Silicon Carbide

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Silicon Carbide

• Department of Electronics
• http//www.ttu.ee/elektron
• Prof. Dr. Toomas Rang
• trang_at_edu.ttu.ee
• Address
• Ehitajate tee 5
• 19086 Tallinn
• ESTONIA
• Phone [phone]
• Fax [phone]

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Silicon Carbide trend to top?
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Silicon Carbide

• The crystal growth quality road map
• In 2005
• 3 wafers available
• with 0.2 micropipes/cm2
• less than 50 dislocations/cm2

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Silicon Carbide

• Electronic Energy processing has many parallels
  with information processing
• Both technologies have electromagnetics as a
  fundamental limit
• Both technologies are eventually
  thermo-mechanically limited (i.e. in terms of
  interface reliability and loss density)
• Both technologies are materials limited
• New applications for both are driven by a
  relentless downward cost spiral

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Silicon Carbide
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Silicon Carbide

• 6.5x103 cm2 in hour
• World Wide is minimum profitable production
  volume for semiconductor wafers
• Reality today is
• Si 6.5x106 cm2 in hour
• SiC 6.5x102 cm2 in hour (military)
• SiC 6.5x101 cm2 in hour (others)

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Silicon Carbide

• Must we nevertheless continue with Silicon?

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Silicon Carbide
Property Si GaAs 3C-SiC 6H-SiC 4H-SiC Diamond
Melting point C 1420 1238 2830 2830 2830 4000
Thermal conductivity W/cmK 1.5 0.46 5 4.9 4.9 20
Bandgap eV 1.1 1.43 2.39 3.02 3.26 5.45
Electron mobility cm2/Vs 1500 8500 1000 370 1000 2200
Hole mobility cm2/Vs 600 400 50 90 50 1600
Saturation electron drift velocity x107cm/s 1 1 2.2 2 2 2.7
Breakdown field x105 V/cm 3 6 - 20 30 100
Dielectric constant 11.8 12.5 9.7 9.7 9.7 5.5
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Silicon Carbide
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Silicon Carbide

• Figures of merit
• KFM Keys Figure of Merit (IC Applications)
• KFJ Johnsons Figure of Merit (High Power
  Applications)

KFM KFJ
Si 1 1
SiC 6.5 281
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Silicon Carbide

• The major demands for metal layers are
• Low resistivity for Ohmic, or low leakage
  currents for Schottky contacts
• Easy to form
• Easy to etch for pattern generation (e.g.
  microelectronics approach)
• Stable in oxidizing ambient (e.g.
  microelectronics approach)
• Mechanical stability - good adherence, low
  stress
• Surface smoothness
• Stability throughout processing
• Generally no reaction with other metals
• Should not contaminate devices, wafers, or
  working apparatus
• Long lifetimes
• Low electromigration

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Silicon Carbide

• Bonding process has the following important
  advantageous
• one-step high temperature process for
  manufacturing multi-layer contacts (low energy
  process)
• extra high adhesion between layers to be joined
• minimum number of inhomogeneities on large area
  (near defect free contacts)
• improves significantly the certain electrical
  characteristics of manufactured semiconductor
  devices compared to other technologies

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Silicon Carbide

• Clines initial proposal of two-stage mechanism
  describes the Diffusion Welding (DW)
• The applied load causes plastic deformation of
  the surface asperities thereby reducing
  interfacial voids.
• Bond development continues by diffusion
  controlled mechanism including grain boundary
  diffusion and power law creep
• Generally the surface should be prepared better
  than 0.4 ?m

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Silicon Carbide

• Materials to be bonded
• Direct Bonding
• Interlayer needed
• Not examined

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Silicon Carbide

• Interlayers
• Generally these layers are needed to join the
  incompatible materials, for example aluminum and
  steel.
• Another use of compliant interlayer is to
  accommodate mismatch strains generated when
  bonding materials have widely different thermal
  expansion coefficient. This is important in
  joining ceramics to metals where a five to ten
  fold difference in thermal expansion coefficients
  is not usual.
• A reason to reduce bonding temperature and time.

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Silicon Carbide
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Silicon Carbide

• Adhesion test

Temp 0C Pressure MPa Bond quality
500 20-50 None
550 20-50 Bad
600 20 Bad
600 30 Very Good
600 50 Excellent
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Silicon Carbide

• Cristal Defects (comet tails, micropipes)

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Silicon Carbide

• Screw and Edge Defects at the SiC Si-face surface

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Silicon Carbide

• 4H-SiC wafer upper surface

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Silicon Carbide

• Structure and examples

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Silicon Carbide

• U-I characteristics

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Silicon Carbide

• Forward voltage drop
• (a) n0-n- 4H-SiC
• (Nd 1x1015 cm3)
• (b) p0-6H-SiC
• (Na 5x1015 cm3)

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Silicon Carbide

• SEM Picture (made in Furtwangen)

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Silicon Carbide

• Inhomogeneities at the SIC surface

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Silicon Carbide

• Schematic barrier height picture

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Silicon Carbide

• Current distribution at Pt-Au-Pt 6H-SiC interface

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Silicon Carbide

• Temperature distribution in Pt-Au-Pt 6H-SiC
  interface

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Silicon Carbide

• Schottky interface
• J q(nm - n0) vR
• n0 NC exp-(q ?Bn/k T)
• nm NC exp-q ?(xm) q ?Bn/k T

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Silicon Carbide

• What will come next?