Growth of Single Crystal Diamond Wafers for Future Device Applications

Due to its unique combination of superior material properties, diamond is often referred to as the ultimate semiconductor material for high-power electronics. Lack of wafer-size electronic-grade single crystals was always considered a crucial bottleneck for the device development and the subsequent transfer to industrial processes. Over the last years, significant progress has been made for the classical high-pressure high-temperature (HPHT) method and in particular for the alternative chemical vapor deposition (CVD) technique. This review first briefly describes the HPHT technique which copies the natural formation process working under conditions under which diamond is thermodynamically the stable phase of carbon. It is capable to produce small crystals virtually free of dislocations. The maximum size of available substrates is currently ≈15 × 15 mm 2 . In contrast, CVD growth takes place at more moderate temperatures, at pressures below ambient conditions and far from equilibrium. The general aspects of diamond CVD comprising the gas phase chemistry, different technical approaches for gas phase activation and reactor design are summarized. There are two competing approaches toward single crystal diamond wafers required for electronic applications. Homoepitaxy is performed on highest quality HPHT seed crystals, and various concepts are explored to increase sample dimensions during CVD processes. In contrast, heteroepitaxy involves nucleation and growth on foreign substrates. While homoepitaxial crystals excel with minimum dislocation densities, they are outperformed in terms of size by 3.5-in.-diameter diamond wafers synthesized by heteroepitaxy on Ir/YSZ/Si(001). Classical and novel concepts for further defect reduction during CVD growth are discussed.