Secondary on yield changes in Si and GaAs due to topography changes during ion bombardment.

Changes in secondary ion yields of matrix and dopant species have been correlated with changes in surface topography during O sub 2 sup + bombardment of Si and GaAs. In Si, profiles were measured in (100) and (111) wafers at 6 keV impact energy. A yield increase of about 70% occurred for Si sup + in (100) silicon over a depth range of 2.5 to 3.5microns with corresponding changes in other matrix species. A smaller increase was noted in the B sup + signal for a bulk doped wafer. The development of a rippled surface topography was observed in scanning electron micrographs over the same depth range. Similar effects occurred in (111) silicon at a depth of 3 to 4microns. No differences were noted between p and n-type silicon, or implanted and unimplanted silicon. In GaAs, profiles were measured in (100) wafers at 2.5, 5.5, and 8 keV impact energies. At 8 keV, a yield increase of about 70% was found for GaO sup + in the range 0.6 to 1. 0micron, with smaller changes to other matrix species. At 5.5 keV, similar effects were observed, but over a depth interval of 0.3 to 0.7micron. No yield changes were detected at 2.5 keV impact energy. The yield changes at the higher energies were again correlated with the onset of changes in topography. It is concluded that changes in surface topography under O sub 2 ion bombardment can affect secondary ion yields of matrix and dopant profiles to a matrix signal must be re-examined.