Exercise 3.6-1

All Class Exercises and Quick Questions to

3. Thin Films

Subchapter 3.1: Thin Films - General
Interference causes the color of a thin film and betrays its thickness? Explain!
Give examples of what "thin" could mean in relation to intrinsic length scales. Provide (and discuss briefly) some intrinsic lengths, in particular with respect to semiconductors
Give a few number for the meaning of "thin":
  • Thickness of a human hair »» ????
  • Thickness of a gate oxide in an integrated transistor »» ????
  • Thickness of antireflection layers of optical lenses »» ????
  • Thickness of a thin film solar cell »» ????
  • Other examples you can come up with ???
Give somer examples of thin film applications outside of semiconductor technology.
Give the equation for the capacity C of a parallel plate capacitor with plate area A for a maximum voltage of 10 V. How can you achieve maximum capacity and what are the limits? Hint: Consider field strength and relvant intrinsic length scales.
     
Subchapter 3.2: Mechanical Properties
How would you define the roughness of the two thin films shown? Give an equation if possible and differentiate between the two cases.
Roughness measurement
Give examples for a thin layer of material B on substrate A for which you would expect good or bad adhesion, respectively: Give reasons for you expectation.    
The "surface" energy of glass is around g(Glas) 300 mJ/m2, for a metal we might have g(Metal) » 2100 mJ/m2. You deposit a noble metal. On which substrate would you expect better adhesion?    
Give an example of how one could measure the adhesion strength of a thin film.    
The red thin layer (thickness dB) on the blue circular Si wafer substrate (thickness dA >>dB) is under compressive stress s; the wafer thus is warped with a radius of curvature = R.
What would R be proportional to?
Hint: It is a two-dimensional problem.		  
Warpage
 
Subchapter 3.3: Nucleation and Growth    
What happens when first incoming atoms hits the surface of the substrate? Give at least 4 different possibilities.    
Where would you expect the first imcoming atoms to be solidly bound? Use the proper terminology.    
Define "sticking coefficient". Discuss the dependenc of the sticking coefficient for a given system on the precise substrate condition for a given substrate.    
Explain briefly the major methods for investigations of the nucleation of thin films on substrates.    
Wetting angle
Explain how you get from interface energies to forces, and from forces to the wetting angle Q  
Discuss and name the two major growth mode following from extreme values of Q  
Discuss and name a third major growth mode  
     
Subchapter 3.4: Structure, Interface and Some Properties
What is epitaxial growth? Consider the possibility of epitaxial growth; giving possible conditions (e.g. with respect to structures, lattice constants, ...) and use simple pictures:
  • A on A.
  • A (fcc) on B (fcc).
  • A (fcc) on C (hex).
  • A (fcc) on B (fcc) with intermediate layer.
  • ....
B (fcc; (100)) with lattice constant aA is deposited on A (fcc; (100) with aB = 0.95 aA. Sketch the structure for
  • Thickness of B only a few atomic layers.
  • Thickness of B > 50 nm
Difficult! Sketch a pure edge misfit dislocation network on a {100} interface plane for a misfit of 10 % for the case of
  • Burgers vector of the dislocations is b = a<100>.
  • Burgers vector of the dislocations is b = a/2<110>.
Difficult! What would happen if the (square) network of misfit dislocations on a {100} type interface would be changed from edge dislocations to screw dislocations?
What are the energetic reasons for introducing misfit dislocations into epitaxial interface it the layer thickness is larger than a critical thickness? What determines the critical thickness?
Sketch the curve for the critical thickness dcrit in a dcrit - misfit diagram, Try to give approximate numbers.
Enumerate and discuss structures obtainable with thin films but not (easily) with bulk materials. Give examples for applications.
Give reasons why thin film properties can be quite different from bulk properties; give examples.
Name some technologically extremely important special thin film properties; discuss with actual numbers.
     

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© H. Föll (Semiconductor Technology - Script)