Characterization

Question 1

Scanning Electron Microscopy (SEM)

Answer 1

Uses E-beam rather than light to image a sample.
- Can also determine material properties

Question 2

What information can SEM give you about a sample?

Answer 2

1) Topography - texture and surface features of an object
2) Morphology - shape and size of crystal grains making up the sample
3) Composition - elements and compounds that the object is composed of
4) Crystallographic Info - diffraction patterns of the backscattered e- allow you to determine the crystallographic structure

Question 3

What are backscattered electrons and what can they be used for?

Answer 3

• High energy e- from the source that are reflected back up from the sample through elastic collisions with the specimen atoms.
• Can be used to determine: crystallographic structure, and chemical composition

Question 4

What are secondary electrons and what can they be used for?

Answer 4

• Lower energy e- that are emitted from the specimen, after inelastic collisions
• Can be used to produces images with sharp edges and 3D appearance

Question 5

What is the process for creating an image with SEM?

Answer 5

• Secondary e– are collected by an SE detector with a low bias voltage. The collector is on an angle which creates shadowing behind features
• Increasing the SE detector voltage will wash out the shadows and lower the contrast by collecting e- from behind the features

Question 6

How do secondary electrons enhance edge contrast?

Answer 6

More of the interaction volume is close to the surface on edges, which means more emitted e-

Question 7

What is a Focused Ion Beam?

Answer 7

Similar to SEM, but uses + ions.
- Can be used to deposit or cut (splutter or mill) materials
- Used for preparation of TEM samples
- Can create nanopatterns
- Can be used for integrated circuit “surgery”

Question 8

Xray / auger

Answer 8

When a core e- is displaced in a collision, an e- from another shell will fall into its place releasing energy as x-rays, or another ejection e- (auger).

-This can be determined from graphical plots, and is base don atomic number and yield per shell vacancy

Question 9

Energy Dispersive Xray spectroscopy

Answer 9

• Some e- collisions will cause the sample to emit xrays
• energy levels of the xrays are dependent on which atoms are present - the emitted spectrum is related to the chemical composition of the material

Question 10

Auger spectroscopy

Answer 10

Looks at a particular category of secondary e- which give info about chemical composition and bonding.
- Only looks at the top few nanometers of the material

Question 11

Transmission e- microscopy

Answer 11

• Must use thin samples.
• can provide atomic resolution
• crystalline substances show a pattern, amorphous substances will look like a glow

Question 12

Atomic Forces Microscopy

Answer 12

• Uses a cantilever with a very sharp tip to query the surface under test. Bending of the cantilever is read out via optical detection.

Question 13

AFM contact mode

Answer 13

• contact mode: drag stylus across surface

Question 14

AFM no contact mode

Answer 14

• no contact mode: tip is oscillated above surface
• surface forces cause changes to the oscillation height
• feedback maintains constant oscillation height

Question 15

AFM tapping mode

Answer 15

tip is oscillated with large amplitude and allowed to contact the sample
- feedback is used to maintain a constant oscillation height

Question 16

Magnetic Force Microscopy

Answer 16

Essentially the same as AFM but with a magnetic tip so that the tip can interact with the magnetic domains of the sample
- this is how hard drives work

Question 17

Scanning Tunneling Microscope

Answer 17

Monitors the tunneling current between a sharp tip and a conductive sample and uses that to maintain a known distance.
- The tip is then scanned using piezoelectric actuators
- Can even be used to do single atom manipulation

Question 18

Stylus profilometer

Answer 18

Drags a sharp tipped (>100nm) stylus across the device surface and measure height change of the tip.
- Good for measuring step heights and topology of large areas

Question 19

White Light Interferometer

Answer 19

Uses interference between light reflected from the sample and a reference to create a surface profile
- Using white light allows easier measurements when step heights are greater than wavelength / 4
* cant tell the difference between bottom or top of waveform unless more than one wavelength is selected

Question 20

Confocal laser scanning microscope

Answer 20

• Only the reflected from the surface that is in the plane if focus is returned
• Raster scanning allows for 3D reconstructed images of devices