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Physical Vapour Deposition of Thin Film
Coatings Part III Thin film growth. Reactive
sputtering.
WITOLD GULBINSKI
Ljubljana, May 25 - June 1, 2008
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• Outline
• Basics of ion interaction with solid surfaces
  sputtering (energy and momentum transfer,
  sputtering yield)
• Thin film growth models
• Structural zone models of thin film growth
• Reactive sputtering
• - process instability,
• - target poisoning,
• - stability conditions,
• - process control methods (OES, QMS)

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Interaction of ions with the surface of solids
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Sputtering yield atom/ion
Ei ion energy Es surface binding energy of
target material a constant dependent on
sputtering geometry
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S atom/ion
Sputtering yield vs working pressure
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Thin film growth - island growth model 1. Island
growth (Volmer - Weber) - three dimensional
ISLANDS are formed WHY - film atoms more
strongly bound to each other than to substrate -
and/or slow diffusion                          
                                                  
        2. Layer by layer growth (Frank - van
der Merwe) - generally highest crystalline
quality WHY - film atoms more strongly bound
to substrate than to each other - and/or fast
diffusion                                         
         
http//www.uccs.edu/tchriste/courses/PHYS549/549l
ectures/film2.html
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Thin film growth - island growth model 3. Mixed
growth (Stranski - Krastanov) - initially layer
by layer - then three dimensional islands are
formed
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• Film grain size dependence on deposition
  conditions
• Grain size typically increases with
• increasing film thickness,
• increasing substrate temperature,
• increasing post-annealing temperature,
• - decreaseing deposition rate

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Structural zone model of thin film growth
(Movchan - Demischin 1969)
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Structural zone model of thin film growth
(Thornton 1974)
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Structural zone models of thin film growth
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Structural zone model of thin film growth
(Messier 1984)
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REACTIVE SPUTTERING Deposition of compound
coatings (oxides, nitrides, carbides) being a
product of chemical reaction between target
material and reactive gas
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• REACTIVE SPUTTERING
• The energy carried by plasma species is high
  enough to activate chemical reaction resulting in
  synthesis of nitrides, carbides, oxides and other
  compounds.
• This reaction occurs at the target surface, at
  substrates and all other surfaces as substrate
  holder or chamber walls, exposed to the reactive
  gas and the stream of sputtered target atoms.
• Properties of reaction product usually strongly
  differ from those of the target material.
• From the point of view of sputtering process,
  compound properties playing the most important
  role are
• enthalpy of formation,
• electrical conductivity,
• sputtering yield,
• secondary electron emission coefficient

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Illustration of the reactive gas flux during
reactive sputtering. Reactive gas is either
gettered at the target (Qt) or substrate (Qs)
metal surfaces or pumped out
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SltS1ltS2
Typical curve shape of the partial pressure vs
mass flow of reactive gas for reactive sputtering
process for three different pumping speeds S of
vacuum system (a) the same curves transformed to
Q vs pr coordinates to make Q a single-valued
function of pr. (b).
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Increase pumping speed? System cost limitation!
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• How to control reactive sputtering process?
• Reactive gas partial pressure control is
  necessary.
• How to do that?
• optical emission spectroscopy (OES) of process
  plasma,
• mass spectrometry (QMS) of process atmosphere

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Actinometric approach
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Slope 2
Emission from TiI (neutral) at 375.3 and 377.1nm
as a function of magnetron discharge current for
a Ti cathode in Ar at 12 mTorr (plotted
logarithmicaly).
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Metallic mode
Transition mode
Reactive mode
Target surface
Dependence of atomic line intensity TiI on
nitrogen partial pressure during titanium
magnetron sputtering in Ar/N2 atmosphere.
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Optical emission spectroscopy (OES) based,
reactive sputtering control system
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TiI optical signal
Leak valve driving signal
OES 100 Controller output signal (sputtering of
Ti in Ar/N2 atmosphere) single channel mode
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OES 100 Controller output signal (sputtering of
Ti in Ar/N2 atmosphere) double channel mode
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Advantages of OES based, reactive sputtering
control system

• driving signal originates from the region where
  reaction is currently taking place
• an information is obtained in real time without
  disturbing the discharge

Drawbacks of OES based, reactive sputtering
control system

• OES signal is sensitive to the sampling position
• Moving elements of the system reflect the light
  and disturb optical signal
• OES signal changes with target erosion

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Quadrupole mass spectrometer (QMS) based,
reactive sputtering control system
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Quadrupole mass spectrometer (QMS) based,
reactive sputtering control
Qr
Plotter output dependence of the equilibrium
nitrogen mass flow rate on the nitrogen partial
pressure.
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Advantages of QMS based, reactive sputtering
control system

• High selectivity of the method

Drawbacks of QMS based, reactive sputtering
control system

• QMS signal disturbed by process ions,
• High QMS response time
• High price of QMS analyzers

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To be continuedas your own adventure with thin
films deposition
THANK YOU!
Witold GulbinskiInstitute of Mechatronics,
Nanotechnology and Vacuum TechniqueKoszalin
University of Technology75-620 Koszalin,
Polandphone 48 94 34 78 227fax [phone]
489e-mail Witold.Gulbinski_at_tu.koszalin.pl www.im
nitp.tu.koszalin.pl