# 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. |  |
|  | 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. |  |

| 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. |  |
|  | 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.

With frame

3.6.1 Summary to: 3. Thin Films

© H. Föll (Semiconductor Technology - Script)