Depth profiles of vacancylike defects have been determined by positron annihilation spectroscopy in 200-nm-thick Si films grown by molecular beam epitaxy on Si(100) substrates at growth temperatures Tgrowth=200- 560°C. The line shape of the radiation emitted from implanted positrons annihilating in the near-surface region of a solid gives quantitative, depth-resolved information on defect concentrations in a nondestructive way. In particular, the method is sensitive to vacancylike defects in a concentration range inaccessible to electron microscopy or ion scattering, but important for electrical device characteristics. The sensitivity limit for these defects in the present experiments is estimated as 5×1015 cm-3. Films grown at Tgrowth≥475±20°C are indistinguishable from virgin wafers. So are samples with Tgrowth=220±20°C, subjected to a 2 min, TRTA≳500°C rapid thermal anneal (RTA) after every ≊30 nm of Si growth. If TRTA=450±20°C, part of the film contains a concentration of vacancylike defects on the order of 1018 cm-3. Our results indicate the importance of the growth parameters, such as temperature and substrate preparation, for the production of high quality films.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)