An effective "quick and dirty" technique is to use the thin film interference equations. After you spin-coat the substrate, hold the film under a white light source and observe the color of the film. You can estimate the wavelength of the light that is constructively interfering based on the color of the film, (or use a small spectrometer if you have one.) Then, if you know the index of refraction of your coating and substrate, you can use the thin film interference equations. This only gives you a rough estimate though.

Here are examples: http://physics.bu.edu/~duffy/py106/Diffraction.html

Weight loss method using amount of polymer thin film grown may be used with a sensitive balance. The estimated thickness using molecular weight, rpm and viscosity may be calibrated and used

You can use the gravimetric method if you know the density and mass of the coated material by the relation density=mass/area*thickness. One can determine the weight of the coated material simply by taking the weight difference of the sample after coating and before coating.

You should know exact density of the coated material.

One can also you the cross section image using optical microscope if the film is having thickness in the order of 5-8 micrometeres.

If the films are characterized by the interference patterns in the weak absorption region of the transmittance spectra, you can use swanpoel's method to calculated the thickness.

Another possibility is the use of Xray reflectivity. but difficult due to low density. Ellipsometry will be a good choice too. Polymer thin film properties being now well documented.

Dear Venkatesh, if you have a micro balance then you can determine the thickness of your film. First you have to select a substrate which as mass as minimum as possible like thin glass cover slips will do. First you should measure the mass of glass cover slip by a micro balance (m1), then coat your film and weigh the coated substrate and if the mass is m2 then the mass of your film will be M=m2-m1. Now you the volume of your film will be area of the substrate x thickness of the film. You know the area of your substrate. If you know the density of your film then you can easily calculate the thickness of your film.

While it is possible to estimate the film thickness using molecular weight of the solution and the spin-coating parameters, I would recommend either ellipsometry or cross-sectional SEM, if possible.

An effective "quick and dirty" technique is to use the thin film interference equations. After you spin-coat the substrate, hold the film under a white light source and observe the color of the film. You can estimate the wavelength of the light that is constructively interfering based on the color of the film, (or use a small spectrometer if you have one.) Then, if you know the index of refraction of your coating and substrate, you can use the thin film interference equations. This only gives you a rough estimate though.

Here are examples: http://physics.bu.edu/~duffy/py106/Diffraction.html

I think the best way to determine the thin film thickness is depended on the used substrate. For example, if you use Si substrate, you can try XRD or ellipsometry measurements. If you use other substrate such as polymer substrate (PC or PET), you can not use XRD or ellipsometry but you can use positron annihilation spectroscopy. You can see the attached paper.

Cross sectional HRSEM is certainly the most simple and suitable for all substrates and stable films.

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In absence of AFM, profilometry or other technique, if you know viscosity of polymer material, rpm and coating time then thickness of spin coated thin film could be calculated.But I am not absolutely sure.

Use AFM for absolute measurement of thickness. The only trick is that you have to know the base. To know that deliberately make a scratch with blade. Now in AFM you can determine the difference between base and film top. That's it. Hope your problem will be solved.

A simple method by using optical microscope is to change the focus depth of the microscope between the substrate and the surface of the polymer layer. You can reset the z-direction on zero for either and check the depth by moving to another one.

A universal technique for the measurement of dielectric film thickness is optical (spectroscopic) ellipsometry

Exept of ellipsometry AFM technique is very good. For instance, see two my papers attached.

Depends on how thick it is ,.. if you are looking for extremely thin films (sub 30 nm), go for VASE with range of wavelengths. IR-VASE will work great and is industry standard for polymers on wafers. It needs n, k and t so you need to do a little more work to fit the model.

Try to measure with cross-sectional SEM.

This is a rather nice film thickness calculator, made available by Brigham Young University, based on the colour (thickness) of SiO2 or Si3N4 films on Si:

http://www.cleanroom.byu.edu/color_chart.phtml

Tolansky method is the easiest if one cannot afford AFM or profilometry. You need to have a clear portion of the substrate and a coated portion. Then you need a semitransparent film on another glass.Usually a thin aluminum fim on glass will do. The last thing is a sodium vapour lamp with an arrangement to get the light reflected on a measurement plane.I forgot to mention a simple optical microscope. You can see Tolansky fringes in this arrangement and measure the thickness. Just google for Tolansky method.

Vladimir, a knowledge of n and k of the material is required to accurately measure thickness with Filmetrics.Right?

First you can try to use ellipsometry if you can afford it.

Second, typicaly when you buy polymer for spin coating there is also data sheet for it specifying what thickness you will get for given parameters.

If you do have a Mirau interferometer hooked to an optical microscope it will do the job nicely. Please google for more information.

I think that can be done by weighting before and after deposition

Only if you know the density precisely

The best is to assess the thickness of the film by optical techniques (UV-Vis or ellipsometry) only if the film is of optical quality and if it is thinner than 5000nm.

You could also try to use Profilometry. It will definitely not be so accurate, but it will give you a rough overview. Quick and Dirty(as you might need to scratch the film)

Cross-sectional TEM and FESEM might have the problem that it might not be compatible with all the polymers as some of them are sensitive to the electron beam, besides being expensive and time consuming methods. XRR is for that good.

thanks for your inputs guys. many of you did not read the question i guess. I wanted to know low cost methods to measure thickness of a film. TEM SEM AFM all can do the job but are expensive.

Interference technique gives fairly accurate value

Dear Venkatesh, you can do it by intereference microscopy - which can be in principle done in a conventional (optical) microscope with some easy changes. Look for "Tolansky-microscopy" or "thickness measurement by Tolansky method". There is a german wikipedia entry (http://de.wikipedia.org/wiki/Tolansky-Verfahren)

But I only found the english page about Samuel Tolansky, but not for his technique.

I remember that there is a book only about this technique - "Interference Microscopy" or something like this. But again, the setup is quite easy, you just need a monochromatic lamp, and couple this to your microscope.

Best regards, Dirk

thanks Dirk. I will read and try to setup in my lab.

You can use spectroscopic ellipsometry technique, this technique is very successful.

http://en.wikipedia.org/wiki/Ellipsometry

With a TGA analysis it´s possible to obtain the amount of polymer deposited on the substrate and from there and with the dimensions of the substrate, the thickness. This only would work in case of complete decomposition of the polymer during the analysis, but might be a quick and non-expensive method.

Dear Venkatesh, Gravemetric measurements wont give you accurate thickness. It is just for rough estimation. If you really want to do rough estimation, you can use thin film interference method as suggested by Mr. Sebastian Requena. Tolansky-Verfahren method gives accurate thickness if your film is thick but if your film is very thin it is better to go reflectance measurements.

Dear Venkatesh, Can you tell me the thickness range in which you are interested in? If it is less than 100 nm then interference and other will not give you the good estimation.

I can calculate the thickness of your polymer films If they are thinner than 1-2 microns. I need the reflectance spectra of the films deposited on pre-cleaned Si substrate measured in the spectral range 320-900 nm. See the attached paper for example. Let me know if you are interested.

@ Aranandan and @ Hidayath: I did thickness measurements using the Tolansky thickness determination on thin films in the range of 20 - 30 nm in the past - this works quite well if you prepare a sharp step (say on a scale of some micrometers). Then your interference pattern will show a step, (i.e. all of the interference fringes will show such a step) and with the spacing of the interference fringes (which is a measure/calibration of your setup and includes all the pure geometry of the experiment, and the used wavelength you are able to calculate the thickness of very thin films. I realized that it is more difficult to measure thicker films, because if the thickness reaches more than half of the used wavelength, then the shift of the interference pattern will be larger than the pattern spacing itself, and it might be hard to trace the correct lines. In the enclosure, you will find some material on Tolansky microscopy and how it works, and a simple experimental realization. We have realized such an apparatus a couple of years ago ... Best regards, Dirk

@Dirk, Method looks convincing.

woooow thats great.. thanks Dirk and Babeva

Good if we may have helped you ;-)

AFM might be helped.

@Dirk Luetzenkirchen-Hecht , wovw it works. Thank you for sharing your information. I read it in undergraduate text book, but never applied in such a way.

Dear Syed, it's nice to realize that my comments have helped - yours and Venkatesh's positive responses make me feel that RG has its justification and makes a lot of sense!!! Good luck for your future work, Dirk

@Dirk Luetzenkirchen-Hecht, Can we use the same method to determine the thickness of organic small molecular thin films. Thickness of the films are expected to be less than 60 nm. Please do suggest...

Dear Hidayath, if the film you are considering is optically too transparent, then coat it with some thin aluminum, silver or gold, and you should be able to resolve a sharp step in such a microscope. We did it in a similar way in the past with transparent ceramics - and it worked well. And 60 nm is a thickness which is not at all problematic e.g. using a Hg-lamp as light source. Good luck, Dirk

Dear Dirk, the organic films that I am coating are optically transparent. I am measuring the thickness while thermally coating the layer. I want to cross check the thickness what I am getting.I will try this. Thanks for the suggestion.

sould be possible. Check this paper: Hall, D. B., P. Underhill, et al. (1998). "Spin coating of thin and ultrathin polymer films." Polymer Engineering & Science 38(12): 2039-2045.

Dear Dirk,

I think for your studies Ellipsometry will be very useful technique. We have measured the thickness of 10 nm of an organic coating on copper by using same technique.

Dear Venkatesh,

I think for your studies Ellipsometry will be very useful technique. We have measured the thickness of 10 nm of an organic coating on copper by using same technique.

Its very simple, just do it by making a scratch on its surface and measure it with Profilometer that could be optical or mechanical in nature. Once one determine the thickness of spin coated films, he could have a rough estimate about the set rpm, viscosity and the thickness for subsequent experimentation.

You placed to hardness testing..

Ellipsometry

a) If thicker films can be peeled off the substrate, you can simply use a screw gauge to measure the film thickness.

b) Now in case you are considering very thin films.

Capacitance measuring method can be one of the options and accurate.

provided you know the dielectric constant of the spin coated polymer material.

Fabricate a metal-insulator-metal (MIM) capacitor structure

Try to deposit/spin coat your polymer films onto a metallized substrate (Al or Au coated glass slide). Define a top electrode of known area,(you can use a mask and deposit a top electrodes by evaporating aluminum film. Now measure the capacitance, between the top and the bottom electrode. The bottom electrode contact can be easily achieved by scratching your polymer film, and connecting a wire to it. Measure the capacitance. If you know the dielectric constant of the polymer you are spin coating, then you can easily determine the thickness of the film.

Note: Polymer films generally have a low dielectric constant, hence try to see that you are firstly fabricating a pin hole free ultra thin film (in clean dust-free conditions), and keep your top electrode area large enough (5-10mm diameter). This will result in a large capacitance value, which can be easily measured in the pF range using a good LCR meter.

c) Now if you do not know the dielectric constant of your material to follow the method described above at point (b)

You can easily measure the thickness of the thick polymer film.

Then make a thick film, peel it off, put electrodes on either side, make an MIM structure easily, determine the capacitance.

Since you know film thickness, the area of the capacitor, and since you have measured the capacitance accurately, you can determine the dielectric constant easily.

Use this value of dielectric constant in the Option-C, to measure the thickness of ultra thin pore free spin coated polymer films.

d) I would not expect the chemical composition of spin coated films to change with film thickness, unlike the case of physically vapor deposited films like (sputtering, laser ablation, etc.,).

Hence the measurement of dielectric constant on a thicker polymer film can be conveniently used to measure the thickness of thin polymer film

If the interface can be distinguished by SEM, TEM or other imaging tech, you can examine the cross-sectional picture of the film after spinning coating. Or you can spin-coat your substance on part of your film, then you can compare the different thickness between the coated part and uncoatd part of the film. By simple calculation, you can obtain the result.

Did you try to calculate the thickness using UV-VIS transmission? Take a look in this reference MANIFACIER, J. C.; GASIOT, J.; FILLARD, J. P. A simple method for the determination of the optical constants n, h and the thickness of a weakly absorbing thin film. Journal of Physics E: Scientific Instruments, London, v. 9, n. 1, p. 102-104, 1976. Good luck

You may want to look at this: Method for Measuring Thickness of Dielectric Films Using Microdielectric Fringe-Effect Sensors

Yunn-Hong Choi,Prashant Tathireddy, and, and Mikhail Skliar*

Analytical Chemistry 2006 78 (10), 3242-3248

You can use profilometer to measure the thickness of your coat

Is it not possible to use variable angle spectroscopic ellipsometry? I have used it to determine both metallic and dielectric thin films in a matter of seconds.

Use of profilometer is the simple and best way

By SEM. could be least convenient method though.

One can use SEM or Profilometer. But for rough measurement weighing technique is a good idea.

You need to know the density (D) of materials. Lets the thickness is d. Take a cover slip of area A and weigh it (Weight=mo) and then deposit thin film then weigh it again (Weight=mf). Different of weight is (mf-mo). Now (mf-mo)=A*d*D.

Theory of the spin coating film thinning works surprisingly well (at least for simple cases). So you can use several measurements d(t) and then use calibration curve to find thickness d for given spinning time t and rot. speed.

Brief discussion, relevant citations and some results can be found in the attached file.

Sorry - here's the file.

If the thin film is thin than:

1) determine extinction coefficient of deposited material in solution

2) get the absorption spectrum after spin-coating

3) knowing extinction coefficient and area of film, get thckness

A number of answers depending on what equipment you have access to. Usually measurements are made using ellipsometry.

You can get an estimate using a quartz microbalance. The substrate chemistry is fixed by the crystal so it won't be exact but should be pretty close. Simply measure the areal mass and from the known density of the polymer calculate the thickness. ie h = M/(A*rho)

What polymer / solvent are you using? If it is something common like PS or PMMA I may have some premeasured tables.

@ Smith ... I use PMMA also

@naji. The spin coating leaves thin films. A 1cm square with a 10-100nm film. Density ~1000kg/m^3 weighs 10^-6 to 10^-5g. Very few balances will be able to weigh that.

A very accurate way would be using an Ellipsometer. But if you don't have access to any equipment ; Given that you know your spin speed; then I think you could make a rough estimation by using a data sheet of PMMA by looking at a spin curve. maybe this one would help you. : http://microchem.com/pdf/PMMA_Data_Sheet.pdf

Regards,

Maria

How to measure the thickness of a photosensitive polymer film? Can we still use optical methods?

Of course, if you consider reflection and absorption, then the optical methods rely on the optical properties of matter, not depending on whether it's a photosensitive material or not.

Perhaps I should have added.. if light changes the properties of the film, can we still use optical methods...? if not, what else can be used?

O.k., if you really have a change in the optical properties by the illumination, then you of course have to consider the change of e.g. the absorption if you want to measure the thickness. But by (spectroscopic) ellipsometry (and other techniques) this should somehow be possible, anyway. And you should always try to change the wavelength to a value, where those effects are only of minor importance. ..

Hi Ananth, If I got correctly your question.. You mean that if you have a photoresist If you would still be able to use optical methods? For example with an Ellipsometer if your photoresist is before the development step then you need to use a filter to screen the UV light. After the development step , you have no fear to get your photoresist exposed from stray light.

Hi, I'd like to offer the use of XPS. If the coating thickness is less than 10 nm, then one can makes several shots with different angles between surface of the substrate and the electron analyzer entrance aperture .

@ A. Fetisov

Although I am a fan of XPS :-) I fear that for conventional XPS with laboratory sources a thickness of 10 nm is too much - if you only have less than 6 nm or so, then angle resolved XPS may help. But for thicker films the mean free path of the electrons is to small, so that substrate signals are presumable not detectable. This may however be different for synchrotron based XPS with higher energies (HAXPES), see the literature ...

Thank you all for the insightful answers.

@ Dirk Luetzenkirchen-Hecht

Totally agree with you. I just made ​​an offer without specifying the source of exciting radiation. In general, the smaller the thickness of the analyzed layer is, the more informative the technique.

I did thickness measurement of thin polymer film in nanometric precision using ellipsometric method. this is highly accurate and easy method to measure thickness. more than that ellipsometric method is a non destructive approach to sensitive polymers and will not damage the film surface.

Theoretically yes. Get to know the density (d) of your resin (may be from viscosity and MW) and mass of the material (M) deposited on the spin coater to the best possible precision. Make sure you discount the material that flows off the substrate. With the knowledge of surface area of the substrate (A) you can calculate the thickness using M/A.d.

For a more precise measurement I'd suggest Ellipsometry.

Another good way to calculate the thickness of a spin coated polymer film (thickness

@Athanasios, is the Saurbrey equation valid for thicknesses in the range of 0.5-10 microns? It seems most of the suggestions here are for much thinner films than this. Since this equation doesn't account for solvent evaporation in spin coating, does it affect the validity of the calculation?

Another good way to calculate the thickness of a spin coated polymer film is the use of Doppler broadened of annihilation radiation using slow positron beam. You can see the attached paper.

The attached paper.

What about simply making a long and thin scratch in the film and then using AFM? You can extract a line profile from an AFM image and have sub-nanometer accuracy...

Just try ellipsometry and cross-sectional SEM images. This should not be a big issue.

@Sankalp Kota

For films with a thickness up to 1 micrometer, the available equations - Sauerbrey relation and the equation proposed by Lucklum et al. [1] - relating the shift in the resonant frequency with the thickness of a glassy coating, will compute the thickness with an error between 0.03% and 0.3%. For thicker films, the relative error, i.e. the deviation between the actual thickness and the computed thickness, becomes much larger (1.6% - hf,real=6 μm).

As I wrote earlier, both equations work well for glassy polymer films and thicknesses up to 1μm. This means that the residual solvent in the film as a result of the coating process, should be removed prior to the measurement of the resonant frequency and the calculation of the film thickness, so as to exclude plasticization effects. Furthermore, the thermal annealing above the polymer's glass transition temperature will relieve the stresses caused from the coating process, because the resonant frequency is affected by film stress.

[1] Lucklum, R., Behling, C., Hauptmann, P., Cernosek, R.W., Martin, S.J., Error Analysis of Material Parameter Determination with Quartz-Crystal Resonators, Sensors and Actuators A 66 (1998) 184-192.

Interferometry can also be a strong technique to be sued for the determination of polymer thin film. Please have a look on the following attachment.

@Murugathas Thanihaichelvan please explain how do you propose estimation of the film through UV Vis.?

1) Scratch gently with a scalper and measure with profile meter. Is the fastest way but not the scientific one! You can have problem to scratch your structure! If you have some SiO under is pretty accurate.

2) More precise is to do one step lithography and after measure with profile-meter.

3) Optical methods like interferometry are more "scientific" and not invasive but you need instruments for that.