Deposition of Coatings by PECVD

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Deposition of Coatings by PECVD

• Jung-Hyun Park
• EE7730
• Department of Electrical Engineering
• Auburn University
• Fall 2003

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Review of CVD

• Film deposition by initiating a chemical reaction
  inside a chamber filled with reagents vaporized
  in an inert carrier gas
• Energy supplied by the surroundings causes the
  diffused reagents to react thus forming the
  desired material film across the target surface

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Growing Steps of CVD

• Gas phase Diffusion
• Gas phase Reaction
• Absorption
• Surface Reaction
• Surface Diffusion
• Incorporation into the crystal lattice
• Desorption
• Gas phase Diffusion

Reactant gases
Exhaust gases
(a)
(h)
(b)
(g)
(c)
(f)
(d)
(e)
Surfase
http//www.postech.ac.kr/mse/tfxs/lecture_2000_1/
chapter4.ppt http//cape.uwaterloo.ca/che100projec
ts/vapourdep/sld001.htm
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CVD Process Types

• APCVD (simply CVD, atmospheric pressure CVD)
  elevated temperature but at near atmospheric
  pressures (105 Pa)
• LPCVD (low pressure CVD) utilizes vacuum (lt
  10 Pa) to increase deposition rate and uniformity
• PECVD (plasma enhanced CVD) enhancing the
  reactions and permitting very low deposition
  temperatures

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Question

• What are the advantages/disadvantages of PECVD
  compared to other types of CVD process ?

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APCVD Reactor

• Advantages
• High throughput
• Good uniformity
• Handle large wafers
• Disadvantages
• Fast gas flows
• Needs frequent cleaning

http//www.timedomaincvd.com/CVD_Fundamentals/Fund
amentals_of_CVD.html
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LPCVD Reactor

• Advantages
• Excellent uniformity
• Large load size
• Hold large wafers
• Disadvantages
• Low deposition rates
• Toxic, corrosive or flammable gases

http//www.timedomaincvd.com/CVD_Fundamentals/Fund
amentals_of_CVD.html
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PECVD Reactor

• 50 kHz 13.56 MHz power source
• Vacuum 0.15 torr
• Advantages
• Low deposition temperature
• Low power source
• Disadvantages
• Limited capacity
• Individual wafer loading
• Easily contaminated

http//www.timedomaincvd.com/CVD_Fundamentals/Fund
amentals_of_CVD.html
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Why PECVD? (1)

• encourage deposition at much lower
  temperatures and pressures than would be required
  for thermal CVD.

TEOS tetraethyl orthosilicate, Si(OC2H5)4
http//www.batnet.com/enigmatics/semiconductor_pro
cessing/CVD_Fundamentals/plasmas/plasma_deposition
.html
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Why PECVD? (2)

• The second reason to use plasma deposition is
  that surfaces exposed to a plasma are subject to
  bombardment by energetic ions, whose kinetic
  energy can vary from a few eV to 100's of
  electron volts.
• Ion bombardment of this nature has very
  significant effects on the properties of the
  deposited film. Increasing ion bombardment tends
  to make films denser and cause the film stress to
  become more compressive
• However, excessive compressive stress can also
  lead to impaired reliability. The ability to
  adjust stress, through changes in process
  conditions, chamber geometry, or excitation

http//www.timedomaincvd.com/CVD_Fundamentals/plas
mas/plasma_deposition.html
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Why PECVD? (3)

• A final important benefit of plasma deposition is
  the ability to easily clean the reactor. For
  example, by introducing a fluorine-containing gas
  (e.g. CF4) and igniting a plasma, one can clean
  silicon, silicon nitride, or silicon dioxide from
  the electrodes and chamber walls.
• Chamber cleaning is of great practical
  importance thick films built up on the parts of
  a chamber may create particles which can fall
  onto the substrates and cause defects in circuit
  patterns in semiconductor

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Disadvantages of PECVD

• Limited capacity PECVD systems
  require wafers to lie flat on the bottom wafer.
  Only one wafer side can be coated at a time
  unlike LPCVD (wafers loaded vertically). PECVD
  can coat 14 wafers at one time whereas LPCVD can
  coat up to 25 wafers

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Deposition of Organic Film

• Plasma Polymerization

Deposition of Inorganic Film

• Amorphous Hydrogenated Silicon (a-SiH)
• Silicon Dioxide (SiO2)
• Silicon Nitride (SiN)
• Silicon Carbide (SiC)
• Poly Silicon (poly-Si)
• Diamond Like Carbon (DLC)

Alfred Grill, Cold Plasma in Materials
Fabrication, IEEE press
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Plasma Polymerization

• Atomic process
• Polymers are most case highly branched and highly
  cross-linked
• Strongly system-dependent process
• Controlled under parameters pressure, plasma,
  gas flow and applied electrical output

http//www.eurobonding.org/Englisch/Oberflaechen/P
lasma_polymerization.htm
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Plasma Polymerization

• characteristics - excellent coating adhesion on
  almost all substrates
• - chemical, mechanical and thermal
  stability
• - high chemical barrier effect
• Applications - scratch resistant coatings
• - corrosion protection
• - anti-bonding, anti-soiling coatings
• - barrier layers

http//www.vergason.com/pdfDocs/VTI20papers,20Pl
asma20Polymerization,20Theo.20Prac..pdf
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Deposition of Inorganic Film

• Diamond Like Carbon (DLC)
  capping material which exhibits
  radiation-hardening characteristics. devices
  developed for the military
• Amorphous Silicon (A-Si)
  production of solar cells
• Poly Silicon (poly-Si) Silicon Nitride (SiN)
  A-Si and poly-Si are
  conductive and depending upon their quantities
  having varying conductive properties

http//www.plasmaequip.com/WHAT20IS20PECVD.pdf
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Dielectric and Poly-Si Films

• Most commonly used films
• Poly-Si, SiO2, Si3N4 and SiNx
• Most commonly deposition methods
• APCVD, LPCVD, PECVD
• Most common applications
• Doped poly-Si as MOS gates
• SiO2 as interlevel dielectric
• Si3N4 as diffusion and sodium barrier
• SiNx as chip passivation layer

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Deposition Processes
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Poly-Si Deposition

• Reactor pressure can be controlled by
• Pumping speed
• Nitrogen flow
• Total gas flow with constant ratio
• Deposition reproducibility is best when the
  pressure is controlled by pumping speed

http//www.engr.sjsu.edu/lhe/lectures/lecture205(
chap2011-20II).pdf
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Poly-Si Deposition

• Poly-Si films deposited below 580C is amorphous
• Poly-Si films deposited above 625C is
  polycrystalline and has a columnar structure

http//mmadou.eng.uci.edu/Classes/MSE621/MSE62101(
14).pdf
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SiO2 Step Coverage

• TEOS at 700C
• Silane-O2 at 450C and low P
• Silane-O2 at 480C and Atm. P

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E5/SX0PO7AF/445,7,Step Coverage over Trench
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Properties of Deposited Oxides
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Properties of Deposited Nitrides

• LPCVD nitride is stoichiometric and a good
  barrier against oxidation and sodium diffusion
• PECVD nitride contains a large amount of hydrogen
  and can be etched with HF

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Low-Temperature Deposited Dielectrics
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Summary
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Answer

• Advantages
  Lower substrate temperatures, Faster
  deposition rate, Good adhesion, Good step
  coverage, Low pinhole density
• Disadvantages
  Chemical and particulate contamination, limited
  capacity