Continuing the task of making the MOS capacitors (1 μm x 1 μm) from the lithography, you have now to choose the suitable etching method. Explain which type of etching (wet, plasma assisted, CMP, lift-off, directional, anisotropic, isotropic, chemical, physical, etc.) is preferable and why. Show all the arguments in favour for the chosen method and indicate why you didn't choose the others.
If in place of aluminium you need to etch Si3N4 on a Si wafer, describe two possible process flows, one dry and one wet, giving the etching time, gases, concentration, etc.
What if the material is copper intead of aluminium?
After fabricating a material and patterning it, sometimes the properties of the material need to be modified in a particular region, in order to fabricate devices, such as transistors. For example the conductivity of the material can be changed by doping it. A few techniques used to modify the properties of the already deposited films are shown:
- ion implantation and diffusion
- are used to introduce dopant atoms in the layers, changing the electrical properties.
- annealing
- can create bonds between the atoms inside the material, improving the film properties or connecting the dopant atoms with the lattice atoms
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Substrate preparation
