Photolithography Essay

651 Words2 Pages

Name: Jai Kant
UFID- 76691873
Date of Experiment: Mar 13th, 2014
Pre Lab Report Sixth week- Photolithography
Problem 1: What is thermionic emission??
Answer: The term thermiionic emission comes from the phenomena of quantumm mechanical tunneling which takes place in some special circumstances. It sometimes happens that electrons with energy less than the barrier height to cross the barrier passing through it instead of over is called tunnneling effect. In semi conductors we can see this in heavily doped material where the current in the forward direction arises due to tunneling of the charged particles with energies close to the Fermi level but not the actual barrier height. This kind of emission due to tunneling is called field emission. Now if we increase the forward bias voltage, the electrons acquire enough energy to tunnel through the thin depletion region. To avoid this kind of tunneling and get a pure current flow we raise the temperature to a certain point such that the electrons get enough energy to cross the barrier and no longer tunnel through it. This temperature generated effect is called pure thermionic emission.

The above figure is a representation of the thermionic emission, where V – applied forward bias, EF is the Fermi level.

Problem 2: What is Schottky Barrier height??
Answer: It is the difference between interfacial conduction band edge (Ec) and the Fermi level (Ef). From the figure below we get a better idea of the barrier height which is given by ΦB(PhiB).

Now the value of the Schottky barrier height is dependent on the contact resistances of the metal and semiconductor under consideration. The idea of a schottky contact is that when metal and semiconductor are brought into contact with eac...

... middle of paper ...

...stead of one gap?
Answer: The advantages of using several gap to measure the transfer or contact resistance using the TLM (transmission line method) are as follows:
1) A cylindrical TLM has been recently developed and it simplifies the fabrication process.
2) It gives a more symmetrical current flow pattern.
3) Using more gaps helps eliminate the edge effects and get a uniform distribution.
Reference:
1) https://elearning2.courses.ufl.edu/access/content/group/UFL-EEE5354L-40146-12014/Week%209%20-%20Presentation%20-%20Photolithographic%20Exposure%20Systems.pdf
2) www.wikipedia.org
3) https://elearning2.courses.ufl.edu/access/content/group/UFL-EEE5354L-40146-12014/Week%209%20-%20Presentation%20-%20Photolithography%20Basics.pdf
4) http://etidweb.tamu.edu/ftp/ENTC250/Lorenzo/Semiconductor%20Po
5) http://www.ece.gatech.edu/research/labs/vc/theory/photolith.html

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