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 Dielectrics 2

Proposed Materials 2,3

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 SiO 2 Anisotropic but solved by increasing k to 2.8

Organic: Parylene 4 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

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.”

Disadvantages of Porous Materials 2 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

CVD vs. Spin-on Deposition 2 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.” 31 Mar (2) Clarke, Michael E. Application Note MAL123: “Introducing Low-k Dielectrics into Semiconductor Processing.” Mykrolis Mar 2006http:// docs/MAL123 (3) Plumber et al. “Back-end Technology.” Silicon VLSI Technology: Fundamentals, Practice and Modeling. Chap. 11. Prentice Hall, NJ, USA (4) Nishi, Yoshio and Doering, Robert. “Alternate Interlevel Dielectrics.” Handbook of Semiconductor Manufacturing Technology. Chap. 12. Marcel Dekker, Inc. NY, USA