I am measuring the thickness of thin layer MoS2 on the SiO2/Si substrate by AFM. However, the surface of the substrate that was oxidized naturally is not so smooth. This leads to big error in measurement. How can I make the surface as flat as possible?
We buy our wafers from http://www.microchemicals.com/.
You can also order polished oxidised and polished Si/SiO2 wafers. The Rq value even for our self-oxidised 100 wafer is in the range of 0.7 nm. After using a shadow mask the determination of the thickness should be possible. Prefer purchasing the oxidised wafer (if you haven’t access to an appropriate furnace) and to not expose a silicon wafer to non-cleanroom conditions (the mentioned dust problem).
Regards
Are you sure that the unsmooth of the SiO2/Si substrate comes from the oxidation? Maybe it is unsmooth itself, and you can buy some better SiO2/Si substrates.
Another reason is that there are many dust particles on the substrate. If the MoS2 is achieved by the reaction of S with MoO3, it is inevitable that there would be many particles to affect the measurement.
We buy our wafers from http://www.microchemicals.com/.
You can also order polished oxidised and polished Si/SiO2 wafers. The Rq value even for our self-oxidised 100 wafer is in the range of 0.7 nm. After using a shadow mask the determination of the thickness should be possible. Prefer purchasing the oxidised wafer (if you haven’t access to an appropriate furnace) and to not expose a silicon wafer to non-cleanroom conditions (the mentioned dust problem).
Regards
You can use nanoindentation technique. On the load / penetration curve, you will obtain different slopes and each slope matches to a layer of your multimaterial.
There is a possibility of chemical-mechanical polishing of silicon. You can also buy polished silicon .It is also a good idea to deposite in a single process thin film on the silicon and on the glass as a reference sample.
Usually roughness of polishing Si wafer is 0.5 nm. If you need more better quality, you can try with HF buffer treatment on Si/SiO2 substrate.
Best wish
After the RCA clean you do a NH4F treatment and subsequent an mild oxidation. If you repeat the etching oxidizing step you flatten the surface. More complicated but even better is an photoelectrochemical etching in the range of an oscillating surface reaction.
You cannot depend on the natural oxidation of Si wafers. Its a dirty process and the wafer surface condition is variable. First check the smoothness of your purchased Si wafers immediately after they are cleaned by the RCA method and HF dipped. Then re-clean and oxidize at above 700C. The wafers should be as smooth as the original Si. If not you have a dirty process. This is well known for 40 years.
Anodic oxidation is a good process to have well controlled oxidised layers
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