Thin Film Deposition Flashcards
How many types of thin film deposition methods do you know?
Physical, Chemical, Mixed
Which are the main stages of a thin film deposition process?
Material flux formation
Material transport
Processes on the surface of the substrate
Please explain the principle of the thermal and e-beam evaporation process
Thermal - source is heated to form plasma (metals)
E-beam - heat produced from high energy e and uses magnetic field to control ions produced
How can we estimate: the amount of material required to deposit a film with a set thickness using thermal/e-beam evaporation? The uniformity of an evaporated film?
Thickness - sputtering rate
Uniformity - depends on mass and area
What should we do to have uniform film thickness during a thermal evaporation process?
r>w(2/q)^0.5
List the main components (incl. vacuum pumps gauges etc) of a deposition system for thermal/e-beam evaporation
thermal - tungsten wire source, vacuum chamber
e-beam -
What is the difference between DC, RF, reactive and magnetron sputtering systems/processes?
plasma
Please explain briefly the principle of flux formation during DC, RF and magnetron sputtering processes
DC - only metals
RF - can use for dielectrics
Magnetron - magnet used to control path of ions, high deposition rate
Please discuss the conditions for self-sustained discharge and Pashcen’s Law
self-sustained discharge/Paschen’s law - V_D=a(p × L)/(ln(p × L)+b)
for a cathode-anode space L and Ar pressure p, p x L >0.5
if L is less than the dark space length - ionisation, few excitations, cannot sustain discharge
If p is too low - large electron mean-free path, 2nd electrons reach anode before colliding with Ar atoms, cannot sustain discharge either
How can we integrate the atom transport process?
sputter yield depends on - target material (binding energy, mass), sputtering gas (mass, energy), geometry
Please discuss the reactive sputtering process and the ways for the improvement of its instability and difficulty to control
During reactive sputter deposition of oxides the formation of oxide, non conducting films is a problem
-> use feedback loop, dual cathodes, gas pulsing, oscillating deposition, increased pumping speed
How do films grow? What does this process depend on?
Layer by layer - frank-van de merwe
Island growth - volmer-weber
Mixed - stranski-krastanov
Kinetic processes determined by - energy of particles, oxidation states, number of addition atoms per unit area or supersaturation
Which are the components of a PLD system?
Excimer laser, mirror, lens, vacuum, gas inlet
What is the principle of laser ablation?
Laser superheats subsurface layer before surface reaches evaporation point, surface breaks apart into large (micron-sized) globule particles when the surface expands
Laser puls
Relaxation of energy
Plasma production
What is the applicability of PLD?
Almost any oxide material, good stoichometry transfer, plume at high energy, fast and directional plume, laser outside chamber, can be done at high pressures
Compare the physical deposition methods you know using the following properties: o Applicability o Deposition rate o Price o Thin film quality
Evaporation
PLD
How do films grow?
Layer-by-layer - full monolayer growth involves nucleation and growth of islands that are only on monolayer thick and grow to essential complete coalescence before significant clusters are developed on the next film layer
Island growth - forms 3D islands, film atoms more strongly bonded to each other than the substrate
Mixed - full monolayer growth may change to 3D island growth after 1-5 monolayers due to a change in the energy situation with successive monolayers
What does affect the equilibrium growth modes?
Surface/interface free energy
Lattice mismatch
supersaturation
Briefly outline some of the metastable growth modes
Diffusion-limited - incoming atoms stick where they land and the film growth is dependent on the interface
Downward funnelling - impinging atoms maintain a component of vertical momentum and tend to fill in the lower areas of the interface
Briefly discuss the thin film growth dynamic for different deposition methods
Evaporation -
PLD -
Sputter -
Briefly discuss the factors affecting film morphology during sputter deposition method
Irradiation Kinetic energy of charged carriers Energy of neutrals Exothermic Recombination External heating
Briefly discuss the zone model for thin film growth during sputter deposition method
Film morphology as a function of substrate temperature and incident ion energy, once reach wafer surface atoms diffuse along surface until they form nuclei, nuclei capture more atoms, forming islands, if surface mobility is high islands may merge forming a smooth continuous film Zone 1 - porous/amorphouse Zone T - small grain polycrystalline Zone 2 - large columnar grains Zone 3 - large non-columnar grains
