Research On The Fabrication Techniques Of The Core Component In Microplasma Etching System

In micro/nano-fabrication, microplasma not only inherits the high etching rate, good etching directivity and material selectivity of macro plasma, but also can realize a maskless localized etching process. Moreover, three-dimensional etching can be carried out even on a nonplanar surface with microplasma which attracted more and more attentions in recent years. However, most of the existing microplasma etching devices work with low efficiency and low resolution, so that they have not become the dominate methods of micro/nano-fabrication. A new integrated microplasma etching system based on scanning micro probe was presented in our group, and a microplasma maskless etching can be realized with high efficiency and high resolution. The cantilever array with nano-aperture hollow tips is the core component of this microplasma etching system. The array is fabricated in this dissertation and integrated with microplasma generators. Further more, key processes in the fabrication and application are researched and discussed in detail.The main research subjects of this dissertation are as follows:(1) Research on the stress-dependent nonuniform Si oxidation. Stress-dependent nonuniform oxidation plays and essential role in the fabrication of nano-aperture hollow tips. According to the oxidation theory, the nonuniformity is radically from the oxidation rate retardation caused by intrinsic stress in oxide layer. It is proved by experiments that the nonuniform silicon oxidation is an interacting result of the stress generation and stress relaxation, and it can be controlled by oxidation temperature and oxidation time. Based on this, proper oxidation parameters are chosen for the fabrication of nano-aperture hollow tips.(2) Fabrication of the nano-aperture hollow pyramid tip arrays. Hollow pyramid tip is the weakest structure in our microplasma etching system, so the mechanical characteristics of the tips are researched at first. The inner stress distribution and the influences of load and width-thickness ratio are discussed. Based on this, nano-aperture hollow pyramid tip arrays are fabricated using the traditional MEMS fabrication process. This is a fabrication process with high efficiency and low cost. After process optimization and controlling, hollow pyramid tips with the base width of 50μm and 100μm are obtained. The width-thickness ratio of these fragile tips is up to 150:1 but the product yield can reach more than 95%. At the apexes of the hollow tips, nano-apertures of 50～200nm in diameter are etched in batches. (3) Optimization of the multilayer cantilever. In the microplasma etching system, microplasma generators are integrated on the SiO2 cantilevers, and there are different inner stresses in each layer, which cause the cantilever bending. The inner stresses are measured with Stoney theory at first. Based on this, the phenomenon of the multilayer cantilever bending and the influence of each layer are researched, and the film thicknesses are optimized(4) Integration of the nano-aperture hollow tips with cantilevers and microplasma generators. With some researches on the integration processes and the key fabrication techniques, the nano-aperture hollow tips are integrated with the cantilever arrays and microplasma generators and this device can almost meet the requirement of microplasma etching in our research.(5) The microplasma testing. Based on the existing equipment in our lab, a set of microplasma testing system is developed in this dissertation. Using this system, V-I curves and emission spectrums are obtained and some preliminary analyses are presented, which provides important information for optimization of the microplasma etching system.There are some creative points in this dissertation as follows:(a) Nano-aperture hollow tips are applied in microplasma etching. Integrated and miniaturized microplasma etching system is developed, (b) Key issues in the system fabrication and application such as nonuniform oxidation, mechanical characteristics of hollow pyramid tips, microplasma extraction, and multilayer cantilever optimization are researched and discussed in detail, (d) A set of microplasma testing system is developed and characteristics of the reactive microplasma are obtained and analyzed.