Nucleation of Special Orientations During Heteroepitaxial Growth of Diamond on Silicon
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ABSTRACT The orientation relationships that develop in the early stages of diamond nucleation on silicon, were examined by TEM and HRTEM. The films were produced by microwave plasma assisted CVD. Two types of interface regions were identified. In one case an amorphous interlayer was observed and the nucleation of diamond was nanocrystalline. In the second case the interface was apparently free from a second phase; in these instances the diamond and silicon lattices formed special orientations. The special orientations were identified as the following: (a) 60 degree rotation, (b) 90 degree rotation and (c) diamond {1111 plane tilted 6 degrees from silicon {220} plane. The orientation relationships are analyzed in terms of geometric models that seek the best fit between the diamond and silicon lattices at the interface plane.
INTRODUCTION Single crystal diamond films are of interest due to their potential application in high temperature, high power/high frequency, and high power/high packing density devices 1 ,2 . Heteroepitaxial diamond films have been demonstrated on substrates such as c-BN1 and 13-SiC2, but these substrates are not readily available. Recent progress has achieved to grow heteroepitaxial diamond film on silicon with small angle grain boundaries through an epitaxial SiC transition layer 3 . There is evidence suggesting that diamond could grow directly on silicon without any extra phase 4 . It is therefore interesting to explore the possibility of growing diamond heteroepitaxially on silicon. In this report, we present the special orientations of diamond grown on silicon and discuss the formation of such orientation relationships by simple geometric models.
EXPERIMENT Diamond films were deposited by Microwave Plasma Assisted Chemical Vapor Deposition on (001) silicon wafer. Typically silicon substrates were scratched by lgnm diamond paste and cleaned by trichloroethylene, acetone and de-ionized water before deposition. The deposition conditions were as following: substrate temperature 850 - 950 'C, pressure 6.7 kPa (50 torr), reactant gas 0.5 1% methane in hydrogen balance, total gas flow rate 200 - 400 sccm and deposition time 15 - 120 minutes. The special diamond orientation was analyzed by transmission electron microscopy (TEM) of the interface seen in crosssection. For TEM specimen preparation the diamond film on silicon was cut into two sections which were cemented back to back. The cemented specimen was inserted into an alumina tube and bonded by epoxy. A disc was cut from the complex, ground, polished, dimpled and ion milled to electron transparency. 517 Mat. Res. Soc. Symp. Proc. Vol. 317. @1994 Materials Research Society
High resolution TEM (HRTEM) was performed on a JEOL 4000EX. Images were taken at Scherzer optimum defocusing condition (-50 nm for JEOL 4000EX).
RESULTS The diamond nucleation density on unscratched silicon is too low and no TEM observation was performed on those specimens. The following results are from deposition on scratched silicon substrates. Interface With Amorphou
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