This task consists of the following sub-tasks:

• Choose an appropriate environment for fabricating experimental devices at low cost and explain why.
• Indicate the substrate materials used for fabricating III-V components and explain why these are preferred instead of Si wafers.
• Choose the orientation and material type most used for microelectronics devices, give the Miller indices and draw a 3-inch wafer with these properties.
• Show how the wafer cleaning takes place.

You have to deposit four layers on top of each other.

• The first layer is an n-type, highly doped Si crystalline film. Choose the appropriate method, the suitable temperature and the dopant used. Show the main chemical reactions and the main steps of the process. Calculate the segregation factor. What kind of substrate should be used to avoid stress and defects? Explain why.
• The second layer is the natural oxide of the first layer. How do you fabricate 25 nm of thin layer with excellent properties? Explain your choice. What kind of temperature and gases are required? Explain how the thickness will vary in time for this situation.
• The third layer is a metal. Choose a deposition method with high deposition rate and good uniformity. Explain why is this method better than the others in obtaining the desired properties. Compare the chosen method with evaporation, by calculating the film thickness variation over a 10-inch wafer if the evaporation source is at 20-inch distance from the layer. Give other differences between the chosen method and evaporation. Explain how a high deposition rate is obtained. If a structure needs to be planarised, give three completely different metal deposition methods that can be used for this purpose. Show how it is done in each case.
• The last layer is a dielectric deposited on top of the metal. Indicate what type of deposition may be used in this case. Explain how a plasma is created and the reactions take place. Choose the method that can deliver the best layers in terms of step coverage and explain what happens in this case in the reactor. What is the rate limiting step for this method, considering that high flows are used? Explain why. What is the problem in obtaining good step coverage layers with this method? How can this be controlled?

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?

The task is to make MOS capacitors with square shape. The silicon wafer is oxidized and aluminium was deposited on top by PVD. You need to pattern the aluminium into squares of 1 μm x 1 μm. Make a plan of 10 steps for this task. Put them in order and indicate the processing details you need to write down: baking time, exposure time, developing time, etc. Consider also the following:

1. Choose the lithography and material type suitable for mask fabrication
2. Considering the fact that the mask will be used for a large number of times and the resolution is quite high, which type of lithography is suitable for patterning the aluminium squares, and how large should the gap mask-wafer be? Explain. Indicate also what are the resolution and DOF with this type of lithography?

Continuing the task of making the MOS capacitors (1 μm x 1 μm), 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 instead of aluminium?

Write the process flow (the main process steps) of a device. You can select one from the four devices shown in the tutorials at this task. The order of the steps is important, also give as much as possible the parameters for each process step. Example: which type of deposition should be used or which type of etchant, etc. In order to do this use also the first five tasks.