Name:________________________ PHGN/CHEN/MLGN435/535 Pre-lab #10

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Name:________________________
PHGN/CHEN/MLGN435/535 Pre-lab #10
Due Tuesday, March 29, 2016 at the beginning of class
Topic: Physical Deposition: Evaporation and Sputtering
Reading: Campbell chapter 12
This will give you some background on metallization techniques used in the industry.
1. Assume you have a vacuum system with a pressure of 5x10-5 torr and that this is
primarily water vapor (that was trapped on the walls of the chamber). Calculate the
approximate number of monolayers of water that will form on a sample surface each
second that it is in this chamber. Eq. 12.2 might help. Assume the system is at room
temperature, that the atomic spacing between water molecules on the surface is about
four angstroms, and that the sticking coefficient is one. This will tell you how fast you
need to evaporate a metal (monolayers per second) to avoid having too many impurities
trapped in the film. (show your work)
2. It is desirable to deposit a mixture of Ga and Al using a single source evaporator. If
the deposition temperature is 1000C, the mixture in the crucible is initially 50% molar,
and both components have a sticking coefficient of one, what would the starting
deposited film composition be (approximately)? How will this change with time
(qualitatively)? Think about using expression 12.2 for flux as a function of temperature
and atomic mass where the pressure of each species is its partial pressure given in Fig.
12.2.
3. Step coverage is a key issue in metallization.
a) In your own words explain why step coverage is so important. A simple sketch might
help.
b) Which gives better step coverage, sputtering or thermal evaporation?
c) Step coverage can be improved in a sputtered film by applying an RF bias to the
substrate. Why does this help?
d) Will step coverage be an issue in your MOSFET design?
4. If I wanted to deposit Ag, could I thermally evaporate it? If the answer is yes, what
approximate temperature would be good to use with Ag. Now answer the same two
questions for Mo. In both cases, be sure to explain your answers. Fig. 12.2 will be
helpful.
5. The melting point of Cu is 1083C (1356 K). Using figure 12.21, if Cu is deposited by
sputter deposition at a temperature of 270C and at a chamber pressure of 1 Pa, what
morphology (grain size or shape, reflectivity of the film etc.) might we expect the film to
have?
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