Uneven Sputtering of Zinc Sulfide Target

To make a uniform sputtered coating, precisely control vacuum chamber pressure (10-100 mTorr), use an inert gas like Argon, maintain a stable plasma by adjusting voltage, ensure proper target cooling, and position the substrate effectively. The uniformity is achieved by the even distribution of sputtered atoms from the target, which is influenced by gas pressure, deposition time, and the geometry of the coating system.

link....

https://www.semicore.com/news/94-what-is-dc-sputtering

Sputtering zinc sulfide (ZnS) involves bombarding a high-purity ZnS target with energetic ions to eject atoms or molecules, which then deposit onto a substrate to form a thin film. This magnetron sputtering or reactive sputtering process allows for the creation of ultimately pure and functional ZnS thin films for applications in electronics, optics, and solar cells. The process parameters, such as substrate temperature and the type of ions used, can be varied to control the structural, electrical, and optical properties of the deposited ZnS films.

https://www.lesker.com/newweb/deposition_materials/depositionmaterials_sputtertargets_1.cfm?pgid=zn5

https://www.msesupplies.com/products/mse-pro-zinc-sulfide-sputtering-targets-zns?srsltid=AfmBOorgYyTaH9LhcTi2Xez27LDA4KY_Az4ozMeh0hyd7GRvk4jto_5p

The parameters must be adjusted to meet the target requirements...some materials are not suitable for ZnS sputtering targets...

How big is the substrate, is the unevenness random or in one area? Is the target stationary during coating or are you using a planetary coater?

The substrate size is 3 inches. The surface roughness is randomly distributed. The target remains stationary during the coating process.

Hi, it would help if you could give some information regarding the size and structure of the materials you are trying to coat and how big the items are.
Also what Disposition thickness are you using ? As (ZnS) is usually measured in nm what differences are you noticing and how are you measuring ?
I have been involved in some Splutter Projects, one where we had a an Interior Mirror in a car which used the Mirror surface as a capacitive "Touch-screen" to turn the interior lights on and off.
Off-Topic: Notice you are based in Hannover, I'm based near Walsrode, just 30 miles up the road from you.