Transmission Electron Microscopy of Hydrogeninduced Defects in Low Temperature Epitaxial Silicon
- PDF / 3,601,905 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 76 Downloads / 194 Views
TRANSMISSION ELECTRON MICROSCOPY OF HYDROGENINDUCED DEFECTS IN LOW TEMPERATURE EPITAXIAL SILICON G. B. ANDERSON, C. C. TSAI and R. THOMPSON Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto CA. 94304, U.S.A.
ABSTRACT Hydrogen is commonly used in crystalline Si for passivation of defects and impurities. When single crystal Si undergoes a post-hydrogenation step, hydrogen-induced platelets have been shown to form in the first 100 nm of the Si. The same hydrogen platelets occur in homoepitaxial Si grown by low temperature (350(C or below) plasma-enhanced chemical vapor deposition with hydrogen dilution. This study has used transmission electron microscopy (TEM) to examine the structure of these hydrogen-induced platelets. TEM has shown that the platelets generally grow in the (111) crystal planes of the Si. The size of the platelets, which ranges from 5 to 100 nm, increases with growth temperature but the density of platelets decrease at higher growth temperatures. The hydrogen platelets are not confined to the epitaxial Si layer only but also grow into the substrate. High resolution TEM shows the platelets dilate the silicon lattice by approximately 60% of a Si plane. TEM has also shown that platelets cause no net displacement of the local Si lattice. Tilting experiments performed in the TEM show that the platelets are composed of a circular twodimensional structure. Our results indicate that the hydrogen-induced platelets found in low temperature epitaxial Si are structurally the same as those seen in crystalline Si that has undergone post-hydrogenation processes. INTRODUCTION Hydrogen has shown the ability to passivate defects and impurities in silicon [1], but recent work [2-41 has shown that hydrogen can also form platelets or microcracks in crystalline Si. These platelets can be formed by exposing single crystal silicon to a post-hydrogenation treatment. These post-hydrogenation treatments can consist of exposing Si to a remote hydrogen plasma source or by hydrogen implantation. These defects are also found in low temperature homoepitaxia/ silicon grown by plasma-enhanced chemical vapor deposition (PECVD) [5]. Hydrogen platelets are incorporated into the epitaxial Si layer during the growth of the thin film. Low temperature Si ep itaxial films grown by PECVD display a variety of hydrogen-induced defects. These defects vary with growth conditions. The growth temperature and hydrogen dilution can control the density and size of the platelets in these Si films and in the substrate. This study has used TEM to examine the effects of the growth temperature on the structure and distribution of these hydrogen-induced defects. EXPERIMENTAL CONSIDERATIONS Low temperature Si films of approximately 200-300 nm in thickness were dilution of the silane plasma. The growth grown by PECVD with 80% hydrogen temperatures range from 150-350 0C and the growth rate was approximately 10 nm/min. The Si films were grown on (100) Si wafers that were ex situ cleaned by immersion in HF reagents. This cleaning process provid
Data Loading...
