Effect of zn on segregation of ZnO-rich SiO2 layer and reduced oxidation rate in thermally oxidized Si(001)

Upon the oxidation of Zn-contaminated Si wafers ("Zn"), most of the Zn atoms added on the Si surface reside inside the bulk oxide (SiO2) and are found to be segregated at the very top surface area of the SiO2 as a ZnO-rich SiO2 layer. This ZnO-rich SiO2 layer is identified to be as thick as 1.3 nm after processing at 810 degrees C for 10 min. During oxidation at 810 degrees C, reduced growth was observed as the oxidation of the "Zn" samples proceeded, indicating a crossover for the oxidation time of about 10 min between samples rinsed in RCA ("RCA") and those of "Zn". By using the interfacial Si emissin model, the retardation phenomenon in the oxidized "Zn" samples can be envisaged, where the ZnO-rich SiO2 layer could be a good diffusion barrier for oxygen and/or emitted Si from the Si-SiO2 interface, suppressing another new interfacial Si from the interface and, accordingly, the oxidation reaction at the Si-SiO2 interface was suppressed. This result gives evidence that emitted Si is oxidized not in the ZnO-rich SiO2 layer, but at the Si-SiO2 interface in accordance with the proposed model. A possible mechanism is speculated on the basis of the interfacial Si emission model. The activation energy for the oxidation in the reduced growth range of the Zn samples was determined to be 2.2 +/- 0.2 eV, which is in good agreement with that for the oxidation of the fourth atomic layer obtained by Yasuda et al.