Most of the etching process involves one or more chemical reaction steps, and various types of reactions are possible, but the common reaction is to first oxidize the surface of the layer to be etched, and then dissolve the oxide layer. With the solution discharged, this is repeated to achieve the effect of etching. For example, when etching silicon and aluminum, this kind of chemical reaction is used.

It can usually be controlled by changing the concentration and temperature of the solution. The concentration of the solution can change the rate at which the reactants reach and leave the surface of the object to be etched. Generally speaking, when the concentration of the solution increases, the etching rate will increase. Increasing the temperature of the solution can accelerate the chemical reaction rate, which in turn accelerates the etching rate.

In addition to the selection of the solution, it is also very important to select a suitable shielding substance. It must have good adhesion to the surface of the material to be etched, and be able to withstand the erosion of the etching solution and be stable without deterioration. The photoresist is usually a good shielding material, and because of its simple pattern transfer step, it is often used. However, when using photoresist as a shielding material, edge peeling or cracking may also occur. Edge peeling is caused by the erosion of the etching solution, resulting in poor adhesion between the photoresist and the substrate. The solution is to use an adhesion promoter to increase the adhesion between the photoresist and the substrate, such as Hexamethyl-disilazane (HMDS). Cracking is because the stress difference between the photoresist and the substrate is too large. The method to slow down the cracking can use a more flexible shielding material to absorb the stress difference between the two.