Wafer Bonding of Diamond Films to Silicon for Silicon-on-Insulator Technology
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Wafer Bonding of diamond films to silicon for silicon-on-insulator technology Gleb N. Yushin, Scott D. Wolter, Alexander V. Kvit, Ramon Collazo, North Carolina State Univ, Dept. of Material Science, Raleigh, NC 27695,U.S.A.; John T. Prater, Army Research Office, RTP, NC, U.S.A.; Brian R. Stoner, MCNC, Material and Electronic Technologies Division, RTP, NC 27709, U.S.A., Zlatko Sitar, North Carolina State Univ, Dept. of Material Science, Raleigh, NC 27695,U.S.A.
ABSTRACT Polycrystalline diamond films previously grown on silicon were polished to an RMS roughness of 15 nm and bonded to the silicon in a dedicated ultrahigh vacuum bonding chamber. Successful bonding under a uniaxial mechanical stress of 32 MPa was observed at temperatures as low as 950°C. Scanning acoustic microscopy indicated complete bonding at fusion temperatures above 1150°C. Cross-sectional transmission electron microscopy later revealed a 30 nm thick intermediate amorphous layer consisting of silicon, carbon and oxygen.
INTRODUCTION Historically, the main driving force for wafer bonding research and development have been applications involving silicon-on-insulator (SOI) technology. The fabrication of high quality SOI wafers by this method is a well-established procedure providing an active silicon layer comparable in quality to that of bulk silicon, while possessing a buried insulator with properties that enable a broader range of operating characteristics of silicon-based devices. Since the conventional SOI technology employs silicon dioxide as the buried insulator layer, the performance of power devices is limited due to early degradation due to a self-heating phenomenon caused by the low thermal conductivity of the oxide. Diamond is considered a promising material as the buried insulator in the SOI scheme due to its ideal combination of thermal and electrical properties. The attributes of a high thermal conductivity (> 20 Wcm-1K-1; a value 1000 times higher than that of silicon dioxide), high electrical resistivity (greater than 1013 Ω⋅cm) and high breakdown electric field (greater than 107 V/cm) [1] may offer a means of managing the self-heating problem associated with the conventional SOI material. The focus of this research specifies wafer bonding of polished, polycrystalline and unpolished (100) oriented diamond films to (100) silicon. The influence of fusion temperature on the bonding process at a constant applied stress is discussed in the context of defect formation and the silicon-diamond fusion interface.
EXPERIMENTAL DETAILS Microwave plasma chemical vapor deposition of diamond The deposition of randomly oriented diamond was performed on 1 mm thick single-side polished (100) silicon substrates using microwave plasma chemical vapor deposition (MPCVD). A2.6.1
Solvent-cleaned silicon substrates, 75 mm in diameter, were patterned using conventional photolithography to produce an array of pads, 3 mm x 4 mm in dimension, comprised of diamond grit suspended in photoresist. Discrete rectangular pads of diamond, nominally 25 µm in thicknes
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