Three-dimensional Microfabrication On GaAs By Using Regular Patterns Molds By The Confined Etchant Layer Technique

Micro- and Nanometer science and technology, which will lead to a great breakthrough in understanding and transforming the world is considered to be a key Hi-tech in 21st century. The micro system or microelectromechanical systems (MEMS), as an interdisciplinary field, will be a core of micro- and nanometer science and technology. In order to exert the potential of MIEMS, a new micromachining method that is capable of generating complex and high performance microstructures must be further developed. The method that is suitable for microfabrication should meet the following three requirements: (1) capable of replication of real complex ultramicro-patters and units; (2) capable of mass product; (3) producing units in the micro/nano-meter scale. The Confined Etchant Layer Technique (CELT) as a new approach of electrochemical three-dimensional micromachining was proposed by Prof Zhao-Wu Tian in 1992.This method is distance sensitive and controls the quantity of survival (in comparison with the current micromachining techniques, which control the quantity of removal), which makes the replication of ultramicro three dimensional patterns possible. In the recent ten years, the further analysis on the CELT theory was done and microfabrication experiments were performed with simple micro-disk electrode and spherical platinum electrode, the results show the method is feasible in fabricating three-dimensional micro-pattern. However, in previous study, the selection of the micro-pattern was arbitrary. Three-dimensional microfabrication using regular pattern mold will outstand the advantage of CELT. The results of present work are described as followed 1. Preparation of electrochemical molds Molds with regular microstructures were fabricated by bulk silicon etching technique on silicon wafers. As the electrochemical mold must have excellent conductance, a Cr or Ti film with thickness of several nanometers was sputtered as adhesion layer before a Pt film with thickness of several hundreds nanometer was deposited on the mold surface .The conductive connector between the mold surface and the lead was also a sputtered Pt film along the side of the silicon after the mold was fixed at the tip of a metal stick. In order to test the lifetime of the electrochemical mold, the etching process was performed using it as the working electrode at different constant currents. It was found that the electrochemical mold could be used for more than 20 times when the current density i is lower than 1.0 X 102k1 cm2 ; However, when the current density was much higher than 1.0 X 10 A/ cm , the sputtered Pt film would be fallen off only after 1-2 experiments 2. Fabrication of GaAs with regular patterns molds Two etched patterns resembled each other were obtained with the same gear-like mold. The etched pattern has nine slots and eight protruding lines, compared with the mold, it is almost the negative copy of the mold. The etched microhole arrays were obtained on a GaAs surface. The depth of the holes varies from 1.61?m to 1.81?m. The distance between the bottom point of the two nearest holes is 14.9 t~?m which is in agreement with that of 15.4 ii m between the highest point of two adjacent pyramids. The precision of the etching in this experiment was ca. I ii in. The reason for the transformation of the shape from pyramid for mold to cone for the workpiece was discussed. 3 .Polisbing surface of semiconductors with CELT...