Information about Epitaxial layer

Hi all,

I am designing an inductor on chip. In modeling the substrate, I need to know the information about the epitaxial layer. Here are my questions:

1) What is this epitaxial layer for ?

2) Normally, is the relative permittivity of the epitaxial layer equal to that of the silicon, e.g. 11.9 ?

Thanks a lot guyssss, ;)

DYL :D