Hey Simon Roa I've done this quite a bit and one of the most important things i've come across is substrate cleaning. Before I would deposit on my glass I would subject the glass to a cleaning process in my case it was a Piranha clean which was 4 parts Sulfuric Acid to 1 part Hydrogen Peroxide for roughly 5 min followed by a DI rinse and N2 dry. I would then immediately place it in the sputtering chamber.

I have done experiment on sputtering deposition of Mo, ZnO, Al:ZnO, Cu, Ni and Ni-Al on glass plate. Let me share you my observations, so it will help you.

1) Cleaning - Clean your substrate with Pirhana solution, as Adam Weidling stated in his answer. Inspect your substrate before putting in deposition chamber. Even if you notice tiny particles, please discard it.

2) power - for metal deposition, try to use higher power (>300 W) it will ensure that enough particles flux on substrate.

3) Temperature - I will suggest you to deposite at temperature higher than 100 C. in my experiment, I observed flakes at lower temperature deposition.

4) Medium - Optimum Ar pressure would be ( 2 - 6 x10^2 mtorr), but it will depend on your chamber.

Good luck, let me know your observations after your experiments.

I agree with Sachin desarada.

Most metallic films will only be continuous films as from thicknesses of some 7 nm. So, don't go below this thickness. Especially Ag will easily form islands when deposited directly on glass (thicknesses below 20 nm). In any case you must deposited with a very pure sputtering target (Ag close to 4N) having low oxygen en nitrogen contamination (each well below 50 ppm). Of course to have ideal Ag properties, also contamination of metallic elements needs to be reduced. Work with a very low base pressure (below 2.E-06 mbar) and Ar (5N/6N purity) pressure between 1.E-03 and 3.E-03 mbar (DC). It will probably be necessary to deposit a thin (1-2 nm) NiCr or ZnO nucleation layer (always for silver).

Reading Paul Lippens comments took me to the basic course on thin films growth and the book "Islands, Mounds and Atoms by Michely and Krug".

I suggest you spend some time changing some important parameters like temperature, power, and pressure, indeed, after getting clean substrate surface. Keep in mind that for a uniform growth high temperature and low deposition rate (power) are crucial.