Hello All,
While my preferred method of depositing Ti is e-beam, I am without this equipment right now and want to make Ti films. I have been running a 2" target DC sputtering system at varied cathode powers and varied partial pressures and the resulting film is always discolored (gold, blue, purple) indicating oxygen content. The cleanest films seem to come from low sputtering power, 100W max, base pressure of 1 x 10^-6 torr, working pressure of 5 x 10^-2 torr. I might add, this is the lowest WP at which I can get a plasma to arc in my chamber for this set-up. I'm using UHP nitrogen from airgas as the sputtering fluid, which should give 99.999% purity. Source to substrate distance has been varied from as little as 1 inch to as much as 5 inches, always with the same result. I'm pretty stumped on this one!
Also, I find it a bit odd, but the area around sputtering target, I guess you could call it the anode ring of the sputtering head, has been getting coated in what I can best explain as "carbon black" looking dust. I have no idea on what the origin would be, or if this is usual for sputtering.
A few thoughts:
1.I could try research plus grade, giving 99.9999% purity, the different is 1ppm for UHP and 0.5ppm for research plus.
2. My mass flow controller might be leaking? Although I've never seen this happen before. I get a nice blue plasma from the argon, not purple like I've seen in air sputtering.
3. I should switch from flex tubing to hardline running from my tank to my mass flow controller? The gas sellers have tried to tell me that there will be "diffusion" through the plastic flex tubing.
4. I'm getting residual moisture in the flex tubing causing issues?
I should add, the end goal of this project is to grow TiN thin films through reactive DC sputtering, which we tried first with a partial pressure of UHP N2 with no luck- same film colors.
Thanks in advance!
Steve
Well ss tubing, and good tight fit connections are zlways advisable
If you are able to get a achieve a goo blue colored plasma with argon, while sputtering titanium, this is enough to ensure, you have no leakage in your systes, and your gas lines.
Now your target may be contaminated. cleaning it may be useful.
1) To obtain pure Ti films you should pre-sputter Ti target in pure argon.
2) Try to pre-sputter your target for some time, with a shield over your substrates.
Pump down the system again, you should achieve a much better and a lower base pressure. Do it a couple of times to ensure a good base vacuum, and a clean target.
don't use nitrogen gas to obtain good quality Titanium films, because you will get TiN films.
You must use pure argon to get pure Titanium films.
K. Sreenivas
Thank you K. Sreenivas.
I am right now using pure Argon and a brand new target which I presputtered for 1 hour at low power. The films appear dull grey, which is more promising. I will produce the same film at a substrate temperature of 400C, which should produce a crystalline Ti film.
My end goal is to deposit TiN films via reactive sputtering, but want to obtain a good Ti film first to make sure I am on the right track.
Good advice k sreenivas. always wise to do a presentation sputter before the real deposition. look into target poisoning when you try to deposit tin. many trials will be necessary
Dear Stephen,
Indeed to make a metallic film you need an inert sputtering gas (Ar). Use 5N pure Ar. If you need to go to such high pressure in order to get a stable plasma, then this is an indication that your magnetic field is far too weak. Can you replace the magnet array of the magnetron ? (put in stronger magnets of NdFeB type). If not, please limit the thickness of the target so that the stray field at the target surface gets stronger. This will allow you to drop the deposition pressure and get purer films.
In case you want to make TiN reactively in the end, you will need a way to control the process in the intermediate mode between metallic and poisoned mode. Can you work in constant voltage sputtering ? The ideal technology to be used is twin magnetron sputtering with MF-AC. I don't think you have this set-up.
Regards,
Paul
You inherently have the issue that titanium is used as an excellent getterer for oxygen due to its high affinity to such (thus its use in gettering pumps for ultra high vacuum systems). So, at the vacuum levels you are using, the films will have what I would guess are decreasing levels of oxygen as a function of thickness, with naturally a spike in oxygen content at and near the surface of the films due to exposure to air. You should consider conducting quantitative Auger or XPS analysis as a function of thickness to get a good profile of the oxygen content and evolution as function of thickness. Then, consider starting the process at the best vacuum achievable and using ultra high purity argon, with the use of a shutter to protect the substrate while you conduct a pre-deposition sputter clean of the chamber with the Ti target to getter and minimize oxygen content in the chamber prior to actual deposition. Hope this helps.
I just purchased a new batch of magnets to upgrade my magnetron. The device is rather old and was acquired second hand. In taking it apart, I found that some of the magnets were nearly dead! NdFeB magnets are on their way.
A pure argon plasma in DC magnetron sputtering has always a purplish colored glow. Any deviation from that indicates a contamination in the discharge.However, If you have a moderate vacuum (1 e-6 mbar) and regular argon purity and target purity, you should do a lot of effort not to end up with almost pure Ti films if you sputter cleaned your target first.
Of course, if you sputter in nitrogen, you end up with TiN (gold looking) films. Reactive magnetron sputtering becomes very complex if you deviate from pure nitrogen or pure argon.
The "black dust" at the edge of your target is redeposited target material with compound formation and ion implantation making it look black and porous.
1) I would take the Ti Target to the workshop, and get is machined (faced), by skimming of 0.25 mm thick layer top layer. Should ask the machinist not to use any oil which doing the facing operation on the lathe. This is to get rid of any oxide layer on the target surface.
2) Clean the target with isopropyl alcohol, and not to wipe with a tissue paper, this will leave fibers, which are nothing but carbon.
3) Pre sputter the target for a some time at a high power. to skim off the top layers. Try to pre sputter for quite some time, till the plasma becomes,
DEEP sea BLUE. ( I just love plasma color) whi ensure there is no oxygen in the sputtering chamber, and on the target surface., and I bet you will get the most cleanest and pure Ti film.
4) Kindly remember, Ti is one of those elements in the periodic table which love oxygen the most. Hence when you take out your substrate out the sputtering chamber, immediately keep them either in a vcuum dessicator, or seal them in Argon or nitrogen filled, goo quality zip lock bags.
The Blue color of the plasma only ensures the quality of the Ti film, and Ti sputters very fast.
Any purplish color in the plasma clearly indicates oxygen contamination in the chamber, or in the sputtering Argon gas, or on the target surface.
K. Sreenivas
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