Advantages Of Al2o3, Koh Wet Etching Process

Wet etching is defined as a process that needs liquid chemicals (also known as etchants) to remove materials from the wafer

. The removal of such material is done based on the pattern defined by photoresist masks on the wafer. In the process, the uncovered parts are etched away by the chemicals used while the covered portion remains intact.

There are a number of types of liquid chemical used in the wet etching process and the two popular are the Al2O3 (aluminum oxide) and KOH (potassium hydroxide). These two are preferred many businesses in the wafer fabrication industry because both have a number of advantages, which include the following:

- It is a lot cheaper especially if compared to dry etching process

- It causes no or very minimal damage to the materials being treated because of its pure chemical nature

- It has a high selectivity over the substrate and other materials in the gate stack

- It covers a wide range of materials that can be etched

The wet etching process

Basically, wet etching process can be broken down in to three steps and these are the following:

1. The diffusion of the etchant to the surface for removal

2. The reaction between the etchant and the material being removed

3. The diffusion of the reaction byproducts from the reacted surface

And the process requirements involve

- Movement of etchant species toward the wafer surface

- Reaction at the surface

- Movement of reactant products away from the surface

The KOH wet etching process

The KOH wet etching process is used for etching of Silicon and it is done in a constant temperature bath using clean quartz glassware. Below are the processes:

1. Constant temperature bath - with constant temperature, fill the bath with water and leave some extra space unfilled (perhaps an inch or so at the top of a large beaker) so that when the solution is placed in, it does not overflow.

2. The use of prescribed labware - the following are used: large glass beaker (with water placed onto the surface of a hotplate at the preset temperature); smaller quartz beaker (used for KOH solution); and a watch glass (used on top of the solution beaker to collect condensate and prevent spilling of the solution).

3. Mixing of KOH solution and pouring - KOH solution is mixed and the beaker is placed into the bath; desired volume of solution is poured into the smaller beaker; KOH crystal is diluted as per desired concentration (usual concentration applied in the lab is 30%).

4. Etching the substrate - the execution of the actual etching of the substrate or wafer.

by: Solisa Maestri

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