Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 4M

• It is a process, where the wafer is immersed into highly concentrated pool of acid and attack the film and not the resist.
• It involves multiple chemical reaction between liquid etchant and material i.e to be removed.
• It is generally isotropic inspect of the mark as the liquid etchant can penetrate underneath the mask.
• It is not possible to achieve small critical geometry with this etching.
• Wet chemical etching of any material can be considered as the sequence of 3 steps:-
  • Transport of the reactant to the surface
  • Reaction at the surface
  • Movement of reaction products into etchant solutions.
• Each of these can serve as a rate limitor and dominate the overall processes.
• An etch process which is limited by rate of surface reaction will tend to enhance surface roughness and promote fetching.
• On the other hand, etching can limited by rate of diffusion of etchant through a layer which covers the surface.
• The result into a polished edge.
• A no. of chemical reagents and their mixture are used for etching purpose.
• Many of this are available in transistor grade which are preferred in order to minimize the contamination of the semiconductor during the processes.
• The table below shows the wet etchants which are required to etch the material given in the table.