Good morning, I'm Michele Bellettato, I'have never worked with Mo, but tha same think appen on my deposition of Si and specially SiN.

I think that your film is stressed and the pinhole are what we cal blistering of the deposited film. The reasons could be more than one.

Maybe the daposition termperature is higher and you grow a good film that becam stress at room temperature, or the adesion of the Mo on the surface is not good and you need a process of sintering.

But the much probably for me is the quantity of H2 or N2 or O2 that you embedded in the film during the deposition and that couse the blistering of the film when temperature reach 25 °C.

The different amont of embedded gas, or more in general, the different tipe of material that you grow during the deposition change alot  by different RF and Power and distance of the sample from target and distance from the sample from plasma, pre-vacuum, ecc.....

Hope that I will gave you the rigt question.

Good work

Michele Bellettato

I think your film is stressed. You can try to decrease slowly the temperature after deposition, maintaining all the other parameters equal, when the temperature is the same of the room temperature you can start to increase the pressure.

Remember you to refill, with the air, the deposition chamber very slowly before to opening the chamber.

Thank you for your answers.

We are using Pure Ar gas for sputtering. Base Pressure of Vacuum Chamber is 1x10-7 mbar. So, I hope there is no H2 / O2 / N2. and this holes appear after 10 mins of removal of sample in air. We use load lock to transfer and remove the sample. We vent the chamber with N2 not with air. We have deposited at room temperature and also at 100 degree centigrate to 400 degree centigrate (various samples). To confirm there is no stress, we havedeposited the film at very very low deposition rate and checked. but still holes are there.

Michele Bellettato, Can you please tell me more about sintering process ?

The pin holes you see are due to stress in the Mo film. Depending on your working Gas pressure, the stress can be compressive ( low P) or tensile (high P).  In the tensile stress state the film becomes porous and with open grain boundary structure. You also need to consider how the working gas pressure effect the morphology and microstructure for fixed power and distance between source and substrate.

You have not stated your working conditions to give a definite answer but hope you will resolve you issues. Please read these references for more info.

 T. J. Vink, M. A. J. Somers, J. L. C. Daams, and A. G. Dirks, Stress, Strain, and Microstructure of Sputter-Deposited Mo Thin Films, J. Appl. Phys. 70, 4301 (1991)

  T. J. Vink, and J. B. D. van Zon, Stress in Sputtered Mo Thin Films: The Effect of the

Discharge Voltage, J. Vac. Sci. Technol. A9, 124, (1991).

"BK"

Hi Balram,

Thank you for your reply.

We have varied the power from 50W to 150W.

We have varied deposition pressure pressure from 1x10-2mBar to 1x10-3 mBar.

Distance between target and substrate is 10-13 cm.

if you can help with any further information.

Is an additional interlayer between the glass and the Mo film an option?

Putting an interlayer can help you accomodate the stress build-up during deposition. Your film is partially de-wetting from your substrate and you can modify this by changing the stress state of the film itself or modifying its wetting behavior of the substrate and the thermal expansion mismatch between film and substrate.

With this regard, cleaning the glass with different chemicals is not going to make a significant effect. If possible, consider a reactive metal interlayer (Cr, Ti are the most used ones).

A prevacuum of 10E-7 is good, and avoid the presence of O2/H2 or N2, Our problem of blistering was dued from the desorbtion of the embedded H2 during the deposition couse from the low temperature of deposition. maybe the glass isn't the right substrate for molibdenum?!

Try with different substrate! If blistering appear, is not a substrate problem, but a deposition problem.

If  blistering disappear the problem is from the Glass.

For Sintering process I know only in general , but is a compleatly different process of deposition/grow; you make a solid from powder with termal or pressure processing.

At 400°C be carefull if you use a normal glass, because the glass lost his physic resistance and became a bit melt! and put out alot of impurities that contains.

Good work and good luck

Michele Bellettato

Thank you Volker,

We have sputtered in both the configurations... both are having same pin holes. now we are using sputter up...  but this configuration causes frequent shorting of magnetron...

Find out your stress levels in your coatings.. at 10cm target distance, you have to adapt your pressure (free mean path, thermalisation of sputtered ions/atoms/recoils). Depending on temperature/power, you can vary from tensile to compressive stress, depending on your microstructures the film may adapt more or less of it.

If the parameter space is to narrow for good control, try to change your plasma excitation, or have some extra bias for the substrate.

Read the books.. this is all known, theoretically.. and Yes, practically it is not easy to anticipate.. each machine is different..  but with time, and characterisation of film and depositiion conditions you should find out the right way.

Of course, dust is an extra task..  (normally from the outside, but who knows if not created in the chamber? unusual at low pressures for pvd)

SEM should help to analyse this.

Good luck.

Reason is the bed adhesion and high mechanical stress in deposited layer. Solutions - sabstrate cleaning immediately before evaporation (RF discharge ore ion source cleaning) and preliminary substrate heting  ( glass temperature: 150 - 250 degrees of Celsius). 

Increase distance, your pinholes are most likely caused by arcing. If you are not using arc suppression, you need too.

thanks for your answer...

we tried low power, increasing distance, solution cleaning, pre heating already.. didn't work.

OK, so how thick is your layer?

I tried 300 nm to 900 nm thick layers on different samples

I tried bilayers also....

but they all were having the pin holes....

And how did you measure your thickness? Are you positive you have the thickness you think you are depositing?

I have deposited polycrystalline and single crystal  Mo on both SiO2 and MgO down two a few nm. I did not see pin hole by naked eyes. Based on your description, I doubt it is due to strain. I believe you know how to verify the residual stain  by XRD.

I suspect it is most likely your film is actually under dense and it gets quickly oxidized to form oxide and hydroxide.

In order to test it is related to oxidation, you can try to take the film out and immediately put it into liquid nitrogen and keep for it for 15mins then check weather pin holes are still formed.

If that is the case, you should raise the power or deposit at high temperature or try insitu annealing after deposition. 

I never worked with Mo, but for other films anneling worked very well in avoiding pin holes after deposition. Try to make a ramping annealing, it might work.

Pinholes are normally caused by some remaining particle or residue left on the substrate surface. This can either be particles from "dirty water", such as a bacteria bloom in your water filtration system. Another thing is how clean is your vacuum chamber? There is a tremendous amount of dust, flakes or particles that are stirred up when you first start your roughing cycle. You may want to clean and refoil your chamber to see if you still get pinholes after cleaning.

How clean is your DI water? It needs to be at least 18 megaohms resistivity.  Check your filters to make sure that you did not have a thermal bloom that allowed bacteria to grow and now you are seeing their "skeletons". This thermal bloom usually occurs during hotter weather like the summer months or if the room where the water system is to hot. 

Your pinholes could also be nucleation sites, where the material is first deposited  on the substrate surface and then grows outwards as more material is deposited. This is also called island growth, named because it grows outward and looks like an island. If your film is too thin you will see this island growth and more material needs to be added so that the "islands" actually grow together and become a uniform film thickness or a solid film.

We are depositing from bottom to top (means sample is mounted horizontally downwards)  so if there is any dust, it will not deposit on the sample....

We tried heating during deposition as well as after deposition... pin holes were same.

We are purchasing packed DI water, we are not doing any water filtering etc....

We are depositing around 400 nm to 800 nm for low resistive film. We have measured the thickness by two means .... SEM image of cross section of the film....  making a step by masking a small area of sample and then measure the step by profilo-meter......

Working on sputtered Mo films using bi-layers,  Im getting the same issue about pin-holes.

After reading all the comments here, I have new ideas. But, Has the problem been solved ? Sagar Agrawal.

Jesus: Problem has not solved yet, but reduced by RCA cleaning .... 

Reason - bed cleaning substrate before deposition. Solution of these problem

- heating of glass to temperature 200-250 grad

- finish cleaning sin vacuum with ion ore RF discharge

-minimisation of time betweens cleaning and deposition processes

-increasing deposition rate

If the film is fine when removed from deposition chamber and pinholes appear soon after, I would strongly suspect stress in the film is causing areas to pop off (compressive) or open up (tensile). I recommend measuring stress in deposited film and shifting deposition parameters to achieve minimum stress.

problem what I understood is about glass cleaning. Similarly we also faced this type of problems, these pin holes are due to improper cleaning. May be this is late reply, I think by this time you might have solved the problem