I have to deposit metal lines for electric contacts on my SOI wafer.
I haven't found any literature on Pt for metal lines and I know that each metal which uses Cr as adhesion layer has its temperature of degradation during annealing.
Is there a specific reason for no one to be using Pt for metal lines while gold (which is a dopant for Si) is so popular?
TiO2/Ti/Pt would provide the most adhesive metallic contact layer which can withstand high temperatures. But etching may be difficult.
K. Sreenivas
Hi Francesco Bellando,
- Patterning: For Pt patterning, wet etching is difficult, while RIBE has a big issue with redeposition at the sidewall of resist (mask), and the redeposition is hard to be removed. So, lift-off is the most common way. Thin Pt layer lift-off is straightforward as Pt is hard and crack on the resist in the acetone lift-off. But for thick one ( ca 100 nm or thicker ), then using LOR below the resist is needed.
- Adhesive layer: Pt needs an adhesion layer, and Ti, Cr is not recommended for relatively high-temperature application in your case as it will diffuse very quickly to the surface, losing the adhesive functions, then the Pt line degraded.
For around 445°C, commonly people used Ta for Pt. Ta does not diffuse too much to the outer surface like Ti or Cr. Also, just a very thin layer of Ta silicides formed, but it does not create any issue.
- However, you do not mention clearly if you need an ohmic contact or not ( as you deposit the metal line on Si). In this case, other adhesive layers are needed to have both the ohmic contact and high-temperature resistance.
Hien
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