I'm studying properties of AlN based cantilever by physics vapor deposition. Our film scheme is AlN200nm/AlN200nm (with different stress to control cantilever warpage).

Currently, I found a weird problem.

At the edge of the wafer, AlN based cantilever warps differently even that the distance between them is less them 1mm.

Moreover, I also found that cantilever in the radial direction warps upwardly than that in the tangential direction.

I'm thinking of anisotropic structure of AlN, but there isn't any difference between center and edge in XRD phi scan or XRD pole figure.

THank for your helping.