Observation of iron pileup and reduction of SiO2 at the Si-SiO2 interface

It was found by secondary-ion mass spectrometry in-depth profiling technique that approximately 1×1020 iron atoms/cm3 accumulated at the Si-SiO2 interface of oxidized silicon crystals where iron was introduced by the indiffusion prior to the oxidation at 1000 °C and above. The origin of iron accumulation is ascribed to the iron precipitation from the bulk silicon. It was also found that iron atoms that diffuse in through the bulk from the lapped backside of a preoxidized sample were trapped and aggregated at the front Si-SiO2 interface. An interesting observation is shown that the above indiffusing iron also entered into the oxide region near the interface possibly to reduce SiO2.