repetition: practical aspects - tu wien · repetition: practical aspects reduction of the cathode...

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