Dear Vinay Sharma ,

As a rule of thumb, for the alloy A_0.8 B_0.2 that you want to obtain, the deposition rate of A should be 4 times larger than that for B. If you already have calibrated the individual target parameters, please take into account that the deposition rate depends linearly on the electromagnetic power (e.g. if you double the power you double the deposition rate).

Good luck with your research.

Jose-Miguel Garcia-Martin , yes i have already calibrated the individual target parameters and deposition rate goes linearly with the power.

Can you explain the relation between deposition rate and stoichiometry ? And how to input my target parameters to get desired thickness and stoichiometry?

Thanks

As 0.8=0.2x4, you need 4 atoms of A per each B atom, so the deposition rate for A must be 4 times higher than that for B. So, adjust the power for the targets in other to get 4 times higher deposition rate for A than for B. For the total thickness, you can assume as a first approximation the deposition time required as if all the atoms were of type A, and then measure the obtained thickness and do the final fine tuning.

Jose-Miguel Garcia-Martin Thank you for you help.

Thickness you can adjust by time. Increase the sputtering time. Better to rotate the sample during deposition for proper stoichiometry.

It is possible that the simultaneous operation of the 2 cathodes may change the sputtering rates compared to the case when they are used individually.

Therefore it would probably be useful to determine the composition of the first films by EDS analysis and then adjust the powers to obtain the desired stoichiometry.

Actually the sputtering rate is proportional to square root of ion energy (voltage) and directly proportional to ion flow (current). In practice the square root dependency is insignificant for a ±150 Volts range and the sputtering rate can be assumed to be directly proportional to the voltage. Thus if one knows a sputtering rate for a given material at some ion current density and energy he can estimate how much would it be for any other values.

Sputtering rates for different materials: http://www.ionbeam.co.uk/downloads/ion_beam_etch_rates_and_sputter_yields.jpg

If you have a reliable data on the sputtering yield of the two element A and B, try to make a target with corresponding areas, and keep the power constant. Special care to be taken if the melting point of the two vary significantly. Don't sputtering at too high a power, the low MP metal will sputter our quickly. Rotate your substrates and have some substrate temperature. Sputtering at slightly high pressure would be beneficial for better thermalisation of the sputtered specie. Make a few trials, thoroughly backed up with quantitative composition analysis (EMPA). If you have only two element, the problem can be cornered, but in case you have many elements in the target, it will be a challenging problem.

You can try Anderesen and Sigmund equation - Article Elements of Sputtering Theory

The problem is that, when you use the rate in Å/s for the first estimation, you assume that the densities of the calibration samples and of your alloy film are the same. From my understanding, you have to calculate with the rate in Atoms/s.

I tried that for cosputtering of Co2CrAl with the attached excel sheet that I wrote. No idea if it contains any wrong assumptions or values, however, it took me a lot of work from this first estimation. As the sources influence each other, I would recommend just guessing and optimize from there...

This can be done via chemical balance, as mentioned above by Jose-Miguel Garcia-Martin. This approach is valid just for ideal (or nearly ideal) case, i.e. case of non-interacting sources. Some particular case studies of this approach containing some remarks with respect to determination of composition and thickness were published (both the same article, just different source) (https://www.mdpi.com/2079-4991/12/11/1830) or ((PDF) Tailoring of Multisource Deposition Conditions towards Required Chemical Composition of Thin Films (researchgate.net)).

However, generally interference between particular sources may appear as mentioned by Gilles Poullain. In such case accuracy of this approach may decrease significantly and even may led to its practical unusability.

Also, it should be emphasized, that even though linear (or nearly linear) dependency between deposition rate and applied power can be often observed, this (i.e. linear) course is not a general rule, as mentioned above. Some courses were traced, e.g. references 24-30 in previously mentioned article.

Martin Wortmann, You are right with necessity of using mols/atoms/molecules/particles deposition rate ratio instead thickness unit deposition rate ratio, which is in fact emphasized in second contribution by Jose-Miguel Garcia-Martin.

I just briefly checked Your xls file, not the values, just procedure.

I found one mistake – in last step (co-deposited film thickness calculation) – You cannot use only one atomic mass, You should weighted it through Your thin film composition. Or, probably more easily to imagine – just calculate total mass deposited and then convert it to volume/thickness by compound/alloy density.

And some problematic assumptions. As I wrote in previous contribution, linear dependency between deposition rate and power may introduce increased level of inaccuracy. Also, my experience is that initial point of deposition rate vs power dependency is not usually [0,0] i.e. zero deposition rate for zero applied power (at least for linear fit mentioned within this discussion or general exponential fit proposed in article mentioned in my previous contribution). May be this will be negligible for high applied powers, but, vice versa, it will be important for low applied powers.