High-rate diamond deposition by microwave plasma CVD

In this dissertation, the growth of CVD (Chemical Vapor Deposition) diamond thin films is studied both theoretically and experimentally. The goal of this research is to deposit high quality HOD (Highly Oriented Diamond) films with a growth rate greater than 1 mum/hr. For the (100)-oriented HOD films, the growth rate achieved by the traditional process is only 0.3 mum/hr while the theoretical limit is ∼0.45 mum/hr. This research increases the growth rate up to 5.3 mum/hr (with a theoretical limit of ∼7 mum/hr) while preserving the crystal quality. This work builds a connection between the theoretical study of the CVD process and the experimental research. The study is extended from the growth of regular polycrystalline diamond to highly oriented diamond (HOD) films.;For the increase of the growth rate of regular polycrystalline diamond thin films, a scaling growth model developed by Goodwin is introduced in details to assist in the understanding of the MPCVD (Microwave Plasma CVD) process. Within the Goodwin's scaling model, there are only four important sub-processes for the growth of diamond: surface modification, adsorption, desorption, and incorporation. The factors determining the diamond growth rate and film quality are discussed following the description of the experimental setup and process parameters. Growth rate and crystal quality models are reviewed to predict and understand the experimental results. It is shown that the growth rate of diamond can be increased with methane input concentration and the amount of atomic hydrogen (by changing the total pressure). It is crucial to provide enough atomic hydrogen to conserve crystal quality of the deposited diamond film. The experimental results demonstrate that for a fixed methane concentration, there is a minimum pressure for growth of good diamond. Similarly, for a fixed total pressure, there is a maximum methane concentration for growth of good diamond, and this maximum methane concentration increases with the total pressure applied.;The high-rate growth of HOD films is realized with the help of nitrogen addition. Following the Goodwin's scaling model, there are several factors that can control the preferred growth orientation: temperature, methane concentration, total pressure, and surface condition. Nitrogen addition can alter the preferred growth orientation by the surface modification. In this work, the reactivity of nitrogen on the substrate surface is verified experimentally. An extended scaling model is established to explain the nitrogen effect on CVD diamond growth. The model shows that nitrogen has two distinct effects on the diamond growth: (1) when the nitrogen concentration is low, nitrogen has a positive effect on the growth, i.e., it improves the growth rate and the crystal quality; (2) when the nitrogen concentration is high, nitrogen has a negative effect on the diamond growth, i.e., it decreases the growth rate and deteriorates the crystal quality. Experimental results have successfully verified all the predictions from the extended model. The most important experimental finding is that for a given temperature and pressure, the growth condition for the best quality film shares the same ratio of methane and nitrogen concentration in the process gas. This finding validates the extended model developed in this work.