Actually, I am using Aluminium as my substrate and coating Copper using Magnetron Sputtering. But once sputtered Copper will not adhere it permanently. How to make it permanent, as I need to make connections on it through soldering? Also, the copper layer can be pulled off by normal transparent adhesive tape or by other tapes too.
This creates problem and copper removed from the aluminium substrate. Can anyone suggest me the solution to this problem, I want to use copper as an electrode over which piezo material to be coated with another copper layer with same aluminium substrate!
Sorry if my question confuses you but I need to form following layers over one another:
Aluminium-Copper-ZnO-Copper
Please suggest a solution to this problem!
I'm not using any substrate heating as there is no provision in sputter machine to introduce temperature variations. So can be done only before or after the sputter deposition.
Have you tried chromium as an intermediate adhesion layer? Chromium adheres well to copper and likely with aluminum
I never tried chromium before. In our lab we mostly sputter aluminium and copper. Do you have any idea about parameters/specs required for chromium magnetron sputtering? (Like- required voltage, current, freq., duty cycle and colour of sputtering electrons)
Sorry I do not have experience with magnetron sputtering, only physical (plasma) sputtering and CVD. But chromium has been used as an intermediary in several applications
Try to decrease total pressure in vacuum chamber to c.a. 4E-3 mbar and put a BIAS voltage about -200V to the substrate. We have done some sputtering of aluminium on SS substrate and then pure copper on it. Total thickness was about 400nm but the adhesion was nice. It was hard to remowe it with a radial bristle. You can also try to perform cathodic cleaning between sputtering of Al and Cu to preheat the substrate and "activate" the surface of Al.
Your problem arises from a simple fact - aluminium is always covered with a thin (a few nanometers on average) layer of native oxide. It prevents the underlying pure metal from further oxidation (aluminium is very reactive and can be oxidized even by water). So, if you want to cover it with a good-quality metal film the first thing to do is to remove the oxide layer. One general approach is to use zincate solution - oxide is chemically etched in a special solution followed by zinc plating of aluminium. Also search for Vogt process.
And do not try to "invert" the recipes of depositing Al on other substrates and apply these to your process. This is a completely different chemistry. When you deposit Al (by sputtering or whatever else technique) you do it under vacuum (sometimes even HV) and aluminium on Al-substrate interface remains metallic (whilst the film surface will oxidize immediately if exposed to air). If Al is the substrate you already have an oxide layer on it and have to do something with that.
Hi Rohit,
I think that Andrey is correct and you need to work out on removing the oxide layer from the Aluminium substrate first to improve the adherence of copper film. Moreover if the surface is oxidized you will not be able to make the electrical connections also as you require.
I will concur with Andrey and Soni. The Al surface will possesses a thin native oxide along with physisobed contamination (gases). These elements will impede adhesion, along with electrical contact issues. So, how does the practioner overcome this problem. One common technique is something we call in-situ preclean. This surface cleaning technique occurs in the vacuum system, so once the substrate suface is "cleaned", the risk of further contmaination or re-oxidation is reduced. A very standard method to execute the in-situ preclean is to use a broad-based ion beam to sputter clean the Al surface in the same system as the deposition process. I suspect your magnetron sputtering system does not have this equipment or you would not have had this problem. A less effective technique, but workable, is to apply a negative bias to your substrate to create a plasma glow discharge. Since your substarte is conductive and I will assume the stage parts are also, you can apply a DC voltage with Ar backfill to the chamber before the deposition. Maybe a DC voltage around -200 to -500V and the pressure in the 10 to 100mTorr. This should create a glow discharge and enough ion bombadment on your substrate to clean and remove the native oxide which is probably 25-100 angstrom thick.
I also agree with Andrey V. Blednov. The oxide layer might be the issue. There are two ways to overcome this. First you can reverse bias the magnetron and substrate so that ions will bombard with the substrate surface and the oxide layer can be removed significantly. Second one is depositing some aluminium alloy which consist copper content (Al 3000 series) in it prior to copper deposition. Chromium also good choice but aluminium alloy is cost effective. Note one thing that, Al alloys consist other elements also like Cr and Ti etc.
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