Algebraic surfaces with canonical map of degree 13 15 17 18 21 22

In this note, we construct some minimal smooth surfaces of general type with canonical map of degree $13,15,17,18,21,22$. These surfaces are constructed as ${\mathbb{Z}}_3^2$-covers of a blow-up of ${\mathbb{P}}^1\times {\mathbb{P}}^1$.