Low-temperature deposition of transparent diamond films with a microwave cavity plasma reactor

Low-temperature diamond deposition with Microwave Cavity Plasma Reactor (MCPR) technology was investigated for application to temperature sensitive substrates. The substrate temperature during most CVD diamond deposition processes is typically greater then 600 C; however, there are some applications where temperature sensitive materials are used and the deposition temperature must be maintained below 550 C. These applications include materials like boro-silicate glass, which has a relatively low strain-point temperature, and integrated circuits that contain low melting point components. Experiments were conducted in three areas. The first area was MCPR development, the second was benchmark deposition and characterization of diamond films on silicon substrates and the third was deposition and characterization of diamond films on boro-silicate glass substrates.; MCPR development included an investigation of various MCPR configurations that were designed and adapted for uniform, low-temperature diamond deposition over areas as large as 80-cm2. Reactors were investigated with end-feed microwave excitation and side-feed microwave excitation for maximum deposition area and uniformity. Various substrate receptor configurations were also investigated including a substrate heater and cooler. From these investigations, deposition parameters such as substrate temperature, deposition rate, deposition area and deposition uniformity were characterized.; The benchmark silicon diamond deposition experiments were conducted for comparison to previous high temperature, >550 C, MCPR research and growth models. Here deposition results such as deposition rate and film quality were compared with applications of diamond growth models by Harris-Goodwin and Bachmann. Additionally, characterization experiments were conducted to investigate film attributes that are critical to optical applications, such as film surface roughness and deposition uniformity. Included as variables in these benchmark experiments were various mixtures of H2, CO2 and CH 4 gases and two substrate pre-treatment methods, which were photo-resist seeding and diamond powder scratch seeding. The typical operating range of the MCPR were gas pressures in the range of 5 to 15 torr and incident microwave power levels in the range of 300 Watts to 1.2 KW. Typical deposition rates at approximately 470 C were in the range of 20 nm/hr to 100 nm/hr. Uniform deposition on the order of +/-10% was achieved over areas as large as approximately 45 cm-2; The focus of diamond deposition on boro-silicate glass substrates was to investigate deposition parameters that influence optical diamond film characteristics such as transmission and adhesion. Two loss mechanisms for optical transmission through poly-crystalline diamond films are bulk absorption and surface scattering, which both tend to have inverse lambda dependencies. Measured optical transmission and fitted rms surface roughness data indicate that diamond films that have a thickness on the order of 1 to 2-mum. can be deposited with transmission as high as 70% at 400-nm. Adhesion was somewhat problematic for films with a thickness of > 2mum, many of them had a tendency to peel. Many films with a thickness under 2mum have exhibited long term adhesion over several years.