repetition: practical aspects - tu wien · repetition: practical aspects reduction of the cathode...
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Repetition: Practical Aspects
Reduction of the Cathode Dark Space!
VE
x- +
Cathode (Target/Source)
Geometric limit of the extension of a sputterplant. Lowest distancebetween target and substrate
Cathode Fall: Ions will no more be neutralized by electrons. Theyare subjected to a high electricfield and are accelerated towardsthe target.
Anode
x0
d
Repetition: Technical Modifications
a) Reduction of the cathode dark spaceb) Increase of the ion current to increase erosion ratec) Reduction of working gas pressure (purity)d) Extension of the material palette
(Semicunuctors/Insulators)
Aims:
Methods:
RF-sputtering: c/dTriode sputtering: a-cMagnetron sputtering a-cRF-Magnetron: a-dIon beam sputtering: c; free choice of ion energy
Repetition: RF-Sputtering
f = 13,56 MHz (free industry frequency)* Higher electron density* Sputtering of insulators possible* Lower working gas pressure* Different plasma characteristics (EEDF, plasma potential)
Repetition: Magnetron-Sputtering
Permanent magnets below the target concentrate the plasma in the vicinity of the target.* Smaller dark space* Higher ion density* Reduction of working gas pressure
Repetition: Target Erosion
Repetition: Ion Gun
1. Ion source2. Target3. Sputtered species4. Substrate
Advantages of the ion gun:
* Control of ion energy* Control of ion
impingement angle* No working gas,
i. e. UHV-capable
Repetition: Sputter-Cleaning
Sputtering can also be used to clean surfaces, if the substrate, which then acts as "target", is biased with negative high voltage.
+
+
++
Substrat
+ Working gas, ionized or neutral
HV
+ -
Magnetic field assistance (optional)
Ion Plating: Fundamentals I
++
Substrate
+ Ionized filling gas
HV (bis ca. 1kV)
+
+ +
++++ +
Source
+ Source material, ionized or neutral
Optional
ionization system
Ion Plating: Fundamentals II
Separated ion source Ions from gas discharge1. Ion probe2. Substrate holder3. Shutter4. Pumps5. Ion source6. Evaporator
1. Substrate holder2. RF-coil3. RF-generator4. Evaporator5. Pumps6. Gas inlet
Ion Plating: Electron Activated Plasma
1. Substrate2. Ring electrode3. Differentially pumped region4. Electron gun5. Pumps6. Gas inlet
Ion Plating: Hollow Cathode Arc Discharge
1. Substrate holder2. Cooling water3. Hollow cathode discharge
(longitudinal magnetic field)4. Pumps5. Cooled crucible6. Reactive gas7. Electron ray
Ion Plating: Low Voltage Arc Discharge
Ion Plating: Thermionic Arc
Ion Plating: Cluster-Beam
Pulsed Magnetron Techniques
Pulsed Magnetron Sputtering: Ignition of a short term (µs -ms) magnetron discharge with extremly high power density; due to the short duration of the discharge the average power corresponds to that of a conventional magnetron discharge. Disadvantage: only 30% deposition rate when compared to a conventional magnetron.
Modulated Pulse Technique: Igniton of a conventional magnetron discharge; Intentionally introduced voltage peak ignites high power discharge which can be sustained for ms to 0.01 s. Advantage: Average deposition rate is equal or even higher when compared to conventional magnetron.
PVD-Methods: Power Densities
103 - 104Pulsed Magnetron
107Arc-Evaporation
105Low Voltage Arc Discharge
1000Electron gun
100Evaporation
10Sputtering
Power Density [Wcm-2]Method
PVD-Methods: Ionization Degrees
High Power density>50Arc-Evaporation
Average Power densitybis 100Pulsed Magnetron
High Power density50Low Voltage-Arc Discharge
Collisions1-10Sputtering
Therm. excitation<0.1Electron Gun
Therm. excitation<0.1Evaporation
Reason of IonizationIonization Degree [%]Method
Ion Bombardement and Film Growth I
Ion Bombardement leads to•good adhesion•small grains•dense films•high internal stresses
Ion Bombardement and Film Growth II
Bombardement with externally generated ions:EvaporationElectron gunSputteringReason: low ionization degree
Bombardement with ions of the coating material:Low Voltage Arc DischargeArc-DischargeReason: high ionization degree
Ion Bombardement and Film Growth III
1. Manipulation of the energy introduction by substrate bias2. Manipulation of the directionality of the impinging
coating particles (collimation in the case of comlexely shaped bodies, all side coating by particles which impinge permanently parallel to the substrate normal, trench-filling)
Advantages of high ionization degrees (ions of coating material):
Chemical Vapor Deposition (CVD)
Reaction types
1. Chemosynthesis (Reactions with Gases)
2. Pyrolysis (thermal decomposition)
3. Disproportionation
4. Photopolymerization
TiCl4(g) + 1/2N2(g) + 2H2(g) TiN(s) + 4HCl(g)600-1000°C10-900 mbar
SiH4(g) Si(s) + 2H2(g)<650°C
2GeJ2(g) Ge(s) + GeJ4(g)
CVD: Typical Plant Schematic
Pasma Assisted CVD (PACVD)
Reduction of growth temperature
PACVD: Reactor Types
Parallel plate reactor Multi level chamber
Plasma Polymerization: Elementary Processes
1. Reactions in the gas phase: Formation of reactive species as excited and ionized Moleculesand molecule fragments. Formation of free radicals and coagulation to chains and clusters.
2. Species formed in phase 1 are adsorbed at the substrate surface.
3. Polymerization of particles and fragments at the substrate surface.
After monomer introduction the following processes are present within the RF-plasma:
Plasma Polymerization: Reactor Schematic
Monomers:
Hexamethyldisiloxane(HMDSO),C6H18OSi2Tetraethylorthosilikate(TEOS)
Deposited material:mostly SiO2