Interface states induced in silicon by tungsten as a result of reactive ion beam etching

Abstract

Interface states induced in silicon by reactive ion beam etching (RIBE) have been investigated using a metal oxide semiconductor capacitance-voltage (MOS-CV) technique, secondary ion mass spectrometry (SIMS), and Rutherford backscattering spectrometry (RBS). RIBE using an ion beam extracted from a C2F6 plasma was used to selectively remove a layer of SiO2 from the surface of single crystal silicon. MOS capacitors formed after the regrowth of a thin SiO2 layer on the silicon showed the presence of a substantial interface state density (Nss =1012–1013 eV−1 cm−2) near the middle of the energy gap of Si. RBS experiments on the Si surfaces exposed to the reactive ion beam showed the presence of tungsten (presumably from the tungsten filaments used to ignite the plasma and neutralize the ion beam). SIMS depth profiles of these samples after reoxidation to form capacitors showed tungsten contamination which was at a maximum at the SiO2-Si interface. The interface state density determined from CV measurements scaled linearly with the tungsten concentration at the interface as determined by SIMS. Interface states were formed only in the case where the Si surface was exposed to the reactive ion beam. As little as 10 nm of SiO2 remaining on the Si surface after RIBE was sufficient to prevent interface states formation.

Reactive ion beam etching of silicon with a new plasma ion source operated with CF4 : SiO2 over Si selectivity and Si surface modification

“…Very few data have been reported about the electrical evaluation of silicon after RIBE since the work of Gildenblat et al [28] which emphasized the contamination by tungsten issued from both the source and neutralization filament. In the present work, the plasma bridge neutralizer avoids the immersion of a hot filament within the beam and the use of tantalum within the ionization chamber strongly reduced this source of metal contamination as already mentioned.…”