Etch stop , Study notes of Mechanical Engineering

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Electrochemical Etch-Stop

By Harry Chiu & Zachary Fjeldheim

What is an Etch-Stop? `

Etch-stop is defined as atechnique that allowstermination of the etchingprocess at a controllabledepth ` Selectivity: S = δ

δ s

Timing Method: V-Groove `

Method to control depthof etch ` At the precise momentthe V-groove develops,the membrane hasreached the correctthickness

Timing Method `

Advantages Simplest of all etch-stops Cheap Disadvantages Low Accuracy ` Not very reliable

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 etchrate modulation ` Electrodless

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

Typical Applications `

Thin membranes Pressure Sensors Actuators ` Micro-needles used by neurophysiologist as aminimally invasive tool to monitor neural signals

Questions