INFLUENCE OF STRONTIUM IMPURITIES ON SILICON SUBSTRATES DURING THERMAL-PROCESSING

The influence of strontium impurities on silicon substrates was evalua ted in order to introduce high dielectric constant SrTiO3 thin films i nto the LSI manufacturing process. Sr metal impurities were intentiona lly diffused into silicon during annealing at 950 degrees C in N-2 for 4 h. A 5-nm-thick SiO2 layer was formed when inserting wafers in and taking them out of the furnace, and the Sr impurity concentration was maximum beneath the SiO2/Si interface. Sr impurities cause an increase in positive charge in the SiO2 layer. However, the recombination life time of minority carriers in Si is not degraded by Sr impurities, even for Sr levels up to 10(14) atoms/cm(2). After annealing at 700 degree s C in O-2 for 2 h, no Sr was detected on the surface of a Si wafer fa cing a wafer covered with a SrTiO3 thin film prepared by metal organic chemical vapor deposition. Therefore, it is believed that Sr can safe ly be introduced into the LSI manufacturing process.