Investigation Of Electro Chemical Deep Etching Technology For Micro-nano-Electro-Mechanical System Device Fabrication

Micro-Electro-Mechanical Systems (MEMS) is a technology based on semiconductor fabrication techniques and integrated a series of other technologies in electronics, mechanics, material science, testing, physics, chemic and biology. And for its advantage on the size and high integration density, MEMS exhibits numerous possible applications on automobile, electronics, electric appliances, mechanical and electrical products, military field etc.Etching of deep trenches or vias in silicon is an important step to fabricate several MEMS devices such as accelerometers, gyroscopes , through wafer interconnections and radio-frequency (RF) application. Photo-assisted electrochemical etching (PAECE) is a newly developed technology for deep wet etching of silicon. Compared to the costly dry etching methods, such as deep reactive ion etching, PAECE has the advantage of high aspect ratio achievement by employing simple and low cost equipment. Therefore, this method has been explored widely for the fabrication of silicon photonic crystal, micromachined devices and through wafer interconnection for 3D integration.Chapter I introduced the basic conceptions, fabrication technologies and the new developments of MEMS have been at the first part. And then the properties, basic theories and developing process of electrochemical deep etching technique have been introduced through comparing it with other silicon material etching technologies. The main diploma work was briefly introduced.In Chapter II, the mechanism of electrochemical deep etching process was investigated. Then the process and systems for electrochemical etching was introduced. A computer control system was developed for the control of the etching process.. The software environment is Labview. This system can be also used for the automatic control of the electro plating and aluminum anodizing process and the DC characteristic measurement of some semiconductor transistor.The influence of technological parameters to the electrochemical etching process in silicon is studied in Chapter III. Where, the concentration of the solutions, bias voltage, illumination, process temperature and magnetic field have been explored to the pore diameter, etching rate, surface morphology and final reachable depth.Chapter IV investigated the effects dominate the electrochemical deep etching process. These effects including boundary effects, electrochemical polishing, current distribution effect and the residual stress in low stress silicon nitride determine the formation of the structure. So these factors must be carefully considered during mask design and etching condition selection.In Chapter V, two different MEMS structures, which include a deep trench array exhibiting typical photonic crystal properties with its photonic band gap near 6 urn and cross finger structure, are fabricated to demonstrate its practicality.The last chapter, Chapter VI, is the summarizing of this paper and the expected applications of the electrochemical deep etching technology in the future.