Hi Mr Vikas,

former answers are really complete and detailed, so I guess you solved your problem. However I'd like to add just a comment: you find different thickness by changing your scanning area as your sample surface is not uniform at nanometer/micrometer scale. For this reason, if you measure the thickness of your sample just at a point, you could not claim that measure actually represents the thickness of the whole sample. If you are not interested in having an "exact" measure at a very small scale, I suggest to calculate an averaged value of your thickness sample on scanning areas properly selected (i.e. not too small). You have different possibilities, for example you can calculate the thickness at different points (randomly chosen) of the scanning area or to average different height profiles traced across your scanning area.

As far as I understood the methods my former colleagues have used you need a clear edge to perform thickness measurement via AFM. You will need to find (or prepare) a spot of your sample where you have a edge from the surface of your substrate up to the top of your film.

Hope that could help you. 

Dear Thomas

Thanks for your advice.

I found the spot and tried to do AFM but its thickness is changing with changing the scan area as I mentioned earlier in my question.

Mr. Vikas,

One way to measure thickness of thin films can be AFM measurement on step created on thin film. Step could be obtained by wet itching or any other suitable way depending on type of material coated and deposition technique. You need to take readings on stepped region. Difference in two readings can give thickness values. 

And as per as scanning area is concerned you need to decide based on equipment capabilities to give accurate values. You may do it by taking reference thin films with known thickness and calibrate your readings.

One way to measure thickness of thin films can be AFM measurement on step created on thin film. Step could be obtained by wet itching or any other suitable way depending on type of material coated and deposition technique. You need to take readings on stepped region. Difference in two readings can give thickness values. 

Make scratch and measure the step. Another ways are described here: https://www.researchgate.net/post/How_to_measure_the_thickness_of_oxide_nano_layer_colored_over_an_anodized_1mm_thick_Titanium_piece_without_disturbing_the_structure/1

You may have non-uniform film or wavy (curved) substrate. In this case, to check this you need to measure the height of a step at the edges where the substrate is visible, and etch pits to the level of the substrate at different locations of the film or to carry out measurements in different places on the scratch across the film surface.

I give you a link with a good answer to a similar question in RG from Pramod Kadukatty (How do I correctly measure the thickness of film using AFM?)

https://www.researchgate.net/post/How_do_I_correctly_measure_the_thickness_of_film_using_AFM2

May be the attached article can lead you to some useful ideas.   Likewise, I found out each different scanning area would give different measurement of surface roughness.  

The article on " Measuring Surface Roughness of an Optical Thin Film With Scanning Tunneling Microscopes". 

Thank you all for your kind help.

Hi Mr Vikas,

former answers are really complete and detailed, so I guess you solved your problem. However I'd like to add just a comment: you find different thickness by changing your scanning area as your sample surface is not uniform at nanometer/micrometer scale. For this reason, if you measure the thickness of your sample just at a point, you could not claim that measure actually represents the thickness of the whole sample. If you are not interested in having an "exact" measure at a very small scale, I suggest to calculate an averaged value of your thickness sample on scanning areas properly selected (i.e. not too small). You have different possibilities, for example you can calculate the thickness at different points (randomly chosen) of the scanning area or to average different height profiles traced across your scanning area.

Thanks Eleonora Stefanutti 

 Dear  Vikas

Obviously, Amol Chintaman Badgujar  suggestion is correct but the AFM gives only apparent thickness. For that, you have to map on a single scan on your sample both deposited and bare surface.  From that 2 scan u will get two "z" value you subtract Zcoated - Z substrate = your thickness. 

Further queries u can conduct my mail id: [email protected]

ear Vikas,

although not an expert on AFM, the short answer should be no, you do not use AFM to measure a thin film thickness. What others do is an extrapolation, depending on a number of simplifying(and often questionable) assumptions. Depending on the film electrical characteristics (resistivity and dielectric constant), here are two suggestions :

1. Dielectric film (resistivity high). Optical reflection and transmission gives a rather precise measurement of film thickness through the measurement of interference fringes. The possible "problem" is the substrate, but this can be usually dealt with easily.

2. Conducting film (resistivity higher or high). Measure the bulk capacitance of the film , using Electrical Impedance Spectroscopy (Impedance Analysator). Also this method is quite precise, but also here one has to deal with the response from the substrate. If a serious problem, one can revert to optical transmission/reflection and/or ellipsometry.

I hope this will help.

With best  regards

Petr

Peter's suggestions are very reasonable, and I'm already in RG gave advice to use ellipsometry or induction methods for such measurements. However, Vikas, apparently, has exactly this equipment or develops ACM. So everyone decided his problem and not tried to offer alternative variations.

Alexander has a point there, but it all boils down to what Vikas really wants to do and how important this thickness is for his AFM system development.

For me there is no doubt that the effect of a thin layer on the AFM quantum tunnelling current across the gap (sample surface-tip) is small. Our experience  has been that the substrate is more important .

regards

Petr

Dear Vikas Singh,

A more experimental suggestion: Are you sure that you correclty correct the piezoelectric scanner non-linearity?

I think the trouble with the thickness changing with sample area may be associated with the scan speed you use to measure the step. If you scan too fast the AFM tip could "skip" and this causes larger than normal readings until it reaches far from the edge of the scratch. Try slowing your scan speed to help reduce this effect. There could also be some build up or film swelling right next to the step that you made depending on your technique (i.e. etch vs. scratch). For this you would want to scan larger areas to get to an unaffected region of your sample.

Also have you tried using X-ray reflectivity to measure your thickness? This way you don't destroy your sample and can use it for other measurements. Just a suggestion.

Good Luck!

Thank you all.

Dear Roddel,

Thank you for your suggestion.

Yes, I'll try to measure by XRR.

Dear Schmitt  Sir,

I do not know how to do it?

Could you please explain me?

Thank you

Compare with the information within the link (2.4).

http://www.physik.uni-wuerzburg.de/fileadmin/11999999/AFM_part3.pdf

A grating or a hole is a good feature on a sample for the determination of the thickness, because there are two steps on both sides of an AFM image. But please make sure a hole is large and deep enough.