Metallic contamination in high purity silane (SiH4) gas is tested through the poly-Si gate process and lifetime measurement of the processed wafers. High purity SiH4 is used to deposit a 420 A thick poly crystalline Si film by low pressure chemical vapor deposition on a 100 A gate oxide under ultraclean conditions. Subsequently, poly-Si is fully oxidized at 1050°C for 120 min. The minority carrier lifetime, as measured by microwave photoconductive decay μpcd) for both the reference and the SiH4 processed wafers are identical, at approximately the bulk lifetime of 900 Thermodynamic μs. analysis of 3d metals behavior at the SiO2/Si interface suggests that Fe, Co, Ni, and Cu elements are unlikely to react with the silicon oxide layer and could potentially be contaminates which diffuse into the bulk Si. Moreover, the quality of the Si/SiO2 interface is probed directly by measuring the effective lifetime, which is found to be about 360 μs. Using a model for the excess carrier decay, it is shown that this effective lifetime value corresponds to a defect state density in the Si/SiO2 interface below approximately 109 states/cm2The μPCD sensitivity to metallic traces on the wafer surface is experimentally confirmed by oxidizing the wafers contaminated with an Fe containing solution.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry