Low-k Dielectrics: Materials and Process Technology

1
Low-k Dielectrics Materials and Process
Technology

• Rebeca C. Diaz
• EE 518, Penn State
• Instructor Dr. J. Ruzyllo
• April 13, 2006

2
Outline

• Motivation for low-k dielectrics
• Required properties of low-k dielectrics
• Proposed materials
• Most promising materials
• CVD vs. Spin-on techniques
• Conclusion

3
Why Low-k Dielectrics?

• Reduce RC constant without reducing size
• R metal interconnect
• minimized with Cu
• C dielectric
• need low-k

4
Why Low-k Dielectrics?2
5
Required Properties of Low-k Dielectrics2
6
Proposed Materials2,3
7
Inorganic/organic Hybrid MSQ (k 2.0)2

• HOSP (Honeywell)
• Carbon-doped oxide
• High thermal stability
• High resistance to cracks
• Reactant with stripping chemicals

8
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

9
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
10
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

11
Organic PTFE (k 1.9)2

• SPEEDFILM
• No moisture absorption
• Temperature resistant
• Good adhesion with metals
• Good mechanical stability
• Compatible with etching chemistries

12
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/
13
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

14
Air Gaps and Bridges (k 1.0)2

• Low breakdown voltage
• Low thermal conductivity
• Low strength
• Deposition method unknown

15
CVD vs. Spin-on Deposition
16
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

17
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

18
References

• (1) Fisica Chimica delle Superfici e Interfacce.
  Low-k Dielectrics. lthttp//fcs.itc.it/MAMeBROCHU
  RE/low-k20dielectrics.pdfgt 31 Mar 2006.
•  
• (2) Clarke, Michael E. Application Note MAL123
  Introducing Low-k Dielectrics into Semiconductor
  Processing. Mykrolis. 2003. lthttp//www.mykrolis
  .com/publications.nsf/ docs/MAL123gt 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.