Study of effects of fractal apertures on diamond growth

Abstract

High-purity and uniform diamond films are required for many applications, such as electronics or medicine. However, depositing a uniform diamond film over a large surface area using state-of-the-art techniques is still difficult to achieve. A promising method to address this challenge is a surface wave plasma (SWP) chemical vapour deposition (CVD) method based on composite right/left-handed (CRLH) metamaterials. Compared to conventional rectangular waveguides, CRLH waveguides operate at infinite wavelength propagation frequency and allow the placement of apertures as excitation slots at arbitrary positions, thus enabling optimization of their design. In this work, we study two fractal designs, the Sierpinski Carpet and the Sierpinski Gasket, as excitation apertures and their impact on the uniformity of diamond films. We numerically study the electromagnetic field distributions of the fractal apertures and compare them with the corresponding distributions for conventional rectangular apertures. The optimized fractal layouts are then implemented in an in-house built SWP CVD system. We deposit nanocrystalline diamond films on 2-in. Si wafers using fractal and rectangular aperture layouts and compare the resulting film thickness variations. We show numerically that fractal aperture layouts can improve the uniformity of the electric field strength by up to 38 % compared to a slotted aperture design. However, the measured film-thickness variations suggest a strong dependence of the growth rate on the gas velocity within the CVD chamber.