Point defects in Si thin films grown by molecular beam epitaxy

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Abstract
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.