Transmission Electron Miscroscopy Study of the Fused Silicon/Diamond Interface
- PDF / 372,717 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 61 Downloads / 198 Views
G2.9.1
TRANSMISSION ELECTRON MISCROSCOPY STUDY OF THE FUSED SILICON/DIAMOND INTERFACE G. N. Yushin*, S. D. Wolter**, A. V. Kvit*, R. Collazo*, J. T. Prater** and Z. Sitar* North Carolina State University, Department of Materials Science and Engineering, Raleigh, NC 27695, USA ** Army Research Office, Research Triangle Park, NC 27709, USA
*
ABSTRACT Bonding of polished, polycrystalline diamond films to silicon was performed in ultra high vacuum at 32 MPa of applied uniaxial stress. The transmission electron microscopy (TEM) investigation revealed that the interface of all bonded samples was non-uniform. An abrupt boundary between the two wafers existed only in some parts of the interface, while other parts contained an amorphous interlayer of up to 40 nm in thickness. Electron energy loss spectroscopy (EELS) revealed that this interlayer consisted of oxygen, carbon and silicon. Based on comparison of the microstructure and chemical composition of the interface formed at different bonding temperatures, we propose a model for the silicon/diamond wafer fusion process. INTRODUCTION Integration of diamond with other electronic materials is of considerable technological interest. Silicon-on-diamond (SOD) technology can significantly enhance power characteristics of devices fabricated on silicon, due in-part to the high thermal conductivity of diamond. Wafer bonding is a promising way to create these substrates, and generally involves an applied load and elevated temperature to promote a robust fusion. As such, the fusion interface must be scrutinized after this processing, since defects incurred are likely to influence the properties of the SOD substrates. This work reports on TEM studies of the bonded silicon/diamond interfaces formed in the temperature range between 950ºC and 1100ºC. EXPERIMENTAL DETAILS In all bonding experiments, we used commercially available CZ (001) Si wafers with a root-mean-square (RMS) surface roughness of ~0.5 nm and polycrystalline diamond films deposited using microwave plasma chemical vapor deposition, which were mechanically polished to an RMS roughness of ~15 nm. Possible graphitic contamination and polishing residues were removed from the diamond surface by cleaning the samples in a mixture of chromium oxide and sulfuric acid heated to 100ºC. Prior to fusion, samples were ultrasonically cleaned in solvents and blow-dried in nitrogen. To limit particulate contamination, this procedure was performed inside a class 1000 clean-room. The final cleaning step was performed in ultra high vacuum (UHV), where diamond and Si samples were heated at 400-500ºC for 2 hrs to desorb adventitious species such as carbon and oxygen. In addition, Si samples were heated at 1100ºC for 60 min in order to remove the native oxide from the Si surface. An in-situ investigation of the surfaces using x-ray photoelectron spectroscopy (XPS), by obtaining both core level spectra and C 1s EELS data, verified removal of the surface contaminants. After the high temperature treatment, no change in the Si surface topography
Data Loading...
