One of the following you may use according to  condition of the film.

Film thickness can be checked by

there are many techniques to measure film thickness:

1-    An interferometric method, more details is available at: TOLANSKY S. Multiple beam interferometry of surfaces and films. London: Oxford University Press, 1988: 147.

2-    Using mass of the film, m according to the next details::

 W1 is the weight of cleaned substrate

W2 is the weight of cleaned substrate plus film

W2-W1= the weight of the film

ΔW=mg

m = ΔW/g

m=ρXV   ;   ρ, is the density of film material and V is the volume of the film                   

the Volume  = (Width X Length X Thickness) of the film

3-    SEM or AFM  (film-substrate ) cross section

One of the following you may use according to  condition of the film.

Film thickness can be checked by

there are many techniques to measure film thickness:

1-    An interferometric method, more details is available at: TOLANSKY S. Multiple beam interferometry of surfaces and films. London: Oxford University Press, 1988: 147.

2-    Using mass of the film, m according to the next details::

 W1 is the weight of cleaned substrate

W2 is the weight of cleaned substrate plus film

W2-W1= the weight of the film

ΔW=mg

m = ΔW/g

m=ρXV   ;   ρ, is the density of film material and V is the volume of the film                   

the Volume  = (Width X Length X Thickness) of the film

3-    SEM or AFM  (film-substrate ) cross section

You have to calculate first, wieght of the thin films before and after deposition (annealed films). i. e. simple weight difference method.  Use the formulas

Density = Mass/Volume

Now, it is essential to calculate Volume.

Volume = Length x Width x Thickness

Density = Mass / (Length x Width x Thickness)

Using the above equation it is possible to calculate the thickness

You have to calculate first, wieght of the thin films before and after deposition tthen use this formula 

(W2-W1)/rho*A

where W2- wt. of thin film after deposition 

W1- of thin film before deposition 

rho is the density of ZnO or deposited material

 and A is the area of thin film

as Mr. A. Eldenglawey mention, but there is AFM and Alfa step, here make some scratch and check the scratch depth.