Synthesis of crack-free thick diamond wafer by step-down control of deposition temperature
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Synthesis of crack-free thick diamond wafer by step-down control of deposition temperature Jae-Kap Lee,a) Young-Joon Park, Kwang Yong Eun, and Young-Joon Baik Thin Film Technology Research Center, Korea Institute of Science and Technology, Seoul, 130-650, Korea
Jong-Wan Park Department of Metallurgical Engineering, Hanyang University, Seoul, 133-791, Korea (Received 30 September 1999; accepted 29 October 1999)
Due to growth tensile stress, which evolves in diamond films during deposition, thick diamond films are easily cracked. In this study we successfully prevented growth cracks by introducing thermal compressive stress with step-down control of deposition temperatures during growth. Three deposition temperature drops of 10 °C each during deposition enabled us to successfully synthesize crack-free four-inch diamond wafers several hundred micrometers in thickness. This method is very simple and may be applicable to coating of films of various materials different from those of substrates.
Chemical-vapor-deposited (CVD) diamond films usually exhibit considerably high stress levels. This has been considered due to their deposition conditions of using nondiamond substrates at high temperatures and/or incorporating defects with microstructural changes during deposition. Such internal stress in films can be classified into two categories of thermal and intrinsic stresses. Thermal stress develops due to the difference in thermal expansion coefficients between the diamond film and substrate and can be calculated mathematically using th =
ED 共␣ − ␣S兲共Td − Tm兲 , 1− D
(1)
where, (ED /1 − ) is the biaxial modulus of a diamond film, ␣D and ␣S are thermal expansion coefficients (TECs) of the diamond film and substrate, respectively, and Td and Tm are the deposition and room temperatures, respectively. At temperatures lower than the deposition temperature, thermal stress is compressive if the TEC of the substrate is larger than that of the diamond. At room temperature, the magnitude of thermal stress in diamond films on refractory metals is reported to be several gigapascals.1–3 On the other hand, intrinsic stress develops during growth and is expected to be induced by variation of microstructure and incorporation of defects in diamond films. However, its detail developing mechanism is still under debate. Although several researchers obtained compressive stress,4–5 tensile intrinsic stress is generally accepted ranging from several hundred megapascals to a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 15, No. 1, Jan 2000
http://journals.cambridge.org
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several gigapascals.6–12 As is well known, in the field of hard coating like diamond deposition, such tensile stress was reported to cause cracks.13 Especially in deposition of free-standing diamond films thicker than several hundred micrometers on a large area of several-inch scale, intrinsic tensile stress may cause serious problems. With increasin
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