Copper diffusion into the silicon bulk is a detrimental obstacle to advanced-CMOS and photovoltaic processes that seek to incorporate copper into the metallization steps because of its deep-level trap nature to carriers. Recent studies have hinted that an organic porphyrin or silane-based self-assembled monolayer (SAM) could be a method of prevention to copper diffusion. Inorganic alternatives using TiO2 or Ni may also present a solution. The self-assembly of 5,10,15,20- Tetrakis(4-hydroxyphenyl)-21H,23H-porphine (OHTPP) over SiO2 has been examined using atomic-force microscopy (AFM), contact angle measurements, and variable angle spectroscopic ellipsometry (VASE). Results indicate that this particular OHTPP chemistry fails to adsorb to the Si02 substrate. Metal- Oxide-Semiconductor (MOS) capacitors with varying dielectric stacks with and without TiO2 over SiO2 or Si3N4 and gate metals varying between Cu and Ni have been fabricated and analyzed via bias-temperature stress (BTS) capacitance-voltage (C-V) tests. Results indicate that Cu-coated TiO2 and Ni MOS stacks with a SiO2 insulator show drastic flat band voltage shifting compared to Cu over SiO2 or with a Si3N4 dielectric over SiO2.
Aiello, Anthony F.
"Investigation of a Self-Assembled Monolayer as a Cu Diffusion Barrier for Solar Cell Metallization,"
Journal of the Microelectronic Engineering Conference: Vol. 20:
1, Article 2.
Available at: https://repository.rit.edu/ritamec/vol20/iss1/2