Study of gas supply way and velocity chosen during the process of MPCVD diamond

Abstract

The Microwave plasma chemical vapor deposition (MPCVD) method was used to make diamond film in this paper. The influence of working gas supply mode and velocity were investigated using numerical simulation method. The distribution of gas flow rate at two different gas supply modes was analyzed by software Fluent. The results showed that, the gas supply mode whose gas inlet is a hole located at the bottom of the plunger is a better choice for the formation of uniform film, gas velocity is chosen between 5m/s to 10m/s。 Introduction Among the various techniques that depositing diamond films, microwave plasma chemical vapor deposition (MPCVD) has gained more attention due to its advantages, such as, no pollution from electrodes, high density of the plasma, well controlled microstructures as well as high quality of deposited diamond films. During the last 20 years, many types of MPCVD devices have been developed, including the quartz tube type [1], the quartz bell jar type [2], the cylindrical type [3], the ellipsoidal cavity type [4] and the non-cylindrical cavity type [5]. In all these MPCVD reactors, the microwave cavities are the most important components. Design and improvement of the cavities are the key issue for the development of the MPCVD techniques. Recently, with the development of computer science, numerical simulation method was used for the design and optimization of the structure of MPCVD devices [6-10]. Research on the gas inlet ways and the velocity optimization were carried out in this paper, the research results will provide reference for the design and improvement of MPCVD device. Selection of supply path and velocity of working gas MPCVD setup and gas supply. Fig.1 shows schematically the cross-sectional view of MPCVD setup, it has been reported in the previous works [11]. The whole microwave plasma chemical vapor deposition system was analyzed by numerical simulation, which including microwave transmission part, coaxial conversion and microwave cavity. International Conference on Applied Science and Engineering Innovation (ASEI 2015) © 2015. The authors Published by Atlantis Press 697 Fig.1The cross-sectional view of MPCVD setup The working gas used in the experiment for diamond film deposition was pumped into the chamber through the top of the cavity. The working gas is a mixture of hydrogen (H2) and methane(CH4). Gas supply in different ways has great influence on the distribution of gas flow rate inside the microwave cavity. The working gas flow in the cavity was analyzed by software Fluent [12]. Two different gas supply modes were designed in this study, as is shown in Fig.3. In mode (I), the mixed working gas flowed into the chamber through the micro-holes on the top of the microwave cavity. The holes was arranged around the plunger, as the dashed line represents in Fig.2 (a) . In mode (II), the gas inlet is a hole located at the middle of the plunger (Fig.2 (b) ). In both mode (a) and mode (b), the inlet gas flow rate was assumed to be 1 m/s, 2 m/s, 5 m/s, 10 m/s. The distribution of gas flow rate inside the cavity was simulated. Fig.2 Two different gas supply mode: (a) mode (I) , (b) mode (II)