Transcript Next Generation of Low

Low-k Dielectrics: Materials and
Process Technology
Rebeca C. Diaz
EE 518, Penn State
Instructor: Dr. J. Ruzyllo
April 13, 2006
Outline

Motivation for low-k dielectrics

Required properties of low-k dielectrics

Proposed materials

Most promising materials

CVD vs. Spin-on techniques

Conclusion
Why Low-k Dielectrics?

Reduce RC constant
without reducing size

R
metal interconnect
minimized with Cu

C
dielectric
need low-k
Why Low-k Dielectrics?2
Required Properties of Low-k
Dielectrics2
Electrical
Mechanical
Thermal
Chemical
good adhesion to
no material change
low thermal
k <3 and isotropic
metal or other
when exposed to
expansion/shrinkage
dielectrics
standard chemistries
high breakdown
voltage
low leakage
current
high reliability
stability
(low brittleness, high thermal stability
crack resistance)
uniform thickness
high thermal
conductivity
General
environmentally
safe
no metal corrosion
commercially
available
<1% moisture
absorption
low cost
low solubility in water
low defect density
Proposed Materials2,3
Material Classification
Inorganic
Inorganic/Organic Hybrid
Organic
Porous
Air gaps/bridges
k value
Deposition
Method
Fluorinated glass (SiOF)
2.8
CVD
Hydrogen silesquioxane (HSQ)
2.9
SOD
Si-O-C polymers (e.g. MSQ)
2.0
SOD
2.6
2.9 / 2.3
2.7 / 2.4
2.6
SOD
SOD
CVD
SOD
2.7 / 2.4
CVD
2.0
CVD
PTFE (Teflon)
1.9
SOD
Porous MSQ
1.8
SOD
Porous PAE
1.8
SOD
Porous SiLK
Porous SiO2
1.5
1.1
1.0
SOD
SOD
???
Material
Poly(arylene ether) PAE
Polyimides / Flourinated
Parylene-N / Parylene-F
B-stage polymers
DLC-Diamond-like Carbon /
Fourinated
Amorphous C / Flourinated
Inorganic/organic Hybrid:
MSQ (k = 2.0)2
HOSP (Honeywell)
 “Carbon-doped oxide”
 High thermal stability
 High resistance to cracks
 Reactant with stripping chemicals
Organic: PAE (k = 2.6)2
FLARE (Honeywell) and VELOX (Schumacher)
 High thermal stability
 Low moisture absorption
 Good adhesion with metals and SiO2
 Anisotropic but solved by increasing k to 2.8
Organic: Parylene4

Parylene-N (k = 2.7)




Mechanically stable
High thermal stability
Poor adhesion with Cu
Parylene-F (k = 2.4)


Same properties as
Parylene-N
Poor adhesion can lead to
corrosion
http://www.paryleneinc.com
Organic:
B-staged polymers (k = 2.6)2
CYCLOTENE
(Dow Chemical)





Fluorine based
Good temperature
stability
Low metal adhesion
Moisture absorption
Currently used in GaAs
interlayer dielectric
SiLK (Dow Chemical)




Phosphorous based
High temperature
stability
Good metal adhesion
Low mechanical stability
Organic: PTFE (k = 1.9)2
SPEEDFILM

No moisture absorption

Temperature resistant


Good adhesion with metals
Good mechanical stability

Compatible with etching chemistries
Porous Organics and Inorganics


Add closed cells of air to materials that show
promising characteristics
Dielectric constants below 2.0
(1) “Low-k Dielectrics.” http://fcs.itc.it/
Disadvantages of Porous Materials2

Weakens mechanical properties

Lower thermal conductivity

Narrow pore distribution to ensure dielectric
constant is homogeneous and isotropic

Pores need to be closed cells to prevent crack
propagation and moisture absorption

Need to add silica to seal surface pores
Air Gaps and Bridges (k = 1.0)2

Low breakdown voltage

Low thermal conductivity

Low strength

Deposition method unknown
CVD vs. Spin-on Deposition
Material Classification
Inorganic
Inorganic/Organic Hybrid
Organic
Porous
Air gaps/bridges
k value
Deposition
Method
Fluorinated glass (SiOF)
2.8
CVD
Hydrogen silesquioxane (HSQ)
2.9
SOD
Si-O-C polymers (e.g. MSQ)
2.0
SOD
Poly(arylene ether) PAE
2.6
SOD
Polyimides / Flourinated
2.9 / 2.3
SOD
Parylene-N / Parylene-F
2.7 / 2.4
CVD
2.6
SOD
2.7 / 2.4
CVD
2.0
CVD
PTFE (Teflon)
1.9
SOD
Porous MSQ
1.8
SOD
Porous PAE
1.8
SOD
Porous SiLK
1.5
SOD
Porous SiO2
1.1
SOD
1.0
???
Material
B-stage polymers
DLC-Diamond-like Carbon /
Fourinated
Amorphous C / Flourinated
CVD vs. Spin-on Deposition2
CVD







k as low as 2.0
Porosity cannot be
added
Better mechanical
stability
Better thermal stability
Technology in place
Less expensive
Batch process
SOD






k as low as 1.9
k below 1.9 by adding
porosity
More promising low-k
materials
More uniform deposition
Extendable to future
technologies
Single-wafer process
Conclusions

Introduction of low-k dielectric is needed in
order to continue to downscale technology

Several CVD or Spin-on deposited materials
look promising for the near-future generations

Spin-on porous materials appear to be the only
option for future generations

Air gaps need more research in order to be
considered for future low-k dielectrics
References
(1) Fisica Chimica delle Superfici e Interfacce. “Low-k Dielectrics.”
<http://fcs.itc.it/MAMeBROCHURE/low-k%20dielectrics.pdf> 31 Mar 2006.
(2) Clarke, Michael E. Application Note MAL123: “Introducing Low-k Dielectrics into
Semiconductor Processing.” Mykrolis. 2003.
<http://www.mykrolis.com/publications.nsf/ docs/MAL123> 31 Mar 2006
(3) Plumber et al. “Back-end Technology.” Silicon VLSI Technology: Fundamentals,
Practice and Modeling. Chap. 11. Prentice Hall, NJ, USA. 2000.
(4) Nishi, Yoshio and Doering, Robert. “Alternate Interlevel Dielectrics.” Handbook
of Semiconductor Manufacturing Technology. Chap. 12. Marcel Dekker, Inc.
NY, USA. 2000.