Lift -Off Process to get Free-Standing High Quality Single Crystal Diamond Films and Suspended Single Crystal Diamond De
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Lift -Off Process to get Free-Standing High Quality Single Crystal Diamond Films and Suspended Single Crystal Diamond Devices Jie Yang1,2, C. F. Wang3, E. L. Hu3, and James E. Butler1 1 Gas/Surface Dynamics Section, Naval Research Laboratory, Washington, DC, 20375 2 NOVA Research Inc., Alexandria, VA, 22308 3 University of California, Santa Barbara, CA, 93106 ABSTRACT Freestanding and suspended single crystal diamond devices, micro disks and beam structures, have been fabricated on single crystal diamond substrates using a lift-off process employing ion implantation followed by electrochemical etching. The ion implantation created subsurface damage in the diamond while the top surface was sufficiently undamaged that a subsequent homo-epitaxial diamond layer could be grown by chemical vapor deposition (CVD). After the CVD growth and patterning by lithography and reactive ion etching, the underlying damage layer was etched/removed by an electrochemical etch. Different implant ions and energies were simulated and tested to optimize the process. The electrochemical etching process was monitored by an optical video technique. The electrochemical etching process used both ac and dc applied electrical potentials. Photoluminescence (PL), Raman spectra, and polarized light transmission microscopy have been used to characterize the implanted substrate and liftoff films. AFM has been used to monitor the surface changes after mechanical polishing, ion implantation, CVD growth and the lift-off process. This research has revealed that the parameters of ion implantation (implant species, dose and energy) dramatically affect the lift-off process. The etching mechanism and critical parameters are discussed in this work. PL spectroscopy indicated differences between the uppermost layers of the homoepitaxial film and the lift-off interface. Three principal classes of defects have been observed: growth defects inherent in the diamond substrates (type Ib, HPHT), defects induced by the polishing process and associated stress, and point defects. INTRODUCTION: Compared with other semiconductor materials, diamond has many theoretical advantages. It has a larger bandgap (5.5 eV) than SiC (3.4 eV), GaN (3.2 eV) and Si (1.1 eV) [1,2]; it is one of the negative electron affinity materials; it is optically transparent; it has high mechanical and chemical stability; and its thermal conductivity is five times higher than that of copper. The combination of all these good properties gives diamond the potential to become a material important to electrical power devices, and to mechanical and optical MEMS devices [3-5]. But many challenges must be overcome for the realization of diamond electronic applications. The first comes from the process of growing single crystal diamond materials, namely, how to grow large, reproducible, semiconductor quality single crystal diamond materials. The second, the formation of micro-scale or nano-scale suspended single crystal diamond devices, is a considerable challenge for fabrication, because of the d
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