Hello Anish Dhungana,

it is better to perform ellipsometry measurements to extract the thickness values of such thin films.

Please provide more details about the profilometry measurements. How exactly were carried out?

Hi Anish,

You should look at more parameters of the sputtering process like RF power (total and reflected) and DC Bias (if measured).

Normally the thickness is linearly increasing with time provided the conditions are the same. If this is not the case then look at the conditions.

Hi Anish,

The different substrate structures, different sputtering time and different working pressures due to different thickness based on abovementioned explain. You should research on the different parameters which affected the sputtering coating. For example the duration of sputtering, working pressure, lattice structure of substrate, substrate temperature, target to substrate distance, and power of rf bias could changed the charactersitics of produced coatings.

Hello Panagiotis Bousoulas,

Thank you. Yeah, I am using profilometer measurement by creating a step in the substrate using tape. This substrate has multilayers with Si/SI02/Al/sputtered si02.

Panagiotis Bousoulas

Panagiotis Bousoulas I think the aluminum is 130 nm and if you use ellipsometer in visible region then instead of considering Si/Si02/Al/Si02 (RF sputtered) , you can consider Al/Si02 and measure the thickness of Si02, right? since 130 nm thickness will reflect back all the visible wavlength region.

Your observation is typical when sputtering SiO₂ onto aluminum. The main issues are:

1) Poor adhesion and interface effects: Aluminum can partially oxidize or react with SiO₂ during deposition, especially at low pressures (4 mT), affecting film growth rates.

2)Surface charging: Since SiO₂ is insulating and aluminum is conductive, differential charging can occur, disturbing the plasma and reducing the effective deposition rate.

3)Nucleation differences: SiO₂ grows differently on metallic surfaces (Al) compared to semiconductors (Si) — slower nucleation and thinner films on metals.

That’s why your Si substrate gets a thicker SiO₂ layer faster, while on Al, the growth is slower and less uniform.

Tips to improve:

1) Try RF biasing of the substrate to stabilize plasma near the Al surface.

2) Use a thin adhesion layer (e.g., Ti, TiN) before SiO₂ deposition.

3) Increase substrate temperature slightly to improve nucleation and adhesion.