Research On SPM-based Microplasma Maskless Scanning Etching Fabrication Method

With the rapid development of micro-nano technology, the limit size of the device will continue to decrease. Fabricating nano-scaled devices with specific function is the goal pursued of the researchers. In micro-nano fabrication technology, microplasmas or microdischarges have gained considerable interests because of their unique properties, such as small size, high-pressure operation and high electron densities etc. These properties make microplasmas suitable for a wide range of materials applications, including the locally maskless material etching. However, most microplasma maskless etching configurations can only achieve etching resolution of a few hundred micrometers, which is far from the requirements of micro/nano fabrication. On the other hand, in addition to its well-known capabilities in imaging and spectroscopy, scanning probe microscopy (SPM)-based technology has become increasingly popular in the fabrication of nanoscale structures due to its low cost and great technical potential. The weakness of this technology is low fabrication rate, low efficiency, relatively narrow range of fabrication material, and hard to meet the need with fabrication diverse product with high throughput and three dimensional structural. So we combined the advantages of microplasma and SPM technology, and proposed a SPM-based maskless microplasma etching method to realize3D nano-fabrication with high efficiency and low cost.The main research subjects and innovations of this dissertation are as follows:(1) PZT piezoelectric probe and SiO2cantilever probe integrated with microplasma and nano-aperture are designed. The structural parameters are optimization by calculation and simulation of sensing, driving and mechanical properties of piezoelectric probe. The structural parameters of SiO2cantilever probe are optimization by simulation of the stress-induced bending deformation of the cantilever. A novel microplasma tip array scanning etching method is proposed, and preliminary structure design of the method is performed.(2) The extraction mechanism and etching mechanism of microplasma ejected through nano-aperture are analyzed and simulated. The concentration, velocity, temperature and diffusion distance of microplasma is simulated on the condition of free diffusion and applied bias electric field. The etching profile and etching rate for silicon in SF6microplasma exported from the nano-aperture are simulated to predict the etching effect under maskless microplasma etching system. High etching rate and etching resolution can be obtained when tip-sample distance is nearly the same with diameter of nano-aperture.(3) Base on the researches of the integration processes and the key fabrication issues of microplasma, nano-aperture, and SiO2cantilever probe, the cantilever probe integrated with50μm and100μm inverted pyramidal microplasma device and nano-aperture at the hollow tip is successfully fabricated. The probe can be used for future maskless scanning etching directly. By adjusting the thickness of reserved silicon layer of the cantilever, the deflection can be minimized to less than5μm for a750-μm-length cantilever. SiO2cantilever array with hollow pyramid tip is successfully fabricated with high yield. Microplasma tip array for high throughput and large area maskless scanning etching is also fabricated.(4) The Paschen curves, V-I characteristics and optical emission spectroscopy characteristics of the dc-driven microplasma devices operating in SF6, CHF3reactive gases and their mixtures with Ar at different gas pressure are investigated. The physics and chemical mechanism of microdischarge characteristics are studied, wthich may lay a foundation for upcoming experiments of maskless scanning plasma etching of Si、SiO2and Si3N4, and also have implications to microplasma material processing in reactive gases using other devices configuration.(5) In order to realize maskless scanning microplasma etching experiments, a complicated etching system should be established. In this dissertation, overall design of scanning plasma etching system is performed. The tip-sample distance controlling method and microplasma extracting method are studied. Specially designed vacuum system and tip-sample3D scanning system are fabricated and established, which may lay a foundation for system integration for maskless scanning etching. A novel microplasma parallel nano-etching and AFM in-situ morphology detection method is proposed. We mount the cantilever probe integrated with the100μm microplasma device on a commercial AFM system, and obtain imaging resolution of20nm.The research of this dissertation is expected to make the scanning plasma etching technology from "ideas" into "reality", and may lay a foundation of fabrication diverse micro-nano devices with high resolution, high efficiency and low cost.