Electrochemical Etch Stop By Harry Chiu Zachary Fjeldheim What is an Etch Stop Etch stop is defined as a technique that allows termination of the etching process at a controllable depth Selectivity S 1 s Etch Stop Techniques Timing Method Boron Etch Stop Electrochemical Etch Stop Timing Method V Groove Method to control depth of etch At the precise moment the V groove develops the membrane has reached the correct thickness Timing Method Advantages Simplest of all etch stops Cheap Disadvantages Low Accuracy Not very reliable Boron Etch Stop Heavily B doped silicon has a very low etch rate Membranes can be created by doping the top of the wafer etching from the back Boron Etch Stop Advantages Relatively simple process High selectivity and reliability Disadvantages Microstructures subjected to high tensile stress Not compatible with CMOS process Introduction P n junction Electrochemical etch rate modulation Electrodless P n junction Reverse biased Anisotropic etch High selectivity Passivation potential TMAH KOH Three electrode vs four electrode system Electrochemical etch rate modulation Open circuit potential Passivation potential SiO2 etch stop Anodic current flow KOH TMAH Electrodless Au Cr n Si TMAH Gold chrome layer Anodic oxide Temperature Electrochemical Etch Stop Advantages Doesn t require as high doping level as boron Better thickness control Less stress on wafer Batch fabrication Electrodless Disadvantages Requires cumbersome fixtures to insulate electrical wiring from etchant Typical Applications Thin membranes Pressure Sensors Actuators Micro needles used by neurophysiologist as a minimally invasive tool to monitor neural signals Questions
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