Abstract
The electrical properties of semiconductor devices are influenced not only by the total concentration but also by the spatial distribution of impurities in/on the bulk material. Diffusion of impurity atoms will occur whenever there is a concentration gradient and the temperature is high enough to drive-in. Very high diffusion coefficients of transition metals at high processing temperatures can result in fast contamination of large wafer areas even from point sources. In order to understand the diffusion behavior of different metals in silicon upon thermal processing, it is highly required to develop analytical techniques to achieve depth profiling of impurity atoms in wafer.A method consisted of anodic oxidation followed by inductively coupled plasma mass spectrometry (ICP-MS) determination was established. The silicon wafers （6 inch p type）were anodically oxidized at a constant current density of 1.38mA/cm2 and electrolysis time of 30 minutes in 0.08 M HNO3 as electrolyte at room temperature. After anodic oxidation, the oxide layer so obtained was subsequently dissolved with 1% HF+3% H2O2, and the resulted solution was subjected to ICP-MS for the determination of analyte concentration. Successively repeating the process of layer formation and dissolution steps followed by elemental determination, the concentrations of analyte elements (Cr, Co, Ni, Cu, and Zn) in respective layers were obtained.From the experimental result on a thermally polluted silicon wafer under the heating condition at 800℃ for 5h, it indicated that a general trend showing exponentially decreasing concentration with increasing depth for the respective elements tested is found, in good agreement with that obtained by secondary ion mass spectrometry. From the reasonably good performance both in precision and accuracy as well as the low detection limits (4.0E+16 atoms cm-3) achievable for the tested elements, it may conclude that the established system combining anodic oxidation with MCN-ICP-MS can be an effectively used for the determination of concentration gradient of trace metals in silicon wafer.In order to understand the diffusion behavior of metals on silicon surface upon thermal processing, metal polluted wafers were prepared and subsequently heated in the thermal furnace. The wafers so obtained were analyzed by the established system. Based on the obtained data, the diffusion coefficients of transition metals in silicon wafer were calculated with the constant impurity diffusion mode and the results were discussed.