Optimizing MPCVD systems for diamond growth through advanced microwave transmission theory

Diamond, renowned for its exceptional properties, stands as the ultimate semiconductor material. Microwave plasma chemical vapor deposition (MPCVD) is pivotal in advancing diamond's functional applications. The effectiveness of the MPCVD system hinges on the efficient transmission of microwave energy to the resonant cavity. Additionally, the system must form a large-area, high-intensity hemispherical standing-wave electric field in the deposition area. Thus, a well-conceived optimization design for the microwave transmission and resonance systems is imperative. This paper introduces a design methodology for MPCVD systems, aligning plasma requirements for diamond growth with the transmission and distribution characteristics of the microwave electromagnetic field, which means that system optimization can be achieved without the need for complex multiple physical fields simulations. The average electric field intensity up to 3.24 × 10⁵ V/m is obtained by using the dual-objective optimization function as the comprehensive optimization objective of the metal boundaries of the reactor. Based on simulation findings, an MPCVD system operating at 2450 MHz was designed, resulting in a single-crystal diamond with a high average growth rate of 11.5 μm/h. Further reduction of the microwave frequency to 915 MHz enabled the preparation of a 4-inch polycrystalline diamond film, achieving an average growth rate close to 3.5 μm/h.