16, No.5, 2776-2785, 1998
Artifacts in low-energy depth profiling using oxygen primary ion beams : Dependence on impact angle and oxygen flooding conditions
The depth resolution and the accuracy of depth calibration in sputter profiling of boron delta distributions in silicon have been investigated using 1 keV O-2(+) ion bombardment at impact angles theta between 2 degrees and 62 degrees (to the surface normal) in combination with secondary ion mass spectrometry. The effect of jet-type oxygen flooding during sputter erosion was studied at 62 degrees. For theta up to 34 degrees, the depth resolution was essentially independent of theta (full width at half maximum, FWHM, 2.9 nm, decay length 1.4 nm) and also independent of depth (for deltas located between 40 and 190 nm). However, the well-known peak shift due to the initial short-term change in erosion rate was a factor of 2.7 larger at 34 degrees than at 2 degrees (3.5 vs 1.3 nm). As theta exceeded about 36 degrees, two other types of artifacts were observed during bombardment in vacuum, (i) a severe profile broadening and (ii) a large long-term change in erosion rate which gave rise to crater-depth dependent peak shifts of the deltas (erosion rate reduced for 41 degrees< theta<62 degrees, but enhanced for 36 degrees