Determination of ultratrace amounts of silicon on gallium arsenide wafers by dissolution of the surface with an ammonia-hydrogen peroxide mixed solution and a measurement by graphite furnace AAS

A method for the determination of ultratrace Si on GaAs wafers has been investigated. A NH4OH and H2O2 mixed solution was suitable for the dissolution of GaAs wafers. In the pretreatment procedure, a NH4OH and H2O2 mixed solution and a polypropylene ring was sandwiched between two GaAs wafers, so that it could dissolve the surface by shaking with a small volume of solution inside the polypropylene ring. The presence of Ga and As in the solution deteriorated the reproducibility of the Si measurement by graphite furnace AAS. The use of a NH4Cl and HBr mixed solution as a matrix modifier recovered the reproducibility. The lower determination limit was 2 ng ml-1, estimated as the concentration corresponding to 10-times the standard deviation of a blank solution. This value corresponded to a surface concentration of 14 × 1011 atoms cm-2 for 2-inch wafer, and 4 × 1011 atoms cm-2 for 3-inch wafer. According to the analytical results of various GaAs wafer samples, it was found that the concentration of Si on the surface of GaAs wafers was in the range of 1011-1013 atoms cm-2.